The demand for renewable energy is growing, due to a growing awareness among people about the effect of burning fossil fuels on the environment. Governments have signed climate agreements and are obliged to decrease their level of exhaust gasses. This change in attitude regarding the environment led to an upcoming market for renewables. A significant part of the demand for renewable energy is covered by the wind industry, both on- and offshore. Especially the offshore wind market holds huge potential, due to stable wind conditions and growth opportunities. A side effect of the evolving industry is that turbines are increasing in size and are being installed in deeper water depths. It is expected that the methods of installation, currently used in the offshore wind market, will no longer be suitable for the installation of new generation turbines. In this research, installation of offshore wind turbine towers using a heavy lift vessel (HLV) is opted as an alternative to the current installation methods (jack-up installation). The major benefits of floating installation, when compared to jack-up installation, are the independency on both soil conditions and jacking operations. A challenge of floating installation, however, is the introduction of vessel motions resulting in excitation of the tower. The main objective of this research is to find the most efficient way to control the motions of the tower during installation using a HLV. To fulfill this objective, first, a conceptual design study has been conducted, which focused on developing concepts for the safe installation of offshore wind turbine towers using a HLV. Safe installation was assumed if the displacements of the tower bottom maintain within limits, as specified in a list of design requirements and criteria. Before examining any concept in more detail, the response of the tower and the effect of applying a form of motion compensation has been examined in a general way. To test the response of the tower in the crane in a general way, with and without motion compensation, the tower in the crane has been represented by a double pendulum system with a moving support point. Then, using the numeric model, the response of the tower in the crane has been computed for certain sea-states in both frequency- and time domain and for both the free hanging- and the motion compensated case. The motion compensation system has been represented by a virtual spring damper system, of which, by changing the simulation parameters, the optimal configuration (position, stiffness and damping) has been determined that minimizes the tower response. From the results, it can be concluded that a significant reduction of the tower bottom displacements can be achieved under the application of an active motion compensation system, the requirements for safe installation, however, are not yet fulfilled.

Over the past years tugs are evolving to more compact designs equipped with large power installations. This inherently increases the risk of accidents, demanding a more reliable prediction of the tug’s dynamical behaviour in critical situations. To capture the dynamic behaviour of a tug, a time domain simulation tool has been developed and used to evaluate the tug’s safety in those critical situations. Multiple methods derived from recent studies are combined and used to establish a reliable description of the involved hydrodynamic forces and moments. Besides a sensitivity study is performed to investigate the impact of inaccurate approximations of those forces and moments. Furthermore, the sensitivity to a change in more design and operation related parameters has been investigated. Finally, the research includes a step by step validation and an evaluation of the current regulations.

Marine structures can sustain damage due to violent wave impacts that are characterized by complex dynamics involving both water and air. Methods that predict impacts loads for structural design often assume the water as incompressible. These predictions can be inaccurate during impacts where air is entrained in water, as that greatly increases its compressibility. Initial impact forces may decrease due to a cushioning effect. However, the total severity of the impact may increase due to temporal spreading and oscillations of impact pressure. Previous research on aerated water impacts covers breaking waves against fixed structures, flat water slamming or green water events, but not the interactive motion of rigid marine structures in free surface waves. This work aims to evaluate the effect of aerated water impacts on the dynamics of floating rigid bodies in irregular waves. As a part of this work, a state-of-the-art numerical simulation method for aerated water impacts is extended with a monolithic coupling for rigid body motion. Additionally, boundary conditions for wave generation were implemented for a validation of the method during breaking wave impact. Results of the verification of both extensions compare well to other literature. It can be concluded from this thesis that the compressibility effects of aeration on penetration depth after cylinder slamming can be neglected for entry Mach numbers below 0.1. For further research, it is recommended that this numerical method is used for a range of experiments with various geometries and higher impact velocities. This could provide more insight into situations where aerated water could have important design implications.It can be concluded from this thesis that the compressibility effects of aeration on penetration depth after cylinder slamming can be neglected for entry Mach numbers below 0.1. For further research, it is recommended that this numerical method is used for a range of experiments with various geometries and higher impact velocities. This could provide more insight into situations where aerated water could have important design implications.It can be concluded from this thesis that the compressibility effects of aeration on penetration depth after cylinder slamming can be neglected for entry Mach numbers below 0.1. For further research, it is recommended that this numerical method is used for a range of experiments with various geometries and higher impact velocities. This could provide more insight into situations where aerated water could have important design implications. It can be concluded from this thesis that the compressibility effects of aeration on penetration depth after cylinder slamming can be neglected for entry Mach numbers below 0.1. For further research, it is recommended that this numerical method is used for a range of experiments with various geometries and higher impact velocities. This could provide more insight into situations where aerated water could have important design implications.

