Ball Contact Research Articles

Contact force calculation and evolution analysis of granular systems based on micro-CT experiment

The calculation of inter-granule contact force in three-dimensional (3D) granular systems is a key and challenging aspect of granular mechanics research. Two elastic rubber balls are used as research objects for in-situ flat pressing Micro-CT experiments. Based on the Hertzian contact theory and Tatara large deformation contact theory, the contact model of elastic balls is verified, and the theoretical formula of the contact force of elastic balls based on the experiment is obtained. Taking the 3D granular systems as research object, in-situ probe loading experiment of micro-CT is carried out to obtain the 2D image sequence of the granules, after a series of digital transformations, the digital body images emerge, the contact force networks of the 3D granular systems under different loading conditions are obtained by constructing pore network models. The contact force distribution and evolution law of the granular systems are analyzed. The relation among the number of strong contacts, the distribution evolution, and the stability of the granular system is explored. The results show that the two elastic ball contact model conforms to the Hertzian contact theory and Tatara large deformation contact theory, and the contact force fitting formula based on experiment can characterize the contact force between two granules reasonably and effectively. The contact force of granules under probe loading is distributed in a net-like pattern starting from the contact point of the indenter and gradually transmitted to the lower and the surrounding area. The trend of average contact force is consistent with the trend of the contact times, showing a significant phase transition. With the increase of contact times, the frequency of particle compression increases, resulting in a greater contact force between granules, ultimately stabilizing at about 10.5 N. The number of strong contacts accounts for 45% to 50% of the total number of contacts, distributed throughout the whole granular system and supporting the network structure of the granular system. The larger values are concentrated below the indenter and exhibit a branching distribution. In the loading process, an equilibrium point is established at <i>z</i> = 14 mm, where the number of strong contacts reaches the peak. The network structure of strong contact force is spread throughout the entire 3D granular system, establishing the main skeleton that can withstand external loads. As the loading continues, the total value of strong contact forces increases, and their distribution within the granular system becomes more uniform.

Inner race dynamics of a high-speed ball bearing with elastic ring squeeze film damper

Abstract This paper aims at the inner race dynamics of a high-speed ball bearing incorporated with Elastic Ring Squeeze Film Damper (ERSFD). Dynamic model of the inner race with three degrees of freedom (DOFs) is established in an ERSFD integrated ball bearing. Ball contact force and operating contact angle are characterized through an improved quasi-static model where the geometric relationship between the bearing displacement and elastic deformation is developed by considering the outer race movement. Numerical simulations were performed for bearings with or without ERSFD. The model was validated using Campbell diagram, measured displacement response and center trajectory of the inner race at different rotor speeds. The results show that the ERSFD provides adequate stable traction on the ball and limits excessive increase in the inner race contact angle. Such load-carrying condition benefits for decrease in ball orbital revolution skid at high rotor speeds. The ERSFD helps rotor unbalance force dominate bearing motion, leading to a stable periodic motion for the inner race at high rotor speeds. For ball bearings without ERSFD inner race possess stable motion at low and moderate rotor speeds, but is more prone to instability at high rotor speeds.

Analysing trunk and arm motion in volleyball jump serve: a comparison of straight line and diagonal line techniques

ABSTRACT This study aimed to clarify the disparities in trunk rotation and attack arm movement and their effect on hand kinematics adjustments between straight-line (SL) and diagonal-line (DL) volleyball jump serves. Thirteen male professional volleyball players (age 21.53 ± 5.39 years, height 1.95 ± 0.06 m, body mass 86.48 ± 11.63 kg, experience 8.61 ± 3.47 years) performed SL and DL jump serve, with three-dimensional coordinate data captured using a motion capture system (200 hz). Paired t-test and statistical parametric mapping examined kinematic differences between the two serving directions. At ball contact (BC), the speed of the attack arm hand was significantly faster in DL (16.99 ± 1.36 m/s) compared to SL (16.37 ± 1.53 m/s), whereas the face angle was significantly smaller in DL (1.98 ± 11.75°) than in SL (17.60 ± 17.98°). Forward rotation angles of the pelvic and upper torso at BC were significantly greater in DL (28.47 ± 10.89°; 21.30 ± 10.25°) than in SL (18.27 ± 12.46°; 9.09 ± 14.41°). During the arm swing phase, the pelvic’s forward rotation angles in DL were significantly greater than in SL at 42–72% spiking motion, and the upper torso’s angles were significantly greater at 49–58% spiking motion. These findings underscore the importance of adjusting pelvic and upper torso rotations to control the hand’s face angle when serving in the diagonal line.

