This thesis investigates whether current Dutch design guidelines adequately account for horizontal ice loads on hydraulic structures under an extreme Atlantic Meridional Overturning Circulation (AMOC) collapse scenario. Climate model results representing extreme winter conditions were used as input for a river ice model in River1D of the representative section of the Maas between Belfeld and Sambeek. Simulations showed that severe river ice conditions, including moving frazil ice, anchor ice, ice jams, and solid ice cover, could develop under both closed and removed weir situations.

The resulting ice conditions were used to evaluate Dutch design guidelines and compare them with Canadian, Russian and European standards. While Dutch guidelines account for thermal expansion and ice accumulation loads, they do not explicitly consider ice collision loads, despite the latter representing the most critical loading mechanism. Computed expected ice loads for thermal expansion and ice accumulation were inconsistent with existing guideline values. Ice jam loads were found to be relatively small and collision loads could not be determined due to the selected module in the river ice modelling program River1D.

The study concludes that Dutch design guidelines do not comprehensively address horizontal ice loading under an extreme AMOC collapse scenario, particularly regarding significant ice collision loads comparable in magnitude to ship collisions. Further research is recommended to model the entire Maas, assess flood risks associated with ice jams, and improve the understanding of relations between ice strength, ice thickness and width of structure, as well as investigate the possibility of standardisation of ice strength used in guidelines. ... Read more

Large-diameter monobucket foundations are a promising alternative for offshore wind turbines in cases where monopiles are not suitable. However, during installation, the induced underpressure leads to compressive stresses in the thin-walled shell, making these structures susceptible to buckling. This is further amplified by the need for slender designs to remain cost efficient. This study investigates an alternative monobucket geometry in which the cylindrical shell is replaced by a segmented configuration composed of multiple curved sections. Two concepts are studied: the Outward Segmented Bucket (OSB) and the Inward Segmented Bucket (ISB). These geometries either increase local curvature or fundamentally alter the load application, both with the aim of improving buckling resistance.

A two-step finite element approach is applied, consisting of Linear Buckling Analysis (LBA) and Geometrically and Materially Nonlinear Analysis with Imperfections (GMNIA). The results show that segmented geometries achieve significantly higher buckling capacities, compared with a conventional cylindrical design. For OSB configurations, this improvement is driven by the increased local curvature, for which a clear relationship with the limit pressure is observed. In contrast, ISB configurations exhibit a different failure mechanism, where buckling is governed by local instabilities at segment edges due to stress concentrations, rather than global buckling. Furthermore, the results show that the buckling limit strongly depends on the eigenmode used as an imperfection, and that higher-order modes should also be taken into account. The improved buckling performance allows for substantial reductions in required shell thickness, demonstrating clear material and thus cost savings.
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This thesis dives into the collision dynamics between an ice ridge and a moored point absorber-type wave energy converter. The collision dynamics in this case encompass the ice–structure interaction forces, the resulting mooring line tensions, and the point absorber’s behaviour after impact.

For this research a 3D-model was developed using DualSPHysics, complemented by MoorDyn for mooring line dynamics and Project Chrono for collision dynamics. This research examined collisions between ice ridges modelled as rigid structures with typical subarctic dimensions and a moored buoy representing the point absorber. Various simulations were run with variations in ice ridge size, surface roughness of the ice ridge and different failure mechanisms for the mooring lines.

Key findings indicated that mooring line failures at a tension limit of 5 MN predominantly resulted from entanglement with rough keel surfaces rather than direct impact forces alone when ice crushing was neglected. Smooth-surfaced ridges allowed mooring lines to withstand tensions up to approximately 2.2 MN. Additionally, reducing ridge dimensions significantly decreased maximum tensions and horizontal contact forces, highlighting the critical role of ridge size and surface roughness in collision dynamics.

From this study it becomes clear that the highest uncertainty lies within ice crushing during the interaction with the ice ridge keel structure, it is expected to happen when the point absorber slides against the ice ridge, which can lead to entanglement of the point absorber within the ridge itself. This study contributes critical insights and provides a computational SPH-model for preliminary testing and analysis of moored point absorbers under ice ridge collision scenarios.
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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. ... Read more

The greenhouse emissions caused by the energy sector must be significantly reduced to slow down the impact on climate. Therefore, a great shift towards renewable energy sources is of importance. A method of doing so is by using offshore wind energy. The development and growth of this renewable energy source introduce new challenges for the future. One of these challenges is designing offshore wind turbines for sea-ice loads. In Europe, the northern Baltic Sea is the main site of interest for the development of offshore wind farms (OWFs) that will be subjected to ice loads. However, little is known regarding how the ice behaves around these structures and how the presence of multiple turbines will influence the ice loads encountered. Therefore, the following research question is defined.

How is the ice loading on and ice drift around an offshore wind turbine influenced by it being
part of an offshore wind farm?

