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10 pages, 637 KiB

Open AccessArticle

The Influence of Badminton on the Anterior Stability of the Knee in Badminton Players between 10 and 12 Years of Age

by Wojciech Kubasik, Piotr Rodak, Krzysztof Przednowek, Kamila Kluczniok and Krzysztof Ficek

Appl. Sci. 2022, 12(20), 10575; https://doi.org/10.3390/app122010575 - 20 Oct 2022

Cited by 2 | Viewed by 2730

The anterior cruciate ligament (ACL) tear is a common injury in athletes and physically active people, for that reason it is a very interesting topic for orthopedics and physiotherapists. The ACL tear can lead to knee joint instability. There are two main mechanisms [...] Read more.

The anterior cruciate ligament (ACL) tear is a common injury in athletes and physically active people, for that reason it is a very interesting topic for orthopedics and physiotherapists. The ACL tear can lead to knee joint instability. There are two main mechanisms of the ACL tear that are described in the literature during which this injury occurs: landing after a jump and dynamic lunges. The purpose of this study was to evaluate the influence of badminton training on sagittal knee stability in young badminton players aged from 10 to 12 years old. Additionally, subjects were tested using the functional movement screen (FMS). One hundred sixteen children were included in this study. The study group consisted of 68 children, practicing badminton on a regular basis. The control group included 48 children who did not practice any sport. The results indicated that regular practice of badminton did not influence sagittal knee stability in youth players. It was also demonstrated that badminton training influences the final score in the FMS in badminton players. Additionally, based on the results of this study, there was a significant relationship between the FMS score and frontal knee stability. Considering these results, we can conclude that adequate motor preparation and badminton training have a beneficial effect on the stability of the knee joints in young badminton players. Full article

(This article belongs to the Special Issue Sports Fluid Mechanics)

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18 pages, 5960 KiB

Open AccessArticle

On the Physics of Kayaking

by Charlie Prétot, Rémi Carmigniani, Loup Hasbroucq, Romain Labbé, Jean-Philippe Boucher and Christophe Clanet

Appl. Sci. 2022, 12(18), 8925; https://doi.org/10.3390/app12188925 - 6 Sep 2022

Cited by 6 | Viewed by 4523

Abstract

The propulsion force of a kayaker can be measured thanks to sensors placed on the paddle. This article aims at linking this force to the evolution of the velocity of the boat. A general model is proposed to describe the motion of a [...] Read more.

The propulsion force of a kayaker can be measured thanks to sensors placed on the paddle. This article aims at linking this force to the evolution of the velocity of the boat. A general model is proposed to describe the motion of a K1 kayak. To validate the model and evaluate the relevant physics parameters, three on-water kayaking trials are proposed: a pure deceleration, a standing start, and 10 × 50 m with two athletes at the national level. These trials were performed with a force sensor on the paddle and video recording. We used the deceleration to evaluate the drag of the boat. Then the standing start showed that there was an active drag coefficient while kayaking. Finally, the 10 × 50 m exhibited a power law of one-third between the velocity and the stroke rate. The acceleration during the standing start together with the relationship between the velocity and stroke rate were well captured theoretically. This approach enabled us to evaluate the important parameters to describe a kayak race: the drag of the boat, an active drag coefficient, the mean propulsive force, and a propulsive length. It can be used to characterize athletes and monitor their performances. Full article

(This article belongs to the Special Issue Sports Fluid Mechanics)

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13 pages, 3766 KiB

Open AccessArticle

A Method for Evaluating the Influence of the Field Wind Environment on Cross-Country Skiing Performance

by Jiawei He, Li Yan, Ming Zhu, Dabo Xin, Yagebai Zhao and Hongfu Zhang

Appl. Sci. 2022, 12(14), 6902; https://doi.org/10.3390/app12146902 - 7 Jul 2022

Viewed by 1373

Abstract

Aerodynamic drag plays an important role in high-speed skiing. The wind-induced thrust or resistance of athletes, the sliding speed, and the work to overcome the aerodynamic drag are greatly affected by wind; therefore, reducing wind-induced drag is a focus of sport science. This [...] Read more.

