With increasing diameters of offshore monopile foundations, impact hammers require more energy per blow in order to drive them into the seabed. This does not only increase the fatigue loading on the monopile, but it also increases underwater noise that affects marine life. The increase in installation costs due to additional material on the monopile, noise mitigation and longer installation times drives contractors to look for alternative installation methods. GBM’s Vibro-drill strives to install monopile foundations through a combination of jetting, liquefaction and fluidization to reduce the soil resistance to such low levels that the monopile will penetrate the soil under its own weight and thereby significantly reducing underwater noise. Although the working principles are still being tested, the Vibro-drill design needs to be improved for commercial application. The design must include the three operational functionalities stated above, but to make the Vibro-drill re-usable for consequential monopile installations, additionally retrieval and structural rigidity are required. For this thesis, the Vibro-drill is re-designed to include these functionalities. Starting from a process description, all load cases and additional design requirements were found. Based on a first global load case, a first selection was made for the connection mechanism. Subsequently, a Multi-Criteria Analysis was performed yielding two suitable concepts: the Vibro-Boxer and the Vibro-Polyp. The Vibro-Boxer relies on three extending arms that connect with a specially designed pile shoe using twelve hydraulic grippers. To feed the system with hydraulic fluid, water and air, an umbilical connects the installation vessel with the central hub of the Vibro-drill. At the end of each arm, eccentric weights are used to vibrate the pile tip. The Vibro-Polyp has a similar lay-out except for the arms and connection mechanism. Nine hinged arms form three sets of folding parallelograms to expand or contract the Vibro-drill. The connection is made through a set of pins on each arm that slide into holes in the pile shoe. Due to unknown soil properties and effectiveness of jetting, liquefaction and fluidization, the loads on the structure cannot be determined deterministically. Therefore, a Monte Carlo simulation is used to perform the structural analysis based on a best guesstimate for the distribution of these unknown parameters. Based on this approach, a tool is created that aims at performing the structural analysis while iteratively improving the design. As test results will become available after finalizing this thesis, input for the unknown parameters can be updated to improve the results of the structural analysis. Subsequently, based on this progressive insight, the design of the Vibro-drill can be optimized further. Note here that for the structural analysis, the system is assumed to be quasi-static which is a gross simplification of reality. Although this imposes limitations to the reliability of the results, this assumption is allowable for the preliminary re-design phase considered in this thesis. The structural analysis described here has been applied to both suitable concepts. For each concept, the external loads were identified and the internal loads were calculated. A series of structural checks in the Monte Carlo simulation provided a probability of failure. For both concepts the probability of failure was initially too high and therefore improvements to the structural components were made. Based on the design criteria, the two optimized design concepts were compared. Due to the smaller frontal area of the Vibro-Polyp its soil resistance on the tip of the monopile and the Vibro-drill is the smallest and therefore requires the least eccentric force. Nevertheless, the structural analysis shows that its hinged arms are fatigue sensitive yielding a higher probability of failure. Therefore, despite its larger frontal area, the Vibro-Boxer has a higher reliability and is the most suitable concept for the Vibro-drill. Finally, a more detailed design of the Vibro-Boxer concept is delivered that complies with all design requirements. For this design, recommendations are given on how to update the design based on the dynamic analysis and future test results.

This study examines the effect of adding helical piles to the foundation mechanism of monopile installation templates. A monopile installation template is a gravity-based structure, which is placed on the seabed. The installation template is utilised for the installation of monopiles, and to ensure its verticality during this installation. At this time, challenges arise for the stability and operability of the installation templates due to the increased dimensions and mass of these structures. The increased demand for green energy leads to the growth of monopiles, in both number and size. The growth in monopile size leads to the increasing required dimensions of the installation templates. The installation templates are, however, often restricted in size and mass by the capabilities of the installation vessel. The installation templates generally use mud-mats as foundation system to ensure stability and prevent the template from excessive settling. The mud-mats cause significant dynamic effects, especially when taken through the water line. Moreover, the sliding capacity of mud-mats is often insufficient, leading to potential sliding failure of the template. A literature review is conducted using different sources, such as reviews, offshore guidelines, research papers, and expert interviews, to investigate installation templates and different foundation mechanisms. The investigated foundation mechanisms are suction buckets, mud-mats, and (helical) piles. The literature review demonstrates that helical piles show greatest potential of being added to the mud-mat foundation. Therefore, solely helical piles are considered in the current study, and the following research question is answered: How, and to what extent, does adding helical piles affect the footprint of the monopile installation template designed for the benchmark project? The current study uses a project carried out by Heerema Marine Contractors as benchmark. All parameters of this project are used as input for the study. Findings of analytical analyses on the (environmental) loading and mud-mat capacity are validated with the benchmark project results. Subsequently, the helical pile geometry is optimised for maximum uplift capacity, using the methodology shown in the figure below. The capacity is optimised for uplift capacity, as it is assumed that the mud-mats can bear the compressive loading. Additionally, the lateral capacity would significantly increase by utilising piles, and therefore optimising for lateral capacity is not recommended. The obtained geometry, optimised for maximum uplift capacity, is then assumed to be constant and used to determine the uplift, compressive, and lateral capacity. The analysis shows a positive correlation between embedment depth and capacity (uplift, compressive, and lateral). The helical pile capacity is added to the mud-mat capacity. Consequently, effects on design variations are examined, such as reduction in template's mass and size, mud-mat size, and variations in helical pile geometry and soil parameters. The analysis shows a significant improvement in capacity of the foundation, in both compressive and lateral capacity. The uplift capacity of the helical piles ensure no uplift of mud-mats occurs. This leads to a more evenly load distribution among the mud-mats, lowering the maximum factored load on the legs. Consequently, the mud-mat size and the template's mass and dimensions could be reduced. It can be concluded that a reduction in mud-mat size directly results in the potential of reducing the template dimensions. The reduction in both template and mud-mat size would automatically lead to a decrease in mass. However, the reduction in template mass could lead to a decrease in structural performance. This should be investigated in further studies. Variations in soil characteristics show that the performance is even more enhanced in denser sands. Concluding, the helical piles have a positive influence on the template's overall capacity. The findings show that a reduction in the footprint of the template is possible, of maximum 13.6%.

