In this thesis, an alternative cable lay system was designed that can be used on existing non-cable lay vessels. This design is conceptualized and analyzed for a specific market, following the steps in the engineering design process. The technical and economic analysis investigates the feasibility and competitiveness of the new cable lay system. Nowadays, cables are installed over a chute at the aft of a vessel, which makes the operation very sensitive to motions, inducing high cable loads that result in limited workability. Also, load carrying capacity is limited for existing cable lay vessels within the Boskalis fleet, making the application of joints a necessity in offshore export power cable installation. The design focuses on the international offshore export power cable installation market (both AC and DC), including interconnectors, from shore to substation or shore to shore. This market was selected because of the limited load-carrying capacity of current cable lay vessels, the internationally growing offshore wind market and the relatively low market share of Boskalis in this segment. New concepts were generated and evaluated using multi-criteria analysis, scoring them on technical and economic criteria determined for the selected market. The concept that has been selected for further development focuses on export power cable laying through a moonpool. A Dockwise semi-submersible heavy transport vessel is targeted for this design because it is being converted into a fall pipe vessel already. This conversion includes the installation of a moonpool, opening up the possibility to make the selected vessel a multi-purpose ship. Making use of static stability software, the maximum load-carrying capacity of this vessel has been determined. From this analysis, it can be concluded that the maximum cable load that can be carried by the selected vessel is 9.000 tonnes of cable equivalent, which is approximately 110 km of currently installed export cable length. Conventional cable lay vessels from Boskalis have load carrying capacity up to 5.000 tonnes. Additionally, a deck-layout with the crucial parts of the cable lay system is designed, taking into account all necessary alterations regarding the conversion of the vessel. The main technical challenge for the newly designed system is the second end cable pull-in. With limited space in the moonpool and vertical laying of the cable, the conventional pull-in method cannot be used here. Three solutions have been developed, based on a deployment quadrant or bight lay down. Two of these are already proven in the field, making the concept technically feasible. A model has been made to evaluate both conventional cable lay, and cable lay through a moonpool. With the use of dynamic time-domain analysis, the operational limits have been determined for both methods, keeping the catenary shape of the cable constant. This analysis concludes that cable laying through a moonpool indeed increases the workability for the selected vessel. No significant increase can be seen for moonpool cable laying with a conventional cable lay vessel. This is due to its sensitivity to roll motions, for which the distance towards the center of gravity is equal in both concepts. For the selected vessel, cable laying over a chute is not possible for the chosen catenary shape and sea states because the maximum allowable curvature is exceeded. This is due to the large arm for pitch motions, from the center of gravity to the chute at the aft of the vessel. Cable laying through a moonpool, however, is possible up to 2 meters significant wave height. The limiting factor for all simulations that were done is the maximum allowable curvature. To investigate the competitiveness of the newly designed cable lay concept, an economic analysis is done. Several recently acquired project cases are introduced to compare project costs for both concepts. This analysis concludes that the newly designed cable lay concept is in average conditions 21 to 40% more expensive for all cases than the conventional way of cable laying. For cable installation during wintertime, the newly designed cable lay system is only 6.5 to 27% more expensive than the conventional cable lay system. This illustrates that the newly designed cable lay system is technically feasible but not competitive with conventional methods at the moment according to this analysis. However, the costs and installation time of joints with the conventional methods are not taken into account here due to limited available data. Therefore, the new cable lay concept still has the potential to be competitive for the selected market. Further research must be done to substantiate this.

For the development of Arctic offshore structures, design ice loads are required. These design loads represent the ice loads a structure may be exposed to for specified requirements. The design ice loads depend on magnitude of the ice loads and on the probability of exposure to the ice loads. Both are impacted by local sea ice conditions. Climate change affects the sea ice conditions causing change in the ice loads Arctic offshore structures are expected to experience. To obtain accurate design loads, the effect of climate change should be considered in defining those. Conventional methods to determine design ice loads are based on historical data and assume this data can be used to represent the loads during the lifetime of the structure. However, historical data cannot represent future ice conditions if climate change is considered as sea ice conditions will change. This means that the effect of climate change is not incorporated in the design ice loads when these are based on conventional methods. To include the effect of climate change a new method needs to be developed. In this thesis, such a new method is proposed that enables to include the effect of climate change into the design ice loads. Instead of historical data, the new method considers the future ice conditions. The method allows to base the design ice loads on sea ice conditions that change over time. To determine design ice loads, extremal distributions are used. Extremal distributions describe the probability of seasonal maximum ice loads. Commonly, the extremal distribution is based on data covering multiple seasons and cannot properly include inter-seasonal change in sea ice conditions. The new method allows to determine the design ice loads based upon changing extremal distributions. The extremal distributions are determined for seasons separately based on sea ice conditions of one season only. For the proposed method, a concept referred to as an 'ice state' is introduced. Ice states describe a period of time in which the sea ice conditions are assumed to be constant. When sea ice conditions are constant, the corresponding short-term ice load distributions and the ice load frequency can be determined. Both are required to be able to determine the extremal distribution for one season. According to the new method, the increase of drift speeds causes increase of design ice loads whereas the decrease of ice concentration, thickness and compressive strength causes decrease of the design ice loads. Based upon expected future climate change scenarios, the new method indicates that design ice loads are lower when compared to the design ice loads according to the conventional method.