Aerodynamic drag plays an important role in high-speed skiing. The wind-induced thrust or resistance of athletes, the sliding speed, and the work to overcome the aerodynamic drag are greatly affected by wind; therefore, reducing wind-induced drag is a focus of sport science. This paper proposes a method for evaluating the influence of wind on cross-country skiing performance, which is based on the athlete’s aerodynamic-drag-work relative to the environmental wind field and the establishment of a racetrack wind field model. Aiming at an athlete’s typical sport posture in the Yabuli Ski Field, the impact of field wind on the skier’s speed, the work done by the athlete to overcome aerodynamic drag, and the ratio of the field wind-induced work to the athlete’s total work are analyzed. Through the analysis of the athlete’s work to overcome aerodynamic drag and the wind resistance energy dissipation ratio in three training cases, it is shown that the field wind has a great influence on the athlete’s performance during sliding, which verified the effectiveness of the method. This method will provide coaches and sport researchers with accurate wind resistance energy dissipation data and provide a scientific basis for routine athletic training. Full article

(This article belongs to the Special Issue Sports Fluid Mechanics)

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17 pages, 12259 KiB

Open AccessArticle

Magnus-Forces Analysis of Pitched-Baseball Trajectories Using YOLOv3-Tiny Deep Learning Algorithm

by Bor-Jiunn Wen, Che-Rui Chang, Chun-Wei Lan and Yi-Chen Zheng

Appl. Sci. 2022, 12(11), 5540; https://doi.org/10.3390/app12115540 - 30 May 2022

Cited by 6 | Viewed by 5350

Abstract

This study analyzed the characteristics of pitched baseballs from TV broadcast videos to understand the effects of the Magnus force on a pitched-baseball trajectory using aerodynamic theory. Furthermore, an automatic measurement and analysis system for pitched-baseball trajectories, ball speeds, and spin rates was [...] Read more.

This study analyzed the characteristics of pitched baseballs from TV broadcast videos to understand the effects of the Magnus force on a pitched-baseball trajectory using aerodynamic theory. Furthermore, an automatic measurement and analysis system for pitched-baseball trajectories, ball speeds, and spin rates was established, capturing the trajectory of the baseball thrown by the pitcher before the catcher catches it and analyzing its related dynamic parameters. The system consists of two parts: (1) capturing and detecting the pitched baseball in all frames of the video using the YOLOv3-tiny deep learning algorithm and automatically recording the coordinates of each detected baseball position; (2) automatically calculating the average speed and spin rate of the pitched baseball using aerodynamic theory. As the baseball thrown by the pitcher is fast, and live-action TV videos like sports and concerts are typically at least 24 fps or more, this study used YOLOv3-tiny algorithm to speed up the calculation. Finally, the system automatically presented pitching data on the screen, and the pitching information in the baseball game was easily obtained and recorded for further discussion. The system was tested using 30 videos of pitched baseballs and could effectively capture the baseball trajectories, throw points, catch points, and vertical displacements. Compared with the values from the TV broadcast, the average errors on the calculated ball speed and spin rate were 1.88% and 7.51%, respectively. Using the ratio of the spin rate and ball speed as a parameter to analyze the pitching state of the pitcher’s four-seam fastball in the Nippon Professional Baseball and Major League Baseball matches, it was observed that when this ratio increased, the Magnus displacement of the ball increased, thereby decreasing its late break. Therefore, the developed system provides scientific pitching data to improve the performance of baseball pitchers. Full article

(This article belongs to the Special Issue Sports Fluid Mechanics)

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16 pages, 28735 KiB

Open AccessArticle

Numerical Investigation of the Hydrodynamic Characteristics of 3-Fin Surfboard Configurations

by Sam Crameri, Paul K. Collins and Saleh Gharaie

Appl. Sci. 2022, 12(7), 3297; https://doi.org/10.3390/app12073297 - 24 Mar 2022

Cited by 3 | Viewed by 4866

Abstract

Surfing is a popular sport, with the associated market forecast to reach 2.6 billion US dollars by 2027. In the published literature, there is a range of investigations into the performance of surfboard fins. Some studies model a single fin or review the [...] Read more.

