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Abstract: The objective of this paper is to develop a realistic model for ice–structure interaction. To this end, the experiments made by Bridges et al. [Bridges FG, Hatzes A, Liu DNC. Structure, stability and evolution of Saturn’s rings. Nature 1984;309:333–5] in order to measure the coefficient of restitution for ice particles are thoroughly analyzed. One particularly troublesome aspect of the aforementioned experiments is fracture of the ice particles during a collision. In the present effort, the collisional properties of the ice particles are investigated using a Finite Element approach. It is found that a major challenge in modeling collision of the ice balls is the prediction of the onset of fracture and crack propagation in them. In simulations of a block of ice collision to a structure, it is crucial that fracture is determined correctly, as it will influence the collisional properties of the ice particles. The results of the simulation, considering fracture criterion implemented into the Finite Element Model [Zamankhan P, Bordbar M-H. Complex flow dynamics in dense granular flows. Part I: experimentation. J Appl Mech (T-ASME) 2006;73:648–57; Zamankhan P, Huang J. Complex flow dynamics in dense granular flows. Part II: simulations. J Appl Mech (T-ASME) 2007;74:691–702] together with a material model for the ice, imply that most of the kinetic energy dissipation occurs as a result of fracturing at the contact surface of the ice particles. The results obtained in the present study suggest that constitutive models such as those proposed by Brilliantov et al. [Brilliantov NV, Spahn F, Hertzsch JM, Poschel T. Model for collisions in granular gases. Phys Rev E;1996;53:5382–92] for collisions of ice particles are highly questionable. [Copyright &y& Elsevier]

Abstract: This paper analyses the fragmentation of kidney stones by direct impact with Swiss Lithoclast Master®. Based on a previous work, the impact of the probe of the Lithoclast is modeled with a displacement control of the nodes inside the impacted area. Different computations are carried out focusing the efforts on new tentative designs of the cross section of the probe, as well as the influence of multiple impacts. The results show that a hollowed probe could improve the results obtained with the existing massive probe. Likewise, it is shown that there is an optimal internal radius of the hollowed probe for which the damage caused to the kidney stone is maximized. Finally the results demonstrate the existence of a synergetic effect of the application of multiple impacts at a high frequency. [Copyright &y& Elsevier]