A Simplified Method for Analyzing Water Impact in the Initial Stages on an Elastic Rectangle Plate

Abstract

For most flat-bottom marine structures, impact loads are generated by complex transient coupling effects of solid, air, and water. However, simplified forecasting methods to obtain impact loads and dynamic responses of flat-bottom structures by considering both hydroelastic and air cushion effects are rare. In this article, a new simplified analytical method of water impact on the elastic plate is proposed based on Verhagen's model for the rigid plate. The analysis is focused on the initial stage during which the highest hydrodynamic loads are generated. Interactions between the plate, the air, and the water are simulated and analyzed. Also, fluid-structure coupling results by simplified method are compared with numerical results from Arbitrary Lagrangian-Eulerian method in LS-DYNA code. Experimental results are used to validate the feasibility and accuracy of the simplified method. Water impact on plates with different drop heights, rigidities, and added mass is analyzed. The air cushion effect, elastic effect, and three-dimensional effect in the simplified model are also discussed. 1. Introduction Over half a century, there has been more and more attention given to the phenomenon known as "slamming" which exists widely in both the natural environment and engineering application. As a complex transient process, slamming can be considered as a three-phase coupling model containing solid, liquid, and gas. Water entry problem is one of the most typical phenomena of slamming. The problem of a rigid wedge entering water was studied in detail starting from the thirties of the last century. This study was motivated by the design of hydroplane landing on water. Von Karman (1929) first carried out an analytical study on water entry problem by potential theory. Considering the deformation of the water surface, Wagner (1932) extended the Von Karman model. In the following several decades, many complex models of water impact were developed by Wagner model (Hirano & Miura 1970; Armand & Cointe 1986; Cointe 1991). In addition, new models are proposed (Dobrovol' skaya 1969; Greenhow 1987; Howison et al. 1991; Muzaferija et al. 1997). More factors in the water impact problem were taken into consideration, including gravity (Greenhow 1987), liquid viscosity (Muzaferija et al. 1998), liquid compressibility (Korobkin 1996; Korobkin 1997; Campana et al. 1998), and so on.