Stroke Velocity Research Articles

SIMULATION OF HOT STAMPING OF THE FORGED PIECE MADE OF AK6 ALUMINUM ALLOY

The possibility of modeling the actual production process of hot bulk forging of the forged piece made of AK6 aluminum alloy is investigated using the DEFORM-3D computer program. Parameters corresponding to production conditions of this process were introduced: die heating temperature of 350 °C, billet heating temperature of 360–470 °C, die working stroke velocity of 5 mm/s, and friction factor (by Siebel) of 0,5. It is shown that computer modeling in the DEFORM-3D program allows us to analyze the actual processes of hot bulk forging of aluminum alloys and introduce recommendations on their correction.

Role of Trailing-Edge Vortices on the Hawkmothlike Flapping Wing

A time-course force measurement and time-resolved particle image velocimetry study were conducted to investigate the unsteady characteristics of an insect wing. In most cases, the tendencies of the aerodynamic forces in the stroke phase were extremely similar to the stroke velocity profiles, which indicated the appositeness of the steady aerodynamic model. The time-course forces showed that the wing–wake interaction appeared in temporally and spatially restricted sections right after the stroke reversal. The time-resolved particle image velocimetry taken near the stroke reversal demonstrated the vortex-dominated flowfields including the leading-edge vortex and the trailing-edge vortices. This was in contrast to the middle of the stroke, which only had a stable leading-edge vortex. The results showed that the unsteadiness was highly associated with the trailing-edge vortex structures. In particular, the wing–wake interaction were substantially influenced by the behavior of the number 2 trailing-edge vortex, which became the element of the counter-rotating vortex pair. The leading-edge vortex of the next stroke was rarely connected to such unsteadiness. This finding implies that the wing kinematics that determines the characteristics of the trailing-edge vortices were the key to the unsteadiness and the wing–wake interaction on the flapping wing.

Characterization of fine motor development: Dynamic analysis of children’s drawing movements

In this study, we investigated children’s fine motor development by analyzing drawing trajectories, kinematics and kinetics. Straight lines drawing task and circles drawing task were performed by using a force sensitive tablet. Forty right-handed and Chinese mother-tongue students aged 6–12, attending classes from grade 1 to 5, were engaged in the experiment. Three spatial parameters, namely cumulative trace length, vector length of straight line and vertical diameter of circle were determined. Drawing duration, mean drawing velocity, and number of peaks in stroke velocity profile (NPV) were derived as kinematic parameters. Besides mean normal force, two kinetic indices were proposed: normalized force angle regulation (NFR) and variation of fine motor control (VFC) for circles drawing task. The maturation and automation of fine motor ability were reflected by increased drawing velocity, reduced drawing duration, NPV and NFR, with decreased VFC in circles drawing task. Grade and task main effects as well as significant correlations between age and parameters suggest that factors such as schooling, age and task should be considered in the assessment of fine motor skills. Compared with kinematic parameters, findings of NFR and VFC revealed that kinetics is another important perspective in the analysis of fine motor movement.

On the Lightning Electromagnetic Fields due to Channel with Variable Return Stroke Velocity

Numerical field expressions are proposed to evaluate the electromagnetic fields due to the lightning channel with variable values of return stroke velocity. Previous calculation methods generally use an average value for the return stroke velocity along a lightning channel. The proposed method can support different velocity profiles along a lightning channel in addition to the widely used channel-base current functions and also the general form of the engineering current models directly in the time domain without the need to apply any extra conversions. Moreover, a sample of the measured lightning current is used to validate the proposed method while the velocity profile is simulated by the general velocity function. The simulated fields based on constant and variable values of velocity are compared to the corresponding measured fields. The results show that the simulated fields based on the proposed method are in good agreement with the corresponding measured fields.

Investigating Forward Velocity and Symmetry in Freestyle Swimming Using Inertial Sensors.

