共查询到20条相似文献，搜索用时 31 毫秒
1.
This study involved a theoretical and an experimental investigation of the direct free kick in soccer. Our aim was to develop a mathematical model of the ball's flight incorporating aerodynamic lift and drag forces to explore this important 'set-play'. Trajectories derived from the model have been compared with those obtained from detailed video analysis of experimental kicks. Representative values for the drag and lift coefficients have been obtained, together with the implied orientation of the ball's spin axis in flight. The drag coefficient varied from 0.25 to 0.30 and the lift coefficient from 0.23 to 0.29. These values, used with a simple model of a defensive wall, have enabled free kicks to be simulated under realistic conditions, typical of match-play. The results reveal how carefully attackers must engineer the dynamics of a successful kick. For a central free kick some 18.3 m (20 yards) from goal with a conventional wall, and initial speed of 25 m·s?1, the ball's initial elevation must be constrained between 16.5° and 17.5° and the ball kicked with almost perfect sidespin. 相似文献
2.
Two different measurement techniques are used to examine the effect of surface geometry on soccer ball trajectories. Five
professional players are observed using high-speed video when taking curling free kicks with four different soccer balls.
The input conditions are measured and the average launch velocity and spin are found to be approximately 24 m/s and 106 rad/s.
It is found that the players can apply more spin (~50%) on average to one ball, which has a slightly rougher surface than
the other balls. The trajectories for the same four balls fired at various velocities and spin rates across a sports hall
using a bespoke firing device are captured using high-speed video cameras, and their drag and lift coefficients estimated.
Balls with more panels are found to experience a higher lift coefficient. The drag coefficient results show a large amount
of scatter, and it is difficult to distinguish between the balls. Using the results in a trajectory prediction programme it
is found that increasing the number of panels from 14 to 32 can significantly alter the final position of a 20 m-curling free
kick by up to 1 m. 相似文献
3.
Alexandra Atack Grant Trewartha Neil E. Bezodis 《Sports biomechanics / International Society of Biomechanics in Sports》2019,18(5):457-469
The appropriate determination of performance outcome is critical when appraising a performer’s technique. Previous studies of rugby place kicking technique have typically assessed performance based on ball velocity, but this is not the sole requirement. Therefore, a mathematical model of rugby place kick ball flight was developed to yield a single measure more representative of true performance. The model, which requires only initial ball flight kinematics, was calibrated and validated using empirical place kick data, and found to predict ball position with a mean error of 4.0% after 22 m of ball flight. The model was then applied to the performances of 33 place kickers. The predicted maximum distance, a single performance measure which accounted for initial ball velocity magnitude and direction, and spin, was determined using the model and was compared against ball velocity magnitude. A moderate association in the rank-order of the kicks between these two measures (ρ = 0.52) revealed that the relative success of the kicks would be assessed differently with each measure. The developed model provides a representative measure of place kick performance that is understandable for coaches, and can be used to predict changes in performance outcome under different ball launch or environmental conditions. 相似文献
4.
《European Journal of Sport Science》2013,13(4):279-284
Abstract The location and outcome of all free kicks taken directly at goal in the 2007 women's football World Cup were assessed to identify areas with the most goal-scoring potential and assist with tactical decisions and training design. Video of all free kicks taken directly at goal in the 32 games was captured and the location of the ball on the pitch was calculated from pitch markings and image pixel coordinates using a customized curve-fitting method. The outcome of each free kick was determined and for those that resulted in a goal or were saved, information on ball flight time and the placement of the ball relative to the goal was reported. All seven free kicks that resulted in a goal were taken from a central area within 7 m of the penalty circle, placed at the edge of the goal within approximately 1 m of the goalpost, and had an average flight time of 1.09 s, which was significantly faster than for those that were saved. All free kicks directed towards the bottom and centre of the goal resulted in straightforward saves for the goalkeeper. It is recommended that teams should consider a direct shot from free kicks awarded within 7 m of the penalty circle. For free kicks from wide areas and areas further from the goal, players should be aware of their individual ability and only take a shot when they perceive the probability of scoring a goal to be high. Otherwise, alternative attacking strategies should be considered to avoid an easy turnover of possession. 相似文献
5.
The aerodynamics of an American NFL football during an end over end kick were investigated utilizing a custom rotating apparatus and large-scale wind tunnel. Non-rotating lift and drag coefficients were measured and agree well with previous data from other athletic balls and a smooth sphere. The rotation effect on an American football increased both the lift and drag coefficients more dramatically than what has been seen with symmetrical objects over a wide range of rotational rates. The results from this study can be used to more accurately predict the flight trajectory of an end over end kick, and help optimize the balance between kick velocity and rotational speed for a given kicker’s leg strength. 相似文献
6.
