The rudders of moored FPSO’s are fixed in the center to avoid unwanted rudder motions. This is often done by mechanical locking of the rudder machine. Due to waves and current, the loads on the rudder are higher than expected, causing failure of the locking system. An empirical study is executed to predict the combined wave and current loads on the rudder in moored conditions.

When working offshore on a floating vessel, the vessel will be subjected to wave induced motions and with a moving crane tip, a suspended load can start to swing. When the motions of the load become too large, the operation is interrupted. Alternatives such as jack-ups, function as a fixed platform to which the crane is attached, therefore eliminating the effect of waves on the workability of the vessel. Within the offshore wind industry, jack-ups are used for installation and maintenance of wind turbines. However, due to their slow transit speed and time-consuming jacking process, an alternative is suggested with which wind turbine maintenance can be performed. In this thesis study, the mechanical feasibility of a motion compensated crane for wind turbine maintenance is assessed by comparing three different crane concepts.

The activities of humans in the marine environment are on a steady rise; this trend follows the exposure of offshore structures and vessels to harsh environmental conditions. On the other hand, there is continuous demand for lighter, faster and more efficient vessels. Technological advancement in composite materials and better design methods invariably leads to more sophisticated computational tools. In these tools, the inherent flexibility of the structure is involved in the calculation of its loading and response – introducing the aspect of fluid-structure interaction. However, more than fluid-structure interaction, hydroelasticity which is a subset of fluid-structure interaction allows for deformation of the structures due to fluid. Current industry practice neglects these deformations and all structures are designed as rigid bodies. These practices lead to overestimation of the frequency which translates to the mass and how stiff the structure is. Design based on hydroelasticity allows for knowing the true behaviour of the structure; thus, a coupling of fluid and structure yields a true appreciation of these designs. The objective of this study is to formulate and solve analytically the coupling phenomenon behind fluid-structure interaction. An experiment designed by Lampros Rizos in 2016 which modelled fluid-structure interaction consisted of a set-up with a cylinder immersed in a larger cylindrical tank. The immersed cylinder having a flexible circular membrane (structure) located at its bottom. The cylinders were filled with non-viscous liquid and exhibited free surface. The designed experiment was decoupled and a systematic build up in understanding the dynamics of all components – structure and fluid were solved. Firstly, the dynamics of the structure when dry (In vacuo) was idealized in 2-D and 3-D. Secondly, the system was coupled and solved in 2-D and 3-D when structure is located at the top and bottom of a single cylinder individually. The use of a series solution: Fourier-Cosine and Fourier-Bessel series solutions were used for 2-D and 3-D cases respectively. Along with these series solutions, the fluid governing equations were employed to solve for the coupled frequencies. Lastly, the entire submerged structure was analysed and solved. The hydroelastic or coupled frequencies and vibration patterns are determined for lower angular and radial modes for which the influences of various parameters are investigated. A trend was observed – that for lower modes, the hydroelastic frequencies are lower than individual membrane natural frequencies at low frequencies. At higher frequencies, the coupling effects are larger making the coupled frequency higher than uncoupled frequencies. There is a strong relationship between the tension of the membrane and the hydroelastic frequencies. An increase in the tension causes an increase in the hydroelastic frequencies. Also, the hydroelastic frequencies increase as the fluid depth increases. More so, the increase in fluid depth tends to converge towards the uncoupled fluid free-surface frequency. The comparison of the analytical solution with experimental and numerical solutions does not match perfectly and thus, further works to improve this study are recommended.

Large water motion inside the moonpool of vessels operating in waves can be excited by pressure fluctuations produced by external waves and vessel motion. Extreme consequences of this effect may include injuries for crew members, and damages to deck equipment resulting in downtime for the vessel. The accepted method to predict this non-linear phenomenon is a combination of model tests and potential solver. Nevertheless, model tests are generally conducted at the end of the design phase leading to serious problems if the moonpool performance is not sufficient. CFD solvers proved their capability of modelling complex flow phenomena and their use as a design tool for the moonpool is growing. However, a complete verification & validation is still missing. In the present work the water motion inside a moonpool and the forces on the hull, for a vessel in head waves without forward speed, are estimated using the MARIN software ReFRESCO. In doing so, the goal is to define the accuracy of the code for a rectangular moonpool with sharp edges without additional damping devices. For a deeper comprehension of the physics involved, a stepwise approach was followed. The work starts with an empty domain in which only regular waves were generated to assess the propagation and absorption of waves in ReFRESCO. Secondly, fixed vessel simulations were performed to study the influence of grid dimension, mesh refinement and boundary conditions. Then forced heave oscillations were simulated to estimate the damping and added mass. Verification studies were carried out for all the presented to this point. Finally, results from free-floating simulations were validated against experimental results.

