Study on Numerical Calculation Method for the Seakeeping of Ships by Means of Higher-Order Boundary-Element Method

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A main purpose of the present project was to apply the higher-order boundary-element method (HOBEM) to unsettled or unsolved seakeeping problems. In particular, emphasis is placed on the hydrodynamic problem of an oscillating and translating ship in waves, in which the HOBEM using quadratic or cubic iso-parametric elements was applied todevelop a computer program with high accuracy and less computation time. Obtained results are summarized as follows :1)Improvement was made on the Green function satisfying the free-surface and radiation conditions, in terms of the computation time.2)A new integral equation based on the HOBEM using the above Green function was derived, in which the effect of steady disturbance due to ship's steady translation on the unsteady free surface condition was rationally taken into account.3)Development was made of a new slender-ship theory which can account for the forward-speed and 3-D effects in a rational way. Numerical computations based on this new theory were also performed, in which quadratic iso-parametric elements were adopted to obtain numerically the particular solution.4)The 3-D Lagrange element, which is one of the higher-order elements, was used to compute the drift force from the pressure integration acting on multiple bodies supporting a very large floating structute. It was shown that the results were very accurate.5)A time-domain full-nonlinear simulation program for the large-amplitude oscillation of a 2-D floating body was developed using quadratic elements. The results were very primising.Also developed was a computer program for predicting the hydrodynamic forces on a shallow-draft huge floating structure, by use of the cubic B-spline function. It was shown that the accuracy by checking the energy-conservation principle was excellent even for the region of very short wavelengths.