Session: 06-14-03 Underwater Vehicles and Design Technology III

Paper Number: 81058

81058 - Experimental Study of the Drag and Wave-Induced Surge Forces on an Underwater Vehicle Operating Near the Surface 

An important contribution to the resistance of a surface ship is the added resistance due to incoming waves. For submerged bodies, this added resistance is negligible when operating deeply submerged. However, when a submerged body is operating near the surface, this added resistance is present in the form of a periodic linear wave-induced surge force. Predicting the mean drag force on the body is complicated due to the viscous effects on the body as well as the free surface waves produced by the body passing near the free surface. The wave-induced surge force however is assumed to be dominated by pressure effects and analytical solutions using potential flow exist for predicting this force. In this study, we experimentally measure the zero frequency, mean drag force and the periodic wave-induced surge force on a submerged body subject to various wavelength single regular waves. Our results provide values for the difficult to predict mean drag force and allow the assessment of a paradoxical prediction from the analytical solution for the wave-induced surge force, namely that it does not depend on the forward speed of the vehicle.  The experiments were conducted in a towing tank with wavemaking capability using a circular cylinder body with hemispheric end caps. Two different forward speeds were examined along with a stationary zero speed baseline case. Since the drag force is viscous driven, and to confirm if any viscous effects exist for the wave-induced surge force, we also tested a circular cylinder body with flat end faces to force flow separation at the sharp leading edges of the body. Our results show a significant increase in the drag force for the flat end face geometry compared to the hemispheric end cap geometry at the higher speed tested and a small increase at the lower speed tested. For the wave-induced surge force, we can confirm that viscous effects play at most a negligible roll as there was no difference between the surge forces on the hemispheric end cap and flat end face geometries. Unfortunately, due to the small nature of the surge force and experimental noise, we were unable to confirm that the surge force does not depend on the forward speed of the body.

Presenting Author: Joseph Klamo Naval Postgraduate School

Authors:

Kristia Suriben Naval Postgraduate School
Kathryn Yeager Yale University
Joseph Klamo Naval Postgraduate School
Young Kwon Naval Postgraduate School