At Damen’s Research and Development department, continuous improvements are made to existing design practices using recent technological developments and fatigue design is currently on the anvil. High speed craft operating around the globe are subject to millions of load cycles (resulting from ocean waves) and therefore suffer from metal fatigue. As per current practice, such vessels are designed for fatigue using inhouse software with a nominal stress approach supported by static sea-state scatter data and judgement based operational profiles.
Recently, new data sources with real time sea-state data over the whole globe have come available, including GPS locations of ships. Together, this enables it to generate real time operational profiles for its ships. A total stress concept has been developed based on results from a JIP called VOMAS. This approach has shown to provide accurate fatigue lifetime estimates for arc-welded aluminium joints. Similar results are expected for steel joints as well.
The main goal of this thesis was to explore possible improvements for the fatigue design methodology. A tool called Tanaav was developed for this purpose which makes use of both remote monitoring data and the total stress concept and provides an estimate of the yearly fatigue damage and fatigue lifetime. The tool has been used to predict the fatigue lifetime for three fatigue sensitive details in 46 FCS5009 vessels. Results have been compared to corresponding predictions using current and past fatigue analysis practices. It was observed that using both remote monitoring data as well as the total stress concept provides significant improvements in the predicted fatigue life time.
Uncertainties in fatigue influence parameters affecting the predicted fatigue damage can be incorporated using probabilistic. This thesis proposes a method for this and presents two cases as a proof of concept. Work done in this thesis will be validated by Damen in future with the help of full-scale testing on an actual FCS5009 vessel during an offshore measurement campaign. After validation, this method will help in improving fatigue design practice, increasing design flexibility and in optimizing vessel weights in a responsible way.

The offshore industry is a conservative industry, sticking to rigid best-practices and reluctant to try new techniques. A promising new technique that hasn't found much adoption in offshore industry is SPH. This thesis aims to improve the reach and use of SPH within the offshore industry. With an abundance of world's unexplored hydrocarbons located in the Arctic Region, 18\%, ice-structure interactions (ISI) are set to increase. Modeling these ISI requires complex dynamics, SPH can model these ISI dynamics without extra treatment. SPH works by interpolation of a set of neighbouring particles using a weighing function. This modeling technique offers many advantages over conventional rules-of-thumb, Finite Element Modeling (FEM), and Finite Volume (FV) methods. SPH is a particle based method, thus, uniquely suited for problems with large displacements, or discontinuities. However, in the standard, weakly-compressible (WCSPH) method spurious pressure fluctuations and particle clustering can occur. By implementing the plethora of correction methods and equations present in literature, such as kernel corrections, incompressible variants, or density corrections, these drawbacks can be circumvented and a robust framework can be formed. An implementation of WCSPH that focuses on adaptability and flexibility is presented in this work. The flexibility of the implementation allows future researchers to focus on the core of their research, only changing the equations they are interested in, instead of implementing all the required equations for a full SPH simulation. A validation study of the implementation assures that it matches closely with existing implementations and real-world results. The mathematical model developed in Keijdener (2018) is implemented in the proposed WCSPH implementation. Comparing the results shows close agreement for the breaking length. However, significant differences are present in the failure time results. Despite this it shows the possibility of combining solid mechanics with SPH, and validates the integration method, solver, and SPH model.

Nowadays, fears over rising sea levels due to global warming have prompted many countries with lands below sea level to find solutions to ensure the safety of nation and citizen. Furthermore, the development and utilization of marine resources have always been a topic of interest. Due to these necessities, the concept of flexible floating islands that can be used for fish farm, energy islands and residence has emerged. The flexible floating island consists of many smaller identical triangles connected by springs. This design is convenient for installation, disassembly, and diversification of functions. The main objective of this thesis is to investigate and analyze the forces acting on and motions of the flexible floating islands due to the interaction with regular waves; a numerical model is an excellent way to complete that mission. The floating islands in waves that are constrained with mooring lines have translational and rotational motions under the combined effect of hydrodynamic, hydrostatic, gravitational and mooring forces. The approach for solving the forces starts with linear potential theory, which means that uncompressed inviscid flow is assumed. After marking out the identical smaller panels on the wetted surfaces of each small triangle, the interface conditions between the triangle and the fluid are satisfied, thereby obtaining the source strength for each panel. With the expressions for the potentials, all the hydrodynamic coefficients including added mass, damping and wave exciting forces can be evaluated. Finally, the response of islands can be evaluated by using the equations of motions of the island in the time domain and converting them to the frequency domain. Two models are created in this thesis, a single island model and a two-island model, the former focuses on learning the methods for solving the hydromechanics coefficients, and the latter focuses on the hydrodynamic interaction between the two islands.