Deep sea minerals can offer an additional resource to meet the increasing mineral demands, instigated by population growth and technological advancements. Deep sea minerals exist in different forms at the bottom of the ocean. In this research, polymetallic or manganese nodules are the kind that are of interest. The nodules are 1 to 12 cm large and contain a variety of minerals like copper, nickel and cobalt, but owe their name to its main component manganese. The region with the highest approximated resource of polymetallic nodules is the Clarion-Clipperton Zone (CCZ), situated in the Pacific Ocean between Hawaii and Mexico. The CCZ has water depth reaching 6000 meters, which is a significantly larger working depth than state-of-the-art deep sea projects within the offshore industry. These depths are accompanied by challenging environmental conditions exerted on the deep sea mining system. A deep sea mining system typically consists out of three components: 1) Production Support Vessel (PSV), 2) Vertical Transport System (VTS) and 3) Seafloor Production Tool (SPT). The SPT harvests the nodules from the seabed, the VTS transports the mined nodules through the water column to the surface where they are transferred to the PSV. The focus in this thesis will be on the Vertical Transport System. Where most deep-sea mining developments are considering hydraulic vertical transport with a riser, Boskalis introduces a concept that utilizes mechanical lifting for the vertical transport. This allows for energy efficient transport, relative simplicity of concept and a maximization of the amount of power units above water. The objective of this thesis is captured in the following research question: What is the behaviour of the combined mining system (ropes, skip and SPT) during vertical transportation by means of mechanical lifting? To answer this question, a wide overview is given of the deep-sea minerals that exist on the seafloor and the existing technologies to harvest them. Whilst the system is in principle relatively simple (just two containers (skips) that are alternatingly filled, hoisted to the surface, emptied and lowered again) many challenges arise. To identify these challenges, the system and the production cycle are discussed in detail. Literature research has been done to ensure realistic modelling of characteristics like structural damping of the rope, drag forces and added mass. The safe working load of steel wires is mostly consumed by its self-weight at a length of 4000 meters, making them unsuitable for deep-sea mining. Instead, the less common but naturally buoyant synthetic fibre rope is envisioned. Many of the challenges in this deep-sea mining system originate from the environment as the system is subject to wave action and currents. Therefore, the current profile and wave spectrum typical for the Clarion-Clipperton Zone are obtained to serve as input for further investigation in the hydrodynamic analysis software Orcaflex. The system will be deployed over the entire 6000 m water column, causing the current but also the forward velocity of the system to possibly lead to high drag forces. A reduction of the forward velocity by introducing a new harvesting method is implemented, resulting in a large reduction of the drag forces and offset. The system consists of at least eight ropes, with two moving skips. Combined with the current and vessel motion, rope entanglement is a risk. A solution to prevent the rope entanglement is presented in this thesis. Possible occurrence of vortex-induced-vibrations (VIV) is identified and future research is recommended. The offset analysis shows that a large offset (500m) between the PSV and SPT results in relatively low horizontal forces on the harvester. The system is connected to the PSV, which is subjected to the Pierson-Moskowitz wave spectrum environment it is situated in, resulting in vessel motions. These motions will govern the dynamic behaviour of the system. The skips with attached fibre ropes have different eigenfrequencies on different water depths, as a longer rope will make for a softer system. This causes both skips, full and empty, to resonate in some regions. Consequently, the dynamic tension in the ropes is higher than the static tension, although it does not come forward as problematic. However, undesired slack rope conditions can occur when lowering the empty skip. To conclude, an analysis of the deep-sea mining system has been done in which the eventual design has been modelled to the best extent currently possible. This research underlines the technical feasibility of this deep-sea mining concept. This research also evaluates the questions that have not been answered yet and recommends a variety of interesting topics for future research.

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.