We develop and use a numerical model to investigate the window of opportunity of free kicks in association football. The planar multibody forward dynamics model comprises a two segment leg model with joint actuations, a football, a wall and the turf. Contact mechanics is defined to model the impact of the foot and the ball’s interaction with the different elements in the environment. The optimum kick is determined using the global optimization algorithm differential evolution, requiring millions of kick simulations. The sensitivity of various solutions to parameter perturbation is investigated. It is concluded that toe kicks are theoretically superior to instep kicks, but are difficult to perform reliably. The results also show that small perturbations in parameters can lead to embarrassingly failed kicks. 相似文献
7.
Flight dynamics of the screw kick in rugby 总被引：1，自引：1，他引：0
This paper describes the aerodynamic forces and the flight trajectory for the screw (spiral) kick in rugby. The screw kick
is defined as that which causes the ball to spin on its longitudinal axis. The aerodynamic forces acting on a rugby ball spinning
on its longitudinal axis were measured in a wind tunnel using a six-component strut type balance. It was found that the drag,
the lift and the pitching moment depend on the angle of attack, while the side force (Magnus force) depends on both the spin
rate and the angle of attack in the range where the wind speed lies between 15 and 30 m s-1 and the spin rate is between 1 and 10 revolutions per second. Moreover, the flight trajectory was obtained by integrating
the full nonlinear six degrees of freedom equations of motion on the basis of aerodynamic data. In a simulation, a ball spinning
on its longitudinal axis tended to hook toward or away from the touchline even if the velocity and angular velocity vectors
were parallel to the touchline. The direction of the hook depends on the direction of the angular velocity vector. The initial
direction of the hook depends on the relationship between the flight path angle and the pitch angle as well as the direction
of the angular velocity vector. 相似文献
8.
Measurements are presented of drag and lift on new tennis balls in flight. Two video cameras were used to measure the velocity and height of the balls at two positions separated horizontally by 6.4 m. The balls were fired from a ball launcher at speeds between 15 and 30 m/s and with topspin or backspin at rates up to 2,500 rpm. Significant shot-to-shot variations were found in both the drag and lift coefficients. The average drag coefficient was 0.507 ± 0.024, independent of ball speed or spin, and lower than the value usually observed in wind tunnel experiments. The lift coefficient increased with ball spin, on average, but significant lift was observed even at very low spin. The latter effect can be attributed to a side force arising from asymmetries in the ball surface, analogous to the side force responsible for the erratic path of a knuckleball in baseball. 相似文献
9.
Masahide Murakami Masato Iwase Kazuya Seo Yuji Ohgi Reno Koyanagi 《Sports Engineering》2014,17(4):217-225
Ski jumping flight posture was analyzed for achieving large flight distance on the basis of high-speed video images of the initial 40 m part of 120-m ski jumping flight. The time variations of the forward leaning angle and the ski angle of attack were measured from the video images, and the aerodynamic forces were calculated from the kinematic data derived from the images. Some correlations were investigated between the initial-speed corrected flight distance and such parameters as the angles of jumper, the initial transition time and the aerodynamic force coefficients. The result indicated that small body angle of attack was a key for large flight distance in the initial phase of flight because of small drag force, and that the most distinctive fault of beginners was too large body angle of attack and ski angle of attack leading to aerodynamic stall. Too small drag force does not give an optimal condition for large flight distance because the lift force is also too small. The ratio of the lift to the drag was larger than 0.95 for advanced jumpers. 相似文献
10.
Ball KA 《Journal of sports sciences》2011,29(14):1545-1552
Kicking with the non-preferred leg is important in Australian Football and becoming important in the rugby codes. The aim of this study was to examine differences between preferred and non-preferred leg kicking in the drop punt kick. Seventeen elite Australian Football players performed kicks with the preferred and non-preferred leg. Optotrak Certus collected kinematic data of the kick leg and pelvis (200 Hz) from kick leg toe-off until ball contact. Foot speed, knee and shank angular velocity at ball contact, and pelvis range of motion were significantly larger for the preferred leg (P < 0.05). In contrast, hip and thigh angular velocity at ball contact and hip range of motion were significantly larger for the non-preferred leg. This indicates different movement patterns, with preferred-leg kicks making greater use of the pelvis, knee, and shank while non-preferred leg kicks rely relatively more on the hip and thigh (P < 0.05). Reasons for this difference might be due to locking degrees of freedom or sub-optimal sequencing in the non-preferred leg. The thigh-knee continuum identified by Ball ( 2008 ) was also evident in this study. Findings have implications for training non-preferred leg kicking for performance and injury prevention. 相似文献
11.
