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1.
Dynamic behaviour of soils used for natural turf sports surfaces 总被引：1，自引：0，他引：1
The modulus and damping properties of soils in compression are a function of soil type, water content, stress history and
loading rate. To model human–surface interaction with natural turf sports surfaces, stiffness and damping properties must
be determined at dynamic loading rates. Two contrasting soil types, a Sand and a Clay Loam, commonly used in sports surfaces
were loaded uniaxially to 2 kN at loading rates between 0.6 and 6 kN s−1 in modified dynamic soil testing apparatus. Soils were compacted prior to loading but initial cycles resulted in viscoplastic
deformation, with strain accumulation with repeated cycles of loading. Ultimately a resilient, viscoelastic steady-state equilibrium
with loading was established. Resilient modulus and damping ratio varied with soil type, water content, stress history and
increased significantly with loading rate. The resilient modulus of the Sand soil, typical of modern free-draining sand construction
natural turf sports surfaces, was significantly greater than that of a Clay Loam soil more characteristic of traditional natural
turf surfaces; reducing water content caused an increase in modulus and a decrease in damping ratio in the Clay Loam soil.
Determination of these properties provides initial data for the modelling natural turf surface behaviour in terms of both
ball and human interactions, with further research required to determine the effect of both grass roots and leaves on mechanical
behaviour. 相似文献
2.
Natural turf pitches are used for many outdoor sports. Turf is a complex network of interacting organic material, soil textures and water content. Turf is susceptible to damage under large surface forces, caused by intensive player movements in rugby union and football. To assess and monitor surface stability, there needs to be a reliable test method for ground staff and other stakeholders. At present, no turf stability mechanical test method exists that represents player–surface interaction, especially to represent a linear movement across the surface such as in a rugby scrummage. This paper describes the development of a novel device for assessing turf stability. Verification was undertaken in the laboratory on a variety of controlled soil samples, and during a field study. The device measurements were shown to be sensitive to the shear strength of a high clay content soil at varying water content and to the density and type of sandy soils. A programme of field data on high quality pitches suggested a large effect of the turf root reinforcement. A conceptual model of soil failure induced by the device was developed to identify the key soil variables and support experimental data interpretation. 相似文献
3.
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
4.
Noriaki Ichihashi Hiroki Umegaki Tome Ikezoe Masatoshi Nakamura Satoru Nishishita Kosuke Fujita 《Journal of sports sciences》2016,34(23):2155-2159
The aims of this study were to investigate the effects of a 4-week intervention of static stretching (SS) on muscle hardness of the semitendinosus (ST), semimembranosus (SM) and biceps femoris (BF) muscles. Shear elastic modulus was measured by using ultrasound shear wave elastography as the index of muscle hardness. Thirty healthy men (age 22.7 ± 2.2 years) volunteered for this study and were randomly assigned to the SS intervention group (n = 15) or the control group (n = 15). Participants in the SS intervention group received a 4-week stretch intervention for the hamstrings of their dominant leg. Shear elastic moduli of the hamstrings were measured at initial evaluation and after 4 weeks in both groups at a determined angle. In all muscles, the shear elastic modulus decreased significantly after SS intervention. The percentage change in the shear elastic modulus from the value at initial evaluation to after 4 weeks intervention was greatest in the SM. These results suggest that SS intervention has chronic effects on reducing hardness of the hamstring muscle components, especially the SM muscle. 相似文献
5.
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
6.
