This sheet deals with analysis of the oblique impact system, which is composed of the golf-ball and club. The impact system is modeled by both a nonlinear spring and a nonlinear dashpot using Hertz's contact theory. This model is applied to the oblique impact system of ball. The characteristics of the oblique impact were obtained by using this model. The results show that experiment and simulation are carried out to demonstrate the accuracy of the proposed model, and good agreement is shown. Also, the results show that the spin rate was proportional to tangential impulse.
For the improvement of the directional stability of the putter club, it is considered that stabilized head path and/or face angle related to a ball before impact at each swing are important. In this study, the joint torques of good and bad shots are obtained with inverse dynamics. And, applying obtained torques to forward dynamics, the specific club head, which is relatively insensitive to head path at various swing motion, will be derived. In this paper, results of the difference of joint torque between good and bad shots are reported.
The sound simulation program forecasts the sound radiation. It was developed in our laboratory. In a past research. the batting sound of the golf club with a ball was forecasted. As for past research results, the difference was seen between "Sound collected by the excitation experiment" and "Sound that had been calculated by the sound simulation program" of the golf club. Therefore. In this paper. the accuracy of sound simulation program is examined by comparing experiment with calculation by using the simple structure mat FEM calculation gets accuracy.
The objective of this study was to construct a finite element (FE) model which can accurately simulate the behaviour of the shaft during a 2D swing and the behaviour of golf impacts between a ball and a simplified club. The club was constructed by holding the simplified clubhead by a locking ring fitted onto a steel shaft. The clubhead was designed based on the mass, volume and position of the centre of gravity of commercial clubheads, so as to enable a typical golf impact. The FE model of the club, which consisted of the clubhead, a locking ring and a shaft, was constructed with linear elasticity. The FE model of the ball consisted of 8-node solid elements, and the material model was expressed as a hyperelastic/viscoelastic model. An experiment, in which the simplified club was swung with circular motion and collided with the ball, was conducted to simultaneously measure the motion of the shaft grip and the behaviours of the shaft and impact. The experiment was also used to confirm the accuracy of the FE model, by comparing the results of the experiment to those of the FE analysis. The simulation results of the behaviour of the shaft during the swing matched the experimental results. The simulation results of the impact behaviour also generally agreed with the experimental results. It is important to represent the higher fidelity of the input conditions for the FE analysis, such as the motion and constraint of the grip, in addition to that of geometry and material properties of the FE models for the ball and club, in order to estimate and evaluate the behaviours of the swing and impact.
The purpose of this study was to understand characteristic of lower limb in golf swing by relationship between movements of knee and hip, and hip joints' torque. Four right-handed professional golfers used their own drivers to hit standard golf balls in our laboratory. The swing motions were recorded using a 3D optical motion capturing system with a 200Hz frame rate, and three-dimensional ground reaction forces were captured by two force plates operating at 1000Hz on the ground. The hip joints' torque was calculated using these sets of data. Also the rotational angle of hips and the knees and the angular velocity of the hips and knees were calculated as kinematic data. In this study, the golf swing time was divided into two phases on the basis of the hips' rotational angle. As for the results, the rotational angle of hips and the knees became parallel to the X-axis at the approximately same time, and the angular velocity of hips coincidentally reached a maximum value in the middle of forward swing. Particularly the two torques of the left hip joint were continuously exerted in the beginning of the forward swing, and then these torques started to decrease after the peak. This suggested that left hip joints were effective at promoting the rotational movement of the pelvis during the golf swing.
When analyzing the swing of a baseball bat, important characteristics include the baseball bat's center of gravity, moment of inertia, length and mass. The purpose of the present study was to investigate the effect of the mass and the center of gravity of a swinging baseball bat. An experimental bat was designed, which provided twenty-five conditions for the mass and center of gravity. The knob of the experimental bat was equipped with accelerometers, which measured the three linear and three angular components of an acceleration applied to the bat. The subjects were trained five baseball players. The six components of acceleration were measured with the experimental bat under twentyfive conditions of the mass and center of gravity. The bat mass and center of gravity had an effect on the linear and angular acceleration during bat swing. Thus, it is necessary to consider the bat characteristics that suit each player.
