Stability Analysis Of Supercavitating Underwater Vehicles And Stucture Optimum Design

The supercavitating underwater vehicle is new conceptual underwater weapon.The cavity which is generated cavitator engulfs the complete structure. This cavity separates the torpedo hull from the water, thereby eliminating much of the viscous drag.This allows tremendous speeds to be achieved that are on the order of five to ten times the speed of conventional underwater weapons.The vehicle body is only marginally in contact with the water at the cavitator and rear control fins. This minimal contact results in stability issues. The size of the supercavity and the magnitude of the drag at the cavitator are greatly affected by the vehicle' s velocity and by the shape and size of the cavitator. This paper investigates the benefits of an adaptive cavitator, capable of adjusting its size with the speed of forward motion of the vehicle. Objective of the cavitator size variation is to maintain the minimum cavity length and the minimum drag at any given speed. The localized drag and the propulsion required to sustain the vehicle' s motion can cause the vehicle to buckle. In addition, propulsion acts as a follower force and may be a source of flutter-type instabilities when the vehicle is accelerating. The insurgence of buckling and flutter is investigated to identify limiting operating conditions and predict stability limits. The case of pulsating thrust is also addressed through the application of the method of Bolotin' s method.At last the effect of tapered shell geometries and of circumferential stiffeners placed along the shell length are described.To successfully design a vehicle that can satisfy the required performance criteria,it is necessary to consider the vehicle structure as a critical component. The structure of a supercavitating underwater vehicle must be designed to survive extreme loading conditions and meet frequency constraints.In this research, an algorithm to determine the optimal configuration of the supercavitating underwater vehicle is presented. Using the Matlab Optimization Toolbox, a high fidelity finite element model of the supercavitating underwater vehicle was developed to determine the optimal dimensions of the stiffening ring and stiffener, and shell thickness of the vehicle when the mass of the vehicle is minimization. Both configurations are here applied and used as means for enhancing the shells stability. Stiffening rings have been already proposed to reduce vibrations in supercavitating vehicles resulting from their periodic impacts with the cavity water. Then the structure of the supercavitating underwater vehicle is optimized in order to make the manufacture simplely. Although the weight of the supercavitating underwater vehicle optimized increase, but the stability is significantly enhanced ,and the cost in manufacturing is also saved more.