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Skiing manufacturers depend on the development of new skis on trial and error cycles and extensive product testing. Simulation
tools, such as the finite element method, might be able to reduce the number of required testing cycles. However, computer
programs simulating a ski in the situation of a turn so far lack realistic ski–snow interaction models. The aim of this study
was to (a) implement a finite element simulation of a ski in a carved turn with an experimentally validated ski–snow interaction
model, and (b) comparison of the simulation results with instantaneous turn radii determined for an actual carved turn. A
quasi-static approach was chosen in which the ski–snow interaction was implemented as a boundary condition on the running
surface of the ski. A stepwise linear function was used to characterise the snow pressure resisting the penetration of the
ski. In a carved turn the rear section of the ski interacts with the groove that forms in the snow. Two effects were incorporated
in the simulation to model this situation: (a) the plasticity of the snow deformation, (b) the influence of the ski’s side-cut
on the formation and shape of this groove. The simulation results agreed well with experiments characterising snow penetration.
Implementation of the groove in the ski–snow interaction model allowed calculation of the instantaneous turn radii measured
in actual turns, but also caused significant numerical instability. The simulation contributes to the understanding of the
mechanical aspects of the ski–snow interaction in carved turns and can be used to evaluate new ski designs. 相似文献
2.
Federolf PA 《Journal of sports sciences》2012,30(10):1063-1068
Alpine ski racing is a popular sport in many countries and a lot of research has gone into optimising athlete performance. Two factors influence athlete performance in a ski race: speed and the chosen path between the gates. However, to date there is no objective, quantitative method to determine instantaneous skiing performance that takes both of these factors into account. The purpose of this short communication was to define a variable quantifying instantaneous skiing performance and to study how this variable depended on the skiers' speed and on their chosen path. Instantaneous skiing performance was defined as time loss per elevation difference dt/dz, which depends on the skier's speed v(z), and the distance travelled per elevation difference ds/dz. Using kinematic data collected in an earlier study, it was evaluated how these variables can be used to assess the individual performance of six ski racers in two slalom turns. The performance analysis conducted in this study might be a useful tool not only for athletes and coaches preparing for competition, but also for sports scientists investigating skiing techniques or engineers developing and testing skiing equipment. 相似文献
3.
摘要：宇宙观是影响一个思想体系及社会制度的重要因素，传统武术体系的形成与发展也离不开对古代宇宙观的认识。为丰富武术哲学体系，揭示中国古代宇宙观与传统武术形成之间的哲学基础，主要采用文献资料法，在古文献史料的基础上阐述古人从对宇宙认识，从中提取传统武术哲学之精华，认为传统武术哲学的形成前提是对宇宙的认识，并超越了神论限制,走向发展的正途；中国古代气论、道论、太极发生论、宇宙生命整体论影响着传统武术哲学的本质观、修炼境界观、平衡观和武术哲学的基本理念。该研究不仅说明武学产生的思想基础，丰富了武学的认识论体系，而且揭示了传统武术哲学的发展过程与规律，对我们认识武学体系的内在精髓提供启示和借鉴。 相似文献
4.
When sharpening ice hockey blades a hollow is created at the running surface of the blade. This study aimed to quantify the effect of different blade hollows on (a) blade–ice friction, (b) skating performance in an agility course, and (c) players’ perception of blade sharpness, performance, and comfort. Friction was quantified by measuring the deceleration of a sled running on the blades. Skating performance was tested with 15 volunteers performing a total of 9 trials on 3 different hollow radii. Perception was assessed using a questionnaire. Friction increased with decreasing hollow radius. Skating performance was significantly impeded at a hollow radius of 3.18 mm. Within the range of 9.53–22.23 mm performance differences were subject specific and several subjects showed no differences. Players appeared to be not sensitive enough to identify hollow radii, and only half of the subjects ranked their performance correctly. 相似文献
5.
GEJZA M. TIMČÁK PETER KOŠĆ JURAJ PAŇKO 《European Journal of Engineering Education》1996,21(3):245-253
Electronic mail entered the Technical University Ko?ice in 1990. Now, instead of the few tens of users at the beginning, the system hosts thousands of them. Interactive teaching programmes as well as teaching programmes that are supported by audio and visual channels have also been used since 1990. The paper presents a short account of past development, the present situation and perspectives within the area of Internet use and of tuition that employs multimedia related means of teaching. 相似文献
6.
Ice friction of flared ice hockey skate blades 总被引：2，自引：0，他引：2
In ice hockey, skating performance depends on the skill and physical conditioning of the players and on the characteristics of their equipment. CT Edge have recently designed a new skate blade that angles outward near the bottom of the blade. The objective of this study was to compare the frictional characteristics of three CT Edge blades (with blade angles of 4 degrees, 60, and 8 degrees, respectively) with the frictional characteristics of a standard skate blade. The friction coefficients of the blades were determined by measuring the deceleration of an aluminium test sled equipped with three test blades. The measurements were conducted with an initial sled speed of 1.8 m s(-1) and with a load of 53 kg on each blade. The friction coefficient of the standard blades was 0.0071 (s = 0.0005). For the CT Edge blades with blade angles of 4 degrees, 6 degrees, and 8 degrees, friction coefficients were lower by about 13%, 21%, and 22%, respectively. Furthermore, the friction coefficients decreased with increasing load. The results of this study show that widely accepted paradigms such as "thinner blades cause less friction" need to be revisited. New blade designs might also be able to reduce friction in speed skating, figure skating, bobsledding, and luge. 相似文献
7.