This paper is a study of FRP (Fiber Reinfoced Plastics) bats. Recently, the FRP bats begin to be focused. But FRP bats have a problem with a strong numbness, hi this paper, the causes of numbness in FRP bats were attempted to be clear by performing experimental modal analysis. First, the modal parameters of FRP bats were identified with experimental modal analysis and damping of bat was studied. Next, to investigate the modal parameters in supporting condition by human's hands, experimental modal analysis was performed. Then, the study and its results were shown, hi the real shot of professional person, questionnaires were done about numbness. Finally, center of impact were measured and calculated.
The purpose of this study was to investigate the changes on mechanical work of the lower limb joints during baseball pitching in a simulated game. One male college baseball pitcher threw 15 pitches in an inning for 9 innings (135 pitches) in an indoor pitcher's mound with two force platforms. Rest time between innings was 6 minutes. Three-dimensional positions of 47 reflective markers attached to subject were tracked by an optical motion capture system (Vicon Motion System 612, Vicon Motion Systems) with eight cameras (250Hz). For subject 75 fastball pitches (1st, 3rd, 5th, 7th, and 9th innings) were chosen for analysis. As the main results, the hip joint extension absolute and negative work of the stride leg decreased with increasing the number of pitches. The ankle joint extension absolute and negative work of the stride leg increased with increasing the number of pitches. These results suggest that the hip joint extension torque of the stride leg was needed to maintain for higher performance in baseball pitching.
In order to clarify pitching mechanism for the progress of pitching performance and the achievement of more long-running career, pitching motions of 2 professional baseball pitchers were analyzed biomechanically using motion capture system and floor force plates. One (pitcher A) is in his 28th year on the active list, and the other (pitcher B) is in his second year on the active list. Both are in the first team. As a result, pitcher A pitched using leg, torso and pitching arm in sequence concentrically. This mechanism was named "triple step rocket system". However pitcher B pitched using only leg and pitching arm concentrically. These differences were quantified through energetic analysis, called "distribution ratio of joint concentric energy". Then we defined "pitching efficiency" as a ratio of kinetic energy of the ball pitched to summation of whole body energy produced in pitching motion. The ball speed of pitcher B was faster than that of pitcher A, nevertheless the pitching efficiency of pitcher A were better than that of pitcher B. These results were caused by the difference of the movement of torso between both pitchers. This shows that torso rotation is important to pitching mechanism.
Pitch control is an important skill for baseball pitchers. In the present study, we investigated the relationship between pitch control and the movements of hand and fingers during ball release. Four collegiate baseball pitchers threw 30 pitches from the mound of official height as fast and accurate as possible to a catcher. The motions of hand, fingers, and ball were recorded using three high-speed cameras. The other high-speed camera was used to record the motion of the catcher. Hand angle at the ball release in the plane, made by pitcher-catcher and vertical directions, was closely correlated with vertical component of ball position at the catcher (p<0.001). In conclusion, it was suggested that pitching a baseball into the strike zone requires a pitcher to complete the ball release within the time accuracy of 1-2 msec.
Today the game of badminton is so popular that over 160 countries are now the official member of the Badminton World Federation (BWF), and the badminton is one of the oldest and popular sports in the world. The aerodynamic characteristics and the flight trajectories of badminton shuttlecocks are significantly different from balls used in other racquet sports. A badminton shuttlecock is an extremely high drag projectile and possesses almost parabolic flight trajectory. In the present study, in order to understand qualitatively the behavior of the shuttlecock during its flight, the relationship between the aerodynamic forces and the vortex behavior in the wake is investigated for wind tunnel tests. Furthermore, the impulsive rotational movement of the shuttlecock simulating the condition just after the impact in badminton stroke is also measured. The shuttlecock behavior is significantly affected by the vortex dynamics in the wake.