Surfing is a popular sport, with the associated market forecast to reach 2.6 billion US dollars by 2027. In the published literature, there is a range of investigations into the performance of surfboard fins. Some studies model a single fin or review the performance of different fin layouts and surface designs. However, the effects of individual fin design features on flow dynamics are not well understood. This study provides numerical analysis into the thruster fin aspects (rake, depth, and base length) and resultant key performance indicators (i) lift and drag coefficients, and (ii) turbulent kinetic energy. The models were simulated in Ansys Fluent R19.1, solving steady Reynolds-averaged Navier–Stokes equations using the SST k−ω turbulence model at a velocity of 7 m/s. The results indicate the performance of fins varies more post-stall. The variations in rake showed the biggest impact on the turbulence intensity at an angle ≥20°. The variations in base length exhibited coefficient trends with greater lift at small angles but significant lift losses at high angles of attack. The variations in depth affected the forces on the fins rather than the performance indicators. Based on these simulations, a proposed fin set was developed that presented the lowest lift losses after the stall point. Full article

(This article belongs to the Special Issue Sports Fluid Mechanics)

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8 pages, 2608 KiB

Open AccessArticle

Baseball Drag Measurements in Free Flight

by Lloyd Smith and Andrea Sciacchitano

Appl. Sci. 2022, 12(3), 1416; https://doi.org/10.3390/app12031416 - 28 Jan 2022

Cited by 4 | Viewed by 6893

Abstract

While baseball is a popular sport with a storied history, the aerodynamic properties of the seamed sports ball are not fully understood. Reported aerodynamic baseball behaviors are primarily based on force measurements from wind tunnels. The following describes a methodology to measure baseball [...] Read more.

While baseball is a popular sport with a storied history, the aerodynamic properties of the seamed sports ball are not fully understood. Reported aerodynamic baseball behaviors are primarily based on force measurements from wind tunnels. The following describes a methodology to measure baseball drag in free flight from changes in its speed. The method relies on a high accuracy ball delivery device and speed measurement system. It avoids the large infrastructure, stinger attachment and blockage effects associated with wind tunnels. In the present work, we examined the baseball drag as a function of orientation and with spin. The drag values retrieved from the proposed method are in good agreement with radar and video measurements. However, they are lower than those reported in other wind tunnel measurements, which was attributed to differences in the balls that were tested or the stinger attachment. Full article

(This article belongs to the Special Issue Sports Fluid Mechanics)

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10 pages, 2727 KiB

Open AccessArticle

Aerodynamic Differences between New and Used Soccer Balls

by Sungchan Hong and Takeshi Asai

Appl. Sci. 2021, 11(16), 7204; https://doi.org/10.3390/app11167204 - 4 Aug 2021

Cited by 2 | Viewed by 3212

Abstract

The surface structure of soccer balls, such as the number and shapes of the ball panels, has recently changed, and research on the aerodynamics and flight trajectories of new soccer balls is actively proceeding. However, these studies are focused on new soccer balls, [...] Read more.

The surface structure of soccer balls, such as the number and shapes of the ball panels, has recently changed, and research on the aerodynamics and flight trajectories of new soccer balls is actively proceeding. However, these studies are focused on new soccer balls, whereas the used soccer balls were never studied. In this study, the aerodynamic characteristics of soccer balls kicked 1000 times by a robot were investigated through wind tunnel tests. The results were compared with those obtained using new soccer balls. Regarding the aerodynamic characteristics of the soccer balls, it was found that the critical Reynold number, Re_crit, changes with usage. This is related to the transition from laminar to turbulent flow of airflow around the ball. The comparison of the drag coefficients of the balls at Re_crit showed that the drag coefficients of the new and used Telstar18 balls were 0.15 (Re = 2.5 × 10⁵) and 0.14 (Re = 2.2 × 10⁵), respectively; those of the new and used Merlin were 0.13 (Re = 2.8 × 10⁵) and 0.13 (Re = 2.2 × 10⁵), respectively; and finally, those of the new and used Derbystar were 0.14 (Re = 2.1 × 10⁵) and 0.14 (Re = 2.1 × 10⁵), respectively. The surface conditions of a soccer ball, such as the surface roughness and surface damages, are essential factors to determine the aerodynamics of the soccer balls. Full article