This thesis explores the feasibility of using a helical pile foundation with a tension leg mooring system to support a 15MW floating offshore wind turbine and assesses its financial viability compared to alternative anchor concepts. The study commenced with an extensive literature review, drawing from a diverse range of sources, including reviews, offshore guidelines, research papers, and expert interviews. The literature review was conducted to enhance the understanding of the use of helical piles in the offshore industry, encompassing their fundamental characteristics, current applications, and potential contributions. For this investigation, a Tension Leg Platform (TLP) featuring a 15 MW wind turbine, engineered by Heerema Engineering Solutions (HES), was employed. Time-domain simulations, accounting for environmental conditions, were carried out using the OrcaFlex software. These simulations led to the determination of the mooring line tensions, with the maximum value identified as the design load case. During the helical pile geometry optimization process, which focused on maximizing uplift capacity, it was established that a single helical pile in dense sand can achieve a maximum uplift capacity of 7.91 MN, while taking into account geotechnical, structural, and installation constraints. As a result, considering the significant uplift capacity demands of TLPs, it is essential to employ helical pile grouping, necessitating a minimum of four helical piles. Consequently, the design of the helical pile group anchors confirms their ability to meet the uplift and lateral capacity requirements of TLPs. Furthermore, the exploration of variations in equipment, steel strength, helical pile geometry, and soil conditions has yielded promising results. It is important to note that achieving the required installation depth for these group anchors involves a significant force and torque during the installation process, presenting potential challenges. Consequently, the development of equipment capable of meeting these installation requirements is vital for ensuring the feasibility of these helical pile group anchors. The performance of helical pile group anchors was analysed from economic, technical, and environmental perspectives, with a comparison to suction and driven pile anchor concepts. The economic evaluation showed that the estimated total costs for the 4-pile helical group anchor, utilizing a singlepile installation method, are notably higher when factoring in the costs related to developing helical pile equipment, making it less financially attractive compared to the developed suction and driven pile anchor concepts. However, when excluding these equipment costs, the 4-pile helical group anchor ranked as the second-most financially attractive option, regardless of the installation technique, with only the single driven pile anchor being less expensive. Notably, it was discovered that, in a scenario where structural, geotechnical, and installation constraints are disregarded, the single pile helical anchor emerges as the most financially attractive among all anchor types, even surpassing the single pile driven anchor. This suggests that overcoming challenges related to scaling up helical pile dimensions, like enhancing their structural integrity, and reducing installation requirements through innovative designs, could make the use of fewer piles in a helical pile group anchor a feasible choice. In addition to these quantifiable factors, helical piles offer the advantage of a low-noise installation method, which becomes increasingly important due to the growing noise disturbance legislation in certain regions. Furthermore, their adaptability to various ground conditions through flexible installation techniques makes them a convenient choice for sites with limited access or specific inclination requirements...

Marine contractors as Heerema Marine Contractors (HMC) have made decommissioning part of their core business. Being the owner of two of the largest semi-submersible crane vessels (SSCVs), the choice for single lift jacket removal is straightforward. However, jackets in the Northern North Sea have a weight and height exceeding the crane capacity of these vessels. Moreover, not all jackets have the structural integrity to be single lifted. Piece small jacket removal can be a solution but is often overlooked by the expectance of being labour-intensive and therefore too expensive. This thesis has the objective to develop a methodology for advising a jacket removal strategy based on a decision support model while comparing piece small versus single lift decommissioning. Comparing the two removal methods is done for a single case study of the Kinsale Bravo jacket, provided by HMC. The budgets of both removal methods, resulting from the case study, are used as input for the decision support model (DSM). Based on the jacket characteristics, the model uses constrains, rules of thumb and calculations to determine several possible outcomes. These outcomes can then be further optimised based on costs, duration and Co2 emissions. Based on either one of these optimisations a removal scenario can be established by the model.