Although the role of a spin is very important for an impact of a hollow spherical sports ball, an understanding of collision characteristics of the ball is extremely difficult because of its large deformation. We consider that the best tool for a study of the hollow ball impact is a finite element analysis. Concerning a tennis ball and a table tennis ball, after the finite element analysis whose program was developed by the author has been validated against experimental results, the effects of inbound spins on rebound velocity, spin and angle are investigated. The following are found for the hollow ball normal and oblique impacts. For the tennis ball, the tangential component of the velocity is widely reduced due to the frictional force, the spin is largely reduced due to the normal component of the impact force and the wide inbound angle produces a considerable amount of the spin. For the table tennis ball, the rebound velocity decreases as the inbound velocity increases in the inbound normal velocity range of over 18 m/s.
In order to observe the rebound characteristics of a tennis ball and the effects on the hand, FEM simulations for tennis ball impact were performed using a solid string model at different coefficients of friction between strings (called string friction). The 3-dimensional models of the tennis racket were achieved in CATIA V5R18 according to the geometry of a full sized Wilson tennis. To be emphasized, the model of strings was made into interlaced solid string model but not simple wire model. All models were made meshes using HyperMeshS.O and FEM simulations were completed in ABAQUS V6.8-Explicit. The FEM analyses results revealed that it is necessary to use a solid string model instead of a wire string model in clarifying the dynamic characteristics of tennis racket and ball. Besides, the results also show that larger coefficient of friction between strings is benefit to control a ball but may injure elbow more easily.
Though the badminton can not be called the major sports, they are the sports which hold considerable players population. However in comparison with the tennis racket, the paper which studied the badminton racket is few. and it is not very much studied and has not been announced. The research was carried out for the purpose of in this study, it does experimental modal analysis on the badminton racket, and examining the vibration characteristics. In this paper, we studied what causes it. the difference of vibration characteristics of the 3 rackets.
The purposes of this study were to quantify the contribution of the upper limb joint torques and shoulder joint reaction force to the racket head speed and make clear the generation factor of motion dependent term during tennis serve motion. The upper limb segments and racket were modeled as a system of 4-rigid linked segments. The axes of the elbow and wrist joints were modeled by a two-axis re volute joint to consider the degree of freedom (DOF) of the joint, and the hand was considered to be connected with the racket via zero DOF joint. The equation of motion with respect to the upper limb and racket was obtained from the equation of motion for each segment and from equations for constraint condition in which adjacent segments are connected by joint, and from constraint axes equations for elbow and wrist joints. The dynamic contributions of the joint moments, shoulder joint force, motion dependent term and gravity term to the racket head speed were derived from the dynamic equation of the system. Collegiate male tennis players' motion were captured by VICON 612 system (9-camera, 250Hz). The results obtained in this study show 1) not only joint moments but also motion dependent term make significant role for generating racket head speed during forward swing motion in tennis serve, and 2) shoulder internal external rotation torque is most important factor of generating motion dependent term.
The flight trajectory of a non-spinning or slow-spinning soccer ball may fluctuate in unpredictable ways as similar as C. Ronaldo's FK in Football. Such anomalous horizontal shaking or rapid falling is ascribed to a phenomenon called the 'knuckling effect'. However, the aerodynamic properties and boundary-layer dynamics of a ball during the knuckling effect are not well understood. The purpose of this study is to analyze the characteristics of vortex structure of the knuckling effect ball using high-speed video images and titanium tetrachloride. Two high-speed video cameras were set to the side and in front of the ball trajectory between the location of the ball and the soccer goal, and photographs were taken at 1,000 fps and a resolution of 1024 x 1024 pixels. A horseshoe vortex on smooth sphere was observed in the range 380000 < Re < 1000000 (Taneda, 1978). However, the vortex structure behind the soccer ball in super critical Re number region might be a distorted loop vortex. After balls that were under the influence of the knuckling effect were airborne, large-scale undulations of the vortex trail were observed.