Ballast water, routinely taken on by ships for stability and structural integrity can contain thousands of mi- crobes, algae and animals. When discharging this ballast water holding these organisms in a non-native ecosystem, new invasive aquatic species can be introduced. This can have to devastating consequences for the local ecosystem. To prevent further disruption of different ecosystems across the globe, the Ballast Water Management Convention (BWM) was adopted by the IMO in 2004. NIBC has a wide portfolio of vessels which will have to comply with the IMO BWM convention. However, the possible solutions and the actual impact of this regulation is still unknown to the bank. Ship owners expect a significant impact on the shipping industry and it is suggested that a lot of vessels will have to be scrapped due to the high investment cost. This research is conducted for ship owners and banks and will reveal the actual impact of the BWM convention. This is realised by calculating the impact on the internal rate of return (IRR) for each specific vessel. It provides the bank with a tool to monitor what effect the BWM convention will have on their clients. In addition, the tool is able to identify high risk vessels with an internal rate of return below 9%.

Once a semi-submersible is operating at an inconvenient draft (A shallow draft with limited water column above the pontoons), the passing waves over the pontoons can not keep their linear motion and energy will be transferred to higher harmonic wave frequencies. This means the hydrodynamic response will also contain energy at these higher frequencies. Conventional linear diffraction solvers are not able to solve the combined response of the wave frequency and its higher harmonics, which then result in a non-physical solution for the wave loads, motions and internal loads. This research aims to obtain a better insight into the hydrodynamic response at the inconvenient draft and ultimately on the internal loads of the semi-submersible. In the first part of this research, model test solutions, linear potential solutions obtained with WAMIT and CFD solutions obtained with ComFLOW are compared. the comparison shows that ComFLOW is able to provide more accurate wave loads compared to the linear potential solver. The higher harmon- ics observed in the measured wave loads during model tests are correctly predicted by ComFLOW, although maximum deviations of 30% are still observed between measured and predicted wave-load amplitudes. However, ComFLOW is not able to solve the motions of a free-floating semi-submersible correctly. Due to pressure peaks in the wave-exciting forces, solving the equation of motion results in an incorrect motion response and ultimately results in incorrect internal loads. Although a significant effort was made - in close collaboration with the ComFLOW developer - to improve this functionality, the results remained unsatisfactory. Even so, in order to obtain an insight into the higher harmonic response contributions to the internal loads, a parameter study has been conducted, using tests in which the semi-submersible was held captive. This parameter study was conducted by systematically varying wave amplitudes and draft, and resulted in situational limits at which the higher harmonic response contribution becomes significant and the linear relation between the incoming wave and the hydrodynamic response is lost. This limit is shown to be dependent on the Ursell number. Furthermore, it is demonstrated that the significance of the higher harmonic response contribution increases from 10% to 40% throughout the inconvenient draft, while the most severe situations resulted in a higher harmonic response contribution of 50% of the total response amplitude. In the final part of this study, an attempt is made to couple the wave loads from ComFLOW to internal loads. A quantitative analysis is made on the effect of the higher harmonic responses of the wave loads on the internal loads. The time domain simulator aNySim is used combined with the wave- exciting forces on a captive semi-submersible calculated with ComFLOW. A multi-body analysis is used to obtain the internal loads on the aft and front part of the semi-submersible. This did not provide the correct answers because the stiffness of the spring damping between the two sections affects the higher harmonic response contribution. This method overestimated the higher harmonic response contribution. A better understanding of the joint and the joint stiffness/damping of a dual-body simulation may solve the encountered problems.

