Stability analysis of supercavitating underwater vehicles with adaptive cavitator

Supercavitating vehicles are characterized by substantially reduced hydrodynamic drag with respect to fully wetted underwater vehicles. Drag is localized at the nose of the vehicle, where a cavitator generates a cavity that completely envelops the body (supercavity). 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. The analysis is performed by using a finite element model developed to predict stability limits. The case of pulsating thrust is also addressed through the application of the method of infinite determinants, also known as Bolotin's method.