The purpose of this study was to discuss the fluid mechanics and frequency of forces acting on a non-spinning and low-spinning flight soccer ball, which called "Knuckleball", using high-speed VTR image of a real place kick. Moreover, the fluid around the knuckleball in flight was visualized using a smoke agent (titanium tetrachloride), and an attempt was made to clarify the fundamental fluid mechanics expressed by the knuckleball as well as to analyze the vortex dynamics. Therefore, in the case of the knuckleball, the peak value of the vortex lift reached approximately 2.0 N, which was larger than that of approximately 0.5 N in the case of an instep kick. Furthermore, the knuckleball was observed to have an average vortex lift force frequency of approximately 3.5 Hz. A comparison of this vortex lift frequency and vortex oscillation frequency indicated that these frequencies tended to act in unison with a high statistical correlation (r = 0.81, p < 0.001). Thus, it is considered that the oscillation of the large-scale vortex structures of the knuckleball was the fundamental mechanism that produced the fluctuating forces acting on the knuckleball in soccer.
Less spinning soccer ball aerodynamics are studied by wind tunnel experiments. Aerodynamic force of unsteady lift and side ones acting on the ball at rest are measured and estimated flight trajectory. Well agreements of flight shift magnitude in lateral direction between observed and calculated ones are obtained. Violent position change of longitudinal twin vortex just behind ball rear surface is observed using flow visualization method by high speed camera and smoke image method. As a result, the cause of this strange behavior of less spinning soccer ball is clarified by self-excited buffeting phenomenon of irregular behavior of omega Ω shaped vortex and longitudinal twin one, which already discovered with supper critical Re number region of smooth sphere by Taneda (1976). These twin vortices appearance are very similar to well known trailing vortices of both side of an air plain wings.
An instrumented device equipped with strain gauges was designed to measure exerting forces upon the ball kicked by the impact type ball ejection unit. The device consists of L-shape aluminum alloy beam, contact plate and a connector with the ejection unit Seven pairs of strain gages were attached on the beam connected to the ejection units. The output of the sensors was converted into the values of forces by resolving the static equilibrium equations. The results from the calibration procedure shows good agreement between actual forces measured with load cell and calculated forces with strain gauge signals exerted on the device. The results obtained from the measurement in kick motion with use of the instrumented device shows : (1) The normal component of the force with respect to the contact plate were large relative to those of other axial components, and (2) the tangential component of the force was oscillating during contact.
The purpose of this study was to reveal interactions during the ball impact phase of soccer kicking in female soccer players. Seventeen female and male soccer players performed maximal instep kicks, in-front kicks, and inside kicks. Behavior of the kicking foot and ball during ball impact were captured three dimensionally by two high-speed cameras at 1,000 fps, and the female players were compared with the male players. For the mean of the coefficient of restitution, there was no significant difference in instep kicks and in-front kicks between the sexes, but the female players had significantly lower values than the male players in inside kicks (p<0.05). The players were also divided into high groups and low groups according to the three categories of foot velocity, ball velocity, and coefficient of restitution. Those interactions were examined at ball impact, and certain tendencies were revealed.
Many badminton players have ruptured their Achilles tendon in scissors jump. In this study, the dynamic model of leg joint was constituted and motion analysis was carried to find the forces in tendons and moments in joints. This dynamic model consists of thigh, tibia and foot segments and knee and ankle joints modeled by rigid rods and springs and dashpots. This analytical method was verified by experiment of jumping on a force plate. Furthermore the method to estimate the forces applied to tendons was proposed. The relationships between the forces and motion were investigated. The force applied to Achilles tendon can be reduced by 20 % by flexing the knee, 30 % by changing the direction of toe and 10 % by locating the weight of body on the heel side.
Badminton is one of the more popular sports in China, Japan etc. The shuttlecocks used in badminton are one of two kinds, either of a feather or synthetic shuttlecock. In an actual badminton match, the feather shuttlecock is always used. Several characteristics of the shuttlecock are its light mass, which is strongly influenced by air resistance and that the wing of the skirt can be easily broken. Also, the highest initial velocity of the shuttlecock exceeds 300km/hr for a professional badminton player. This paper describes the badminton machine with the rollers developed by the author. Finite element models of a feather shuttlecock and the badminton machine with two rollers are made, and the throw simulations proceed with the moving behavior and contact stress of the shuttlecock using commercial dynamic finite element analysis code (ANSYS/LS-DYNA). The friction coefficient is examined from the surfaces in contact with the shuttlecock and the roller in the analysis. Also, the three types of roller edges are analyzed. From the analytical results, it is found that the convex type of roller attains a higher accuracy than the other rollers for every throw. Additionally, these analytical results are inspected by the throw experiments using the badminton machine.