With the transition towards renewable energy, offshore wind power farms are being constructed or planned in many places involving placing wind turbines in the sea. The monopiles for these wind turbines are vertical cylinders which are situated in a flow with high Reynolds numbers and low to intermediate Keulegan- Carpenter numbers. The Reynolds and Keulegan-Carpenter number are dimensionless numbers for the quantification of respectively currents and waves. Previous research has not covered the Reynolds and Keulegan-Carpenter numbers in which energy generating devices are situated. The current research is focused on filling the gap and investigating the drag forces on these cylinders via means of experiments. Additional simulations focussing on the free surface and end effects were also conducted. The forces at play and the Morison equation to model these forces have been evaluated. It was discovered that in the investigated range, the drag and inertia coefficients depend on both Reynolds and Keulegan-Carpenter numbers. By analyzing the results of the experiments in the time and frequency domain, indications of vortex shedding and second-order harmonic wave forces, as well as forces from wave-wave interaction were found. The Morison equation itself is analyzed to find that it either underestimates or neglects these forces. By means of simulations, the effects of the free surface and the aspect ratio of the cylinder on the drag and inertia coefficients are found. Lastly, it is proposed to use a rewritten Morison equation to find the drag on a cylinder in a flow with irregular waves. This equation is found to describe the drag forces more accurately.

When waves break, air and water mix and small air bubbles are formed in the water, creating aeration. The mixture of air and water alters the behavior of the fluid. Traditionally, it has been assumed that aeration has a damping effect on impact, as exemplified by the use of air bubbles in the swimming pool below the Olympic 10m platform and during synchronized 10m platform jumps to reduce the force exerted on the swimmer's body. However, in recent years, it has been found that this assumption does not hold true in all situations involving aeration. When treating aerated water as a non-compressible fluid, it does exhibit a damping effect on impact. However, when treating aerated water as a compressible fluid, the speed of sound of the mixture can actually change with implications for the propagation of density waves. This means that an aerated water impact can feature pressure oscillations that increase the force instead of reducing it. Consequently, hydraulic structures that have been or will be constructed with the assumption that aeration only has a damping effect, may be affected. Understanding the effect of wave-induced aeration on a horizontal platform is crucial for the design of new hydraulic structures in a more efficient and cost-effective manner. This research aims to determine the maximum force experienced by a horizontal surface during an aerated wave impact. The investigation involves using a numerical method, followed by a series of self-conducted small-scale sloshing experiments. The simulations contribute in two ways: they aid in understanding the problem and the magnitude of forces acting on the experimental setup, and they assist in verifying the experimental results once the experiments are completed. For the experiments, a new tank layout has been designed to facilitate the creation of aerated water inside the tank. The tank is used for conducting experiments where aerated wave impacts are compared to non-aerated wave impacts for different wave impacts. The experimental results confirm both the effect of pressure reduction due to aeration when the aeration level is near to 4%, as well the effect that the maximum pressure can increase for aeration levels between 1 and 2%.

Offshore floating wind turbines are one of the newest technologies in the renewable markets today. The world’s first floating wind farm, the Hywind Scotland Pilot Park, was commissioned in October 2017 and has been competitive with fixed bottom offshore wind turbines. There is a global push to make more renewable energy available, but less desire to have wind turbines cluttering the coastline. Floating wind turbines enable the developer to take advantage of unused offshore space, at depths where traditional fixed bottom structures are impractical and at locations that do not spoil the vista of the coastline. This thesis project aims to develop a working mooring system at depth of 600 m in the Norwegian North Sea, and then investigates the possibility of shared anchors in a wind park with this mooring system. The DTU 10MW reference wind turbine atop a classic spar substructure is used. First, the mooring system at 320 m is tested under decay and environmental loads. Then a chain-polyester-chain mooring line with a bridle was developed for 600 m so that the surge offset is limited to <60 m for 3 load cases. A simplified model of the wind turbine was then developed for these three load cases. The simplified model was then used to create a wind farm arrangement with 5-6 turbines each. Each wind farm varied in layout and in the number of shared anchors. It was found that while the mooring system designed passes the surge offset and natural frequency requirements, and the normal ULS safety class, it failed the high safety class in some cases. For shared anchors with multidirectional loads, the resultant force on the anchor is significantly less as long as the lines are distributed equally around the anchor point. The resultant force does not increase with two lines 120± apart. The footprint of a single turbine with the designed mooring is larger than the footprint of the entire Hywind Scotland Farm, so suggestions are made for improvement and further work.