Part of the innovative character of Jumbo Maritime is a constant search into a more efficient operation of their heavy lift transport vessels. Areas of improvement involve optimizing port time. Currently Jumbo Maritime requires the onboard cranes to open the hold, decreasing effective use of the cranes. Furthermore an expensive load shifting system is needed when a piece of cargo heavier than 900 tonnes has to be loaded on front of aft of the ship, due to crane limitations. In this report a study is done into an integrated solution for both issues experienced by Jumbo Maritime. A system that is able to open the hold and to shift a load to front and aft of the vessel. First, specifications of the new system are defined, after which a literature study is done exploring the options currently available in the industry. After that, multiple concepts are generated, after which an integrated system is selected using a comparison method between concepts. The concept selected consists of a load shifting system using the hatches. Opening of the hold is accomplished by rolling the hatches to the aft where a stacking system is located. First the concept is dimensioned and further designed. The new design incorporates a new seafastening design of the hatches, one of the major challenges encountered in the assignment. The new design is evaluated in structural sense using the finite element analysis program ANSYS to prove its feasibility. After structural feasibility is proven, the design is tested to its functional requirements and implications on operations for Jumbo Maritime are considered. The new system could reduce the minimum opening time of the hold by a factor two and could save around half a million euros on skidding rental costs yearly. As the system is autonomous, the risks involved for humans decrease significantly, beneficial for Jumbo Maritime’s goal of zero Lost Time Injuries. Furthermore the impact on the stability of the vessel is minimal, so there is no impact on cargo loading operations. An economic analysis is conducted to see if it is attractive for Jumbo Maritime to convert the current system onboard of the J1800-class vessels. Considering conversion rates of €4/kg for the structural conversion costs, a total conversion time of 33 days, it is proven that it is beneficial for Jumbo Maritime to convert the current vessels, with an overall value investment ratio of 1.04 and the payback time being 5.3 years. Overall is concluded that a new integrated system for load shifting and hold opening is attractive to further investigate for Jumbo Maritime, both for their current vessels as well as new build vessels.

Throughout the offshore industry large structures installed on the seabed use mudmats as a foundation to provide in sufficient bearing capacity and stability. Due to their size, the mudmats have a significant influence on the hydrodynamic behaviour and installation requirements. It is proposed to change the design of the mudmats from a near solid design to a perforated structure in order to reduce the total loads. When describing the hydrodynamic behaviour of a structure in a body of water, two terms are of importance: the added mass and added damping. For solid flat plates there is much data available to compute the coefficients for models. However the coefficients are influenced by the degree of perforation and the presence of boundaries. Since there is little information available where the presence of a boundary is combined with a perforated structure, it is proposed to conduct experiments to elaborate on the hydrodynamic behaviour of a perforated structure close to an impermeable boundary. A total of six scale models were constructed with a perforation ranging from 0 up to 75%, these models were oscillated in the water with different amplitudes, from 10 mm up to 160 mm. These oscillations were performed at different frequencies, from 0.2 Hz to 2 Hz. These tests were performed in still water and subjected to a uniform current of 5 mm/s and a current of 20 mm/s. All data obtained with these experiments was collected and analysed. The first conclusion drawn from the analysis of the experimental data is that both the added mass as the damping decrease with an increasing perforation. The added damping is found to be larger for high excitation frequencies, however the difference decreases for increasing perforation ratios. The added mass is smaller for high frequencies, but this relative difference does not decrease for larger perforation ratios. Where the damping is not significantly affected by the presence of a current, it is observed that the added mass decreases when a current is present and this effect is larger for lower perforation. The added damping shows linear behaviour when plotted against the amplitude of oscillation, except for experiments where the smallest amplitudes are tested in combination with a low excitation frequency. For the latter experiments a more quadratic behaviour of the damping is observed. The majority of the energy is found at the excitation frequency. For the added damping it is noticed that similar trends are distinguished for the first order and third order, the energy at three times the excitation frequency. At two times the excitation frequency there is only little energy found for the added damping. For the added mass there is no significant trend observed when comparing the first, second and third order energy at the load signal against the perforation. It is however found that there is a similar trend in the dependency of the added mass on the excitation frequency in both the second and third order, although the energy is decreasing for higher orders.

