Hydrodynamic Numerical Calculation Method of Small-scale Objects in Ocean Engineering Based on Immersion Boundary Method

Abstract

Isolated piles, jacket platforms, submarine pipelines, etc. are ubiquitous structures in marine engineering. When the ratio of the lateral dimension D to the wavelength L of the part surrounded by waves is less than 0.2, it is generally called a small-scale structure. Current and waves are the two most important external loads in ocean engineering. The interaction between current and waves and small-scale structures in ocean engineering has always been the focus of research, and it is also one of the main problems that have not been well resolved in ocean engineering. In this paper, under the premise of considering the viscosity, turbulence and free surface flow of the fluid, the hydrodynamic problems related to small-scale objects in marine engineering are selected as the research content, and the numerical calculation model combining the immersion boundary method and the fluid volume method is selected for numerical calculation. The numerical expressions, solution steps and method verifications of the immersion boundary method and the fluid volume method are given respectively. A numerical calculation method by directly solving the external force source term in the immersion boundary method is proposed. The advantages, disadvantages and calculation steps of two different processing methods of applied force source terms in the immersion boundary method, continuous force method and discrete force method, are given. Instead of solving the force source term by means of interpolation and extrapolation, this paper adopts the discrete force method and the immersion boundary method for numerical calculation. Bounds method for numerical calculation. The realization process of establishing the numerical model of the immersion boundary method is given in detail. The finite difference method is used to discretize the governing equations and the semi-implicit two-step projection method is used to solve the NS equation. Finally, the numerical model of the immersion boundary method is given. Numerical realization process. The numerical model established in this paper is verified by the classical examples of numerical calculation of flow around a fixed cylinder and a flow around a rotating cylinder under laminar flow conditions, and the numerical calculation results are compared with the experimental and numerical results of others. The established numerical calculation model is correct and feasible. Experiments show that this model can well generate first-order Stokes linear waves. When a=0.25, according to the method proposed Frontiers in Ocean Engineering 2 in this paper, the lift can be reduced to 75%-80%; when a=0.5, the lift can be reduced to 60%; when a=0.75, the lift amplitude can be suppressed to 50% or less.