共查询到20条相似文献，搜索用时 15 毫秒
1.
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.
Takeshi Yoneyama 《Sports Engineering》2018,21(4):277-282
The relation between the ski side-cut radius and deflection during a turn has been investigated. Using a model wherein the ski slides along a turn of a constant radius with an edging angle, it was found that the side-cut radius increases and the ski-deflection radius decreases as the edging angle increases. Even if additional deflection is necessary in the front part of the ski to form the turn groove, the side-cut radius is still the same in the groove. Owing to the constant side-cut radius of existing skis in the turn groove with a large edging angle, the top wide part of the ski causes an increase in skiing resistance. To reduce the skiing resistance, a prototype variable side-cut ski was fabricated, and test skiing was performed. Athletes felt more stable in the turn with the variable side-cut ski and found it easier to increase speed. 相似文献
3.
Y. Hirano 《Sports Engineering》2006,9(4):221-228
Time differences between medalists at Olympic or World Cup alpine ski races are often less than 0.01 s. One factor that could
affect these small differences is the line taken between the numerous gates passed through while speeding down the ski slope.
The determination of the ‘quickest line’ is therefore critical to winning races. In this study the quickest lines are calculated
by direct optimal control theory which converts an optimal control problem into a parameter optimization problem that is solved
using a nonlinear programming method. Specifically, the problem is described in terms of an objective function in which state
and control variables are implicitly involved. The objective function is the time between the starting point and finishing
gate, while state variables are positions of the ski-skier systems on a ski slope, rotational angles of skis, velocities,
and rotational velocity at a discrete time, i.e., a node. The control variable at each node is the skier-controlled edging
angle between the ski sole and snow surface. Equations of motion of the ski-skier system on a ski slope are numerically satisfied
at the midpoint between neighbouring nodes, and the original problem is converted into a nonlinear programming problem with
equality and inequality constraints. The problem is solved by the sequential quadratic programming method in which numerical
calculations are carried out using the MATLAB Optimization Toolbox. Numerical calculations are presented to determine the
quickest lines of an uphill and a downhill ski turn with a starting point, first gate, and second gate (finish line) having
been successfully carried out. The quickest line through four gates could not be calculated due to numerical difficulty. Instead,
the descent line was respectively calculated for an uphill and downhill turn and simply added, giving a resultant time that
represents an upper bound. 相似文献
4.
A new sensor for detecting ski bending and torsional deflection during an actual ski turn on the snow has been developed.
It consisted of bending and torsion sensors connected by light rigid beams. This structure was fixed to the upper surface
of a ski and passed through a tunnel in the central binding plate. The bending and torsion sensors were strain cells, designed
to reject strain orthogonal to the desired measurement direction. The calibration factor for each sensor was determined in
a jig, then the calibration of the overall sensor assembly was checked by static bending experiments and a free vibration
test. A data logger recorded the strain signals synchronously with other data such as the components of the earth’s magnetic
field measured by a sensor on the ski. The data set allowed reconstruction in software of the instantaneous shape, direction
and edge angle of the ski. The purpose of this paper is mainly to introduce the equipment used and methods developed. Tests
of the sensor performance are described. Results from a ski run on snow are presented to show how the various types of data
can be combined. A skilled ski athlete performed long turns with the ski at about 60 km/h on a groomed snow surface at Shiga
Kogen in Japan. The experiment on snow showed that the deformation of the ski was predominantly bending; torsional deflection,
although measurable, had only a small effect on the shape of the running edge. The ski edge adopted a symmetrical circular
bent shape with an unexpectedly small radius when on the outside, but was unconstrained, lightly loaded and nearly straight
when on the inside. 相似文献
5.
A robot that simulates a number of human leg joint motions during carved turns has been developed. Each leg had six degrees
of freedom like those of human athletes. An on-board computer controlled the sequence of joint angles in an open-loop mode
during skiing on an artificial grass slope. The relations among joint motions, reacting forces and turn trajectory were investigated
by programming various motions of the robot. At first, the effect of basic joint motions, such as abduction–adduction and
flexion–extension of the hip, knee and ankle joints were investigated. Then the sequence of a top athlete’s joint motions,
measured in a separate study, was applied to investigate its effect on the ski turn. The human-inspired programme produced
a more even force balance between the skis and also a higher-quality turn. The requirements for a successful physical model
of a human skier are discussed. 相似文献
6.
