scholarly journals Statistical Analysis of Table-Tennis Ball Trajectories

2018 ◽  
Vol 8 (12) ◽  
pp. 2595
Author(s):  
Ralf Schneider ◽  
Lars Lewerentz ◽  
Karl Lüskow ◽  
Marc Marschall ◽  
Stefan Kemnitz
Keyword(s):  
Statistical Analysis ◽  
Graphics Processing Units ◽  
Initial Conditions ◽  
Statistical Significance ◽  
Equations Of Motion ◽  
Distribution Functions ◽  
Tennis Ball ◽  
Table Tennis ◽  
Ball Size ◽  
The Impact

In this work, the equations of motion for table-tennis balls were numerically solved on graphics processing units (GPUs) using Compute Unified Device Architecture (CUDA) for systematical statistical studies of the impact of ball size and weight, as well as of net height, on the distribution functions of successful strokes. Half a billion different initial conditions involving hitting location, initial spin, and velocities were analyzed to reach sufficient statistical significance for the different cases. In this paper, an advanced statistical analysis of the database generated by the simulation is presented.

scholarly journals Table Tennis Ball Impacting Racket Polymeric Coatings: Experiments and Modeling of Key Performance Metrics

2019 ◽  
Vol 9 (1) ◽  
pp. 158 ◽  
Author(s):  
Renaud G. Rinaldi ◽  
Lionel Manin ◽  
Sébastien Moineau ◽  
Nicolas Havard
Keyword(s):  
Performance Metrics ◽  
Incident Angle ◽  
Mechanical Analysis ◽  
Tennis Ball ◽  
Table Tennis ◽  
Polymeric Coatings ◽  
Compression Tests ◽  
Compliant Behavior ◽  
The Impact

The performance of a table tennis racket is often associated with subjective or quantitative criteria such as the adhesion, the control and the speed. Overall, the so-called performance aims at characterizing the impact with the ball. Ultimately, the polymeric layers glued onto the wooden blade play a key role, as evidenced in a previous work where the normal linear (no spin) impact of a ball onto polymeric layers was experimentally and numerically investigated. In this work, more realistic loading conditions leading to varying the incident angle and spin of the ball, were explored. While the sole linear restitution coefficient was determined in the anterior normal impact study, new physical metrics were identified to describe fully the trajectory of the reflected ball after impact. A companion 3D finite elements model was developed where the polymeric time-dependent dissipative compliant behavior measured with dynamic mechanical analysis and compression tests was accounted for. The confrontations with the experimental data highlighted the key role of the polymer intrinsic properties along with the friction coefficient between the ball and the polymer external layer.

Modeling Impacts Between a Continuous System and a Rigid Obstacle Using Coefficient of Restitution

2009 ◽  
Vol 77 (2) ◽  
Author(s):  
Chandrika P. Vyasarayani ◽  
John McPhee ◽  
Stephen Birkett
Keyword(s):  
Initial Conditions ◽  
Equations Of Motion ◽  
Continuous System ◽  
Coefficient Of Restitution ◽  
Continuous Systems ◽  
Rigid Obstacle ◽  
Unit Impulse ◽  
Before And After ◽  
System Equations ◽  
The Impact

In this work, we discuss the limitations of the existing collocation-based coefficient of restitution method for simulating impacts in continuous systems. We propose a new method for modeling the impact dynamics of continuous systems based on the unit impulse response. The developed method allows one to relate modal velocity initial conditions before and after impact without requiring the integration of the system equations of motion during impact. The proposed method has been used to model the impact of a pinned-pinned beam with a rigid obstacle. Numerical simulations are presented to illustrate the inability of the collocation-based coefficient of restitution method to predict an accurate and energy-consistent response. We also compare the results obtained by unit impulse-based coefficient of restitution method with a penalty approach.

Decadal predictability in the North Atlantic as seen by EC-Earth3.

