Hydrodynamic Analysis of Underwater Bodies for Efficient Station Keeping in Shallow Waters with Surface Waves
Author: Matthew Bradley
Publisher:
Published: 2014
Total Pages: 88
ISBN-13:
DOWNLOAD EBOOKTo determine the effect of body shape on the response of underwater vehicles to surface waves in shallow water, the wave radiation hydrodynamic forces are evaluated for a family of (i) prolate spheroidal hull forms and (ii) cylindrical bodies with hemispherical nose and conical tail sections by systematically varying the geometric parameters but keeping displacement constant. The added-mass and wave damping coefficients are determined using a frequency-domain, simple-source based boundary integral method. Results are obtained for a range of wave frequencies and depths of vehicle submergence all for a fixed water depth of 10 m. With the wave exciting force and moment determined using the Froude-Krylov theory, the response transfer functions for heave and pitch are then determined. The heave and pitch response spectra in actual littoral seas are then determined with the sea state modeled using TMA spectral relations. Results show that vehicle slenderness is a key factor affecting the hydrodynamic coefficients and response. The results show two characteristics that increase the radiation hydrodynamic forces corresponding to heave and pitch motions: namely, vehicle length and further-away from mid-vehicle location of the body shoulder. The opposite is true for the oscillatory surge motion. By utilizing these observed characteristics, one can design the lines for maximum radiation forces and consequently minimum hull response for the critical modes of rigid-body motion in given waters and vehicle missions. In the studies carried out in the thesis, a hull with a long parallel middle body with hemispherical nose and conical tail sections has better heave and pitch response characteristics compared prolate spheroid geometry of same volume. The methodology developed herein, which is computationally efficient, can be used to determine optimal hull geometry for minimal passive vehicle response in a given sea.