Effects of Grip Style and Contact Point on Force Production in a Tennis Forehand Groundstroke.

Modern tennis forehand grip style and ball contact points have evolved to enhance power and topspin. Different grip styles and ball contacts are recommended; however, little data are available to support one over another. Through a quantitative experimental study, we sought to determine which grip style and ball contact point produced the greatest forces at static contact. The continental, eastern, and semi-western forehand groundstroke grips of 100 volunteers were evaluated. Participants stood in three defined positions and applied maximum force against a dynamometer with each grip style. The associations of force produced at contact with the grip style, age, sex, tennis experience, and handedness were evaluated using univariate and multivariate linear mixed-effects regression models separately for early, mid, and late contact, including a random effect for each participant. Force production was significantly greater with eastern grip at early, mid, and late contact than with the other two grips (p < 0.001). Force was greater at early contact with semi-western grip than with continental. Force was also significantly greater for men at early, mid, and late contact (p < 0.001). Participants using an eastern grip were able to generate more force compared to those using a continental or semi-western grip, regardless of the ball contact point. Tennis players currently using other forehand grip styles who want to maximize power production may consider transitioning to an eastern forehand grip. The results of this study may improve tennis instruction and training for beginning and novice players who lack force generation.

How does it end? Endpoints of boundaries lead to completion in macro-events.

While watching someone kicking a ball, missing moments of ball contact can be incorrectly identified as seen if the event is continued in a causal manner (i.e., the ball flying off). Does event completion also occur for events of a larger scale such as having breakfast (macro-event), which consists of multiple sub-steps like toasting bread (micro-event)? We conducted two experiments to measure event completion in macro-events presenting portions of multiple micro-events. In Experiment 1, video summaries were formed with or without event boundary information where a macro-end was either present or absent. Macro-end signified an overarching goal achievement that signaled the completion of previous tasks (such as leaving the kitchen with a full breakfast plate). More completion occurred for summaries with event boundary information and macro-ends. In Experiment 2, we tested two alternative hypotheses to explore the underlying process by showing the beginnings or ends of a micro-event. While the predictive processing hypothesis suggests that event completion is based more on predicting the future states of the event based on beginning information, the backward inferences hypothesis suggests that event completion relies more on deductions formed after the fact based on event endings. Results of Experiment 2 suggest that the ends of event boundaries lead to more event completion, possibly due to their role in forming causal connectivity. These results help to further understand event completion on a macro level.

Optimizing Volleyball Bottom Passing Skills: Unveiling the Impact of the STAD Learning Model on Learning Outcomes

The study focused on improving the lower passing skills of 8th-grade female students at SMP Negeri 6 Sumedang in volleyball. Recognizing the significance of passing in enhancing team attacks and overall match performance, the researcher employed the student teams achievement division (STAD) learning model to address existing skill deficiencies. The research identified common issues in lower passing execution, including imperfect movement stages, improper ball contact in the hands, ball deviation from the intended target, and an inability to control the ball’s direction. The results indicated a positive impact, with a significant increase in the lower passing skills observed during the volleyball underpassing tests. The t-test results, with T_count = 16.4 &gt; T_table = 1.725, demonstrated a statistically significant improvement, confirming that the STAD learning model contributed to enhanced learning outcomes. In summary, the research concluded that the application of the STAD learning model positively influenced the learning outcomes related to lower passing skills in volleyball among 8th-grade female students at SMP Negeri 6 Sumedang. The findings emphasized the efficacy of employing cooperative learning strategies, such as STAD, to address specific skill challenges in sports education. Keywords: STAD, bottom passing, volleyball

The influence of scanning behaviour on performance during 4v4 small-sided games in youth female football

