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arXiv 1107.5539gr-qc
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广义相对论Z4c公式的约束阻尼

Constraint damping for the Z4c formulation of general relativity

Andreas Weyhausen, Sebastiano Bernuzzi, David Hilditch

摘要:

在采用自由演化方案的数值相对论模拟中,避免约束违反的一种可能性是修改连续演化方程,以便抑制约束违反。冈拉克等等人证明,这种方案对广义相对论的Z4公式化的低振幅、高频率约束违反模式进行指数衰减。在这里,我们分析的阻尼方案在数值应用上的Z4的共形分解的效果。在再现了理论预测的阻尼率的约束违规的线性政权,我们探索的数值解不包括的理论分析。特别是,我们研究的阻尼方案的低频和高振幅扰动的平坦时空以及长期动力学的穿刺和紧凑的恒星初始数据的背景下,球对称的效果。我们发现,阻尼方案是有效的,提供的约束违反是解决的数值网格。在网格噪声上,人工耗散和阻尼的组合有助于抑制约束违反。我们发现,在模拟穿刺黑洞时,选择阻尼参数必须小心。否则,阻尼方案可能会导致不期望的增长的约束,甚至定性不正确的演变。在一个紧凑的静态星的数值演化,我们发现,阻尼参数的选择是更加微妙的,但可能会导致一个小的约束违反减少。对于大范围的值,它会导致非物理行为。

英文摘要:

One possibility for avoiding constraint violation in numerical relativity simulations adopting free-evolution schemes is to modify the continuum evolution equations so that constraint violations are damped away. Gundlach et. al. demonstrated that such a scheme damps low amplitude, high frequency constraint violating modes exponentially for the Z4 formulation of General Relativity. Here we analyze the effect of the damping scheme in numerical applications on a conformal decomposition of Z4. After reproducing the theoretically predicted damping rates of constraint violations in the linear regime, we explore numerical solutions not covered by the theoretical analysis. In particular we examine the effect of the damping scheme on low-frequency and on high-amplitude perturbations of flat spacetime as well and on the long-term dynamics of puncture and compact star initial data in the context of spherical symmetry. We find that the damping scheme is effective provided that the constraint violation is resolved on the numerical grid. On grid noise the combination of artificial dissipation and damping helps to suppress constraint violations. We find that care must be taken in choosing the damping parameter in simulations of puncture black holes. Otherwise the damping scheme can cause undesirable growth of the constraints, and even qualitatively incorrect evolutions. In the numerical evolution of a compact static star we find that the choice of the damping parameter is even more delicate, but may lead to a small decrease of constraint violation. For a large range of values it results in unphysical behavior.

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