Green water events on ships in extreme waves pose a considerable risk to personal, operational, and structural safety. Considering these issues, novel experiments were done to investigate the interaction between focused breaking waves and a ship at forward speed. The investigated interactions are global motion, global loads, and forces on a deck structure. For the experiments focused, breaking waves were created, which served as loads of the green water events. First, wave focusing with prescribed characteristics was investigated in numerical settings. It was shown that focusing the waves with iterative methods does not lead to a converging solution. Three breaking waves were created in a wave basin. The characteristics of the waves were retrieved from 2D numerical simulations. The parameters of the spectrum of each wave were calculated from the simulation results. The experiments were conducted systematically, where the position of the longitudinal center of gravity (LCG) of the ship was varied with respect to the focus point of the breaking wave at the focusing time. Using the same wave input resulted in green water events and loads on deck structure with different characteristics caused by different breaking stages of the focused wave. The effects of different ship velocities and different focused breaking waves were also explored throughout the experiments. It was shown that using the same focused wave, i.e., the same energy input, the breaking stage of the wave during the impact has a large influence on both the magnitude and time development of the loads on the deck structure. Force and pressure peaks were the largest and had an initial spike-like development when the wave during impact was in an unbroken stage. Impacts with the wave in its broken stage resulted in significantly lower loads and longer-duration load development. Such changes in the loads show that the ship's position with respect to the breaking wave is essential to consider even for the same input energy, posing additional challenges for establishing the maximum load in a sea state.

Surrogate modelling techniques such as Kriging are a popular means for cheaply emulating the response of expensive Computational Fluid Dynamics simulations. These surrogate models are often used for exploring a parameterised design space and identifying optimal designs. Multi-fidelity Kriging extends the methodology to incorporate data of variable accuracy and costs to create a more effective surrogate. This work recognises that the grid convergence property of CFD solvers is currently an unused source of information and presents a novel method that, by leveraging the data structure implied by grid convergence, could further improve the performance of the surrogate model and the corresponding optimisation process. Grid convergence states that the simulation solution converges to the true simulation solution as the grid is refined. The proposed method is tested with several problems involving both synthetic and realistic multi-fidelity data acquired with Computational Fluid Dynamics simulations. The synthetic results indicate that our method surpasses the most well-known multi-fidelity Kriging model in terms of both accuracy and cost given the proper conditions. The performances of both surrogates in the optimisation cases using Computational Fluid Dynamics simulations were similar. Data-supported conditions for the proposed method to be effective, and a procedure to cheaply recognise them, are provided. To further improve and validate the method, recommendations are given at the end.

The development of renewable energy applications has become increasingly important in the past couple of years due to a growing global energy demand and increasing consciousness of global warming. A recent development in renewable energy is the application of offshore floating solar systems. A prototype design for this application, as developed by the company ’Oceans of Energy’, consists of multiple floating platforms (floaters), moored to the sea bed. One of the challenges for offshore floating solar systems is the continuous wave induced force acting on the floater that can become significant in severe weather conditions. Numerical simulations are often used to analyse and predict these forces. Combined frequency-time domain solvers are the most promising tool for this design to obtain reliable results within reasonable computational time. However, it is unknown what the capabilities of this solver is for the novel offshore floating solar system. The goal of this study is therefore to determine to what extend the frequency-time domain solver is able to accurately simulate the behavior of the multi-body, offshore floating solar system. A numerical model was developed in the simulation tool ’aNySIM’. Experiments conducted in the offshore basin at MARIN were used for the model structure development and validation. Additionally, viscous damping effects were implemented from empirical data based on the experiments. Decay tests were used for damping determination. This resulted in inaccurately determined forces and motion amplitudes for regular and irregular wave tests. A new damping determination method was introduced, using regular wave results as input. The accuracy of the model improved with 4% using this method. Nonetheless, inaccuracies in mooring line forces, oscillating behaviour and motion amplitudes are present. These inaccuracies have been addressed with an uncertainty analysis and sensitivity studies. Trends within the accuracy of the simulation model were linked to physical phenomena that occurred during the experiments. Analysis showed that several effects, related to the novel design characteristics, influence the model accuracy. Multi-body (e.g. shielding of floaters) and mooring system aspects (e.g. hydrodynamic loads on mooring lines) have been identified, influencing the viscous damping of the system. Additionally, nonlinear effects due to, amongst others, breaking waves have been identified. For regular wave tests and lower irregular wave tests, the simulation model gives reliable results with errors in the mooring line forces below 10%. These errors are mainly ascribed to viscous damping effects. For higher sea states the simulation behaviour shows discrepancies and errors in the mooring line forces increase. In these tests, nonlinear effects due to breaking waves become more relevant. For future work, different uncertainty causes must be further isolated in the simulation model. This can be done by obtaining more experimental data. To quantify the effects, studies in other numerical tools can be performed (e.g. CFD calculations) and more extended sensitivity studies must be executed in aNySIM. We present a structured

