SPORTS FLUID DYNAMICS: AERODYNAMICS OF SPORTS BALLS

Recently, newer soccer balls named Cafusa, Teamgeist 2, and Jabulani were respectively produced from 32, 14, and 8 panels with shapes and designs dramatically different from those of conventional balls. The newest type of ball, named Brazuca, was produced from six panels and will be used in the 2014 FlFA World Cup in Brazil. There have, however, been few studies on the aerodynamic properties of balls constructed from different numbers and shapes of panels. Hence, we used wind tunnel tests and a kick-robot to examine the relationship between the panel shape and orientation of modem soccer balls and their aerodynamic and flight characteristics. We observed a correlation between the wind tunnel test results and the actual ball trajectories, and also clarified how the panel characteristics affected the flight of the ball, which enabled prediction of the trajectory

Flow Visualization of Downhill Ski Racers Using Computational Fluid Dynamics

AbstractIn downhill alpine skiing, racers often exceed speeds of 120km/h, with air resistance substantially affecting the overall race times. To date, studies on air resistance in alpine skiing have used wind tunnels and actual skiers to examine the relationship between the gliding posture and magnitude of drag, as well as for the design of skiing equipment. However, these studies have not revealed the flow velocity distribution and vortex structure around the skier. In the present study, we used computational fluid dynamics with the lattice Boltzmann method to derive the relationship between flow velocity in the full tuck position (the downhill racer's speed) and total drag. Furthermore, we visualized the flow around the downhill racer and examined its vortex structure. The results show that the total drag force in the downhill racer model is 27.0N at a flow velocity of 15 m/s, increasing to 185.8N at 40 m/s. Moreover, the visualization of the flow field indicates that the primary drag locations at a flow velocity of 40 m/s are the head, upper arms, lower legs, and thighs (including the buttocks)

FORCE AND POWER OUTPUTS OF TRUNK-TWIST DURING BAR TWIST EXERCISE -INFLUENCE OF LENGTH AND MASS OF BARS-

The purpose of this study was to investigate force and power outputs during bar twist exercises using barbell shafts, considering various moment of inertia (MOI), corresponding to changes in the bar length and mass. Twenty-one male college athletes performed the bar twist exercise using five barbell shafts: one normal barbell shaft, two long barbell shafts (with changes only in the length), and two heavy barbell shafts (with changes only in the mass). Kinematic and kinetic data were recorded using the Vicon system (250 Hz) and two force platforms (1,000 Hz). The results obtained in this study revealed that: (1) Peak angular velocity of bar and upper trunk for the long barbell shaft condition was higher than the heavy barbell shaft condition; (2) For higher MOI, the trunk-twist torque was higher; and (3) Even when the barbell shaft had equal MOI, the heavy bar showed higher trunk-twist torque prior to the bar rotation

Effect of panel shape of soccer ball on its flight characteristics

Soccer balls are typically constructed from 32 pentagonal and hexagonal panels. Recently, however, newer balls named Cafusa, Teamgeist 2, and Jabulani were respectively produced from 32, 14, and 8 panels with shapes and designs dramatically different from those of conventional balls. The newest type of ball, named Brazuca, was produced from six panels and will be used in the 2014 FIFA World Cup in Brazil. There have, however, been few studies on the aerodynamic properties of balls constructed from different numbers and shapes of panels. Hence, we used wind tunnel tests and a kick-robot to examine the relationship between the panel shape and orientation of modern soccer balls and their aerodynamic and flight characteristics. We observed a correlation between the wind tunnel test results and the actual ball trajectories, and also clarified how the panel characteristics affected the flight of the ball, which enabled prediction of the trajectory

Aerodynamic drag of modern soccer balls

Soccer balls such as the Adidas Roteiro that have been used in soccer tournaments thus far had 32 pentagonal and hexagonal panels. Recently, the Adidas Teamgeist II and Adidas Jabulani, respectively having 14 and 8 panels, have been used at tournaments; the aerodynamic characteristics of these balls have not yet been verified. Now, the Adidas Tango 12, having 32 panels, has been developed for use at tournaments; therefore, it is necessary to understand its aerodynamic characteristics. Through a wind tunnel test and ball trajectory simulations, this study shows that the aerodynamic resistance of the new 32-panel soccer ball is larger in the high-speed region and lower in the middle-speed region than that of the previous 14- and 8-panel balls. The critical Reynolds number of the Roteiro, Teamgeist II, Jabulani, and Tango 12 was ~2.2 × 105 (drag coefficient, Cd ≈ 0.12), ~2.8 × 105 (Cd ≈ 0.13), ~3.3 × 105 (Cd ≈ 0.13), and ~2.4 × 105 (Cd ≈ 0.15), respectively. The flight trajectory simulation suggested that the Tango 12, one of the newest soccer balls, has less air resistance in the medium-speed region than the Jabulani and can thus easily acquire large initial velocity in this region. It is considered that the critical Reynolds number of a soccer ball, as considered within the scope of this experiment, depends on the extended total distance of the panel bonds rather than the small designs on the panel surfaces

