In offshore construction, there is a demand for vessels with ample deck space. Large catamarans could provide larger deck space for the same tonnage. However, one operational concern for catamarans is wet deck slamming. Wave impact with the wet deck can excite the global flexible vibration modes of the vessel. While extensively studied for high-speed catamarans, the dynamic response induced by slamming in large, slow-moving, heavy-lift catamarans remains poorly understood.

This thesis presents a fast numerical method for predicting the dynamic response of a heavy-lift catamaran subjected to wet deck slamming in head seas. The method combines Capytaine, a BEM potential flow solver, with ANSYS Mechanical, a finite element software package. ANSYS calculates the dry modal properties, and Capytaine includes the water effects to obtain the wet modal properties. Capytaine also finds the rigid body motions resulting from wave loading. A simplified slamming pressure formulation based on immersion velocity and wetted length is applied. Both monochromatic and bichromatic wave conditions are investigated to assess their influence on the immersion behaviour.

It was found that monochromatic waves produce immersion of long duration. The proposed method cannot accurately determine forces and responses due to the varying properties during a slamming event. Additionally, the limited impulse can not effectively excite the eigenmodes due to the long wetting time compared to the natural periods. In contrast, bichromatic wave conditions lead to shorter and more severe immersion events. For the bichromatic wave loading, the modal dynamic oscillatory response was found as a result of wet deck immersion.

To assess the accuracy of the proposed numerical method, a validation against experimental measurements is performed. The comparison focused on accelerations resulting from slamming events and the intervals between such events. The resulting accelerations of the proposed numerical method slightly underestimated the measured accelerations. One problematic finding was that significant slamming events could disrupt the vessel's oscillatory motions and that resolving the disruption cannot be achieved in the frequency domain. The proposed numerical method can be used to identify conditions where slamming can be problematic quickly. However, to obtain accurate displacements, accelerations, and stresses, further analysis by another method is required.

The thesis provided insight into the dynamic behaviour of a heavy-lift catamaran induced by slamming. An indication of slamming effects can be calculated in the early design stages. More importantly, identifying problematic wave loading cases can be done at a relatively low numerical cost. The exact magnitude of the slamming effects requires a more detailed time-domain analysis.

The offshore wind market is expanding rapidly due to the growing demand for offshore wind energy. This drives the development of larger, more advanced wind turbines and increases the diameter of monopiles. Transporting these massive monopiles presents challenges, particularly in ensuring secure seafastening. Traditional seafastening systems rely on mechanical support to prevent motion, such as saddles for the transverse direction and lashing wires for the longitudinal direction. With the increasing weight of monopiles, these solutions are becoming increasingly impractical, heavy and costly.

During monopile transportation, waves cause the vessel to move and deflect, with the saddles moving accordingly. The monopile, which has separate stiffness properties, experiences different deflections and displacements. Due to these different deflections and displacements, the vertical forces exerted by the monopile on the individual saddles are not distributed equally. In the least favourable conditions, this can result in loss of contact, also called intermittent contact. Longitudinal vessel accelerations generate forces in the monopile’s longitudinal direction, where friction between the monopile and saddles opposes these forces. However, as friction depends on the contact pressure, any reduction of the vertical force, and so the contact force, affects the friction force.

Seafastening arrangements are designed according to DNV-ST-N001 Marine Operations and Marine Warranty standards. Seafastening requirements are based on seafastening design loads calculated for each shipment and cargo item. DNV-ST-N001 set a minimum seafastening capacity based on cargo weight, not considering friction. The latest update (December 2023) allows cargo transport without seafastening if the friction capacity is at least twice the seafastening design loads. Otherwise, seafastening capacity defaults to a weight-based function, creating a gap between the minimum seafastening capacity and calculated seafastening design loads.

Roll Group’s current seafastening designs do not incorporate friction to prevent longitudinal motion, leading to conservative seafastening systems with high equipment- and installation costs. Therefore, there is growing interest within Roll Group in whether accounting for friction between the monopile and the saddles could reduce the required seafastening arrangement, potentially leading to more efficient and cost-effective designs. This knowledge gap leads to the following research question:

”How does friction between a monopile and its saddles affect the seafastening arrangement of a monopile?”