First, an introduction to sea-ice terminology and ice action is given. This forms the theoretical framework for this thesis. Multiple methods are explored to analyse and summarise the ice loads experienced by a structure. These are later used to interpret the results obtained from simulations. In this thesis, the main area of interest is the northern Baltic Sea (Bay of Bothnia). Therefore, the environmental conditions and sea-ice in this area have been thoroughly investigated. Image processing of ice fields over the years yields a starting point for generating ice fields that are used in the simulations.

Furthermore, all relevant ice properties are considered and, when possible, adjusted for the lower salinity present in the Baltic Sea water. In addition, current and wind conditions are determined to determine in which way these play a role in the drift of the ice.

In this thesis, both the effect of the wind directions and ice concentration are investigated. Combining these results in 16 total simulation scenarios that will be modelled using the Simulator for Arctic Marine Structures (SAMS) software. In total, four different wind directions (0, 15, 30 and 45 degrees) and four different ice concentrations (50%, 60%, 70% and 80%) are used. The OWF used has a grid layout with 5x5 turbines and an ice field of 15x15 km. The ice field is simulated such that it drifts into the OWF, no ice is initially present in the wind farm. Due to computational limitations, for each scenario, 45000 seconds (12.5 hours) of data is simulated.

To analyse the obtained force data, the Ice Load Factor (ILF) and the Ice Load Contact Factor (ILCF) are defined. Both use rainflow counting to analyse the number of force cycles that occur over time. A lower threshold of 100 kN is used to focus on the higher impact interaction. In addition, an upper limit of 10.8 MN is used to eliminate numerical peaks from the results. Both factors use the sum from the product of each force bin and it’s corresponding amount of cycles. Each load bin has a size of 0.5 MN and the average value of this bin is used in the product. Summing this over all load bins yields the numerator for both factors. The main difference between the factors is the denominator. For the ILF the total potential exposed time is used based on the free-drift velocity of the ice. Since this does not take into account the actual time that the interaction occurs, the ILCF uses the total contact time of the ice with the structure. Both fractions are multiplied by the total simulated time to obtain a unit of Newton in both factors.

Based on the obtained data one can analyse each individual turbines and also group them. In this thesis the term, ”Lines of turbines” is used to refer the order in which the ice interacts with the OWTs. Hence, the first line of turbines represents the turbines that first interact with the ice field. Moving further downstream, the following up lines are defined and can be analysed for all wind directions. Analyses on these lines of turbines gains insight on how the ice action changes when moving further down the OWF.

For the lowest ice concentration (IC = 50%) the ILF decrease for all wind directions in the lines of turbines is approximately the same. Only when the ice concentration increases, a more clear difference is seen for changing wind directions. Since a higher IC results in more ice floes in the ice field. Therefore, it is more likely that a turbine interacts with an ice floe. This influences the drift in and around the wind farm. Generally, more sideward movement is caused by higher ice concentrations. This makes ice more likely to interact with turbines further downstream. For lower concentrations, the ice continues to move along the same streamline resulting in less ice-structure interactions. The mean ILF is decreased by >70% and the sum by >75% after interacting with the first line of turbines in all scenarios. Hence, a significant reduction is present in the wind farm.

The interaction times for a 0 and 15 degree heading decrease significantly more over the lines of turbines. Furthermore, these wind angles result in the lowest ILCF sum and mean values for all ice concentrations. Based on the ILCF, one can conclude that these two wind directions result in the best reduction of ice loads based on the total interaction time. Furthermore, one concludes that the 30 degree wind angle yields the lowest reduction in interaction time and therefore has the lowest ice-structure interaction blockage effect. This could potentially be caused by the fact that this angle has the highest offset in the position of the turbine in y-direction. Therefore, turbines in previous lines do not prevent other turbines further downstream to interact with the ice field.

The computational times of these kinds of simulations are found to be significant. Therefore, it is explored whether machine learning (ML) could be used to predict the encountered ice loads. This could greatly influence the pace with which different OWF layouts or ice conditions can be tested more thoroughly. From the data obtained, different ML regressors are trained and tested for their performance. The usage of a Random Forest Regressor resulted in the most accurate results. However, these result are found not to be accurate enough to use them for prediction purposes. Therefore, it is found that first more data need to be gathered to train and test these models more extensively, and the usage of more complex ML models could potentially also improve the performance. Doing so could greatly influence the speed with which different parameters of influence can be analysed.








