Parametric study of a new HOS-CFD coupling method in OpenFOAM

A new numerical method of potential theory High-Order-Spectral (HOS) coupled with CFD method is introduced in this paper. The CFD method is applied by our solver naoe-FOAM-SJTU developed using tool package of OpenFOAM. The HOS method provided the external wave information, and wave-structure interaction will be simulated in CFD domain. This kind of coupled method can reduce the calculation sources and solve wave-structure interaction in nonlinear wave conditions efficiently.

To bring this new coupled method into application, the steady of wave propagation is considered. A periodic boundary condition is employed to test the numerical steady of the interpolation zone, which is the relaxation zone. The relaxation zone is used for importing the wave signal of HOS domain into CFD domain, therefore it’s important to test the numerical error in it. The wave condition is a nonlinear regular Stream Function wave. The dissipation error due to mesh generations or time integrated schemes during the wave propagation is also discussed. After the verification of the interpolation zone, the parametric study of length of the relaxation zone is considered.

In engineering, the most common conditions which meet by ocean structures is nonlinear wave conditions. However, the nonlinear wave condition is not easy to simulate well in CFD. A parametric study of nonlinear wave propagation in CFD zone is considered. Mesh convergence, time step convergence and length of relaxation zone are all carried out. Meanwhile, a FPSO is put into the viscous wave tank to test the size of CFD zone. To achieve a better solution with least calculating resources and best numerical results, the length of relaxation zone and CFD zone are all discussed. These parametric studies can give reference to employment of the potential-viscous coupled method.