Offshore wind energy has very recently begun expanding into subarctic regions with seasonally ice-infested waters like the Baltic Sea. For offshore wind turbines with conventional support structures such as monopiles and jackets that are typically flexible and vertically sided, the phenomenon known as ice-induced vibrations can develop. In response to the growing interest in offshore wind in the Baltic Sea and in further validating a state-of-the-art numerical model for ice-structure interaction, the Ice-induced Vibrations of Offshore Structures (IVOS) project has been coordinated with the Hamburg Ship Model Basin (HSVA) and many academic and industry partners—including TU Delft and NTNU—in order to enhance understanding of the topic via a comprehensive laboratory testing campaign. In this thesis, specific data are selected fromthe extensive IVOS Phase 2 tests such that a comparative analysis is performed between two different model-scale structures, one with circular cross-section and another with rectangular cross-section, that were subjected to ice-induced vibrations in the frequency lock-in regime. Preceding the comparative analysis, the data from the IVOS Phase 2 tests are organized into a database and post-processing tools are developed to facilitate further research by supplying analysis-ready data sets. Included in the post-processing tools is an attempt to determine ice-induced global loads from uncalibrated tactile sensor data, which offers insight into the relationship between the relative pressure distributions along the ice-structure interface and the ice-induced global forces on the model structure. The comparative analysis garnered qualitative information about the frequency lock-in regime and buckling failure of ice. It is observed that frequency lock-in vibrations usually persisted regardless of buckling events. For the frequency lock-in regime, the ice-induced global loads on the circular cross-section structure are generally lower than those for the rectangular cross-section structure. It is unclear whether the difference in global loads between the structures is caused by the difference in cross-sectional shape, other structural properties, ice properties, or combinations thereof. The analysis of the energy of the system is intriguing but does not offer lucid conclusions. However, the quasi-figure-eight pattern from the x-direction and derived y-direction structural displacements is an enlightening discovery that may explain inconsistencies in the energy of the system. Based on the general configuration of the test apparatus from the IVOS Phase 2 tests and the results from the comparative analysis, it can be concluded that ice-induced vibrations of the model-scale structures in the frequency lock-in regime should be regarded as a two-dimensional problem.

The offshore wind industry has been extended over the last years in areas of active seismicity, such as East Asia, where the design of offshore wind turbines becomes significantly challenging, because albeit aerodynamic and hydrodynamic loads mainly act on the offshore structures, earthquake could emerge as a potentially enormous threat. The demand for reliable and economical design of offshore wind turbine foundations has driven the research for analysis of the structural behaviour under the combined action of loads and the study of the parameters that could influence it. The present master thesis deals with the dynamic analysis of the response of an offshore wind turbine monopile, one of the most common types of foundations, subjected to the application of hydrodynamic and earthquake loads. This study focuses on the understanding of the dynamic properties contributing to the dissipation of energy experienced by the structure. More specifically, the sources of damping leading to reduction of the structural vibration in time are investigated, of which the numerical determination is considerably uncertain, while emphasizing on the hydrodynamic and the soil damping. A numerical approach for the estimation of the hydrodynamic viscous damping is presented based on the calculation of the drag coefficient CD and its dependency on the Reynolds number (Re), the Keulegan-Carpenter number (KC) and the surface roughness (k/D). The drag coefficient, and accordingly the hydrodynamic viscous damping, are derived over the length of the monopile where the waves act, highlighting also the consequences of the changes in diameter and depth. Furthermore, the soil radiation damping due to the seismic waves is studied by including the interaction of the soil with the structure. Particularly, the supporting soil is modelled around the monopile with frequency-dependent springs and dampers to represent the soil stiffness and damping, respectively. The estimation of the soil coefficients is accomplished by integrating in the model of the structure, an advanced soil model developed by Dr. J. De Oliveira Barbosa, which gives the dynamic impedance function for the desired band of frequencies. The analysis of the structural response is executed by examining three load cases for the hydrodynamic and earthquake loads. The overall outcome reveals that a noticeable amount of energy is dissipated because of the presence of the soil radiation damping, drawing also the conclusion that the soil-structure interaction should be considered as frequency-dependent during earthquake. Despite the fact that the approach for the estimation of the hydrodynamic viscous damping constitutes a more precise method, its participation in the specific tested cases is limited to the total amount of damping.

A stinger is a steel space frame structure, used on pipe-lay vessels, to support the weight of a suspended pipeline. A stinger is highly fatigue loaded due to environmental loads, vessel motions and variable pipe loads. In the design phase, predictions for the structural behaviour of the stinger were made. However, inspection history showed discrepancies between the design phase and reality. A stinger monitoring system was proposed to provide a solution for this problem. The goal of the thesis was formulated as follows: Design of an optimised sensor placement method for a stinger monitoring system to localise and quantify damage. A method based on the vibration characteristics of a stinger model was chosen for damage localisation and quantification. This method correlates the measured modal property changes with analytical modal property changes to identify damaged members and to estimate the damage extent in these members. A sequential sensor placement method was applied to determine the sensor locations contributing most to the modes of vibration of the stinger model. The proposed method can accurately localise damage for damage situations with one damaged member. For damage situations with multiple damaged members, the method is able to correctly identify one of the damaged members. To identify the other damaged members, a modification of the method was proposed. On the condition of a damage threshold, this modified method is able to localise multiple damaged members in a selected number of damage situations. The damage quantification method was able to give a good estimate of the damage extent.

