J.S. Hoving
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59 records found
1
Going-on-Location (GoL) is a critical phase in jack-up vessel operations, during which the unit transitions from a free-floating condition to seabed support. During touchdown, the spudcans may experience short-duration, high-magnitude impact forces due to the coupled effects of wave-induced vessel motions, nonlinear soil-spudcan contact, and leg deformation. Current GoL workability assessments rely on detailed time-domain simulations to determine impact forces, structural unity checks, and allowable sea states. Although these methods provide a physics-based basis for operational decision-making, they are computationally demanding and mainly describe simulation outcomes rather than the underlying relation between vessel motion and touchdown severity.
This thesis investigates whether the global mechanical energy response of a jack-up vessel can be used as a physically interpretable indicator for touchdown severity and GoL workability assessment. An energy formulation is developed within an existing time-domain GoL simulation framework and verified using energy and power balance relations. The method is applied to transient impact simulations with seabed contact enabled and to free-floating steady-state
simulations in which seabed contact is disabled.
The results show that global mechanical energy provides useful physical interpretation, but does not directly predict impact severity. Critical wave realisations do not exhibit a consistent pre-impact energy level, energy build-up, or common energy peak. Instead, elevated periods in the free-floating global mechanical energy response are most relevant when they occur within the
same time window as the touchdown interval identified in the corresponding impact simulation. Three-hour free-floating simulations can characterise the timing, magnitude, and persistence of these elevated energy periods, but do not provide a consistent threshold between allowable and non-allowable GoL cases.
It is concluded that global mechanical energy should not be used as a standalone workability criterion. Its main value lies in identifying potentially critical response periods and interpreting touchdown behaviour relative to seabed contact. Future work should focus on near-touchdown and initial-contact simulations to relate energy transfer more directly to impact magnitude, while RAO-based reconstruction of the free-floating energy response could be investigated as an efficient screening method. ...
This thesis investigates whether the global mechanical energy response of a jack-up vessel can be used as a physically interpretable indicator for touchdown severity and GoL workability assessment. An energy formulation is developed within an existing time-domain GoL simulation framework and verified using energy and power balance relations. The method is applied to transient impact simulations with seabed contact enabled and to free-floating steady-state
simulations in which seabed contact is disabled.
The results show that global mechanical energy provides useful physical interpretation, but does not directly predict impact severity. Critical wave realisations do not exhibit a consistent pre-impact energy level, energy build-up, or common energy peak. Instead, elevated periods in the free-floating global mechanical energy response are most relevant when they occur within the
same time window as the touchdown interval identified in the corresponding impact simulation. Three-hour free-floating simulations can characterise the timing, magnitude, and persistence of these elevated energy periods, but do not provide a consistent threshold between allowable and non-allowable GoL cases.
It is concluded that global mechanical energy should not be used as a standalone workability criterion. Its main value lies in identifying potentially critical response periods and interpreting touchdown behaviour relative to seabed contact. Future work should focus on near-touchdown and initial-contact simulations to relate energy transfer more directly to impact magnitude, while RAO-based reconstruction of the free-floating energy response could be investigated as an efficient screening method. ...
Going-on-Location (GoL) is a critical phase in jack-up vessel operations, during which the unit transitions from a free-floating condition to seabed support. During touchdown, the spudcans may experience short-duration, high-magnitude impact forces due to the coupled effects of wave-induced vessel motions, nonlinear soil-spudcan contact, and leg deformation. Current GoL workability assessments rely on detailed time-domain simulations to determine impact forces, structural unity checks, and allowable sea states. Although these methods provide a physics-based basis for operational decision-making, they are computationally demanding and mainly describe simulation outcomes rather than the underlying relation between vessel motion and touchdown severity.
This thesis investigates whether the global mechanical energy response of a jack-up vessel can be used as a physically interpretable indicator for touchdown severity and GoL workability assessment. An energy formulation is developed within an existing time-domain GoL simulation framework and verified using energy and power balance relations. The method is applied to transient impact simulations with seabed contact enabled and to free-floating steady-state
simulations in which seabed contact is disabled.
The results show that global mechanical energy provides useful physical interpretation, but does not directly predict impact severity. Critical wave realisations do not exhibit a consistent pre-impact energy level, energy build-up, or common energy peak. Instead, elevated periods in the free-floating global mechanical energy response are most relevant when they occur within the
same time window as the touchdown interval identified in the corresponding impact simulation. Three-hour free-floating simulations can characterise the timing, magnitude, and persistence of these elevated energy periods, but do not provide a consistent threshold between allowable and non-allowable GoL cases.
It is concluded that global mechanical energy should not be used as a standalone workability criterion. Its main value lies in identifying potentially critical response periods and interpreting touchdown behaviour relative to seabed contact. Future work should focus on near-touchdown and initial-contact simulations to relate energy transfer more directly to impact magnitude, while RAO-based reconstruction of the free-floating energy response could be investigated as an efficient screening method.
This thesis investigates whether the global mechanical energy response of a jack-up vessel can be used as a physically interpretable indicator for touchdown severity and GoL workability assessment. An energy formulation is developed within an existing time-domain GoL simulation framework and verified using energy and power balance relations. The method is applied to transient impact simulations with seabed contact enabled and to free-floating steady-state
simulations in which seabed contact is disabled.
The results show that global mechanical energy provides useful physical interpretation, but does not directly predict impact severity. Critical wave realisations do not exhibit a consistent pre-impact energy level, energy build-up, or common energy peak. Instead, elevated periods in the free-floating global mechanical energy response are most relevant when they occur within the
same time window as the touchdown interval identified in the corresponding impact simulation. Three-hour free-floating simulations can characterise the timing, magnitude, and persistence of these elevated energy periods, but do not provide a consistent threshold between allowable and non-allowable GoL cases.
It is concluded that global mechanical energy should not be used as a standalone workability criterion. Its main value lies in identifying potentially critical response periods and interpreting touchdown behaviour relative to seabed contact. Future work should focus on near-touchdown and initial-contact simulations to relate energy transfer more directly to impact magnitude, while RAO-based reconstruction of the free-floating energy response could be investigated as an efficient screening method.
This thesis presents the design of a reusable jacket pile gripper (RJPG) concept and assesses its technical and economic feasibility. The motivation behind this is to explore the potential for innovation and cost saving for offshore wind farms (OWFs) that currently require hundreds of jacket pile grippers (JPGs) to ensure grout integrity. First, the design requirements were laid out. Through a design cycle, several potential design candidates emerged. After consideration, a single RJPG design was selected to work out into a full concept. This concept was fleshed out by designing for a reference jacket in a hypothetical OWF. The definitive concept is a design where hydraulic cylinders lay in circumferential positioned welded on the outside of the jacket leg. The hydraulic cylinders press onto the pile and secure it in place. When the grout is sufficiently cured, the cylinders retract and are automatically disconnected. Then, an offshore support vessel can come by and retrieve the RJPG by using a deck mounted crane or winch, helped by buoyancy aids. The selected lifting points in combination with hinges make sure the device clears the jacket geometry during lift-out. By carefully selecting the design wave and current, the hydraulic components could efficiently be selected. This led to a design with fewer cylinders than initially expected from a conventional JPG. When the device comes back into the yard it can be cleaned, inspected, tested and remounted on the next jacket. To gain better insight into the economics of the RJPG, an installation simulation was done. It was found that, depending on the weather and installation strategy, 10 to 16 sets of RJPGs are needed for an OWF of any size, including 2 spare sets. The simulation was also used to get estimates of the costs compared to the single-use JPG. The steelworks, hydraulic system, inspection, testing, remounting, assembly, gripper heads, vessel and other costs were estimated based on quotes, industry rules of thumb and expertise from Iv-groep. The economic analysis showed that the RJPG already edged out the single-use JPG around 25 turbines, or equivalent to 100 JPGs. These findings were further substantiated by conducting a sensitivity analysis. The potential fluctuations in four key cost drivers were analysed. They were the installation rate, the installation strategy, the steel price and the vessel day rate. This was then combined into an adverse scenario and a favourable scenario, and it showed that even in the adverse scenario, the break-even point was around 60 turbines or equivalent to 240 JPGs.
...
This thesis presents the design of a reusable jacket pile gripper (RJPG) concept and assesses its technical and economic feasibility. The motivation behind this is to explore the potential for innovation and cost saving for offshore wind farms (OWFs) that currently require hundreds of jacket pile grippers (JPGs) to ensure grout integrity. First, the design requirements were laid out. Through a design cycle, several potential design candidates emerged. After consideration, a single RJPG design was selected to work out into a full concept. This concept was fleshed out by designing for a reference jacket in a hypothetical OWF. The definitive concept is a design where hydraulic cylinders lay in circumferential positioned welded on the outside of the jacket leg. The hydraulic cylinders press onto the pile and secure it in place. When the grout is sufficiently cured, the cylinders retract and are automatically disconnected. Then, an offshore support vessel can come by and retrieve the RJPG by using a deck mounted crane or winch, helped by buoyancy aids. The selected lifting points in combination with hinges make sure the device clears the jacket geometry during lift-out. By carefully selecting the design wave and current, the hydraulic components could efficiently be selected. This led to a design with fewer cylinders than initially expected from a conventional JPG. When the device comes back into the yard it can be cleaned, inspected, tested and remounted on the next jacket. To gain better insight into the economics of the RJPG, an installation simulation was done. It was found that, depending on the weather and installation strategy, 10 to 16 sets of RJPGs are needed for an OWF of any size, including 2 spare sets. The simulation was also used to get estimates of the costs compared to the single-use JPG. The steelworks, hydraulic system, inspection, testing, remounting, assembly, gripper heads, vessel and other costs were estimated based on quotes, industry rules of thumb and expertise from Iv-groep. The economic analysis showed that the RJPG already edged out the single-use JPG around 25 turbines, or equivalent to 100 JPGs. These findings were further substantiated by conducting a sensitivity analysis. The potential fluctuations in four key cost drivers were analysed. They were the installation rate, the installation strategy, the steel price and the vessel day rate. This was then combined into an adverse scenario and a favourable scenario, and it showed that even in the adverse scenario, the break-even point was around 60 turbines or equivalent to 240 JPGs.
Operational strategies for hydrogen production powered by offshore wind
Evaluating multi-stack PEM electrolyser systems for optimised hydrogen production and minimised stack degradation
This thesis investigates how operational strategies influence the performance of offshore PEM electrolyser systems powered by intermittent offshore wind power. The central research question is:
“How does the operational strategy for managing intermittent offshore wind power supply in an
offshore PEM electrolyser system affect hydrogen production, stack degradation and the LCOH?”
The study follows three phases. A literature review establishes PEM electrolysis as the most suitable technology for offshore hydrogen production, identifies degradation mechanisms under intermittent power operation, and derives a degradation relation. A dynamic Simulink model is then developed to simulate stack performance under variable power inputs. Finally, a techno-economic model in Python integrates the Simulink results with degradation data to evaluate operational strategies.
The analysis compares three strategies: equal-, serial-, and optimal efficiency power distribution over the stacks. Results show that operational strategy is a decisive factor. Equal distribution achieves the lowest LCOH of 12.17 $/kg with 68 stack replacements over a 15 year horizon, while serial distribution results in a 30% higher LCOH of 15.83 $/kg and requires 90 replacements. Hydrogen output differences between strategies are minimal. Strategy performance is best when operation under high current density is avoided, as this is a driving factor for degradation. The LCOH values remain significantly higher than those of fossil fuel based hydrogen.
The findings of this thesis also expose a critical knowledge gap: PEM electrolyser degradation under intermittent operation is poorly understood. Testing protocols are inconsistent, datasets fragmented, and long-term field data scarce. This complicates the viability assessment of future offshore hydrogen projects.
This research contributes by (1) highlighting the urgent need for standardized degradation testing and long-term datasets, (2) introducing a simulation framework that combines time-resolved dynamic modelling with techno-economic analysis, and (3) establishing operational strategy as a critical design factor for offshore hydrogen systems.
Future research should focus on (i) long-term degradation testing under realistic renewable power profiles, (ii) advanced time-resolved modelling with higher time resolution and incorporation of transient effects, (iii) development of optimization-based operational strategies, and (iv) integrated techno-economic analysis that includes dynamic electricity prices, offshore infrastructure, and possible integration of batteries.
To answer the research question: the operational strategy for managing intermittent offshore wind power supply has a significant impact on the performance of offshore PEM electrolyser systems, as strategies that avoid high current density operation substantially reduce degradation and lower the LCOH by up to 30%, while having only a limited effect on hydrogen production.
...
“How does the operational strategy for managing intermittent offshore wind power supply in an
offshore PEM electrolyser system affect hydrogen production, stack degradation and the LCOH?”
The study follows three phases. A literature review establishes PEM electrolysis as the most suitable technology for offshore hydrogen production, identifies degradation mechanisms under intermittent power operation, and derives a degradation relation. A dynamic Simulink model is then developed to simulate stack performance under variable power inputs. Finally, a techno-economic model in Python integrates the Simulink results with degradation data to evaluate operational strategies.
The analysis compares three strategies: equal-, serial-, and optimal efficiency power distribution over the stacks. Results show that operational strategy is a decisive factor. Equal distribution achieves the lowest LCOH of 12.17 $/kg with 68 stack replacements over a 15 year horizon, while serial distribution results in a 30% higher LCOH of 15.83 $/kg and requires 90 replacements. Hydrogen output differences between strategies are minimal. Strategy performance is best when operation under high current density is avoided, as this is a driving factor for degradation. The LCOH values remain significantly higher than those of fossil fuel based hydrogen.
The findings of this thesis also expose a critical knowledge gap: PEM electrolyser degradation under intermittent operation is poorly understood. Testing protocols are inconsistent, datasets fragmented, and long-term field data scarce. This complicates the viability assessment of future offshore hydrogen projects.
This research contributes by (1) highlighting the urgent need for standardized degradation testing and long-term datasets, (2) introducing a simulation framework that combines time-resolved dynamic modelling with techno-economic analysis, and (3) establishing operational strategy as a critical design factor for offshore hydrogen systems.
Future research should focus on (i) long-term degradation testing under realistic renewable power profiles, (ii) advanced time-resolved modelling with higher time resolution and incorporation of transient effects, (iii) development of optimization-based operational strategies, and (iv) integrated techno-economic analysis that includes dynamic electricity prices, offshore infrastructure, and possible integration of batteries.
To answer the research question: the operational strategy for managing intermittent offshore wind power supply has a significant impact on the performance of offshore PEM electrolyser systems, as strategies that avoid high current density operation substantially reduce degradation and lower the LCOH by up to 30%, while having only a limited effect on hydrogen production.
...
This thesis investigates how operational strategies influence the performance of offshore PEM electrolyser systems powered by intermittent offshore wind power. The central research question is:
“How does the operational strategy for managing intermittent offshore wind power supply in an
offshore PEM electrolyser system affect hydrogen production, stack degradation and the LCOH?”
The study follows three phases. A literature review establishes PEM electrolysis as the most suitable technology for offshore hydrogen production, identifies degradation mechanisms under intermittent power operation, and derives a degradation relation. A dynamic Simulink model is then developed to simulate stack performance under variable power inputs. Finally, a techno-economic model in Python integrates the Simulink results with degradation data to evaluate operational strategies.
The analysis compares three strategies: equal-, serial-, and optimal efficiency power distribution over the stacks. Results show that operational strategy is a decisive factor. Equal distribution achieves the lowest LCOH of 12.17 $/kg with 68 stack replacements over a 15 year horizon, while serial distribution results in a 30% higher LCOH of 15.83 $/kg and requires 90 replacements. Hydrogen output differences between strategies are minimal. Strategy performance is best when operation under high current density is avoided, as this is a driving factor for degradation. The LCOH values remain significantly higher than those of fossil fuel based hydrogen.
The findings of this thesis also expose a critical knowledge gap: PEM electrolyser degradation under intermittent operation is poorly understood. Testing protocols are inconsistent, datasets fragmented, and long-term field data scarce. This complicates the viability assessment of future offshore hydrogen projects.
