This work studies crownwalls with a fully curved face versus a vertical wall in non-breaking wave conditions. Its aim is to provide appropriate tools that can be used to compare the performance of the two structures in terms of loading and overtopping. To this end, small scaled experiments of the two structures are carried in a flume with a flat bottom. These are performed in intermediate water depths and consist of different combinations of wave height and wave steepness. A box is positioned behind the superstructures to collect overtopping volumes. Pressure signals are retrieved from pressure sensors positioned on the surface of the crownwall and the vertical wall, while water elevation signals are retrieved from wave gauges in the flume and in the overtopping box. Several analyses are performed in order to retrieve results of individual waves regarding the wave characteristics, reflection coefficient, overtopping volume, maximum pressure, impulse, impulse duration, maximum force, force angle and point of application of the force. The effectiveness of the crownwall in reducing overtopping volumes is found to decrease for more severe wave attacks with larger wave height and wave length. The lowest loading cases result in a quasi-static pressure signal which has approximately the same maximum value for both structures. More severe wave attacks generate impacts at the seaward top outer edge of the crownwall, which result in an increase of maximum pressure up to 1100%. For these cases, impulses are calculated and the results are found to be less uncertain compared to maximum pressure, while their duration shortens for higher and longer waves. The variables describing force are retrieved by integrating the pressure signals on the surface of the superstructures and the results of maximum force are found to follow a similar trend to these of maximum pressure. Corresponding equations from curve fitting are derived for each of the mentioned variables regarding the crownwall. In lack of design overtopping formulas for regular waves, an equation is derived for the prediction of overtopping for the vertical wall in order to allow comparison between the two shapes. The formula of Goda is evaluated for the case of the vertical wall and is found to accurately predict pressure at still water level, while it underestimates pressure at higher positions. Nevertheless, using this formula to estimate loading on a vertical wall is suggested due to its range of applicability and high accuracy at still water level. These equations can serve as a tool to compare solutions of a crownwall and a vertical wall, and assess which of the two is the optimal solution.

Coastal structures with horizontal overhangs are built due to design constraints, but wave loadings substantially increase under these confined geometries. Vertical structure elements, such as steel gates, are vulnerable to damage caused by impulsive wave impacts, potentially exposing the coastal zone to flooding and erosion. Existing formulas to determine impulsive loadings in engineering practice are limited to purely vertical structures. Research has shown that openings along the surface of structures relieve wave impact pressures, but there are currently no design methods available to quantify this pressure release. The stochastic nature of impulsive impacts and uncertain influence of air adds to the problem complexity. This study aims to investigate the influence of ventilations to reduce wave impact loadings on vertical structures with horizontal overhangs, applying a theoretical pressure-impulse approach and computational fluid dynamics. In this study, the pressure-impulse model is implemented for experimental cases in two and three dimensions using a finite difference numerical scheme and validated against semi-analytical solutions with high accuracy. Boundary conditions are modified to include and assess the influence of venting holes on the pressure-impulse contours. To achieve the largest efficiency in the reduction of pressure-impulses, rectangular ventilations are located at the critical corner between vertical wall and overhang and spaced across the structure width. Based on physical model dimensions, the open source CFD software OpenFOAM is also employed to simulate standing wave impacts on structures. Waves are generated in the CFD model using the waves2Foam toolbox, in conjunction with the OceanWave3D utility. Convergence of the CFD model is achieved by gradually refining the mesh near the wave impact region. Validation between simulated and experimental total wave forces on the vertical wall shows very good agreement for both overhang sizes considered. The distribution of first impact pressure-impulses along the vertical structure show similar trends among the pressure-impulse theory and CFD models. While large discrepancies are observed for predicted maximum pressure-impulses, the relative error of total impulse at wall between both models is low. From both CFD and pressure-impulse model results, empirical relations are derived between relative venting area and total impulse release. The assumption adopted in the theory of zero pressure-impulse at the venting position is not reproduced in CFD results, which leads to overestimation of the impact mitigation effects of ventilations using the pressure-impulse theory. This divergence in the venting boundary condition is possibly linked to the omission of convective acceleration terms in the pressure-impulse model. Two ventilation design methods for vertical structures with overhangs subject to wave impacts are proposed based on the research conducted in this study. The first design method employs the derived empirical relations, standing wave theories and theoretical pressure distributions to determine the total impulse affecting the structure. The second design method applies the splitting approach of measured impulsive forces with low-pass filters to calculate the total impulse, requiring numerical or physical modelling. Further research is needed to support the models with small and large scale experiments using ventilations and expand the validity range of the results.

Wave impact on vertical structures with overhangs is studied. 3 research questions are addressed: 1. How does the entrapped air change during the process of wave impacts ? 2. How is the wave loading influenced by the presence of horizontal overhang ? 3. How is the wave loading influenced by the presence of air pocket?