Steady wave drift force on basic objects of symmetry
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An exponential growth in the offshore industry has resulted in a corresponding increase in demand for quick, accurate, and implementable designs. With the increase in size of the structure relative to the wave amplitude, analysis should be performed using the diffraction theory. The steady wave drift force on a submerged body is a second-order quantity. With a potential flow assumption, the force arises from the diffraction and radiation of the waves from the interaction with the body. For a fixed body in waves the steady force is contributed from the wave diffraction effect alone. Numerical solutions for are generally needed for the computation of the steady drift force on submerged structures. In this study the steady wave drift forces on several fixed bodies of basic shapes are derived in closed form. The thesis addresses the steady drift forces on the following basic structures: a box, a vertical circular cylinder, a submerged horizontal cylinder, a bottom-seated horizontal half cylinder, a bottom-seated hemisphere, a submerged sphere, and an ellipsoid. The results developed demonstrate the importance of various independent non-dimensional parameters. To achieve speed and accuracy of the analytical/numerical solutions for the second order forces on the basic bodies with symmetry has been presented. Mathematical formulation of the boundary value problem and its second order solution have been described using the different coordinates depending on the symmetry and nature of the object. Charts and formulas have been developed to provide solution for the second order wave forces on different basic structures like cylinder, sphere and ellipsoids. This study is helpful for a first pass estimate of the steady drift force where the translational and rotational contributions are neglected. The illustrative examples provide a sense of the accuracy and an approach to bound the results of complex geometries by approximating them as simpler geometries.