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The expanding offshore wind industry is facing challenges with excessive movement of the power cables that connect offshore turbines to the grid. The casings that surround the exposed parts of cables near structures, known as cable protection systems (CPS), show damage before the end of their expected service life, requiring costly repair and maintenance. A potential solution is to stabilise the CPS by placing one or more rock-filled mesh bag (rock bag) on top of it. There are multiple rock bag manufacturers and distributors. The bags are made of polyester netting that is relatively flexible. The sizes considered for this study are 4 and 8 ton (4000 and 8000 kg), but smaller and larger sizes are available. Currently, little is known about the behaviour and stability of these rock bags in offshore environments. The goal of this study is to expand the knowledge through empirical model testing.
480 experiments were conducted in a flume in the hydraulic engineering laboratory of Delft University of Technology. Two set-ups were used, one with a flat rough bed, to test two or three rock bags side by side and grouped formations of bags. The other is a realistic halved model of a monopile, scour protection and CPS. Regular wave, irregular wave and combined wave-current conditions have been tested.
Analysis of before and after top images of the tests is used to establish a failure criterion. In this way, a stability limit applicable for irregular wave fields is found. The effects of grouping and near monopile flow amplification are quantified.
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The transition to more sustainable energy has led to a growing demand for offshore wind energy, necessitating larger structures and heavier foundation piles. During pile installation this increases the risks of uncontrolled pile run, which can have fatal outcomes and project delays. Offshore superstructures predominantly rely on largediameter open-ended driven piles. Intermediate soils pose significant challenges in determining soil resistance during driving and pile run, with calculations typically performed using Static Soil Resistance to Driving (SRD) methods. The Alm & Hamre method is preferred for deep foundation piles in mixed soils due to its inclusion of friction fatigue.
The goal of this research with corresponding research objective is to improve pile run velocity and trajectory predictions for offshore open-ended pile installation in intermediate soils. This objective is reached through research on drainage state, identifying soils susceptible to a shift in this drainage state, and analyzing velocitydependent resistance for CPT and pile velocities. The findings are then incorporated into a modified SRD model. The results are compared to a case study using CPT and borehole data as input, and installation video’s and driving data as validation material.
Key findings indicate that with increased pile velocity the drainage state of several soils can shift towards the more undrained spectrum and therefore the soil will have a smaller soil resistance. These soils with a lower soil resistance during pile installation velocities then predicted include intermediate soils such as silt, sandy silt, and silty clay. Thin alternating layers of sand, clay, and silt are also likely to experience a shift in drainage state. Later silty sand is identified as a soil with a high possibility of being prone to such drainage state shifts.
The SRD method, incorporating velocity-dependent resistance, predicts pile run 31% more accurate than models without this consideration. By including velocity-dependent resistance drops, the model accounts for the changes in soil resistance that occur during pile run, leading to more accurate predictions compared to the standard SRD model. The model used in this research uses a single SRD update for velocity dependent resistance. However, in scenarios with large pile runs trajectories and high pile velocities, or when a substantial portion of the soil is prone to a drainage shift, performing a single update for velocity-dependent resistance will not result in a converged solution. As such for a correct solution, multiple iterations are necessary.
When the model predicts a deeper Self weight penetration depth than observed, the predictions for pile run initiation are not reliable. Given that pile run initiation can be very delicate, further research is needed for locations with CPT and borehole data directly beneath the pile. Additionally, incorporating hammering parameters, such as the added weight due to hammer momentum, should be explored to improve these predictions. ... Read more

This thesis explores the occurrence of salt dry-out and hydrate formation when injecting CO2 into porous media. In large-scale CCS projects, injecting CO2 can potentially lead to salt precipitation or hydrate formation. These processes diminish injectivity and negatively alter reservoir rock properties. To gain deeper insight, experiments were conducted utilizing microfluidic setups, which allow for visual observation of salt-crystal or hydrate formation. Using microfluidic chips, ten salt dry-out experiments were conducted with varying pore sizes and six hydrate experiments were conducted with varying pulse trigger times. For the dry-out experiments, it was shown that salt crystals form mostly at the outlet side and that heterogeneity has a large impact on the precipitation process. A heterogeneous pattern results in a shift in salt distribution to the small pores, with results showing salt saturation at 7% in the small pore section of the medium-small pore chip, exceeding the 3% in the larger pore section. This shows the significant role of capillary action on salt precipitation. Results highlight that higher CO2 flow rates accelerate water evaporation and salt formation, yet final salt precipitation levels remain similar across varied flow rates. For instance, in the small pore size chip, final salt saturation was observed at 7% with a flow rate of 4.38 mm/s, decreasing to 4% at 0.78 mm/s. Additionally, the importance of high water saturation for salt dry-out and the impact of water backflow is shown. For hydrate formation, the importance of temperature and pressure was noted in these experiments. Three different pressure pulses were employed: manual control, a 0.5-second electronic pulse, and a 0.2-second electronic pulse, which all showing great effect on hydrate formation, yet no correlation could be determined between pulse length and hydrate saturation. Specifically, manual control yielded a 15% hydrate saturation with a 9.4% conversion factor, while the 0.5-second pulse achieved a 7% saturation and 9.1% conversion factor. The 0.2-second pulse resulted in 8% saturation and a 5.9% conversion factor. For the dissociation, the large effect of temperature was observed. All experiments showed a stable hydrate concentration, and a dissociation temperature between 5 and 9°C where temperature differences as small as 0.1°C were shown to be the difference between no dissociation and complete disappearance of all hydrates. Next to this kinetics, an interesting observation regarding the hydrate morphology was made. In addition to the five hydrate morphologies found in literature, a sixth, ‘sheet’-like type was observed. ... Read more

In recent years, there has been growing interest in exploring the deployment of wave energy converters (WECs) in remote and harsh environments. However, research in this area remains limited, particularly concerning offshore environments with sea ice. This study focuses on investigating the energy production and economic feasibility of a point absorber in the Baltic Sea, specifically off the coast of Åland, which experiences seasonal ice cover. Four winter seasons with varying ice conditions are examined, ranging from ice-free to severe ice conditions. Additionally, the study aims to assess the survivability of the WEC under extreme level ice action and extreme wave conditions.