This research aims to determine the friction resistance between the monopile and the saddles when the vessel is exposed to waves, including cases with intermittent contact of the saddles. Based on this information, the seafastening arrangement can be defined when friction is included in the seafastening calculations.

For this research, a coupled fluid-ship model from another research is revised and used to calculate the forces between the saddles and the monopile. This calculation is based on the vertical displacements of the vessel and monopile for all wave heights that can occur during monopile transport. As a result, the loss-of-contact cases were defined. Since this coupled fluid-ship model only focuses on the vertical displacements of the monopile, a longitudinal monopile model is developed. The longitudinal monopile model focuses on the relative horizontal displacement of the monopile caused by heave and pitch motions. This model is a mass-spring system where the monopile represents the mass, behaving as a rigid body to prevent axial vibrations.

An in-depth analysis of the longitudinal monopile model is done for a case excluding friction and a case including friction. The analysis of the longitudinal displacement of the monopile with lashing wires, but without considering friction, resulted in a seafastening arrangement consisting of sixteen lashing wires to prevent all longitudinal motions of the monopile for all wave heights. When friction is considered, the analysis shows that the total friction capacity remains sufficient for all wave heights to prevent the longitudinal motion of the monopile without applying lashing wires.

In this research case, the total friction capacity of the saddles is at least twice the design loads during the whole wave cycle for all wave heights. Based on this, DNV can agree that meeting only the minimum seafastening capacity requirements is acceptable. The last step of executing a friction-based seafastened monopile transport is getting permission from the marine warranty surveyor and the captain.

This thesis investigates a floating truss structure’s local and global response to breaking waves slamming loads. The case study of interest is the supporting structure of SolarDuck’s (SD) platform FPV. Their design consists of different triangular modules, with the solar panels at a safe height from wave impacts. In future designs, the truss supporting structure underneath them, made of non-circular aluminum braces, may be exposed to slamming events.

The literature research concluded that the current state-of-the-art lacks methods to estimate local and global load on truss structures accurately, and the most relevant physical aspects to correctly represent such phenomena are uncertain. Among them, hydroelasticity, in particular, may play a role. Consequently, the research is structured into three parts, and, in each of them, two cross-sections are considered for the structure, SD’s one and an equivalent circular hollow tube (HT) one.

In the first one, the local analysis on individual braces is performed and four methods are applied to compare the relevance of different assumptions. The structure is expected to show a hydroelastic response at the local level according to the Bereznitsky criterion. Faltinsen’s method takes hydroelasticity takes into account, and provides lower values for the response, being the best method to calculate the actual deformation of the structure. Nevertheless, good estimations of the deflections were offered also by the General Wagner Method and Modified Logvinovich Method for the asymmetric loading, assuming the brace as rigid.

These two methods are included in the global analysis: one triangular module is modeled in ANSYS, and a transient analysis is performed. The structure shows mainly a local behavior, and the non-circular cross-section geometry shows double values for the deformation. The local analysis can be used to approximate the global one, even though additional proof is needed.

A CFD simulation is performed to verify the analytical models through COMFlow, and the MLM applied to the symmetric load case offers the closest response to the numerical calculations. From this analysis, the local slamming coefficient is also derived to be equal to 4.78 for the circular cross-section and 10.38 for the square one.

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This research investigates the influence of material properties in additively manufactured, fully elastic models produced with 3D printing, with a focus on mitigating these effects in the design process. The study emphasizes the orthotropic and frequency-dependent behavior of 3D-printed PETG material and the impact of an epoxy coating required for waterproofing.

Experimental testing was conducted using thin-walled specimens printed in three principal directions. Designed to capture torsional and bending responses, the specimens underwent shaker tests in weighted and unweighted configurations. While the weighted setup extended the measurable frequency range, it introduced inconsistencies in eigenfrequencies, leading to reliance on unweighted shear test data for further analysis despite associated errors.

These material properties informed a numerical model divided into orthotropic and laminated sections, with laminate theory applied to transverse structures and orthotropic properties assigned to longitudinal walls. The effect of an epoxy layer and water interaction was incorporated through boundary element analysis, generating hydrodynamic stiffness and added mass matrices.