This research contributes by (1) highlighting the urgent need for standardized degradation testing and long-term datasets, (2) introducing a simulation framework that combines time-resolved dynamic modelling with techno-economic analysis, and (3) establishing operational strategy as a critical design factor for offshore hydrogen systems.
Future research should focus on (i) long-term degradation testing under realistic renewable power profiles, (ii) advanced time-resolved modelling with higher time resolution and incorporation of transient effects, (iii) development of optimization-based operational strategies, and (iv) integrated techno-economic analysis that includes dynamic electricity prices, offshore infrastructure, and possible integration of batteries.
To answer the research question: the operational strategy for managing intermittent offshore wind power supply has a significant impact on the performance of offshore PEM electrolyser systems, as strategies that avoid high current density operation substantially reduce degradation and lower the LCOH by up to 30%, while having only a limited effect on hydrogen production.
“How does the operational strategy for managing intermittent offshore wind power supply in an
offshore PEM electrolyser system affect hydrogen production, stack degradation and the LCOH?”
The study follows three phases. A literature review establishes PEM electrolysis as the most suitable technology for offshore hydrogen production, identifies degradation mechanisms under intermittent power operation, and derives a degradation relation. A dynamic Simulink model is then developed to simulate stack performance under variable power inputs. Finally, a techno-economic model in Python integrates the Simulink results with degradation data to evaluate operational strategies.
The analysis compares three strategies: equal-, serial-, and optimal efficiency power distribution over the stacks. Results show that operational strategy is a decisive factor. Equal distribution achieves the lowest LCOH of 12.17 $/kg with 68 stack replacements over a 15 year horizon, while serial distribution results in a 30% higher LCOH of 15.83 $/kg and requires 90 replacements. Hydrogen output differences between strategies are minimal. Strategy performance is best when operation under high current density is avoided, as this is a driving factor for degradation. The LCOH values remain significantly higher than those of fossil fuel based hydrogen.
The findings of this thesis also expose a critical knowledge gap: PEM electrolyser degradation under intermittent operation is poorly understood. Testing protocols are inconsistent, datasets fragmented, and long-term field data scarce. This complicates the viability assessment of future offshore hydrogen projects.
This research contributes by (1) highlighting the urgent need for standardized degradation testing and long-term datasets, (2) introducing a simulation framework that combines time-resolved dynamic modelling with techno-economic analysis, and (3) establishing operational strategy as a critical design factor for offshore hydrogen systems.
Future research should focus on (i) long-term degradation testing under realistic renewable power profiles, (ii) advanced time-resolved modelling with higher time resolution and incorporation of transient effects, (iii) development of optimization-based operational strategies, and (iv) integrated techno-economic analysis that includes dynamic electricity prices, offshore infrastructure, and possible integration of batteries.
To answer the research question: the operational strategy for managing intermittent offshore wind power supply has a significant impact on the performance of offshore PEM electrolyser systems, as strategies that avoid high current density operation substantially reduce degradation and lower the LCOH by up to 30%, while having only a limited effect on hydrogen production.
Framework for Evaluation of Silent Installation Technologies
Evaluating Installation and Mitigation Strategies for Offshore Monopiles in an Early Project Phase: Balancing Noise Regulations with Technical, Operational, and Cost Considerations
Master thesis
(2025)
-
E.A.F. Wentink, J.S. Hoving, A. Metrikine, Gudmund Eiksund, Gustav Grimstad, Apostolos Reppas, Ferdy Hengeveld
As offshore wind turbines grow in size, the installation of monopile foundations faces increasing technical, operational, and environmental challenges. A key concern is underwater noise pollution generated during pile driving, which poses risks to marine life and must comply with increasingly strict environmental regulations. While conventional impact piling is still the most commonly used technique, it often requires extensive mitigation measures to reduce noise levels. As turbine dimensions, and consequently the required driving energy, continue to increase, these mitigation measures may no longer be sufficient to ensure compliance with noise limits. This has led to growing interest in alternative installation techniques, such as vibropiling and vibrojetting, which are expected to operate more quietly but introduce technical uncertainties, particularly regarding drivability.
This thesis presents a comparative evaluation framework to support early-phase decision-making for low-noise monopile installation and related mitigation strategies. The framework quantifies trade-offs between underwater noise emissions, technical feasibility (drivability risk), operational duration, and total cost across a wide range of installation-mitigation combinations. It is implemented as a modular Python model with Excel-based inputs, in which the user can specify the relevant project parameters. This setup enables flexible and transparent comparison of fundamentally different technological strategies.
The framework was developed through an iterative process of four main steps. First, the current state of installation methods and mitigation technologies was assessed, including recent innovations. Second, internal Van Oord data was analysed to identify key parameters, complemented by expert interviews to validate assumptions and fill data gaps. Third, a dynamic model was implemented and verified through logic testing. Lastly, the framework was applied to case studies to evaluate performance trends, with sensitivity analyses to assess robustness under varying assumptions.
The results demonstrate how the framework enables systematic comparison of installation strategies and the trade-offs between noise, technical feasibility, and cost. This integrative approach is made possible by linking expertise from different specialisation fields within Van Oord. Information that was previously considered in isolation is now combined, creating a holistic overview. While still in its early stages, the framework shows strong potential to provide valuable insights for decision-making, particularly as it is further expanded and refined with additional data.
The case studies indicate that, under current conditions, impact piling remains the most cost-efficient option, primarily due to uncertainties in the drivability of alternative methods. For Van Oord, meeting noise regulations is essential, but achieving the required penetration depth is equally critical, and this is still most reliably achieved with impact piling. According to the model, compliance with noise limits can be reached using an impact hammer with full mitigation, although this relies on idealised assumptions and leaves very little margin, as the hammer operates close to the noise threshold. In practice, site-specific conditions may still lead to exceedances. Moreover, this framework is based on a 15~MW turbine, and as turbine sizes are expected to increase towards 20~MW or beyond, the likelihood that impact piling can meet noise regulations will further diminish. This underlines the importance of advancing alternative installation methods...
...
This thesis presents a comparative evaluation framework to support early-phase decision-making for low-noise monopile installation and related mitigation strategies. The framework quantifies trade-offs between underwater noise emissions, technical feasibility (drivability risk), operational duration, and total cost across a wide range of installation-mitigation combinations. It is implemented as a modular Python model with Excel-based inputs, in which the user can specify the relevant project parameters. This setup enables flexible and transparent comparison of fundamentally different technological strategies.
The framework was developed through an iterative process of four main steps. First, the current state of installation methods and mitigation technologies was assessed, including recent innovations. Second, internal Van Oord data was analysed to identify key parameters, complemented by expert interviews to validate assumptions and fill data gaps. Third, a dynamic model was implemented and verified through logic testing. Lastly, the framework was applied to case studies to evaluate performance trends, with sensitivity analyses to assess robustness under varying assumptions.
The results demonstrate how the framework enables systematic comparison of installation strategies and the trade-offs between noise, technical feasibility, and cost. This integrative approach is made possible by linking expertise from different specialisation fields within Van Oord. Information that was previously considered in isolation is now combined, creating a holistic overview. While still in its early stages, the framework shows strong potential to provide valuable insights for decision-making, particularly as it is further expanded and refined with additional data.
The case studies indicate that, under current conditions, impact piling remains the most cost-efficient option, primarily due to uncertainties in the drivability of alternative methods. For Van Oord, meeting noise regulations is essential, but achieving the required penetration depth is equally critical, and this is still most reliably achieved with impact piling. According to the model, compliance with noise limits can be reached using an impact hammer with full mitigation, although this relies on idealised assumptions and leaves very little margin, as the hammer operates close to the noise threshold. In practice, site-specific conditions may still lead to exceedances. Moreover, this framework is based on a 15~MW turbine, and as turbine sizes are expected to increase towards 20~MW or beyond, the likelihood that impact piling can meet noise regulations will further diminish. This underlines the importance of advancing alternative installation methods...
...
As offshore wind turbines grow in size, the installation of monopile foundations faces increasing technical, operational, and environmental challenges. A key concern is underwater noise pollution generated during pile driving, which poses risks to marine life and must comply with increasingly strict environmental regulations. While conventional impact piling is still the most commonly used technique, it often requires extensive mitigation measures to reduce noise levels. As turbine dimensions, and consequently the required driving energy, continue to increase, these mitigation measures may no longer be sufficient to ensure compliance with noise limits. This has led to growing interest in alternative installation techniques, such as vibropiling and vibrojetting, which are expected to operate more quietly but introduce technical uncertainties, particularly regarding drivability.
This thesis presents a comparative evaluation framework to support early-phase decision-making for low-noise monopile installation and related mitigation strategies. The framework quantifies trade-offs between underwater noise emissions, technical feasibility (drivability risk), operational duration, and total cost across a wide range of installation-mitigation combinations. It is implemented as a modular Python model with Excel-based inputs, in which the user can specify the relevant project parameters. This setup enables flexible and transparent comparison of fundamentally different technological strategies.
The framework was developed through an iterative process of four main steps. First, the current state of installation methods and mitigation technologies was assessed, including recent innovations. Second, internal Van Oord data was analysed to identify key parameters, complemented by expert interviews to validate assumptions and fill data gaps. Third, a dynamic model was implemented and verified through logic testing. Lastly, the framework was applied to case studies to evaluate performance trends, with sensitivity analyses to assess robustness under varying assumptions.
The results demonstrate how the framework enables systematic comparison of installation strategies and the trade-offs between noise, technical feasibility, and cost. This integrative approach is made possible by linking expertise from different specialisation fields within Van Oord. Information that was previously considered in isolation is now combined, creating a holistic overview. While still in its early stages, the framework shows strong potential to provide valuable insights for decision-making, particularly as it is further expanded and refined with additional data.
The case studies indicate that, under current conditions, impact piling remains the most cost-efficient option, primarily due to uncertainties in the drivability of alternative methods. For Van Oord, meeting noise regulations is essential, but achieving the required penetration depth is equally critical, and this is still most reliably achieved with impact piling. According to the model, compliance with noise limits can be reached using an impact hammer with full mitigation, although this relies on idealised assumptions and leaves very little margin, as the hammer operates close to the noise threshold. In practice, site-specific conditions may still lead to exceedances. Moreover, this framework is based on a 15~MW turbine, and as turbine sizes are expected to increase towards 20~MW or beyond, the likelihood that impact piling can meet noise regulations will further diminish. This underlines the importance of advancing alternative installation methods...
This thesis presents a comparative evaluation framework to support early-phase decision-making for low-noise monopile installation and related mitigation strategies. The framework quantifies trade-offs between underwater noise emissions, technical feasibility (drivability risk), operational duration, and total cost across a wide range of installation-mitigation combinations. It is implemented as a modular Python model with Excel-based inputs, in which the user can specify the relevant project parameters. This setup enables flexible and transparent comparison of fundamentally different technological strategies.
The framework was developed through an iterative process of four main steps. First, the current state of installation methods and mitigation technologies was assessed, including recent innovations. Second, internal Van Oord data was analysed to identify key parameters, complemented by expert interviews to validate assumptions and fill data gaps. Third, a dynamic model was implemented and verified through logic testing. Lastly, the framework was applied to case studies to evaluate performance trends, with sensitivity analyses to assess robustness under varying assumptions.
The results demonstrate how the framework enables systematic comparison of installation strategies and the trade-offs between noise, technical feasibility, and cost. This integrative approach is made possible by linking expertise from different specialisation fields within Van Oord. Information that was previously considered in isolation is now combined, creating a holistic overview. While still in its early stages, the framework shows strong potential to provide valuable insights for decision-making, particularly as it is further expanded and refined with additional data.
The case studies indicate that, under current conditions, impact piling remains the most cost-efficient option, primarily due to uncertainties in the drivability of alternative methods. For Van Oord, meeting noise regulations is essential, but achieving the required penetration depth is equally critical, and this is still most reliably achieved with impact piling. According to the model, compliance with noise limits can be reached using an impact hammer with full mitigation, although this relies on idealised assumptions and leaves very little margin, as the hammer operates close to the noise threshold. In practice, site-specific conditions may still lead to exceedances. Moreover, this framework is based on a 15~MW turbine, and as turbine sizes are expected to increase towards 20~MW or beyond, the likelihood that impact piling can meet noise regulations will further diminish. This underlines the importance of advancing alternative installation methods...
The rapidly expanding global offshore wind market and the declining number of high-quality, shallow-water sites are driving the industry to seek innovative and cost-effective foundation solutions for deep-water applications. This shift to deeper waters introduces new challenges to traditional foundation types such as conventional monopiles (CMP) and jacket structures, which face technical and economic challenges due to escalating material demands and increased installation complexity. Although monopile foundations have historically facilitated cost reduction because of their ease of manufacturability, transportability, and installability, they have been limited to relatively shallow water depths. Given that jacket-type and floating support structures remain costly, the possibility of scaling up or adapting monopile designs for water depths beyond 40–60 meters merits investigation. A promising solution is the guyed monopile (GMP) concept, which integrates a mooring system with a CMP to provide additional lateral restraint. This integration reduces the required structural dimensions and steel usage under deep-water loading conditions, thereby extending the feasibility of monopile structures into deeper waters.
The goal of this study is to investigate the use of a guyed monopile as a more favourable, cost-effective alternative to CMPs and jackets for deep-water applications with large wind turbine generators (rated at 15 MW) in water depths ranging from 60 to 100 meters, and to determine the specific water depth range at which this concept proves both technically and economically advantageous over the CMP and jackets. To ensure broad applicability, the Hollandse Kust West wind farm site in the North Sea is selected as the reference location.
Conceptual designs for the GMP, CMP, and jackets were developed and optimized for case study water depths of 60, 80, and 100 meters at the representative North Sea site. Using in-house Python tools and a comprehensive dataset covering environmental conditions, soil properties, and wind turbine characteristics, key design parameters such as diameter, wall thickness, and embedment depth were optimized. The designs are checked against and found to be in compliance with both ultimate limit state (ULS) and fatigue limit state (FLS) criteria, revealing that while CMP designs suffer from a steep increase in material requirements with depth, the GMP benefits from its fixed-cost mooring system and exhibits a more gradual cost evolution. In fact, comparative analysis indicates that the GMP reduces capital expenditures by roughly 20–30\% relative to CMPs and by around 10–25\% relative to jackets across the examined water depth range.
Lifecycle cost assessments are conducted using constructed cost models that incorporate fabrication, installation, maintenance, and decommissioning costs. The study shows that lifecycle costs for CMPs escalate dramatically with increasing depth due to their steel-intensive designs, whereas the GMP maintains a lower overall cost beyond approximately 70 to 75 meters. Moreover, as water depths approach 85 to 90 meters, it is found that jackets become competitive by exhibiting more moderated cost escalation. A sensitivity analysis conducted in this study further reveals that member thickness and diameter are the most critical cost drivers across all foundation types in this study.
Overall, the findings of this research establish the GMP as a technically robust and economically attractive foundation solution for deep-water offshore wind applications. Based on the assumptions and restrictions of this study, the GMP offers a promising alternative that successfully meets the load-bearing and stiffness requirements for large wind turbines while significantly reducing steel consumption, thereby supporting the extension of monopile use to water depths of up to 90 meters.
Future research should build upon these insights by conducting a more in-depth investigation of the GMP design, validating its performance through advanced dynamic analyses and targeted field trials. Expanding the applicability range of the GMP across varied offshore environments will further strengthen its appeal and unlock its full potential as a foundation concept for deep-water WTGs. ...
The goal of this study is to investigate the use of a guyed monopile as a more favourable, cost-effective alternative to CMPs and jackets for deep-water applications with large wind turbine generators (rated at 15 MW) in water depths ranging from 60 to 100 meters, and to determine the specific water depth range at which this concept proves both technically and economically advantageous over the CMP and jackets. To ensure broad applicability, the Hollandse Kust West wind farm site in the North Sea is selected as the reference location.