Based on literature review, a hexagonal slope-shaped buoy has shown promise in withstanding ice conditions up to 15 cm thickness in the Baltic Sea and is selected as the WEC design in this study. Metocean and sea ice data spanning from 2006 to 2021 are analysed from the NORA3 database. Through extreme value analysis, key parameters such as wave height, period, and ice thickness are determined. Survivability analysis is conducted to understand the forces exerted on the WEC during extreme ice load cases and extreme sea states. To evaluate energy production, hydrodynamic coefficients are computed using the Boundary Element Method solver Capytaine in the frequency domain. Subsequently, simulations are conducted using WEC-Sim to derive the power output of the WEC under varying sea states. Optimisation of the Power Take-Off (PTO) damping is performed to enhance performance for the specific site conditions. A comparison of power output is made among different WEC configurations with varying translator sizes.

The survivability analysis reveals important design considerations, especially regarding extreme ice conditions. When subjected to an extreme level ice thickness of 60 cm this results in calculated horizontal and vertical forces of 615 kN and 315 kN, respectively. In extreme sea states, simulations in WEC-Sim shows a maximum heave response of 4.16 m and a maximum heave force of 133 kN. Additionally, the investigation reveals significant fluctuations in wave energy converter (WEC) power production across the analysed winter seasons, characterised by varying ice conditions. During severe ice conditions (2009-2010), energy output decreased by nearly 50% compared to ice-free periods (2019-2020), potentially leading to a 95% increase in the levelised cost of energy (LCOE) if solely derived from that single season. These findings give valuable insights into the optimal WEC configuration, the maximising of power output and offer important considerations to WEC survivability for deployment in ice-covered regions. ... Read more

Sea turtle nesting beaches are under increasing pressure from climate change, rising sea levels, and human activity, making the protection of critical habitats like Ostional Beach, Costa Rica, an urgent priority. This study integrates the analysis of wave runup dynamics, groundwater behavior, stakeholder collaboration, and coastal squeeze mitigation to address the unique challenges at this vital olive ridley turtle nesting site.

Wave runup was examined using timestack imagery analysis. Two automated extraction models— entropy-only and entropy-saturation—were compared against manually digitized data. Results show that the entropy-only model is more reliable in capturing peak wave run-up values, a critical measure for understanding inundation risks. Challenges in accuracy, particularly for the entropy-saturation model, were linked to the site’s unique environmental conditions, such as dark volcanic sand. The findings fill a gap in understanding how specific extraction methods perform under unique site conditions, with implications for improving future modeling efforts.

Groundwater dynamics were studied using pressure sensors installed in custom-built wells, revealing significant interactions with tidal forces. These measurements highlighted the role of tidal cycles in influencing groundwater levels, providing crucial insights into the potential for nest inundation. These findings extend existing knowledge by combining tidal and hydrodynamic factors specific to turtle nesting sites.

Collaboration within the TURTLE project was analyzed through semi-structured interviews and structural evaluation of partner interactions. A tailored framework was developed to enhance communication and coordination among stakeholders, addressing identified gaps and leveraging existing strengths. This framework contributes to more effective project management and the application of scientific insights in conservation strategies.

To mitigate coastal squeeze—a phenomenon where natural habitats are compressed by rising sea levels and human development—the study evaluated strategies such as foreland restoration and managed retreat. Findings suggest that integrating habitat restoration with community involvement is critical to preserving the ecological and social balance at Ostional Beach.

This study takes an interdisciplinary approach to explore how wave runup, groundwater behavior, and collaboration strategies can be effectively combined to support conservation efforts. The results stress the need for tailored, site-specific solutions that blend engineering, ecological, and social perspectives to protect endangered species and their habitats. By bridging knowledge gaps and offering practical recommendations, the research bolsters both local and global initiatives aimed at preserving vulnerable coastal ecosystems.  ... Read more

This report, titled Expanding Puerto Rawson: Enhancing Fishery Capacity and Project Cargo Logistics, presents a conceptual masterplan for the eco-friendly expansion of the Port of Rawson. The port’s proximity to a region abundant in marine resources makes it an attractive location for expansion. However, the port is facing strategic expansion problems and it could fail to accommodate the rise in demand from the fishery industry. This report carefully maps out the gap between the expected rise in demand and the currently existing infrastructure. After that, two models are created to transform the rise in demand that is expected by 2030 & 2040, to nautical demands for the port, like number of berths and required waterway width. The results from these model in combination with a strategic overview of the landscape, were used to come up with three conceptual designs that eventually converged into one final conceptual design by conducting an MCA. This conceptual design, together with the port waste management plan, could enable an eco-friendly and future-ready expansion of the Port of Rawson. ... Read more

