The Sensitivity of Wave Force Computations to Common Errors, Uncertainties, and Hydrodynamic Approximations.
NAVAL RESEARCH LAB WASHINGTON DC
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The present investigation examines the methods and the hydrodynamic approximations commonly employed in wave force analysis. Alternatives and modifications are sought which improve the resolution of a general Morison approach. This is accomplished by considering two basic arrangements a vertical cylinder and a horizontal cylinder in progressive waves. The physical differences between the flows are explored and the results are compared to previous planar harmonic flow measurements. It was found that modifications to the usual Morison approach are required to adequately account for the orbital motions of the fluid and to account for the orientation of the orbits with respect to the cylinder axis. The consequences of these findings are discussed for inclined cylinders in waves and for cylinders in short-crested seas. The axial variations of the wave force on vertical cylinders are examined in order to establish error bounds for the common practice of assuming constant values of CM and CD over the entire span. Also, the methods of computing force transfer coefficients from a force record are examined and errors of method are identified and briefly discussed. Author
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