The previous papers of the authors made clear the mechanism of top spin performance in tennis and its improvement by lubrication of string intersections according to the high speed video analysis. As the main strings stretch and slide side ways more, the ball is given more spin.due to restoring force parallel to the string face when the main strings spring back and the ball is released from the strings. Since the notches of strings decrease spin rate, the lubricant materials are effective to the notched strings. Furthermore, it was shown that the top spin rate of newly strung tennis racket without notches is much larger than that of used racket with notches in the case of the nylon strings and the natural gut. It was also shown that the more spin results in the reduction of shock vibrations of the wrist joint during impact. This paper showed the underspin behavior when a pro and an amateur hits a ball. Furthermore, it also showed the comparison of the spin behavior between a tennis ball and a smooth surface ball without felt and made clear the mechanism of ball control by using high speed video camera and flow visualization.
Several former top players sent a letter to the ITF (International Tennis federation) that tennis has become unbalanced and one-dimensional, because rackets today allow players to launch the ball at previously unthinkable speeds.Modern racket technology has developed powerful, light, wide-bodied rackets. There's even a racket with a chip built into the handle that allows the racket to stiffen upon impact with the ball. All of this technology has led to major changes in how the game is played at the top level. ITF seems to have started the test to examine the performance of tennis racket against the above claims. Since the sport should be learned from the experience, it is the subjective thing. Accordingly, it is quite difficult to see how the physical property of equipment has an effect on the performance of a player. The terms used in describing the performance of a tennis racket are still based on the feel of an experienced tester or a player even today. This paper investigated the physical properties of the racket that was manufactured by ITF for performance test, predicting its performance in terms of the coefficient of restitution, the rebound power coefficient, and the post-impact ball velocity relevant to the racket power. It is based on the experimental identification of the racket dynamics and the simple nonlinear impact analysis. The predicted results could explain the difference in mechanism of performance between the the racket ITF and the recent representative racket. The racket ITF provides higher coefficient of restitution particularly at the topside of string face and slightly higher post-impact velocity despite lower racket head speed compared to the recent representative racket. Prediction and estimation of feel will be reported in a separate paper.
Several former top players sent a letter to the ITF (International Tennis federation) that tennis has become unbalanced and one-dimensional, because rackets today allow players to launch the ball at previously unthinkable speeds. Modern racket technology has developed powerful, light, wide-bodied rackets. There's even a racket with a chip built into the handle that allows the racket to stiffen upon impact with the ball. All of this technology has led to major changes in how the game is played at the top level. ITF seems to have started the test to examine the performance of tennis racket against the above claims. Since the sport should be learned from the experience, it is the subjective thing. Accordingly, it is quite difficult to see how the physical property of equipment has an effect on the performance of a player. The terms used in describing the performance of a tennis racket are still based on the feel of an experienced tester or a player even today. This paper investigated the physical properties of the racket that was manufactured by ITF for performance test, predicting its performance in terms of the impact shock vibrations of player's wrist joint, which might be related to the feel. It is based on the experimental identification of the racket-arm dynamics and the simple nonlinear impact analysis. The result showed that the magnitude of shock vibration at the handle and the wrist joint with the racket ITF is remarkably small due to the stiffer handle compared to the recent representative racket. Prediction and estimation of power will be reported in a separate paper.
We realized the simple self-sustained humanlike robust walking & running NANBA of humanoid biped robot GENBE based on distributed control of physical body in a martial art, which uses only small active power with simple chaotic limit cycle utilizing instability. Instability makes the natural movement and can be applied to walking of a physically handicapped person, rehabilitation, sports, and so on. This paper showed the development of robust NANBA walking of humanoid Biped Robot GENBE to NANBA-Tennis making full use of instability as a source of driving force.
