Impact Dynamics of Elastic Stiffened Supercavitating Underwater Vehicles

Abstract

The dynamic behavior of and the vibration in supercavitating underwater vehicles are here investigated and controlled. Supercavitating vehicles exploit supercavitation as a means to reduce drag and increase their underwater speed. The forces acting on supercavitating vehicles are completely different from those on conventional submerged bodies, since only a tiny percentage of their external surface area is wetted and water-vapor forces are almost negligible. The hydrodynamic stability of supercavitating bodies is achieved through after-body planing, or surfing, along the internal surface of the cavity, or through periodic impacts, or 'tail-slaps', with the interior surface of the cavity. The interactions between the vehicle and the water/cavity interface are sources of structural strains and vibrations, which undermine the structural reliability of the vehicle and affect its guidance. The dynamic behavior of supercavitating vehicles is here analyzed. The vehicles are modeled as slender elastic beams in order to predict their dynamic response under 'tail-slap' conditions both in terms of rigid body motion as well as dynamic strains and vibrations. The developed numerical model predicts the response of the considered class of supercavitating vehicles and it is used to estimate the effect of periodically placed stiffening rings on the amplitude of the vibrations induced by the tail-slap impacts. The analysis is motivated by the need to accurately model the structural characteristics of supercavitating vehicles in order to estimate the vibration transmission paths along the structure and to envision and design systems that improve their guidance and control efficiency. The models here presented will be included in a simulation-based design procedure for supercavitating vehicles, where optimal design configurations will be identified through a multidisciplinary design optimization (MDO) approach. The MDO process will consider structural performance trade-offs in order to determine configurations that simultaneously provide minimum vibrations and maximum structural reliability, with minimum added weight and costs.