Currently there are three methods of calculating the Dynamic Positioning capability of a vessel namely: static calculations, real-time time domain simulations and fast-time time domain simulations, although the outcome of the last two should be identical. In each of these methods a set of input variables is required to perform the calculations. These inputs are not always exactly known and are therefore sometimes estimated or taken from databases. It is not always clear how big the uncertainty in these estimated inputs is, and on top of that: how big the effect on the predicted DP capability is. To be able to quantify how certain a DP capability calculation is and which input data contribute most to the output uncertainty, in this thesis the input uncertainties for both static and fast-time dynamic calculations are investigated. Each method is subdivided in three different design stages which are: conceptual design, preliminary design and as built design. For the static calculations all three design stages are evaluated but for the fast-time dynamic simulations only the as built stage is considered. The static calculation part of the analysis consists of determining the input uncertainties, the input sensitivities to the output and finally calculating the output uncertainty. The method used for this calculation assumes that either the relation between input and output is linear or can be linearised at the point of interest. The input uncertainties are calculated using historical data of the Bibby Wavemaster 1 which is the vessel used as case study throughout this thesis and is specifically designed for the purpose of servicing offshore wind farms. It is observed that the input uncertainties of the main dimensions of the vessel are clearly reducing when moving through the design stages. Furthermore it is concluded that the environmental coefficients of wind, waves and current are the most uncertain, even in the conceptual design stage where input parameters of the main dimensions of the vessel vary the most. When considering the sensitivity in the three design stages no big changes were observed, meaning that in all design stages the main dimensions of the vessel are most sensitive to the output. Finally the uncertainty in the output was evaluated were it was observed that for the as built stage still a standard deviation of 4% uncertainty of the output is present, resulting in a calculated 99.7% confidence interval of either 12% too high or too low. In the dynamic calculation part only the as built stage is considered. Again the uncertain parameters are defined but due to the PID controller in the dynamic model some new input parameters are now present. The gains of this PID controller are assumed to be uncertain and are therefore taken into account during the dynamic uncertainty analysis. Due to a limitation in the aNySIM licence bought by Damen it is impossible to change the wave coefficients which causes their uncertainty not to be taken into account. Since the dynamic simulations are considered to have strong non linearities and possibly even discontinuities due to thruster saturation, the calculation method used for the static part is not applicable anymore. Therefore it is decided to use Monte Carlo simulations to quantify the uncertainty in dynamic DP calculations. Due to the large computational time required to perform large amounts of Monte Carlo simulations with aNySIM, a machine learning method is used to capture the dynamic behaviour of the vessel. A small number of simulations performed by aNySIM is required to train the model which are selected using the Sobol design of experiments technique. This technique optimises the choice of the simulation points to make sure the complete space of possible inputs is covered. By using the machine learning model to obtain an output of a dynamic simulation only a fraction of a second is required instead of 17 minutes when using aNySIM. By running the Monte Carlo simulation on the created machine learning model it was observed that the 97.7% confidence interval for offset can either be calculated up to 8.7% too low or too high whereas the prediction for heading up to 23.1% too low or too high when compared to the base case. It is concluded that using DP for the purpose of people transferring by means of a "Walk To Work" bridge, uncertainties should be taken into account to reduce both safety and contractual requirements risks.

A conventional dynamic positioning system is used to control vessel motions in the horizontal plane, i.e. surge, sway and yaw. However, the safety and operability of several offshore operations can be increased when also the roll motion is actively controlled, especially in beam seas. A control system model is proposed for combined thruster induced roll reduction and DP station keeping when the vessel is operating in beam seas. The proposed control system model is applied to a offshore construction vessel and the performance is demonstrated by time domain simulations. The DP footprint is compared to a conventional dynamic positioning control model. The proposed control model enables active roll reduction while the effect on the station keeping performance is unaffected.