Erich Muller Roger Bartlett Christian Raschner Hermann Schwameder Ulrike Benko-Bernwick Stefan Lindinger 《Journal of sports sciences》2013,31(6):545-559
We compared selected kinematic variables for four different ski turn techniques performed by five experienced and five intermediate male skiers. The four ski turn techniques were the upstem turn, the downstem turn, the parallel turn and the parallel step turn. Each turn was divided into the initiation phase and the first and second steering phases. Most of the statistically significant differences (P < 0.05) between the two groups were found for the initiation phases of the four turns. Both the hip axis-hand axis angle and the edging angle of the uphill ski were significantly different between the two groups for the upstem turn at the beginning of the initiation phase. For the downstem turn, significant differences between the groups were found at the start of the initiation phase for the hip axis-hand axis angle, the shoulder axis-fall line angle, and the edging angle of the uphill ski. The standard deviation of the distance between the tips of the two skis over the second steering phase also differed significantly between the two groups. For the parallel step turn, significant differences were found at the start of the initiation phase for the edging angle of the downhill ski and the downhill ski to movement direction angle. Significant differences were also found for the edging angle of the downhill ski in the middle of the second steering phase and the shoulder axis to movement direction angle at the end of this phase. For the initiation phase of the parallel turn, significant differences were found for the timing of setting the ski pole, the uphill knee angle at the start of this phase and the range of the knee angle of the uphill leg from the start to the end of this phase. For this turn, significant differences between the two groups were also found for the edging angle of the downhill ski in the middle of the second steering phase and the shoulder axis to movement direction angle at the end of this phase. One of the reasons it was possible to identify a few significant differences only for the turns analysed, was the variability within the intermediate group: for most of the variables analysed, the standard deviation was much higher for the intermediate than for the experienced group. 相似文献
7.
Background:During an experiment,a ski racer equipped with various measurement devices suffered an anterior cruciate ligament(ACL)rupture in his right knee.The aim of this study was to describe the underlying injury mechanism from a functional perspective.Methods:Eight giant slalom turns(i.e.,4 left turns),followed by 1 left turn at which the ACL injury occurred,were recorded by 2 video cameras,electromyography of 4 relevant muscle groups,inertial measurement units to measure knee and hip angles,and pressure insoles to determine ground reaction forces.Results:Due to a loss of balance,the ski racer began to slide sideways at the apex of a left turn.During sliding,his right(outside)leg was actively abducted upward without touching the ground.The ski racer then attempted to stand up again by dropping his leg back towards the snow surface.The end of this dropping was accompanied by a decrease in electromyographic activity in the knee stabilizing muscles.Once the inside edge of the outer ski caught the snow surface,a rapidly increasing peak force,knee flexion,and an aggressive sudden activation of the vastus medialis muscle were observed,while biceps femoris and rectus femoris further decreased their activation levels.This likely resulted in excessive anterior translation of the tibia relative to the femur,causing damage to the ACL.Conclusion:Our example emphasizes that ski racers should not get up until they stop sliding.Remember:“When you’re down,stay down.” 相似文献
8.
The aim of this work is to develop a methodology for the glide testing of waxed skis at an indoor ski centre, using artificial
snow. Two skiers, one acting as a control with unwaxed skis, undertook the test runs over a 50-m course. Timing gates allowed
split times to be measured for a selection of waxes, as well as unwaxed skis. Five runs were conducted for each ski preparation,
interlaced with control runs. Unwaxed skis produced similar run times to waxed skis for the complete course, with measurements
showing their probable superiority over the first 10 m. A tentative interpretation involves the delay in forming a lubricating
meltwater film under waxed skis by comparison with unwaxed skis. Recommendations are made for future measurements, including
a longer course, close matching of skiers’ masses and ski sizes, all timing systems accurate to 0.001 s, a start 3 m above
the first timing gate and more effective methods of wax removal. 相似文献
9.
Designing tomorrow’s snow park jump 总被引：1，自引：1，他引：0
Recent epidemiological studies of injuries at ski resorts have found that snow park jumps pose a significantly greater risk
for certain classes of injury to resort patrons than other normal skiing activities. Today, most recreational jumps are built
by skilled groomers without an engineering design process, but the Snow Skiing Committee (F-27) of the American Society for
Testing and Materials is considering the inclusion of recreational jumps in their purview which may lead to a greater role
for engineering jump designs in the US in the future. Similar efforts are underway in Europe as well. The purpose of this
work is to review the current state of the science of snow park jumps, describe the jump design process, and outline the role
that modelling will play in designing tomorrow’s snow park jumps. 相似文献
10.