The erosion problem along Playá Union presents significant challenges for future port expansion at Puerto Rawson. This research seeks to address the question of how to achieve a sustainable and durable port expansion, while minimizing environmental impacts, particularly concerning sediment imbalance along the coastline? Using 30 years of wave data, both normal and extreme wave conditions are simulated with SWAN, a numerical based wave model. Conceptual port expansion designs are developed, resulting in a final design with an integrated fully dimensioned breakwater. Based on visual inspections, data, and research, a new cement mixture is proposed for the breakwater armour units. A Life Cycle Assessment evaluates the environmental impact, while the effect on alongshore sediment transport is assessed using the SWAN model outcomes and the CERC formula. Visual inspection of the current breakwaters lead to a 6.3% reduction in material use in the new breakwater through reuse of armour units. Furthermore, the proposed cement mixture integrates porphyry quarry waste as the coarse aggregate, a choice also supported by prior research in sustainability. With the new End-of-Life approaches added, the total shadow costs are reduced by 22%. The hydrodynamical analysis and model result in extreme wave heights up to 3.98 m at the toe of the breakwater. By applying a neural network and a k-means algorithm on the wave data, five regular wave conditions are run in the SWAN model. The alongshore sediment transport is impacted by new breakwater concepts. Relying solely on the breakwater layout to counteract erosion north of the port, however, does not prove to be a viable approach. Based on design criteria and aspirations, the final conceptual design proposes the removal of the existing southern breakwater, while retaining sufficient space for future port expansion. The breakwater, integrated in the final design, is dimensioned based on standard design principles. To conclude, the data and model provide valuable insights into the coastal dynamics around Puerto Rawson. The proposed concrete mixture, along with the End-of-Life solutions, minimize environmental impact and enhance durability of the armour units. The sustainable breakwater design, effectively integrated into Puerto Rawson, accommodates for future port expansions ... Read more

The imminence of anthropogenic climate change has motivated a global energy transition towards sustainable power generation. Offshore wind—an important contributor to the energy transition—is expanding, not only in turbine size and number of installations, but also into regions with harsher environmental conditions. One of those conditions in places such as the Baltic Sea is drift ice. Offshore wind turbine support structures, with vertical sides at the waterline, must be designed to survive dynamic ice-structure interaction when ice fails in crushing against the structure. For a safe and efficient design of the support structure, dynamic ice-structure interaction resulting in ice-induced vibrations must be considered. Therefore, both an understanding of the problem and accurate modeling for the prediction of the development of ice-induced vibrations are required.

Significant progress has been made in recent years on the topic of ice-induced vibrations, and a numerical model for prediction of ice-induced vibrations has been developed based on the principles of velocity-dependent deformation and failure behavior of ice, and contact area variation between ice and structure during interaction. However, uncertainty remains regarding physical mechanisms within the ice which govern ice-induced vibrations. The ice mechanics involved in the development of ice-induced vibrations is therefore the main topic of this thesis.

The main objective was to investigate and identify the ice mechanics involved in the development of ice-induced vibrations, especially in the regime of frequency lock-in as historically defined. It was hypothesized that dynamic recrystallization played a relevant role in the ice mechanics involved in ice-induced vibrations. To test the hypothesis, ice mechanics experiments were performed at the ice laboratory specifically developed at Delft University of Technology for this purpose.

To identify grain-scale mechanisms in ice, such as dynamic recrystallization, a method was devised to elucidate ice thin section textures and (quarter) fabrics by means of crossed-polarized transmitted light and interference coloration of ice. An attempt was made to apply the method to the laboratory experiments which applied compressive loading to the edge of a thin freshwater columnar-grained ice plate, laterally confined by glass plates. Crossed-polarized transmitted light was shone through the glass plates to observe the grain structure of the ice during cyclic compression with a haversine velocity waveform. The loading and confinement scenario was intended to reproduce a vertical section of the ice edge during frequency lock-in vibrations. The experimental design demonstrated that the grain-scale mechanics of dynamic recrystallization did not obviously contribute to the peak load-velocity relation associated with frequency lock-in vibrations. As expected, fracture initiated on the grain scale was responsible for load drops. But, more interestingly, stress relaxation during periods of low relative velocity between ice and structure occurred rapidly. Following the stress relaxation, when velocity increased, the peak load was higher than previous brittle peak loads. The results indicated that the mechanisms involved in the stress relaxation were occurring on a scale smaller than the grain size. A loading path dependency was also observed with respect to the peak load-velocity relation.

Ice penetration experiments at the Aalto Ice and Wave Tank in ethanol-doped cold model ice were performed with a rigid structure, controlled oscillation, and a single-degree-of-freedom structure, and comparison of results showed that the peak global ice loads depended on the amount of time spent at low relative velocities where an ice strengthening effect developed. This has implications for the so-called velocity effect and compliance effect in design of structures subject to dynamic ice-structure interaction.