Structures at sea, which can either be floating or bottom-founded, are always affected by several types of dynamic loads from wind, waves and currents; with floating offshore structures subjected to more motion and loading from these loads. Hence, necessitating more in-depth hydrodynamic analyses. Increasing size and weight of these floating structures together with industry demands have led to unsuitability of existing models – which make use of rigid body (no hydroelasticity) assumptions. This, in addition to other reservations about current practices, has led to the need for more realistic formulations of the interaction between fluids and our offshore structures, taking hydroelasticity into account. Extreme wave impacts, which are responsible for severe damage of offshore structures, have for a long period been only studied with experimental methods, as non-linear nature of the complex wave kinematics make solutions not straightforward. More recent advancements have seen the development of numerical techniques and programs, based on the Navier-Stokes equations, to better understand extreme waves and impacts on offshore structures. This thesis focuses on the topic of experimental validation of fluid-structure interaction (FSI) in ComMotion – an advancement in the ComFLOW program (an improved Volume of Fluid (iVOF) Computational Fluid Dynamics (CFD) code) to capture motion of flexible structures in the presence of free surface effects and a two-way coupling between the fluid and the structure. This has led to the need to provide reliable data for validation purposes. The research is conducted in continuation of the studies carried out by Rizos (2016) in which an electromagnetic drive linear motor produced noise and variable amplitude enforcement obtained in the analyzed results, amidst other uncertainties in the measurement techniques used. The current methodology principally makes use of a different motion technique – rotary to linear motion to obtain more reliable data. Firstly, rotary to linear motion was chosen (motivated from the internal combustion engine of an automobile) and then verified computationally with analytical derivations. The experiments were then designed, with the initial step being to verify the said linear motion. A sensitivity of the motion signal to weights in the system was carried out. Further, the experiment designed made use of a latex rubber membrane, applied with a clamped boundary condition at the bottom of a partially-filled rigid cylindrical structure. Tension existing in the membrane, due to water columns above it, was analytically obtained, as complete knowledge of system parameters was crucial. Linear oscillatory motion at the end of the converted rotary motion was applied to the fluid-structure system. Motion signals were obtained – rigid body measurements, to subtract them from the membrane motion measurements obtained. Motion measurements were acquired with laser triangulation displacement devices and a force transducer was used to monitor applied forces in the plunger during the experiments. The output of the transducer can offer validation data to the FSI solver. Membrane measurements were taken at half radius at a 30° step over a 180° span, and at the centre. This was in a bid to capture maximum deflections of the membrane, as interest was to obtain the coupled frequency mode shape. Finally, the obtained membrane motion data were analysed to prove their reliability, and to draw conclusions from them. Volume (of liquid), frequency and polar dependence analyses were carried out. Recommendations were subsequently outlined, for future research.

The Poineering Spirit is a heavy lift vessel that can lift offshore platforms in a single lift. Due to the waves, the vessel moves with respect to the platform. To make sure the vessel does not hit the platform, a motion compensation system is installed on the Pioneering Spirit. The maximum allowable vessel motions during the operation are restricted by the capacity of the motion compensation system. Comparison of the predicted motions with measurements have shown good comparison for the deep water situation. It was found that prediction of the vessel motions in shallow water does not agree with the measuredmotions. Therefore the prediction of the vessel motions in shallow water is investigated, to find out how do predicted vessel motions compare to measured motions. The goal is to quantify and reduce the uncertainty in vessel motion prediction in shallow water. First the calculation method of comparing the predictions to measurements was investigated and validated. The wave spectrum and as well as the Response Amplitude Operator (RAO) are available in 2D, The vessel response is available as a time series. To compare the predictions to measurements, both prediction andmeasurement are translated to a 1D response. For the prediction, first the 2D response is calculated, which is then added over all wave directions to get the 1D response. The measured time series of the vessel motions are translated to a 1D frequency domain response using the Fast Fourier Transform (FFT). The comparison of the 1D response spectra is done by comparing Significant Double Amplitude (SDA) and peak period Tp . Comparison of the peak period has a relatively large error, with errors exceeding 0.5 s for most of the comparison for heave, roll and pitch. Looking at the SDA, the heave motions are underestimated for most of the time for low amplitudes. As the amplitudes increase, there is a spreading of the predicted motions above and below the measured values. Taking into account the motions with at least 0.4 m measured heave, the SDA is within 10 cm from the measured motions for 25% of the measurements. For the roll,the motions were underpredicted for larger motions, being at an incoming peak wave direction between than 220 and 260 degrees. The heave motions at the location of the topside lift system are dominated by the contribution of the pitch motions. The motions in shallow water are not accurately predicted in most cases, with a deviation from the heave at the sensor location by more than 10 cm. The response deviates above and below the measured motions. A possible explanation for the overestimation is the cushioning and sticking effect due to the presence of the seabed, this needs to be further investigated. The prediction of the peak period is limited by the precision of the buoy data. In order to do a good comparison for the peak period, the precision of the wave spectrum should be increased. This can be done by fitting the measured spectrum, or by using buoy data which has a smaller frequency step.