Knee joint forces during downhill walking with hiking poles 总被引：1，自引：0，他引：1
Schwameder H Roithner R Müller E Niessen W Raschner C 《Journal of sports sciences》1999,17(12):969-978
The aim of this study was to determine external and internal loads on the knee joint during downhill walking with and without hiking poles. Kinematic, kinetic and electromyographic data were collected from eight males during downhill walking on a ramp declined at 25 degrees. Planar knee joint moments and forces were calculated using a quasi-static knee model. The results were analysed for an entire pole-cycle as well as differentiated between single and double support phases and between each step of a pole-cycle. Significant differences between downhill walking with and without hiking poles were observed for peak and average magnitudes of ground reaction force, knee joint moment, and tibiofemoral compressive and shear forces (12-25%). Similar reductions were found in patellofemoral compressive force, the quadriceps tendon force and the activity of the vastus lateralis; however, because of a high variability, these differences were not significant. The reductions seen during downhill walking with hiking poles compared with unsupported downhill walking were caused primarily by the forces applied to the hiking poles and by a change in posture to a more forward leaning position of the upper body, with the effect of reducing the knee moment arm. 相似文献
7.
In this paper, we present results on the measurement and analysis of the sound that is produced by the sharp impact loading of a golf ball by a flat massive object (e.g. the face of a golf club). We discuss: (a) the motivation for such a study; (b) some necessary background information on how golf balls vibrate; (c) the techniques used to acquire and analyse the data; and (d) an analysis of the sound made by dropping balls on a smooth, massive concrete target surface. These results establish a simple method for rapid and non-destructive measurement of the effective high-frequency elastic shear moduli of balls and ball cores. 相似文献
8.
In this paper, we present results on the measurement and analysis of the sound that is produced by the sharp impact loading of a golf ball by a flat massive object (e.g. the face of a golf club). We discuss: (a) the motivation for such a study; (b) some necessary background information on how golf balls vibrate; (c) the techniques used to acquire and analyse the data; and (d) an analysis of the sound made by dropping balls on a smooth, massive concrete target surface. These results establish a simple method for rapid and non-destructive measurement of the effective high-frequency elastic shear moduli of balls and ball cores. 相似文献
9.
The purpose of this study was to compare the knee extensor demands and low back injury risks of the front and back squat exercises. Highly strength-trained college-aged males (n = 8), who performed each type of squat (Load = 75% of front squat one repetition maximum), were filmed (50 fps) from the sagittal view. The body was modeled as a five link system. Film data were digitized and reduced through Newtonian mechanics to obtain joint forces and muscle moments. Mean and individual subject data results were examined. The maximum knee extensor moment comparison indicated similar knee extensor demands, so either squat exercise could be used to develop knee extensor strength. Both exercises had similar low back injury risks for four subjects, but sizable maximum trunk extensor moment and maximum lumbar compressive and shear force differences existed between the squat types for the other subjects. The latter data revealed that with the influence of trunk inclination either exercise had the greatest low back injury risk (i.e., with greater trunk inclination: greater trunk extensor demands and lumbar shear forces, but smaller lumbar compressive forces). For these four subjects low back injury risk was influenced more by trunk inclination than squat exercise type. 相似文献
10.
Alireza Karimi Reza Razaghi Seyed Mohammadali Rahmati Toshihiro Sera Susumu Kudo 《Sports Engineering》2018,21(4):359-365
Eye injuries from blunt forces and penetrating objects can cause morbidity, disability, and blindness. Most of these injuries are preventable not only by understanding the detail of injury, but also by portraying the role of the ball’s characteristics. Basketball can induce severe forms of injuries to the eye. This study was aimed at performing a numerical analysis through the fluid–structure interaction on ocular trauma. Balls with different diameters, elastic moduli, and pressures were shot to the eye. Injury in terms of the stresses and deformations in each component of the eye was computed at ~?0.72 mm deformation in the apex of the cornea. By increasing the diameter of the ball from 20 to 26 cm the stress in the eye components, excluding the aqueous body, vitreous body, and extraconal fat, increased. Stresses of 2.68 and 3.19 MPa were observed in the cornea under the ball diameters of 20 and 26 cm, respectively. Conversely, the elastic modulus and pressure of the ball in the defined range showed no considerable role on the stress in the eye components. The results revealed the importance of the ball size compared to the elastic modulus and pressure in the stress accumulation as a result of ocular trauma. 相似文献
11.