Investigating the performance of an athlete and monitoring them is important to athletes and coaches because it can provide information about the training progress and injury recovery. Coaches are not always on side when athletes doing their training, so a device which is small and easy to use will increase the monitored training sessions significantly and allow the athlete to compare multiple training sessions. This technology has seen rapid development over the last years and is now available in very small sizes which have little effect on the swimmer. Using this kind of sensor, kinematics can be measured and extracted for stroke characteristics investigations. This research used an sacrum mounted self-developed inertial sensor, providing a triaxial accelerometer, gyroscope and RF capability in a waterproof casing to investigate the arm symmetry and swimming velocity in freestyle swimming. The recorded data were filtered using a high-pass Hamming windowed FIR filter to remove the gravity components from the wanted signal. The acceleration signal was then processed to find the velocity of the swimmer. A zero-crossing detection algorithm was used to investigate the arm symmetry and to find the individual stroke rates (SR), the differences between left and right arm stroke durations and the left and right arm stroke velocities (asymmetry). The investigation of the left and right arm velocity patterns of each individual swimmer allowed the investigation of each swimmers asymmetry in propulsion and velocity for the individual arms. The results of the mean lap velocities showed that the two different methods agree with an R2 of 0.92. Furthermore a conducted Bland-Altman analysis showed a low bias of -0.04 with an upper limit of agreement of 0.03 and a lower limit of agreement of -0.11.

The effects of "grunting" on serve and forehand velocities in collegiate tennis players.

The aim of this study was to examine the effects of grunting on velocity and force production during dynamic and static tennis strokes in collegiate tennis players. Thirty-two (16 male and 16 female) division II and III collegiate tennis athletes with a mean age of 20.2 ± 1.89 years participated as subjects. Demographic and survey data were obtained before subjects completed a 10- to 15-minute warm-up of serves and ground strokes while grunting and not grunting. The subjects performed randomized sets (3 grunting and 3 nongrunting trials) of serves and forehand strokes both dynamically and isometrically. Stroke velocities and isometric forces were measured with a calibrated radar gun and calibrated dynamometer, respectively. Electromyographic (EMG) data from subjects' dominant pectoralis major and contralateral external oblique muscles were recorded and averaged for data analysis. A repeated measures multivariate analysis of variance (RM-MANOVA) compared dynamic stroke velocity, isometric muscle force, and peak EMG activity during each breathing condition at the 0.05 alpha level. The RM-MANOVA indicated that dynamic velocity and isometric force of both serves and forehand strokes were significantly greater when the subjects grunted (F = 46.572, p < 0.001, power = 1.00). Peak muscle activity in the external oblique and pectoralis major muscles was also greater when grunting during both types of strokes (F = 3.867, p = 0.05, power = 0.950). Grunt history, gender, perceived advantages, and disadvantages of grunting, years of experience, highest level of competition, and order of testing did not significantly alter any of these results. The velocity, force, and peak muscle activity during tennis serves and forehand strokes are significantly enhanced when athletes are allowed to grunt.

Dynamic characteristics of signatures: effects of writer style on genuine and simulated signatures.

The aims of this study were to determine if computer-measured dynamic features (duration, size, velocity, jerk, and pen pressure) differ between genuine and simulated signatures. Sixty subjects (3 equal groups of 3 signature styles) each provided 10 naturally written (genuine) signatures. Each of these subjects then provided 15 simulations of each of three model signatures. The genuine (N = 600) and simulated (N = 2700) signatures were collected using a digitizing tablet. MovAlyzeR(®) software was used to estimate kinematic parameters for each pen stroke. Stroke duration, velocity, and pen pressure were found to discriminate between genuine and simulated signatures regardless of the simulator's own style of signature or the style of signature being simulated. However, there was a significant interaction between style and condition for size and jerk (a measure of smoothness). The results of this study, based on quantitative analysis and dynamic handwriting features, indicate that the style of the simulator's own signature and the style of signature being simulated can impact the characteristics of handwriting movements for simulations. Writer style characteristics might therefore need to be taken into consideration as potentially significant when evaluating signature features with a view to forming opinions regarding authenticity.

Optimization approach for synthesis of 5 point double toggle mechanism

This paper deals with double toggle mechanism used for exerting clamping force between movable and fixed dies of a die casting machine. Loop closure method has been adopted to determine the displacement of the movable plate. In addition to stroke ratio, velocity ratio and mechanical advantage, this paper also investigates the effect of link lengths on the dwell period, a very important manufacturing parameter. The problem of momentary opening of the dies during the clamping period has also been eliminated in an interactive way, else there would be molten metal leakage and would give rise to distorted products. The link lengths of the toggle mechanism are optimized corresponding to the customer specifications of the piston stroke and movable platen stroke using genetic algorithm in an interactive way.

