Internal wave fields and drag generated by a translating body in a stratified fluid

Abstract

Asymptotic approximations to the velocity and pressure fields generated by steadily towing a body through a uniformly stratified fluid in an arbitrary direction are calculated. This is done explicitly for point sources, both oscillatory and non-oscillatory in strength, and for a spherical source of non-oscillatory strength. The flow fields are divided into regions by causality and radiation conditions which have contributions containing up to three significant internal waves in the non-oscillatory cases, and up to six in the oscillatory cases. A method for describing the caustics is given. The drag due to the internal wave field induced by towing a body through the fluid is calculated for a spherical source, of non-oscillatory strength, being towed at a general tow angle and Froude number. Dependence of the drag coefficient on the tow angle and the Froude number is shown in particular the tow angle can significantly affect the magnitude of the drag coefficient for a given Froude number.