Airborne Wind Energy (AWE) is a field of engineering that utilizes tethered aircraft for the generation of electrical power. The potential for the application of AWE in deep-water offshore environments on top of floating foundations is enormous. Where conventional wind turbines would require a very stable platform to reduce motions at the nacelle, AWE requires just enough stability to survive extreme conditions, take-off and land horizontally, and not negatively affect cross-wind performance. The requirements scale well with increasing capacity of AWE systems, which mostly influences the mooring configuration instead of the steel structure. That is why Ampyx Power started an investigative study into the floating offshore application of AWE in collaboration with Mocean Offshore, MARIN and ECN. A driving factor in the design of the floating foundations is the maximum allowed motions in different sea states. The objective of this research is to determine the relative magnitude of the effect of platform motions on the landing performance. This will result in more clearly defined design requirements for both the floating platform and the aircraft. The method used in this research can be extended to more advanced numerical models at a later stage of the design to obtain quantified motion constraints or operational limits. It is assumed that standard deviations of several parameters at the end of the landing approach serve as good indicators of successful landings. A numerical model of a tethered aircraft (RPA) making a horizontal landing in time domain is developed to determine these parameters in a multitude of wind conditions. By performing a Monte-Carlo analysis, the standard deviations of these parameters can be acquired. Especially symmetric motions (X, Z and RY) are expected to affect landing performance, which is why a 3DOF model is used. Then harmonic platform motions are included in the model in order to investigate what type of platform motions are most critical. Finally, the platform designed by Mocean Offshore is examined. By combining the motion response of this platform with metocean data at a reference location, the standard deviation of critical parameters is obtained in comparison to an onshore application. The motion response of the platform is determined using a numerical model that combines potential theory with semi-empirical drag formulations. This model is validated with basin tests at MARIN. Simulations with harmonic platform motions indicate that both frequency and amplitude of platform motions are critical for the landing performance. The landing performance appear to be mainly related to the platform motion velocities. Therefore, increasing damping and added mass of the platform will both have a positive effect on the landing of the RPA. When looking further at the results of the simulations with platform motions based on metocean data and the hydrodynamic, numerical model, it was found that the current design of the floating platform by Mocean Offshore leads to an expected decrease in landing performance compared to the onshore application. The performance decrease is not insurmountable, and multiple methods of reducing the negative effects on landing performance are presented.

In the early 00 of this century, Keuning et al. (2007) looked into the hydrodynamic forces on the rudder and the influence of the hull and keel on these forces. Among others, they have assessed the lift and drag forces on the rudder. One of the outcomes of this study was an asymmetric lift curve; for negative rudder angles the rudder seems to stall at angles more than five degrees smaller than for the positive rudder angles. The goal for this research is to find and clarify the physical phenomenon which induces the rudder to stall at smaller rudder angles when subjected to a negative rudder angle (during bearing away). The main question to be answered in this report is: What physical phenomenon is at the basis of the asymmetric stalling behaviour on the rudder of a sailing yacht? Towing tank tests are used to validate the data from Keuning et al. (2007). After which RANS CFD simulations are conducted in NUMECA to compare the towing tank tests to and to visualise the wake of the yacht in attempt to clarify the phenomena found. A number of conclusions were found in this study. Firstly, the results of the towing tank experiments showed similarities to the previous experiments by Keuning et al. (2007). Differences are found in stall angles for positive rudder angles. These differences raise questions on the correctness of either of the experiments. Secondly, no reasonable explanation is found for the negative drag forces found in the towing tank experiments. It is expected that these originate from the set-up of the rudder. Thirdly, the lift curve found in the experiments is confirmed by the CFD data for the test cases. The physical effect behind the early stall behaviour of the rudder is still unknown. It is indicated that a part of the decrease in stall angle, a couple of degrees, is caused by the influence of the keel, when the disturbance passes on the low pressure side of the rudder. The hull is responsible for the remaining decrease. The CFD data indicates an influence of the vorticity of the keel and the boundary of the hull to cause a disturbance on the rudder. Further research in necessary to clarify the results found in this study.

Two important performance parameters of a ship are fuel consumption and motions in a seaway. Besides a well-designed hull, several appendages can be used to increase the performance. One of these is a resistance reducing fixed foil behind the transom of the ship. This wing has the potential to create large lift forces near the aft of the ship, thereby changing the resistance and dynamic position of the vessel. In this thesis an algorithm is designed that controls the pitch angle and thus lift of this foil. The goal is to investigate the potential of such a dynamic foil for further reduction of (added) resistance and ship motions. The resistance reduction is investigated by creating thrust on the foil trough an oscillating foil principle (i.e. vertically moving the foil to create propulsion). The research is done with the use of the FINE/Marine CFD package. A model from the AMECRC OPV series is used for analysis, in combination with a foil optimized in earlier research. From the literature review can be concluded that a dynamic, rotating foil behind a ship will not generate thrust in the same manner as an oscillating foil does. Furthermore, an initial CFD study showed that the pitching velocity of the ship has the greatest influence on the changing angle of attack on the foil. Additionally a study into basic wing theory showed that the foil would produce the most thrust at low angles of attack. With the use of this information, four algorithms were developed. Two of these algorithms focused on reducing the overall resistance by increasing the generated thrust on the foil. The results showed that the generated thrust cannot be significantly increased in comparison to a static foil. Two other algorithms were designed with the goal to reduce the pitching motion of the vessel. These two algorithms both achieved a significant reduction of the pitching motion, which also lead to a reduction in added wave resistance. Although the foil dampened the pitch motion, the generated thrust was found to be less than for the case with a static foil. The reduction in thrust was similar in size to the reduction in added wave resistance. It can be concluded that the rotating foil was able to provide similar resistance reduction as a static foil, with the added benefit of a significant reduction in pitch motion.