Assessment and analysis of indirect lightning performance of overhead lines

This paper presents an efficient method for the assessment of the indirect lightning performance of overhead power lines and analyses the influence of some relevant parameters on the flashover rate. The method is based on a formula to calculate the peak value of lightning-induced voltages in overhead lines over a lossy ground, which considers the front-time of the channel-base current. The results of the method are validated by comparison with results available in the literature. The method is then used to investigate the effect of subsequent strokes on the line flashover rate, leading to the conclusion that their contribution is negligible, as long as no correlation is assumed between front-time and peak value of the strokes (first and subsequent). In the following, the method is used to analyze the influence of some parameters on the lightning performance of overhead lines. The results show that the stroke current front-time influence decreases as the soil resistivity increases, and that a higher front-time leads to a lower flashover rate. It is shown that the use of a fixed front-time T=5.63μs for the first strokes leads to results that match well the results obtained from Cigré’s front-time probabilistic distribution. Regarding the return stroke velocity, the results show that, for soils with resistivity higher than 100Ωm, the flashover rate increases as the return stroke velocity increases. The results also show that a relative velocity vr=0.4 leads to flashover rates that match well the results obtained considering some correlations between return stroke velocity and peak current proposed in the literature. The influence of the correlation between current peak value and front-time for first strokes is also analyzed and it is shown that the correlation reduces the flashover rate. It is also shown that considering this correlation for first strokes and not for subsequent strokes increases the contribution of the latter to the flashover rate, especially for good conducting soils.

Effects of different swimming race constraints on turning movements

The aim of this study was to investigate the effects of different swimming race constraints on the evolution of turn parameters. One hundred and fifty-eight national and regional level 200-m (meters) male swimming performances were video-analyzed using the individualized-distance model in the Open Comunidad de Madrid tournament. Turn (p<.001, ES=0.36) and underwater distances (p<.001, ES=0.38) as well as turn velocity (p<.001, ES=0.69) significantly dropped throughout the race, although stroke velocity and underwater velocity were maintained in the last lap of the race (p>.05). Higher expertise swimmers obtained faster average velocities and longer distances in all the turn phases (p<.001, ES=0.59), except the approach distance. In addition, national level swimmers showed the ability to maintain most of the turn parameters throughout the race, which assisted them in improving average velocity at the end of races. Therefore, the variations in the turning movements of a swimming race were expertise-related and focused on optimizing average velocity. Turning skills should be included in the swimming race action plan.

An Approximate Formula for Estimating the Peak Value of Lightning-Induced Overvoltage Considering the Stratified Conducting Ground

In this paper, we present an improved and extended approximate formula for estimating the peak value of lightning-induced voltages in an overhead line, considering the horizontally stratified conducting ground. The approximate formula proposed in this paper is based on the return stroke transmission-line model (TL) and a trapezoidal lightning return stroke current waveform with the typical representative front time of 3.8 μs and the return stroke velocity of 120 m/ μs according to CIGRÉ and the IEEE Standard 1410 Guide. The extended approximate formula is validated by using the 2-D finite-different time-domain method and Agrawal field-line coupling model. The results show that the proposed approximate formula in this paper is simple and suitable for estimating the lightning-induced voltage peak value considering the horizontally stratified ground with satisfied accuracy.

Analysis of Residence Time Distributions of Different Solid Biomass Fuels by using Radio Frequency Identification (RFID)

AbstractThe residence time distributions of different typical solid biomass fuels such as wood pellets, wood chips, and wood cubes are measured on a scaled model of a forward‐acting grate in continuous operation by using radio frequency identification (RFID). A variation of motion patterns, grate operational conditions, and bed material is performed. Based on the residence time distributions, diffusion coefficients are derived, which are a measure for mixing on the grate and are of importance as input parameters of fuel–bed models in CFD simulations of grate‐firing systems. RFID measurements have the advantage to be capable of tracking multiple particles without requiring visual contact. Residence time distributions are obtained without any artifacts introduced by the feeding equipment or manual charging. It is found that the diffusion coefficients obtained are in agreement with the results of other measurements performed in literature. The diffusion coefficients increase with enhanced stroke length and stroke velocity as well as with decreasing bed layer thickness and particle sizes. Particle shape has a strong influence on longitudinal mixing and the diffusion coefficients.