It is expected by the EWEA that in the North Sea only the wind energy capacity will increase to 45 GW. In 2015 the capacity was only 5.2 GW. Offshore contractors should be capable of installing lots of turbines and just that is a problem. As turbines increase in size installation vessels need significant upgrades. Therefore, most contractors look for cheaper and better solution for installing these large offshore wind turbines. The Sitting Up System or SUS is a new concept designed by Marine Innovators B.V. and installs fully assembled wind turbines with their foundation. It decreases offshore installation time and decreases operational cost significantly. The SUS is designed to transport and upend wind turbines to a vertical position while anchored to the seabed. For now, the SUS is a concept and has multiple design possibilities, using either a hydraulic or a buoyant lifting system. Analysis on these lifting methods and their operational functionality resulted in a buoyant type lifting system. The SUS 3: 'Buoyant upend 2' concept consists of latticed structure and two buoyant modules. The large module is sunk to anchor the SUS and the small buoyancy module is pulled along the lattice to create an upending moment. Using the software Matlab the upending motion of SUS 3 is modelled as a rigid body to find limiting wave conditions. The model uses second order stokes theorem and Jonswap to simulate waves on the structure. Loads on the structure are calculated using the Morison equation. Two DOFs are considered as the SUS can rotate around a hinge at the seabed and move the buoyancy module. In the simulation a wind turbine of 200 meters height is upended in 30 minutes, while operating at 40 meters water depth. The first phase of the upending wave loads is most critical. The criteria for the SUS to operate depends on the acceleration of the top tower assemble of the wind turbine, these cannot exceed 0.1 g. In this case the limiting sea state is a Hs of 1 m with a Tp of 4.5 s, leading to a workability of about 16 percent. During the beginning stages of upending the natural frequency of the system operates around 10 seconds. This is critical as waves oscillate near this frequency. Though the simulation does not account for radiation or diffraction, the performance in later stages of upending gives a better result. Here, it can operate with a Hs of 2.5 meters resulting in a workability of 75 percent. The SUS 3 is anchored with spudcans during upending and shear loads are most significant. These spudcans can experience a shear load of 24 MN, when considering a Hs of 3.5 with a Tp of 8.5. Therefore, anchoring method should be designed such that it can comprehend these shear loads more efficiently. The work done by the winches pulling the buoyancy module is 13 percent more than the potential energy gained after upending with no waves. When waves are applied, energy is gained due to the uplifting force of waves. As the structure is lifted, resistance of pulling the buoyancy module decreases and can move more efficiently. Considering a Hs of 1.5 m and a Tp of 5.5 s will results in an energy gain of 5 percent. Therefore, this method is quite efficient in upending wind turbines offshore.

Due to the rapidly growing offshore wind market, there is a high demand for capable wind turbine installation vessels. Current wind turbine installation vessels struggle with the installation of large diameter monopiles due to a lack of crane capacity and with the installation of wind turbine components at hub height due to a lack of crane height. Most jack-up vessels currently have a crane capacity of 1600 tonnes or lower. This is adequate for the current average diameter monopile but already too low for the larger diameter monopiles. Due to a lack of crane capacity, these vessels are at risk of no longer being capable of installing wind turbine foundations in the near future. However, if it would be possible to reduce the crane loads during the installation process of monopiles, the commercial viability of these vessels can be extended. Previous research and practical experience have shown that a floating monopile upending process is feasible. A theoretical research with an experiment has been performed on the upending of a monopile where the buoyancy is utilized, but this research does not include the environmental conditions that can impact the monopile during the upending. This research also does not show the maximum amount of buoyancy that can be utilized during the installation process. This thesis determines the maximum installation capacity that can be reached with a floating upending method, using a 1600 tonnes crane. It also analyzes the impact of the environmental conditions and presents the workability of the upending method. An analytical model has been made to calculate the motions of the monopile while it is partially submerged and hanging in the crane. The analytical model is used to validate the numerical model made in Orcaflex that was developed to consider five different concepts for the upending of the monopile. The best-chosen concept is further developed in the floating upending method. To make the monopile water and airtight during transportation and upending, both ends of the monopile are plugged. The monopile is transported to the installation site by two tugboats that connect it to a rotating gripper which is placed on the side of the jack-up vessel. Then, the crane upends the monopile while the pile stays connected to the rotating gripper and maintains a certain amount of submergence during the upending which creates the buoyancy force. After the upending, the lower plug is removed by increasing the air pressure inside the monopile whereafter the monopile can be lowered to the seabed. This method is analyzed in the frequency domain for six upend angles whereafter the workability of the method is determined by simulations of the three most critical upend angles in the time domain. The floating upending method increases the installation capacity by 40% while maintaining a workability of 60-70% depending on the monopile diameter. It extends the lifetime of jack-up vessels and is a cost-competitive alternative when compared to mobilizing a floating heavy lift vessel instead.

Due to the increasing size of offshore wind turbines, the jack-up vessels and cranes installing them need to increase in size. The increase in length of the crane boom results in an increase of the dynamic response of the crane. This increase in response results in higher loads in the crane. The magnitude of the higher loads are unknown and not yet accounted for in crane design. To get a better insight in the dynamic response of the crane and higher loads, a probabilistic model is developed to quantify the annual probability of the crane. To define the different crane operations, a measurement data set of crane operations is made available. From this data set, the different lifts types, exposure times and occurrences are identified. Multiple jack-up configurations are chosen with different water depth and wave heading. Next to the crane and jack-up configuration, long-term wave statistics are used for the environmental conditions, as input for the probabilistic model. Time-domain simulations are performed in a rigid multi-body analysis software, to simulate the dynamic response of the crane, due to wave induced excitations. Due to the random nature of waves, convergence of the results is researched. For this, numerous time-domain simulations with different sea-states have to be performed, this is unwanted. A methodology is developed, using the frequency domain, to limit the number of required time-domain simulations. Using the devised methodology, configurations with similar statistical description can be identified and grouped. The annual probability of failure can be calculated using the devised methodology and probabilistic model. The resulting annual probability of failure is small, much smaller than required. A sensitivity analysis is performed, it is found that the annual probability of failure depends greatly on the input of the probabilistic model. From the results and sensitivity analysis, multiple recommendations are given to decrease the sensitivity of the result. It can be said that from the devised methodology, a basis has been laid to quantify the annual probability of failure of the crane in normal operations.