Conceptual designs for the GMP, CMP, and jackets were developed and optimized for case study water depths of 60, 80, and 100 meters at the representative North Sea site. Using in-house Python tools and a comprehensive dataset covering environmental conditions, soil properties, and wind turbine characteristics, key design parameters such as diameter, wall thickness, and embedment depth were optimized. The designs are checked against and found to be in compliance with both ultimate limit state (ULS) and fatigue limit state (FLS) criteria, revealing that while CMP designs suffer from a steep increase in material requirements with depth, the GMP benefits from its fixed-cost mooring system and exhibits a more gradual cost evolution. In fact, comparative analysis indicates that the GMP reduces capital expenditures by roughly 20–30\% relative to CMPs and by around 10–25\% relative to jackets across the examined water depth range.
Lifecycle cost assessments are conducted using constructed cost models that incorporate fabrication, installation, maintenance, and decommissioning costs. The study shows that lifecycle costs for CMPs escalate dramatically with increasing depth due to their steel-intensive designs, whereas the GMP maintains a lower overall cost beyond approximately 70 to 75 meters. Moreover, as water depths approach 85 to 90 meters, it is found that jackets become competitive by exhibiting more moderated cost escalation. A sensitivity analysis conducted in this study further reveals that member thickness and diameter are the most critical cost drivers across all foundation types in this study.
Overall, the findings of this research establish the GMP as a technically robust and economically attractive foundation solution for deep-water offshore wind applications. Based on the assumptions and restrictions of this study, the GMP offers a promising alternative that successfully meets the load-bearing and stiffness requirements for large wind turbines while significantly reducing steel consumption, thereby supporting the extension of monopile use to water depths of up to 90 meters.
Future research should build upon these insights by conducting a more in-depth investigation of the GMP design, validating its performance through advanced dynamic analyses and targeted field trials. Expanding the applicability range of the GMP across varied offshore environments will further strengthen its appeal and unlock its full potential as a foundation concept for deep-water WTGs. ...
The rapidly expanding global offshore wind market and the declining number of high-quality, shallow-water sites are driving the industry to seek innovative and cost-effective foundation solutions for deep-water applications. This shift to deeper waters introduces new challenges to traditional foundation types such as conventional monopiles (CMP) and jacket structures, which face technical and economic challenges due to escalating material demands and increased installation complexity. Although monopile foundations have historically facilitated cost reduction because of their ease of manufacturability, transportability, and installability, they have been limited to relatively shallow water depths. Given that jacket-type and floating support structures remain costly, the possibility of scaling up or adapting monopile designs for water depths beyond 40–60 meters merits investigation. A promising solution is the guyed monopile (GMP) concept, which integrates a mooring system with a CMP to provide additional lateral restraint. This integration reduces the required structural dimensions and steel usage under deep-water loading conditions, thereby extending the feasibility of monopile structures into deeper waters.
The goal of this study is to investigate the use of a guyed monopile as a more favourable, cost-effective alternative to CMPs and jackets for deep-water applications with large wind turbine generators (rated at 15 MW) in water depths ranging from 60 to 100 meters, and to determine the specific water depth range at which this concept proves both technically and economically advantageous over the CMP and jackets. To ensure broad applicability, the Hollandse Kust West wind farm site in the North Sea is selected as the reference location.
Conceptual designs for the GMP, CMP, and jackets were developed and optimized for case study water depths of 60, 80, and 100 meters at the representative North Sea site. Using in-house Python tools and a comprehensive dataset covering environmental conditions, soil properties, and wind turbine characteristics, key design parameters such as diameter, wall thickness, and embedment depth were optimized. The designs are checked against and found to be in compliance with both ultimate limit state (ULS) and fatigue limit state (FLS) criteria, revealing that while CMP designs suffer from a steep increase in material requirements with depth, the GMP benefits from its fixed-cost mooring system and exhibits a more gradual cost evolution. In fact, comparative analysis indicates that the GMP reduces capital expenditures by roughly 20–30\% relative to CMPs and by around 10–25\% relative to jackets across the examined water depth range.
Lifecycle cost assessments are conducted using constructed cost models that incorporate fabrication, installation, maintenance, and decommissioning costs. The study shows that lifecycle costs for CMPs escalate dramatically with increasing depth due to their steel-intensive designs, whereas the GMP maintains a lower overall cost beyond approximately 70 to 75 meters. Moreover, as water depths approach 85 to 90 meters, it is found that jackets become competitive by exhibiting more moderated cost escalation. A sensitivity analysis conducted in this study further reveals that member thickness and diameter are the most critical cost drivers across all foundation types in this study.
Overall, the findings of this research establish the GMP as a technically robust and economically attractive foundation solution for deep-water offshore wind applications. Based on the assumptions and restrictions of this study, the GMP offers a promising alternative that successfully meets the load-bearing and stiffness requirements for large wind turbines while significantly reducing steel consumption, thereby supporting the extension of monopile use to water depths of up to 90 meters.
Future research should build upon these insights by conducting a more in-depth investigation of the GMP design, validating its performance through advanced dynamic analyses and targeted field trials. Expanding the applicability range of the GMP across varied offshore environments will further strengthen its appeal and unlock its full potential as a foundation concept for deep-water WTGs.
The goal of this study is to investigate the use of a guyed monopile as a more favourable, cost-effective alternative to CMPs and jackets for deep-water applications with large wind turbine generators (rated at 15 MW) in water depths ranging from 60 to 100 meters, and to determine the specific water depth range at which this concept proves both technically and economically advantageous over the CMP and jackets. To ensure broad applicability, the Hollandse Kust West wind farm site in the North Sea is selected as the reference location.
Conceptual designs for the GMP, CMP, and jackets were developed and optimized for case study water depths of 60, 80, and 100 meters at the representative North Sea site. Using in-house Python tools and a comprehensive dataset covering environmental conditions, soil properties, and wind turbine characteristics, key design parameters such as diameter, wall thickness, and embedment depth were optimized. The designs are checked against and found to be in compliance with both ultimate limit state (ULS) and fatigue limit state (FLS) criteria, revealing that while CMP designs suffer from a steep increase in material requirements with depth, the GMP benefits from its fixed-cost mooring system and exhibits a more gradual cost evolution. In fact, comparative analysis indicates that the GMP reduces capital expenditures by roughly 20–30\% relative to CMPs and by around 10–25\% relative to jackets across the examined water depth range.
Lifecycle cost assessments are conducted using constructed cost models that incorporate fabrication, installation, maintenance, and decommissioning costs. The study shows that lifecycle costs for CMPs escalate dramatically with increasing depth due to their steel-intensive designs, whereas the GMP maintains a lower overall cost beyond approximately 70 to 75 meters. Moreover, as water depths approach 85 to 90 meters, it is found that jackets become competitive by exhibiting more moderated cost escalation. A sensitivity analysis conducted in this study further reveals that member thickness and diameter are the most critical cost drivers across all foundation types in this study.
Overall, the findings of this research establish the GMP as a technically robust and economically attractive foundation solution for deep-water offshore wind applications. Based on the assumptions and restrictions of this study, the GMP offers a promising alternative that successfully meets the load-bearing and stiffness requirements for large wind turbines while significantly reducing steel consumption, thereby supporting the extension of monopile use to water depths of up to 90 meters.
Future research should build upon these insights by conducting a more in-depth investigation of the GMP design, validating its performance through advanced dynamic analyses and targeted field trials. Expanding the applicability range of the GMP across varied offshore environments will further strengthen its appeal and unlock its full potential as a foundation concept for deep-water WTGs.
Scaling the ice strength
What are the limitations of using local ice strength measurements from the Borehole Jack and brine based estimations to determine a site-specific CR coefficient according to the ISO 19906 guideline?
As offshore wind energy is expanding into seasonally ice-covered regions, accurate estimation of sea ice strength becomes critical for safe and cost-effective design. ISO 19906 provides an empirical method to estimate the global ice force based on the width of the structure, thickness of the ice, and an ice strength coefficient, CR. It suggests predefined reference values for this coefficient depending on the region of interest. However, if the wind farm is located outside one of these predefined refer- ence regions, the ISO standard gives limited guidance on how to adjust the ice strength coefficient to the local ice conditions. This study investigates the method proposed in ISO 19906 to estimate a site-specific ice strength coefficient, CR,s. The method uses the ratio of the ice strength index obtained from strength measurements at a reference site and at a new site.
In this study, two sites were selected to determine this strength index ratio. Hjellbotn, a temperate brackish ice zone near Trondheim, was selected as a potential offshore wind site and falls outside ISO’s predefined CR regions. Svea, in the Svalbard archipelago, was used as a proxy for the Arctic region for which the ice strength coefficient has been determined by ISO. The ice strength index at both locations was estimated using two ISO-recommended approaches: a direct mechanical measurement with the BHJ and an indirect estimate based on brine volume derived from temperature and salinity.
ISO 19906 provides a predefined ice strength index for the Arctic region when using the brine volume method. However, the standard does not offer a similar reference value for measurements taken with the BHJ. BHJ tests from Svea were used as the Arctic BHJ reference. The same test procedure was used at Hjellbotn for comparison. The BHJ strength ratio suggested lowering the ice strength coefficient for Hjellbotn. Brine-based strength ratios used either the ISO Arctic reference or Svea data. The ISO-based approach also indicated a lower strength coefficient for Hjellbotn, as expected for more temperate ice. Using Svea as the proxy for the Arctic gave a higher strength coefficient for Hjellbotn, which was unexpected. It showed that the choice of method and reference value affects the outcome of the strength estimation. This difference indicated a limitation of the brine volume strength method when trying to scale the ice strength coefficient from the Arctic to warm ice conditions. For warm ice, small temperature changes caused large strength variations, which showed the brine-based method’s high sensitivity.
The findings of this work suggest that while the ISO framework provides a basis for estimating an ice strength coefficient for a new area, careful interpretation is required when scaling the ice strength to temperate and marginal ice regimes. The brine volume method is sensitive to measurement uncertainty at high ice temperatures and may not always reflect the full mechanical strength of the ice. ...
In this study, two sites were selected to determine this strength index ratio. Hjellbotn, a temperate brackish ice zone near Trondheim, was selected as a potential offshore wind site and falls outside ISO’s predefined CR regions. Svea, in the Svalbard archipelago, was used as a proxy for the Arctic region for which the ice strength coefficient has been determined by ISO. The ice strength index at both locations was estimated using two ISO-recommended approaches: a direct mechanical measurement with the BHJ and an indirect estimate based on brine volume derived from temperature and salinity.
ISO 19906 provides a predefined ice strength index for the Arctic region when using the brine volume method. However, the standard does not offer a similar reference value for measurements taken with the BHJ. BHJ tests from Svea were used as the Arctic BHJ reference. The same test procedure was used at Hjellbotn for comparison. The BHJ strength ratio suggested lowering the ice strength coefficient for Hjellbotn. Brine-based strength ratios used either the ISO Arctic reference or Svea data. The ISO-based approach also indicated a lower strength coefficient for Hjellbotn, as expected for more temperate ice. Using Svea as the proxy for the Arctic gave a higher strength coefficient for Hjellbotn, which was unexpected. It showed that the choice of method and reference value affects the outcome of the strength estimation. This difference indicated a limitation of the brine volume strength method when trying to scale the ice strength coefficient from the Arctic to warm ice conditions. For warm ice, small temperature changes caused large strength variations, which showed the brine-based method’s high sensitivity.
The findings of this work suggest that while the ISO framework provides a basis for estimating an ice strength coefficient for a new area, careful interpretation is required when scaling the ice strength to temperate and marginal ice regimes. The brine volume method is sensitive to measurement uncertainty at high ice temperatures and may not always reflect the full mechanical strength of the ice. ...
As offshore wind energy is expanding into seasonally ice-covered regions, accurate estimation of sea ice strength becomes critical for safe and cost-effective design. ISO 19906 provides an empirical method to estimate the global ice force based on the width of the structure, thickness of the ice, and an ice strength coefficient, CR. It suggests predefined reference values for this coefficient depending on the region of interest. However, if the wind farm is located outside one of these predefined refer- ence regions, the ISO standard gives limited guidance on how to adjust the ice strength coefficient to the local ice conditions. This study investigates the method proposed in ISO 19906 to estimate a site-specific ice strength coefficient, CR,s. The method uses the ratio of the ice strength index obtained from strength measurements at a reference site and at a new site.
In this study, two sites were selected to determine this strength index ratio. Hjellbotn, a temperate brackish ice zone near Trondheim, was selected as a potential offshore wind site and falls outside ISO’s predefined CR regions. Svea, in the Svalbard archipelago, was used as a proxy for the Arctic region for which the ice strength coefficient has been determined by ISO. The ice strength index at both locations was estimated using two ISO-recommended approaches: a direct mechanical measurement with the BHJ and an indirect estimate based on brine volume derived from temperature and salinity.
ISO 19906 provides a predefined ice strength index for the Arctic region when using the brine volume method. However, the standard does not offer a similar reference value for measurements taken with the BHJ. BHJ tests from Svea were used as the Arctic BHJ reference. The same test procedure was used at Hjellbotn for comparison. The BHJ strength ratio suggested lowering the ice strength coefficient for Hjellbotn. Brine-based strength ratios used either the ISO Arctic reference or Svea data. The ISO-based approach also indicated a lower strength coefficient for Hjellbotn, as expected for more temperate ice. Using Svea as the proxy for the Arctic gave a higher strength coefficient for Hjellbotn, which was unexpected. It showed that the choice of method and reference value affects the outcome of the strength estimation. This difference indicated a limitation of the brine volume strength method when trying to scale the ice strength coefficient from the Arctic to warm ice conditions. For warm ice, small temperature changes caused large strength variations, which showed the brine-based method’s high sensitivity.
The findings of this work suggest that while the ISO framework provides a basis for estimating an ice strength coefficient for a new area, careful interpretation is required when scaling the ice strength to temperate and marginal ice regimes. The brine volume method is sensitive to measurement uncertainty at high ice temperatures and may not always reflect the full mechanical strength of the ice.
In this study, two sites were selected to determine this strength index ratio. Hjellbotn, a temperate brackish ice zone near Trondheim, was selected as a potential offshore wind site and falls outside ISO’s predefined CR regions. Svea, in the Svalbard archipelago, was used as a proxy for the Arctic region for which the ice strength coefficient has been determined by ISO. The ice strength index at both locations was estimated using two ISO-recommended approaches: a direct mechanical measurement with the BHJ and an indirect estimate based on brine volume derived from temperature and salinity.
ISO 19906 provides a predefined ice strength index for the Arctic region when using the brine volume method. However, the standard does not offer a similar reference value for measurements taken with the BHJ. BHJ tests from Svea were used as the Arctic BHJ reference. The same test procedure was used at Hjellbotn for comparison. The BHJ strength ratio suggested lowering the ice strength coefficient for Hjellbotn. Brine-based strength ratios used either the ISO Arctic reference or Svea data. The ISO-based approach also indicated a lower strength coefficient for Hjellbotn, as expected for more temperate ice. Using Svea as the proxy for the Arctic gave a higher strength coefficient for Hjellbotn, which was unexpected. It showed that the choice of method and reference value affects the outcome of the strength estimation. This difference indicated a limitation of the brine volume strength method when trying to scale the ice strength coefficient from the Arctic to warm ice conditions. For warm ice, small temperature changes caused large strength variations, which showed the brine-based method’s high sensitivity.
The findings of this work suggest that while the ISO framework provides a basis for estimating an ice strength coefficient for a new area, careful interpretation is required when scaling the ice strength to temperate and marginal ice regimes. The brine volume method is sensitive to measurement uncertainty at high ice temperatures and may not always reflect the full mechanical strength of the ice.
Develop a framework to be used to improve planning and execution of offshore T&I operations
Case Study: Concrete caisson T&I operations in the North Sea
Offshore T&I operations of large and heavy structures are complex and high-risk activities, highly sensitive to uncertainties. This thesis presents the outcomes of a simulation-based model designed to analyze the impact of such uncertainties on offshore operation workflows.
