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ON THE USE OF A POROUS-MEDIA APPROACH FOR THE MODELLING OF WAVE INTERACTION WITH THIN PERFORATED CYLINDERS
This work evaluates the use of a porous-media approach for CFD modelling of the wave interaction with thin perforated cylinders. A detailed model which resolves the microstructural geometry is possible, but the computational requirements for this are prohibitive. Alternatively, the impact of the porous structure on the flow can be represented using a volume-averaged macro-scale model. Since this can be beneficial in terms of computational cost as well as mesh generation efforts, the porous-media approach could be an efficient approach for marine engineering applications where large-scale effects are of the main interest. This method has only been used for large volumetric coastal structures yet and is now evaluated in the new context of thin perforated cylinders. The OpenFOAM Foundation v5 is used in combinations with and modifications of the OlaFlow and waves2Foam libraries. Both of them use solvers based on the volume-averaged RANS-equations and provide wave modelling boundary conditions. For thin perforated sheets in oscillatory fluid flow, the flow regime tends to be turbulent. Hence, a constant turbulent drag term with the drag coefficient described as a function of porosity is applied as a momentum source term in order to represent the porous structure. Two types of porosity implementation in terms of material characteristics are assessed. One method adopts the assumption that the pressure drop through the porous material is independent of the flow direction by means of isotropic material characteristics. The other represents porosity with anisotropic properties where a pressure drop is only applied in the normal direction to the porous surface assuming that the pressure drop is related to the flow velocity normal to the surface. For the present models, both the isotropic and anisotropic porosity representation are used in combination with and without the application of the k-omega-SST turbulence model The CFD results are compared against experimental results and the differences between the two porosity implementations as well as the effect of the turbulence model are assessed for one combination of wave and porosity parameters.