Allseas Engineering B.V. is an offshore contractor, focussed on offshore pipeline installation. Since the late 80's, Allseas has been working on the design and construction of the Pioneering Spirit, a heavy lift vessel designed for the single-lift installation and removal of offshore topsides. From 2019, it is scheduled to be able to single-lift install or remove jackets with the jacket lift system. The jacket lift system is located at the aft of the vessel and consists of two 170 meter tilting lift beams, hinged around the stern. During a jacket removal, the jacket is cut-off at the bottom, hoisted from the tip of the beams, partially rotated, and then tilted inboard. In between the hoisting and tilting is the transition phase. At the interface between jacket and the tilting lift beams, jacket support structures are located. In this thesis, the behaviour of the free-hanging of the jacket and the loads on these support structures due to the mating with the jacket are researched. Jacket removal operations will take place in open sea and are thus subjected to environmental actions. The jacket, suspended from the tip of the beams, is excited due to fluid acceleration and velocity causing inertia forces and predominantly drag forces on the slender members of the jacket, as well as the excitation of the vessel through the suspension point. These motions are calculated with two different approaches. A direct-time domain model is developed of the jacket as submerged pendulum. To accelerate model simulations, the jacket is modelled as one single cylinder with different equivalent diameters to account for the total of drag and inertia. The second model is a full geometrical time-domain model simulation in AQWA. In the design sea state, simulations showed that the most probable maximum momentum of the jacket due to environmental excitation is 4.5 106 kg m/s, and the motions of the centre of gravity of the jacket are all within a range of 1 meter, for the single and double pendulum and the full model. The influence of the environmental actions on motions of the structure is concluded to be small. This suggest that the jacket mating loads are governed by the tilting velocity of the tilting lift beams and the motion of its tip. The jacket mating simulations are done in the full AQWA model approach. Fenders are modelled to absorb energy during the jacket mating. A sensitivity analysis showed that the parameters that have most influence on the mating phase characteristics are the tilting velocity and the stiffness of the fender. From still water conditions it seems that by increasing or decreasing the tilting velocity, this can affect the number of re-bounces and the maximum deflection. With increasing sea state, the duration and intensity of the mating phase increases. The fender deflection will increase for increasing significant wave height. The wave period does not have a significant influence on the maximum fender force. The amount of re-bounces reduces significantly for higher damping coefficients, while its influence on maximum deflection decreases. The maximum force on the jacket support structures caused by the static gravitational force by the jacket once it is fully tilted is approximately 10 times higher than the maximum occurring force exerted on one of the fenders. Therefore, this static gravitational force is critical for the design of the jacket support structure, not the force caused by the mating.

Floating offshore wind energy is being widely implemented in deep-water sites thanks to its numerous advantages, which among others include the access to stronger and undisturbed wind resources. In addition, considering the fast-paced growth in size and power generating capacity of offshore wind turbines, the designs of floating foundations need to be continuously improved. Therefore, proper testing (at model-scale) is necessary. To achieve this, several factors need to be taken into account. For instance, down-scaling for testing of floating structures brings challenges due to the so-called Reynolds effects, which degrade the aerodynamic response of the mounted turbine. Likewise, the rotation of the blades and the motions of the platform as a result of its interaction with waves, have an impact on the wind inflow acting upon the rotor. Thereby, modifying its instantaneous performance. This Master thesis, carried out in cooperation with MARIN (Maritime Research Institute Netherlands), focuses on developing a reliable methodology that renders in the design of a scaled-down thrust-matched 10MW wind turbine rotor blade, for its further implementation in the testing of a floating offshore support structure. For this purpose, the aforementioned effects are investigated, and a suitable set of design tools is selected and coupled, in order to realise an optimised blade geometry. For predicting the wind turbine behaviour, this implementation relies on the Blade Element Momentum Theory. Furthermore, the resulting blade's aerodynamic performance is validated using ReFRESCO (MARIN’s in-house CFD code), against the non-dimensional parameters of the DTU 10MW reference wind turbine.