(This article belongs to the Special Issue Sports Fluid Mechanics)

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16 pages, 39447 KiB

Open AccessArticle

Aerodynamics Analysis of Speed Skating Helmets: Investigation by CFD Simulations

by Guillermo Puelles Magán, Wouter Terra and Andrea Sciacchitano

Appl. Sci. 2021, 11(7), 3148; https://doi.org/10.3390/app11073148 - 1 Apr 2021

Cited by 6 | Viewed by 4569

Abstract

In this work, we investigate the flow field around speed skating helmets and their associated aerodynamic drag by means of computational fluid dynamics (CFD) simulations. An existing helmet frequently used in competition was taken as a baseline. Six additional helmet designs, as well [...] Read more.

In this work, we investigate the flow field around speed skating helmets and their associated aerodynamic drag by means of computational fluid dynamics (CFD) simulations. An existing helmet frequently used in competition was taken as a baseline. Six additional helmet designs, as well as the bare-head configuration, were analysed. All the numerical simulations were performed via 3D RANS simulations using the SST k-

ω

turbulence model. The results show that the use of a helmet always reduces the aerodynamic drag with respect to the bare head configuration. Besides, an optimised helmet design enables a reduction of the skaters aerodynamic drag by 5.9%, with respect to the bare-head configuration, and by 1.6% with respect to the use of the baseline Omega helmet. Full article

(This article belongs to the Special Issue Sports Fluid Mechanics)

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11 pages, 4458 KiB

Open AccessArticle

Aerodynamics of Cycling Skinsuits Focused on the Surface Shape of the Arms

by Sungchan Hong and Takeshi Asai

Appl. Sci. 2021, 11(5), 2200; https://doi.org/10.3390/app11052200 - 3 Mar 2021

Cited by 4 | Viewed by 4334

Abstract

In cycling, air resistance corresponds to 90% of the resistance on the bicycle and cyclist and 70% of this is applied to the body of the cyclist. Despite research on postures that could reduce air resistance, few studies have been conducted on full-body [...] Read more.

In cycling, air resistance corresponds to 90% of the resistance on the bicycle and cyclist and 70% of this is applied to the body of the cyclist. Despite research on postures that could reduce air resistance, few studies have been conducted on full-body cycling suits. As the aerodynamics of the surface shape of clothing fabric are still unclear, the airflow around cyclists and air resistance were examined using a computational fluid dynamics (CFD) method and wind tunnel experiment. Specifically, in this study, we focused on how different surface shapes of cycling suit fabrics affect air resistance. CFD results indicate that air resistance during a race was high at the head, arms and legs of the cyclist. In the wind tunnel experiment, a cylinder model resembling the arms was used to compare the aerodynamic forces of various fabrics and the results showed that air resistance changed according to the fabric surface shape. Moreover, by changing the fabric shape of the arms of the cycling suits, reduction of air resistance by up to 8% is achievable. These results suggest that offering the most appropriate suit type to each cyclist, considering race conditions, can contribute to further improvement in their performance. Full article

(This article belongs to the Special Issue Sports Fluid Mechanics)

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18 pages, 6126 KiB

Open AccessArticle

The Impact of Skinsuit Zigzag Tape Turbulators on Speed Skating Performance

by Nando Timmer and Leo Veldhuis

Appl. Sci. 2021, 11(3), 988; https://doi.org/10.3390/app11030988 - 22 Jan 2021

Cited by 4 | Viewed by 3525

Abstract

At the 1998 Nagano Winter Olympic Games, zigzag tape was introduced on the race suit lower legs and cap of speed skaters. Application of these zigzag devices on live skaters and cylinders in the wind tunnel showed large improvements in the aerodynamic drag. [...] Read more.

