This study investigates the effect of dynamic properties of a structure on the magnitude of impacts loads of breaking waves. A literature review in the field of violent wave impact on flexible structures is done. From this review, it is concluded that the hydro flexibility of structures have great impact on the fluid-structure interaction. In earlier studies, it is found that models of constructions in breaking waves are not accurate yet, using knowledge that is available up until now. There are studies that show suggestions of influence on the structures own properties. However, no extensive research had been done in this field. That is why the main objective of this study is to research if the natural frequency of a construction is of influence on the impact force of violent waves.

To answer the research question, a model is made and an experiment is carried out. The model consists of two parts, first a pendulum is used to represent a simplified structure to interact with a breaking wave. Using the model, a simulation of pendulums with different natural frequencies is done. The pendulums interact with the same wave each time. The second part of the model consists of a beam that is impacted by a breaking wave. Simulations are carried out where beams with different natural frequencies are impacted by the same wave.

To verify the model and further elaborate on the research question, an experiment is done. This experiment is done in the Sloshing rig at the faculty of Mechanical Engineering at the TU Delft. During the experiment, four different plates with different natural frequencies are used. They are exposed to the same wave impact each time. The model and the experiment results are compared and used to form a conclusion.

It is concluded that wave impacts are of higher magnitude on structures with a higher natural frequency. The difference between the measured and predicted forces indicates that the fluid- structure interaction of these plates lead to this difference. This can be explained by the different fluid- structure interaction for plates with different natural frequencies. If velocities of the plates with higher natural frequencies are higher, the Morison component of the impact force becomes larger. Therefore these impacts can become higher than for other structures. As the natural frequency of the plate increases, the results show relatively higher measured deflections as well.

To facilitate the installation of larger monopiles multiple players in the offshore wind market are investigating the floating transport of monopiles to installation locations. This brings the challenge that when these floating monopiles are to be installed by heavy lift vessels, they must safely be handed over to the installation vessel and hooked onto the main crane of the installation vessel for installation. Current literature mainly focusses on two topics. Some studies exist on the behaviour of a floating monopile near a heavy lift vessel. Studies also exist that study the behaviour of a monopile hanging on the crane of a heavy lift vessel. The step between these two moments in time, where the floating monopile is handed over from the tug towing the monopile to installation vessel, is the focus of this study. This thesis presents a method for the hooking of a floating monopile to the crane of heavy lift vessel Oleg Strashnov and a model for the hooking operation. This model is used to determine a maximum allowable sea state for this operation. Two methods for hooking a floating monopile to the crane of a heavy lift vessel were defined. In the first option, the monopile would be moored alongside the vessel and kept in position by a supporting tug while the rigging is handed over to the heavy lift vessel and the rigging can be hooked onto the vessel crane. The second option entails positioning the monopile perpendicular to the heavy lift vessel, with fenders placed between the monopile and vessel...

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.