INTRODUCTION: In a recent study, Wu et al. (2006) have developed a new simplified mathematical model to describe the lift mechanics of downhill skiing and snowboarding, where the lift contributions due to both the transiently trapped air inside a snow layer and the solid phase (snow crystals) were determined for the first time, and a model for the stability and control of a ski/snowboard was developed. Wu et al.'s theory is applicable to the simple case where the planing surface is of constant width in the axial direction. However commercially available skis/snowboards have complex geometries and variable width in order to reduce the weight, improve performance while maintaining the strength and rigidity. In the current study, we shall extend Wu et al.'s theory to more complex planar shapes and examine the performance of the commercial snowboards using the new theory. The study presented herein and the previous skiing mechanics theory developed by Wu et al., have laid the foundation for the optimization of a ski/snowboard from lift generation point of view. METHOD: For a snowboarder gliding with velocity U over a snow layer, the sudden compaction of the snow leads to the generation of pore air pressure inside the compressed layer as well as the solid phase lifting force from the ice crystals. We use Shimizu's empirical relation to predict the local Variation in Darcy permeability due to the compression of the solid phase, A width factor, f(x), is introduced to characterize the Variation of width from the leading to the trailing edge of the snowboard. The forces and moments on the skier or snowboarder are used to predict the angle of attack of the planing surface and the Penetration depth at the leading edge. In the case when there are no edging or turning marteuvers, we numericaily predict the lifting force distribution beneath a snowboard surface. The contribution of the pore air pressure to the total lift, fair, is then used as the criterion to evatuate the performance of various snowboards with different shape factors. RESULTS: Figure 1 shows the centerline pore pressure distribution beneath five commercially available snowboards named A, B, C, D and E. The snowboards differ in their characteristic dimensions and thus the trapped air's contribution to the total lift differs. fair is the highest in E (56.4%) and the lowest in A (51.9%). DISCUSSfON: The two pressure peaks at the nose of a snowboard are due to the fact that the increased width of the snowboard prolongs the outflow of the trapped air in the lateral direction, and hence an increase in the local pore air pressure built-up. For a smooth air cushioned glide and reduced frictional force, one wants a high value of fair. Obviously, snowboard E is better in pore pressure generation. CONCLUSION: This paper develops a new realistic model for lift mechanics of downhill snowboarding which incorporates the shape variation effect on the lift forces generation. It could have important applications in future snowboard design.
© Copyright 2007 4th International Congress on Science and Skiing. Julkaistu Tekijä University of Salzburg. Kaikki oikeudet pidätetään. / Kääntänyt https://www.DeepL.com/Translator