INTRODUCTION: The performance of ski turns mainly depends on skier actions, material properties, snow conditions, and speed of the skier. In this work we focus on effects due to ski material properties among which bending and torsional stiffness are important ones. METHOD: A Computer model was developed to simulate a sequence of ski turns. The model consists of a segment model for the two skis and a single body for the skier. The interaction of the ski with the snow was modeled by a hypoplastic force-penetration relation normal to the snow surface and by orthogonal metal cutting transversal to the ski movement. The model was validated in case of a single turn with constant edge angle {Mössner et al., 2006a). To complete a sequence of ski turns the skier had to edge the skis according to the Position in the turn and to lean inward to compensate the centrifugal force. With this choice the trajectory of the skier for four turns was simulated. For evaluating the effect of bending and torsional stiffness on the trajectory of the skier a reference Simulation was computed using measured stiffness data of two real carving skis. Next the stiffness data of the two skis were varied and the effect on the trajectory and the turn radius was determined. RESULTS: The trajectories of the skier for two types of carving skis and varied stiffness data were computed for a sequence of turns. At the Start the skier carved but due to increasing speed he skidded more and more. Increased bending or increased torsional stiffness caused larger turn radii. In all cases the influence of increased bending stiffness was larger than the influence of increased torsional stiffness but in one case the effect due to torsional stiffness even was as large as the effect due to bending stiffness. Torsional stiffness mainly effected the movement of the skier during the phase of edge change. Variation of both bending and torsional stiffness caused less change of the turn radius then Variation of bending or torsional stiffness, only. Effects were small in carved turns and large in skidded turns. DISCUSSION: The importance of bending and torsional stiffness in a sequence of turns could be outlined. In contrast to prior work (Mössner et al, 2006b), where a single turn with constant edge angle was investigated, the influence of torsional stiffness was observed. Effects occur since in the phase of edge change the skis are rapidly bent and twisted whereas during turn phase the skis are constantly bent and twisted. For small velocities the shear strength of snow is not reached. In this case skis bend and twist till the whole edge has snow contact. The ski moves along the circle given by the ski edge. When speed increases and the contact pressure on the running surface of the ski reaches the shear stress of snow, then the ends of the ski begin to shear and consequently the turn radius gets larger. The higher the stiffness of the skis the larger gets the effect. At still higher speed the shear strength of snow is considerably exceeded and the skis are accelerated in transversal direction. Then the turn radius of the skier mainly depends on the shearing behavior of snow.
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