ABSTRACT Scanning is an important perceptual skill that enables football players to gather information about opponents, teammates and the environment in real-time. This study investigated scanning before and during ball possession and its effect on the success of the subsequent action in U19 female footballers. Sixty-one elite and grassroots players (age: 16.7 ± 1.4) were recruited and analysed during 4v4 small-sided games. A total of 2010 game situations were video recorded for subsequent manual tagging. Multilevel logistic regression models revealed that elite players performed significantly more scans prior to first ball contact than their grassroots counterparts, but the number of scans performed during ball possession did not differ between competition levels. Furthermore, scans before and during ball possession positively influenced player’s performance, whereas opponent pressure negatively influenced the success of subsequent actions, regardless of competition level. Differentiating between various subsequent actions revealed that scans before ball possession had a positive effect on the success of dribblings and passes, whereas scans during ball possession only had a positive effect on dribblings. Our results underline the importance of scanning in youth female football. These findings should be considered by coaches in the long-term development of players to increase the level of performance at elite age.

Effect of stick and slip zones on fatigue life of a slewing ball bearing

Prediction of fatigue life of slewing ball bearings is challenging due to the influence of large deformations and adverse lubrication conditions. The present study presents an elegant simulation model that considers the flexibility of the supporting elements of the slewing bearing along with stick/slip zones at the raceway-ball contact interface. Using the stresses predicted by the simulation model, relative fatigue life using stick/slip condition versus no-friction condition is computed. A sensitivity study of the ball contact force, ball contact angle, coefficient of friction and raceway conformity is also performed. The present study also evaluates the results in comparison with full-sliding assumptions. The final results show that the stick/slip zone determination at the contact interface is beneficial for accurate determination of fatigue life of slewing bearings.

Oil Distribution around Ball–Raceway Local Contact Region in Under-Race Lubrication of Ball Bearing

The distribution of oil and gas phases around ball–raceway local regions is an important basis and foundation for determining whether a bearing is sufficiently lubricated. To obtain the oil phase distribution law in the inner raceway–ball contact local region (IBCR) and outer raceway–ball contact local region (OBCR) of the ball bearing with under-race lubrication, the numerical simulation method is used. The effects of bearing rotation speed, oil flow rate, oil viscosity, and oil density on these two regions are studied. The results indicate that the oil phase exhibited significant periodic changes in both time and space. Compared with that in the IBCR, the oil phase distribution in the OBCR is more uniform. Increasing the bearing rotation speed and reducing the oil flow rate made the IBCR and OBCR more uniform. Changing the oil viscosity only alters the distribution pattern of the OBCR. The oil density may not affect the fluid flow state or the oil phase distribution in the bearing.

Perceptual training with implicit and explicit learning improves the prediction of ball direction in soccer penalty kicks.

Perceptual training enhances the ability to anticipate crucial information for decision-making, for example, a soccer goalkeeper predicting penalty kick direction. However, it remains unclear whether perceptual practice alone (implicit method) is sufficient for optimal decision-making improvement, or whether emphasising pertinent details during practice (explicit method) could yield better results. This study compared implicit and explicit methods of learning ball direction prediction during soccer penalties, involving both goalkeepers and non-soccer players (novices). Participants engaged in a single training session, either through the explicit method (watching videos highlighting relevant information) or implicit method (watching regular videos). Specialised software was used to display penalty kick videos, mimicking the goalkeeper's viewpoint up to 200 ms before ball contact, and measuring reaction time and response choice. Both implicit and explicit training led to consistent performance gains for goalkeepers and novices alike, notably enhancing ball direction prediction accuracy. Reaction time was unaffected by training. This suggests that both explicit and implicit training methods exhibit similar effectiveness, applicable to soccer goalkeepers and novices.

Dynamic contact and stiffness characteristic analysis of angular contact ball bearings under combined external loads

A nonlinear dynamic model of angular contact ball bearing under combined external loads is established based on the nonlinear elastic Hertz contact theory and raceless control theory. The established dynamic model is solved by employing variable step size Newton Raphson iteration method and the validation of model is verified by comparing the proposed results with the corresponding results come from the existing literatures. The solution of the presented model has high accuracy compared with the existing experimental results. In addition, the computational efficiency of the proposed model is improved significantly by introducing iteration step size adjustment factor. According to the proposed model, the dynamic contact and stiffness characteristics of angular contact ball are studied systematically by investigating the effects of combined external load working conditions on the contact parameters including contact angle and contact force and the stiffness parameters including diagonal stiffness and off-diagonal stiffness. This research can provide the theoretical basis and technique guidance for the designation and manufacture of angular contact ball bearing under combined external loads.

