Experimental and numerical investigation for a reliable simulation tool for oblique water entry problems

Oblique water entry of different marine structures involve several two-phase fluid dynamics phenomena including splash, asymmetrical cavity formation and cavity collapse that have been observed in experimental work. Correct prediction of the applied forces and moments that define the trajectory during water entry is dependent on precise simulation of the mentioned fluid dynamic effects. This study investigates and compares the performance of three different algorithms. i.e.: a) finite volume Eulerian; b) finite difference Eulerian, c) Arbitrary Lagrangian Eulerian (ALE), applied in different software codes. In order to achieve this goal, an experimental task, including normal and oblique water entry cases, was defined to provide the data set for comparing and verifying performance of these different software packages. These experiments have been designed and implemented, concentrating on oblique water entry of blunted nose models with various moment of inertia, center of gravity, and other dynamical properties that affect the water entry problem. Verification of computational results of the three software are carried out through comparison with the experimental results in two stages. Firstly, the fluid dynamics of splash, cavity formation and its collapse for normal water entry of a sphere are compared between experimental and three software numerical results. It is shown that two of the codes, i.e. "a" and "b" as defined above, cannot even predict the much simpler problem of normal water entry problem, therefore, fail to be a candidate for the more involved problem of oblique water entry, i.e., the second stage of the comparison. Through comparison with the experimental results it is shown that ABAQUS software, i.e. the "c" algorithm, is the most capable software among the three compared codes for the correct simulation of the involved fluid dynamic effects. Therefore, the ABAQUS software is applied for simulation of oblique water entry problem in the second stage and the results are compared with experiments. Upon comparison of various experimental results with this software output, it is shown that the numerical algorithm in this computer program (ALE) can be reliably used to simulate this kind of fluid solid interaction problem and determine the impact forces and moments more precisely even in the extreme angles and velocities of water entry problems.