By first identifying the key uncertainties that cause delays in offshore T&I projects through an in-depth literature review, the model was then tailored to capture them effectively. A hypothetical case study on transporting and installing prefabricated concrete caissons for the construction of an energy island is used to verify and demonstrate the capabilities of the model. Two strategies were assessed, one using a semi-submersible barge and one using the wet-tow method for transportation. Monte Carlo simulations were applied to capture the impact of the weather and operational uncertainties, as well as the probability of failure events. The results show that project performance is strongly influenced by factors such as execution timing, the simplicity of the operational step sequence and the operability limits.
The model is designed to be easily adaptable to a wide variety of offshore operations. Its structured outputs provide engineers and planners with a powerful tool to evaluate how critical parameters (e.g. weather conditions) affect the project performance and explore alternatives to determine the optimal one, in terms of time and resource availability.
...
By first identifying the key uncertainties that cause delays in offshore T&I projects through an in-depth literature review, the model was then tailored to capture them effectively. A hypothetical case study on transporting and installing prefabricated concrete caissons for the construction of an energy island is used to verify and demonstrate the capabilities of the model. Two strategies were assessed, one using a semi-submersible barge and one using the wet-tow method for transportation. Monte Carlo simulations were applied to capture the impact of the weather and operational uncertainties, as well as the probability of failure events. The results show that project performance is strongly influenced by factors such as execution timing, the simplicity of the operational step sequence and the operability limits.
The model is designed to be easily adaptable to a wide variety of offshore operations. Its structured outputs provide engineers and planners with a powerful tool to evaluate how critical parameters (e.g. weather conditions) affect the project performance and explore alternatives to determine the optimal one, in terms of time and resource availability.
...
Offshore T&I operations of large and heavy structures are complex and high-risk activities, highly sensitive to uncertainties. This thesis presents the outcomes of a simulation-based model designed to analyze the impact of such uncertainties on offshore operation workflows.
By first identifying the key uncertainties that cause delays in offshore T&I projects through an in-depth literature review, the model was then tailored to capture them effectively. A hypothetical case study on transporting and installing prefabricated concrete caissons for the construction of an energy island is used to verify and demonstrate the capabilities of the model. Two strategies were assessed, one using a semi-submersible barge and one using the wet-tow method for transportation. Monte Carlo simulations were applied to capture the impact of the weather and operational uncertainties, as well as the probability of failure events. The results show that project performance is strongly influenced by factors such as execution timing, the simplicity of the operational step sequence and the operability limits.
The model is designed to be easily adaptable to a wide variety of offshore operations. Its structured outputs provide engineers and planners with a powerful tool to evaluate how critical parameters (e.g. weather conditions) affect the project performance and explore alternatives to determine the optimal one, in terms of time and resource availability.
By first identifying the key uncertainties that cause delays in offshore T&I projects through an in-depth literature review, the model was then tailored to capture them effectively. A hypothetical case study on transporting and installing prefabricated concrete caissons for the construction of an energy island is used to verify and demonstrate the capabilities of the model. Two strategies were assessed, one using a semi-submersible barge and one using the wet-tow method for transportation. Monte Carlo simulations were applied to capture the impact of the weather and operational uncertainties, as well as the probability of failure events. The results show that project performance is strongly influenced by factors such as execution timing, the simplicity of the operational step sequence and the operability limits.
The model is designed to be easily adaptable to a wide variety of offshore operations. Its structured outputs provide engineers and planners with a powerful tool to evaluate how critical parameters (e.g. weather conditions) affect the project performance and explore alternatives to determine the optimal one, in terms of time and resource availability.
Small-diameter pile installation by the GBM Works Vibrojet®
A technical feasibility study into the application of the GBM Works Vibrojet® in the installation of small-diameter piles used for foundations in offshore wind applications
The offshore wind energy sector requires efficient and environmentally conscious installation of founda-tion piles. Impact-hammering generates significant noise pollution, requires mitigation measures, andcan cause pile fatigue, while vibro-hammers face limitations in achieving target depths in dense soils. This thesis investigates the technical feasibility of applying the GBM Works Vibrojet® – a new method combining vibro-hammering with water jetting near the end of the pile to fluidize internal soil and reduce friction for installing small-diameter piles (0.5-4 meters) used in jacket structures and floating windturbine foundations.
The study employs literature reviews, adapts existing soil resistance (SRD) and bearing capacity (API) models, and introduces a ”Vibrojet® potential reduction ratio” to quantify the resistance of the soil inside the pile, which can potentially be reduced to zero. It analyses various pile dimensions and soil conditions representative of the North Sea. Findings suggest the Vibrojet® can likely be scaled down for small-diameter piles, although submerged installation and the soil plugging effect, for piles with a diameter smaller than 1.5 meters, need further study. The potential reduction in the resistance of the soil in the pile is comparable to monopiles for unplugged small-diameter piles but significantly higher for plugged piles. Consequently, the impact of the Vibrojet® on the axial bearing capacity in comparison to impact-hammering is similar to that of monopiles (20-25% reduction) in the analysed non-uniform soil conditions for unplugged piles, but can be substantially higher for plugged piles, particularly shorter ones.
The study concludes that installation by the Vibrojet® has technical feasibility for small-diameter piles, offering significant soil resistance reduction potential, especially in plugged conditions. While the bearing capacity reduction for unplugged piles is manageable, the impact on plugged piles requires careful design consideration, particularly given the axial loading demands on jacket and mooring piles. Recommendations include using more advanced CPT-based models, conducting physical tests, and further investigating the precise effects of fluidization on soil properties and bearing capacity. ...
The study employs literature reviews, adapts existing soil resistance (SRD) and bearing capacity (API) models, and introduces a ”Vibrojet® potential reduction ratio” to quantify the resistance of the soil inside the pile, which can potentially be reduced to zero. It analyses various pile dimensions and soil conditions representative of the North Sea. Findings suggest the Vibrojet® can likely be scaled down for small-diameter piles, although submerged installation and the soil plugging effect, for piles with a diameter smaller than 1.5 meters, need further study. The potential reduction in the resistance of the soil in the pile is comparable to monopiles for unplugged small-diameter piles but significantly higher for plugged piles. Consequently, the impact of the Vibrojet® on the axial bearing capacity in comparison to impact-hammering is similar to that of monopiles (20-25% reduction) in the analysed non-uniform soil conditions for unplugged piles, but can be substantially higher for plugged piles, particularly shorter ones.
The study concludes that installation by the Vibrojet® has technical feasibility for small-diameter piles, offering significant soil resistance reduction potential, especially in plugged conditions. While the bearing capacity reduction for unplugged piles is manageable, the impact on plugged piles requires careful design consideration, particularly given the axial loading demands on jacket and mooring piles. Recommendations include using more advanced CPT-based models, conducting physical tests, and further investigating the precise effects of fluidization on soil properties and bearing capacity. ...
The offshore wind energy sector requires efficient and environmentally conscious installation of founda-tion piles. Impact-hammering generates significant noise pollution, requires mitigation measures, andcan cause pile fatigue, while vibro-hammers face limitations in achieving target depths in dense soils. This thesis investigates the technical feasibility of applying the GBM Works Vibrojet® – a new method combining vibro-hammering with water jetting near the end of the pile to fluidize internal soil and reduce friction for installing small-diameter piles (0.5-4 meters) used in jacket structures and floating windturbine foundations.
The study employs literature reviews, adapts existing soil resistance (SRD) and bearing capacity (API) models, and introduces a ”Vibrojet® potential reduction ratio” to quantify the resistance of the soil inside the pile, which can potentially be reduced to zero. It analyses various pile dimensions and soil conditions representative of the North Sea. Findings suggest the Vibrojet® can likely be scaled down for small-diameter piles, although submerged installation and the soil plugging effect, for piles with a diameter smaller than 1.5 meters, need further study. The potential reduction in the resistance of the soil in the pile is comparable to monopiles for unplugged small-diameter piles but significantly higher for plugged piles. Consequently, the impact of the Vibrojet® on the axial bearing capacity in comparison to impact-hammering is similar to that of monopiles (20-25% reduction) in the analysed non-uniform soil conditions for unplugged piles, but can be substantially higher for plugged piles, particularly shorter ones.
The study concludes that installation by the Vibrojet® has technical feasibility for small-diameter piles, offering significant soil resistance reduction potential, especially in plugged conditions. While the bearing capacity reduction for unplugged piles is manageable, the impact on plugged piles requires careful design consideration, particularly given the axial loading demands on jacket and mooring piles. Recommendations include using more advanced CPT-based models, conducting physical tests, and further investigating the precise effects of fluidization on soil properties and bearing capacity.
The study employs literature reviews, adapts existing soil resistance (SRD) and bearing capacity (API) models, and introduces a ”Vibrojet® potential reduction ratio” to quantify the resistance of the soil inside the pile, which can potentially be reduced to zero. It analyses various pile dimensions and soil conditions representative of the North Sea. Findings suggest the Vibrojet® can likely be scaled down for small-diameter piles, although submerged installation and the soil plugging effect, for piles with a diameter smaller than 1.5 meters, need further study. The potential reduction in the resistance of the soil in the pile is comparable to monopiles for unplugged small-diameter piles but significantly higher for plugged piles. Consequently, the impact of the Vibrojet® on the axial bearing capacity in comparison to impact-hammering is similar to that of monopiles (20-25% reduction) in the analysed non-uniform soil conditions for unplugged piles, but can be substantially higher for plugged piles, particularly shorter ones.
The study concludes that installation by the Vibrojet® has technical feasibility for small-diameter piles, offering significant soil resistance reduction potential, especially in plugged conditions. While the bearing capacity reduction for unplugged piles is manageable, the impact on plugged piles requires careful design consideration, particularly given the axial loading demands on jacket and mooring piles. Recommendations include using more advanced CPT-based models, conducting physical tests, and further investigating the precise effects of fluidization on soil properties and bearing capacity.
Student report
(2025)
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F.N. Brummer, L.W. Couturier, J. Hoepman, T.J. Jeletich, M.J. Ruiter, R.W.I. Weber, José A. Á. Antolínez, F.L. Hooimeijer, J. Jovanova, J.S. Hoving
The Nahuel Huapi National Park, in the Lake District of Northern Patagonia, Argentina, is well known for its tourism industry all year round. After COVID-19, the area saw a significant increase in the number of tourists traveling to the area. This means that the lake located in the heart of the district, Lago Nahuel Huapi, is being used more and more to explore the environmental richness of the area by boat. Now, the capacity of mooring spaces is no longer sufficient in the region, resulting in the construction of illegal private docks along the shore. To reduce this impact on the environment the authorities granted in 2024 a concession to develop one of the last not yet commercialized marina’s in the region: the marina in Bahía López.
This report provides a consult for the concessionaire of this development. The process begins with a research phase, consisting of an area study, and the mapping of environmental and hydrodynamic constraints. Subsequently, stakeholders are categorized, as the development of a marina in a national park entails complex regulations from multiple organizations. The outcomes of the research phase are translated into specific functional requirements for the marina. These functional requirements are the basis for the next phase, the design phase. This phase begins with the formulation of a design vision statement, formulating the project response to local conditions. Based on this, three different conceptual designs with various technical solutions are developed. Through a multi-criteria analysis, the concepts are tested on their robustness in order to chose a final concept. This concept is then elaborated into a preliminary design. Presenting an overview of the marina’s facilities, including structural designs, operational needs, and capital costs. Finally, suggestions for future development
are provided, outlining the next steps to advance the marina to a next phase.
...
This report provides a consult for the concessionaire of this development. The process begins with a research phase, consisting of an area study, and the mapping of environmental and hydrodynamic constraints. Subsequently, stakeholders are categorized, as the development of a marina in a national park entails complex regulations from multiple organizations. The outcomes of the research phase are translated into specific functional requirements for the marina. These functional requirements are the basis for the next phase, the design phase. This phase begins with the formulation of a design vision statement, formulating the project response to local conditions. Based on this, three different conceptual designs with various technical solutions are developed. Through a multi-criteria analysis, the concepts are tested on their robustness in order to chose a final concept. This concept is then elaborated into a preliminary design. Presenting an overview of the marina’s facilities, including structural designs, operational needs, and capital costs. Finally, suggestions for future development
are provided, outlining the next steps to advance the marina to a next phase.
...
The Nahuel Huapi National Park, in the Lake District of Northern Patagonia, Argentina, is well known for its tourism industry all year round. After COVID-19, the area saw a significant increase in the number of tourists traveling to the area. This means that the lake located in the heart of the district, Lago Nahuel Huapi, is being used more and more to explore the environmental richness of the area by boat. Now, the capacity of mooring spaces is no longer sufficient in the region, resulting in the construction of illegal private docks along the shore. To reduce this impact on the environment the authorities granted in 2024 a concession to develop one of the last not yet commercialized marina’s in the region: the marina in Bahía López.
This report provides a consult for the concessionaire of this development. The process begins with a research phase, consisting of an area study, and the mapping of environmental and hydrodynamic constraints. Subsequently, stakeholders are categorized, as the development of a marina in a national park entails complex regulations from multiple organizations. The outcomes of the research phase are translated into specific functional requirements for the marina. These functional requirements are the basis for the next phase, the design phase. This phase begins with the formulation of a design vision statement, formulating the project response to local conditions. Based on this, three different conceptual designs with various technical solutions are developed. Through a multi-criteria analysis, the concepts are tested on their robustness in order to chose a final concept. This concept is then elaborated into a preliminary design. Presenting an overview of the marina’s facilities, including structural designs, operational needs, and capital costs. Finally, suggestions for future development
are provided, outlining the next steps to advance the marina to a next phase.
This report provides a consult for the concessionaire of this development. The process begins with a research phase, consisting of an area study, and the mapping of environmental and hydrodynamic constraints. Subsequently, stakeholders are categorized, as the development of a marina in a national park entails complex regulations from multiple organizations. The outcomes of the research phase are translated into specific functional requirements for the marina. These functional requirements are the basis for the next phase, the design phase. This phase begins with the formulation of a design vision statement, formulating the project response to local conditions. Based on this, three different conceptual designs with various technical solutions are developed. Through a multi-criteria analysis, the concepts are tested on their robustness in order to chose a final concept. This concept is then elaborated into a preliminary design. Presenting an overview of the marina’s facilities, including structural designs, operational needs, and capital costs. Finally, suggestions for future development
are provided, outlining the next steps to advance the marina to a next phase.
Student report
(2025)
-
Sophie ten Hoor, Olivier Stades, Julia van Beurden, Jelle Rigter, Anahí Witzenburg, Floor Dijkstra, S.C. Santema, J.S. Hoving, José A. Á. Antolínez, A.T. Gebremariam, J. Dankelman, M. Walraven
The Port of Santa Fe was once a major hub for both domestic and international trade, but changing river dynamics have reduced its accessibility and economic importance. As a result, the port now faces the challenge of redefining its role and exploring new functions that reconnect the port with the public. The Dyke 2 waterfront in the Port of Santa Fe, is currently in a deteriorated and underdeveloped state, lacking essential public facilities, accessible green spaces, and safe access to the river. Most importantly, the site faces severe riverbank instability, confirmed by a calculated Safety Factor (SF) of 0.67.
This report presents an integrated vision and technical design for the sustainable redevelopment of the project site area, commissioned as an advisory document for the Ente Administrador del Puerto de Santa Fe (EAPSF). The project employed a strategic track, guided by four pillars, and a slope protection track, using a Multi-Criteria Decision Analysis (MCDA) to select a solution, resulting in a design containing both technical stability and a public urban concept.
The resulting urban concept, The Santa Fe Riverside Park, serves as a project embodying the strategic vision. The design integrates adaptive infrastructure, including stepped terraces and docking places, engineered to accommodate significant seasonal river fluctuations. This concept is supported by the delivery of a 15-year long-term roadmap. The unstable slope is protected using an ecosystem-friendly Articulated Concrete Block mattress system, improving the calculated sliding SF from 0.67 to 1.9, and achieving an erosion SF of 2.10.
Finally, the report provides the Port Authority with a strategic foundation of recommendations to realise the project.
...