Bulge-disc type pressure sensors of diameter 6 mm were fitted as near as possible to the running edge of a modern carved ski.
The pressure signals were sampled at 30 Hz during long turns on snow, synchronously with signals from a geomagnetic compass
and a pressure pad in the ski boot. The pressure from the snow was found to be highly variable with a mean value of about
50 kPa and dynamic pressure spikes up to 300 kPa. With the outside leg, the snow contact width in the rear part of the ski
was found to be slightly wider, on average, than for the front part, as expected for a carving turn. Correlation within the
pressure sensor data showed that the rapid pressure fluctuations were probably not due to bumps or features on the snow; instead
they were probably caused by many small-scale collapses of the snow structure as the ski passed. 相似文献
11.
The spin-stabilised sports disc, more commonly known as the Frisbee, is used for a variety of recreation and sporting activities.
Frisbees have unique flying characteristics compared to other sports projectiles because they depend on spin for stability
during flight and, at typical launch speeds, aerodynamic lift is greater than or equal to the weight of the disc. In this
paper, a six degree of freedom mathematical model of a spinning disc wing is developed and a simple analytical expression
derived for the disc roll rate in straight and level flight. It is shown that dimensionless disc trajectories will be similar
for similar values of a parameter based on the ratio of the disc static margin to the disc advance ratio. The mathematical
model is implemented as a simulation in Matlab using steady model parameters obtained from wind tunnel tests and unsteady
parameters from flight tests. Simulation results are shown to be in reasonable agreement with limited available experimental
flight data. The effect of launch conditions has been investigated using a series of numerical experiments. It is found that
flight path curvature in the horizontal plane increases with decreasing advance ratio, as expected. Pitch angles at launch
for maximum range and maximum duration are approximately 10° and 20° respectively. Also, the locus of disc landing position
as a function of launch roll angle has been shown to be an ‘S’ shaped curve, with the straightest flight occurring for an
initial roll angle of-6°. Finally, the simulation has been extended to include the effects of hypothetical control inputs,
enabling simulation of novel Frisbee manoeuvres. 相似文献
12.
简要回顾了中国冰雪运动三十多年来在世界大型比赛中的成绩,指出雪上项目一直是中国冬季运动短板的现实和困境所在。通过对我国雪上项目发展存在的问题进行分析,提出除了经费投入严重不足以外,困扰中国雪上项目发展的深层原因还包括体制、后备人才培养、社会基础和文化氛围等诸多因素。针对这些深层次的因素,提出了更新发展理念、完善管理体制、注重运动员全面发展、积极发展滑雪文化和滑雪产业等扩大根基的解决出路与途径。旨在改变雪上项目整体水平落后的局面,进一步促进我国雪上运动的繁荣发展。 相似文献
13.
Konstantin I. Matveev 《Sports Engineering》2017,20(4):293-298
This paper addresses sliding friction of a ski during steady horizontal gliding on snow. A simple mathematical theory accounting for both dry and wet friction is developed. The water film evolution along a ski is calculated with a lumped-element thermal model. An analytical solution is obtained for the ski friction force. Representative calculation results are demonstrated for a range of ski velocity, contact surface area fraction, snow temperature, and ski aspect ratio. 相似文献
14.
A continuously waxed ski has been developed that releases a thin film of lubricant under the base of a ski. This replicates the melt water layer observed in snow skis which is caused by frictional and solar heating. The system is particularly effective on artificial (dry) slopes where skiers slide on plastic bristles rather than snow. Speeds comparable to those achieved on snow are achieved using this system and this improves the experience for the skier. Speed enhancements on plastic slopes of up to 50?% have been achieved using solutions of polyethylene glycol in water. There is speed enhancement of approximately 9?% on artificial snow and 2?% on fresh alpine snow. The latter value is highly significant as it can be the difference between winning a medal in ski competitions and finishing outside the top ten. In addition to the quantitative data, qualitative athlete perceptions were also recorded and show that a feel like snow can be achieved on artificial surfaces. Because the lubrication system is attached to the ski, it allows personal performance enhancement irrespective of a water misting system being in operation or not. The design complies with the equipment regulations of the skiing??s international governing body so it can be used in competition. 相似文献
15.
