吸积盘SPH模拟中人工粘性的控制
Controlling Artificial Viscosity in SPH simulations of accretion disks
摘要：
我们测试的操作的两种方法选择性地应用人工粘度（AV）的开普勒吸积盘的SPH模拟，使用环扩展测试，以量化有效粘度，和相关系数技术来测量形成不必要的粒子的横向排列。Balsara Switch和Time Dependent Viscosity都不能有效地工作，因为它们在平滑剪切流区域中使AV处于活动状态，并且不能消除粒子在横向方向上的排列累积。这两种开关的效果是周期性的，周期性取决于半径，不受粒子密度的影响。我们证明，一个非常简单的算法激活AV只有当真正收敛的流量被检测到，并减少不必要的形成的crossde对齐。新开关的工作原理是测试一个粒子的所有邻居是否都在围绕同一点的开普勒轨道上，而不是计算速度场的发散度，这受到SPH粒子位置的泊松噪声的强烈影响。
英文摘要：
We test the operation of two methods for selective application of Artificial Viscosity (AV) in SPH simulations of Keplerian Accretion Disks, using a ring spreading test to quantify effective viscosity, and a correlation coefficient technique to measure the formation of unwanted prograde alignments of particles. Neither the Balsara Switch nor Time Dependent Viscosity work effectively, as they leave AV active in areas of smooth shearing flow, and do not eliminate the accumulation of alignments of particles in the prograde direction. The effect of both switches is periodic, the periodicity dependent on radius and unaffected by the density of particles. We demonstrate that a very simple algorithm activates AV only when truly convergent flow is detected and reduces the unwanted formation of prograde alignments. The new switch works by testing whether all the neighbours of a particle are in Keplerian orbit around the same point, rather than calculating the divergence of the velocity field, which is very strongly affected by Poisson noise in the positions of the SPH particles.
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