Heerema Marine Contractors is assigned to execute the installation of 64 monopiles for the He Dreiht Offshore Wind Farm provided by Energie Baden-Württemberg (EnBW). The installation of the monopiles is done by means of a template structure. This template is specifically designed for this project and is installed on the seabed temporarily. The initial design of the template includes large mudmats to ensure the required stability during the full monopile installation sequence. Analysis shows that this initial template design does not perform well with regard to the template installation sequence. Additionally, when lifting the template through the wave zone, the large horizontal surface area of the mudmats yields significant hydrodynamic forces acting on the template in vertical direction. . Therefore, the main objective of this thesis is to generate and develop alternative foundation concepts to optimize the template installation sequence. The foundation concepts considered in this research are a mudmat, suction bucket, push-in pile and helical pile foundation concept. Using the mudmat as a foundation concept yields a foundation area of 924 m^2 in order to ensure stability on the seabed, independent of the soil type. The suction bucket foundation concepts results in a horizontal foundation area of 390 m^2 for sand, or 117 m^2 for a clay seabed. The push-in pile and helical pile foundation concepts developed for a sand seabed, result in an area of 306 m^2 and 319 m^2. For a clay seabed respectively a foundation area of 75 m^2 and 88 m^2 is required. The operability of each foundation concept is determined by means of a hydrodynamic analysis of the template when lifting it through the wave zone. The operability is the amount of time the template can be lowered through the wave zone, expressed in percentage based on 24 hours. A simplified method stated by DNV is used to determine the hydrodynamic loads acting on the foundation in heave direction. For the considered homogeneous sand and clay seabed, the mudmat foundation concept proved to have the lowest operability. The suction bucket concept scored second, and the push-in pile and helical pile foundation concept showed the best performance on operability for both types of seabed. To evaluate which concept yields the most optimal template installation sequence, a multi-criteria analysis (MCA) is performed. This MCA also takes the installation time, construction costs and the risk of damage into account as criteria. Taking all these criteria into account, it is obtained that the mudmat foundation concept does provide the best performance when considering the template installation sequence, based on the assumptions stated throughout this thesis. Even though the mudmat foundation concept has the lowest performance of all foundation concepts when lifting the template through the wave zone, this concept overall performs better than the alternative foundation concept due to a short installation time on the seabed, low construction costs and low damage risks. The suction bucket foundation concept shows an average score on all criteria. This resulted in the second preferred option. The push-in pile and helical pile foundation concepts show a good operability, however, these concepts score low on the construction costs, installation time and damage sensitivity. As a result, these concepts show the lowest performance considering the template installation sequence.

A split hopper barge is a dredging vessel that can split over its longitudinal axis to discharge its cargo. To allow for such an operation, the barge consists of two half-hulls that are connected by hinges at the top and hydraulic cylinders at the bottom. Any forces that act at the interface between the half-hulls have to be transferred by the hinges and cylinders as a result. The aim of this thesis is to develop a method to determine the workability limits of split hopper barges in irregular seas. For this workability of the barge, the design limits of the hinges and hydraulic cylinders are assumed to be governing. A quasi-static model is formulated to determine the effects of roll, different types of cargo, opening the barge and discharging the cargo on the forces in the hinges and cylinders. The results of the quasi-static model are a set of governing load cases for the split hopper barge. From the quasi-static model, it is found that the forces of interest are the largest for a closed split hopper barge and that either a solid or a liquid cargo will yield the governing load case. To account for the dynamics in irregular sea conditions, a calculation method is proposed based on Ansys AQWA. Since AQWA is not able to account for liquid cargo motions, its effects are incorporated separately. Using WAMIT simulations, the influences of the liquid cargo to the added mass and stiffness of the barge are determined. Based on the WAMIT results the AQWA model is adjusted. Superimposing the results from the quasi-static and dynamic models, the maximum forces in the hinges and hydraulic cylinders are obtained for the governing load cases. By comparing the obtained maximum forces to the design forces, a conclusion on the workability limits of the split hopper barge is drawn. For the barge carrying a solid cargo only one resonance frequency is found, while, due to the liquid cargo motions, the barge with a liquid cargo has two resonance frequencies. As a result, a larger number of combinations of wave directions and periods yield considerable forces. For a 3-hour-extreme with a significant wave height of 3 meters, the governing hydraulic cylinder forces are found for a barge carrying a liquid cargo. The maximum resulting hinge forces however, are found for a barge carrying a solid cargo. Because the limits of the hinges are exceeded before the limits of the hydraulic cylinders, it is concluded that the workability limits of the split hopper barge in irregular waves are most limited, and therefore governing, for a barge carrying a solid cargo.