When drilling for oil or gas, wells are typically constructed using a conventional or telescopic well design. After a section of the well has been drilled, a steel casing (or liner) is inserted into the hole preventing the collapse of the hole. The next well section has a smaller diameter as it’s casing must pass through the previously installed casing. This process leads to a stepwise reduction of the well diameter which, especially in deep or complicated wells, restricts the maximum production rate of oil and gas. Mono-diameter technology utilizes casings which are plastically deformed after they have been placed in the well. This plastic deformation is done by pulling a conically shaped tool, known as the cone, through the newly installed casing. The plastic deformation increases the diameter of the new casing to (nearly) the same as that of the previous casing, therefore the well diameter no longer decreases with every new section. The expansion requires a force in the order of 1000-2500[kN]. The work done by this force leads to high local heat generation due to friction and plastic deformation. This heat, poses a risk for the expansion process as the lubricant (RPSLF) decomposes above 250[C]. Decomposition of the lubricant leads to an increase of the friction, inducing more heat release and further decomposition of the lubricant. The expansion force may then exceed the pulling capacity of the drill rig or strength of the drill string, leaving the cone stuck in the well. Previous research provides the distribution of pressure on the contact surface of the cone, the strain distribution inside the liner and the temperature dependent friction coefficient of the lubricant, by combining these the frictional heat is calculated. Heat generation from plastic deformation is a complex phenomenon especially at low strain (-rates). The Taylor-Quinney coefficient defines the ratio between the work done on a material and the heat generated. A strain-dependent model for the Taylor-Quinney coefficient, developed by Zehnder, is used to determine the heat release from plastic deformation. A numerical heat transfer model is built in Matlab, based on the finite volume method. The model uses a mesh based on skewed quadrilateral cells. Numerical stability of the model is verified for the cell size, time step and time integration method. Movement of the cone and the plastic deformation of the casing are modeled by taking a reference frame fixed relative to the motion of the cone and adding a ”convective” term inside the liner. Heat transfer phenomena at all boundaries are investigated using thermal resistance models. A series of experiments is executed to verify the numerical model. The experiments consist of full-scale expansion test using a cone equipped with 30 thermocouples placed just below the contact surface. Additionally also the temperature of the liner, expansion speed and expansion force are measured and recorded. Comparison of the experimental and numerical results leads to the observation that the pressure profile determined in previous work is likely valid at the first onset of expansion. Over time, the forming of a lubricant film however leads to the re-distribution of roughly 20% of the force from the rear of the cone to the front. When the pressure profile is corrected for this effect; the temperatures inside the cone, temperature of the liner, expansion force and overall heat balance show a good match between the numerical and experimental results with an error of around 5%. From the heat balance based on the experimental results, it follows that between 54% - 60% of the work done on the system is converted into heat. As all work done in the form of friction is converted into heat the remaining energy must be lost in the work done to plastically deform the casing, this provides indirect evidence for the validity of the Zehndermodel. The validated numerical model is used to simulate a reference case field expansion, the maximum contact temperature here is 164.4[C]. This value is well below the lubricant decomposition temperature of 250[C], which leads to the conclusion that the process is safe and the expansion speed could even be increased from a thermal point of view.

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.