2021 ◽  
Author(s):  
Bo Christiansen ◽  
Shuting Yang ◽  
Dominic Matte
Keyword(s):  
North Atlantic ◽  
Lead Time ◽  
Initial Conditions ◽  
Statistical Significance ◽  
Lead Times ◽  
The North ◽  
Weak Evidence ◽  
The North Atlantic ◽  
The Impact ◽  
Decadal Predictability

<p>We study the decadal predictability in the North Atlantic region using  ensembles of historical and decadal prediction experiments with EC-Earth3  and other CMIP models. In particular, the focus is on the NAO and the sub-polar gyre region. In general the impact of initialization is weak  for lead-times larger than one to two years and we investigate different ways to isolate and estimate the statistical significance of this impact. For the sub-polar gyre region the prediction skill is found to be mainly due to an abrupt change in the late 90ies and models disagree on whether this skill is due to forcing or initial conditions. Also the predictability of the NAO is weak and varies with lead-time and length of the predicted period. We only see weak evidence of the 'signal-to-noise paradox'. The importance of the ensemble size is also studied.                                                              </p>

Modeling of Impact Dynamics of a Tennis Ball With a Flat Surface

2005 ◽  
Author(s):  
Syed Muhammad Mohsin Jafri ◽  
John M. Vance
Keyword(s):  
Flat Surface ◽  
Equations Of Motion ◽  
Contact Forces ◽  
Rolling Contact ◽  
Tennis Ball ◽  
Computationally Efficient ◽  
Mass Model ◽  
Experimental Findings ◽  
Tennis Balls ◽  
The Impact

A model of impact of a tennis ball with a flat surface is developed based on a planar, two-mass, linear, four degree of freedom vibration system idealization. The impact is assumed to be incident on a flat surface with friction. The incident parameters of the ball include the centre of mass translational velocity, angle of impact with the surface and the incident angular spin of the ball. The linear, piecemeal vibration model predicts the corresponding rebound parameters of the tennis ball. The model also predicts the duration of contact of the tennis ball with the flat surface, the transition of motion of the tennis ball during contact with the ground from sliding to rolling contact, and the resulting contact forces developed between the tennis ball and the flat surface. The model is computationally efficient because the governing differential equations of motion are linear and their standard solutions can be easily implemented on a personal computer. Predictions of the rebound parameters from the model are compared with experimental findings on tennis balls which are incident on a flat surface with various angles, velocities and angular spins (zero spin, topspin and backspin). For selected parameters of the two-mass model, the comparisons show excellent agreement between the model and the measurements.

scholarly journals Identifying Vehicle and Collision Impact by Applying the Principle of Conservation of Mechanical Energy

2019 ◽  
Vol 20 (3) ◽  
pp. 191-204
Author(s):  
Stanimir Karapetkov ◽  
Lubomir Dimitrov ◽  
Hristo Uzunov ◽  
Silvia Dechkova
Keyword(s):  
Mathematical Modelling ◽  
Initial Conditions ◽  
Mechanical Energy ◽  
Equations Of Motion ◽  
Standard Test ◽  
Linear Displacement ◽  
Road Accident ◽  
Impact Testing ◽  
Test Method ◽  
The Impact

Abstract Various methodologies and tools applied to identification of vehicle and collision impact seek to present more and more accurate solutions to reproduce, restore, recreate and investigate the casualty. Modern computer technology and software provide the tools to solve specific problems developing mathematical modelling of complex mechanical systems involving vehicles and other objects in a road accident. Scientists generally utilize the Standard Test Method for Impact Testing calculating the energy of deformation of both vehicles, however, one of its limitations is the evaluation of the kinetic energy of the vehicles in post-collision taking into consideration vehicle rotation and linear displacement. To improve the analysis, dynamic traffic simulation is used, taking into account the variations in the coefficient of friction, suspension elasticity and damping. The proposed method is based on a system of two equations derived from two principles: the Principle of Conservation of Mechanical Energy and the Principle of Conservation of Momentum in the impact phase. The new approach is conducted on mathematical modelling and computer simulation of vehicle motion after the impact, wherefrom the linear and angular velocities are analysed. This is achieved by the numerical solution of the differential equations of motion of the cars after the impact, and the given initial conditions that satisfy the solution are used to solve the system of equations. The main findings of the study can be grouped as follows: 1) The positions of the vehicles prior to the moment of first impact and the post-impact orientation of velocity vectors are more precise. 2) The variability of the tire-road friction coefficient is taken into consideration. 3) The value of coefficient of restitution according to Newton’s theory of impact is unnecessarily determined.

scholarly journals COVID-19: a study about the impact of coronavirus on physicians of La Plata, Argentina

2021 ◽  
Author(s):  
Maria Virginia Croce ◽  
Elsa Chiappa ◽  
Adriana Moiso ◽  
Martin Enrique Rabassa
Keyword(s):  
Statistical Analysis ◽  
Statistical Significance ◽  
Well Being ◽  
Cross Sectional Study ◽  
Capital City ◽  
Categorical Variables ◽  
Buenos Aires Province ◽  
Cross Sectional ◽  
La Plata ◽  
The Impact

