Hydraulic structures can be prone to impulsive wave impact, which is a highly stochastic and uncertain process. This type of impact, defined by extreme pressure peaks and a very short duration, is not only caused by breaking waves, but also by non-breaking standing waves on structures with an overhang, such as culverts and steel gates. In this study, the capabilities of the Lagrangian numerical tool Smoothed Particle Hydrodynamics (SPH) are validated by means of experimental research conducted at the Hydraulics lab of the Delft university of Technology, in which two short overhang configurations were subjected to multiple non-breaking wave conditions. SPH distinguishes itself by discretizing the numerical domain in particles instead of a grid, unlike traditional computational fluid dynamics (CFD). In doing so, it excels in free surface modelling and complex wave-structure interaction. In this thesis, the theory of pressure-impulse is applied, which is defined as the integral of the pressure over the impact duration. This method is more stable than using pressure peaks and can be used to obtain the reaction forces on hydraulic structures. However, the theory is in development and subject of recent literature. This research includes the theoretical pressure-impulse model, which is based on the Laplace equation and solely includes the vertical impact by assuming a circular profile under the overhang with a constant impact velocity. Furthermore, a new conceptual model is introduced, which is based on integration by the particle velocities in both horizontal and vertical direction as described by Linear Wave Theory. The assumptions of the velocity fields of both models are assessed by the SPH method. As a result, modifications are proposed to the conceptual model and validated with the experiment. SPH shows good agreement with the experiment in terms of wave generation, pressure distribution and pressure-impulse profile. However, the lack of air in the numerical model result in overestimations of the pressure peaks. The more air is entrapped in the experimental wave impact, the higher the deviation. That said, the impact duration also becomes longer the more air is entrapped while the SPH model shows a somewhat constant and shorter duration. As a result, the pressure-impulse profiles shows corrective behavior over the vertical, mitigates the absence of air and thus greatly increases the accuracy and stability of the results. Finally, an analytical validation is performed in which the theoretical models for overhang configurations and design formulae for vertical walls are compared to SPH and the experiment.

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?

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.

At this moment hydraulic structures are designed based on a simple method: the Dynamic Amplification Factor (DAF) method. This method does not consider the full dynamic interaction between the wave impacts, structure and water. The research project DynaHicS focusses on the dynamic behaviour of hydraulic structures, taking into account fluid-structure interaction (FSI). The main goal of the DynaHicS project is to develop new design guidelines to identify dynamic behaviour of hydraulic structures, so that more economical designs can be made in the future. The master thesis focusses on improving the current design method, which can contribute to the development of a new design method for hydraulic structures in the future. The present design method, the DAF method, is extended in time and space. This is done by developing a method to determine the force-time signal of multiple wave impacts, whereby the results from scale model tests are no longer required. In this method the spatial variation (height and width) of the wave impact force over the structure surface is taken into account.

A new semi-analytical model is developed to predict the dynamic response of slender gates in combination with an overhang, which are subjected to standing waves. Still little is known for these types of gates for this specific forcing type. The semi-analytical model is still in its development phase and must be validated on its performance. This thesis aims for validation of the modal calculations performed by the Semi-Analytical model for submerged gates, which include fluid structure interaction. Several experiments were executed in the wave flume at the faculty of Civil Engineering at the Technical University of Delft. Dry hammer tests, wet hammer tests and wave tests were executed for different water levels. Different plates were investigated in the experiments: Solid Plate and Reinforced Plate. A measurement plan was designed to obtain reliable results from the measurement devices (strain gauges and accelerometers). The experimental data was subjected to an Experimental Modal Analysis algorithm. The Frequency Domain Decomposition turned out to be most suitable for this situation. The mode shapes that were found were subjected to a Modal Assurance Criterion (MAC), in order to compare them with the semi-analytical prediction. The results from the wet modal analysis showed that the Solid Plate had good correspondence with the prediction of the semi-analytical model. The mode shapes turned out to have a high MAC values, while the natural frequencies showed small relative errors for the modes under consideration. The Reinforced Plate was less accurate. In the wave experiments the first three modes were found, which were also believed to have the highest energy input. Considerable high MAC values assured that the identified modes were indeed the same as the modes of the semi-analytical prediction. The natural frequencies showed larger errors for especially the first mode (approx. 30%). It was observed that several measurement errors might have influenced the results of the Reinforced Plate. After finalizing the experiments for this plate, I discovered that the stiffeners and front plates came loose from the U-frame. The dynamic quantities of the Reinforced Plate were therefore adjusted during the experiments. The datasets of the experiments that were most trustworthy were selected for the different analyses. The Regular Wave Impact experiments showed good correspondence and where therefore assumed to be correct. The Solid Plate was concluded to behave as predicted by the semi-analytical model. High correlation between the predicted and identified modes and small errors in the natural frequencies were observed. The data from the Reinforced Plate showed that the high energy modes were identified for the wave experiments. Modal shapes had high correlation between predicted and identified ones, while the natural frequencies had somewhat large errors. It was observed that small natural frequency errors for the input modes resulted in relatively small errors for the calculated modes. Further validation of the model should focus on the prediction of maxima and time series of the response. The step from modal analysis to a time series is a final step in the semi-analytical model.

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.