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.

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%.

Jumbo Maritime is a heavy lift shipping and offshore transportation & installation contractor. The Fairplayer is one of the J-class vessels that is capable of performing offshore installation work. The two 900 ton Huisman cranes can lift up to 1800 ton combined, but the insufficient static stability of the Fairplayer results in a maximum lifting capacity of 1000 ton in offshore conditions. This limited lifting capacity in offshore conditions is a missed opportunity to make use of the Fairplayer in a wider segment of the offshore installation market. In this research, the increase of static stability is obtained by the use of a sponson. A sponson is an extension of the hull, which can be seen as a local widening on the side of the Fairplayer. This sponson is expected to result in an increase of the total resistance. The goal of this thesis is to investigate the influence of the position and shape of a sponson on the Fairplayer with respect to the resistance. The influence of the position and shape of a sponson is analysed by the variation of the longitudinal position, the vertical position and the length over width ratio of the sponson. A combination of the Holtrop-Mennen method and the potential flow program RAPID is used to give an estimation of the increase in resistance. RAPID is used to calculate the influence of the wave-making resistance of the Fairplayer, whereas the frictional resistance is calculated according to the ITTC-57 flat plate friction formula and a form factor. It can be concluded that the position of the sponson turned out to have a significant influence on the wave pattern and therefore on the wave-making resistance of the vessel. The sponson can be positioned in a way that the wave system generated by the sponson interferes with the wave systems generated by the vessel. With this combination of the Holtrop-Mennen method and RAPID, a position of the sponson is found where the increase of the total resistance is minimized to 7%.

This master thesis describes a method to determine the workability of an offshore heavy lift operation. By creating wave realisations based on and statistically equivalent to measured ocean weather data, a quick assessment of the risk of failure can be achieved.