Anaerobic Threshold Individualized Assessment in a Young Swimmer

The assessment of blood lactate concentrations is considered one essential procedure in physiological diagnosis of swimming performance. Our purpose was to assess the metabolic anaerobic threshold of an 11 year old swimmer through an individualized intermittent incremental protocol. Complementarily, stroking parameters were also determined. The subject performed a front crawl 5 x 200 m test, being the velocity controlled by an acoustic signal. The blood samples were collected from the ear lobe at rest and after each step. Stroke rate was registered by a chronofrequencemeter base 3, and stroke length and velocity were calculated at the end of each 200 m. The individual anaerobic threshold occurred at 1.2 mmol/l, rather lower than the traditionally used 4 mmol/l value suggested for trained swimmers. The velocity corresponding to anaerobic threshold was 1.06 m/s, representing a 5 s difference in a 100 m effort comparing to the velocity of 4 mmol/l. Stroke rate increased and stroke length decreased throughout the incremental protocol, i.e., with the velocity increments. It was concluded that the velocity corresponding to 4 mmol/l does not represent the individual anaerobic threshold in this young trained swimmer, and that he prefer to increase their velocity through the raise of stroke rate. Thus, given the importance of developing swimming technique in age-group swimmers, this swimmer should implement the lengthening of his stroke cycles in the training practice routines, trying to resist to the degradation of the stroke length when velocity increases.

Anatomy of F 1 -ATPase powered rotation

F1-ATPase, the catalytic complex of the ATP synthase, is a molecular motor that can consume ATP to drive rotation of the γ-subunit inside the ring of three αβ-subunit heterodimers in 120° power strokes. To elucidate the mechanism of ATPase-powered rotation, we determined the angular velocity as a function of rotational position from single-molecule data collected at 200,000 frames per second with unprecedented signal-to-noise. Power stroke rotation is more complex than previously understood. This paper reports the unexpected discovery that a series of angular accelerations and decelerations occur during the power stroke. The decreases in angular velocity that occurred with the lower-affinity substrate ITP, which could not be explained by an increase in substrate-binding dwells, provides direct evidence that rotation depends on substrate binding affinity. The presence of elevated ADP concentrations not only increased dwells at 35° from the catalytic dwell consistent with competitive product inhibition but also decreased the angular velocity from 85° to 120°, indicating that ADP can remain bound to the catalytic site where product release occurs for the duration of the power stroke. The angular velocity profile also supports a model in which rotation is powered by Van der Waals repulsive forces during the final 85° of rotation, consistent with a transition from F1 structures 2HLD1 and 1H8E (Protein Data Bank).

Kinematics of Signature Writing in Healthy Aging

Forensic document examiners (FDE) called upon to distinguish a genuine from a forged signature of an elderly person are often required to consider the question of age-related deterioration and whether the available exemplars reliably capture the natural effects of aging of the original writer. An understanding of the statistical relationship between advanced age and handwriting movements can reduce the uncertainty that may exist in an examiner's approach to questioned signatures formed by elderly writers. The primary purpose of this study was to systematically examine age-related changes in signature kinematics in healthy writers. Forty-two healthy subjects between the ages of 60-91 years participated in this study. Signatures were recorded using a digitizing tablet, and commercial software was used to examine the temporal and spatial stroke kinematics and pen pressure. Results indicated that vertical stroke duration and dysfluency increased with age, whereas vertical stroke amplitude and velocity decreased with age. Pen pressure decreased with age. We found that a linear model characterized the best-fit relationship between advanced age and handwriting movement parameters for signature formation. Male writers exhibited stronger age effects than female writers, especially for pen pressure and stroke dysfluency. The present study contributes to an understanding of how advanced age alters signature formation in otherwise healthy adults.