As climate change seems to become more and more of a serious issue, a sudden surge of interest in clean and renewable energy sources is inevitable. Ocean Thermal Energy Conversion (OTEC), or the process of harnessing energy from the temperature difference between the warm upper ocean layer and the cold bottom ocean layer, is one of these renewable energy production methods. In order to pump up this cold water, a large diameter pipe of a length in the order of 1000 m is deployed. A pipe of such large properties will indubitably suffer from problems related to production, installation and drag forces. Up till now these problems have all largely been evaluated. One phenomenon that has been explored less frequently is VIV in OTEC, and this is therefore the main scope of this research. Vortex-induced vibrations (VIV) are the vibrations that occur when a current flows past a cylinder, shedding vortices at higher Reynolds numbers, leading to an asymmetrical pressure distribution. For this research, the pipe is modelled as a slender Euler-Bernoulli beam conveying fluid, with gravity and ambient flow considered. The model is discretised and rewritten into state-space representation, in order to make it suitable for Python’s odeint ordinary differential equation-solver. A wake oscillator model is introduced to model the VIV phenomenon, and the complete model is used to evaluate multiple scenarios to evaluate the influence of variables as pipe diameter, ballast mass and current velocity. A typical cold water pipe is made of a light material as for example HDPE, has a length in the order of 1000 m and a diameter of around 2.5 m, kept under tension by a ballast mass in the order of magnitude of 350 tonnes. For this research, this typical cold water pipe is taken as a starting point and subjected to a uniform current flow of 0.4 m/s. The VIV response of the pipe is then evaluated with a range of different variables. First, the pipe is evaluated in steel, FRP and HDPE to establish which material is most suitable. HDPE shows the best fatigue resistance, and is therefore chosen as the material in which the further research will be conducted. The pipe diameter is varied between 2.0 and 6.0 m, the diameter to wall thickness ratio between 12 and 26, the effect of the magnitude of the ballast mass is evaluated and the inflow velocity is changed between 1.0 and 6.0 m/s. Finally, the current flow is varied between a uniform current of 0.1 m/s and 0.8 m/s and a location specific sheared current profile is applied, in order to check whether VIV in the OTEC cold water pipe might occur in a realistic setting. Depending on the chosen variables, in general the pipe will experience a maximum cross-flow displacement per diameter ranging between 0.6 and 1.0. Furthermore, for each set of variables the pipe will vibrate in a different normal mode, which might lead to the fact that a pipe with less maximum displacement will still experience more fatigue damage. Pipes in larger diameters will definitely suffer from a higher fatigue, however the maximum experienced damage per year was in the order of 10-15, meaning that this is insignificant. The wall thickness will not have a lot of effect. The ballast mass however, can better be chosen high since it prevents vibrations at a high mode and it seems that HDPE is strong enough in terms of yield strength to survive a large mass. Finally, when the pipe is subdued to high currents, it seems as if in-line displacement will become a larger problem then VIV, as the in-line bending reaches dangerously high levels when subjected to a current of 0.8 m/s. It has to be noted however that certain measures can be taken against this displacement. It is very likely that VIV occurs in a cold water pipe of an OTEC plant as it is subjected to certain current flows, but in the case HDPE is used, this does not seem a large concern.

