Importance of Hydrodynamic Considerations for Underwater Vehicle Design

Proper hydrodynamic design is necessary in order to achieve the effective performance of an underwater vehicle. An incorrect shape can cause excessive drag, noise, and instability even at low speeds. This paper explains how a reasonable hydrodynamic design can result in low drag and noise with minimum compromise in volume, and reduced development and production costs. Rules-of-thumb and simplified automated programs are discussed to predict the drag, stability and noise, as well as the speed corresponding to the inception of cavitation. Detailed computer programs are identified for those who require the best shape and hydrodynamic characteristics possible. After a brief overview of how hydrodynamics affects underwater vehicle performance, this paper suggests methods for estimating the drag as a function of speed, shape and size. The inception of cavitation is explained along with a simple method for predicting it as a function of speed, shape, and depth. The instability of bluff body shapes is discussed with simplified formulae for predicting the magnitude and frequency of oscillation. Computer programs are identified that define the external shape as well as the shape of fairings that minimize drag, noise, and cavitation. The paper concludes with a discussion of hydrodynamic stability and references literature that defines simple formulae which estimate the size, shape and placement of control surfaces.