Green water events—where large masses of water wash onto a ship’s deck—pose a significant threat to breakwaters and other deck structures. The impacted structures are often treated as if they were rigid, overlooking potential hydroelastic responses. This thesis investigates the role of hydroelasticity in green water impacts on forward-tilted, flexible breakwaters through a combined experimental and numerical study. The research question of this thesis is ”What is the importance of hydroelastic effects during a green water impact on a steel breakwater?”, which was divided into four sub-questions:

RQ1: What is the relation between the variables of the impact (plate angle θ, fluid wedge angle α, impact velocity v) and the resulting load and pressure during impact of a rigid plate?
RQ2: For what combination of θ, α, v and plate stiffness does hydroelasticity occur during impact of a flexible plate?
RQ3: In what manner does hydroelasticity affect the load on the breakwater and what is the magnitude of these effects?
RQ4: What is the magnitude, shape and frequency of the deformation that occurs during a hydroelastic impact and what is the relation between the variables of the impact (θ, α, v, plate stiffness) and the resulting deformation?

Experiments were conducted using a sloshing tank that generates wave impacts that are similar to dam-break type green water events. A range of plate angles and thicknesses was tested to capture rigid and flexible responses. Load cells, pressure sensors and laser displacement sensors measured force, pressure and structural deformation. A high-speed camera was used to study the shape and velocity of the incoming wave.

Numerical simulations performed with a VOF type numerical method based on the Navier-Stokes equations provided initial estimates of force magnitudes, rise times, and impact velocities. Comparison with experimental data showed similarities between the numerical model and the experimental data, but differences were also found. In part, these differences could be attributed to the numerical method being a one-phase model which means that the effect of air entrainment was ignored by the solver.

In the experiments, a large hydroelastic effect on the maximum impact force and the force over time was found. Rise times were decreased and force maxima were increased by up to 31% or decreased by up to 49% relative to the maximum force on the rigid breakwater. Maximum deformation was reduced by up to 83% relative to deformation that was predicted by a quasi-steady analysis. It was concluded that the interaction between deformation and wave loading should always be considered, because this interaction can significantly affect the applied loads and the deflection of the structure.