The results highlight the dominant influence of the transverse Young’s modulus, 𝐸1 , on eigenfrequencies, particularly in bulkheads and plating, while 𝐸3​ primarily affected higher modes. The epoxy coating increased eigenfrequencies by 2.6%, while frequency dependence contributed minimally to variations. To minimize epoxy influence, thinner coatings or alternative waterproofing methods are recommended. Addressing orthotropic behavior may require refined printing settings for isotropic properties or scaling strategies prioritizing
𝐸1​ .

These findings provide valuable insights for designing 3D-printed elastic models with improved dynamic response and reduced material property effects.

The demand for clean energy has led to potential cost-effective solutions for the offshore industry. One of these solutions is shared mooring systems, where floating offshore structures for renewable energy are coupled to each other. While this approach saves mooring lines and anchors, it introduces new dynamic loading compared to conventional mooring systems. This study focuses on the feasibility of using a shared mooring system to combine floating offshore wind and floating solar support structures in different configurations in a farm layout.

This research uses the Volturn US-S platform to model the floating wind turbines and recreates the Tractebel Seavolt concept for the modelling of the floating solar arrays. Six configurations are simulated, undergoing irregular waves under various wave headings, load cases, and line materials. The configurations involve two wind turbines with one or more solar arrays in between them. A Quasi-dynamic model is used to identify critical cases. These cases are re-evaluated using OrcaFlex. The assessment of these configurations is done based on two Key Performance Indicators, related to line tensions and the floating support structures' displacements. During the process, polyester lines are chosen due to their favourable characteristics.

The four configurations that met the Key Performance Indicators are compared to a base case of a single turbine regarding its displacements and anchored line tensions. Effective utilisation of the shared lines and limited displacements lead to a preference for the configuration with three solar arrays. Additionally, the anchored line tensions of the turbine in this configuration increase the least compared to other configurations.

In summary, using a shared mooring system to combine both floating offshore wind structures and floating solar structures in a farm layout is feasible. Further research should be done on other configurations and the impact of these mooring systems on the Levelized Cost Of Energy. Additionally, wind and current loading should be incorporated in future studies.

Floating Offshore Wind Turbines (FOWTs) have emerged as a promising technology for generating clean energy in deep water locations. Bluewater Energy Services proposes a Tension Leg Platform (TLP) as the floating support structure. An effective Structural Health Monitoring (SHM) system (of which there are various types) can facilitate timely interventions and optimize inspection and maintenance activities by providing continuous insights into their structural condition. Fatigue damage is especially critical for the support structures of FOWTs, as they are subject to cyclic loads that can cause structural damage.

This research proposes a fatigue monitoring system for a TLP supporting FOWTs. The methodology used is Modal Decomposition and Expansion (MDE). Due to the complexity of the studied structure in terms of structural dynamics, MDE is selected for its ability to capture dynamic behaviour. The main objective of the fatigue monitoring system is to perform the full-field strain estimation based on a limited number of sensors. This could also allow for the verification of the design considerations. With the presented response reconstruction approach, the stress in the locations prone to fatigue of the platform can be monitored and therefore, enabling estimation of the remaining lifetime of the structure and optimize maintenance planning.

Different analytical and numerical models are used in this investigation. The application of MDE in a simple structure (i.e. a cantilever beam) is first assessed to verify the performance and to gain insights of the methodology. Later, MDE is applied to a simplified TLP model to validate the response reconstruction approach and demonstrate its applicability for TLP-like structures.

Finally, a FOWT numerical model is used to design the fatigue monitoring system. The proposed system consists of two layouts of two strain gauges in the upper column of the TLP, and two layouts of two strain gauges on each pontoon. This system can provide full-field strain estimations with over 88.9% accuracy and predict fatigue damage accumulation with errors of less than 0.01%. Also, the system presented in this thesis only predicts global responses. However, the fatigue of the structure is also influenced by local structural responses due to sea pressures. Therefore, future research to include local effects in the predictions is recommended.

