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

本项目的一个主要目的是将高阶界面元方法(HOBEM)应用于尚未解决或尚未解决的耐波性问题。重点研究了船舶在波浪中的水动力问题，采用二次或三次等参元的HOBEM，编制了精度高、计算时间短的计算程序。1)对满足自由面和辐射条件的格林函数进行了改进，在计算时间上进行了改进。2)利用上述格林函数建立了基于HOBEM的积分方程组，合理地考虑了船舶定常平移引起的定常扰动对非定常自由面的影响。3)发展了一种新的细长船理论，合理地考虑了航速和三维效应。基于这一新理论进行了数值计算，采用二次等参元对特解进行了数值求解。4)采用三维拉格朗日元作为高阶单元，计算了大型浮体支承的多体压力积分产生的漂移力。5)利用二次单元开发了二维浮体大振幅振动的全非线性时域仿真程序。利用三次B样条函数编制了浅吃水巨型浮式结构物水动力计算程序。结果表明，即使在波长很短的区域，用能量守恒原理检验的精度也是很好的。

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.