Does rock shape matter to the mitigation effects of trees on rockfall hazards? This question must be resolved in order to better quantify the protective role of mountain forests against rockfall. To probe this question, we investigate a single rock-tree interaction using non-smooth, hard-contact mechanics that allows us to consider rock shape at impact. The interaction of equant shaped rocks with cylinder-like tree stems is modeled. The equant shaped rocks are close to spherical but have a certain shape variability governed by the rock’s surface area ratio and aspect ratio. This work serves as an important follow-up study to the existing investigations from Toe et al. (Landslides 14: 1603-1614, 2017 ), where the effects of trees on block propagation are numerically investigated using spherical shaped rocks. The objective of our simulations is to understand how and to what extent, shape will influence energy dissipation and trajectory change. The primary results include: surface area ratio plays a more important role than aspect ratio in determining the rock’s post-impact dynamics. The primary parameters governing the rock kinematics after impact (i.e., block’s energy reduction, reflected rotational speed, and trajectory change) are impact velocity, impact eccentricity, and the tree stem diameter. The latter observation aligns well with previous findings and suggests that the shape factors, at least for nearly spherical rocks, can be integrated into the current block propagation models. However, from a statistical viewpoint, the anisotropic distribution of mass and hence the asymmetric moment of inertia of non-spherical rocks leads to stronger or weaker spin effects compared to mass- and volume-equivalent spheres. Apparently, the rotational motion of an irregular object serves as a kinetic energy reservoir leading to subsequent rock-tree impacts, and therefore significant differences in energy loss and trajectory in comparison to spherical shaped rocks. This effect must be further investigated using elongated and flattened blocks and underscores the importance of measuring rockfall rotation in experimental investigations.

中文翻译：

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树木对落石危害的缓解作用：岩石形状重要吗？

岩石形状对树木对落石危害的缓解作用是否重要？为了更好地量化山地森林对落石的保护作用，必须解决这个问题。为了探讨这个问题，我们使用非光滑的硬接触力学研究了单一的岩石-树相互作用，这使我们能够考虑撞击时的岩石形状。模拟了等形岩石与圆柱状树干的相互作用。等形岩石接近于球形，但具有受岩石表面积比和纵横比控制的一定形状可变性。这项工作是对 Toe 等人现有调查的重要后续研究。(Landslides 14: 1603-1614, 2017)，其中使用球形岩石对树木对块体传播的影响进行了数值研究。我们模拟的目的是了解形状将如何以及在多大程度上影响能量耗散和轨迹变化。主要结果包括：在确定岩石的冲击后动力学方面，表面积比比纵横比起着更重要的作用。冲击后控制岩石运动学的主要参数（即块的能量减少、反射旋转速度和轨迹变化）是冲击速度、冲击偏心率和树干直径。后一个观察结果与之前的发现非常吻合，并表明形状因子，至少对于接近球形的岩石，可以整合到当前的块传播模型中。但是，从统计的角度来看，与质量和体积等效的球体相比，质量的各向异性分布以及非球形岩石的不对称惯性矩会导致更强或更弱的自旋效应。显然，不规则物体的旋转运动充当了动能库，导致随后的岩石树撞击，因此与球形岩石相比，能量损失和轨迹存在显着差异。必须使用细长和扁平块进一步研究这种影响，并强调在实验研究中测量落石旋转的重要性。因此，与球形岩石相比，能量损失和轨迹存在显着差异。必须使用细长和扁平块进一步研究这种影响，并强调在实验研究中测量落石旋转的重要性。因此，与球形岩石相比，能量损失和轨迹存在显着差异。必须使用细长和扁平块进一步研究这种影响，并强调在实验研究中测量落石旋转的重要性。