Factors of unpredictable shots concerning new soccer balls

AbstractThe configuration of new soccer balls has closely approached a perfect round shape by not only reducing the number of panels but also by eliminating roughness of the panel joints by utilizing thermal bonding process recently. Therefore, in a non-rotating or low-rotating moving shot, a soccer ball drops and curves, i.e. motion by the change of wake flow, which is called a knuckle ball effect. Factors of the knuckle ball effect on the new soccer balls were investigated in case of a non-rotating shot and a low-rotating one. A correlation between fluctuation of the wake and fluid forces was identified in a symmetric panel configuration of the ball. The asymmetric configuration of the ball panel was also investigated as a factor to bring unpredictable change of the ball flight path. The low-rotating ball changes its frontal area against the moving direction and it produces irregular lateral forces. Consequently, the factors which produced the knuckle ball effect were found to be different from the case of non-rotating shots and low rotating shots

A KINETIC COMPARISON OF THE INSIDE SOCCER KICK BETWEEN HIGH PERFORMANCE PLAYER AND JUNIOR PLAYERS

Kinetic aspect of the inside soccer kick was investigated and comparison was made between those of a high performance player and junior players. One high performance player and five junior players volunteered to participate in this study. Their kicking motions were analyzed through three-dimensional cinematograpgic technique. Joints torques, generated at hip and knee joints, were computed by a three-link kinetic chain composed of thigh, shank, and foot. A marked difference was observed for the hip external rotation torque. All the junior players exhibited hip external rotation torque, and its magnitude was particularly dominant in the latter part of leg swing. Conversely, the magnitude of hip external rotation torque for the professional player was negligible. These results may help to explain differences in kicking techniques between the two levels of players

ショウニ センコウセイ チュウスイエン ニタイスル カイフク シュジュツ ト ヒシタ フククウキョウ シュジュツ ノ ユウヨウセイ ノ ケントウ

【Background】 The role of laparoscopy in the management of perforated appendicitis in children is still somewhat controversial. We evaluated outcomes between open and laparoscopic surgery for perforated appendicitis in children. 【Patients and methods】 The medical records which underwent appendectomy for perforated appendicitis in children less than 15 years old from April 2003 to March 2015 were retrospectively reviewed. 【Results】 A total of 78 patients were enrolled. Twenty-five children underwent open appendectomy（OA）and 53 had laparoscopic appendectomy（LA） for perforated appendicitis. The mean operative time for LA（80.4±40.2 minutes for OA vs 109.0±29.7 minutes for LA, p＜0.01）was significantly longer. Patients in the LA group returned to oral intake earlier（2.3±1.1 days for LA vs 3.6±1.7 days for OA, p＜0.01）and had a shorter length of hospital stay（8.5±4.9 days for LA vs 12.7±6.3 days for OA, p＜0.01）. The incidence of postoperative complication in LA group was lower（6 cases for LA vs 8 cases for OA, p＜0.05）. 【Conclusions】 Laparoscopic appendectomy for perforated appendicitis in children was a feasible procedure which effects early postoperative oral intake, shortened length of hospital stay, and reducepostoperative complications

Search for Lepton Flavor Violating Decay at FASER

FASER is one of the promising experiments which search for long-lived particles beyond the Standard Model. In this paper, we consider charged lepton flavor violation (CLFV) via a light and weakly interacting boson and discuss the detectability by FASER. We focus on four types of CLFV interactions, i.e., the scalar-, pseudoscalar-, vector-, and dipole-type interaction, and calculate the sensitivity of FASER to each CLFV interaction. We show that, with the setup of FASER2, a wide region of the parameter space can be explored. Particularly, it is found that FASER2 has a sensitivity to very small coupling regions in which the rare muon decays, such as $\mu \rightarrow e\gamma$, cannot place bounds, and that there is a possibility to detect CLFV decays of the new light bosons.Comment: 27 pages; v2: minor changes, final versio

Dark Photon from Light Scalar Boson Decays at FASER

FASER is one of the promising experiments which search for long-lived particles beyond the Standard Model. In this paper, we focus on dark photon associating with an additional U(1) gauge symmetry, and also a scalar boson breaking this U(1) gauge symmetry. We study the sensitivity to the dark photon originated from U(1)-breaking scalar decays. We find that a sizable number of dark photon signatures can be expected in wider parameter space than previous studies.Comment: 12 pages, 3 figures; v2: typos corrected, discussions and references added; v3: added references, figures, and comments on the light scalar case, calculated event number by Monte Carlo simulations, version to be published in JHE