Overall, the load signals from the ice mechanics experiments on freshwater ice resembled the load signals obtained from the controlled-oscillation experiments from the model-scale ice tank tests. The qualitatively similar velocity and resulting load patterns give confidence in the idea that the mechanisms involved in both types of experiments were similar, even for different ice types and loading scenarios.

These similar results demonstrate a link in the ice mechanics across different ice types and loading scenarios, which may be explained with further research on path-dependent constitutive ice behavior, and with scrutiny regarding ice dislocation and grain boundary mechanics. Suggestions for future research are proposed, including the testing of strain rate-varying uniaxial compression of ice and ice penetration experiments with haversine velocity waveforms. ... Read more

Offshore wind turbines, given their structural properties, are expected to experience severe ice-induced vibrations. However, full-scale events neither have been observed nor published yet and thus predictions of existing numerical models could not yet been validated. Model-scale experiments, aiming to investigate ice-induced vibrations of offshore wind turbines, have been inconclusive as structures with low natural frequencies would exceed the capacity of test facilities (i.e., size and weight limits), while geometrical scaling introduced scaling effects (e.g., buckling) compromising the validity of conducted experiments.

In the absence of full-scale testing capabilities, the main goal of this work was thus to demonstrate how offshore wind turbines behave under dynamic ice loads in smallscale experiments. In total four research questions (RQ) have been formulated and are addressed in this thesis, collectively serving to achieve the primary objective of this thesis.

RQ1: How can ice-induced vibrations of vertically sided offshore structures be scaled?

RQ2: How can offshore structures with low and multiple eigenfrequencies be tested in
ice tank experiments?

RQ3: What types of ice-induced vibrations can an offshore wind turbine experience?

RQ4: What is the effect of wind-ice misalignment on the development of ice-induced
vibrations of offshore wind turbines? ... Read more

Arribadas, a phenomenon of mass nesting behavior of sea turtles, attract millions of olive ridley turtles (Lepidochelys olivacea) to Playa del Ostional, a nesting beach in Costa Rica. The timing and size of these arribadas are influenced by various environmental factors, including temperature, tides, and moon phase [1]. The sea turtles are threatened by a variety of factors, like amongst others climate change.
Rising temperatures and sea levels, changes in ocean currents, and more frequent and intense storms are all likely to have negative impacts on sea turtles [2]. Without intervention, climate change could lead to the disappearance or flooding of sea turtle nesting beaches, resulting in a loss of critical habitat for these creatures. To prevent such an outcome, it is imperative to gain a deeper understanding of the morphological and hydrodynamic characteristics of nesting beaches, as well as identify the factors that influence sea turtle nesting behavior.
This study aimed to identify and map the critical factors that must be considered to ensure persistence of the olive ridley sea turtle and arribadas at Playa del Ostional, Costa Rica. The objectives of this research were, therefore, (1) to map the seasonal morphological and hydrodynamical differences of the arribada nesting beach, (2) to identify the environmental parameters that have the greatest influence on the occurrence of an arribada, and (3) to map out the stakeholders involved. The study site is the beach that ranges from the northernmost part of Playa del Ostional down to the southernmost part of Playa Nosara, which is located on the northern peninsula at the west coast of Costa Rica. The part at Playa del Ostional where most turtles nest is called ‘Main Nesting Beach’ (MNB). A field investigation was carried out to determine the seasonal morphological and hydrodynamical differences of the nesting beach. This field study comprised of two distinct components: (1) a characterization of the morpho- and hydrodynamics of Playa del Ostional in the dry season, and (2) a comparative analysis of these conditions during the wet and dry season. The morpho- and hydrodynamic beach characteristics consisted of the beach profile, sediment composition, hydrodynamic properties and other general environmental characteristics, such as vegetation and nearby rivers. The beach profile was measured by walking transects perpendicular to the shoreline using RTK-GPS equipment. Moreover, a drone was flown that made an orthophoto and collected 30 million data points. The difference in sediment composition was analyzed by obtaining sediment samples in the dry season, sieving these and comparing the obtained particle size distributions and D50 values of the dry and wet season. The hydrodynamical properties and the other general environmental characteristics are analyzed by means of literature review, observations and photography. In order to identify the environmental parameters that have the greatest influence on the occurrence on an arribada, an autoregressive logistic regression model was used. The model that was made the previous research of 2022, was updated and automated. Also, design choices of the model were made and new data was added.
To map out the stakeholders, interviews have been conducted and a stakeholder map was created. Through the use of GPS transects the beach profiles taken in dry season (February 2023) were compared to wet season (October 2022). To tackle normal spacial variance the comparison is done through the calculation of averages on three beach stretches with equal characteristics. Main findings were that beach width is equal in both seasons, slopes are more gradual in dry season, beach plateaus are on average 3.0m wider in wet season. Crossing rivers do not influence the beach profile below waterline in the dry season. For more river characteristic more offshore research is needed. The sediment composition of the beach turned out to show significant differences between the dry and wet season. A significant difference is present in D50 values between the dry and wet season for almost all sediment samples. Moreover, during the wet season, the sediment tends to be coarser compared to the dry season. Additionally, during the dry season, coarser sediment tends to accumulate at the top of the slope, whereas during the wet season, coarser sediment accumulates near the waterline. These observations suggest that coarse sediment may move from areas close to the waterline to the submerged part of the slope over time. This behavior implies that sediment transportation is affected by the seasonal fluctuations in wave energy. The findings altogether indicate that the sediment composition at Playa del Ostional, particularly at Main Nesting Beach, is notably affected by seasonal changes. The impact is more pronounced from the low tide waterline to the high waterline’s end at the top of the slope, with a particular emphasis on the low tide waterline. The wave climate surrounding Playa del Ostional is expected to be less turbulent, with lower wave energy during the dry season. However, the exact distinctions in both wave climate and tidal surroundings between the two seasons cannot be ascertained due to inadequate data availability.
The different stretches of Playa del Ostional demonstrate notable differences in environmental characteristics during the wet and dry seasons. The majority of rivers that flow out during the wet season are absent during the dry season. In addition, a beach scarp appeared during the dry season and not during the wet season, and an estuary that was observed in the dry season was not reported during the wet season research. On the other hand, the beach is mostly surrounded by vegetation in both seasons, with comparable grass and trees. Moreover, no significant difference in wildlife presence was observed between the dry and wet seasons at Playa del Ostional.
The autoregressive logistic regression model was trained on five year of arribada data and 116 individual environmental parameters. The weights of the parameters were plotted and analysed in multiple groups. This resulted in six parameters with the biggest influence: pdTIDE_P1, pdTIDE_mf, pdVELOCITY_IHC_rho, pdVELOCITY_IHC_rho, Mooncycle_third and Moon_v. The maximum probability of an arribada occurring during a certain day was 80%.
By conducting interviews and conducting a stakeholder analysis, the degree of awareness about climate change is assessed and mapped out, which appears to be quite high. The residents of Ostional are aware of the changes and willing to work in new projects. Moreover, the analysis showed that it is important to engage with two key stakeholders: the Refugio Nacional de Vida Silvestre Ostional and CITES. ... Read more