Background: In Argentina, the burden of COVID-19 on health systems and physicians was substantial with difficulties on daily triage decisions which have to be made in the context of grave shortages of basic equipment and consumables. Purpose: this study was performed to understand what physicians were experiencing during the COVID-19 pandemic in La Plata (capital city of Buenos Aires province, Argentina). Methods: A cross-sectional study was performed; a questionnaire was sent by e-mail to physicians who work in this city during November 2020. The questionnaire was made based on Medscape US and International Physicians COVID-19 Experience Report: Risk, Burnout, Loneliness. Statistical analysis: test for normality was performed employing the Kolmogorov-Smirnov test while Chi-square test of independence to examine the relationship between sex and workplace with nominal variables. For categorical variables, Kendall tau correlation was performed to test for independence. ANOVA was developed to examine differences between physician age. Statistical significance was set to p < 0.05 in all cases. All statistical analysis was done employing SPSS Statistics, Version 24 (IBM, USA). Results: 203 physicians answered the questionnaire; the majority of physicians (96%) considered stressful their experience during pandemic and reported distress episodes being for more than 60% the most stressful of their practices, 30% presented depression and were medically treated, while 32.7% felt loneliness with 4 physicians with suicidal thoughts. Conclusion: The results highlight the need to protect the psychological well-being of the healthcare community, and to invest resources to significantly promote the mental health of professionals.

scholarly journals Hemoptysis from Complex Pulmonary Aspergilloma Treated by Cavernostomy and Thoracoplasty

2019 ◽  
Author(s):  
Nguyen Truong Giang ◽  
Nguyen Tien Dung ◽  
Nguyen Thanh Hien ◽  
Truong Thanh Thiet ◽  
Phan Sy Hiep ◽  
...  
Keyword(s):  
High Risk ◽  
Statistical Significance ◽  
Tissue Expander ◽  
Tennis Ball ◽  
Table Tennis ◽  
High Risk Patients ◽  
Co Morbidity ◽  
Risk Patients ◽  
Pulmonary Aspergilloma

Abstract Background In high-risk patients with complex pulmonary aspergilloma but unable for lung resection, cavernostomy and thoracoplasty could be performed. This study aimed to evaluate this surgery compared two material used (table tennis ball and tissue expander) as a filler. Methods: The prospective study evaluated 63 in high-risk patients who had hemoptysis due to complex pulmonary aspergilloma that submitted to cavernostomy and thoracoplasty surgery from November 2011 to September 2018. Patients were allocated to the table tennis ball group (46 patients) and tissue expander group (17 patients). We evaluated at the time of before operation, six months and 24 months after operation. Results The most common comorbidity diseases were tuberculosis in two groups. Upper lobe occupied almost location. Hemoptysis symptoms plunged from time to time. Statistically significant Karnofsky score was observed in both groups. BMI showed slightly increasing but not statistically significant. Postoperative pulmonary functions (FVC and FEV1) have remained in both groups at all time points. The remarkable results were no death in the postoperative period, and long-term complication of surgery was low. There was no statistical significance between two groups in operative time, blood loss during operation, ICU length-stay time. Four patients died because of co-morbidity in 24 months follow-up. Conclusion: Cavernostomy and thoracoplasty was safe and effective surgery for the treatment of high-risk patients with complex pulmonary aspergilloma. There was no mortality related to surgery. The postoperative complications and long-term complication were low. The was no inferiority when compared table tennis ball group and tissue expander group. Keyword: Complex Pulmonary Aspergilloma (CPA), Hemoptysis, Cavernostomy, Thoracoplasty, Table Tennis Balls, Tissue expander,

scholarly journals Impact of Soil Moisture Assimilation on Land Surface Model Spinup and Coupled Land–Atmosphere Prediction

2016 ◽  
Vol 17 (2) ◽  
pp. 517-540 ◽  
Author(s):  
Joseph A. Santanello ◽  
Sujay V. Kumar ◽  
Christa D. Peters-Lidard ◽  
Patricia M. Lawston
Keyword(s):  
Soil Moisture ◽  
Land Surface ◽  
Initial Conditions ◽  
Weather Prediction ◽  
Wrf Model ◽  
Distribution Functions ◽  
Cumulative Distribution ◽  
Satellite Monitoring ◽  
Surface Model ◽  
The Impact