Fine finishing of internal surfaces using elastic abrasives

The paper describes a simple and innovative approach of using elastic abrasives for generating ultra fine finish on internal surfaces of tubular specimens. Elastic abrasive is a unique concept of using abrasive embedded elastomeric balls having the special capability to deform in conformity to work surface and thereby imparting a very fine refinement of its profile without altering the form. The mechanism of material removal in the proposed methodology is analysed using a mathematical model and its validation was done using a systematic experimentation procedure. Response surface methodology using central composite design is applied for the experimental study to investigate the effect of axial pressure, abrasive grain size and longitudinal stroke velocity of elastic abrasives on the surface finish. The process discussed in this paper is a simple and cost effective option to produce micro/nano-finish on the internal surfaces of a wide range of industrial components including hollow specimens, high aspect ratio bores and sleeves.

Estimation of Lightning Current and Return Stroke Velocity Profile Using Measured Electromagnetic Fields

To evaluate lightning current using measured electromagnetic fields, an inverse procedure algorithm is proposed in this article, where the variation of return velocity stroke velocity is considered as opposed to previous methods where the velocity is set at a constant value. The proposed algorithm considers all electromagnetic fields components directly in the time domain without needing to apply any extra conversions. Moreover, it can support the wide range of current models based on the general form of engineering current models. The proposed method is validated using a sample of triggered lightning data and measured electromagnetic fields at two stations with different distances from the lightning channel. The results illustrate that the proposed method could estimate the behavior of current along the channel and can thus be used for preparing a data bank to record lightning current parameters of a wide range of lightning occurrences based on measured fields.

A deterministic model based on evidence for the associations between kinematic variables and sprint kayak performance

The aim of this narrative review was to propose a deterministic model based on a review of previous research documenting the evidence for the associations between average kayak velocity and kinematic variables in sprint kayaking. Literature was reviewed after searching electronic databases using key words ‘kayak,’ ‘biomechanics,’ ‘velocity,’ ‘kinematics,’ and ‘performance.’ Our kinematic deterministic model for sprint kayaking performance shows that the average kayak velocity is determined by kayak stroke displacement and stroke time. Stroke time had the strongest correlation with 200-m race time (r = 0.86, p < 0.001), and stroke rate (inversely proportional to stroke time) was strongly correlated with average horizontal velocity over two consecutive strokes at race pace (r = − 0.83, p < 0.05). Increased stroke rate via decreased absolute water phase time and increased relative water phase time were indicative of more elite performance. There was no significant relationship between stroke displacement and velocity; however, a large decrease in stroke displacement may be detrimental to performance. Individual characteristics may be responsible for a paddlers’ ability to achieve and sustain a given stroke rate. Coaches should theoretically focus interventions on increasing stroke rate while maintaining stroke displacement; however this hypothesis should be confirmed with prospective studies.

Handwriting movement analyses comparing first and second graders with normal or dysgraphic characteristics

Dysgraphia of sufficient severity to interfere with the school work has been recognized as representing a distinct deficit; characterization of its movement problem is a necessary step toward offering improved intervention. From among children aged 6-8, 69 children with dysgraphic characteristics (study group) and 69 matched proficient hand-writers (control group) were recruited into this study. Four copying tests of differing complexity levels were administered using a digital tablet. The acquired data included direct measure (axial pen tip force) and derived parameters (stroke velocity, pause time, number of velocity peaks and ratio of In Air to On Paper measures). The major finding is that children with dysgraphic characteristics had increased pause time per stroke and an increased number of directional changes in velocity. Significant differences were also found between students in two different grades, especially in the control group. The parameters extracted and observed in this study can further differentiate and characterize the handwriting problems originating from fine motor deficits.

Developing a DSP-Based Control System of Servo Punch Press Using Model-Based Method

Servo punch press uses a servo motor to drive. It can set different stroke length and velocity according to different production requirements, and can always ensure the formation precision of the bottom dead center. It has the advantages of high efficiency, high precision and low noise, and it presents the development trend of punch press. The key point of the servo punch press development is its control system. According to the functional requirements and technical performance of the servo punch press, the general approach of the servo punch press material forming control law is discussed in this paper. The development platform based on DSP control system has built up as well. By means of the Simulink and the Target for TI C2000 tools in Matlab, the dynamic model of punch press system and controlling model, including forming model, DSP-based controller model and plant model,etc., have been designed. Base on this, the forming characteristics of different materials, forming control algorithms have been studies through simulation and virtual experiments.The controller algorithm can be transferred automatically to the target controller. This approach can reduce developing time and costs of servo punch press control system and improve developing efficiency.