The success of offshore wind farm installations is often related to the costs and time taken to be completed. Current installation strategies require several critical offshore lifts for the completion of a single wind turbine, as in most cases each component gets installed separately. This is time-consuming and has a direct link to the cost of the operation. Therefore trying to find more efficient methods of offshore wind turbine installation should be one of the main focuses in the industry. A possible solution to the problem involves the single-lift wind turbine installation. For this method, the whole wind turbine is pre-assembled and lifted onto the offshore foundation with one lift. This way the number of critical lifts offshore is reduced, which has the potential to reduce overall installation time and cost. The downside of this method is that, for the lifting of a whole wind turbine, very calm environmental conditions are required, leading to low workability. Calm environmental conditions do not often occur at offshore wind farm locations, and hence, solutions to improving the workability of this particular method are required to make it competitive with current installation methods.

The solution proposed in this thesis is to utilise the Upper Stabiliser Frame (USF), a Heerema Marine Contractors concept, which helps to eliminate unwanted motions of the wind turbine while in the air. The frame gets mounted at a height on the tower above the combined centre of gravity of the whole wind turbine. Since this frame is only a concept, its exact effect on the installation has not yet been studied in detail, and the actual design of the frame has not yet been fully developed. Therefore, the aim of this thesis was to analyse the loads experienced by the whole system (floating vessel and wind turbine) during such an installation and to investigate how the USF frame could be designed to constrain the relative rotation between the tower and the USF.

To reach the objective of the thesis, various analyses were conducted in LiftDyn, an in-house Heerema software, and OrcaFlex, where the whole system, or parts of the system, were investigated. A modal analysis and frequency domain analysis were done in LiftDyn while time domain analyses of different environmental loads were performed in OrcaFlex. The response of the system was examined, and based on the results, the maximum yaw moment acting on the tower under limiting environmental conditions was determined.

The results of the investigation showed that the WTG motions are limiting for safe operation and lead to very low acceptable environmental conditions compared to other installation methods. Based on these conditions, the maximum tower yaw-moment recorded was 2100 kNm. This moment was transformed into a tangential force acting on the tower, which the frame had to counteract. Two possible designs of the USF, both utilising friction, were created. The first design consisted of friction pads spaced around the circumference of the tower, while the second used a band brake to deliver the necessary friction. A multi-criteria analysis with weighted factors was conducted to evaluate which design performed better. Based on this analysis, the band brake design showed better performance, making it the most suitable design for the USF.

The novel concept of the single lift installation strategy with the USF is still not ready to be used yet for real projects and will require further development to become competitive with currently used strategies. This thesis has formed the basis for further research in the field by identifying key problems that must be resolved and suggesting innovative solutions for the USF design. This installation strategy has the potential to revolutionise wind turbine installation by decreasing installation time, increasing operational efficiency, and in general, streamlining the whole process.

In this thesis, the friction performance of polyurethane tensioner pads used in offshore pipe-laying was investigated. Tensioner pads are used in pipe-lay to create tension in a pipe. The need to understand the pads better is because of the increased use of pipe coatings and pipe lay in deeper waters. Deep water leads to more pipe tension, and polymeric coating reduces friction.

A literature review was conducted on the friction of polyurethane. From the literature review, a few variables that influence polyurethane friction behaviour were summarised into the following research question: What is the influence of normal force on the pads, pad hardness, pad geometry, and pad temperature on the friction performance of polyurethane tensioner pads?

Experiments were performed at a full-scale setup. Polyurethane has a nonlinear coefficient of friction, making it difficult to upscale results from laboratory testing. In the full-scale setup, existing pads can be tested to find the influence of the different variables from the research question. The test setup was found to be flawed. Not only did it deform due to the massive forces, but the data gathered from the hydraulic pressures was not robust and accurate enough to estimate the static coefficient of friction, which is important in tensioners. Therefore, only trends in the pad behaviour were observed.

Increased normal force on the pads was found to increase the coefficient of friction. This contradicted the literature but was likely due to the geometry of flat pads versus round pipes, where the contact surface increased when the pads were loaded. Softer pads were found to yield higher friction than pads made from harder grades of polyurethane. This effect was also found in the literature. The influence of temperature was difficult to test. Since the pads could only be heated externally before testing, temperatures were inconsistent, and test results were inaccurate. The temperature did affect the friction significantly, though, so some newly produced pads were fitted with internal heating.