Shell is working on mono-diameter drilling (MOD). A MOD well, or MOD well section, has a (nearly) constant diameter over several sections. This is achieved by deploying expandable liners: a liner is lowered into position and is expanded by pulling an over-sized cone through it. This plasticly deforms the pipe, increasing its inner diameter to that of the previous section. MOD eliminates many of the constraints of conventional well design. Greater depths may be reached and zonal isolation may be performed without paying the penalty of reduced production rates. While lowering an expandable assembly (expandable liner and expansion tools) into a well, caution is required. Displacement of the drilling mud causes a pressure drop due to fluid friction and acceleration. The running speed of the assembly into the well is limited by the surge (overpressure) or swab (underpressure) pressure. Pressure must remain within a predefined window to ensure well control. The current understanding of the mechanisms governing surge/swab pressure, as well as the models used to predict it, are deemed insufficient. The effect of unorthodox MOD conditions is unknown. This study is conducted to overcome these obstacles. Firstly, a model is programmed so that transient surge and swab pressures, induced by assembly movement, may be predicted. The drilling mud’s velocity and pressure are described by the water hammer equations, which are solved using the interpolated method of characteristics. One dimensional (1D), unsteady and nonuniform flow of a slightly compressible fluid in a conduit with linearly elastic walls is considered. The annular pressure drop for flow with a moving inner pipe is solved considering both laminar and turbulent flow of a Herschel-Bulkley fluid. Flow over the expansion tools is solved separately and is considered 1D and incompressible. Secondly, the model is validated. The model is first validated under conventional conditions using field measurements presented in literature and performs better than existing models. The validity of the model while dealing with extremely small clearances, as found in MOD applications, is investigated through a full-scale experiment on Shell’s test rig. The surge and swab pressures are generally predictable. Some discrepancies between predictions and measurements are observed and are attributed to the relatively large uncertainty in clearance size and shape, which results from imperfect pipes. The surge/swab pressure’s sensitivity to the size and shape of the pipes means that predictions should be treated with care. The effect of local annular flow restriction over the expansion tools is investigated too. The tools are found to cause acceleration induced transient pressures not predicted by the model. This implies that the 1D and/or incompressible assumption at the interface does not describe the flow adequately. Thirdly, the effect of MOD well design at true well depths and assembly lengths is investigated through a case study. The surge pressure is significant. The pressure drop generated in the narrow annulus between assembly and wellbore is too high to allow significant flow. Instead, all drilling mud is displaced upwards through the drillstring. Swabbing occurs behind the assembly. Circulation while tripping in expandable assemblies is therefore impossible. At these depth and length scales, the effect of fluid compression and borehole expansion becomes significant, causing steady state models to become increasingly inaccurate with depth.

The Arctic is warming more rapidly than other latitudes, which can result in the release of additional greenhouse gasses, global sea level rise and increase in extreme weather events. Additionally, this causes the rapid decline of sea ice and an ice free Arctic might occur during the summer in the 2040s. The decreasing sea ice cover accelerates the warming of the Arctic, which is known as the albedo feedback system. Solar radiation management (SRM) can be a solution to diminish or possibly stop sea ice decline. Within SRM a proposed technology, known as Arctic Ice Management (AIM), is distributing water on top of existing sea ice to increase the ice thickness enough to survive the summer melt. This raises the question: What water volume should AIM distribute on top of existing sea ice to counteract the annual Arctic sea ice volume loss? Based on data obtained during the period 1979-2020, the September trends for ice extent, ice area and ice volume are -83 400 km2yr-1, -49 200 km2yr-1 and -322 km3yr-1 respectively. The ice volume is considered as target parameter, as it accounts for both absolute areal ice loss and overall decreasing ice thickness. There are two main ice drift patterns in the Arctic: The Beaufort Gyre in the Beaufort Sea and the Transpolar Drift, of which the latter exports ice through Fram Strait into the Greenland Sea. Literature shows the ice remains within the Arctic for about five years when located in the Beaufort Sea and one to two years when located in the Transpolar Drift. For both locations, the ice decay is determined using an analytical approach first. This approach shows resemblance for ice located in the Beaufort Sea, but generally overestimates the ice decay in the Transpolar Drift. For this reason, an empirical approach is developed to determine the survival ice thickness. This results in accurate trends for ice decay of -2.1 to -2.7 cm day-1 in the Beaufort Sea and -0.8 to -1.4 cm day-1 in the Transpolar Drift. Considering 91 melting days results in an average survival thickness of 2.18 and 1 m respectively. AIM can be used to increase the ice thickness beyond this survival thickness and an AIM model is developed to show ice growth including AIM. The model concludes the AIM thickness, initial ice thickness prior to flooding and freezing duration after AIM define the effective ice thickness increase. The model is validated with small scale experiments, which indicate a delay between the flooding phase and continued natural ice growth. This delay can be the effect of the duration required to restore the temperature profile in the ice after flooding as shown by COMSOL Multiphysics simulations. Considering the AIM model, it is discouraged to implement AIM on ice thicknesses below 0.6 m and suggested for ice thicknesses approaching 1 m or higher to optimize the effective increase. The required water volume to compensate the annual sea ice volume loss highly depends on the location, initial ice thickness and target ice thickness and varies between 707 to 1095 km3 in the Beaufort Sea and between 386 to 464 km3 in the Transpolar Drift for the methods discussed in this research. To pump up this water volume, the expected power requirements are 4.5 to 7.0 GW and 2.5 to 3.0 GW respectively.

