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光滑粒子动力学方法是一种拉格朗日型无网格粒子方法, 在模拟大变形和自由表面流方面具有特殊的优势, 已经在工程和科学领域得到了广泛的应用. 然而, 长期以来, 传统光滑粒子动力学方法一直受到应力不稳定性的困扰, 从而限制了它的进一步发展和应用. 应力不稳定性的根本原因在于应力状态与核函数的不匹配:负压状态下粒子间产生吸引力, 吸引力随着粒子间距的减小而增大, 导致拉伸不稳定性;正压状态下粒子间产生排斥力, 排斥力随着粒子间距的减小而先增大后减小, 导致压缩不稳定性. 本文通过改进光滑粒子动力学方法的核函数和离散格式, 使得无论在正压还是负压状态下粒子间的作用力恒为排斥力, 且排斥力随着粒子间距的减小而增大, 从而防止粒子聚集等现象, 解决应力不稳定问题. 分别使用改进前后的光滑粒子动力学方法模拟两个典型的应力不稳定算例, 结果表明本文的改进方法能够有效地消除应力不稳定性.Smoothed particle hydrodynamics (SPH) is a Lagrangian meshfree particle method. It has special advantages in modeling large deformation and free surface flow, and has been widely applied to different problems in engineering and science. However, the classical SPH suffers from stress instability which resticts its further development and applications. The fundamental reason of stress instability is that the stress state and the kernel do not match each other. For frequently used bell-shaped kernel function, in tensile state the attraction between particles increases as particle spacing decreases, thereby leading to tensile instability. In a compressible state, the repulsive force between particles increases, and then decreases as particle spacing decreases, thereby leading to compressible instability. In this paper is presented an approach to removing stress instability in SPH by proposing a new kernel function and a modified SPH discrete form. In the modified SPH, the force between particles is always repulsive and it increases as particle spacing decreases. Two numerical examples are given to test the proposed approachs, and the obtained numerical results clearly demonstrate that the new approach can eliminate stress instability effectively.
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Keywords:
- smoothed particle hydrodynamics/
- stability/
- kernel/
- discrete form
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