EOS/Resolution阴谋：原行星碰撞模拟中的收敛
The EOS/Resolution Conspiracy: Convergence in Proto-Planetary Collision Simulations
摘要：
我们研究如何选择状态方程（EOS）和决议合谋影响巨大的影响（GI）模拟的结果。我们专注于两个地球一样的$0.5\,M_\oplus$原行星等质量碰撞的简单情况下，EOS的选择有深远的影响，这种碰撞的结果，以及对数值收敛与分辨率。在使用Tillotson状态方程的模拟中，由于缺乏对相变和混合物的热力学一致性处理，撞击会产生过量的蒸汽。在斜碰撞中，这增强了从行星到环行星盘的人工角动量（AM）传输，减少了行星随时间的旋转周期。即使在$1.3 \times 10^6$粒子的分辨率下，结果也不收敛。在迎面碰撞中，缺乏适当的处理的固体/液体-蒸气相变允许绑定的材料膨胀到非常低的密度，这反过来又导致在非常缓慢的数值收敛的临界特定的冲击能量的灾难性的破坏$Q_{RD}^*$与增加的分辨率，在以前的工作中报道。ANEOS用于斜向碰撞的模拟已经收敛到$10^5$粒子的中等分辨率，而迎头碰撞则在它们证明冲击后形成致密的富铁环时收敛，这促进了物质的引力再积累。一旦达到足够的分辨率来解析ANEOS情况下铁的液-汽相变，并且该环被解析，则$Q_{RD}^*$的值收敛。
英文摘要：
We investigate how the choice of equation of state (EOS) and resolution conspire to affect the outcomes of giant impact (GI) simulations. We focus on the simple case of equal mass collisions of two Earth-like $0.5\,M_\oplus$ proto-planets showing that the choice of EOS has a profound impact on the outcome of such collisions as well as on the numerical convergence with resolution. In simulations where the Tillotson EOS is used, impacts generate an excess amount of vapour due to the lack of a thermodynamically consistent treatment of phase transitions and mixtures. In oblique collisions this enhances the artificial angular momentum (AM) transport from the planet to the circum-planetary disc reducing the planet's rotation period over time. Even at a resolution of $1.3 \times 10^6$ particles the result is not converged. In head-on collisions the lack of a proper treatment of the solid/liquid-vapour phase transition allows the bound material to expand to very low densities which in turn results in very slow numerical convergence of the critical specific impact energy for catastrophic disruption $Q_{RD}^*$ with increasing resolution as reported in prior work. The simulations where ANEOS is used for oblique impacts are already converged at a modest resolution of $10^5$ particles, while head-on collisions converge when they evidence the post-shock formation of a dense iron-rich ring, which promotes gravitational re-accumulation of material. Once sufficient resolution is reached to resolve the liquid-vapour phase transition of iron in the ANEOS case, and this ring is resolved, the value of $Q_{RD}^*$ has then converged.
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