Combined force decomposition approach and CFD simulation methods for 2D water entry and exit problem

Abstract

The force decomposition approach is extended to solve the two-dimensional (2D) water entry and exit problems. Two typical scenarios, direct water exit and continuous water entry and exit, are examined. It reveals that the total force is irrelevant to the body velocity but to the acceleration. More specifically, the force can be expressed as the multiplication of constant values, body acceleration and a non-dimensional coefficient, and the coefficient is related only to the displacement and immersion condition of the body while independent of its motion condition. Two typical body shapes, a widely used wedge model and a practical ship section model, are examined here. CFD simulation is employed here to directly extract the non-dimensional coefficients, which avoids complex calculations for the wetted length of body by analytical models. The force decomposition approach with the obtained coefficients provides a means to quickly and accurately predict the hydrodynamic force acting on body for water exit scenarios. The proposed method is verified by comparing its results with CFD simulations in the complicated motion cases with varying acceleration. Furthermore, this work provides a potential tool to calculate the total force acting on any entire 3D hull that is divided into several independent 2D slices.