Breaking water waves still represent a very active research area, as they are involved in a broad spectrum of situations ranging from safety at sea to climate change. The detailed knowledge of the location of the free surface in case of breaking waves or wave impacts could prevent structural damages, increase the efficiency of ship hulls and improve the understanding of gas exchanges between the ocean and the atmosphere. Several state-of-the-art numerical and experimental studies rely on qualitative or intrusive, punctual evaluation of the free surface location. Agreement is found in the relevant literature regarding the need for alternative, quantitative methods in free surface measurements. With the intention of filling this gap, the goal of this thesis consists in the dense, two- and three-dimensional, experimental measurement and reconstruction of the free surface during a large-scale breaking dam flow impact with a vertical wall. The breaking wave event is recreated in a purposely designed acrylic 821 x 130 x 280 mm tank with a sliding gate system and recorded in multiple locations by a pair of identical and synchronized sensors in stereo configuration, and an additional side camera. The experimental campaign of this project consists of 71 runs in which different aspects of the breaking dam event are recorded and different initial conditions and fluid properties are tested. A repeatability analysis of the main flow structures is carried out successfully. A preliminary numerical study supports the comparison between the results obtained with the present setup and data taken from the literature. All the cameras are calibrated with standard procedures and sub-pixel accuracy in the root-mean-square directional reprojection error is achieved. Computer vision techniques are adopted for the quantitative measurements. The two-dimensional free surface profile is obtained applying a combination of motion saliency and contour detection on the frames extracted from the side camera's recordings. The dense point clouds representing the three-dimensional free surface in the impact region are reconstructed from the stereo pairs in the common metric reference system using WASS, an open-source stereo processing pipeline. Dense and quantitative data regarding the location of the free surface in space and time is successfully obtained. Agreement is found comparing the 2D and 3D experimental measurements. Furthermore, the numerical method ComFLOW is used for the numerical simulation of the same breaking dam flow and is validated with the experimental results obtained in this project. The numerical and experimental results agree overall, though differences can be observed in the shape of the free surface during the breaking of the impact wave and the consequent formation of the secondary wave. Additionally, good agreement is found comparing the present results with punctual (numerical and experimental) free surface measurements taken from the relevant literature. The results obtained are unique as similar continuous, quantitative, large-scale, dense and three-dimensional laboratory measurements of breaking waves and wave impacts have not yet been presented in the scientific literature, to the knowledge of the author at the time of writing this thesis. This work is considered to give an important contribution to the future validation of numerical methods for the study of large-scale wave impacts.

Trim optimization is an approach considered by the industry to improve the energy efficiency of ships, having a potential in both reducing operational costs and to decrease the emissions of the ship. Potential fuel consumption reduction by trim optimization is 0.5 to 3 % and to up to 7% in extreme cases. Stolt Tankers, a shipping company active in the chemical tanker market, wants to increase the energy efficiency of their ships in operation by trim optimization. For a limited number of ships, trim tables from model scale towing tests are available, but these are not used and the accuracy of these tables are unknown. The objective of this research was to develop a method to decrease fuel consumption by trim optimization, by a dynamic fuel consumption estimation model based on available operational data, that can be integrated in the voyage management system of Stolt Tankers. A dynamic fuel consumption estimation model has been developed, using mainly the noon report data of the C-38 ship class, consisting of six sister vessels of 38 000 DWT chemical tankers. Quality of noon report data is an issue: human error in observing and recording data causes noise and a mismatch exists between the snapshot of conditions on one hand, and the 24 hr averaged sailing speed and recorded shaft power or fuel consumption on the other hand. A data pre-processing framework has been developed and applied to integrate and transform the data, clean and filter the data. The model is able to extract the effects of speed through water, mean draft, trim, sea water temperature, wind force, sea state and swell state and their relative direction to the ship and days since last hull cleaning and propeller polishing. The model has shown to perform optimal using the regression model of Lutzen and Kristensen (2013), combined with a multiple layer feed-forward neural network, consisting of 1 hidden layer with 15 neurons. The model is able to estimate the shaft power with an average accuracy of 6.58 % for a random test set of the noon report data. It is able to extract the effect of trim on shaft power and to consider the effect of weather and fouling conditions. Model results show that about 1 to 2% of shaft power per 0.50 m can be saved, with trim by bow being the optimal trim. Based on sea trial results, it is concluded that the model performs most accurate for conditions that are represented by a high quantity of historical data. The model can be applied for speeds between 12 and 14 knots and for mean draft conditions of 9.5 m and more. Within this range, the effect of trim and weather conditions are followed with reasonable accuracy. It is confirmed by the sea trial that trim by bow is the optimal trim, with a much stronger magnitude of the effect of trim on shaft power. A difference of 6 to 8% in shaft power was found for a change in trim of 0.50 m.

