水线源强消弃法在船舶定常兴波计算中的应用

当采用等强度源汇分布法求解线性船舶水动力学问题时,船体的水线源强必须等于零,基于这一假定,杜双兴在基于边界元法的数值计算中,令水线附近面元上的源强为零,且水线积分项也自动消失,称这种方法为"水线源强消弃法".本文应用Kelyin移动兴波源格林函数,研究水线源强消弃法在定常航行船舶的兴波计算中的应用,首先以潜航椭球体为例,对Kelvin移动兴波源格林函数进行了计算和验证,然后分别采用常规面元法和水线源强消弃法,对Wigley船型的兴波阻力、波形及船体压力分布进行了计算及试验比较,另外为了考查水线源强消弃法的工程实用性,最后对一艘SWATH船型的兴波阻力进行了计算.结果表明:与考虑水线单元和水线积分的常规面元法相比,水线源强消弃法能够较好地消除水线积分时格林函数的奇异性所引起的误差,给出的预报结果与试验值吻合更好;另外水线源强消弃法的预报结果受网格划分形式、忽略水线单元尺寸大小的影响,文中的算例表明:忽略10%-15%吃水以上的水线单元能够给出较为合理的预报结果.

Application of the waterline source strength elimination method in the computation of the steady ship waves

The ship's waterline source strength must be zero when solving the linear ship hydrodynamics with the boundary integral method.Based on this assumption,in the BEM based numerical computation,the source strength of the element near the waterline is set to be zero and the waterline integral term vanished automatically.This numerical method is named as "Waterline source strength elimination method(WSSEM)" in Du(1996).In this paper,the Kelvin translating source Green function is utilized to study the application of the Waterline Source Strength Elimination Method in the Computation of the Steady Ship Waves.At first a submerged ellipsoid is selected as an example to verify the accuracy of numerical algorithm of the Kelvin translating source Green function.And then the panel methods and the WSSEM are employed respectively to compute the wave resistance,wave profile and the hydrodynamic pressure for the Wigley ship hull.Finally,the wave resistance of a SWATH ship is calculated to demonstrate the application of the WSSEM method in engineering practice.It is shown that: compared with the conventional panel methods,WSSEM can remove the numerical errors brought from the singular behavior of the Green func-tion in the waterline integral and better agreement can be achieved with the corresponding model tests data.In addition,the mesh discretization style and the size of the waterline element will influence the predicted results by WSSEM.In this computation models,it is found that when the waterline elements above the 10%-15% draught are neglected,WSSEM can give reasonable prediction results.