Next to the experiments, different pad geometries were tested in finite element analysis. A new pad shape was found that decreased stresses, leading to higher friction.

Next to the variables of the polyurethane itself, the relative humidity was recorded. The relative humidity changed significantly during the different tests, and it was found to affect friction more than anticipated.

Three sets of new pads were produced for future testing to validate the influence of geometry and further investigate the influence of the pad temperature. Moreover, a new test setup was designed to test the coefficient of friction more accurately.

Huisman has introduced the Windfarm Installation Vessel as a complete solution to assemble and install offshore wind turbines at sea.
Installing a floating wind turbine at sea brings two main challenges, the relative motions between the floating structures and the load transfer of the wind turbine.
The proposed installation procedure considers a connection between the installation vessel and a semi-submersible floating support structure to reduce the relative motions and facilitate the load transfer.
This research investigates how the connection's structural configuration affects the system's relative motions and loads during five defined installation stages.
The different installation stages cover varying amounts of ballast transfer, as well as the mating phase of the wind turbine.
A two-dimensional multi-body model has been formulated considering a rigid link between the installation vessel and the floating support structure.
The hydrodynamics of the floating structures and the regular wave loads on the structures are calculated using Ansys AQWA.
A system analysis is performed to investigate the effect of adding stiffness in one or combined directions of motion of the connection.
The change in dynamic effects during the installation stages are minimal, the ballast transfer mainly changes the static load on the connection.
Overall, it can be concluded that a combination of stiffness in the different connection directions will provide the most favourable results.
To limit the relative heave motions, coupled surge or pitch and heave stiffness is required.
A different stiffness on both sides of the connection is also shown to improve the system’s behaviour.
Fixing the rotation of the connection on one side improves the relative pitch motions between the wind turbine and the support structure.
More research is required to investigate favourable combinations of limiting motions on each side of the connection.
The presented model could be used for a future optimization study to find optimal stiffness values for the connection.

An important trend exhibited by the offshore wind market is the increase in the size of wind turbines, leading to longer and stiffer monopiles with larger diameter-to-thickness ratios. Current transport analysis is focused on loads resulting from hydrodynamic accelerations, without taking loads into account resulting from differences in bending deflection between the vessel and cargo. This thesis covers a study carried out on the structural response of a monopile and sea-fastening system subjected to displacement-based loads. The loadcase follows from a vessel excited using a regular wave leading to bending deflections and rigid body accelerations. The saddles used to support the monopile are modeled as unilateral springs, emphasizing the need to use a non-linear solution method to obtain structural responses. The harmonic nature of hydrodynamic-based loads led to the selection of the harmonic balance method (HBM) used as solution method in the structural model. A novel understanding how cargo properties, seafastening properties and seafastening arrangements influence the structural response of the coupled cargo-seafastening system. Various parametric studies are performed to identify behaviors related to the total structural response. Based on this study, the conclusion can be drawn that a large number of saddles in combination with a low stiffness is desired to minimize the structural response of the cargo and sea-fastening system. Furthermore, the influence of lashing stiffness and pretension is limited with respect to the total response. At last, a parametric analysis on the properties of the cargo showed that certain sea-fastening arrangements can be identified which comply with design criteria.

Catamarans are popular in the offshore sector as they combine good transverse stability and ample deck space with low wave resistance. However, their slender hull shape results in low restoring qualities in heave and pitch motions. The large motions in rough weather can often result in water impacting the underside of the deck connecting the two hulls, a phenomenon called cross-deck slamming. The impulse excitation from cross-deck slamming can then produce a transient hydroelastic response of the structure called whipping. Whipping excites mode shapes that would not normally be present in the response, as their natural frequencies are significantly higher than the wave encounter frequency. This results in detrimental contributions to fatigue life through high-amplitude cyclical bending moments. Both the calculation of slamming loads and the prediction of resulting structural responses have been a challenge for several decades. The highly nonlinear and three-dimensional character of the phenomenon, combined with the strongly coupled fluid-structure interaction means that it is unpredictable, and even the definition of slamming events has been a matter of disagreement among researchers.\\