Offshore oil and gas projects usually require the presence of more than one facilities in the same location. These facilities need to be connected with each other in order to enable the transfer of personnel among each other. As a result, bridges are implemented for such purposes with their ends being positioned at extensions of the two connected platforms, known as the bridge landings.
Such a bridge should be able to follow the excitations that are imposed at its two ends from the response of the connected platforms due to the applied environmental loads. Thus, in its longitudinal direction, the bridge should be pinned-supported at one platform and sliding-supported at the other. Such a configuration enables the bridge to adapt to the continuously varying relative movement that is induced by the motion of the two connected platforms. This results in the generation of friction at the sliding end of the bridge.
Similarly to any other offshore structure, a bridge landing should be able to withstand the maximum operating loads and its configuration should be checked against the different limit states. Although a jacket substructure is commonly analysed against the serviceability, ultimate and fatigue limit states, a bridge landing is checked against only the first two states. However, the generated friction at the sliding bridge supports results in varying stresses at the corresponding bridge landing. This indicates that the fatigue limit state should also be examined and thus investigation is required in order to highlight its significance in the design of such a structure.
This is the motivation behind the certain thesis, which intends to clarify the sensitivity of a bridge landing into the varying dynamic load of the generated friction. In order to do so, a specific case is examined, with real information about the structure and the environmental details. The analysis comprises examining three limit states (SLS, ULS, FLS), concluding into the governing one for the case of the bridge landing. The structural analyses were performed using the SACS software, which enables performing all the SLS and ULS checks. Regarding fatigue, though, the whole analysis was conducted independently, using a simplified approach that enables to deal with the issue in a quick way. This comprises the base case approach, through which assumptions are made regarding the wave and friction main characteristics.
After verifying the significance of the fatigue limit state in the design, an assessment of the base case approach follows. This is performed through the examination of the main sensitivity parameters that influence the simplified approach through which the fatigue assessment was conducted. The results of the sensitivity analyses are then incorporated in order to review the method and conclude into any possible improvements.
Finally, enhancement of the structure is examined through four different ways, aiming to turn it to be sufficient against the fatigue requirements. The improvement actions consist of improving the existing weld details, modifying the existing structure and reinforcing of members.
It should be noted that the problem was also approached through a numerical approach that was generated using the Matlab software. Through this, it was intended to capture the behaviour of friction in a more realistic way before incorporating it in the fatigue assessment, something that was not possible to be done inside SACS. However, the model didn’t show rational results and thus it could not be used in the fatigue analysis. The whole procedure and theory, though, are described in detail since it is possible that they can set a useful background for further investigation.