为了研究在比赛中双飞踢反击技术出腿的时机,文章通过挑选2006年全国跆拳道锦标赛决赛男子4个级别和女子4个级别,总共8场比赛录像中的运动员,对双飞踢技术运用的情况进行整理。文章采用文献资料法、观察法和数据统计法等研究方法并结合实践经验,对跆拳道的双飞踢反击技术动作进行分析和研究。跆拳道比赛进攻和反击中运用双飞技术已成为重要的得分动作之一,合理运用双飞踢反击技术是比赛取胜的关键。因而在比赛中要想取得优异的成绩,就必须合理运用技术动作,在实战中合理运用双飞踢反击技术动作是比赛中重要的得分手段。 相似文献
12.
The aim of this study was to develop a new method for the determination of lift on spinning baseballs. Inertial trajectories of (a) ball surface markers during the first metre of flight and (b) the centre of mass trajectory near home-plate were measured in a pitch using high-speed video. A theoretical model was developed, incorporating aerodynamic Magnus-Robins lift, drag and cross forces, which predicts the centre of mass and marker trajectories. Parameters including initial conditions and aerodynamic coefficients were estimated iteratively by minimizing the error between predicted and measured trajectories. We compare the resulting lift coefficients and spin parameter values with those of previous studies. Lift on four-seam pitches can be as much as three times that of two-seam pitches, although this disparity is reduced for spin parameters greater than 0.4. 相似文献
13.
The aim of this study was to develop a new method for the determination of lift on spinning baseballs. Inertial trajectories of (a) ball surface markers during the first metre of flight and (b) the centre of mass trajectory near home-plate were measured in a pitch using high-speed video. A theoretical model was developed, incorporating aerodynamic Magnus-Robins lift, drag and cross forces, which predicts the centre of mass and marker trajectories. Parameters including initial conditions and aerodynamic coefficients were estimated iteratively by minimizing the error between predicted and measured trajectories. We compare the resulting lift coefficients and spin parameter values with those of previous studies. Lift on four-seam pitches can be as much as three times that of two-seam pitches, although this disparity is reduced for spin parameters greater than 0.4. 相似文献
14.
目的:探讨环境风对跳台滑雪空中飞行气动特性的影响。方法:通过计算流体力学(computational fluid dynamics,CFD)方法数值模拟预测了不同环境风下跳台滑雪空中飞行空气动力学特性,并探究了水平方向环境风、竖直方向环境风以及侧向环境风对气动特性的影响。将跳台滑雪运动员与滑雪板看成一个多体系统,建立在空中飞行某一种普遍姿态下此多体系统的精细化三维几何模型与网格模型,采用部分时均(partially averaged Navier-Stokes,PANS)湍流模型进行数值模拟,提取多体系统的受力及力矩情况,直观地显示多体系统周围的流场信息。数值预测涉及的水平方向风风速包括-4 m/s、-2.5 m/s、-1 m/s、0 m/s、1 m/s、2.5 m/s、4 m/s等工况;竖直方向风风速包括-8 m/s、-4 m/s、-2.5 m/s、-1 m/s、0 m/s、1 m/s、2.5 m/s、4 m/s、8 m/s等工况;侧向风风速包括1.5 m/s、3.0 m/s、4.5 m/s、7.5 m/s、10.5 m/s、13.5 m/s等工况。结果:1)水平方向环境风下多体系统升力、阻力以及俯仰力矩变化明显,与风速呈现近似线性关系,同时水平逆风情况下力学特性数值结果的增长速度大于水平顺风情况下力学特性数值结果的减小速度;2)在竖直方向风速较小时(小于2.5 m/s),升力、阻力以及俯仰力矩增加缓慢,在竖直方向风速较大时(大于4 m/s),升力、阻力以及俯仰力矩开始相对快速增加,同时,竖直向上环境风使得升力、阻力、俯仰力矩增大,竖直向下环境风使得升力、阻力以及俯仰力矩减小,而且竖直向上环境风情况下增长幅度明显小于竖直向下环境风情况下减少幅度;3)侧向环境风产生偏航力、偏航力矩、翻滚力矩,同时,侧向环境风对运动员的升力、阻力以及俯仰力矩产生影响。在风速较小(小于3 m/s)时,这些力和力矩很小,在风速较大(大于4.5 m/s)时,比较明显。结论:1)水平方向环境风对跳台滑雪空中飞行气动特性的影响非常明显,相较而言,竖直方向环境风和侧向环境风对空中飞行气动特性的影响小很多,但侧向环境风的影响情况较为复杂,对多体系统产生较为明显的偏航力、偏航力矩、翻滚力矩;2)环境风对跳台滑雪空中飞行气动特性的影响机理能够为比赛临场预判与决策提供有效的辅助支持,也为运动员空中飞行稳定性控制与技术训练提供科学指导。 相似文献
15.
