发表机构
Westlake University; University of Cambridge（西湖大学; 剑桥大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
针对软球DEM中Langevin与Nosé-Hoover恒温器的互补缺陷，提出两种成对混合恒温器，实现精确控温并调控速度统计，在固定惯性数下升高颗粒温度可降低表观摩擦。
AI 中文摘要
密集颗粒流通常使用软球离散元法（DEM）进行研究，而大规模应用一般需要连续介质模型。颗粒温度定义为颗粒速度波动的方差，是归纳流变标度的一个相关变量。然而，用于控制温度的实验施力方法也会影响颗粒状态的其他方面。另一种方法是使用恒温器算法直接控制波动能量。尽管恒温器算法在分子动力学（MD）中已得到充分确立，但其在耗散性DEM系统中的行为受到的关注相对较少。我们表明，传统的Langevin和Nosé-Hoover恒温器表现出互补的局限性：Langevin控制需要强耦合以抵消碰撞耗散，从而抑制颗粒动力学；而Nosé-Hoover不能独立地破坏由重复非弹性碰撞产生的相关性和分离，导致非遍历和数值不稳定的状态。为解决这些局限性，我们引入了两种成对混合公式，将确定性温度调节与随机去相关相结合。两者均强制施加指定温度，而随机去相关时间尺度的变化会改变速度统计量和相关的介观性质（如扩散率）。最后，应用于压力控制的简单剪切表明，在固定惯性数下增加颗粒温度会降低表观摩擦，与先前报道的趋势一致。因此，该框架为比较不同施力方式的颗粒系统以及识别温度相关本构模型所需的变量提供了受控参考状态。
英文摘要
Dense granular flows are commonly investigated using the soft-sphere Discrete Element Method (DEM), whereas large-scale applications generally require continuum models. Granular temperature, defined as the variance of particle velocity fluctuations, is a relevant variable to collapse rheological scaling. However, experimental forcing approaches used to control temperature also affects other aspects of the granular state. An alternative is to use a thermostat algorithm to control the fluctuation energy directly. Although thermostat algorithms are well established in Molecular Dynamics (MD), their behaviour in dissipative DEM systems has received comparatively little attention. We show that conventional Langevin and Nosé-Hoover thermostats exhibit complementary limitations: Langevin control requires strong coupling to offset collisional dissipation, thereby damping particle dynamics, whereas Nosé-Hoover does not independently disrupt the correlations and segregation generated by repeated inelastic collisions, leading to non-ergodic and numerically unstable states. To address these limitations, we introduce two pairwise hybrid formulations combining deterministic temperature regulation with stochastic decorrelation. Both enforce the prescribed temperature, while variation of the stochastic decorrelation timescale modifies velocity statistics and associated mesoscopic properties such as diffusivity. Finally, application to pressure-controlled simple shear shows that increasing granular temperature at fixed inertial number reduces the apparent friction, consistent with previously reported trends. The framework therefore provides controlled reference states for comparing differently forced granular systems and identifying the variables required for temperature-dependent constitutive models.
Comments27 pages main text, 31 with appendix, 34 with references. 14 figures. Relevant data is available at https://data.mendeley.com/datasets/yt9pvmvz9t/1. The paper has been submitted to Physics Review Research