Abstract Advances in satellite monitoring of the terrestrial water cycle have led to a concerted effort to assimilate soil moisture observations from various platforms into offline land surface models (LSMs). One principal but still open question is that of the ability of land data assimilation (LDA) to improve LSM initial conditions for coupled short-term weather prediction. In this study, the impact of assimilating Advanced Microwave Scanning Radiometer for EOS (AMSR-E) soil moisture retrievals on coupled WRF Model forecasts is examined during the summers of dry (2006) and wet (2007) surface conditions in the southern Great Plains. LDA is carried out using NASA’s Land Information System (LIS) and the Noah LSM through an ensemble Kalman filter (EnKF) approach. The impacts of LDA on the 1) soil moisture and soil temperature initial conditions for WRF, 2) land–atmosphere coupling characteristics, and 3) ambient weather of the coupled LIS–WRF simulations are then assessed. Results show that impacts of soil moisture LDA during the spinup can significantly modify LSM states and fluxes, depending on regime and season. Results also indicate that the use of seasonal cumulative distribution functions (CDFs) is more advantageous compared to the traditional annual CDF bias correction strategies. LDA performs consistently regardless of atmospheric forcing applied, with greater improvements seen when using coarser, global forcing products. Downstream impacts on coupled simulations vary according to the strength of the LDA impact at the initialization, where significant modifications to the soil moisture flux–PBL–ambient weather process chain are observed. Overall, this study demonstrates potential for future, higher-resolution soil moisture assimilation applications in weather and climate research.

scholarly journals Effect of Changing Table Tennis Ball Material from Celluloid to Plastic on the Post-Collision Ball Trajectory

2017 ◽  
Vol 55 (1) ◽  
pp. 29-38 ◽  
Author(s):  
Yuki Inaba ◽  
Sho Tamaki ◽  
Haruhiko Ikebukuro ◽  
Koshi Yamada ◽  
Hiroki Ozaki ◽  
...  
Keyword(s):  
High Speed ◽  
Initial Conditions ◽  
Contact Point ◽  
Equation Of Motion ◽  
Tennis Ball ◽  
Table Tennis ◽  
Plastic Ball ◽  
Before And After ◽  
Ball Trajectory ◽  
Tennis Balls

AbstractThe official material used in table tennis balls was changed from celluloid to plastic, a material free of celluloid, in 2014. The purpose of this study was to understand the differences and similarities in the two types of ball materials by comparing their behavior upon collision with a table. The behavior of the balls before and after collision with a table, at various initial speeds ranging from 15 to 115 km/h, was captured using high-speed cameras. Velocities and spin rates before collision and velocities after collision were computed to calculate the coefficients of restitution and friction. Based on the computed variables, the post-collision trajectories of both balls were calculated by integrating the equation of motion of the ball for simulated service, smash and drive conditions with respect to time. The coefficients of restitution were higher for the plastic balls than the celluloid ones when the initial vertical velocities were higher. The coefficients of friction were higher for plastic balls when the initial horizontal contact point velocities were slower. Because of the differences in the material characteristics, the plastic ball trajectories of services with backspin and drives with great topspin were expected to be different from those of celluloid balls. Since the extent of differences between the two ball types varied depending on the initial conditions, testing at various initial conditions was suggested for comparing and understanding the characteristics of the balls.

Differential Formulation for the Coefficient of Restitution of a Rigid Link

2015 ◽  
Vol 762 ◽  
pp. 175-182 ◽  
Author(s):  
Dorian Cojocaru ◽  
Dan B. Marghitu
Keyword(s):  
Mobile Robots ◽  
Initial Conditions ◽  
Equations Of Motion ◽  
Coefficient Of Restitution ◽  
Numerical Techniques ◽  
Differential Impact ◽  
Differential Formulation ◽  
Nonlinear Contact ◽  
Nonlinear Equations Of Motion ◽  
The Impact

The differential impact equations of motion are developed using an nonlinear contact force. The nonlinear equations of motion are written using symbolical MATLAB and are solved using numerical techniques. The impact equations are based on the Kogut-Etsion model. The numerical results are obtained for different geometries of the link, different coefficients of friction, and different initial conditions. The coefficient of restitution (COR) is discussed for specific cases. The results can be used for the impact of mobile robots with different type of surfaces.

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