With the shift towards a more sustainable energy society, the increase in the electricity produced by renewable energy sources is steadily rising. However the cost of renewable energy sources still remains high compared to the traditional fossil fuel based energy sources. With the total worldwide energy demand also rising, combining renewable energy sources helps to reduce the cost through a shared infrastructure and increase in energy production. This thesis investigates the feasibility of a combination of floating offshore wind and marine current energy. As a basis the Hywind spar type floating offshore wind turbine is used. This 5 MW system is combined with a 1 MW marine current turbine. The characteristics of the current turbine will be examined with the program Aerodyn and the blades are designed with the program Harp_opt. As a cost reduction, the effect of scaling down the weight of the mooring system in combination with reversing the direction of the thrust of the current turbine is also investigated. The program ANSYS AQWA is used to investigate the dynamic behavior of the combined system. The thrust forces of the wind and current turbines are calculated via an external python server and added to the simulation in AQWA. The structure is modeled in a rigid body approximation, assuming no structural deformations. The behavior of the combined system is investigated in 3 operational and 1 survival load case. The operational load cases represent the environmental conditions of the cut-in, rated and cut-out wind speed of the wind turbine. In the fourth load case the system is subjected to survival conditions and the direction of the thrust of the current turbine is reversed. The environmental conditions are simulated with a steady wind velocity and the sea state is modeled using the JONSWAP wave spectrum. In all 4 load cases the system is subjected to a strong current. By using a levelized cost of energy prediction model, a first estimation of the levelized cost of energy of the combined system is obtained. Adding a current turbine to the Hywind spar increases the cost of the initial investments and operational cost of the system, but also increases the total energy generation. Compared to the original Hywind spar, adding a current turbine to the system lowers the levelized cost of energy from 149.4 €/MWh to 142.3 €/MWh. Scaling down the weight of the mooring system lowers the levelized cost of energy to 141.9 €/MWh. From the results of the simulations it is found that using the current turbine during survival conditions has a positive effect on the motions and maximum tension in the lines. It is concluded that by using the thrust of the turbine the weight of the mooring system could be scaled down, but the effect on the levelized cost of energy is minimal and doesn’t justify the increased risk of failure.

There lies an opportunity for significant cost savings in the installation of subsea cables in offshore wind farms which is why the current work proposes a state-of-the-art method for monitoring the cable during installation. The proposed method enables offshore crew to look through the water with the use of augmented reality. To this end a real-time numerical model of the subsea cable dynamics is developed. The model is created in programming language C# and visualization in augmented reality is done using the game-engine Unity. This development environment is uncommon for engineering and scientific purposes and has been selected based on its ability to visualize model results in augmented reality, its extensive graphics library, its capability to process real-time in- and outputs and its free availability. Relevant physics are analyzed on contribution to global cable geometry and tension for the case of shallow water cable laying, resulting in an equation of motion which is sufficiently accurate for representing the physical phenomena occurring during cable lay. An assessment of the measurements required by the model during operation is made. The main challenge of modeling in real-time is that the average model time step is limited by available computational power, in turn limiting the axial stiffness range which can be modeled without the occurrence of numerical instability. Discretization is done using a lumped mass method. It is shown that cable dynamics can be modeled in real-time using an explicit method and that overcoming the associated limitation on axial stiffness does not lead to inaccurate results. The developed numerical solution is verified using OrcaFlex, which is typical software for dynamic analysis of offshore marine systems. An augmented reality interface is developed, including color codes indicating the structural state of the cable. The current work enables the visualization of the real-time model in augmented reality. Potential legal issues related to the implementation of augmented reality during offshore cable lay are outlined during a collaboration with Tilburg University. Successful practical implementation of the proposed innovation is associated with promising opportunities.