Peter Andreas Federolf 《Journal of sports sciences》2013,31(10):1063-1068
Abstract Alpine ski racing is a popular sport in many countries and a lot of research has gone into optimising athlete performance. Two factors influence athlete performance in a ski race: speed and the chosen path between the gates. However, to date there is no objective, quantitative method to determine instantaneous skiing performance that takes both of these factors into account. The purpose of this short communication was to define a variable quantifying instantaneous skiing performance and to study how this variable depended on the skiers' speed and on their chosen path. Instantaneous skiing performance was defined astime loss per elevation difference dt/dz, which depends on the skier's speed v(z), and the distance travelled per elevation difference ds/dz. Using kinematic data collected in an earlier study, it was evaluated how these variables can be used to assess the individual performance of six ski racers in two slalom turns. The performance analysis conducted in this study might be a useful tool not only for athletes and coaches preparing for competition, but also for sports scientists investigating skiing techniques or engineers developing and testing skiing equipment. 相似文献
8.
Abstract In ice hockey, skating performance depends on the skill and physical conditioning of the players and on the characteristics of their equipment. CT Edge have recently designed a new skate blade that angles outward near the bottom of the blade. The objective of this study was to compare the frictional characteristics of three CT Edge blades (with blade angles of 4°, 6°, and 8°, respectively) with the frictional characteristics of a standard skate blade. The friction coefficients of the blades were determined by measuring the deceleration of an aluminium test sled equipped with three test blades. The measurements were conducted with an initial sled speed of 1.8 m · s?1 and with a load of 53 kg on each blade. The friction coefficient of the standard blades was 0.0071 (s=0.0005). For the CT Edge blades with blade angles of 4°, 6°, and 8°, friction coefficients were lower by about 13%, 21%, and 22%, respectively. Furthermore, the friction coefficients decreased with increasing load. The results of this study show that widely accepted paradigms such as “thinner blades cause less friction” need to be revisited. New blade designs might also be able to reduce friction in speed skating, figure skating, bobsledding, and luge. 相似文献
9.
Peter Federolf Emily Bakker 《Sports biomechanics / International Society of Biomechanics in Sports》2013,12(4):452-463
A large proportion of elite cross-country skiers suffer from chronic anterior compartment syndrome (CACS). This study used surface electromyograms (EMGs) to investigate whether differences existed in the activation characteristics of the tibialis anterior muscle between elite cross-country skiers with a history of anterior compartment pain (symptomatic group) and a pain-free control group. Based on self-reported pain symptoms, twelve young, national-level cross-country ski athletes were assigned to a symptomatic group (N = 5), a control group (N = 4), or analyzed individually if their diagnosis was not certain (N = 3). During skating, EMGs were recorded on five lower leg muscles. The relative increase in EMG power per step when increasing the effort level of skating was larger in the symptomatic group than in the control group for tibialis anterior (143 ± 12% vs. 125 ± 23%; Cohen's d = 1.17), peroneus longus (123 ± 24% vs. 107 ± 6%; d = 0.91), and gastrocnemius lateralis (167 ± 51% vs. 117 ± 12%; d = 1.64). The symptomatic group showed more power in the lower frequency bands of the tibialis anterior's EMG spectra (p < 0.001), whereas no group differences were found in other muscles (all p>0.2). Within the step cycle, these differences appeared in the swing phase and in the gliding phase during single leg support. The observed differences in the EMG spectra may serve as an early identification of athletes who are at risk of developing CACS. 相似文献
10.
For ski manufacturers, it is important to know how a given ski-binding system performs under different loading conditions.
Important performance parameters are the ski deformation and the resulting turn radius. This study focuses on carving turns. The aims of this study were: (1) to investigate the dependence of the turn radius on edging angle, load on the binding,
and snow hardness using a finite element (FE) simulation, and (2) to compare the results with predictions of a frequently
used model introduced by Howe. The FE simulation used a quasi-static approach (similar to Howe’s model), but the ski–snow
interaction model incorporated the groove that forms in the snow during a carved turn. Up to edging angles of 40°, the results
of the FE simulation agreed well with Howe’s model. However, for large edging angles (>50°) the calculated turn radius leveled
out, whereas Howe’s model tends to zero. This effect was more pronounced for soft snow than for hard snow conditions. Increasing
forces on the binding caused a decrease in the calculated turn radii. In summary, the FE simulation showed that particularly
at large edging angles the groove in the snow needs to be considered in models of the ski–snow interaction or in computations
of the turn radius. 相似文献
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