This paper describes the aerodynamic characteristics on the non-spinning rugby ball. The drag, the lift, the side force and the pitching moment were measured as functions of the Reynolds number, the angle of attack and the seam angle which represents the position of the seam. It was found that the critical Reynolds number increases with increasing the angle of attack. The Reynolds number dependence of the drag coefficient at the angle of attack of 90° is similar to that of a circular cylinder. At the angle of attack of 90°, the seam angle dependence of the side force coefficient does not depend on the lace but the seam. At the angle of attack of 30°, it depends on the lace as well as the seam.
Wind tunnel experiment has been conducted to investigate the knuckle effect of a soccer ball (Teamgeist). For the new experiment, pressure transducers were used to measure the surface pressure of a ball as well as an aerodynamic force balance to measure the drag and the side force. A tuft grid was used to visualize the flow structure in the wake region. Each of these measurements was synchronized to take the mutual correlation among the data. The surface pressures were measured at the front stagnation point, 90 deg. from the stagnation point. The correlation coefficients between the time variation data of the side force and the drag, and the surface pressure at 90 deg. and the side force were very high. The tuft visualization was capable of recording vortex shedding behind a ball in the supercritical Re region, which may be attributed to the cause of the knuckle effect.
Aerodynamic forces and torque acting on the ball were measured under various flight conditions in a wind tunnel flow. Using the aerodynamic force coefficients, mathematical calculation of flight trajectory equation was made by time integral calculus, and 3-dimensional flight trajectory, changes in velocity as well as rotation velocity were obtained. Furthermore the logarithmic law was applied to trajectory formation of a golf ball in order to include influence of atmospheric boundary layer. The trajectory formation considering atmospheric boundary layer was verified by two experiments. One of the experiments was conducted to measure wind velocity distribution. The other was to compare the actual measured drop position with calculated data. Wind direction and velocity and initial condition of golf ball flight just after impact were measured to calculate. Flight trajectory considering natural wind was calculated by using 3-dimensional flight trajectory formation applied logarithmic law under various initial conditions in detail. As a result, we found out that there are conditions that distance reduces by tailwind and showed the conditions. In addition, we could get quantitative data: the influence of spin rate and launch angle including wind upon distance. Moreover we analyzed the quantitative influence of spin rate and launch angle including wind upon curving e.g. hooks and slices.
Precise evaluations of aerodynamic forces on highly spinning golf ball are very difficult because of less method and technique to measure these basic characteristics. We are challenging this problems using newly introducing air suspension balance method. Atmospheric and supplying air pressure change on air force of Z-direction measurement are studied by introducing cancelling technique by using a dummy balance. In this stage, cancelling result of atmospheric and supplying air pressure change is shown. Drag forces on ψ0.3mm piano wire is measured and is well agreement with well known data. The drag force measurement on spinning golf ball is reported as a result of trial experiments.
The purpose of this study was to observe separated regions around a rotating baseball in a wind tunnel and to clarify the influence of seam positions. First of all, the rotational-ball supporting device was developed, and it was set in the wind tunnel. Then, the drag forces of 2-seam and 4-seam gyro-ball were measured. It was found that the drag coefficient of 2-seam gyro-ball was smaller than 4-seam one by 0. Based on this result, smoke visualization was used to obtain the flow pattern around the gyro-balls with high-speed camera. As a result, the separated regions of 2-seam gyro-ball were smaller than that of the 4 seam one.
Using a high-speed video camera, we measured the trajectory and the rotation of a sphere and a hard baseball thrown by a pitching machine. We determined the drag- and lift- coefficients (C_D, C_<LZ>) by analyzing the video images. The measurements were performed in the range of 0.6 × 10^5 <Re< 2.4 × 10^5, and 0<SP<0.7 (SP : dimensionless spin rate). The dependence of C_D and C_<LZ>on the parameters Re and SP is investigated in detail. Negative Magnus force is exerted on a back-spinning sphere in a relatively wide Re- SP parameter range, whereas only usual Magnus force works on a back-spinning hard baseball. The influence of seam patterns on the aerodynamical properties is discussed.