Six competitive soccer players were recruited to examine EMG activation in three quadriceps muscles during a kicking accuracy task. Participants performed three maximum instep place kicks of a stationary ball, 11 m perpendicular from the centre of the goal line towards targets (0.75 m(2)) in the four corners of the goal. Surface EMG of the vastus lateralis, vastus medialis, and rectus femoris of the kicking leg was normalized and averaged across all participants to compare between muscles, targets, and the phase of the kick. Although no significant difference were observed between muscles or kick phases, kicks to the right targets produced significantly greater muscle activity than those towards the left targets (P < 0.01). In addition, kicks towards the top right target demonstrated significantly greater muscle activity than towards the top and bottom left (P < 0.01). Under accurate soccer shooting conditions, kicks aimed to the top right corner of the goal demonstrated a higher level of quadriceps muscle activation than those towards the other corners. 相似文献
16.
To determine the flight of a ski jumper it is essential to know what aerodynamic forces are acting on the ski jumper. However,
few data on this are available, especially for a V-style ski jumping flight. We have measured the aerodynamic forces during
the free flight phase for a V-style, as well as a parallel-style, ski jump by employing a full-size model in a wind tunnel.
The aerodynamic force data, (drag, lift and pitching moment) were obtained to create an aerodynamic database. These forces
are given in polynomial form as functions of the angle of attack, the body-ski (forward leaning) angle and the ski-opening
(V-style) angle. Using the polynomial form database is a convenient way of obtaining the aerodynamic forces. Moreover, the
wind tunnel was equipped with a ground effect plate to measure the aerodynamic forces during the landing phase. It was found
that the difference between the lift with and without the ground effect plate increases with the ski-opening angle. The longitudinal
stability in the pitching motion of a body-ski combination is also discussed on the basis of the pitching moment data. This
indicates that a stable pitching oscillation of the body-ski combination may arise around an equilibrium point in the angle
of attack, the trim angle of attack, during flight. 相似文献
17.
Chase M. Pfeifer Timothy J. Gay Jeff A. Hawks Shane M. Farritor Judith M. Burnfield 《Sports Engineering》2018,21(2):95-102
A mechanical field-goal kicking machine was used to investigate toppling ball flight in American football place-kicking, eliminating a number of uncontrollable impact variables present with a human kicker. Ball flight trajectories were recorded using a triangulation-based projectile tracking system to account for the football’s 3-dimensional position during flight as well as initial launch conditions. The football flights were described using kinematic equations relating to projectile motion including stagnant air drag and were compared to measured trajectories as well as projectile motion equations that exclude stagnant air drag. Measured football flight range deviations from the non-drag equations of projectile motion corresponded to deficits between 9 and 31%, which is described by a football toppling compound drag coefficient of 0.007 ± 0.003 kg/m. Independent variables including impact location and impact angle orientation resulted in 15 impact conditions. We found that an impact location of 5.5 cm from the bottom of the ball maximized trajectory height and distance. At the 5.5-cm impact location, alterations in impact angle produced minimal change in football trajectory, including launch angle (range = 1.96 deg), launch speed (range = 1.06 m/s), and range (range = 0.94 m). 相似文献
18.
