Slamming force decomposition with gravity effect

Abstract

In this paper, the original slamming force decomposition, where the total vertical slamming force is decomposed into speed and acceleration terms with coefficients depending on the penetration depth only, is further developed by including the gravity effect through an additional term that is only dependent on the penetration depth as well. The speed, acceleration and gravity related coefficients are extracted by Computational Fluid Dynamics (CFD) approach, where gravity can be readily included or excluded, using only small number of CFD computations for particular body motions. Then the components of the hydrodynamic force acting on the entering body can be evaluated using these coefficients and the force decomposition formula for any motion of the body avoiding direct CFD computations for each particular motion. CFD results show that the gravity significantly affects the slamming force for relatively small values of the entry speed. It is shown that the improved force decomposition provides an accurate approximation of the computed forces under various speed/acceleration combinations for arbitrary two-dimensional body shapes including vertical entry of symmetric/asymmetric bodies and oblique entry of symmetric bodies, except for penetrations with large deceleration when the body stops shortly after the flow separation.