16.
Participants in the sport of snow skiing devote considerable effort to reduce sliding friction of the ski. A large industry is devoted to providing products and ski preparation methods with claims of improved ski performance, sometimes at considerable expense. Despite this attention to the topic, there are very little data available to skiers that quantify the effect these products and methods have on reducing ski friction. Determining the coefficient of friction of a ski on snow presents a significant technical challenge. Our approach has been to develop a tribometer incorporating a series of proximity sensors to test commercially available ski equipment and waxes on natural snow. We developed a test protocol that significantly reduces the experimental noise associated with variable environmental conditions enabling us to differentiate the difference in friction between two pairs of skis with a resolution of 0.001. A large body of test data was acquired over a wide range of environmental conditions to quantify the effect of ski wax and base texturing treatments in terms of coefficient of friction in a way that is of practical use to skiers. An exercise physiology power model was used to estimate the ski race time difference that could be expected from changing the coefficient of friction. 相似文献
17.
在“后哥本哈根时代”,全球变暖已成为当今全球棘手的问题,其影响是全面的,针对于此现象对最近几年雪上赛事的影响进行研究,总结出温度升高造成的雪期缩短、人工造雪产生弊端等全球变暖对雪上赛事的直接影响和滑雪场运营成本增加、影响雪上竞技项目的训练、影响雪上项目社会普及程度等间接影响。提出雪场选址要有科学性、注重天然雪的保护、人人做节能减排带头人等解决的对策,为应对全球变暖给雪上赛事带来的不利影响提供理论参考。 相似文献
18.
A forward dynamics computer simulation for replicating tennis racket/ball impacts is described consisting of two rigid segments
coupled with two degrees of rotational freedom for the racket frame, nine equally spaced point masses connected by 24 visco-elastic
springs for the string-bed and a point mass visco-elastic ball model. The first and second modal responses both in and perpendicular
to the racket string-bed plane have been reproduced for two contrasting racket frames, each strung at a high and a low tension.
Ball/string-bed normal impact simulations of real impacts at nine locations on each string-bed and six different initial ball
velocities resulted in <3% RMS error in rebound velocity (over the 16–27 m/s range observed). The RMS difference between simulated
and measured oblique impact rebound angles across nine impact locations was 1°. Thus, careful measurement of ball and racket
characteristics to configure the model parameters enables researchers to accurately introduce ball impact at different locations
and subsequent modal response of the tennis racket to rigid body simulations of tennis strokes without punitive computational
cost. 相似文献
19.
湖北省九宫山滑雪场既是中部地区为数极少的滑雪场之一,真正实现了"北雪南展"的新突破,更使国家4A级旅游景区九宫山成为了名副其实的四季皆游的著名风景名胜。然而,通过走访调查、现场咨询、对比分析等研究方法发现,九宫山滑雪场在经营管理、营销手段、宣传规划、硬件设施等方面还存在着很多问题,与国内外先进滑雪场相比还有一定的欠缺和差距,尤其是市场营销定位不够明晰。从突显南方冰雪体育独特旅游资源特色,重视市场营销模式的多元化,拓展对九宫山滑雪场资源的利用整合等方面提出对策与建议,以期能使九宫山滑雪场不断优化体育旅游市场营销的定位,真正实现其冰雪体育旅游的与时俱进和可持续性发展。 相似文献
20.
Modern treadmills allow cross-country skiers, biathletes and ski-orienteer’s to test their physical performance under laboratory
conditions using classical and freestyle techniques on roller skis. The differences in performance between tests are quite
small for elite athletes, and it is therefore of great importance to control the rolling resistance of the roller skis. Otherwise
different physiological tests cannot be accurately compared. This study shows that during a warm-up period of 30 min the coefficient
of rolling resistance (μ
R) decreases to about 60–65% and 70–75% of its initial value for freestyle and classical roller skis, respectively. Simultaneous
measurements of temperature and μ
R shows that stabilized rolling resistance corresponds to a certain running temperature for a given normal force on the roller
ski. Tests were also performed on the influence on μ
R of normal force, velocity and inclination. Normal forces produced significant influence on μ
R, while different velocities and inclinations of the treadmill only resulted in small changes in μ
R. 相似文献