The goal of this research is to optimize the fiber layup of a carbon windsurfing boom for weight and stiffness. A windsurfing boom should be stiff to provide an efficient basis for the energy transfer from the sail through the surfer to the board. The weight of the boom is important as the total weight of the rig influences the performance, especially during movements where the swing weight of the rig is important. To optimize the fiber layup the FEM simulation software of SolidWorks is used. This software allows the user to divide the part in sections and specify the layup per section in terms of orientation, thickness, and material. The output of the FEM simulation is the mass and the displacement under different load cases. The load cases are based on an experiment where the loads during sailing are determined with load cells and strain gauges.
The FEM simulation is validated and scaled based on two experimentally determined force-displacement relations. The FEM is scaled with the force-displacement relation of the first loading point by scaling the given material parameters by 0.78. The FEM is then validated with the force-displacement relation of the second loading point. New fiber layups are generated based on stress direction, previous iterations, and engineering intuition. The 50 new generated layups and their respective mass and displacement results are evaluated with a performance equation to determine which layup has the highest performance for the combination of mass and displacement. The coefficients in the performance equation are chosen so that both parameters have equal weight. The chosen layup is further evaluated with a required fiber overlap section. Two booms with the new layup are evaluated with the same experiment that is used to validate and scale the original FEM. At the first loading point, where the main loading during sailing is applied, the new layup is 16 percent stiffer than the original layup, as predicted by the FEM. The experiment results for the second loading point showed that the new layup was 5.5-7.5 percent stiffer than the original layup instead of the predicted 13 percent. This difference is due to the straight tubes that are glued to the end of the optimized boom body which are made by a different manufacturer. Changing the stiffness of these pipes makes the FEM results converge to the experimentally determined values. The experiment results of both layups are evaluated with the performance equation as the stiffness has increased but the mass has increased from 2.19 to 2.25 kg as well. The performance equation showed that the new layup outperforms the original layup for both loading points. The project goal to optimize the layup for mass and stiffness is therefore achieved. For the layup of the boom, a sandwiched layup of unidirectional fibers with biaxial fibers at the in- and outside of the circular cross-section was determined as the best performing layup for the sections loaded under bending. For sections that are loaded under both torsion and bending additional layers of biaxial fibers are added at the inside of the circular cross-section. These biaxial fibers are added at the inside as the unidirectional fibers are used at the outside to create the largest moment of inertia for these fibers as the displacement due to bending is leading in this case. Even the small translation of fibers from the inside to the outside of the layup can make a significant difference.

The demand for blade installation and maintenance is increasing with each additional installed offshore wind turbine. In 2017, 560 additional turbines were installed in Europe, reaching 4149 turbines in total. Currently, they are serviced with cost and time inefficient methods, such as rope access and jack-up vessels. Rope access is slow and requires the deployment of expensive technicians in dangerous environments. Jack-up vessels are overqualified, expensive and not readily available. Identifying the short comings of these methods, TWD saw an opportunity to design a dedicated tool for blade installation. This resulted in the floating Blade Installation Tool (BIT). The BIT is a state-of-the-art solution that allows for blade installation from a floating platform. By incorporating motion compensation and decoupling it can mitigate the vessel motions, thereby reducing the relative motion of the top element of the BIT. After the BIT is connected to the tower, a blade handling kart can safely transport and install the blades to and from the nacelle. The goal of this thesis is to gain insight in the dynamic behaviour of the system, with the focus on the interaction between the turbine and the BIT. For this purpose, a numerical model is created for the governing plane of motions, the vertical plane on the longitudinal axis of the vessel. Using this model, several simulations are performed under a variety of conditions to assess the BIT for the following sub-questions: Are the interface forces on the tower acceptable in conditions comparable to the operational limits of jack-up vessels? What is the relation between the vessel-tower distance and the interface forces? How much does the significant wave height affect the forces and stresses on the tower? The results show that the BIT’s motion compensation system will effectivelymitigate the first order wave force induced motions of the vessel. However, it also shows that at multiple stages of the lifting process the BIT will exert a force exceeding the allowable force limits. To satisfy the constraints imposed by the tower manufacturers, adaptations to the design of the BIT must be made. Some of the possible solutions to be explored are as follows: The increase in contact surface area between the BIT and tower. The stresses, which is the limiting factor, are reduced allowing for higher interface forces. Applying additional mechanical systems, such as winches and hydraulic cylinders, to add an additional layer of control to the system. TThis is expected to be a necessary option, although it will increase the complexity
of the tool.