Experiments are still a vital part of these investigations, for validating ever-improving numerical techniques. An essential issue with experiments is the extent to which mode shapes and natural frequencies can be emulated in model scale. Traditional hydroelastic models are segmented and use either a flexible backbone or flexible joints to introduce stiffness. This often results in an excellent description of the 2-node bending mode, but an increasing error for higher modes leads to stress inaccuracies. In this investigation, a fully elastic model of a catamaran is designed and produced for hydroelastic experiments. The advantages and limitations of the concept are identified, and the verification against structural models is presented.

The energy transition requires us to explore all options for generating non-fossil energy. Companies are starting to invest in technologies such as offshore floating PV systems (OFPV) to avoid congested urban population centres. OFPV structures are likely to consist of many small, simple, flexibly connected floaters. The entire structure must be able to survive extreme offshore conditions. The OFPV response in various sea states is heavily influenced by the connector design.
In this thesis, a 3D boundary element based numerical model is used which was developed by Tuitman [2]. The model is expanded to output the forces and moments experienced by the compliant connectors which have linear stiffness in 6 degrees of freedom. After successful verification and validation, three case studies are presented which are a three floater serially connected model and a 3x3 and 4x4 grid connected model. Various sea states and wave headings are analysed to show the effect on dynamic behaviour of a compliant connector. The time domain-based approach is used to capture nonlinear Froude-Krylov and hydrostatic forces. The remaining hydrodynamic terms are linearised by solving in the frequency domain. The connector response is linearised by using a finite stiffness matrix but the forces are solved in the time domain to include the effects from the nonlinear hydrostatic terms.
The results show that the resonant response of the structure and connectors is critical in determining the floater motions and loads in the connectors. Additionally, the stiffness of the connector influences the natural frequencies of the structure. The forces and moments in the connectors of the grid are much more varied than the serially connected structure because of the complex interaction of the floater hydrodynamics and connector resonance. The floater motions and connector response becomes less evenly distributed for oblique seas and when sea states match the natural frequency of the structure. The grid experiences bending in multiple directions which results in large connector loads at some locations on the structure. When expanding to a larger 4x4 grid there is a different distribution of connector loading than the 3x3 grid because of the extra degrees of freedom. The aft connectors experience lower loads than connectors facing the waves due to a shielding effect.

The increasing demand for renewable energy sources, to achieve ‘green goals’ such as the Paris agreement, and their related projects, are becoming increasingly challenging to accomplish. Nowadays, offshore wind farm projects move into deeper waters and require larger individual Offshore Wind Turbines
(OWT’s), which results in larger monopiles. As a result, heavy lift vessels shipping and installing the monopiles can transport fewer monopiles at a time, as they have outgrown the cargo hold and can only be shipped on the top deck. Considering the stiff nature of the monopile and that it spans almost the entire length of a ship nowadays, companies involved in such projects, such as Jumbo Maritime, have concerns this might heavily affect the ships dynamic behaviour. Therefore, the research presented in this thesis is focused on investigating what effects a lashed monopile on the deck of a heavy lift vessel causes and if friction contact between ship and monopile plays a role. To answer these questions the ship and monopiles are modelled as a coupled system with appropriate boundary conditions. The research is focused on finding lashing & friction contact effects, but also what effects of the number of monopiles introduces onto the system.

Reducing the levelised cost of energy is crucial to accelerating the energy transition. To develop offshore wind solutions in greater water depths, a floating solution is required. The time-domain simulations of these Floating Offshore Wind Turbines (FOWTs) under wind-wave misalignment used in research and industry projects are computationally intensive and limits researchers and industry in their developments. To better understand the sensitivities of the fatigue loads of FOWTs to different parameters and environmental conditions, a computationally efficient method is needed. The aim of this research is to develop a frequency-domain method to quantify the effects of misaligned wind and waves on the response of a semi-submersible floating offshore wind turbine. Therefore, the following research question is defined: What is the effect of misaligned wind, windsea waves, and swells on the loads at the tower base of a semi-submersible type floating offshore wind turbine?