In the Netherlands, there is an increasing need to create residential spaces in its already crowded cities to accommodate the growing population. Constructing high-rise buildings is one way to try to solve the issue. However, high-rise buildings are sensitive to wind-induced vibrations. The accurate prediction of the dynamic response is important in high-rise building design. In building design practice, calculating the dynamic response of high-rise buildings under wind loading typically involves simplifying the structure as a single degree of freedom system, characterised by the first eigenmode properties and subjected to a white noise spectrum. The damping and natural frequency of the building substantially impact its dynamic response. These parameters are challenging to predict with accuracy. Additionally, in the presence of soft soils, soil-structure interaction can play an important role in energy dissipation and influence the structure's natural frequency. In practice, soil-structure interaction is either disregarded or simplified. In order to assess the effect of soil-structure interaction on the dynamic response of the building, this study models in a robust manner: the foundation, the tower structure, and the wind load. This newly developed model is addressed as the HF model. The investigation consists of a case study and a parametric study. Additionally, this study compares the predictions by the newly developed model with those obtained with a model as specified in the Eurocode. The case study provides a comparison between the models and the measured dynamic response of the New Orleans Tower. The parametric study looks into the influence of soil stiffness and material damping on the dynamic response of high-rise buildings. Furthermore, it investigates how these parameters affect the dynamic response of structures with various slenderness ratios. The case study was used to demonstrate that the developed model accurately predicts the measured dynamic response of the New Orleans Tower in the along-wind direction. For all the examined dynamic properties, the error compared with the measurements was lower than 7%. In the case of the Eurocode model, the results demonstrate that, when using the natural frequency estimation recommended by the Eurocode, it provides a 30%–35% underestimation of the peak acceleration compared to measurements. This Eurocode model overestimates the natural frequency and overall damping, which causes it to underestimate peak acceleration. However, the natural frequency determined in the design phase of the New Orleans Tower was significantly lower than the value obtained with the recommended estimation method in the Eurocode. With this lower natural frequency, the peak acceleration is overestimated by around 50%. This underestimation of the natural frequency and overestimation of the damping provided acceptable conservative results. Although this showcases the importance of accurate predictions of both natural frequency and damping, having poor predictions that cancel out each other’s effects is not desirable. The results from the parametric study support the findings from the case study. This shows that the case study’s findings apply to the more extensive range of building configurations investigated in the parametric study. In general, the Eurocode model, for slender structures on soft soil, overestimates the natural frequency and overall damping, which causes it to underestimate peak acceleration. The parametric study revealed that the building's first natural frequency and global damping ratio are significantly influenced by the soil stiffness and soil material damping, which can result in various effects on the peak acceleration. In the case of soil material damping, not considering it at all or considering a higher value could lead to 20% overestimation and 40% underestimation of peak acceleration, respectively. Soil stiffness had more intricate effects since it affected the natural frequency and the amount of energy dissipated by the soil radiation damping, the soil material damping and the structure material damping. For particular combinations of parameters, soil stiffness had up to a 40% increase in the peak accelerations compared to the fixed foundation. The results of this research show that the soil stiffness and soil material damping, for the ranges of properties relevant to the Netherlands, significantly influence the accurate predictions of the wind-induced dynamic response of high-rise buildings. Especially, there was found a higher influence on the dynamic response for the extreme cases of high slenderness ratio structures on very soft soils.

Cities are growing and more land is reclaimed. Reclamation is the process of creating new land from ocean, riverbeds or lake beds. New land is created by hydraulic placement of sand. The hydraulically placed fills are characterized by low densities and show a high variety in packing throughout the field. The relative density of the fills depend on placement method and whether the placement takes place aqueous or subaqueous. After the placement Vibro-densification techniques are used to densify the soil. Conventional vibro-densification techniques have difficulties penetrating hard soil layers to reach the loosely packed layers. This makes that land reclamation is not always financially feasible. The Sonic drilling technique might be used to improve the penetration in hard layers. Reducing the process time make the use of land reclamation more accessible. However, the sonic drill technology is not well understood at the moment. There are no reliable guidelines that make it able to estimate the driveability of a certain profile in to the ground with the help of sonic vibrations. This research focusses on better understanding of the sonic drill technology and the contribution of a sonic drill to a new compaction technique. On a reclaimed land site in Amsterdam an innovative method for installing elements in dense and hard sand layers was tested. The method focuses on sonic drilling/installation with vibrations up to 180Hz to reduce soil resistance whilst pushing the elements into the ground. This method has shown to generate less disturbances to the surroundings whilst achieving a higher penetration rate in comparison to conventional installation methods. The sonic vibrator generates pressure waves at the top of the element. The elasticity together with the inertial properties of the element allow the waves to propagate through the element. The pressure waves travel through the element and become partially transmitted to the surrounding soil. At the sides the mainly shear waves occur while at the tip both pressure and shear waves are present. During the wave propagation energy is lost due to scattering, radial damping and proper damping. The sonic drill technology uses high frequency vibrations to strongly reduce soil resistance. The resistance of the element against penetration is reduced by liquefaction, inertia effects and a temporary reduction of porosity of the soil. The observations from the tests form the basis for the establishment of model which simulates vibratory pile driving. The model is able to describe the installation process for different type of elements. The model might be used in the future to predict the penetration time using only the CPT data. It can be concluded from the tests that the sonic vibration method is an effective solution for installing elements in a short amount of time in challenging ground conditions and with minimal vibration and settlement disturbance. Finally, in terms of further study, it must be noted that several major simplifications and assumptions underlie the model, which may be improved upon with more rigorous constitutive modelling and numerical analysis.

Infrastructures have become important for the holistic growth of any country. With the number of such projects being constantly on the rise each year, its efficient maintenance has become a primary requirement for any asset owner. Among the many techniques available, FMECA is widely used for maintenance planning. In this method, different critical components are identified based on their likelihood of failure and impact on the infrastructure. Based on the inferences obtained, maintenance plans are developed where interventions are prioritized based on a component’s criticality within the system. FMECA uses risk matrices to assess criticalities semi-quantitatively. This lacks the required quantifiable information of a component in a system. A component by design can either be individual or exist as a subsystem comprising several components. To analyze criticalities accurately, quantitative information that can provide insights on a component’s state in the system is required. Hence, this thesis develops a new approach that could eliminate subjective errors in conventional criticality analysis. The new and conventional approach was applied to two infrastructures to observe and discuss the variations in results obtained. The comparative study showcased that the new approach provided better quantitative reasonings for criticalities obtained for each component. Using the unique implementation of the obtained quantitative data as done in the current research, developing realistic and accurate maintenance strategies is possible.