This report presents an integrated vision and technical design for the sustainable redevelopment of the project site area, commissioned as an advisory document for the Ente Administrador del Puerto de Santa Fe (EAPSF). The project employed a strategic track, guided by four pillars, and a slope protection track, using a Multi-Criteria Decision Analysis (MCDA) to select a solution, resulting in a design containing both technical stability and a public urban concept.
The resulting urban concept, The Santa Fe Riverside Park, serves as a project embodying the strategic vision. The design integrates adaptive infrastructure, including stepped terraces and docking places, engineered to accommodate significant seasonal river fluctuations. This concept is supported by the delivery of a 15-year long-term roadmap. The unstable slope is protected using an ecosystem-friendly Articulated Concrete Block mattress system, improving the calculated sliding SF from 0.67 to 1.9, and achieving an erosion SF of 2.10.
Finally, the report provides the Port Authority with a strategic foundation of recommendations to realise the project.
...
The Port of Santa Fe was once a major hub for both domestic and international trade, but changing river dynamics have reduced its accessibility and economic importance. As a result, the port now faces the challenge of redefining its role and exploring new functions that reconnect the port with the public. The Dyke 2 waterfront in the Port of Santa Fe, is currently in a deteriorated and underdeveloped state, lacking essential public facilities, accessible green spaces, and safe access to the river. Most importantly, the site faces severe riverbank instability, confirmed by a calculated Safety Factor (SF) of 0.67.
This report presents an integrated vision and technical design for the sustainable redevelopment of the project site area, commissioned as an advisory document for the Ente Administrador del Puerto de Santa Fe (EAPSF). The project employed a strategic track, guided by four pillars, and a slope protection track, using a Multi-Criteria Decision Analysis (MCDA) to select a solution, resulting in a design containing both technical stability and a public urban concept.
The resulting urban concept, The Santa Fe Riverside Park, serves as a project embodying the strategic vision. The design integrates adaptive infrastructure, including stepped terraces and docking places, engineered to accommodate significant seasonal river fluctuations. This concept is supported by the delivery of a 15-year long-term roadmap. The unstable slope is protected using an ecosystem-friendly Articulated Concrete Block mattress system, improving the calculated sliding SF from 0.67 to 1.9, and achieving an erosion SF of 2.10.
Finally, the report provides the Port Authority with a strategic foundation of recommendations to realise the project.
This report presents an integrated vision and technical design for the sustainable redevelopment of the project site area, commissioned as an advisory document for the Ente Administrador del Puerto de Santa Fe (EAPSF). The project employed a strategic track, guided by four pillars, and a slope protection track, using a Multi-Criteria Decision Analysis (MCDA) to select a solution, resulting in a design containing both technical stability and a public urban concept.
The resulting urban concept, The Santa Fe Riverside Park, serves as a project embodying the strategic vision. The design integrates adaptive infrastructure, including stepped terraces and docking places, engineered to accommodate significant seasonal river fluctuations. This concept is supported by the delivery of a 15-year long-term roadmap. The unstable slope is protected using an ecosystem-friendly Articulated Concrete Block mattress system, improving the calculated sliding SF from 0.67 to 1.9, and achieving an erosion SF of 2.10.
Finally, the report provides the Port Authority with a strategic foundation of recommendations to realise the project.
Internal cutting of offshore wind turbine monopiles
Operability analysis of the application to large and multiple piles
Master thesis
(2024)
-
N. Jüngerhans, Jeroen Hoving, Bernt Johan Leira, Pim van der Male, Benjamin Haak
Offshore wind energy is considered one of the most promising solutions for sustainably meeting the society's growing energy needs. This is why there are major construction projects and massive expansion plans for new offshore wind farms worldwide. In the North Sea in particular, the technology has been used to generate electricity for several years. Looking at the oldest wind farms still in operation, it will soon be time to decommission them once the turbines have reached their service life of 20 to 25 years. However, especially the removal of the foundations is considered challenging because not many comparable projects have already been realised. The most commonly used type of foundation is the monopile due to its simplicity. During installation, these long steel piles are driven deep into the seabed to provide a secure foundation over the entire service life. One option for decommissioning is to cut the piles from the inside a few metres below the seabed and then pull them out. So far, this procedure has mainly been used for individual small piles. Scaling up to several large monopiles of a wind farm involves uncertainties. On the one hand, it is unclear how larger monopiles will behave during the cutting process, and on the other hand, the operational performance of several piles that are removed one after the other is uncertain.
When cutting monopiles, theoretically no complete cutting progress can be achieved because the pile breaks off beforehand. In this work, a calculation model was developed that predicts the cutting progress at which a monopile fails due to the hydrodynamic forces acting on it. Based on an existing project in which the internal cutting technology was used, a minimum progress was defined that must be reached before failure is allowed to occur. This makes it possible to determine which sea states are permissible in order to achieve the specified cutting progress. With the calculation model, a parameter study was carried out to find out which structural and environmental parameters have the greatest influence on failure. Additionally, two real wind farms were considered as case studies to investigate realistic parameter sets. One of these wind farms has relatively small monopiles as foundations, while the other has much larger ones. An operability analysis was also carried out for these case studies in order to determine the duration of the foundation decommissioning operation and to be able to analyse the weather downtime. In addition to calculating when a monopile fails during the cutting process, the forces required to pull the pile out of the seabed afterwards were calculated. This allows to determine the required crane capacity of the working vessels used for the operation.
The results of the calculations show that larger monopiles fail at an earlier cutting process than smaller monopiles. However, this difference is not large, which is due to the fact that together with the hydrodynamic forces, which increase with the pile size and length, also the wall thicknesses increase. This means that larger forces can generally be withstood. The operability is good for both wind farms from the case studies. Furthermore, it was found that it is important for the operability how the connection between monopile and transition piece was realised and whether ROVs have to be used. The crane capacity of the vessels used can be lower than that of the vessels used during installation. The additional force required to pull the monopiles out of the seabed does not make up for the weight lost by leaving a large part of the foundation in the soil. ...
When cutting monopiles, theoretically no complete cutting progress can be achieved because the pile breaks off beforehand. In this work, a calculation model was developed that predicts the cutting progress at which a monopile fails due to the hydrodynamic forces acting on it. Based on an existing project in which the internal cutting technology was used, a minimum progress was defined that must be reached before failure is allowed to occur. This makes it possible to determine which sea states are permissible in order to achieve the specified cutting progress. With the calculation model, a parameter study was carried out to find out which structural and environmental parameters have the greatest influence on failure. Additionally, two real wind farms were considered as case studies to investigate realistic parameter sets. One of these wind farms has relatively small monopiles as foundations, while the other has much larger ones. An operability analysis was also carried out for these case studies in order to determine the duration of the foundation decommissioning operation and to be able to analyse the weather downtime. In addition to calculating when a monopile fails during the cutting process, the forces required to pull the pile out of the seabed afterwards were calculated. This allows to determine the required crane capacity of the working vessels used for the operation.
The results of the calculations show that larger monopiles fail at an earlier cutting process than smaller monopiles. However, this difference is not large, which is due to the fact that together with the hydrodynamic forces, which increase with the pile size and length, also the wall thicknesses increase. This means that larger forces can generally be withstood. The operability is good for both wind farms from the case studies. Furthermore, it was found that it is important for the operability how the connection between monopile and transition piece was realised and whether ROVs have to be used. The crane capacity of the vessels used can be lower than that of the vessels used during installation. The additional force required to pull the monopiles out of the seabed does not make up for the weight lost by leaving a large part of the foundation in the soil. ...
Offshore wind energy is considered one of the most promising solutions for sustainably meeting the society's growing energy needs. This is why there are major construction projects and massive expansion plans for new offshore wind farms worldwide. In the North Sea in particular, the technology has been used to generate electricity for several years. Looking at the oldest wind farms still in operation, it will soon be time to decommission them once the turbines have reached their service life of 20 to 25 years. However, especially the removal of the foundations is considered challenging because not many comparable projects have already been realised. The most commonly used type of foundation is the monopile due to its simplicity. During installation, these long steel piles are driven deep into the seabed to provide a secure foundation over the entire service life. One option for decommissioning is to cut the piles from the inside a few metres below the seabed and then pull them out. So far, this procedure has mainly been used for individual small piles. Scaling up to several large monopiles of a wind farm involves uncertainties. On the one hand, it is unclear how larger monopiles will behave during the cutting process, and on the other hand, the operational performance of several piles that are removed one after the other is uncertain.
When cutting monopiles, theoretically no complete cutting progress can be achieved because the pile breaks off beforehand. In this work, a calculation model was developed that predicts the cutting progress at which a monopile fails due to the hydrodynamic forces acting on it. Based on an existing project in which the internal cutting technology was used, a minimum progress was defined that must be reached before failure is allowed to occur. This makes it possible to determine which sea states are permissible in order to achieve the specified cutting progress. With the calculation model, a parameter study was carried out to find out which structural and environmental parameters have the greatest influence on failure. Additionally, two real wind farms were considered as case studies to investigate realistic parameter sets. One of these wind farms has relatively small monopiles as foundations, while the other has much larger ones. An operability analysis was also carried out for these case studies in order to determine the duration of the foundation decommissioning operation and to be able to analyse the weather downtime. In addition to calculating when a monopile fails during the cutting process, the forces required to pull the pile out of the seabed afterwards were calculated. This allows to determine the required crane capacity of the working vessels used for the operation.
The results of the calculations show that larger monopiles fail at an earlier cutting process than smaller monopiles. However, this difference is not large, which is due to the fact that together with the hydrodynamic forces, which increase with the pile size and length, also the wall thicknesses increase. This means that larger forces can generally be withstood. The operability is good for both wind farms from the case studies. Furthermore, it was found that it is important for the operability how the connection between monopile and transition piece was realised and whether ROVs have to be used. The crane capacity of the vessels used can be lower than that of the vessels used during installation. The additional force required to pull the monopiles out of the seabed does not make up for the weight lost by leaving a large part of the foundation in the soil.
When cutting monopiles, theoretically no complete cutting progress can be achieved because the pile breaks off beforehand. In this work, a calculation model was developed that predicts the cutting progress at which a monopile fails due to the hydrodynamic forces acting on it. Based on an existing project in which the internal cutting technology was used, a minimum progress was defined that must be reached before failure is allowed to occur. This makes it possible to determine which sea states are permissible in order to achieve the specified cutting progress. With the calculation model, a parameter study was carried out to find out which structural and environmental parameters have the greatest influence on failure. Additionally, two real wind farms were considered as case studies to investigate realistic parameter sets. One of these wind farms has relatively small monopiles as foundations, while the other has much larger ones. An operability analysis was also carried out for these case studies in order to determine the duration of the foundation decommissioning operation and to be able to analyse the weather downtime. In addition to calculating when a monopile fails during the cutting process, the forces required to pull the pile out of the seabed afterwards were calculated. This allows to determine the required crane capacity of the working vessels used for the operation.
The results of the calculations show that larger monopiles fail at an earlier cutting process than smaller monopiles. However, this difference is not large, which is due to the fact that together with the hydrodynamic forces, which increase with the pile size and length, also the wall thicknesses increase. This means that larger forces can generally be withstood. The operability is good for both wind farms from the case studies. Furthermore, it was found that it is important for the operability how the connection between monopile and transition piece was realised and whether ROVs have to be used. The crane capacity of the vessels used can be lower than that of the vessels used during installation. The additional force required to pull the monopiles out of the seabed does not make up for the weight lost by leaving a large part of the foundation in the soil.
Floating single-lift installation of WTGs equipped with C1 Wedge Connection
Modelling and assessment of stability and operability during mating operation
This master thesis proposes a method for assessment of the allowable sea states for the single-lift installation of a Wind Turbine Generator (WTG) with a Quick Connection System (QCS) on a bottom-founded support structure with focus on the landing (mating) operation. The thesis also determines the operability of this installation and examines how it could be optimised.
Due to an increase of WTG size, the current lifting height of state-of-the-art floating Heavy Lift Vessels (HLVs) is insufficient to lift the WTG components to the required installation height. To overcome this limitation, and to further reduce installation time, new installation techniques are being developed. The single-lift installation methodology; where the WTG is lifted at the bottom of the WTG and just above the combined Centre of Gravity, in combination with the C1 Wedge Connection; a newly developed connection with a high ULS and FLS strength and large installation tolerances, forms a promising setup for dual crane HLVs. The Quick Connection System (QCS) of the C1 Wedge Connection can create a temporary connection able to provide sufficient restoring moment, required to keep the WTG upright. In this thesis the operability of a floating single-lift installation of a WTG with a QCS is determined and optimised. The performance of the QCS is compared to alternative connections and design improvements for the operation are proposed.
Two computer simulation models are built and compared, where-after the most promising model is expanded and further developed. This OrcaFlex model includes wave and wind loading in in-plane directions (3 Degree of Freedom directions). Nine critical events and limiting parameters are identified, containing motion limits of the WTG and QCS limits.
The results show that the operability for the base case (no Heave Compensation and strict limiting parameters) is negligible. In all cases assessed, the time required to activate the QCS turned out to be the governing limit. If heave compensation is incorporated and some parameters are altered (e.g. increasing the allowed WTG rotation or the maximum C1 Wedge Connection gap between the flanges) the operability can be increased to become feasible for wave peak periods up to Tp < 9s and significant wave heights Hs < 2m. In this optimised situation the activation of the QCS is the governing installation activity, with respect to the load transfer phase situation. Here, a minimum of 16 QCS Wedges are required for the load transfer phase and the pre-activation load transfer should be around 20% of the WTG static weight. For Hs < 1.4m, the mating operation was found to be feasible without a QCS. Here, it should be noted that optimal wind loading was assumed, and zero DP drift is incorporated.
It is recommended to expand the model to include all 6 DOF directions to verify if these results are still valid for non-optimal wind loading conditions. Furthermore, with these results, a study could be set up to determine the economic feasibility of this installation methodology. Such a study is essential as the economic viability determines the adoption of the technology. ...
Due to an increase of WTG size, the current lifting height of state-of-the-art floating Heavy Lift Vessels (HLVs) is insufficient to lift the WTG components to the required installation height. To overcome this limitation, and to further reduce installation time, new installation techniques are being developed. The single-lift installation methodology; where the WTG is lifted at the bottom of the WTG and just above the combined Centre of Gravity, in combination with the C1 Wedge Connection; a newly developed connection with a high ULS and FLS strength and large installation tolerances, forms a promising setup for dual crane HLVs. The Quick Connection System (QCS) of the C1 Wedge Connection can create a temporary connection able to provide sufficient restoring moment, required to keep the WTG upright. In this thesis the operability of a floating single-lift installation of a WTG with a QCS is determined and optimised. The performance of the QCS is compared to alternative connections and design improvements for the operation are proposed.
Two computer simulation models are built and compared, where-after the most promising model is expanded and further developed. This OrcaFlex model includes wave and wind loading in in-plane directions (3 Degree of Freedom directions). Nine critical events and limiting parameters are identified, containing motion limits of the WTG and QCS limits.
The results show that the operability for the base case (no Heave Compensation and strict limiting parameters) is negligible. In all cases assessed, the time required to activate the QCS turned out to be the governing limit. If heave compensation is incorporated and some parameters are altered (e.g. increasing the allowed WTG rotation or the maximum C1 Wedge Connection gap between the flanges) the operability can be increased to become feasible for wave peak periods up to Tp < 9s and significant wave heights Hs < 2m. In this optimised situation the activation of the QCS is the governing installation activity, with respect to the load transfer phase situation. Here, a minimum of 16 QCS Wedges are required for the load transfer phase and the pre-activation load transfer should be around 20% of the WTG static weight. For Hs < 1.4m, the mating operation was found to be feasible without a QCS. Here, it should be noted that optimal wind loading was assumed, and zero DP drift is incorporated.
It is recommended to expand the model to include all 6 DOF directions to verify if these results are still valid for non-optimal wind loading conditions. Furthermore, with these results, a study could be set up to determine the economic feasibility of this installation methodology. Such a study is essential as the economic viability determines the adoption of the technology. ...