根据材料力学理论,利用测力—摄影同步采集的方法,在弹性材料电测技术的帮助下,计算出撑杆跳高运动员握杆两手对撑杆的作用力,发现了运动员的一些用力特点。在撑杆跳高技术的研究方法上作了进一步的探索。 相似文献
12.
Reaction forces experienced by gymnasts swinging on the high bar may be determined indirectly using inverse dynamics analysis
or may be measured using strain gauges. The accuracy of inverse dynamics analysis may be poor because of errors in the estimated
inertia parameters and in the accelerations obtained from digitized data. On the other hand the use of strain gauges is not
always possible in elite competition. This paper presents a method for estimating the reaction forces based on the linear
displacements of the bar.
The bar was modelled as a point mass attached to horizontal and vertical linear springs (obeying Hooke’s law) with stiffness
coefficients determined from static loading. The stiffness coefficients of the bar were determined with three different tensions
in the stabilizing cables of the high bar. A force and video analysis of backward giant circles was performed. Estimates for
the reaction forces were obtained by multiplying the bar displacements from the video analysis by the stiffness coefficients
determined from the static loadings. Comparisons were made between the estimated reaction forces and the reaction forces recorded
using strain gauges attached to the high bar.
Varying the tension in the stabilizing cables of the high bar did not effect the stiffness of the bar. Root mean squared differences
between estimated and recorded reaction forces were on average within 99 N for three ‘regular’ and three ‘accelerated’ giant
circles. This was less than 3.5% of the range of forces recorded. The bar displacement method was able to estimate the peak
reaction forces to within 7% on average, which compares favourably with 24% reported by Gervais (1993) using inverse dynamics. 相似文献
13.
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
14.
In this paper, we report the discrete frequencies at which golf balls can vibrate, the mode patterns of these vibrations and how these modes can be excited. There are two broad classes of modes: those that radiate sound waves and those that do not. Both silent and acoustic modes are excited by tangential (i.e. spin-producing) impact forces; only acoustic modes are excited by radial impact forces. Exact analytical results for a homogeneous ball core are compared with finite element numerical results for both a core and a model two-piece ball. Correspondences are readily established for the important low-frequency modes, and the good agreement suggests the validity of these results for real golf balls. The results potentially provide the basis for a rapid, simple and non-destructive method of measuring the effective high-frequency elastic shear modulae of balls (and ball cores) as well as a method for 'tuning' the performance of balls for specific clubs. Some of these aspects are explored further in our companion paper in this issue. 相似文献
15.
In this paper, we report the discrete frequencies at which golf balls can vibrate, the mode patterns of these vibrations and how these modes can be excited. There are two broad classes of modes: those that radiate sound waves and those that do not. Both silent and acoustic modes are excited by tangential (i.e. spin-producing) impact forces; only acoustic modes are excited by radial impact forces. Exact analytical results for a homogeneous ball core are compared with finite element numerical results for both a core and a model two-piece ball. Correspondences are readily established for the important low-frequency modes, and the good agreement suggests the validity of these results for real golf balls. The results potentially provide the basis for a rapid, simple and non-destructive method of measuring the effective high-frequency elastic shear modulae of balls (and ball cores) as well as a method for 'tuning' the performance of balls for specific clubs. Some of these aspects are explored further in our companion paper in this issue. 相似文献
16.
Abstract The purpose of this investigation was to examine the fluid dynamic characteristics of the two most commonly used oar blades: the Big Blade and the Macon. Scaled models of each blade, as well as a flat Big Blade, were tested in a water flume using a quasi-static method similar to that used in swimming and kayaking research. Measurement of the normal and tangential blade forces enabled lift and drag forces generated by the oar blades to be calculated over the full range of sweep angles observed during a rowing stroke. Lift and drag force coefficients were then calculated and compared between blades. The results showed that the Big Blade and Macon oar blades exhibited very similar characteristics. Hydraulic blade efficiency was not therefore found to be the reason for claims that the Big Blade could elicit a 2% improvement in performance over the Macon. The Big Blade was also shown to have similar characteristics to the flat plate when the angle of attack was below 90°, despite significant increases in the lift coefficient when the angle of attack increased above 90°. This result suggests that the Big Blade design may not be completely optimized over the whole stroke. 相似文献
17.