Several sensitivity studies are conducted to quantify the contribution of yaw-roll coupling effects and aerodynamic damping to the responses and loads. From these studies, it appears that the yaw-roll coupling can increase the response when excited at wind/wave directions in which the structure is asymmetric.
The magnitude of this effect is related to the wave peak period (and the resulting wavelength), the angle of misalignment with respect to the structure, and the apparent length of the structure. Also, the lack of aerodynamic damping in the direction of the rotor plane (side-side direction) leads to a noticeable
increase in the response, directly or through coupling effects. Finally, the frequency-domain method is compared with the time-domain simulations (BHawC-OrcaFlex) carried out by Siemens Gamesa. Although reasonable agreement is found for the load driving rigid body modes, significant differences in the tower bottom loads are found for the lowest and highest production wind speeds.

These results show that misaligned wind and waves can increase the response for headings where the structure is asymmetric due to coupling effects. Wind-wave misalignment leads to an increased response in the direction of the rotor plane due to the lack of aerodynamic damping. In general, the wind-wave misalignment can also have a mitigating effect on the maximum equivalent moment at the tower base, as the aerodynamic damping also reduces the response in the wave frequency range. Furthermore, the comparison shows the need to extend the frequency-domain method with the first tower bending modes and improvement of aerodynamic/mooring property estimation. Based on the findings and the conclusions, the recommendation is to investigate the floater specific sensitivities at an early stage of the design. Future research should focus on: the implementation of tower flexibility, improvement of the quasi-static estimation of mooring stiffness, frequency dependent aerodynamic properties, and implementation of second-order wave forcing.

Marine structures are frequently equipped with rubber fender systems, which absorb the berthing en­ergy in order to protect both the marine structure and the berthing vessel. These fender systems absorb the kinetic berthing energy by elastic deflection and the associated reaction fender force introduces a berthing impact load acting on the vessel’s side hull. In guidelines and rules on ship design, recommendations regarding the structural resistance due to external fenders are not present. On the other hand, special requirements state minimal strengthening for tug resistance, which results in marked areas on a vessel’s side hull at which tug contact is allowed. Also for ships equipped with integrated steel fenders in their side hull, also known as beltings, minimal strengthening is required. Since the use of fender systems in ports is common, and all ships require to berth in a port the maximum hull loading due to fender contact is an important factor to take into account from the vessel’s perspective. PIANC WG33 published design recommendations for the maximum allowable hull pressure in kN/m2 for different types of vessels. The size of the fender contact area is in practice determined by dividing the design reaction force by the maximum allowable hull pressure. However, the hull pres­sures in this recommendation are based on the pressure on the keel of a fully laden vessel. Based on this background information, not all values are reliable, since some pressures correspond to a draft of 70 meters. Besides that, the pressure formulation does not contain information on the specific geom­etry of the contact area, i.e. height and width. This thesis systematically analyses the strength of the vessels’ parallel side hull for different failure modes, e.g. yielding in the stiffeners due to excessive bending­ or shear stresses. The structural ge­ometry of various vessel types is represented by various grillages. Two different pressure distributions were considered: a soft contact area, and a rigid contact area, to cover the most extreme behaviour of a fender panel. The results of this study show that the allowable load is largely influenced by the geometry of the contact area. The fender panels designed using the PIANC WG33 fender design are not always opti­mal. Especially for fender panels having large widths, the current guidelines seem to be too optimistic. Consequently, it is necessary to define a maximum width to what extent the current guidelines are allowable. This study shows that a specific allowable force in kN for a specific geometry is preferred over the current guidelines. In this study, a general formulation for the maximum allowable hull loading is proposed. This for­mulation requires the specific structural lay­out of the vessel that encounters the berthing facility. If the specific ship’s particulars are not known, recommendations are provided for different vessel types. These recommendations consist of a new acceptance criterion for each vessel type, which can be used to optimise the geometry of fender panels. The findings of this study can be used in the design of fender systems and the new design criterion has been submitted to the members of PIANC WG211.