This master thesis proposes a method for assessment of the allowable sea states for the single-lift installation of a Wind Turbine Generator (WTG) with a Quick Connection System (QCS) on a bottom-founded support structure with focus on the landing (mating) operation. The thesis also determines the operability of this installation and examines how it could be optimised.
Due to an increase of WTG size, the current lifting height of state-of-the-art floating Heavy Lift Vessels (HLVs) is insufficient to lift the WTG components to the required installation height. To overcome this limitation, and to further reduce installation time, new installation techniques are being developed. The single-lift installation methodology; where the WTG is lifted at the bottom of the WTG and just above the combined Centre of Gravity, in combination with the C1 Wedge Connection; a newly developed connection with a high ULS and FLS strength and large installation tolerances, forms a promising setup for dual crane HLVs. The Quick Connection System (QCS) of the C1 Wedge Connection can create a temporary connection able to provide sufficient restoring moment, required to keep the WTG upright. In this thesis the operability of a floating single-lift installation of a WTG with a QCS is determined and optimised. The performance of the QCS is compared to alternative connections and design improvements for the operation are proposed.
Two computer simulation models are built and compared, where-after the most promising model is expanded and further developed. This OrcaFlex model includes wave and wind loading in in-plane directions (3 Degree of Freedom directions). Nine critical events and limiting parameters are identified, containing motion limits of the WTG and QCS limits.
The results show that the operability for the base case (no Heave Compensation and strict limiting parameters) is negligible. In all cases assessed, the time required to activate the QCS turned out to be the governing limit. If heave compensation is incorporated and some parameters are altered (e.g. increasing the allowed WTG rotation or the maximum C1 Wedge Connection gap between the flanges) the operability can be increased to become feasible for wave peak periods up to Tp < 9s and significant wave heights Hs < 2m. In this optimised situation the activation of the QCS is the governing installation activity, with respect to the load transfer phase situation. Here, a minimum of 16 QCS Wedges are required for the load transfer phase and the pre-activation load transfer should be around 20% of the WTG static weight. For Hs < 1.4m, the mating operation was found to be feasible without a QCS. Here, it should be noted that optimal wind loading was assumed, and zero DP drift is incorporated.
It is recommended to expand the model to include all 6 DOF directions to verify if these results are still valid for non-optimal wind loading conditions. Furthermore, with these results, a study could be set up to determine the economic feasibility of this installation methodology. Such a study is essential as the economic viability determines the adoption of the technology.
Due to an increase of WTG size, the current lifting height of state-of-the-art floating Heavy Lift Vessels (HLVs) is insufficient to lift the WTG components to the required installation height. To overcome this limitation, and to further reduce installation time, new installation techniques are being developed. The single-lift installation methodology; where the WTG is lifted at the bottom of the WTG and just above the combined Centre of Gravity, in combination with the C1 Wedge Connection; a newly developed connection with a high ULS and FLS strength and large installation tolerances, forms a promising setup for dual crane HLVs. The Quick Connection System (QCS) of the C1 Wedge Connection can create a temporary connection able to provide sufficient restoring moment, required to keep the WTG upright. In this thesis the operability of a floating single-lift installation of a WTG with a QCS is determined and optimised. The performance of the QCS is compared to alternative connections and design improvements for the operation are proposed.
Two computer simulation models are built and compared, where-after the most promising model is expanded and further developed. This OrcaFlex model includes wave and wind loading in in-plane directions (3 Degree of Freedom directions). Nine critical events and limiting parameters are identified, containing motion limits of the WTG and QCS limits.
The results show that the operability for the base case (no Heave Compensation and strict limiting parameters) is negligible. In all cases assessed, the time required to activate the QCS turned out to be the governing limit. If heave compensation is incorporated and some parameters are altered (e.g. increasing the allowed WTG rotation or the maximum C1 Wedge Connection gap between the flanges) the operability can be increased to become feasible for wave peak periods up to Tp < 9s and significant wave heights Hs < 2m. In this optimised situation the activation of the QCS is the governing installation activity, with respect to the load transfer phase situation. Here, a minimum of 16 QCS Wedges are required for the load transfer phase and the pre-activation load transfer should be around 20% of the WTG static weight. For Hs < 1.4m, the mating operation was found to be feasible without a QCS. Here, it should be noted that optimal wind loading was assumed, and zero DP drift is incorporated.
It is recommended to expand the model to include all 6 DOF directions to verify if these results are still valid for non-optimal wind loading conditions. Furthermore, with these results, a study could be set up to determine the economic feasibility of this installation methodology. Such a study is essential as the economic viability determines the adoption of the technology.
Due to the increasing demand of renewable energy to combat climate change, renewable energy is experiencing a rapid growth. To match this demand for renewable energy, especially offshore wind is popular due to its status as a proven technology. To build offshore wind farms in a space and cost-effective way, wind turbines are increasing in size and the farms are shifting towards deeper water. This also has an effect on the monopiles, the most used wind turbine foundation. They are increasing in size and weight to handle the deeper waters and larger turbines. At this moment, monopile installation is limited to approximately 30 meters water depth because of a scarcity of installation vessels with sufficient capacity. To install these large-size monopiles either the fleet of installation vessels must be expanded or new installation methods must be developed.
This thesis addresses the challenge of installing large expected size monopiles without the use of traditional heavy lift vessels, which are reaching their operational limits due to increasing monopile sizes and water depths. The aim of this study is to develop a craneless upending method for a 130 meters long, 13 meters diameter monopile weighing 3500 tonnes, suitable for deployment in waters 50 meters deep.
Five craneless upending methods are evaluated. Two axes of rotation are considered, namely upending by rotation about a fixed point and upending by rotation about a floating point. Furthermore, to rotate the monopiles during upending, a moment can be applied around the axis of rotation and by ballasting parts of the monopile. After considering the four models that follow from combining the given options, a fifth method was developed that includes upending by rotation about a floating point and rotating the monopile by ballasting and applying a moment both.
A numerical model is developed for each concept to analyse the forces, moments, buoyancy, and draft throughout the upending process. The models were verified against each other and validated through a scaled experiment. The experiments highlighted the importance of friction in the upending process and, after adjusting the numerical model to account for the friction, confirmed its validity.
Of the five methods evaluated, the method that incorporates ballasting and applying a moment is found to be the most optimal. Due to combining the two methods of rotation, the water depth and moment required for the upending process can be minimalized.
In this approach, a floating monopile with end caps arrives at the site and is connected to a gripper frame which allows for axial movement and rotation of the monopile. Once the pile is connected, the ballasting phase starts. During this phase, ballast water is pumped into the monopile through the bottom end cap which causes rotation of the pile through the water. When a certain clearance between the monopile and sea bed is reached, de-ballasting starts while applying a moment around the axis of rotation to continue the upending while maintaining the minimum clearance between sea bed and pile.
The findings demonstrate that the presented hybrid craneless upending method is feasible and offers a practical solution to the installation challenges posed for larger monopiles and installation sites at deeper waters.
...
This thesis addresses the challenge of installing large expected size monopiles without the use of traditional heavy lift vessels, which are reaching their operational limits due to increasing monopile sizes and water depths. The aim of this study is to develop a craneless upending method for a 130 meters long, 13 meters diameter monopile weighing 3500 tonnes, suitable for deployment in waters 50 meters deep.
Five craneless upending methods are evaluated. Two axes of rotation are considered, namely upending by rotation about a fixed point and upending by rotation about a floating point. Furthermore, to rotate the monopiles during upending, a moment can be applied around the axis of rotation and by ballasting parts of the monopile. After considering the four models that follow from combining the given options, a fifth method was developed that includes upending by rotation about a floating point and rotating the monopile by ballasting and applying a moment both.
A numerical model is developed for each concept to analyse the forces, moments, buoyancy, and draft throughout the upending process. The models were verified against each other and validated through a scaled experiment. The experiments highlighted the importance of friction in the upending process and, after adjusting the numerical model to account for the friction, confirmed its validity.
Of the five methods evaluated, the method that incorporates ballasting and applying a moment is found to be the most optimal. Due to combining the two methods of rotation, the water depth and moment required for the upending process can be minimalized.
In this approach, a floating monopile with end caps arrives at the site and is connected to a gripper frame which allows for axial movement and rotation of the monopile. Once the pile is connected, the ballasting phase starts. During this phase, ballast water is pumped into the monopile through the bottom end cap which causes rotation of the pile through the water. When a certain clearance between the monopile and sea bed is reached, de-ballasting starts while applying a moment around the axis of rotation to continue the upending while maintaining the minimum clearance between sea bed and pile.
The findings demonstrate that the presented hybrid craneless upending method is feasible and offers a practical solution to the installation challenges posed for larger monopiles and installation sites at deeper waters.
...
Due to the increasing demand of renewable energy to combat climate change, renewable energy is experiencing a rapid growth. To match this demand for renewable energy, especially offshore wind is popular due to its status as a proven technology. To build offshore wind farms in a space and cost-effective way, wind turbines are increasing in size and the farms are shifting towards deeper water. This also has an effect on the monopiles, the most used wind turbine foundation. They are increasing in size and weight to handle the deeper waters and larger turbines. At this moment, monopile installation is limited to approximately 30 meters water depth because of a scarcity of installation vessels with sufficient capacity. To install these large-size monopiles either the fleet of installation vessels must be expanded or new installation methods must be developed.
This thesis addresses the challenge of installing large expected size monopiles without the use of traditional heavy lift vessels, which are reaching their operational limits due to increasing monopile sizes and water depths. The aim of this study is to develop a craneless upending method for a 130 meters long, 13 meters diameter monopile weighing 3500 tonnes, suitable for deployment in waters 50 meters deep.
Five craneless upending methods are evaluated. Two axes of rotation are considered, namely upending by rotation about a fixed point and upending by rotation about a floating point. Furthermore, to rotate the monopiles during upending, a moment can be applied around the axis of rotation and by ballasting parts of the monopile. After considering the four models that follow from combining the given options, a fifth method was developed that includes upending by rotation about a floating point and rotating the monopile by ballasting and applying a moment both.
A numerical model is developed for each concept to analyse the forces, moments, buoyancy, and draft throughout the upending process. The models were verified against each other and validated through a scaled experiment. The experiments highlighted the importance of friction in the upending process and, after adjusting the numerical model to account for the friction, confirmed its validity.
Of the five methods evaluated, the method that incorporates ballasting and applying a moment is found to be the most optimal. Due to combining the two methods of rotation, the water depth and moment required for the upending process can be minimalized.
In this approach, a floating monopile with end caps arrives at the site and is connected to a gripper frame which allows for axial movement and rotation of the monopile. Once the pile is connected, the ballasting phase starts. During this phase, ballast water is pumped into the monopile through the bottom end cap which causes rotation of the pile through the water. When a certain clearance between the monopile and sea bed is reached, de-ballasting starts while applying a moment around the axis of rotation to continue the upending while maintaining the minimum clearance between sea bed and pile.
The findings demonstrate that the presented hybrid craneless upending method is feasible and offers a practical solution to the installation challenges posed for larger monopiles and installation sites at deeper waters.
This thesis addresses the challenge of installing large expected size monopiles without the use of traditional heavy lift vessels, which are reaching their operational limits due to increasing monopile sizes and water depths. The aim of this study is to develop a craneless upending method for a 130 meters long, 13 meters diameter monopile weighing 3500 tonnes, suitable for deployment in waters 50 meters deep.
Five craneless upending methods are evaluated. Two axes of rotation are considered, namely upending by rotation about a fixed point and upending by rotation about a floating point. Furthermore, to rotate the monopiles during upending, a moment can be applied around the axis of rotation and by ballasting parts of the monopile. After considering the four models that follow from combining the given options, a fifth method was developed that includes upending by rotation about a floating point and rotating the monopile by ballasting and applying a moment both.
A numerical model is developed for each concept to analyse the forces, moments, buoyancy, and draft throughout the upending process. The models were verified against each other and validated through a scaled experiment. The experiments highlighted the importance of friction in the upending process and, after adjusting the numerical model to account for the friction, confirmed its validity.
Of the five methods evaluated, the method that incorporates ballasting and applying a moment is found to be the most optimal. Due to combining the two methods of rotation, the water depth and moment required for the upending process can be minimalized.
In this approach, a floating monopile with end caps arrives at the site and is connected to a gripper frame which allows for axial movement and rotation of the monopile. Once the pile is connected, the ballasting phase starts. During this phase, ballast water is pumped into the monopile through the bottom end cap which causes rotation of the pile through the water. When a certain clearance between the monopile and sea bed is reached, de-ballasting starts while applying a moment around the axis of rotation to continue the upending while maintaining the minimum clearance between sea bed and pile.
The findings demonstrate that the presented hybrid craneless upending method is feasible and offers a practical solution to the installation challenges posed for larger monopiles and installation sites at deeper waters.
Optimising Vibrojet® Performance for Offshore Installation
Using 2D Lab Tests and Particle Recognition Software
Offshore wind energy is a pivotal element in the renewable energy transition and achieving net-zero emissions by 2050. Most offshore wind turbines require the installation of a sturdy foundation called a monopile. The current method of installing monopiles offshore is known as piling, which involves driving large steel cylinders into the seabed with a hydraulic hammer. One of the major problems with this method is that it generates high levels of noise, which travel through the water and are harmful to marine life. Therefore, several European governments have introduced laws that regulate the amount of noise that may be emitted.
Multiple solutions have been developed to reduce the amount of noise that is generated but they are costly or negatively impact operational speed. Therefore, GBM Works, a startup in the offshore wind industry, is developing an innovative method for installing monopiles known as the Vibrojet®. The Vibrojet® combines both a Vibrohammer on top of the monopile with a jet at the bottom. The jet aims to fluidise the sand inside the monopile to reduce the friction on the inner shaft. This not only reduces the amount of noise emitted but also increases the installation speed of the monopile and may reduce the required pile dimensions.
This research aims to optimise the Vibrojet® performance during offshore installation by reducing shaft friction as much as possible while minimising jet flow. This approach maximises the installation speed of the monopile while reducing the capacity requirements for all parts of the Vibrojet® system. When installing a monopile while jetting, a soil skeleton forms (soil plug) in the middle of the pile while all sand particles near the inner shaft gets fluidised. The displacement of the surface of the soil plug has been assessed in this research to estimate the plug shape and optimise the performance of the Vibrojet®.
At Deltares a test setup of a soil container was constructed to imitated a 2D version of the inside of a monopile during Vibrojet® installation. The front of the container was made of see-though Perspex to enable analysis of the processes inside the pile. Inside the container holding 1,500 kg of sand, 0.3\% of the particles were ultraviolet (UV) coated to enable tracking. Visual software was written to track these particles with a camera, allowing for the measurement of flow velocities and visualise the surface of the plug shape.
It was discovered that the equation for plug surface displacement overestimated the displacement observed in the laboratory tests. By analysing the results from various installation settings, discrepancies in the equation were identified. The following improvements were recommended to enhance the accuracy of the equation:
• Addition of a seepage force term to the equation
• Addition of separate term for sedimentation effect
• Factor for the return flow of particles
• Influence of the slope angle on flow erosion
A relationship was discovered indicating that the optimal flow rate for Vibrojet® installations can be determined by the total volume of sand that needs to be fluidised. A model was proposed to optimise the performance of the Vibrojet® by assessing the displacement of the plug and utilising this relationship to calculate the connection between the flow rate and the volume of the fluidised zone.
...
Multiple solutions have been developed to reduce the amount of noise that is generated but they are costly or negatively impact operational speed. Therefore, GBM Works, a startup in the offshore wind industry, is developing an innovative method for installing monopiles known as the Vibrojet®. The Vibrojet® combines both a Vibrohammer on top of the monopile with a jet at the bottom. The jet aims to fluidise the sand inside the monopile to reduce the friction on the inner shaft. This not only reduces the amount of noise emitted but also increases the installation speed of the monopile and may reduce the required pile dimensions.