With a rapidly growing population and subsequent technological developments, an increase in demand of rare-earth metals evolves. Land-based deposits seem to be insufficient and shortage impends within the coming decades. Mineral resources from the deep ocean are considered as a possible complement. These minerals occur in various forms. One of these forms is lying on the subsea sediment of the deep ocean; polymetallic nodules. The nodules can be best described as potato shaped objects containing amounts of rare earth minerals like copper, nickel and cobalt. The economic feasibility depends on nodule abundance per square meter. An exploitation region with high prospectiveness in terms of economic feasibility is the Clarion-Clipperton Zone, a region in the centre of the Pacific Ocean. As deep-sea mining implies, the mining site is located at a water depth of approximately 4000m. Characteristics such as these automatically result into challenging conditions. Exploitation of the nodules includes subsea harvesting and vertical transportation towards the sea surface. Activities which are within the scope of Boskalis, appealing their know-how and experience in dredging and marine operations. Currently, most developments are focused on vertical transport by means of hydraulic lifting through a riser. In order to avoid challenges such as flow assurance, riser handling and efficiency, Boskalis proposes an alternative solution; mechanical lifting. Mechanical lifting can be considered as a newcomer in the relative early field of deep-sea mining. However, experience can be gathered from successive deep-sea lowering operations in the oil and gas industry. The objective of this thesis is to investigate the static configuration and dynamic response of the proposed mining system during operation, identify potential showstoppers and in the end asses whether deep-sea mining by mechanical lifting is technical feasible. When simplified, it is merely a matter of collection of nodules in transportation skips and hoisting of these skips towards the sea surface. Nevertheless, within this simple procedure various challenges arise. Therefore a start is made with a proper description of the proposed production method and identification of potential hazards and showstoppers. In complementing the initial research, the project site has been studied in terms of sea floor characteristics and metocean data. These obtained results served as input in further analysis. For example a sheared current is present, influencing the geometry of the hoisting wires. The sheared current phenomenom has been studied in which a quasi-static analysis is performed. The analysis has been carried out by discretization of the hoisting wires in a number of elements with a payload attached at the tip acting as a sinker. Here it became clear that for the applied hoisting setup, the influence of the local current is minimal and the influence of a forward vessel motion significant. When acting in an offshore environment, the vessel motions might affect the deep-sea mining operation as a result of the connection with the nodule collector. Preliminary to a dynamic analysis, typical vessel motions are determined. This is done by selection of an appropriate mining vessel and implementation of a characteristic sea state using a Pierson-Moskowitz spectrum. Vessel motions are calculated with the software package Seaway, resulting in an output in the frequency domain. The suspended hoisting wires are still numerically modelled by a discretization method. Axial analysis for the applied hoisting setup shows significant magnification of the response of the attached payload at full depth (4000m). This hurdle should be overcome by applying heave compensation, which has become a commonplace in this type of marine operations. Transversal motions for the applied setup are expected to be minimal as a result of the submerged state. Conclusively, within this research first insight in technical feasibility is gained, but as a matter of fact yield further valuable questions along the lines of deep-sea technology. Therefore, we can conclude that deep-sea mining by means of mechanical lifting is feasible, but still offers numerous interesting topics in future research exceeding the current standards.

For the offshore market an increase in renewable projects can be observed. The technological innovations are continuously decreasing the costs of renewable projects. Especially offshore wind is getting more cost effective, and is receiving a lot of attention. However, with the growth of the sector, new challenges arise. Water depths are increasing, soil parameters worsening and greater distances from shore need to be overcome. Whereas prices of installation are under pressure. This drives the market towards larger and more innovative installation vessels. A trend can be observed towards monohull craning vessels which combine a large crane with a large storage space on deck. During lifting the monohull vessel experiences large motions of the lifting configuration at even small wave loading. The large motions are mainly the result of resonance within the system, which results in large crane forces. It is these forces which decreases the vessels work-ability. Applying damping to the system is a way to counter the resonance. The tugger winches can be used to apply damping to the lifting configuration. The aim of the thesis is to investigate the potential damping effect of a tugger damping system for the Bokalift 1 during a jacket lifting operation. With special emphasis on the effect of different control systems of the tugger winches. Two different models are used in the thesis to research the effects of tugger damping on the dynamic behavior of the lifting configuration. Namely, a 2D matlab model, and a more extensive 3D Orcaflex model. The Orcaflex model is build for researching the effects of tugger damping and different control systems. Comparing the responses of the model to airy waves loading. To have control in both longitudinal and transverse direction boom winches on the crane are used, in combination with deck winches. Which are located on both ends of the deck. The hydro static properties of the model are calculated with the program GHs. The hydro dynamic properties are calculated with the help of AQWA. The matlab model is used to enable quick research on the effects of tugger damping and different control systems. The model is based on a 5 degree of freedom (DOF) mass-spring-damper-system. The equations of motion (EOM) are derived using the lagrange formalism with help of the program Maplesoft. The model is validated with help of proven software Orcaflex. Seven different control systems are made and tested in the matlab model. The control systems are examined in two different simulations. Firstly the roll motion is studied when the model is subjected to wave loading. Secondly the damping capabilities for the lifting configuration with initial displacement are tested. The first analysis shows the PID controller has the highest roll motion reduction of the jacket. Linear control system scores higher than quadratic. The results from the second analysis shows that stepwise controller takes the shortest to fully damp the lifting configuration. Following on the results of the 2D model analysis the 3D model will further inspect the effect of tugger winches for the linear, quadratic, and PID controller. A model analysis shows there are 4 important modes within the wave excitation range. The combination of these modes results in the highest crane forces at a wave period of 5.5s. The linear and quadratic control system are once again compared, only now in the 3d model. The assessment shows the linear model as more efficient in reducing the crane tip forces. Lastly the linear and PID control systems are compared towards each other and a model without tugger damping. Based on the results, the linear control system increases the total forces on the crane. Where as the PID reduces all forces. It is shown that tugger damping does not necessarily decrease forces acting on the crane tip for head on waves. From the tested control system the PID controller reduces the forces most effectively and efficiently. However the effect of the PID controller depends on the loading wave frequency and for which it is tuned.

