Study on the characteristics of impact load of wedge during water entry based on a fully nonlinear boundary element method

DOI:	10.11809/bqzbgcxb2024.06.004
Keywords:	water entry impact; free fall test; boundary element method; stretched coordinate system; impact pressure;wall effect
Abstract:	The problem of water entry impact of structures such as water entry of weapons and aircraft landing water surface is a strong nonlinear fluid solid coupling problem. The division and reconstruction of grids, numerical stability and transmission, and the accurate solution of the jet root in the calculation usually restrict the success or failure of the calculation simulation. A boundary element method that fully satisfies nonlinear boundary conditions were established in this paper, which were used to predict impact loads more accurately. By introducing a stretched coordinate system, the problems of grid reconstruction and numerical transmission on the free liquid surface were solved effectively.By introducing an auxiliary function, the motion equation in the time domain is decoupled, and the velocity, acceleration and impact pressure of the wedge at each time step are accurately solved. The validity of this numerical method is verified by a free fall test of a two dimensional wedge. The results show that the fluid gravity has a significant effect on the impact pressure. The water entry impact pressure of the wedge with 45° dead rise angle is mainly distributed in the half width area of 1.6 times the depth of water entry. The peak and sub peak pressure generally occur at the tip of the wedge and the root of the jet. The impact pressure of the wedge is very sensitive to the smaller bottom angle. In this paper, the nonlinear relationship between the two is described quantitatively. There is no significant correlation between the wall effect and the initial velocity of water entry, but the smaller the dead rise angle, the more significant the wall effect. When the water entry depth of the 45°dead rise angle wedge is less than 1/3 of the water depth, the wall effect is particularly obvious. The research results provide a reference for theoretical research and engineering applications.
Published:	2024-06-28
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