Aerodynamics of vertical slider changing baseball ball is studied by wind tunnel experiment data. The direction of the good vertical ball rotation axis orients toward the home base, straightly. And sharp drop trajectory is observed with less lift force. In the case of slightly change of orientation of rotation direction of spinning axis, how about aerodynamic characteristics and resultant trajectory is? According these small change of the rotation direction angle ranging +10°〜+30°, strange aerodynamic forces appeared on ball air force. These results well explain the real direction shift of ball spinning axis and the resulting ball trajectory of Meager League pitcher named D. Matsuzaka.
A commonly used pitching machines equipped with two same diameter wheels parallel to each other can only pitch balls such as a straight ball and a curve ball, whose angular velocity vectors are perpendicular to their translational directions. Actually, the balls pitched by real pitchers have the angular vector directions slanted to the translational directions. To overcome the defect of this type pitching machine a new pitching machine has been invented to pitch a gyro-ball and slider ball, whose angular velocity vectors are not perpendicular to the translational directions. This is achieved by arranging the two wheel shafts of a pitching machine to be twisted. To control the pitching machine for an arbitrary angular velocity vector of the ball and its velocity formulas are derived to define the surface velocities of the two wheels and their twist angles.
Motion analysis of baseball pitching with some inertial sensors was executed. Three baseball pitchers who were put some sensors on upper limb and trunk pitched fast ball into net. The accelerations of upper limb and the angular velocities of trunk were measured with the sensors, and the angular velocities of the upper limb were calculated from those accelerations. Some characteristics of motion were understood from those kinematics measured and calculated.
The purpose of this study was to clarify the influence of the hitting point height in the baseball T-batting motion by using an instrumented bat via inverse kinetic analysis. Sixteen collegiate male baseball players' motion were captured VICON 612 system (9-camera, 250Hz), and kinetic data at each hand were collected by using an instrumented bat equipped with 28 strain gauges (lOOOHz). Three heights of hitting point (high, middle, low) were set according to the baseball rules. We extracted coupled force components from forces exerted by each hand in the kinetic data. From the results we obtained the facts that the longitudinal force along the bat modifies the translational movement of the bat in the vertical direction during down swing phase, and that the coupled force, which is exerted by both hands about the axis of bat inclination, modifies the rotational movement of the bat to respond to the difference between the hitting point heights.
Knowledge of forces and moments applied to a baseball bat is important for a number of applications in training and analysis of biomechanics. The purpose of this study was to develop an instrumented grip handle designed to simultaneously measure the forces and moments exerted by both hands on a grip handle connected to a bat during baseball swing motion. The grip handle is designed to functionally equivalent to standard grip handles of baseball bats. Twelve pairs of strain gages were attached on the surface of an aluminum alloy bar inserted under the grip handle parts, such as knob-side and barrel-side grip parts. The bar is connected to the barrel side of cut bat with a connector so as to be able to connect to various types of bat, such as baseball bat and soflball bat. Strain signals were transmitted via a cable tethered to the batter's knob-side arm from the knob-end of the grip handle to twelve dynamics strain amplifiers. The output of the sensors was converted into the values of forces and moments exerted by each hand by resolving the static equilibrium equations. From calibration procedure, the sensor output voltages showed good linearity with respect to the applied loads, but cross-talking occurred between the longitudinal axial forces and the applied bending moments measured at the sensing points. Therefore, the interferences terms were approximated by using polynomial functions to reduce the interferences.
The purpose of this study was to examine the factors influencing the behavior of the baseball during and after the impact with a wooden bat. A finite element approach was used to model the behavior of a baseball and a wooden bat at the impact and the linear and angular velocities of the ball after the impact were determined for given sets of impact condition. The simulation outcome was validated with 23 sets of actual measurements taken during a "free batting practice" performed by the members of a collegiate baseball team. The simulation results demonstrated high level of matching with the experimentally measured values.
