The effect of natural preferences on serving biomechanics: a new approach to the motor skills of tennis players

Research has demonstrated the existence of two 'natural preference' profiles in running. The objective of this study was to determine the influence of the natural preferences of ground (with a "posterior and flexion" movement) and air (with an "anterior and extension" movement) on the ball speed and impact position during the service of 19 professional players. The results allow to propose a new reading grid of the service technique to consider the preferential motricity of each player while respecting the biomechanical principles

Numerical Analysis on Erosion and Optimization of a Blast Furnace Main Trough

The main trough of a blast furnace (BF) is a main passage for hot metal and molten slag transportation from the taphole to the torpedo and the slag handling. Its appropriate working status and controlled erosion ensure a safe, stable, high-efficiency and low-cost continuous production of hot metal. In this work, the tapping process of a main trough of a BF in the east of China was numerically studied with the help of a CFD library written in C++, called OpenFOAM, based on the use of the Finite Volume Method (FVM). The results show that turbulence intensity downstream of the hot metal impact position becomes weaker and the turbulence area becomes larger in the main trough. During the tapping, thermal stress of wall refractory reaches the maximum value of 1.7 × 107 Pa at the 4 m position in the main trough. Furthermore, baffles in the main trough placed between 5.8 m and 6.2 m were found to control and reduce the impact of the turbulence on the refractory life. The metal flowrate upstream of the baffles can be decreased by 6%, and the flow velocity on the upper sidewall and bottom wall decrease by 9% and 7%, respectively, compared with the base model. By using baffles, the minimum fatigue life of the refractory in the main trough increases by 15 tappings compared with the base model, so the period between the maintenance stops can be prolonged by about 2 days.

Drone Ground Impact Footprints with Importance Sampling: Estimation and Sensitivity Analysis

This paper addresses the estimation of accurate extreme ground impact footprints and probabilistic maps due to a total loss of control of fixed-wing unmanned aerial vehicles after a main engine failure. In this paper, we focus on the ground impact footprints that contains 95%, 99% and 99.9% of the drone impacts. These regions are defined here with density minimum volume sets and may be estimated by Monte Carlo methods. As Monte Carlo approaches lead to an underestimation of extreme ground impact footprints, we consider in this article multiple importance sampling to evaluate them. Then, we perform a reliability oriented sensitivity analysis, to estimate the most influential uncertain parameters on the ground impact position. We show the results of these estimations on a realistic drone flight scenario.

Experiment and Simulation of Erosion Mechanism and Deformation Characteristics in Al6061-T6 beam due to Rhomboid Particle Impacts

The erosion mechanism and deformation characteristics of rhomboid-shaped particle impacting metal beam are studied. Physical experiments of rhomboid-shaped particle impacting cantilever beam and fixed-fixed beam are carried out respectively. The erosion behavior of particles and deformation characteristics of beam are captured by high-speed imaging system. Meanwhile, the numerical models of rhomboid-shaped particle impacting beam, based on FEM-SPH coupled method, are established. The effects of the geometrical parameters of the beam, the incident conditions of particle and the impact position on the elastic-plastic deformation of beam and rebound behavior of particles are further analyzed. The results show: (1) The width of cantilever beam affects its maximum deflection and deformation; (2) The threshold value of breakdown velocity is controlled by the substrate size; (3) The increment of internal energy is basically independent of the impact position; (4) The deflection value at impact position of beam is maximized under the critical impact condition.

