Wave impact on rigid and flexible plates

Wave impact on offshore and coastal structures, such as oil and gas rigs, offshore wind turbine platforms, breakwaters, flood protection systems and wave energy converters, involve complex wave-structure interactions. These interactions are particularly challenging for flexible structures and may result in structural damage in extreme cases. Some studies found reduced wave forces on flexible compared to rigid walls. However, the technical literature includes inconclusive results on this aspect and an accurate understanding of wave-structure interaction is still lacking. The present study comprehensively investigates wave-structure interaction with the numerical toolbox solids4foam to resolve this shortcoming. The numerical pressures, forces and plate deformations have been successfully validated with new and already available laboratory experiments, e.g. the numerical plate displacement deviates less than 35% from the laboratory observation. 117 two-dimensional (2D) tests of waves impacting plates of different stiffnesses located in the open sea (offshore) and on the coast (onshore) were then conducted, complemented with 2 three-dimensional (3D) tests with offshore plates. For most of the offshore and onshore tests, the plate stiffness had a negligible effect on the upwave force. However, for the most flexible offshore plates, the downwave water depth increased due to plate deformation, resulting in up to 40% smaller total forces on the flexible than the rigid plates. This was also confirmed in the 3D tests. The response of the offshore plates was then successfully examined in view of the Euler–Bernoulli beam theory. In the onshore tests, the wave force showed two peaks confirming previous observations. The second force peak was up to 3.3 times larger than the first one, with the rigid plates not necessarily resulting in the largest peaks. New semi-theoretical correlations to predict wave forces on onshore plates are finally suggested, as a simple function of the offshore wave energy. Such findings enhance the physical understanding of wave-structure interaction and are aimed at supporting the design of coastal and offshore structures.