波动问题中流体介质的动力人工边界

DYNAMICAL ARTIFICIAL BOUNDARY FOR FLUID MEDIUM IN WAVE MOTION PROBLEMS

无限域流体介质的波动辐射效应是影响海域工程动力反应的重要因素,人工边界是实现此类开放系统近场波动问题数值分析的有效方法.基于位移格式的流体波动理论推导开放域流体介质的人工边界,分别给出一维、二维和三维空间中平面波、柱面波和球面波的流体介质动力人工边界条件,其中一维平面波动人工边界为经典的黏性边界,二维柱面波、三维球面波的人工边界处节点应力与节点速度和加速度成正比,可等效为由阻尼与质量系统构成的人工边界条件.讨论相应的数值模拟技术,给出流体介质动力人工边界在ANSYS软件平台的具体实现方法.近场流体介质动力反应问题的算例表明,所发展的流体动力人工边界对于轴对称波动与非轴对称波动在近场有限域截断处的透射吸收作用的模拟计算精度均较为良好,说明此流体介质人工边界具有较高的可靠性与实用性.所发展的流体介质动力人工边界可较为方便地与大型商用有限元软件结合,可为包括海域地形和海岛在内的海域工程的动力分析提供一定的方法借鉴.

The wave radiation effect of infinite fluid medium is an important factor affecting the dynamic response of sea area engineering.Artificial boundary is an effective method to realize the numerical analysis of near-field wave motions in such open systems.In this paper,the dynamic artificial boundaries of open domain fluid medium are deduced based on the theory of fluid wave motions in displacement scheme.The dynamic artificial boundary conditions of wave motions in one-dimensional,two-dimensional and three-dimensional fluid media are formed respectively.As a result,the dynamic artificial boundary of plane wave in one-dimensional fluid medium is classical viscous boundary.On the twodimensional artificial boundary of cylindrical wave and three-dimensional artificial boundary of spherical wave,the nodal stress is proportional to the speed and acceleration of the node.Therefore,the boundary conditions of these two dimensions can be equivalent to the artificial boundaries composed of the damping-mass system.Furthermore,the corresponding numerical simulation techniques of the fluid medium dynamic artificial boundaries proposed in this paper are discussed,and the realization methods on ANSYS platform are given.Examples of the near-field dynamic response problems show that,for the simulation of the transmission and absorption of the axisymmetric and the non-axisymmetric wave motions.in fluid medium,the calculation accuracies of the dynamic artificial boundaries proposed in this paper are relatively high.The reliability and practicality of those artificial boundaries are verified.The artificial boundaries of fluid medium developed in this paper can be combined with large commercial finite element software,which can provide some insight in the dynamic analysis methods of sea area engineering including sea area terrains and islands.