Design and Simulation of Adiabatic–Damping Dual–Function Strut for LH2 Storage Tank

In the process of the on–board transportation of liquid hydrogen storage and transportation tanks, apart from considering the support strength and adiabatic performance, it is imperative to take into account the vibration characteristics of the carrying platform. The present work introduces a versatile support structure comprising a damping module and a ball contact insulation structure, enabling effective isolation of external vibrations while simultaneously providing support and insulation. The first step involves describing the principle of a flexible support structure and designing the mechanical structure. Subsequently, a damping analysis is conducted based on dynamic theory to establish the relationship between the spring and damping. Finally, the structural parameters of the dual–function strut are determined, followed by simulation of heat transfer performance. The results demonstrate that the dual–function strut exhibits exceptional vibration damping performance by reducing the amplitude of external vibrations greater than 5 Hz to less than 6%. Moreover, owing to the compact linear diameter spring structure of the vibration damping module and its ball contact effect, the thermal resistance of the dual–function strut is significantly enhanced, resulting in a mere heat leakage of only 22 W/m2 in a single rod section.

Technical and Physical Load Variables at Different Positions in U18 Semi-Professional Soccer Players: Differences between the First and Second Half

Among the many factors that can affect men’s soccer performance, technical and tactical actions can obscure relevant game data, even affecting specialists in both the programming and design of training tasks. We aimed to evaluate the technical and physical load variables of different positions in U18 semi-professional soccer players and observe the differences between the first and second halves during 10 matches of the 2021/2022 Spanish Football U18 National League Championship. A total of 246 match records (10 matches) were collected from the 2021/2022 Spanish Football U18 National League Championship. Two teams participated, with a total of 49 athletes. Our study’s results indicate that, concerning technical performance, no significant differences between halves were found for goalkeepers, wingers, and forwards. However, significant declines were observed in the number of ball contacts, different actions per time, and possessions per time among central defenders, lateral defenders, and central midfielders. Regarding the observed physical load demands, it was noted that in outfield players, there was a significant decline in total distances covered at different speed thresholds, as well as a decrease in the number and distance of acceleration measures, most of which were lower in the second halves compared to the first, irrespective of playing positions. This study contributes to enhancing our understanding of the multifaceted dynamics of soccer performance and provides valuable insights for coaches, players, and researchers aiming to optimize player performance.

Impact of game format and age group on technical performance in youth football

This study aimed to analyse technical action variations among 5, 7, 9, and 11-a-side game formats and investigate the effects of age groups (U8, U10, U12, and U14) on these actions. A total of 197 soccer players aged between 6.94 ± 0.7 and 13.46 ± 0.5 years participated, with three matches conducted weekly, totalling 48 matches. Two-way ANOVA was employed to analyse age group and game format as independent factors. The study revealed the influence of age group on players' technical actions variability: front pass success p &lt; .001; side pass success p &lt; .001; back pass success p &lt; .001; short pass success p &lt; .001; reception success p &lt; .001; goal p &lt; .002; unsuccessful short pass p &lt; .001; unsuccessful long pass p &lt; .001; ball contacts p &lt; .001. Additionally, the study highlighted the impact of game format on success rates: front pass success p &lt; .001; side pass success p &lt; .001; back pass success p &lt; .001; short pass success p &lt; .001; reception success p &lt; .001; goal p &lt; .036; shot on target p &lt; .001; ball contacts p &lt; .001; interception p &lt; .001. These findings enhance understanding of how game format and age group affect technical performance in youth soccer, emphasizing the need for interventions that optimize players’ development trajectories.

