Forces and Moments Due to Unsteady Motion of an Underwater Vehicle

Abstract

Abstract : Unmanned Underwater Vehicles (UUV's) perform many of their missions in shallow water environments subject to the forces of ocean waves and the proximity to the ocean floor. Under these conditions, accurate vertical position control is necessary to prevent broaching or hitting the ocean floor. Accurate horizontal position control is necessary to enable the UUV to conduct its mission with accuracy and return to a predetermined recovery point. Shallow water position control is made more difficult by ocean waves. In deep water the effects of these waves are negligible, but the effects in shallow water are significant. Important shallow water missions include pollution monitoring, marine life sampling, bottom contour mapping, and mine location. Currently, UUV's are controlled in shallow water by altering empirical control parameters for better shallow water performance and by establishing empirically based operating depth limits on the UUV operations. These operating depth limits are based upon wave conditions. With a thorough understanding of the dynamics of UUV's in shallow water and the forces and moments on vehicles due to sea waves in these waters, improved control systems and vehicle designs can be achieved to allow the UUV to operate in shallower water and in larger waves than is commonly done. This will allow the UUV to be more effectively perform its missions. This thesis explores the effects of variation in water depth and vehicle submergence on added mass, damping, and restoring forces.