Fluid droplets behave significantly different from larger fluid bodies. At smaller scales, surface tension and friction between fluids and the boundary play an essential role and are even able to counteract gravitational forces. There are quite a few existing approaches that model surface tension forces within an SPH environment. However, as often as not, physical correctness and simulation stability are still major concerns with many surface tension formulations. We propose a new approach to compute surface tension that is both robust and produces the right amount of surface tension. Conversely, less attention was given to friction forces at the fluid-boundary interface. Recent experimental research indicates that Coulomb friction can be used to describe the behavior of droplets resting on a slope. Motivated by this, we develop a novel friction force formulation at the fluid-boundary interface following the Coulomb model, which allows us to replicate a new range of well known fluid behavior such as the motion of rain droplets on a window pane. Both forces are combined with an IISPH variant into one unified solver that is able to simultaneously compute strongly coupled surface tension, friction and pressure forces.

中文翻译：

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SPH 流体的统一压力、表面张力和摩擦


液滴的行为与较大的流体体明显不同。在较小的尺度上，表面张力和流体与边界之间的摩擦起着至关重要的作用，甚至能够抵消引力。在 SPH 环境中，有相当多的现有方法可以模拟表面张力。然而，物理正确性和仿真稳定性通常是许多表面张力公式的主要关注点。我们提出了一种新的方法来计算表面张力，该方法既稳健又能产生适量的表面张力。相反，对流体边界界面处的摩擦力的关注较少。最近的实验研究表明，库仑摩擦可用于描述液滴在斜坡上的行为。受此启发，我们遵循库仑模型在流体边界界面处开发了一种新的摩擦力公式，这使我们能够复制一系列新的众所周知的流体行为，例如雨滴在窗玻璃上的运动。这两种力与 IISPH 变体组合成一个统一的求解器，能够同时计算强耦合的表面张力、摩擦力和压力。