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.

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.

The port authority of the Port of Talcahuano has the desire to expand the port. The goal of the expansion is to increase the berth space and attract more vessels, thus increasing their throughput. This report is an advise to the port authority on the possibilities of expanding. Four preliminary port designs aremadewith the requirement of the ability to berth two 180mvessels. AMulti-Criteria Analysis has been used to determine the most suitable scenario. The detailed design for this scenario is composed of a quay design, a dredging plan, an earthquake and tsunami impact analysis, market prospect analysis and a financial analysis. A technical design for port expansion, as well as a market strategy has been advised to the port authority.

The Arctic presents a great opportunity for two major industries. First, since the region is expected to contain a significant amount of hydrocarbon reserves, it is very attractive for the oil and gas industry. Second, the receding extent of sea ice is making the region more accessible for shipping and, therefore, an opportunity is emerging for the shipping industry. In order to exploit both economic opportunities in a safe and sustainable manner, a thorough understanding of the interaction between ice and floating structures is needed. The most common method for studying ice-floater interaction (IFI) is via numerical modeling, which the fluid is a major component of. As fluid-ice interaction is challenging to model, a wide range of simplified and sophisticated models are employed to meet the challenge. A literature study was performed on the usage of fluid models employed in IFI and it was found that they can be divided into four categories: hydrostatic models, models based on potential flow, models based on Reynolds-averaged Navier–Stokes or a similarly advanced method, and effective fluid models. The hydrostatic models are by far the most prevalent despite only accounting for buoyancy. Most IFI models that account for hydrodynamics make use of potential theory. These models account for fluid flow and surface waves, which together alter the dynamic behavior of floating ice, resulting in hydroelastic effects. The surface-wave-based coupling between ice and floater has not been studied before and there are still open questions regarding the effects of hydroelasticity on the bending failure of ice. The advanced fluid models are a recent trend in IFI and, consequently, most of those are still under development. These models are very promising and may be the future of IFI modeling. Finally, the effective models avoid the practical issues associated with hydrodynamic models in terms of development and calculation time by capturing hydrodynamics in an effective manner, employing, for instance, added mass and damping coefficients. While several studies investigated the efficacy of these models, currently no satisfactory effective fluid model exists. The main goal of this thesis is to further the understanding of how hydrodynamics affects the interaction between ice and a sloping structure and to assess whether it is possible to create an effective model that can replicate the observed effects. The full scope encompasses three smaller studies. First, the surface-wave-based coupling between an elastic ice sheet and nearby floater structure is investigated. This interaction has not been studied before and the solution method that is developed for this problem is also used in the subsequent two studies. Second, a thorough study of the effects of hydrodynamics on the interaction between a sloping structure and level ice is accomplished. This study resulted in the identification of the parameter range wherein hydrostatic models are valid, which is essential given that they constitute the majority of all models. In addition, this study improved the understanding of the effects of hydrodynamics by means of investigating the importance of various components such as the rotational inertia of the ice, axial compression, and the nonlinear hydrodynamic pressure. Furthermore, the relation was analyzed between the temporal development of the contact force and the velocity dependence of the breaking length. Lastly, based on the findings of the second study, an attempt was made to develop an effective fluid model for ice-slope interaction. The efficacy of this model was studied in this thesis for a range of parameters. The main findings of the three studies are summarized next. In the first part of this thesis, the interaction is investigated between an ice floe and a floater through surface waves. This problem is considered first as the Green's functions that are derived for this problem are required for the subsequent studies on ice-slope interaction. The floater is modeled in-plane as a thin rigid body that floats on the surface of a fluid layer of finite depth. On one side of the floater, an ice floe is present which is modeled as a semi-infinite Kirchhoff-Love plate. The floater is excited by external loads and the resulting motions generate waves. Those waves hitting the ice edge are partly transmitted into the ice floe and partly reflected back towards the floater. The reflected waves exert pressure on the floater, altering its response. The resulting motions of the floater were analyzed, revealing several interesting facts. The study showed that below