At the 1998 Nagano Winter Olympic Games, zigzag tape was introduced on the race suit lower legs and cap of speed skaters. Application of these zigzag devices on live skaters and cylinders in the wind tunnel showed large improvements in the aerodynamic drag. These wind-tunnel results were unfortunately not widely published, and the impact of the zigzag strips in a real skating environment was never established. This paper aims to show the background of the application of the zigzag tape and to establish the impact it may have had on speed-skating performance. From comparisons of 5000 m races just before, during and just after the Nagano Olympics and an analysis of historic world record data of the 1500 m men’s speed skating, the impact of the zigzag tape turbulators on average lap times on 1500 and 5000 m races is calculated to be about 0.5 s. Full article

(This article belongs to the Special Issue Sports Fluid Mechanics)

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14 pages, 18844 KiB

Open AccessArticle

Effect of Soccer Ball Panels on Aerodynamic Characteristics and Flow in Drag Crisis

by Yuki Sakamoto, Masaki Hiratsuka and Shinichiro Ito

Appl. Sci. 2021, 11(1), 296; https://doi.org/10.3390/app11010296 - 30 Dec 2020

Cited by 3 | Viewed by 3799

Abstract

The panel patterns of soccer balls that change with each World Cup have a significant impact on the balls’ aerodynamic and flight characteristics. In this study, the aerodynamic forces of eleven types of soccer ball with different panel patterns were measured in a [...] Read more.

The panel patterns of soccer balls that change with each World Cup have a significant impact on the balls’ aerodynamic and flight characteristics. In this study, the aerodynamic forces of eleven types of soccer ball with different panel patterns were measured in a wind tunnel experiment. We characterized the panel shapes of soccer balls by the length, cross-sectional area, and the panel grooves’ volume. The results confirmed that the drag and drag crisis characteristics are dependent on the groove length and volumes. Flow separation points were visualized by an oil film experiment and particle image velocimetry (PIV) measurement to understand the drag crisis of the soccer balls. The results showed that the panel shape of the ball significantly changes the position of the separation point near the critical region, where the drags crisis occurs. In the critical region, laminar and turbulent flows coexist on the ball. On the other hand, the effect of panel shape on the separation point position is small in subcritical and supercritical states. Full article

(This article belongs to the Special Issue Sports Fluid Mechanics)

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15 pages, 5836 KiB

Open AccessArticle

Investigation of Reverse Swing and Magnus Effect on a Cricket Ball Using Particle Image Velocimetry

by Richard W. Jackson, Edmund Harberd, Gary D. Lock and James A. Scobie

Appl. Sci. 2020, 10(22), 7990; https://doi.org/10.3390/app10227990 - 11 Nov 2020

Cited by 6 | Viewed by 6452

Abstract

Lateral movement from the principal trajectory, or “swing”, can be generated on a cricket ball when its seam, which sits proud of the surface, is angled to the flow. The boundary layer on the two hemispheres divided by the seam is governed by [...] Read more.

Lateral movement from the principal trajectory, or “swing”, can be generated on a cricket ball when its seam, which sits proud of the surface, is angled to the flow. The boundary layer on the two hemispheres divided by the seam is governed by the Reynolds number and the surface roughness; the swing is fundamentally caused by the pressure differences associated with asymmetric flow separation. Skillful bowlers impart a small backspin to create gyroscopic inertia and stabilize the seam position in flight. Under certain flow conditions, the resultant pressure asymmetry can reverse across the hemispheres and “reverse swing” will occur. In this paper, particle image velocimetry measurements of a scaled cricket ball are presented to interrogate the flow field and the physical mechanism for reverse swing. The results show that a laminar separation bubble forms on the non-seam side (hemisphere), causing the separation angle for the boundary layer to be increased relative to that on the seam side. For the first time, it is shown that the separation bubble is present even under large rates of backspin, suggesting that this flow feature is present under match conditions. The Magnus effect on a rotating ball is also demonstrated, with the position of flow separation on the upper (retreating) side delayed due to the reduced relative speed between the surface and the freestream. Full article