A 2‐Dimensional Data Detrending Technique for Equatorial Plasma Bubble Studies Using GOLD Far Ultraviolet Observations

AbstractWe formulate a numerical data detrending technique that can be used to help reveal large‐scale equatorial plasma bubble (EPB) structures in 2‐dimensional data from the Global‐scale Observations of the Limb and Disk (GOLD) mission. This GOLD data detrending technique is inspired by and is a generalization of a previous rolling‐barrel data detrending method for 1‐dimensional total electron content (TEC) observations on individual global positioning system (GPS) satellite passes. This 2‐dimensional GOLD data detrending technique treats the observed 135.6 nm radiance as a function of longitude and latitude as an uneven terrain, where EPBs appear as deep but narrow elongated valleys. The unperturbed background radiance is inferred by rolling a ball on the 2‐dimensional terrain to skip over the EPB valleys. The two degrees‐of‐freedom possessed by the rolling ball allow it to smoothly trace the edges of EPB depletions, without falling into the deep valleys. Surface interpolation of radiance values at the ball's contact points onto the whole domain produces the baseline radiance. Subtracting the baseline from the original radiance data yields the net detrended radiance. As a result of the detrending, sharper contrast is present between EPB depletions and the ambient surroundings. As such, this new 2‐dimensional GOLD data detrending may potentially open the door to the development of other more advanced techniques for automated EPB detection and tracking, or data assimilation into low‐latitude space domain awareness (SDA) information ecosystems.

Correlations of Aerobic Capacity with External and Internal Load of Young Football Players during Small-Sided Games.

Aerobic capacity plays a crucial role in football performance, making it a focal point in training processes. Small-sided games (SSGs) are widely used in football training, but the relationship between aerobic capacity and running performance during SSGs remains unclear. The aim of this study was to investigate possible correlations between maximum oxygen uptake (VO2max) and running performance in youth football players in SSGs (4:4, 3:3, 2:2, 1:1) with three different pitch sizes per player (150, 100, 75 m2/player). Sixteen male U15 football players participated in the study. Players underwent the Yo-Yo intermittent recovery test level 1, and their VO2max was estimated based on their performance. Subsequently, players participated in SSGs wearing GPS devices to measure internal and external load. Pearson or Spearman correlation was applied for statistical analysis depending on the normal distribution of the data. The results reveal that, for 4:4 and 3:3 relationships, larger pitches led to a greater impact of aerobic capacity (total distance (TD): 4:4, 150 m2/pl, r = 0.715, p = 0.002; 100 m2/pl, r = 0.656, p = 0.006; 75 m2/pl, r = 0.586, p = 0.017). In the 2:2 relationship, the opposite was observed, with more correlations appearing on smaller pitches (TD: 2:2, 100 m2/pl, r = 0.581, p = 0.018; 75 m2/pl, r = 0.747, p < 0.001). In the 1:1 relationship, correlations with VO2max, total distance, and speed were observed only on the larger pitch. In conclusion, the aerobic capacity of young football players can influence running performance indicators in SSGs. Therefore, aerobic capacity could serve as a criterion for team composition, making SSGs more competitive. Additionally, the variation in correlations in the 2:2 relationship and their limited presence in the 1:1 relationship may be attributed to technical-tactical factors, such as increased ball contacts and one-on-one situations typically occurring in smaller setups.

Non-destructive experimental technique to determine ball contact load in rolling machine elements

Rolling machine elements, such as ball bearings, ball screws, or guiding systems are commonly used in diverse industrial applications. These components typically assume uniform load distribution among the balls or rely on analytical expressions. However, experimental load distribution measurement remains a challenge. This research work proposes a non-destructive experimental technique designed to determine ball contact load. The method uses painted surfaces to visualize the contact area under each rolling element, combined with an analytical formulation that modifies Hertz’s original contact equations to account for the influence of the painted layer thickness. Analytical results are compared with experimental tests on flat and curved surfaces. The results show a good agreement between the proposed painted surface formulation and measured contact areas.

No evidence that visual exploratory activity distinguishes the super elite from elite football players

ABSTRACT Visual exploratory activities (VEA) refer to head and body movements that football players make prior to receiving the ball to search possibilities for action. VEA is considered a key performance indicator that differentiates the skill level of players. This study revisited whether VEA also distinguishes super elite, award winning players from their elite teammates without awards. To this end, video footage from the men’s UEFA Champions League season 2018–2019 featuring the super elite players (n = 18) and the elite players (n = 18) was analyzed. To reduce the potential differences in match dynamics as much as possible, the selected players in the two groups were of the same team, playing the same match, in the same positioning line. VEA (i.e. frequency per unit time) during the penultimate and final pass prior to ball reception and performance (i.e. percentages of adequate ball contacts and subsequent actions) were compared between the two groups of players using ANOVA and Mann-Whitney tests, respectively. In addition, hierarchical stepwise regression analyses were conducted to explore the degree to which VEA was predicted by group and subsequent performance. The results showed that the players had higher VEA during the final pass (M = 0.45) than the penultimate pass (M = 0.41). There were no significant differences in VEA or performance between the two groups. Also, the regression analyses did not deliver significant models. We conclude that with partial control for match dynamics, no evidence emerged to support that VEA distinguishes super elite players from elite football players.

