Study on Computational Method of Predicting Ship Viscous Flow

本研究的最终目的是通过应用计算流体力学的一些方法来阐明与复杂的三维流动分离相关的船体周围粘性流场的性质。为此目的，本项目旨在制定计算方案，进行流量和力的测量，然后利用计算方法澄清船舶粘性流动。在第一年，对现有的求解Napier-Stokes方程的数值格式、离散化方法、计算网格和求解压力方程的方法的有效性进行了讨论，以获得合理的方法。第二年，即最后一年，致力于对几个流动问题进行试验计算，以检验所开发方法的有效性。第一个试验是应用该方法在二维平面上计算具有最小粘性阻力的最佳体型。该方案与非线性规划技术相结合。所解决的机身形状为透镜形状，两端有尖角。下一个案例应用于大阪湾的水流问题，模拟了明石湾附近的大尺度涡旋运动。最后对弦向变直径圆柱的绕流进行了试验计算。得到了一种典型的三维非定常流分离模式，其性质与船舶绕流相似。第二年进行了水动力测量，并将测量不确定度分析应用于船舶模型阻力试验。虽然这些结果与船舶的粘性流动没有直接关系，但可以肯定的是，它们为今后研究船体周围粘性流动的基本机理提供了坚实的依据。

The final goal of the present research is to clarify the nature of the viscous flow fields around a ship hull associated with complicated three-dimensional flow separation, by applying some methods of computational fluid dynamics. For this purpose the present project has aimed to develop computational schemes, to carry out measurements of flow and forces, and then to clarify the ship viscous flow by use of the computational methods.In the first year discussions were made on the validity of existing numerical schemes of solving Napier-Stokes equation, discretization methods, computational grids, and methods of solving pressure equation, in order to obtain reasonable methods.The second year, i. e., the final year is devoted to make trial computations on several flow problems for examining the validity of the methods developed. The first trial is an application of the methods to compute an optimal body shape with minimum viscous resistance in two-dimensional plane. The scheme is associated with an nonlinear programming technique. The body shape solved has a lens shape with sharp corners at both ends. The next case is applied to a problem of current flow in Osaka Bay, by which an large scale vortex motion near Akashi channel is simulated. The final trial computation is applied to the flow around a circular cylinder with varying diameter in chord direction. A typical three-dimensional pattern of unsteady flow separation is obtained showing a similar nature to the flow around ship hull.Measurements of hydrodynamic forces are also made in the second year, in which an analysis of measurement uncertainty is applied to the resistance test of a ship model.Although these results are not directly related to the ship viscous flow, it is certain that they offer firm basis of treating the fundamental mechanism of the viscous flow around ship hull in near future.