(This article belongs to the Special Issue Sports Fluid Mechanics)

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8 pages, 2388 KiB

Open AccessArticle

Effect of Surface Groove Structure on the Aerodynamics of Soccer Balls

by Sungchan Hong and Takeshi Asai

Appl. Sci. 2020, 10(17), 5877; https://doi.org/10.3390/app10175877 - 25 Aug 2020

Cited by 3 | Viewed by 3952

Abstract

Soccer balls have undergone dramatic changes in their surface structure that can affect their aerodynamics. The properties of the soccer ball surface such as the panel shape, panel orientation, seam characteristics, and surface roughness have a significant impact on its aerodynamics and flight [...] Read more.

Soccer balls have undergone dramatic changes in their surface structure that can affect their aerodynamics. The properties of the soccer ball surface such as the panel shape, panel orientation, seam characteristics, and surface roughness have a significant impact on its aerodynamics and flight trajectory. In this study, we performed wind-tunnel tests to investigate how the introduction of grooves on the surface of a soccer ball affects the flight stability and aerodynamic forces on the ball. Our results show that for soccer balls without grooves, changing the panel orientation of the ball causes a significant change in the drag coefficient. Soccer balls with grooves exhibited a smaller change in air resistance (Cd) in the supercritical region (20 to 30 m/s; 3.0 × 10⁵ ≤ Re ≤ 4.7 × 10⁵), compared to the ungrooved ball where only the panel orientation was changed. Furthermore, at power-shot speeds (25 m/s), the grooved ball exhibited smaller variations in lift force and side force than the ungrooved ball. These results suggest that a long groove structure on the surface of the soccer ball has a significant impact on the air flow around the ball in the supercritical region, and has the effect of keeping the air flow separation line constant. Full article

(This article belongs to the Special Issue Sports Fluid Mechanics)

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15 pages, 3906 KiB

Open AccessFeature PaperArticle

Flow Visualization of Spinning and Nonspinning Soccer Balls Using Computational Fluid Dynamics

by Takeshi Asai, Yasumi Nakanishi, Nakaba Akiyama and Sungchan Hong

Appl. Sci. 2020, 10(13), 4543; https://doi.org/10.3390/app10134543 - 30 Jun 2020

Cited by 6 | Viewed by 5794

Abstract

Various studies have been conducted on the aerodynamic characteristics of nonspinning and spinning soccer balls. However, the vortex structures in the wake of the balls are almost unknown. One of the main computational fluid dynamics methods used for the analysis of vortex structures [...] Read more.

Various studies have been conducted on the aerodynamic characteristics of nonspinning and spinning soccer balls. However, the vortex structures in the wake of the balls are almost unknown. One of the main computational fluid dynamics methods used for the analysis of vortex structures is the lattice Boltzmann method as it facilitates high-precision analysis. Studies to elucidate the dominant vortex structure are important because curled shots and passes involving spinning balls are frequently used in actual soccer games. In this study, we identify the large-scale dominant vortex structure of a soccer ball and investigate the stability of the structure using the lattice Boltzmann method, wind tunnel tests, and free-flight experiments. One of the dominant vortex structures in the wake of both nonspinning and spinning balls is a large-scale counter-rotating vortex pair. The side force acting on a spinning ball stabilizes when the fluctuation of the separation points of the ball is suppressed by the rotation of the ball. Thus, although a spinning soccer ball is deflected by the Magnus effect, its trajectory is regular and stable, suggesting that a spinning ball can be aimed accurately at the outset of its course. Full article

(This article belongs to the Special Issue Sports Fluid Mechanics)

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