The Vietnamese Mekong Delta, a vital region in the country’s economy, faces the dual challenges of coastal erosion and mangrove degradation, which threaten its long-term sustainability and flood protection capabilities. This research focuses on the coastal area of the Bac Lieu province, characterized by severe erosion and degrading mangrove forests. The study investigates the applicability and potential impacts of hydraulic measures to decrease the net rate of coastal erosion, utilizing numerical modeling with Delft3D and a comprehensive socio-economic analysis. The research hypothesizes that the coastal erosion is partly driven by the placement of a sea-dike to protect aquaculture farms, initiating a positive feedback loop. This loop explains the relation between coastal erosion and mangrove degradation. The proposed hydraulic measures to interfere with this feedback loop are a porous detached breakwater, a shoreface nourishment and the removal of the existing sea-dike. The socio-economic analysis involves questionnaires for local residents, field investigations, and insights from experts in Ho Chi Minh City. While the questionnaires provide inconclusive results, the overall socio-economic impact of the nourishment and breakwater is deemed positive and worth further exploration, particularly in light of the critical role of mangroves in future flood protection. On the other hand it is concluded that the measure of removing the sea-dike will have a negative impact on the coastal area of Bac Lieu due to the intensive land-use and the lack of individual protection of the farms and villages. Therefore, this measure is not modelled. Numerical modeling with Delft3D assesses the hydraulic impact of the breakwater and nourishment on the heavily eroded and partially eroded coasts of Bac Lieu. Results indicate that the nourishment method exhibits a positive effect in reducing net erosion, especially in low energy conditions. Conversely, the porous breakwater shows minimal impact on cumulative erosion and sedimentation. Since this is against all expectations, the validity of the schematization of the porous breakwater is questioned. It is observed that the schematization does not grasp the complex behaviour of the breakwater and therefore it is concluded that Deft3D is not a suitable modelling tool for modelling a porous breakwater. The findings suggest that the nourishment method is a promising approach for reducing erosion in Bac Lieu, benefiting both the heavily and partially eroded coasts. To determine the best course of action for Bac Lieu, further research into the long-term effects and configurations of nourishment is recommended. Additionally, informing local inhabitants on the threats of relative sea-level rise and flood protection, and fostering consensus between the government and engineering agencies on the importance of protecting the Mekong Delta and its mangrove ecosystems are essential steps toward a more resilient future. ... Read more

