At present, computational fluid dynamics (CFD) is widely used in the field of ships and the sea. The Cartesian grid CFD algorithm has the advantages of simple mesh division, small numerical dissipation and fast calculation speed. The Cartesian grid CFD method is based on a cartesian coordinate system and the finite difference method is used to discretize the N-S equation in space. A compact CIP method (constrained interpolation method) with third-order accuracy is used to solve the convective term, which can restrain the numerical dissipation effectively. By introducing the CIP improvement method, namely THINC/SW algorithm, it can effectively simulate wave propagation, climbing, rolling, breaking and other violent free surface motion. In this paper, the Cartesian grid algorithm is used to simulate irregular waves. By changing the mesh size, time step, number of linear wave superpositions and transition function type to study and compare with the wave spectrum. The effects of various factors on the accuracy of wave simulation are analyzed and the appropriate wave simulation strategy is finally proposed. The results show that the simulated irregular wave inversion results agree well with the theoretical wave spectrum by using the Cartesian grid CFD algorithm and selecting appropriate parameters. Therefore, the algorithm can provide the basis for the accurate prediction of slamming load and ship structure design.
At present, hydrodynamic research is very important in the field of Marine structures. The accuracy of wave numerical simulation directly affects the accuracy of load simulation. The wave simulation methods mainly include potential flow simulation, viscous flow simulation and coupled potential-viscous flow method. Because irregular waves with viscosity are closer to the real environment of Marine structures, CFD numerical simulation of irregular waves has attracted much attention.
Gatinet et al. (2017) proposed a framework for efficient irregular wave simulations using higher order spectral method coupled with viscous two phase model. Based on this method, he conducted a numerical simulation of three-dimensional extreme waves encountered by a large container ship. Wang et al. (2019) presented a multi-directional irregular wave implementation in the open-source CFD model REEF3D. The non-directional frequency spectra Joint North Sea Wave Observation Project (JONSWAP) together with a cos-squared-type directional spreading function is used for the simulation. Ramezanzadeh et al. (2019) proposed a numerical scheme to model irregular wave systems through a Lagrangian, particle-based numerical method, namely, Smoothed Particle Hydrodynamics (SPH). Uniform current effects on the characteristic of irregular waves along with its uncertainty are presented considering wave-current interaction in the actual ocean environment by Yao et al. (2021). Based on the given or real times series in certain space along the incident wave boundary, Luo et al. (2022) established the Inhomog-Bound-EEED and Inhomog-Bound-PTPD methods for simulating the inhomogeneous incident wave boundary of the multidirectional irregular waves. In the numerical calculation domain, some scholars generated waves by means of source function method, such as Liu et al. (2005), Kim et al. (2007) and Luo et al. (2019), some by model coupling approaches (Yang et al., 2013). At present, there are intensive studies on irregular wave with numerical methods. But the feasibility of irregular wave numerical simulation by using the Cartesian grid CFD algorithm, especially the numerical dissipation characteristics of long-term simulation were not studied.