Numerical and Experimental Investigations on the Impact on water of Simple Metallic Structures

Abstract

In order to improve the knowledge of the numerical simulation methods for analysing structures impact phenomena on water, the Italian Aerospace Research Centre (CIRA) has performed two campaigns of drop tests on water. The intention was to generate an experimental database to be compared with the results coming from the numerical simulations performed with different methods. The main objective of this paper is to show the correlation between the experimental results coming from the impact tests on water performed on semi-circular structures made of two different materials (steel and aluminum), with the results obtained from the numerical simulations performed at DLR. The tests campaigns were performed at CIRA/LISA laboratory using the drop tower. Each campaign, one for the steel structures and the other for the aluminum ones, consisted in two main tests. The first test had to simulate a rigid body behavior with no plastic deformations while the second test had to simulate a deformable body behavior. The test articles have been provided with sensors suitable to catch the main parameters (accelerations and pressures) characterizing the phenomena. Furthermore, to support the simulation activities a dedicated mechanical characterisation to evaluate the stress/strain curve at different strain rate was performed too. The simulation activities comprising pre-test and post-test analyses were performed with the PAM-CRASH code, in which the behavior of water was modeled using the Smoothed Particle Hydrodynamics (SPH) method. Using a gridless method especially enables to get rid of mesh distortion, which is a major concern when large deformations are expected as in an impact on water. In a first step, the simulations helped defining the impact velocities for both structures types according to the above mentioned requirements. In a post-test phase, calculated deformations were extensively compared to the structures deformations observed after the test. In addition, acceleration and pressure time histories gained from the tests and the simulation work were correlated.