New floating wind turbine designs are needed to reduce production costs and to increase mass production feasibility. The TetraSpar floating wind turbine achieves these goals by being constructed using components highly suitable for standardization and industrialization. The design makes use of a suspended submerged counter weight to obtain a low center of gravity for the floating system, while also allowing a low draft during transport and installation. An analytic analysis of the counter weight suspension system is presented that investigates the behavior of the system. The main concern of the novel system is its motion relative to the upper floating platform which it is connected to. It is demonstrated that the suspended system's motion is described by the axial elongation of the suspension lines when positive tension is maintained in all suspension lines. An analytic solution for the equivalent stiffness of the suspension system is given. This suspension system stiffness introduces additional natural frequencies into the system, and the effects of these frequencies are demonstrated. This novel concept requires a multibody modeling approach to perform a dynamic loads and response analysis, as the stiffness between the floating platform and the counter weight is provided by chains. Additional design criteria are required for the counter weight system dependent on a combination of chain capacity and maintaining positive tension in all of the suspension lines. To satisfy these design criteria a global hydrodynamic load and response analysis of the floating system is performed. In this concept, the counter weight depth contributes significantly to the dynamic properties of the system and therefore a parametric study is conducted. The global response parameters of the rigid-body motion, natural frequencies, nacelle accelerations, counter weight chain tensions, and maximum platform-pitch angles are compared. Following the parametric study, an ultimate limit state analysis is conducted on the original and alternative designs. Design recommendations are made for the counter weight depth and configuration of the suspension system layout.

The new rapidly growing wind energy market has been moving to offshore waters the last few years. New techniques and growing experiences make it possible to move to challenging offshore domains and towards harsher conditions and deeper waters. From the oil & gas industry a lot of expertise is already available on support structures. The focus in this thesis is on the installation of a jacket type sub-structure for an offshore wind turbine. In more detail: the horizontal added mass for suction bucket jackets during installation was studied, from the moment the bucket touches the water till the buckets are fully submerged. This is a period during installation with a lot of uncertainties and unknowns, especially inside the buckets. A suction bucket jacket is identical to the commonly known jacket type support structure, however, at the bottom of each leg a suction anchor is attached. For a structure of about 60[m] in height and 1000[tonne], these anchors have a rough dimension of 8-9[m] in diameter and have similar heights. Note that the combined mass of the enclosed water inside the buckets can almost reach twice the weight of the dry structure. A benchmark suction bucket with dimensions 10[m] in diameter, 10[m] in height and a wall thickness of 10[cm] was used to design a scale model of 50[cm] diameter, 62.5[cm] in height and a wall thickness of 0.5[cm]. This corresponds to a Froude scaling factor of 1:20. The experiments were executed at the hydrolab at Boskalis, Papendrecht. A tank of 20x3.5x3[m] was available there to execute the experiments. The water-depth in the tank was 1.12[m]. During the experiments a vertical pipe segment was forced to oscillate at a known frequency. The pipe was attached to a guiding system, restraining all motions but the surge direction. The applied force by the actuator was measured by a load-cell attached at the point where the crankshaft was connected to the pipe. Simultaneously a LBT-sensor measured the position of the pipe versus time. The experiments were done for the following settings for draft and scale model wave period range, each experiment was executed three times to reduce the error: Periods: 2.46 2.24 2.01 1.79 1.57 1.34 1.12 0.89 seconds. Drafts: 0, D/4, D/2 3D/4 D. The data was filtered and analyzed with the use of the linear Least Squares Method (LSM). The raw data was fitted by adjusting the amplitude and phase of a sinusoidal fit signal. The amplitude and phase provide information on the relation between damping and added mass in the system. Finally the results added mass (and damping) were checked with the theoretical potential theory. While for all frequencies the added mass stayed more or less constant for each draft, during sloshing the added mass decreased. The damping was more or less constant for all drafts at low frequency, but at a wave period of 9[s] the damping start to increase for deeper drafts. Sloshing occurred at the shortest two periods. This had a significant impact on the damping and added mass terms. At sloshing the added mass decreased rapidly with 40%, while the damping increased up to 300%.

Dykstra Naval Architects are regularly designing large classic sailing yachts or motor-sailors, of which the draft is an important design restriction.The sailing performance is increased by adding lift-generating appendages,without increasing the draft. An example is a retractable centre board, havinga big influence on the sailing properties. Predicting the performance of the centre board contribution in a hull-keel-centre board configuration is the subject of this research. When predicting the performance of large sailing yachts, Dykstra wants to keep the ability to superpose an appendage to the data of a hull-keel configuration obtained from towing tank experiments or CFD simulations. This means that a method must be developed to estimate the contribution of the centre board, in terms of side force, resistance and centre of effort. Both towing tank experiments and CFD simulations are conducted for this research. The Maltese Falcon is used as the 'case ship'. A towing tank model of the Maltese Falcon was already made and tested at the TU delft in 2002. This model is again subjected to towing tank experiments, with a new keel and two new centre boards, resulting in 9 different hull-keel-centre board configurations. The main focus was on the towing tank experiments, executed in the Delft Hydromechanics Laboratory. CFD simulations were done to validate the results of the towing tank experiments and to gain visual insight in the flow around the vessel. The lift-carry-over on the keel and hull above the centre board can clearly be seen, as well as the influence of the centre board on the circulation in the flow around the underwater body of the yacht. After post-processing all experimental data, the results of the towing tank experiments are used to develop formulations to predict the performance contribution of the centre board. The measured lift of the centre board contribution was roughly a factor 2 higher than the centre would generate according to Wicker & Fehlner theory. Additionally, it was found that the lift-carry-over does not only have a positive effect on the generated side force, but also on the resistance. Furthermore, it was found that heeling the Maltese Falcon model by 15 degrees, yields the same magnitude oflift-carry-over as for the upright conditions. This resulted in the conclusion that heeling the yacht has no influence on the lift-carry-over from centre board to keel-hull. The new prediction methods, derived from the towing tank experiment data, are validated on YACHT1 and Adela. These are existing yachts with hull-keel-centre board configurations, but both very different. This enabled an interesting examination on the influence of certain aspects of the configuration on the performance of the centre board contribution. All in all, it was found that the predicted centre board contribution corresponded really well to the measured data of YACHT1 and Adela. This provides enough trust to implement the new centre board performance prediction methods in the Dykstra performance prediction tool. Every new design cycle of a yacht with hull-keel-centre board configuration will serve as a validation of the derived performance prediction methods.