This research aims to optimise the Vibrojet® performance during offshore installation by reducing shaft friction as much as possible while minimising jet flow. This approach maximises the installation speed of the monopile while reducing the capacity requirements for all parts of the Vibrojet® system. When installing a monopile while jetting, a soil skeleton forms (soil plug) in the middle of the pile while all sand particles near the inner shaft gets fluidised. The displacement of the surface of the soil plug has been assessed in this research to estimate the plug shape and optimise the performance of the Vibrojet®.
At Deltares a test setup of a soil container was constructed to imitated a 2D version of the inside of a monopile during Vibrojet® installation. The front of the container was made of see-though Perspex to enable analysis of the processes inside the pile. Inside the container holding 1,500 kg of sand, 0.3\% of the particles were ultraviolet (UV) coated to enable tracking. Visual software was written to track these particles with a camera, allowing for the measurement of flow velocities and visualise the surface of the plug shape.
It was discovered that the equation for plug surface displacement overestimated the displacement observed in the laboratory tests. By analysing the results from various installation settings, discrepancies in the equation were identified. The following improvements were recommended to enhance the accuracy of the equation:
• Addition of a seepage force term to the equation
• Addition of separate term for sedimentation effect
• Factor for the return flow of particles
• Influence of the slope angle on flow erosion
A relationship was discovered indicating that the optimal flow rate for Vibrojet® installations can be determined by the total volume of sand that needs to be fluidised. A model was proposed to optimise the performance of the Vibrojet® by assessing the displacement of the plug and utilising this relationship to calculate the connection between the flow rate and the volume of the fluidised zone.
...
Offshore wind energy is a pivotal element in the renewable energy transition and achieving net-zero emissions by 2050. Most offshore wind turbines require the installation of a sturdy foundation called a monopile. The current method of installing monopiles offshore is known as piling, which involves driving large steel cylinders into the seabed with a hydraulic hammer. One of the major problems with this method is that it generates high levels of noise, which travel through the water and are harmful to marine life. Therefore, several European governments have introduced laws that regulate the amount of noise that may be emitted.
Multiple solutions have been developed to reduce the amount of noise that is generated but they are costly or negatively impact operational speed. Therefore, GBM Works, a startup in the offshore wind industry, is developing an innovative method for installing monopiles known as the Vibrojet®. The Vibrojet® combines both a Vibrohammer on top of the monopile with a jet at the bottom. The jet aims to fluidise the sand inside the monopile to reduce the friction on the inner shaft. This not only reduces the amount of noise emitted but also increases the installation speed of the monopile and may reduce the required pile dimensions.
This research aims to optimise the Vibrojet® performance during offshore installation by reducing shaft friction as much as possible while minimising jet flow. This approach maximises the installation speed of the monopile while reducing the capacity requirements for all parts of the Vibrojet® system. When installing a monopile while jetting, a soil skeleton forms (soil plug) in the middle of the pile while all sand particles near the inner shaft gets fluidised. The displacement of the surface of the soil plug has been assessed in this research to estimate the plug shape and optimise the performance of the Vibrojet®.
At Deltares a test setup of a soil container was constructed to imitated a 2D version of the inside of a monopile during Vibrojet® installation. The front of the container was made of see-though Perspex to enable analysis of the processes inside the pile. Inside the container holding 1,500 kg of sand, 0.3\% of the particles were ultraviolet (UV) coated to enable tracking. Visual software was written to track these particles with a camera, allowing for the measurement of flow velocities and visualise the surface of the plug shape.
It was discovered that the equation for plug surface displacement overestimated the displacement observed in the laboratory tests. By analysing the results from various installation settings, discrepancies in the equation were identified. The following improvements were recommended to enhance the accuracy of the equation:
• Addition of a seepage force term to the equation
• Addition of separate term for sedimentation effect
• Factor for the return flow of particles
• Influence of the slope angle on flow erosion
A relationship was discovered indicating that the optimal flow rate for Vibrojet® installations can be determined by the total volume of sand that needs to be fluidised. A model was proposed to optimise the performance of the Vibrojet® by assessing the displacement of the plug and utilising this relationship to calculate the connection between the flow rate and the volume of the fluidised zone.
Multiple solutions have been developed to reduce the amount of noise that is generated but they are costly or negatively impact operational speed. Therefore, GBM Works, a startup in the offshore wind industry, is developing an innovative method for installing monopiles known as the Vibrojet®. The Vibrojet® combines both a Vibrohammer on top of the monopile with a jet at the bottom. The jet aims to fluidise the sand inside the monopile to reduce the friction on the inner shaft. This not only reduces the amount of noise emitted but also increases the installation speed of the monopile and may reduce the required pile dimensions.
This research aims to optimise the Vibrojet® performance during offshore installation by reducing shaft friction as much as possible while minimising jet flow. This approach maximises the installation speed of the monopile while reducing the capacity requirements for all parts of the Vibrojet® system. When installing a monopile while jetting, a soil skeleton forms (soil plug) in the middle of the pile while all sand particles near the inner shaft gets fluidised. The displacement of the surface of the soil plug has been assessed in this research to estimate the plug shape and optimise the performance of the Vibrojet®.
At Deltares a test setup of a soil container was constructed to imitated a 2D version of the inside of a monopile during Vibrojet® installation. The front of the container was made of see-though Perspex to enable analysis of the processes inside the pile. Inside the container holding 1,500 kg of sand, 0.3\% of the particles were ultraviolet (UV) coated to enable tracking. Visual software was written to track these particles with a camera, allowing for the measurement of flow velocities and visualise the surface of the plug shape.
It was discovered that the equation for plug surface displacement overestimated the displacement observed in the laboratory tests. By analysing the results from various installation settings, discrepancies in the equation were identified. The following improvements were recommended to enhance the accuracy of the equation:
• Addition of a seepage force term to the equation
• Addition of separate term for sedimentation effect
• Factor for the return flow of particles
• Influence of the slope angle on flow erosion
A relationship was discovered indicating that the optimal flow rate for Vibrojet® installations can be determined by the total volume of sand that needs to be fluidised. A model was proposed to optimise the performance of the Vibrojet® by assessing the displacement of the plug and utilising this relationship to calculate the connection between the flow rate and the volume of the fluidised zone.
The installation of two M-100 Chlorinators at the border of the Amazon in Tena, Ecuador
Multidisciplinary project
Student report
(2024)
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R.R. Rutgers, B.H. Kurstjens, J.H. Drost, E.O.L. Lantsoght, J.S. Hoving, Miguel Andrés Guerra
Design of a Reusable Elevation System for Offshore Topsides Float-Over Installation
An Alternative to the Use of Deck Support Frames
Master thesis
(2024)
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A.C.M. Dekkers, J.S. Hoving, F.C. Lange, A. Metrikine, A.G.J. van den Munckhof
This thesis presents the design and evaluation of a reusable elevation system for topsides float-over installations in the offshore industry, aimed at addressing inefficiencies and environmental impacts associated with the current Deck Support Frame (DSF) methodology. Through a structured design approach, the system is developed in four distinct phases: recognition of need, problem definition, concept design, and basic design.
The need for a reusable elevation system arises from the limitations of the DSF, which is a single-use structure fabricated for each project and disposed of afterward. The proposed system offers multiple advantages, including cost savings through the elimination of single-use components, reduced environmental impact by minimizing material waste, adaptability to varying topsides dimensions and weights, and simplified installation processes by integrating functions. Market research into offshore wind trends confirms the relevance and potential demand for a modular, reusable elevation system.
The concept design phase involved generating a wide range of potential solutions and narrowing them down to the most feasible concept. During brainstorm sessions, 126 ideas were generated by 23 participants, resulting in 41 distinct working principles grouped into 21 concept categories. These were refined using the COCD-box framework, which balances practicality and innovation. The skidding-on-a-slope concept emerged as the most viable solution due to its low driving force requirements, direct load transfer, alignment with established offshore methodologies, and streamlined installation sequence. By extending horizontal skidding into a sloped configuration, the concept eliminates the need for the DSF and jacking system while optimizing the overall installation process.
In the basic design phase, the skidding-on-a-slope concept was further refined into a functional system layout. This phase included two sub-phases: modeling the operation and developing the structural design. A shallow slope angle was chosen to minimize driving forces, while a wedge facilitated topsides elevation. Strength analyses revealed insufficient bending capacity under hogging configurations, but recalculations confirmed that bending moments remain within safe limits. Stability evaluations showed that the concept improved barge stability by lowering the center of gravity. The structural design effectively accommodates normal loads but requires further development to manage lateral forces during skidding and mating operations. Modularity was highlighted as a key factor for transport, storage, and reusability across projects.
The thesis concludes that the skidding-on-a-slope system offers clear advantages over the DSF methodology in terms of environmental impact and long-term cost efficiency, provided the system is used more than once. The more the system is reused, the greater the reduction in costs and carbon footprint, with a projected 70% reduction after five installations. This reduction stems from the reusable steel components in the skidding-on-a-slope system compared to the single-use DSF. The adaptability of the system to varying topsides configurations and its streamlined installation sequence further enhance its practicality and relevance. The reduced carbon footprint also strongly aligns with Heerema Marine Contractors’ net-zero goals. Future research and optimization efforts should focus on operational and structural refinements to fully realize the potential of this innovative elevation system.
...
The need for a reusable elevation system arises from the limitations of the DSF, which is a single-use structure fabricated for each project and disposed of afterward. The proposed system offers multiple advantages, including cost savings through the elimination of single-use components, reduced environmental impact by minimizing material waste, adaptability to varying topsides dimensions and weights, and simplified installation processes by integrating functions. Market research into offshore wind trends confirms the relevance and potential demand for a modular, reusable elevation system.
The concept design phase involved generating a wide range of potential solutions and narrowing them down to the most feasible concept. During brainstorm sessions, 126 ideas were generated by 23 participants, resulting in 41 distinct working principles grouped into 21 concept categories. These were refined using the COCD-box framework, which balances practicality and innovation. The skidding-on-a-slope concept emerged as the most viable solution due to its low driving force requirements, direct load transfer, alignment with established offshore methodologies, and streamlined installation sequence. By extending horizontal skidding into a sloped configuration, the concept eliminates the need for the DSF and jacking system while optimizing the overall installation process.
In the basic design phase, the skidding-on-a-slope concept was further refined into a functional system layout. This phase included two sub-phases: modeling the operation and developing the structural design. A shallow slope angle was chosen to minimize driving forces, while a wedge facilitated topsides elevation. Strength analyses revealed insufficient bending capacity under hogging configurations, but recalculations confirmed that bending moments remain within safe limits. Stability evaluations showed that the concept improved barge stability by lowering the center of gravity. The structural design effectively accommodates normal loads but requires further development to manage lateral forces during skidding and mating operations. Modularity was highlighted as a key factor for transport, storage, and reusability across projects.
The thesis concludes that the skidding-on-a-slope system offers clear advantages over the DSF methodology in terms of environmental impact and long-term cost efficiency, provided the system is used more than once. The more the system is reused, the greater the reduction in costs and carbon footprint, with a projected 70% reduction after five installations. This reduction stems from the reusable steel components in the skidding-on-a-slope system compared to the single-use DSF. The adaptability of the system to varying topsides configurations and its streamlined installation sequence further enhance its practicality and relevance. The reduced carbon footprint also strongly aligns with Heerema Marine Contractors’ net-zero goals. Future research and optimization efforts should focus on operational and structural refinements to fully realize the potential of this innovative elevation system.
...
This thesis presents the design and evaluation of a reusable elevation system for topsides float-over installations in the offshore industry, aimed at addressing inefficiencies and environmental impacts associated with the current Deck Support Frame (DSF) methodology. Through a structured design approach, the system is developed in four distinct phases: recognition of need, problem definition, concept design, and basic design.
The need for a reusable elevation system arises from the limitations of the DSF, which is a single-use structure fabricated for each project and disposed of afterward. The proposed system offers multiple advantages, including cost savings through the elimination of single-use components, reduced environmental impact by minimizing material waste, adaptability to varying topsides dimensions and weights, and simplified installation processes by integrating functions. Market research into offshore wind trends confirms the relevance and potential demand for a modular, reusable elevation system.
The concept design phase involved generating a wide range of potential solutions and narrowing them down to the most feasible concept. During brainstorm sessions, 126 ideas were generated by 23 participants, resulting in 41 distinct working principles grouped into 21 concept categories. These were refined using the COCD-box framework, which balances practicality and innovation. The skidding-on-a-slope concept emerged as the most viable solution due to its low driving force requirements, direct load transfer, alignment with established offshore methodologies, and streamlined installation sequence. By extending horizontal skidding into a sloped configuration, the concept eliminates the need for the DSF and jacking system while optimizing the overall installation process.
In the basic design phase, the skidding-on-a-slope concept was further refined into a functional system layout. This phase included two sub-phases: modeling the operation and developing the structural design. A shallow slope angle was chosen to minimize driving forces, while a wedge facilitated topsides elevation. Strength analyses revealed insufficient bending capacity under hogging configurations, but recalculations confirmed that bending moments remain within safe limits. Stability evaluations showed that the concept improved barge stability by lowering the center of gravity. The structural design effectively accommodates normal loads but requires further development to manage lateral forces during skidding and mating operations. Modularity was highlighted as a key factor for transport, storage, and reusability across projects.
The thesis concludes that the skidding-on-a-slope system offers clear advantages over the DSF methodology in terms of environmental impact and long-term cost efficiency, provided the system is used more than once. The more the system is reused, the greater the reduction in costs and carbon footprint, with a projected 70% reduction after five installations. This reduction stems from the reusable steel components in the skidding-on-a-slope system compared to the single-use DSF. The adaptability of the system to varying topsides configurations and its streamlined installation sequence further enhance its practicality and relevance. The reduced carbon footprint also strongly aligns with Heerema Marine Contractors’ net-zero goals. Future research and optimization efforts should focus on operational and structural refinements to fully realize the potential of this innovative elevation system.
The need for a reusable elevation system arises from the limitations of the DSF, which is a single-use structure fabricated for each project and disposed of afterward. The proposed system offers multiple advantages, including cost savings through the elimination of single-use components, reduced environmental impact by minimizing material waste, adaptability to varying topsides dimensions and weights, and simplified installation processes by integrating functions. Market research into offshore wind trends confirms the relevance and potential demand for a modular, reusable elevation system.
The concept design phase involved generating a wide range of potential solutions and narrowing them down to the most feasible concept. During brainstorm sessions, 126 ideas were generated by 23 participants, resulting in 41 distinct working principles grouped into 21 concept categories. These were refined using the COCD-box framework, which balances practicality and innovation. The skidding-on-a-slope concept emerged as the most viable solution due to its low driving force requirements, direct load transfer, alignment with established offshore methodologies, and streamlined installation sequence. By extending horizontal skidding into a sloped configuration, the concept eliminates the need for the DSF and jacking system while optimizing the overall installation process.
In the basic design phase, the skidding-on-a-slope concept was further refined into a functional system layout. This phase included two sub-phases: modeling the operation and developing the structural design. A shallow slope angle was chosen to minimize driving forces, while a wedge facilitated topsides elevation. Strength analyses revealed insufficient bending capacity under hogging configurations, but recalculations confirmed that bending moments remain within safe limits. Stability evaluations showed that the concept improved barge stability by lowering the center of gravity. The structural design effectively accommodates normal loads but requires further development to manage lateral forces during skidding and mating operations. Modularity was highlighted as a key factor for transport, storage, and reusability across projects.
The thesis concludes that the skidding-on-a-slope system offers clear advantages over the DSF methodology in terms of environmental impact and long-term cost efficiency, provided the system is used more than once. The more the system is reused, the greater the reduction in costs and carbon footprint, with a projected 70% reduction after five installations. This reduction stems from the reusable steel components in the skidding-on-a-slope system compared to the single-use DSF. The adaptability of the system to varying topsides configurations and its streamlined installation sequence further enhance its practicality and relevance. The reduced carbon footprint also strongly aligns with Heerema Marine Contractors’ net-zero goals. Future research and optimization efforts should focus on operational and structural refinements to fully realize the potential of this innovative elevation system.