During specific operations, offshore marine contractor Heerema Marine Contractors reduces the draft of their Semi-Submersible Crane Vessel (SSCV) such that the floaters are submerged in close proximity to the free surface. This draft is also known as inconvenient draft. At this draft the motions of the vessel do not fully comply anymore with the computed prediction using linear diffraction theory. A proper motion prediction is required to ensure a safe execution of the offshore operation. The key issue is the submerged part of the floater, since discrepancies occur as soon as there is only a small water column on top of the floaters. Motion RAOs are computed via the hydrodynamic coefficients and wave loads. The reason why this leads to discrepancies in the motion RAO is not yet known. In addition, qualitative hydrodynamic data should be gathered for an object submerged in close proximity of the free surface. Therefore, in this study the cause of the discrepancies in motion RAO is studied on an experimental basis for an object submerged in close proximity to the free surface. The scope is narrowed down to a two-dimensional cross-section of a SSCV-floater. Numerical simulations using linear diffraction theory are performed in WAMIT. The results are compared to experimental data obtained via model tests performed at the towing tank facilities at the faculty 3mE at Delft University of Technology. Based on experimental data is concluded that linear diffraction theory does not predict physical phenomena that satisfy the boundary conditions and that underlie principles of the theory. Despite the fact that the experimental data does satisfy the boundary conditions of the numerical simulation, discrepancies occur at the hydrodynamic coefficients and wave load. As a result, it can be concluded that linear diffraction theory malfunctions at the inconvenient draft region, and therefore is not the correct theory to determine RAOs for an object on inconvenient draft. Discrepancies in motion RAO are found to be dominated by the discrepancies the wave load, except for the frequency at which the added mass equals negative inertia of the body. Discrepancies for added mass are less significant than for the damping coefficient and wave load. At higher frequencies inertia becomes dominant over damping and damping deviations affect the RAO less. The pitch motion about the center of the cross-section does not represent a rotational motion about same the degree of freedom for an SSCV. However, it allowed to experimentally investigate the global numerical extremes. In addition, it led to the finding that it seems that the rotational data is more affected than the heave data. There is a strong suspicion that poles in the complex plane are the cause of the discrepancies in the hydrodynamic data, which result of the used Green's function by Wehausen and Laitone. This suspicion is based on characteristics of the numerical data in combination with findings in literature and the experimental data, accumulate. Currently, an approach that makes use of free surface damping is applied to predict the motion of an SSCV at inconvenient draft. Based on experimental data can be concluded that the use of free surface damping without further modifications does not result in an accurate motion prediction. Lastly, the effect of nonlinearities when increasing the oscillation or wave amplitude. The wave load is found to be more prone to nonlinear effects than the hydrodynamic coefficients.The force signal remained dominantly harmonic, but higher harmonic forces did show up. Furthermore, with the exception of most tests at the largest tested submergence, higher harmonic waves were measured and visually observed during the tests. These higher harmonic waves arose at the transition from the shallow to deep water regime and vice versa. These forces were found to have hardly any effect on the force signal.

In order to collect validation data for the study of the mechanism of fluid-structure interaction (FSI), an lab experiment was conducted by L. Rizos in the towing tank, 3ME,TUDelft in 2016. The concept of the experiment is shown in the figure 1. A cylindrical container is partially filled with water. A small cylindrical oscillator with flexible bottom is placed in the container. The oscillator is driven harmonically by a motor. During the experiment, the deflection of the flexible bottom, the motion of the free surface and the driven force were monitored and recorded. The figure 2 is the photo of the experiment. In order to better understand Rizos’ experiment, a series of researches are conducted in the Section Ship Hydromechanics, which includes analytical simulation and several numerical simulations with different methods. A linear algorithm is developed in this thesis, which applies implicit, monolithic (solving the fluid domain and structure domain simultaneously) and one-step (without iteration) methods. The model of the numerical simulation is shown in the figure 3, a small cylinder with flexible bottom is placed in the big cylindrical container. The two cylinders are partially filled with water and the still water levels are the same. The inner cylinder does not moves up and down as a whole. The oscillation of the whole system is the result of the initial wave elevation in the fluid domain and/or the initial deflection in the structure domain. The result of the numerical simulation is shown in the figure 4. The effect of added mass for a structure submerged in water results in that smaller eigen frequency of the structural vibration. The structure interacts with the ambient fluid, especially the free surface. For a pre-defined initial condition, the influence of the free surface results in the mode dispersion. The numerical periods of this FSI system agrees with the analytical periods. Significant numerical dissipation exists in the 1st order time integration techniques. Thus, the second order implicit Adam Moulton method, i.e., the trapezoidal rule, is implemented to improve the algorithm. in this way, the numerical dissipation is decreased drastically (5% less dissipation after 10 periods) without increasing the computational costs.

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.