Applications of Computational Fluid Dynamics in Violent Water-Impact Problems

Abstract

Slosh-induced impact and water-entry impact are two typical cases of violent water-impact that causes highly distorting free-surface and large loads in transient time. Extensive studies have been carried out by experiments and potential theories in the past decades. This thesis has investigated the applications of a commercial computational fluid dynamics (CFD) code, Star-CCM+, in sloshing and water-entry problems.

In sloshing problem, computation efficiency of adaptive mesh models was observed before carrying out parametric sensitivity study. Several mesh models were designed by different refinements around impact region. It has shown that an efficient mesh model with appropriate numerical conditions reduces computation time significantly and produces similar pressure signals and free-surface shapes with experiment.

Then, two-dimensional ship-like sections were studied in water-entry problems. Appropriate overlapping meshes were arranged so that the section can move inside computational domain without losing numerical stability. Moreover, in order to compare with the analytical solutions which have been developed based on high Froude number (Fn) condition, Fn effect was also investigated and CFD computation showed reasonable performance. The CFD analysis has presented reasonable agreement in impact loads and free-surface developments with analytical solutions and experiments

Water-entry study was then extended to a 3-D modified Wigley case. Impact characteristic was found that both maximum body acceleration and maximum impact force are linear proportional to drop height. Moreover, the peak impact force occurs at the same water-entry depth, which is independent of drop height.

These results show that CFD analysis is becoming matured for engineering application nowadays.