Analysis of Time Loss Injury in Korean Professional Baseball Players

PURPOSE: This prospective cohort study aimed to investigate the epidemiology of time-loss (TL) injuries in 68 Korean Baseball Organization (KBO) players aged 26.6±5.4 years (31 pitchers and 37 field players).METHODS: Injury data collected during the 2021-2022 KBO league seasons were used to calculate the injury rate (IR), IR ratio (IRR), and TL. IR was calculated as follows: (total number of injuries×100)÷(total number of game exposures). IRR was computed as follows: (IR of pitchers)÷(IR of fielders). TL was defined as an injury that resulted in the inability to compete or participate in standard routines.RESULTS: A total of 92 TL injuries were recorded from 5,320 athlete-exposures (1.7 per 100 athlete-exposures). Pitchers exhibited a 1.7-fold increase in IR (IRR =1.69, 95% CI=1.05-2.61, &lt;i&gt;p&lt;/i&gt;=.018) and a 2.6-fold increase in the rate of severe injuries that resulted in a TL of ≥3 weeks (IRR=2.59, 95% CI=0.93-7.10, &lt;i&gt;p&lt;/i&gt;=.045) compared to field players. The trunk/spine (20.6%) among pitchers and thigh/groin (22.4%) among field players were the most frequently injured body parts. Overuse (38.2%) and batted ball contact (38.2%) were the leading causes of injury among pitchers, whereas noncontact (36.2%) and overuse (17.2%) were the leading causes of injury among field players. Pitchers were most likely to be injured while pitching (55.9%) and fielding (38.2%), whereas field players were most likely to be injured while batting (31.0%) and base running (31.0%).CONCLUSIONS: The current findings indicate that the characteristics of the injuries of KBO players differ by position, emphasizing the importance of a position-specific injury prevention program.

Effect of changes in the net height, court size, and serve limitations on technical-tactical, physical, and psychological aspects of U-14 female volleyball matches.

The objective was to analyze the effect of a reduction of the net height and the court size and serve limitations on the technical-tactical actions, physical actions, and psychological aspects in youth volleyball players. The sample was 29 under-14 female volleyball players (three regional club teams). A quasi-experimental design was implemented to assess the effect of modification in three tournaments. The independent variables were: a) official rules tournament (no changes in the rules), b) Experimental Tournament 1 (reduction in the net height from 2.10 m to 2 m, no jump serves, and a maximum of two serves per player and rotation), and c) Experimental Tournament 2 (reduction in net height from 2.10 m to 2 m, reduction in court size from 9 × 9 m to 8 × 8 m, no jump serves, and a maximum of two serves per player and rotation). The dependent variables were: ball contact done (type), quality and efficacy of the technical actions, team game phases occurrence, quality and efficacy, continuity index, number of jumps, player's jump load in the take-off and landing, number of hits, average heart rate, Rate of Perceived Effort, time between ball contacts, serve velocity, perceived individual and collective self-efficacy, perceived enjoyment, and perceived satisfaction. Experimental Tournament 1 involved an increase in the efficacy of serves and a decrease in the efficacy of side-out phases. The imbalance between serve and reception did not impact game continuity but reduced the attack and blocks. Experimental Tournament 2 involved a decrease in the efficacy of serves and an increase in the efficacy of side-out phases. The balance between serve and reception increased reception efficacy, the occurrence of attacks and blocks, game continuity, and players' effort. players' effort. Scaling the net and court and adapting the serve rules (Experimental Tournament 2) resulted in game dynamics for these U-12 teams that were more similar to those of posterior stages of player through the balance between serve and reception and the adaptation of the net height and court size.