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arXiv 2108.08392math.OCmath-phmath.MP
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基于线性投影算子的非光滑力学

Nonsmooth Mechanics Based on Linear Projection Operator

Farhad Aghili

摘要:

基于线性投影算子,提出了变拓扑多碰撞非光滑多体系统的统一动力学方程。斜投影矩阵普遍地导出这样的系统的所有特征变量,如下:i)跳跃不连续之前的约束加速度,来自无约束加速度的投影,ii)撞击后速度,来自撞击前速度的投影,iii)撞击期间的冲量,来自撞击前动量的投影,iv)广义约束力,来自广义输入力的投影,以及v)基于投影惯性矩阵从撞击前动能得到撞击后动能。所有的解决方案都以封闭的形式与优雅的几何解释。该公式足够通用,可以应用于同时受到多个冲击的MBS,这些冲击具有不同的恢复系数,改变拓扑结构,即,单侧约束变为无效,反之亦然,或者甚至当整体约束雅可比矩阵变为奇异时。不仅在不考虑约束条件的情况下解总是存在的,而且为了减小投影矩阵计算对舍入误差的数值敏感性,使广义约束惯性矩阵的条件数最小化.该模型被证明是能量一致的,如果一个全球恢复系数假设。在不同的恢复系数的情况下,能量一致的恢复矩阵的集合的特征在于使用线性矩阵不等式(LMI)。

英文摘要:

This paper presents a unifying dynamics formulation for nonsmooth multibody systems (MBSs) subject to changing topology and multiple impacts based on linear projection operator. An oblique projection matrix ubiquitously derives all characteristic variables of such systems as follow: i) The constrained acceleration before jump discontinuity from projection of unconstrained acceleration, ii) post-impact velocity from projection of pre-impact velocity, iii) impulse during impact from projection of pre-impact momentum, iv) generalized constraint force from projection of generalized input force, and v) post-impact kinetic energy from pre-impact kinetic energy based on projected inertia matrix. All solutions are presented in closed-form with elegant geometrical interpretations. The formulation is general enough to be applicable to MBSs subject to simultaneous multiple impacts with non-identical restitution coefficients, changing topology, i.e., unilateral constraints becomes inactive or vice versa, or even when the overall constraint Jacobian becomes singular. Not only do the solutions always exist regardless the constraint condition, but also the condition number for a generalized constraint inertia matrix is minimized in order to reduce numerical sensitivity in computation of the projection matrix to roundoff errors. The model is proven to be energetically consistent if a global restitution coefficient is assumed. In the case of non-identical restitution coefficients, the set of energetically consistent restitution matrices is characterized by using Linear Matrix Inequality (LMI).

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