Allseas' Pioneering Spirit is the largest heavy lift vessel in the world. It uses its u-shaped bow to sail around an offshore platform and lift topsides up to 48.000t in a single lift. Despite being the largest vessel in the world, platforms exist that are simply too heavy, or too large to fit in between the bows of the vessel. Besides, smaller platforms also offer challenges as the capacity of the lifting beams decreases when the beams are extended towards the platform. This results in a set of platforms that cannot be lifted by the vessel.
To be able to lift this set of platforms, a novel lifting method is proposed based on the twin-barge float-over method, where two separate vessels lift a topsides in a tandem lift. The method offers a solution to the described challenges as the vessels can be moved closer to the platform, resulting in an optimal utilisation of the lifting beam capacity. To improve the hydrodynamic behaviour of the concept, mechanical connections between the barges are incorporated. Allseas is interested in the technical feasibility of this concept in the North Sea. As an effect, the goal of the thesis is to evaluate and improve the hydrodynamic behaviour of mechanically coupled barges. The aim is to assess the motions of the concept using a dynamical model, improve the concept by changing the dimensions and investigate the workability of the concept in the North Sea.
Throughout the decommissioning operation three limits are considered: the impact velocity between the lifting beam and the topsides, the relative pitch between the vessels (leading to stresses in the topsides), and the axial forces in the connection beams. The modelling of the concept is split up in two parts: the determination of the hydrodynamic properties of the vessels, and the influence of the connection beam forces. The potential solver ANSYS Aqwa is used to assess the hydrodynamic parameters, after which a Matlab model is created to include the connections in the model. Since preliminary results showed a standing wave effect between the two vessels for certain frequencies, an additional roll damping of 10\% of the critical damping was added and an external damping lid was included.
A sensitivity study is performed to investigate the influence of reconfiguring the dimensions and the gap between the barges on the motions. For a certain width over gap ratio, motions tend to resonate for an incoming JONSWAP wave with a peak period of Tp = 7s. When the peak period is increased to 9s this effect becomes invisible and the hydrodynamic behaviour improves with increase of the dimensions. Therefore these are increased (L=275, B=70, T=25m and gap=50m) to assess the workability of the concept in the North Sea. The linear Matlab model is translated from frequency- to time-domain to make a probability distribution of the critical limits. The critical incoming wave angle is 120°, where a significant wave height of 1.3m with a peak period of Tp = 9s results in an infeasible design due to excessive relative pitch. For other incoming wave angles the workability improves, with the most favourable incoming wave angle being 180°. For the Brent field location in the North Sea, the summer period workability varies between 61% and 88% depending on the incoming wave angle and the orientation of the platform. This is sufficient enough to speak of a technically feasible concept.

Subsea pipelines that are used for the transportation of oil or gas are installed by pipe-laying vessels. When a pipeline is laid to the seabed, both ends of the pipeline are sealed with an end-piece. This end-piece fulfills an important role when the pipeline is being commissioned. In order to be accepted, the pipeline has to undergo Flooding, Gauging and Testing. For the hydro-test, water is pumped into the pipeline from the supply vessel through a flexible hose. The connection between the flexible hose and the end-piece is made with a so-called hot stab. To align and to connect male and female sections of the hot stab, a Remotely Operated Vehicle is used. This alignment, and stabbing process is proven to be challenging and sometimes resulting in damaged equipment and project delays. This thesis comprises a conceptual design and motion analysis for an improved concept of the subsea hot stab operation specifically developed for large diameter flexible hoses and heavy stabs.

The approach for this thesis starts with a research to find out limitations of the current equipment used. As a result, it has been concluded that a high stiffness of the flexible hose is the main cause of time consuming alignment and related problems, experienced by the Remotely Operated Vehicle operator. Various concepts have been generated, combined and rated using a Multi Criteria Analysis. The solution that scored the highest rank has been analyzed in order to predict the dynamic behavior of the whole system. System parameters have been optimized to reduce the undesired motions and to minimize forces that are required for alignment of a stab by the Remotely Operated Vehicle.

Combining the obtained knowledge from the research, the concept study and the analytical model, the following is concluded: it is beneficial to use a vertical orientation of the hot stab, instead of a commonly used horizontal orientation, in combination with buoyancy modules to support the flexible hose in an ‘S’ shape orientation as it reduces the loads during a subsea hot stab operation. This solution is adaptable for large range of water depths and does not exceed the maximum load capacity for the manipulators of the Remotely Operated Vehicle thereby preventing damaged equipment and project delays.