Meshing Contact Impact Properties of Circular Arc Tooth Trace Cylindrical Gear Based on Rotating Knife Dish Milling Process

Taking the circular arc tooth trace (CATT) cylindrical gear as a research object, in order to obtain the CATT cylindrical gear’s meshing contact impact properties, the meshing contact impact hypothesis of the CATT cylindrical gear was put forward based on the contact dynamics theory and gear transmission physical model, and the gear mesh contact impact model was set up further. The finite element solution algorithm for solving the impact problem was given. Then, the accurate 3D model was set up based on the gear tooth surface equation, and the finite element analysis models of the meshing contact impact with different impact positions were established further. The model was to study the distribution rule of the gear surface meshing contact impact stress and relationship between the impact velocity, impact position, and the impact stress. Moreover, the reason for the maximum impact stresses distribution rule of primary and secondary impact tooth surface was discussed. Research result shows the driven wheel dangerous areas of gear root impact are the gear top of the primary impact tooth surface and the gear root of the secondary impact tooth surface; the driven wheel dangerous areas of gear top impact are the gear root of the primary impact tooth surface and gear top of the secondary impact tooth surface; the driven wheel dangerous areas of pitch circle are the gear root and pitch circle of secondary impact tooth surface; and impact velocity and impact position have a major influence on the impact stress. The study results provide a theoretical basis for the dynamic design and industrial application of CATT cylindrical gears.

Ball Impact Position in Recreational Male Padel Players: Implications for Training and Injury Management

Racket sports such as padel are characterized by the repetition of unilateral gestures, which can lead to negative adaptations like asymmetries or overuse musculoskeletal injuries. The purpose of this study was to determine the differences in ball impact positions (i.e., forward or backward of the center of gravity) in nine stroke types in a sample of forty-eight recreational male padel players. The sample included 14,478 shots corresponding to 18 matches from six tournaments. Forty-eight male padel players were classified into two groups according to their level: trained (n = 24) and novice (n = 24). Type of stroke and ball impact position were registered using a computerized motion tracking video system. The ball impact position was computed from the distance (cm) between the coordinates of the ball and the player’s center of gravity. Results show that trained players hit the ball in a more backward position (from 11 to 25 cm, compared to novice) in serve and offensive strokes (volleys, trays, and smashes) but used more forward strokes (from 7 to 32 cm, compared to novice) in defensive shots (groundstrokes, wall strokes, and lobs). Because the current differential variables are trainable and demonstrated to be of relevance for performance, the findings of this study may assist padel coaches in designing proper training plans to improve effectiveness and to prevent musculoskeletal injuries regarding the type of stroke and ball impact position. Such knowledge may constitute a very important factor affecting technique, biomechanics, and injury management in padel players of different competitive levels.

How HR needs to change to get to the big table

Purpose This paper provides an overview of the challenges that HR departments and TA practitioners are facing and provide actionable takeaways to address these issues and improve company practices. Design/methodology/approach The insights provided in this paper come from the author's 30 years of experience in the industry and references from companies in the USA and India that have met with the author to shared their issues when recruiting quality candidates. Findings HR is bound to move from a tactical and complacent role to a high impact position. The HR and TA teams that have a deep understanding of complex people’s behavior and aspirations will get to the pilot seat in the industry, and their development will be nothing short of smooth. Originality/value This piece compiles 30 years of talent management insights collected from some of the biggest companies in India to give a cohesive idea of the aspects that need changed to ensure the quality of recruitment and satisfaction of employees.

Identification of Axial and Radial Impacts for Pneumatic Artificial Muscles in Static and Dynamic Processes Based on Autocorrelations of Differential Pressure Signals

Since the pneumatic artificial muscle is usually employed to actuate the robot, it is inevitable that it will collide with obstacles and/or other objects such that there will be impacts. The typical impacts include the axial and radial ones. This paper detects these two kinds of impact by a designed differential pressure measurement system, and achieves the goal of identifying them by the autocorrelations of their differential pressure signals in both static and dynamic processes, which are the two main work processes of the pneumatic artificial muscle. In detail, first we design an experiment scheme by connecting the pneumatic artificial muscle to the differential pressure sensor through two pressure tubes; then the axial and radial impact signals are acquired via the impact experiments under different work conditions (impact strength, internal pressure, load, and impact position); finally, the identification of the axial and radial impact signals are achieved based on the autocorrelation technique with a well-selected threshold. The experiments illustrate the effectiveness of the whole method.