a certain onset frequency, the waves are almost fully transmitted into the ice floe and, consequently, the response of the floater is unaffected by the presence of the ice. The susceptibility of a floater to the waves reflected by a nearby ice floe can thus be estimated by checking how much of its open water response occurs above or below the onset frequency. The onset frequency is sensitive to changes of the ice thickness and insensitive to changes of the Young's modulus and water depth. Above the onset frequency, the waves reflected by the ice have a pronounced effect on the response of the floater. In certain frequency ranges, quasi-standing waves occur within the gap between ice floe and floater. Within these frequency ranges, the response of the floater is significantly altered. Depending on the phasing between the reflected waves and the floater's motions, resonance or anti-resonance can occur which can greatly amplify or reduce the floater's motions when compared to the case when no ice is present. Even when there is no gap between ice and floater, the amplitude of the floater can still be amplified and its natural frequency somewhat increased. The second study of this thesis focuses on the effect of hydrodynamics on the bending failure of an elastic ice floe due to the interaction with a downward-sloping floater, i.e. the effects of hydrodynamics on ice-slope interaction (ISI). A novel, semi-analytical in-plane ISI model is proposed that is based on potential theory in conjunction with the nonlinear Bernoulli equation to describe the fluid pressure. The ice is modeled as a semi-infinite Kirchhoff-Love plate. The predictions of the hydrodynamic model are compared with those of a hydrostatic ISI model, thereby obtaining a quantitative measure of the effect of hydrodynamics on ISI. The comparison revealed several interesting facts. First, the importance of several components of the model was investigated to determine which ones are essential for ISI. It was found that the contribution of the rotational inertia of the ice, axial compression and the nonlinear hydrodynamic pressure is insignificant. Being able to ignore the last two components greatly simplifies the modeling of ISI as it removes all sources of spatial nonlinearity. The terms that were found to be essential for ISI, listed in the order of importance, are: bending of the ice floe, linear hydrodynamic pressure, hydrostatic pressure and the inertia of the ice floe. The contribution of the fluid's inertia is on average four to ten times bigger than that of the inertia of the ice. The study also demonstrated that the effect of wave radiation on ISI is minimal. Second, the relation between the temporal development of the contact force and the velocity-dependence of the breaking length was studied. The study showed that the breaking length has two regimes which are separated by a transition velocity. When the ice velocity is below the transition velocity, the ice fails during the initial impact. Alternatively, when the ice velocity is above the transition velocity, the ice floe survives the impact and fails with a breaking length that is close to the static breaking length. The transition velocity of the hydrodynamic model is much lower than the transition velocity of the hydrostatic model, 0.0725 m/s compared to 0.275 m/s. This major difference in transition velocity is the primary reason for the limited applicability of the hydrostatic model. The results show that the hydrostatic model should not be used when the ice velocity is higher than 0.6 times the transition velocity of the hydrodynamic model as its predictions will deviate significantly, with errors ranging from 30% to 100%. This upper bound corresponds to values between 0.02 m/s and 0.1 m/s for the parameters considered. Lastly, this study underlined the stochastic nature of the breaking length of the ice floe. When the floe fails, a relatively large segment of the floe is, in fact, close to failure. A defect in the ice can locally amplify the stresses, causing the ice to fail at the defect rather than at the location predicted by a homogeneous model. This can cause the breaking length to vary by 10% to 30%. The last part of this thesis builds on the knowledge gained in part two by attempting to create a simple effective fluid model (EFM) that captures the effects of hydrodynamics on ISI as observed in part two. Based on the observations, an EFM is proposed that uses frequency-independent added mass and damping coefficients. This EFM was added to the hydrostatic model, thereby obtaining an ISI model that contains all four essential components of the ISI model. The resulting effective ISI model is very simple and, consequently, its implementation is trivial compared to a true hydrodynamic model such as the one proposed in part two. Its simplicity should help to improve the adoption of hydrodynamics in ISI. The performance of the effective ISI model is assessed. Investigated are the velocity-dependent breaking length, the maximum contact force that occurred during the interaction, and the contact force as a function of time. The predictions of the effective model are far more accurate than those of the hydrostatic model. The coefficients of the EFM were found to be relatively insensitive to changes in the parameters, allowing the effective model to be used for a fairly broad range of parameters. @en

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.