DAMEN tugs can be found in nearly any port or terminal around the world. Operating in ports and terminals requires the tugs to be highly efficient in ship handling in order to quickly escort larger vessels. To predict the escort capabilities of a tug, DAMEN has developed the computer program DAMEN TUGSIM. Since the tool is becoming a decisive tool in the design process, DAMEN wants to strengthen their confidence in the simulation tool TUGSIM by gaining more understanding related to the thruster performance. The goal of this study is to quantify and increase understanding into the following regions: Thruster performance in oblique flow; hydrodynamic interaction effects encountered between thrusters; hydrodynamic interaction effects encountered between the thruster and hull. Recently performed model tests of the RSD (Reverse Stern Drive) tug provided the opportunity to gain insight into these topics and to derive prediction models. Mathematical models are developed and finally implemented in TUGSIM. Implementation of the new models in TUGSIM enabled to harvest new insight into escort capabilities of the RSD tug, especially into the braking capabilities.

Due to a low restoring force as well as lack of damping, the roll motion of a vessel is usually the motion with the highest amplitude of all degrees of freedom. Therefore, in history many have tried to stabilize rolling ship starting with Watts in 1883. He described the damping of the roll motion by having a group of men running to the "high" side of the vessel. Since then, a great deal have been written about the subject of roll damping for stationary vessels. The principle however has been the same ever since, a shift of mass to counter the roll motion. Water tanks, carts on a curved track and sliding masses, all tend work with this principle. In 1904 Schlick introduced another device to damp roll motions was introduced, the gyroscope. By controlling the precession angle, the roll motion could be damped. Following from an increase in computational power more advanced control strategies could be applied, leading to a renewed interest in the subject as well as different methods to model the vessel for controller design. In the current paper, the performance of a gyroscope is compared with the performance of a moving mass, modeled as a double pendulum, for dynamic performance of a showcase vessel, the Huisdrill P10000. Results of this analytic study are promising, a reduction of more than 80% for both systems was achieved at the natural frequency of the Huisdrill. The decay time after a roll amplitude of 5.7 degree was reduced from about 250 seconds to 60 seconds for the gyroscope controller model and 70 seconds for the double-pendulum controller model. A static heel control system is modeled based on the double- pendulum equations. This proves to be able to compensate for the heeling moment depending on the weight at the crane tip as well as the weight and distance available to compensate. Combing the static an dynamic approach is possible with the note that there should be sufficient space for the mass to deviate after compensating for static heel. In irregular waves the 4-DoF model shows good performance for the showcase of the Huisdrill P10000. The RMS value for the roll-roll motion was decreased by 65% For other degrees of freedom, similar reductions were obtained. From this it can be included that for the given seastate, significant reductions can be achieved using the ballast train. In the time domain, it was shown that great reductions in most probable maximum of reduction of roll amplitude were achieved for time periods close to the natural frequency of the vessel. For no time period, reductions in performance were measured. It was found that the most probable maximum roll angle linearly increased with the wave height, as well as the most probable deviation did. Interpreting the results of this study, it can be stated that both the gyroscopic control system as well as the double-pendulum system are able to introduce great reduction in dynamic roll motions. The main benefit of using the double-pendulum system is its ability to compensate for the heeling moment induced by the swiveling crane as well as compensating for the dynamic motions that a vessel will undergo offshore. It is recommended to do a simulation of a non-linear time-domain model or to perform model tests for verification of the results found in this report. The gap between static and dynamic control should be filled by a master control which is to be designed and run in the time domain.