Allseas Group S.A. is a leading offshore contractor in the field of pipeline installation, heavy lifting and subsea construction. One of Allseas’ vessels is Pioneering Spirit. The main activities of Pioneering Spirit can be subdivided into pipeline installation, topside installation/removal and jacket installation/removal. The equipment of the first two activities has been successfully put into operation. The equipment to install and remove jackets (Jacket Lift System (JLS)) is currently under development. The mechanism to upend/tilt-over the Jacket Lift System is the subject of this graduation project.

The design challenge of Pioneering Spirit’s Jacket Lift System is to install or remove a jacket with a height of at least 70 meters and a mass of up to 20 000 mt (in air) in a single lift/operation. In this thesis project, an additional design solution has been investigated and developed. The objective was to investigate the feasibility and favourability of various principles and concepts to upend/tilt-over a jacket using Pioneering Spirit. Key topics in the development of the design solution were the controllability of the operation, the compatibility of the system in the current appearance of Pioneering Spirit’s, the complexity of the operation and the investments costs to construct, operate and maintain the system.

The design solution found in this graduation project consists of a tilting system that rotates over the stern of Pioneering Spirit. The system is driven by a pushing system installed on the reinforced transverse frames on the aftdeck of Pioneering Spirit. The system must be movable to relocate the centre of gravity before upending or after tilting-over of the system. The system is controlled by two winch systems, one attached to the tip of the tilting lift beams (Derrick Hoist system, consisting of 10 winches) and the other to the upper pivot point of the pushing system (Upend/Tilt-over Mechanism, consisting of 8 winches). The system can be controlled in both rotational directions using the two winch systems. The tilting lift beams and pushing system are connected by means of a roller/slider connection.

The maximum forces, stability and controllability of the system were checked with a coarse dynamic mathematical model. The natural frequency of the system with and without jacket appeared to be in the same frequency range as the excitation response spectra. This was solved by stiffening the system by increasing the effective diameter of the winch systems and by applying pre-tension. Subsequently, the system appeared to be possibly instable during the first/last 18 degrees of the tilting operation. This was solved by applying an auxiliary construction during the first/last 30 degrees of the tilting process. The maximum response amplitude of the system was calculated by means of a calculation of the maximum excitation in the frequency domain (regular waves) and for time series (irregular waves) for the positions in which the Jacket Lift System can be positioned and all incoming wave directions. The maximum response amplitude of the system occurs in beam waves when the system is positioned vertically. Although the maximum response amplitude of the system is small, mainly because of the stiffness, the maximum forces in the system are exorbitantly large. To give an indication, the maximum tension in the Derrick Hoist System is 4125 mt. At a certain moment in the tilting procedure, the entire mass of the Jacket Lift System (15 000 mt) and Jacket (20 000 mt) is applied to the pivot points at the stern of Pioneering Spirit. In general, the static forces deliver the greatest contribution to the total force. The maximum loads are considered feasible, although strengthening measures must be taken.

With the conversion of a heavy transport vessel into a crane vessel, Boskalis aims to strengthen its position in the offshore wind and decommissioning markets. The BOKALIFT 1, as the crane vessel will be named, is equipped with a 3,000 tonne crane and a class-2 Dynamic Positioning system. In order to utilise its exceptional large and strong deck area to its full extend, the crane is installed amidships at the starboard side of the vessel. Offshore lifts are consequently performed in transverse direction of the vessel, resulting in a large heeling moment during the lift operation. As the conversion is currently ongoing no operational experience has been gained yet. This thesis is therefore an assessment on the behaviour of this new asset and the crane loads during a lifting operation close to the maximum crane capacity. This is the case for a single-lift decommissioning operation, lifting a topside from a jacket support structure.

Two transient phenomena can occur throughout the decommissioning operation: snap loads and impact loads. Both phenomena cause large peaks in the crane loads. Snap loads occur in the rigging lines during the pre-tensioning. During this phase the rigging lines become taut and the motions of the crane hook are constrained. Impact loads can occur during the final lift phase of the topside. This phase is estimated to last several minutes and is driven by the capacity of the dedicated anti-heeling system. Its purpose is to compensate the large heeling moments. Since this operation will last multiple wave periods, the wave induced motion at the crane tip causes tension variations in the hoisting system. When this tension exceeds the required lift tension the topside is temporary lifted, with impact loads as a result.