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
18.
Liang-Ching Tsai Yi-An Ko Kyle E. Hammond John W. Xerogeanes Gordon L. Warren Christopher M. Powers 《Journal of sports sciences》2017,35(24):2405-2411
Although most ACL injury prevention programmes encourage greater hip and knee flexion during landing, it remains unknown how this technique influences tibiofemoral joint forces. We examined whether a landing strategy utilising greater hip and knee flexion decreases tibiofemoral anterior shear and compression. Twelve healthy women (25.9 ± 3.5 years) performed a drop-jump task before and after a training session (10–15 min) that emphasised greater hip and knee flexion. Peak tibiofemoral anterior shear and compressive forces were calculated using an electromyography (EMG)-driven knee model that incorporated joint kinematics, EMG and participant-specific muscle volumes and patella tendon orientation measured using magnetic resonance imaging (MRI). Participants demonstrated a decrease in peak anterior tibial shear forces (11.1 ± 3.3 vs. 9.6 ± 2.7 N · kg?1; P = 0.008) and peak tibiofemoral compressive forces (68.4 ± 7.6 vs. 62.0 ± 5.5 N · kg?1; P = 0.015) post-training. The decreased peak anterior tibial shear was accompanied by a decrease in the quadriceps anterior shear force, while the decreased peak compressive force was accompanied by decreased ground reaction force and hamstring forces. Our data provide justification for injury prevention programmes that encourage greater hip and knee flexion during landing to reduce tibiofemoral joint loading. 相似文献
19.
The purpose of this investigation was to examine the fluid dynamic characteristics of the two most commonly used oar blades: the Big Blade and the Macon. Scaled models of each blade, as well as a flat Big Blade, were tested in a water flume using a quasi-static method similar to that used in swimming and kayaking research. Measurement of the normal and tangential blade forces enabled lift and drag forces generated by the oar blades to be calculated over the full range of sweep angles observed during a rowing stroke. Lift and drag force coefficients were then calculated and compared between blades. The results showed that the Big Blade and Macon oar blades exhibited very similar characteristics. Hydraulic blade efficiency was not therefore found to be the reason for claims that the Big Blade could elicit a 2% improvement in performance over the Macon. The Big Blade was also shown to have similar characteristics to the flat plate when the angle of attack was below 90 degrees , despite significant increases in the lift coefficient when the angle of attack increased above 90 degrees . This result suggests that the Big Blade design may not be completely optimized over the whole stroke. 相似文献
20.
Bicycle suspensions aim to improve riding performance and rider comfort through reduced impact and vibration transmission
to frame and rider. This study compared vibration damping of five mountain bike suspension systems and a rigid fork on gravel
and in trail conditions by quantifying accelerations at the axle and frame. Spectral analyses of the acceleration signals
revealed two distinct frequency regions from 0 to about 100 Hz and from about 300 to 400 Hz. The various suspension systems
were all effective in attenuating vibration over the low frequency region. Vibration amplitudes at the frame were considerably
less than at the axle for the suspension conditions (30–60% reduction) while only minor attenuation was observed with the
rigid fork (10–15%). In the high frequency region between 300–400 Hz, the signal was strongly attenuated at the frame for
all conditions, including the rigid fork. Trail conditions elicited greater amplitude low frequency vibrations than did gravel
conditions. While all suspension systems were somewhat effective in reducing vibration of the frame, air-oil forks had significantly
better vibration attenuation than did elastomer or linkage systems. 相似文献