This thesis investigates the important physical processes related to underwater sound propagation due to offshore pile driving with the first commercial and numerical model called the Underwater Acoustic Simulator (UAS). To make adequately use of noise mitigation measures during offshore wind projects and to protect marine life the prediction of sound levels in water is important. The aim of this thesis is to assess if the UAS is suitable to give insight in the physics contributing to sound propagation and if the UAS is suitable to quantify sound levels in water for the application in future wind park projects. This is done by comparing the predicted sound levels with the UAS with the measured sound levels obtained during the construction of the Gemini wind park. The results obtained with the UAS identify the parameters related to the seabed properties as the most important for governing the attenuation of the noise levels as function of distance and frequency. In the UAS the seabed is modelled as a fluid. Especially frequencies < 800 Hz are sensitive to the choice of geo-acoustic parameters. These frequencies show a trend of underestimation of the sound levels compared to the acoustic data. An increase of the predicted sound levels is observed for increasing the coarseness of the sediment of the upper seabed layer and decreasing this layer thickness. The UAS parameters can be tuned to obtain sound levels that agree with the measured sound levels in the Gemini area. However, these parameter values do not represent the properties of a realistic seabed. Additionally, no evident choice of values exist to arrive at sound levels that agree with the acoustic data. It is concluded that the choice of values compensates for the exclusion of the shear effect in the fluid approximation of the seabed in the UAS. The exclusion of the shear effect in the representation of the seabed in the UAS is regarded as essential. Tsouvalas (2015) shows that the propagation of sound energy at low frequencies is governed by the shear of the soil. These lower frequencies propagate in the deeper parts of the seabed where shear effects play a role. Also, sound energy in the form of Scholte waves propagates at the water-seabed interface, thereby contributing to the sound levels in water. The reason the sound levels propagating at low frequencies is sought in two aspects. In a fluid seabed the geo-acoustic parameters are adjusted and account for the damping associated with shear, while the propagation of sound energy at these wave forms is not modelled. Another possible explanation is the trapping of the low frequency pressure waves in the seabed. Although the UAS is able to predict sound levels in the Gemini area that agree well with the measured sound levels, this is not due to the correct implementation of the physic regarding the seabed. As a consequence, the model is tweaked to arrive at the measured. The UAS is therefore not considered suitable for application in future wind park projects.

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.

The energy transition results in large offshore windfarms being installed. The most common support structure for a wind turbine at sea is a monopile. These are currently installed by large hydraulic hammers. However, hammering produces a lot of underwater noise which may harm marine life (Kastelein, 2014). Therefore, the industry is looking for new installation methods that are more environment friendly. GBM Works aims to implement such a new installation technique called the Vibro-drill. They introduce a revolutionary new design which is to replace the hammering technique. Vibrations, jetting and liquefaction are used to reduce the soil resistance. This reduction is so powerful that the monopile sinks into the ground under its own weight without producing the harmful underwater noise. Before each monopile is installed an analysis is made of the factors determining the chance of a successful installation. This process is called a penetration prediction. For the industry to accept the Vibro-drill installation method, penetration predictions are required to prove the applicability of the new technique. The radical changes in the installation process used by this technique make it impossible to use current penetration prediction methods. This means that a new prediction method needs to be developed that takes into account the specific features of the Vibro-drill. This thesis aims to address this problem by way of providing building blocks for the development of a fully-fledged penetration prediction model that is applicable to the Vibro-drill method. To this end, this thesis will focus on delivering a two-dimensional soil model in penetrated by a pile. The two-dimensional approach, which is the basis of this thesis, has of course its limitations as only a part of the pile and soil are included in the model. The assumed point symmetry over the centreline of the monopile leads to only a slice of the pile being modelled. The soil is captured using a lattice model. A well-known practice for modelling soil in a two-dimensional way. The properties of the lattice are determined using Cone Penetration Test data. As a result the model represents different layers of soil along the depth. The model uses a rigid pile to penetrate the soil. The penetration of the pile causes a reaction force in the soil. This force is used to calculate the friction forces. The reaction force and the friction force are the basis for calculating the penetration speed of the pile. From this it follows that the penetration speed and final installation depth depend on the different soil layers within the soil model. A first step towards validation is made. The pile/lattice interaction is verified and the results are compared to test data. A sensitivity analysis is performed to verify the independence of the lattice size and resolution on the modelled penetration speed of the pile. Subsequently the penetration predictions of the model in its current form are analysed. The results are compared to the real-life outcome of tests with the Vibro-drill. From this first attempt to validation the conclusion can be drawn that the two-dimensional model, as developed in this thesis, could be a suitable basis for further work on a viable penetration prediction method for the Vibro-drill technique. Finally, recommendations are made for further enhancing the model with a view to its eventual implementation as a fully functional penetration prediction model for the Vibro-drill.