An OrcaFlex model is built to perform time domain simulations of the pre-tensioning and lift phases of the decommissioning operation for several irregular sea states. For both phases, a crane load comparison is conducted for two different lifting schemes. In the first scheme the hoisting speed is dictated by the anti-heeling system in order to maintain even-keel conditions. This is favourable for the operation limits. For the second scheme this is disregarded and the maximum hoist speed is applied. The latter is expected to reduce the duration where impact loads are present.

In the pre-tensioning phase, the higher hoisting speed results in a larger amplitude of the load variation since the snap loads are dictated by the relative velocity of the crane hook. During the lift phase, the higher hoisting speed reduces the time during which impact loads occur and thereby also reduces the crane loads. However, the topside motions are significantly increased. The crane tip- and topside motions have shown to be the limiting criteria for the lift operation. Limiting the topside motions by bumpers, guides or extra tugger lines can increase the workability for sea states where the peak period is close to the vessels natural heave and pitch period. Conclusively this thesis shows that the BOKALIFT 1 is a very well-suited vessel for offshore decommissioning operations.

In the last couple of decades, Arctic Engineering has become a topic of interest. There are still plenty rooms of research to understand the unique characteristic of sea ice, especially in relation to offshore engineering. This includes the most fundamental problem in floating body motion analysis: the radiation-diffraction problem. A powerful mathematical concept, - so called Greens Function – is one of the favourable tools to be used for solving this mathematical problem. This is because the radiation-diffraction problem can be formulated as a boundary value problem expressed by partial differential equations. Although the application is already quite advanced for the open water case, the same cannot be said for the vessel operating in ice infested waters. The integral solution of 3D Greens Function for ice-infested waters which has not been studied before, was derived in this thesis. The open water case is also studied to gain more insight in the implementation of an arbitrary floating body thoroughly. As a closure, interpretation about the difference between open and ice-infested waters is discussed.

For Greens Function in the open water case, numerical evaluation of the principal value integral is not straightforward due to the hyperbolic term inside the integrand. This term makes the integrand exceed the limit of floating point number (in MATLAB) and cannot be evaluated into infinity. On the other hand, a numerical integration is quite time consuming (whereas the analytical solution, as far as the writer’s concern, is not found yet). A well-known alternative form of the solution which formulated as an infinite series might improve the computation speed. The rate of convergence depends solely on the ratio of horizontal distance between source and field point (R) and water depth (H). Another numerical issue arises in the deep water case. A finite water depth causes a catastrophic cancellation, both for the integral and the infinite series solution, due to the extremely small difference of the wave number between deep water and infinite water depth. This is where the infinite depth solution needs to be used.

In numerical implementation, an influence function at a panel can be approximated by multiplying the potential with panel's surface area. Due to the singularity of the Rankine source term in the integral or the modified Bessel function in the series, this approach fails and the solution need to be integrated over the panel. Although the analytical solution is available, a numerical approach is chosen to simplify the problem. The surface integration procedure can be done by transforming the global arbitrary panel orientation into the local element coordinate system, and subsequently, perform a bilinear mapping to reshape the quadrilateral panel into the desired rectangular panel. This transformation procedure is needed since MATLAB is only capable to handle double numerical integration of a function bounded between four lines perpendicularly each other. This encloses the whole challenge that needs to be addressed and might be re-occur in the ice-infested waters as well.

From the derivation of the Greens Function for ice-infested waters, it is shown that the hyperbolic term inside the integrand is present. This discloses that the obtained solutions cannot be used instantaneously. Another effort to rewrite them in the exponential term might be useful. Moreover, the radiation condition is not satisfied yet in this thesis. However, the suggested approach of the derivation by introducing an imaginary line to represent the source depth location avoids the use of a singular term. Generally speaking, this thesis initiates a promising foundation for further research in the hydromechanics analysis of sea ice.