A badminton shuttlecock flies in a high-drag, and thus, the sport has been a subject of research from the point of view of aerodynamics. A badminton shuttlecock generates significant aerodynamic drag and has a complex flight trajectory. It also has the smallest ballistic coefficient and exhibits the largest in-flight deceleration of any airborne sporting projectile. The ballistic coefficient of a projectile is a measure of its ability to overcome air resistance in flight and is inversely proportional to deceleration. The primary objectives of this study were to measure the aerodynamic properties of feather shuttlecocks under a range of the wind speed (10–60 m/s) and pitch angle (0°–25°). In particular, measurements of aerodynamic forces were performed at high Reynolds numbers (more than Re = 210,000), and the effect of shuttlecock deformation on aerodynamic properties was also investigated, because it is presumed that the flight dynamics is affected by the deformation of the shuttlecock skirt. A shuttlecock skirt is composed of an array of diverging stems, the ends of which are at the convergent end of the skirt, joined together in an end ring. The shuttlecock rotates about its major axis in actual flight, and thus, the experiments were performed on shuttlecocks with and without rotation (spin). Furthermore, the effect of the flow passing through the gaps between the slots (stiffeners) located at the leg portion of the shuttlecock skirt on aerodynamic characteristics is demonstrated by means of a shuttlecock model without gaps, which was completely covered with cellophane tape. The free rotation rate of a shuttlecock increased with an increase in the Reynolds number, and the drag coefficient gradually decreased above Re = 86,000 for a non-rotating shuttlecock. The reduction of drag can be explained by the deformation of the skirt observed in wind tunnel experiments at high speed. In this study, for a rotating shuttlecock, a reduction of drag was not observed over a whole range of Reynolds numbers, because deformation of the skirt for a rotating shuttlecock becomes smaller than that for a non-rotating shuttlecock. However, there was no significant difference in drag coefficient between rotating and non-rotating shuttlecocks, in contrast to the difference in drag coefficient between shuttlecocks with and without gaps. The drag coefficient for a shuttlecock without gaps was significantly smaller than that for a standard shuttlecock (with gaps). For a standard shuttlecock, the air flowed through the gaps into the shuttlecock skirt, and this flow was related to high aerodynamic drag. 相似文献
19.
The penalty shoot-out is used to break tied games in the knock-out stages of soccer competition. The shoot-out, which consists of an alternating series of penalty kicks, is won by the team with the highest goal tally after n kicks per team (n = 5). In the event of a tie after five penalty kicks each, the shoot-out progresses to 'sudden death' by increasing n in iterative fashion (i.e. n = n + 1) until one team obtains a higher goal tally than the other after an equal number of kicks per team. The team to strike first is determined at the end of extra time by the toss of a coin. As each on-field player can be awarded only a single penalty kick, the line-up order in which the penalty kicks are taken allows for the possibility of tactical influence on the final outcome. Consequently, we report a probability analysis of the penalty shoot-out in soccer from which we identify the following pre- and post-game strategies. The best five ranked penalty takers from the on-field players should be assigned to the first five penalty kicks in their reverse order of ability. That is, the fifth best penalty taker should take the first penalty kick, the fourth best penalty taker should take the second penalty kick, and so on. In the event of sudden death, the next highest ranked on-field player should be assigned to the next penalty kick until the shoot-out ends. For this tactic to be successful, players should be ranked a priori on their penalty-taking ability. Similarly, goalkeepers should be ranked a priori on their penalty-stopping ability. These findings indicate that the tactical substitution of on-field players for higher ranked penalty takers, including higher ranked penalty stoppers (i.e. goalkeepers), with a view to an impending penalty shoot-out should be given due consideration. These results are of practical importance in that they are shown to maximize the likelihood of winning the penalty shoot-out under certain initial conditions. 相似文献
20.
On winning the penalty shoot-out in soccer 总被引：1，自引：1，他引：0
The penalty shoot-out is used to break tied games in the knock-out stages of soccer competition. The shoot-out, which consists of an alternating series of penalty kicks, is won by the team with the highest goal tally after n kicks per team (n = 5). In the event of a tie after five penalty kicks each, the shoot-out progresses to 'sudden death' by increasing n in iterative fashion (i.e. n = n + 1) until one team obtains a higher goal tally than the other after an equal number of kicks per team. The team to strike first is determined at the end of extra time by the toss of a coin. As each on-field player can be awarded only a single penalty kick, the line-up order in which the penalty kicks are taken allows for the possibility of tactical influence on the final outcome. Consequently, we report a probability analysis of the penalty shoot-out in soccer from which we identify the following pre- and post-game strategies. The best five ranked penalty takers from the on-field players should be assigned to the first five penalty kicks in their reverse order of ability. That is, the fifth best penalty taker should take the first penalty kick, the fourth best penalty taker should take the second penalty kick, and so on. In the event of sudden death, the next highest ranked on-field player should be assigned to the next penalty kick until the shoot-out ends. For this tactic to be successful, players should be ranked a priori on their penalty-taking ability. Similarly, goalkeepers should be ranked a priori on their penalty-stopping ability. These findings indicate that the tactical substitution of on-field players for higher ranked penalty takers, including higher ranked penalty stoppers (i.e. goalkeepers), with a view to an impending penalty shoot-out should be given due consideration. These results are of practical importance in that they are shown to maximize the likelihood of winning the penalty shoot-out under certain initial conditions. 相似文献