Numerical And Simulation Studies Of Slamming Load For 3D Axisymmetric Geometries

In recent years, with the development of marine industry people have recognized the damage of slamming in actual projects and started to pay attention to this problem. Especially for large marine engineering equipment in bad sea conditions, it is one more severe challenge.The instantaneous huge impact generated by the violent collisions between the structures and the waves could lead to a sudden rupture of the structures. Even if the structure remains no damage in short terms, as time passes the high-frequency vibration caused by slamming can also lead to a final fatigue of the structure itself. So the studies of the impact generated in the slamming phenomena should be important and valuable in the design of the marine structures.The theory of algorithm based on 3D BEM for slaming impact calculation and its application is mainly talked about in this paper. The 3D mechanical model and Wagner’s theory which considering the uplift free surface were both used in the numerical code. Cw which was called wetting factor was introduced here to ensure the exact height of the uplift free surface and at the calculated height a new free surface was built which was called"effective water surface" in this paper. The grids’movement was also considered here and the coordinates of the nodes at every time point were calculated so that the wet grids could be traced exactly. Near the effective water surface one group of grids were modified for a precise wet area. After a series of loop computation two kinds of load could be determined which one is the hydrodynamic pressure and the other is the total slamming force. Numerical simulations for the Nisewanger and Alaoui’s slamming test of 3D axisymmetric geometries were conducted to measure the code’s accuracy and applicability.In order to improve the applicability of the code in the whole slamming process a solution to the problem was proposed by means of designing the boundary-element model.This method make the code be not only used in the entering process but also in the flooding period in which the highest point of the model was below the effective water surface.Considering more and more kinds of structure form and moving form exists in the practical engineering, the Ls-dyna code,an explicit finite element analysis program,was introduced at the end of the paper. 2D and 3D simulation were both conducted using the Ls-dyna code. The calculated results were both compared with Faltinsen and Nisewanger’s slamming tests’ data for assessing the Ls-dyna code’s applicability.