Swimming is a successive motion of the propulsive movement and the recovery movement in the water. It is very helpful to grasp a total swimming form for the improvement of the swimming technology. But it is very hard to visualize a series of motion on account of different refractions of the water and the air especially in a swimming pool. An underwater camera and an over water camera were loaded onto a cart placed on a rail of poolside. Underwater and overwater images were blended into a continuous image in a real time by a video mixer. Swimming motion data could be also visualized by three-dimensional acceleration and angular velocity data logger. Both motion picture and corresponding data were put together into a series of motion picture in order to observe the swimming motion. Captured data were patterned by wavelet transform.
The purpose of this study was to estimate swimming drag force during front crawl swimming based on a mass model and to discuss the validity of the estimation. The subject was a male swimmer (height : 1.74m, weight : 67.0kg, age : 23.2yrs, record of 50mFr. : 23.2sec). The trial was front crawl swimming without kicking in swimming flume, which was set the flowing velocity to 1.3m/s. The acceleration of the visual marker on swimmer's umbilicus instead of the center of gravity of whole body was calculated by movie analysis. The propulsive force by swimmer's hands was calculated by measured pressure distribution and attitude of hands. The swimming drag force was estimated by the difference of the inertial term and propulsive force. It was suggested that the estimated drag force would be acceptable compared with previous researches, although it would be needed to improve the methodology.
The aim of this study was to visualize and to analyze the unsteady flow field around swimmer's hand during sculling motion using two-component Particle Image Velocimetry (2C-PFV). Also 3D-DLT motion analysis was executed to check the relationship between flow and the attack angle of the swimmer's hand. PIV allows us to visualize the unsteady flow field instantaneously and to estimate the fluid force. Two subjects were participated in this study. One was the ex-competitive swimmer (Sub.M), and the other (Sub.O) has no competitive carrier. Subjects were asked to keep their position by sculling motion in a swimming flume tank with 0.5 m/s flow speed. We focused on the transition phase from out-scull to in-scull. The attack angle of Sub.M reached nearly 90 degrees at just before the transition phase ; meanwhile that of Sub.O was nearly 70 degrees. As the result of flow visualization, Sub.M seemed to shed the vortex after the transition phase and to create the jet flow for thrust between his hand and shed vortex. On the other hand, Sub.O seemed not at the same situation. The results of present study suggested that ex-competitive swimmer created the propulsive force by generating the shed vortex using proper attack angle change, but the beginner could not obtain the propulsive force effectively.
The objective of this study was to extend the swimming human simulation model SWUM, which has been developed by the authors, to multi agent/object simulation. By this extension, SWUM can analyze the multiple bodies, that is, the other swimmers and equipments such as fins, starting block, pool wall, and so on. In this paper, the method of extension and its implementation to the software are firstly described. Two examples of analyses are next shown. The first example is simple synchronized swimming by three swimmers. In this simulation, virtual springs and dampers were employed to represent hand connections among the swimmers. Another example is the monofin swimming. In this simulation, the monofin was modeled as a series of five rigid plates. The virtual springs and dampers to represent the connection of the plates were employed. In addition, in order to represent the elasticity of the monofin, rotational springs and dampers among the plates were also employed. The reasonable results obtained in these simulation indicate the validity and usefulness of the present extension.
Although it is important for baseball players to select a suitable bat to achieve higher performance in hitting motion, they usually select their bat depend on feeling and experience. We developed a bat select system for each player to select a suitable bat based on kinematic and kinetic parameters of the bat motion in swing movement. This system has two components ; such as, the instrumented bat for measuring bat motion under various inertial properties, and a selection algorithm to choose suitable bats based on kinematic and kinetic information of the bat. The bat contains accelerometers and gyroscopes in the bat handle end to measure kinematic parameters of the bat and a movable weight can be fixed at arbitrary position in the bat barrel to shift the center of gravity of the bat. And the other is software to select the suitable bat based on bat energy, swing time, bat head speed and apparent momentum of hitting point of the bat.
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