One of the ways that Transmission System Operators (TSOs) can become more sustainable is by integrating sustainable goals in their projects using the associated procurement and tender processes. However, there are several limitations related to this integration. This research aims to identify these challenges by looking at the Dutch TSO, TenneT and its specific context. Furthermore, the research aims to provide a decision-support framework through which these limitations can be countered and the integration of sustainable goals in projects can be achieved. First, a literature study was conducted to define sustainability and the concepts associated with it. To properly understand the context of TenneT and identify the limitations associated with sustainability, company professionals were interviewed. This pointed to the need for prioritisation and gradual integration of sustainability measures. A desktop study was also conducted to identify the company’s sustainable goals, their associated measures, and their real-life applications. A decision-support framework for integrating sustainable goals in projects, based on Multi-Criteria Decision-Analysis (MCDA) was proposed. Using the Best-Worst Method (BWM), as the selected MCDA method, developed by Rezaei (2015), a sustainability workshop was organised where decision-makers from TenneT were asked to select relevant sustainability goals for TenneT, and the ones selected by three or more decision-makers were then used for performing the BWM. To avoid focusing on already well-performing sustainability goals, the performance of their associated measures was studied, using a Maturity Model based on the work of Silvius and Schipper (2015). Finally, an Importance-Performance Analysis (Martilla and James 1977) was performed, to assess future actions for each sustainable goal. The BWM showed that the Planet aspect was selected as the most important one for stimulating sustainability in projects. Additionally, Reducing Emissions was selected as the most important sub-aspect while in the People aspect, Health and Safety ranked first. The Maturity Model showed that the least integrated goals in projects are Human Rights, Labour Conditions and Decent Work, Energy Consumption, Materials and Natural Resources and Circularity and Waste. The BWM and Maturity Model also produced interesting results regarding the awareness of decision-makers and how they perceive sustainable goals and the performance of their associated measures in projects. Based on the Importance-Performance analysis, the research suggests integrating the sustainable goal of Circularity and Waste in the company’s following projects. This can be achieved by using existing sustainable measures, such as the Raw Material Passport (RMP), in the tender process. Using measures such as the RMP in the pre-qualification phases or selection phase, as entry requirements with specific targets to be met, or as an award criterion, aiming to create added value for the project, can stimulate the contractors and suppliers to act more sustainably. This will in turn increase TenneT’s sustainable performance and will help the company meet its own sustainable targets.

Due to a high demand for offshore wind energy the industry is expanding to evermore challenging locations such as seismic prone areas. The corresponding seismic shocks and vibrations can be transmitted to jack‐up vessels and their cranes used for the installation of these offshore wind turbines. Since a potential collapse due to seismic activity carries large human and financial risks, the main objective of this thesis is: ”To determine the best solution to mitigate the dynamic response of cranes for offshore wind turbine installation in seismic prone areas.” Therefore, we study existing mitigation measures and find that the dynamic absorber and base isolation systems are promising solutions. However, we only find the dynamic absorber to be feasible for implementation. Subsequently, we investigate the influence of the dynamic absorber on the dynamic response of the crane by performing seismic time history analyses. We find a mitigating influence for the vast majority of simulated cases. More specifically, the dynamic response in the out‐of‐plane direction is reduced by 10 percent on average. Furthermore, the dynamic absorber is highly effective in the mitigation of harmonic vibrations such as those that are induced by Rayleigh waves that occur near the end of earthquakes. This finding suggests that a dynamic absorbers might also be suitable for mitigating wave and wind loads in the crane as these loads prescribe a rather harmonic signal. The conclusions of this thesis give the offshore wind industry a clear indication that a dynamic absorber is an effective measure to mitigate the dynamic response of a crane that is based on a jack‐up.

Wave or vehicular action on an ice sheet as well as structural vibrations and thermally induced loading cause cyclic loading on an ice sheet. To better understand the effects of cyclic loading on the strength of sea ice, cyclic loading tests have been conducted at the University Centre in Svalbard (UNIS). In addition, the corresponding ice behaviour was modelled based on Cole (1995), thereby describing the viscoelastic response of saline ice subjected to a cyclic stress. The aim of this study was to design and execute a reproducible experimental campaign for saline ice subjected to a cyclic compression, and to model the stress-strain relationship of the ice. Specifically, the effects of frequency and displacement amplitude were studied. The laboratory-grown saline ice was frozen from a mixture of sea water and fresh water with a salinity of approximately 8. The structure was classified as S2 columnar ice through inspection of thin sections. The specimens were retrieved from horizontal and vertical cylindrical cores. The porosities of the specimens ranged from 22 to 34 ppt and the salinities from 2 to 4. The experiments were performed by applying a sinusoidal varying uniaxial displacement of one piston of the loading frame using a stepper engine. An initial compressive load (equivalent to 1 MPa) was reached by applying a constant strain rate. The model uses kinematics to describe the ice behaviour, which is explained by the line defaults in the ice lattice, so-called dislocations. The input parameters of the model are the central relaxation time of dislocation relaxation, the dislocation density and an empirically derived distribution factor. The model results were given by the amplitude and phase lag of the steady-state stress response for an applied sinusoidal strain. The experimental campaign proved to be reproducible and demonstrated the stress response of saline ice subjected to a cyclic compression well. However, some improvements of the experiments are recommended; most importantly, a higher resolution of the strain sensors and more stringent displacement control, such that the input strain can be defined. The results from the experiments furthermore showed a dependence of the energy dissipation on the loading frequencies, as well as a considerable influence of stress relaxation on specifically the first cycle of the tests. To compare the tests and the model, the strain signal was filtered to remove the influence of the strain sensor location. The parameter used to compare the experimental results to the model was the loss compliance, which describes the energy dissipation per load cycle and is derived from the area per loop of the stress-strain curve. A discernible trend was an apparent increase in the loss compliance for an increasing frequency or per consecutive test, which may be caused by an increase of the dislocation density. In conclusion, the experimental method provides a successful experimental campaign that demonstrates the energy dissipation per cycle. The model provides solid results for the steady-state response of saline ice subjected to cyclic compression.