Student report
(2024)
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J.W. van den Berg, S.M.S. van Eps, B.N. Posma, O.R. Schultze, J.D. van der Wulp, J.A. Arriaga Garcia, J.S. Hoving
This report presents a design study focused on a floating offshore barrier for catching sargassum to protect the coastline of the Yucatan region in Mexico. The research was conducted as part of the multidisciplinary course offered by the Civil Engineering faculty. The study involved five students from diverse disciplines: two hydraulic offshore students, one hydraulic engineering student, one structural engineering student, and one chemical engineering student.
...
This report presents a design study focused on a floating offshore barrier for catching sargassum to protect the coastline of the Yucatan region in Mexico. The research was conducted as part of the multidisciplinary course offered by the Civil Engineering faculty. The study involved five students from diverse disciplines: two hydraulic offshore students, one hydraulic engineering student, one structural engineering student, and one chemical engineering student.
Rising waters, Resilient lives: The Can Tho region in 2075
Multidisciplinary project on the Mekong Delta
Student report
(2024)
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I.A.J. Helwes, S. Hooijmaijers, W.L. Horeman, J.P. van der Linden, F.D.J. Pallandt, Y. Yang, Luca Iuorio, Anne Baar, J.S. Hoving, J.E.A. Storms
An MDP project performed in the scope of the Delta Futures Lab in collaboration with the Dragon Institute. The report delves into the enviromental threats the Mekong Delta is facing and provides a design framework to deal with these problems. Furthermore, a case study is chosen to display how the framework can be adopted in a practical setting, envisioning what a future looks like where the Mekong Delta co-exists with water.
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An MDP project performed in the scope of the Delta Futures Lab in collaboration with the Dragon Institute. The report delves into the enviromental threats the Mekong Delta is facing and provides a design framework to deal with these problems. Furthermore, a case study is chosen to display how the framework can be adopted in a practical setting, envisioning what a future looks like where the Mekong Delta co-exists with water.
High-strength steel: ultimate material or expensive alternative?
Feasibility and optimization of using high-strength structural steel in offshore topsides
Steel is a widely used material in construction because of its availability, high strength-to-weight ratio, and recyclability. However, steel manufacturing consumes a lot of energy, and there is an increasing demand for more environmentally friendly building materials. Consequently, high-strength steel is becoming more popular as it reduces the mass of a structure. Although high-strength steel has been available for many years, its use in offshore topsides is limited due to stability and deflection issues. This research aimed to assess the feasibility of utilizing high-strength structural steel in offshore topsides, and investigated how the use of high-strength steel can be optimized in topside design.
Two different screening tools were constructed to assess the feasibility of high-strength steel within an entire topside. It was concluded that the length of a particular beam can tell an engineer if it is worth further investigating the potential of high-strength steel, while columns showed potential in all cases. The methods were tested with a case study in which an topside was assessed for its feasibility of utilizing high-strength steel beams and columns. Only hot-rolled primary and secondary beams combined with the columns and bracings were considered for this topside. When S460M steel was used for strength-governing beams and seamless tubulars, in combination with S690Q steel for welded tubular columns, the highest benefits were found and a maximum steel weight reduction of 15% was found for the considered components. At the same time, the material costs were reduced by 10%, the welding costs by 13% and the embodied carbon savings equalled 14%. When comparing these results with the total topside steel weight, 5% of the topside steel weight was reduced by using a combination of S460 and S690 steels. It was concluded that high-strength steel is feasible for offshore topsides and is more environmentally friendly and cost-effective, providing a promising alternative to conventional steels within certain components on offshore topsides.
This research presented a screening tool that is simple to use and assessed the feasibility of high-strength steel. Other engineers can easily extend this tool. As more detailed calculations are included in the screening tool, it is expected that additional cost reductions and embodied carbon savings can be found. Furthermore, including additional steel components in the assessment, such as plate girders, may result in finding much higher total weight reductions.
...
Two different screening tools were constructed to assess the feasibility of high-strength steel within an entire topside. It was concluded that the length of a particular beam can tell an engineer if it is worth further investigating the potential of high-strength steel, while columns showed potential in all cases. The methods were tested with a case study in which an topside was assessed for its feasibility of utilizing high-strength steel beams and columns. Only hot-rolled primary and secondary beams combined with the columns and bracings were considered for this topside. When S460M steel was used for strength-governing beams and seamless tubulars, in combination with S690Q steel for welded tubular columns, the highest benefits were found and a maximum steel weight reduction of 15% was found for the considered components. At the same time, the material costs were reduced by 10%, the welding costs by 13% and the embodied carbon savings equalled 14%. When comparing these results with the total topside steel weight, 5% of the topside steel weight was reduced by using a combination of S460 and S690 steels. It was concluded that high-strength steel is feasible for offshore topsides and is more environmentally friendly and cost-effective, providing a promising alternative to conventional steels within certain components on offshore topsides.
This research presented a screening tool that is simple to use and assessed the feasibility of high-strength steel. Other engineers can easily extend this tool. As more detailed calculations are included in the screening tool, it is expected that additional cost reductions and embodied carbon savings can be found. Furthermore, including additional steel components in the assessment, such as plate girders, may result in finding much higher total weight reductions.
...
Steel is a widely used material in construction because of its availability, high strength-to-weight ratio, and recyclability. However, steel manufacturing consumes a lot of energy, and there is an increasing demand for more environmentally friendly building materials. Consequently, high-strength steel is becoming more popular as it reduces the mass of a structure. Although high-strength steel has been available for many years, its use in offshore topsides is limited due to stability and deflection issues. This research aimed to assess the feasibility of utilizing high-strength structural steel in offshore topsides, and investigated how the use of high-strength steel can be optimized in topside design.
Two different screening tools were constructed to assess the feasibility of high-strength steel within an entire topside. It was concluded that the length of a particular beam can tell an engineer if it is worth further investigating the potential of high-strength steel, while columns showed potential in all cases. The methods were tested with a case study in which an topside was assessed for its feasibility of utilizing high-strength steel beams and columns. Only hot-rolled primary and secondary beams combined with the columns and bracings were considered for this topside. When S460M steel was used for strength-governing beams and seamless tubulars, in combination with S690Q steel for welded tubular columns, the highest benefits were found and a maximum steel weight reduction of 15% was found for the considered components. At the same time, the material costs were reduced by 10%, the welding costs by 13% and the embodied carbon savings equalled 14%. When comparing these results with the total topside steel weight, 5% of the topside steel weight was reduced by using a combination of S460 and S690 steels. It was concluded that high-strength steel is feasible for offshore topsides and is more environmentally friendly and cost-effective, providing a promising alternative to conventional steels within certain components on offshore topsides.
This research presented a screening tool that is simple to use and assessed the feasibility of high-strength steel. Other engineers can easily extend this tool. As more detailed calculations are included in the screening tool, it is expected that additional cost reductions and embodied carbon savings can be found. Furthermore, including additional steel components in the assessment, such as plate girders, may result in finding much higher total weight reductions.
Two different screening tools were constructed to assess the feasibility of high-strength steel within an entire topside. It was concluded that the length of a particular beam can tell an engineer if it is worth further investigating the potential of high-strength steel, while columns showed potential in all cases. The methods were tested with a case study in which an topside was assessed for its feasibility of utilizing high-strength steel beams and columns. Only hot-rolled primary and secondary beams combined with the columns and bracings were considered for this topside. When S460M steel was used for strength-governing beams and seamless tubulars, in combination with S690Q steel for welded tubular columns, the highest benefits were found and a maximum steel weight reduction of 15% was found for the considered components. At the same time, the material costs were reduced by 10%, the welding costs by 13% and the embodied carbon savings equalled 14%. When comparing these results with the total topside steel weight, 5% of the topside steel weight was reduced by using a combination of S460 and S690 steels. It was concluded that high-strength steel is feasible for offshore topsides and is more environmentally friendly and cost-effective, providing a promising alternative to conventional steels within certain components on offshore topsides.
This research presented a screening tool that is simple to use and assessed the feasibility of high-strength steel. Other engineers can easily extend this tool. As more detailed calculations are included in the screening tool, it is expected that additional cost reductions and embodied carbon savings can be found. Furthermore, including additional steel components in the assessment, such as plate girders, may result in finding much higher total weight reductions.
The ongoing global energy transition has led to significant growth in the offshore wind sector. This growth has resulted in a high demand for offshore installation vessels like the Aeolus, and the need to push up their limits to meet the rapidly changing market. In the Saint-Brieuc offshore wind project, the Aeolus had to be installed on a stiff seabed, a situation that was expected to induce high impact forces on the jack-up legs. To mitigate these forces, leg modifications were installed to increase the operational limits for jacking operations. However, Van Oord's operational limits for installation on stiff seabed conditions differed from DNV's Joint Industry Project, leading to the need to reassess the necessity of the leg modifications.
The objective of this research was to identify the main physical phenomena that govern the forces in jack-up legs during installation on a stiff seabed, and to understand how these physical factors and a specific leg modification could influence them. This research followed a systematic approach to address the research objective, comprising a literature study on impact mechanics, model development for axial impact forces, model validation, a sensitivity study, and an analysis of the leg modification. Insights from the literature study guided the development of the model to analyse the governing forces. Validation was performed using field data from the Aeolus, specifically oil pressure readings from the vertical jacking cylinders and vessel motion measurements.
The research found that what governs the forces in jack-up legs during installation on a stiff seabed depends on the energy contained within the system prior to impact and how this energy is absorbed by the soil and structure. Key factors include wave-induced vessel motions, wave height and period, hull characteristics, vessel inertia, jacking velocity, and the leg length below the hull. The energy absorbed by the soil and structure depends on their stiffness characteristics and behaviour, which primarily concluded that axial forces dominate over lateral forces during impacts on a stiff seabed. However, lateral forces should be considered in deeper waters or where seabed protrusions are anticipated.
The sensitivity analysis indicated that vessel mass, initial velocity, and normal soil stiffness significantly influence the impact force, with initial velocity predominantly influencing the impact force, and the overall system stiffness dictating the impact duration. By introducing the leg modification, the impact force was reduced by approximately 70–75%, along with an increased impact duration of 320–370%. Moreover, it was found that impact force and duration are interconnected rather than separate occurrences. The leg modification also reduced the influence of soil stiffness variability. Furthermore, for a more realistic representation, incorporating the nonlinear behaviour of soil load-deformation and leg modification characteristics is needed, but this would increase the computational demand. Consequently, this suggests the need for advanced solutions and an engineering assessment to balance desired accuracy against computational complexity. ...
The objective of this research was to identify the main physical phenomena that govern the forces in jack-up legs during installation on a stiff seabed, and to understand how these physical factors and a specific leg modification could influence them. This research followed a systematic approach to address the research objective, comprising a literature study on impact mechanics, model development for axial impact forces, model validation, a sensitivity study, and an analysis of the leg modification. Insights from the literature study guided the development of the model to analyse the governing forces. Validation was performed using field data from the Aeolus, specifically oil pressure readings from the vertical jacking cylinders and vessel motion measurements.
The research found that what governs the forces in jack-up legs during installation on a stiff seabed depends on the energy contained within the system prior to impact and how this energy is absorbed by the soil and structure. Key factors include wave-induced vessel motions, wave height and period, hull characteristics, vessel inertia, jacking velocity, and the leg length below the hull. The energy absorbed by the soil and structure depends on their stiffness characteristics and behaviour, which primarily concluded that axial forces dominate over lateral forces during impacts on a stiff seabed. However, lateral forces should be considered in deeper waters or where seabed protrusions are anticipated.
The sensitivity analysis indicated that vessel mass, initial velocity, and normal soil stiffness significantly influence the impact force, with initial velocity predominantly influencing the impact force, and the overall system stiffness dictating the impact duration. By introducing the leg modification, the impact force was reduced by approximately 70–75%, along with an increased impact duration of 320–370%. Moreover, it was found that impact force and duration are interconnected rather than separate occurrences. The leg modification also reduced the influence of soil stiffness variability. Furthermore, for a more realistic representation, incorporating the nonlinear behaviour of soil load-deformation and leg modification characteristics is needed, but this would increase the computational demand. Consequently, this suggests the need for advanced solutions and an engineering assessment to balance desired accuracy against computational complexity. ...
The ongoing global energy transition has led to significant growth in the offshore wind sector. This growth has resulted in a high demand for offshore installation vessels like the Aeolus, and the need to push up their limits to meet the rapidly changing market. In the Saint-Brieuc offshore wind project, the Aeolus had to be installed on a stiff seabed, a situation that was expected to induce high impact forces on the jack-up legs. To mitigate these forces, leg modifications were installed to increase the operational limits for jacking operations. However, Van Oord's operational limits for installation on stiff seabed conditions differed from DNV's Joint Industry Project, leading to the need to reassess the necessity of the leg modifications.
The objective of this research was to identify the main physical phenomena that govern the forces in jack-up legs during installation on a stiff seabed, and to understand how these physical factors and a specific leg modification could influence them. This research followed a systematic approach to address the research objective, comprising a literature study on impact mechanics, model development for axial impact forces, model validation, a sensitivity study, and an analysis of the leg modification. Insights from the literature study guided the development of the model to analyse the governing forces. Validation was performed using field data from the Aeolus, specifically oil pressure readings from the vertical jacking cylinders and vessel motion measurements.
The research found that what governs the forces in jack-up legs during installation on a stiff seabed depends on the energy contained within the system prior to impact and how this energy is absorbed by the soil and structure. Key factors include wave-induced vessel motions, wave height and period, hull characteristics, vessel inertia, jacking velocity, and the leg length below the hull. The energy absorbed by the soil and structure depends on their stiffness characteristics and behaviour, which primarily concluded that axial forces dominate over lateral forces during impacts on a stiff seabed. However, lateral forces should be considered in deeper waters or where seabed protrusions are anticipated.
The sensitivity analysis indicated that vessel mass, initial velocity, and normal soil stiffness significantly influence the impact force, with initial velocity predominantly influencing the impact force, and the overall system stiffness dictating the impact duration. By introducing the leg modification, the impact force was reduced by approximately 70–75%, along with an increased impact duration of 320–370%. Moreover, it was found that impact force and duration are interconnected rather than separate occurrences. The leg modification also reduced the influence of soil stiffness variability. Furthermore, for a more realistic representation, incorporating the nonlinear behaviour of soil load-deformation and leg modification characteristics is needed, but this would increase the computational demand. Consequently, this suggests the need for advanced solutions and an engineering assessment to balance desired accuracy against computational complexity.
The objective of this research was to identify the main physical phenomena that govern the forces in jack-up legs during installation on a stiff seabed, and to understand how these physical factors and a specific leg modification could influence them. This research followed a systematic approach to address the research objective, comprising a literature study on impact mechanics, model development for axial impact forces, model validation, a sensitivity study, and an analysis of the leg modification. Insights from the literature study guided the development of the model to analyse the governing forces. Validation was performed using field data from the Aeolus, specifically oil pressure readings from the vertical jacking cylinders and vessel motion measurements.
The research found that what governs the forces in jack-up legs during installation on a stiff seabed depends on the energy contained within the system prior to impact and how this energy is absorbed by the soil and structure. Key factors include wave-induced vessel motions, wave height and period, hull characteristics, vessel inertia, jacking velocity, and the leg length below the hull. The energy absorbed by the soil and structure depends on their stiffness characteristics and behaviour, which primarily concluded that axial forces dominate over lateral forces during impacts on a stiff seabed. However, lateral forces should be considered in deeper waters or where seabed protrusions are anticipated.
The sensitivity analysis indicated that vessel mass, initial velocity, and normal soil stiffness significantly influence the impact force, with initial velocity predominantly influencing the impact force, and the overall system stiffness dictating the impact duration. By introducing the leg modification, the impact force was reduced by approximately 70–75%, along with an increased impact duration of 320–370%. Moreover, it was found that impact force and duration are interconnected rather than separate occurrences. The leg modification also reduced the influence of soil stiffness variability. Furthermore, for a more realistic representation, incorporating the nonlinear behaviour of soil load-deformation and leg modification characteristics is needed, but this would increase the computational demand. Consequently, this suggests the need for advanced solutions and an engineering assessment to balance desired accuracy against computational complexity.