Numerical modelling of wave forces acting on circular piles

Abstract

Pile supported structures have a wide range of use in the offshore industry. These structures are much expensive to build. Therefore, it is important to evaluate unpredictable results before implementation. At this point, physical models are very convenient for designers and help to optimize the design. However, these types of models have some difficulties in terms of time and cost. With the help of numerical models, this loss of time and cost can be reduced significantly. In addition, numerical models provide flexibility in the design process of complex structures, but it is important that the results of numerical models must be compatible with the results of physical models. In this study, it is aimed to model a pile subject to waves. In order to solve the numerical model created within the scope of this study, the open-source REEF3D tool is used. A mesh convergence study has been done for the numerical domain and the optimum mesh size has been calculated. Secondly, relevant experimental data for wave run-up is compared with the numerical model. For that purpose, the surface profile at a certain point of a wave propagating to a coast with a slope of 1:6 had been replicated numerically. As a result, it has been seen that the wave profile obtained from the numerical model agrees well with the wave profile obtained in the experimental study. Hence, as a final step, a pile is located on a plane bottom and non-breaking wave forces acting on it have been calculated for various wave heights and periods. Wave force results and wave surface elevations are compared. Comparison of wave forces is done with the empirical formulae proposed by Morison and with a new approach presented by Beji. For the surface elevation comparison, a wave gauge is located 1.5 times of wavelength away from the inlet boundary to generate the wave surface of the simulation and a theoretical wave with the parameters used in the simulation is generated and compared. It has been seen that the wave surfaces showed an agreement as the wave force calculations did. The results for both wave run-up and wave forces show promise that REEF3D is much capable tool for CFD world, especially for civil engineering use. This study does not cover the non-breaking wave forces and wave forces acting on floating bodies. A further study, however can be done using the same tools with available experimental data.