Playa Unión and Puerto Rawson are facing severe coastal erosion and increasingly the negative effects. Since the first half of the 20th century there have been signs of erosion, but also of sedimentation. However, the coastline in the project area is retreating over the years. The situation has recently been declared an emergency. Furthermore, there are several expansion plans for the port consisting of new quay walls and dredging. It is unsure if these plans will influence the erosion. In this report, the following research question is formed: ”What are valued, preferably nature-based, interventions that can mitigate the coastal erosion in Playa Unión and Puerto Rawson considering the planned expansion of the port?” Due to the limited information and data available, assumptions have been made during the research. A site analysis and a CoastSat analysis are conducted to research the morphology of the coastline and its drivers. The coast has been shaped into a steep upper section of coarse granular material and a gentle lower slope with finer material. The main driver of longshore sediment transport in the area are swell waves, with predominant directions SSE and E. This transport is directed from south to north, resulting in the inflow and outflow of sediments. Furthermore, there is a sediment flow from the Chubut river. Due to the construction of the port’s breakwaters, the longshore sediment transport is interrupted, which causes an imbalance in the sediment flow in the system. More sediment flows out of the system than enters, causing coastal erosion. The development of the port contains public as well as private expansion plans and maintenance dredging. The expansion plans will have little effect on its surroundings. The private plan include a parallel breakwater, which alters the natural balance in the area and dredging works, for which the stability of the existing breakwaters has to be figured out. A stakeholder analysis was done to get insights in the opinions and visions of the stakeholders. This was done by interviewing stakeholders and by doing a questionnaire, resulting in a power-interest grid and overview of interests and attitudes. The boundary conditions for the interventions and criteria for the multi-criteria analysis are partly formulated as a result of the stakeholder analysis. The following interventions were considered in this report: • Permeable pile groynes and low crested groynes
• Opening the northern breakwater: opening and reshaping with a curve, constructing tunnels underneath the breakwater and a sediment bypass
• Port expansion and a sediment bypass with power supply southern of the port
• Dredging and moving sediment
• Sediment trap
• Plant vegetation with beach nourishment
• Gravel engine
• Temporary longitudinal flood barrier as a short term intervention.
A conceptual multi-criteria analysis in combination with a nature-based assessment has been conducted to distinguish the most promising interventions in the conceptual design phase. The criteria formulated were effectiveness, easiness of implementation, maintenance, environmental impact and the benefits for recreation. From this, it can be concluded that the gravel engine and the plant vegetation with beach nourishment score the best.
... Read more

The increasing popularity of offshore wind as a result of the demand for renewable energy, forces the industry to consider the development of wind farms in sub-arctic areas. One of these areas is the Baltic Sea, where the potential for wind energy is very large, but which is also prone to the occurrence of ice. For the design of offshore foundations it is paramount that ice-structure interaction is appropriately considered as ice-induced vibrations are known to significantly increase the loads. As a result, ice-mitigating measures may need to be included in the design. However, such measures will substantially increase the cost estimates required
for competitive tenders. Hence it is valuable for developers to have early screening tools to assess this. The aim of the research was to provide a ‘feasibility map’, which predicts the necessity for ice-mitigating measures in the entire Baltic region. Feasibility of monopiles was considered both technically and economically. The former by imposing design, installation & fabrication constraints and the latter was measured in terms of weight increase of monopiles.
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To accommodate the growing demand for renewable energy, installation of new offshore wind energy capacity is increasing in many countries. New projects will be proposed for waters in which floating (sea) ice is a common occurrence in winter. Currently, projects remain limited to regions with mild ice conditions, such as the Southern Baltic Sea, but projects further north are expected. In preparatory work for this thesis, performed at Siemens Gamesa Renewable
Energies, it was shown that (edgewise) blade loads increase significantly for Northern Baltic sites when compared to Southern Baltic sites due to ice induced vibrations.

The phenomena of ice extrusion and rubble loads are expected to provide added damping to an ice-structure interaction system. This added damping may lead to less severe structural vibrations, and thus blade loads for an offshore wind turbine, than for a system with only intact ice crushing. VANILLA is the leading ice crushing model in the industry to evaluate the effects of ice induced vibrations for vertical offshore structures such as wind turbines, but the model
currently does not (explicitly) consider ice extrusion and rubble loads. Therefore, the aim of this work is to investigate the phenomena of rubble and ice extrusion in crushing and propose a modelling approach.

Following a literature study, a rubble model and an extrusion model are proposed as extensions of the VANILLA ice model. The rubble model shows to be consistent and compute plausible rubble loads for model and full scale, while the extrusion model only predicts reasonable extrusion loads at full scale. Forcing and dynamics found from using the Standard and Adjusted VANILLA model with simplified global bending mode shapes of the SG 14-222 DD offshore wind turbine were compared.

Rubble loads were found to be small in magnitude and of negligible influence on the dynamics. The loads stemming from extrusion introduce additional damping to the system when the relative velocity between the structure and the ice increases, such that (i) the immediate load drop to zero after a failure event observed in Standard VANILLA is omitted, (ii) initiation ice drift velocities for IIV regimes become lower, (iii) dynamic amplitudes reduce, and (iv) a positive force-velocity gradient arises in the CBR regime. ... Read more

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. ... Read more