Threshold Velocity Research Articles

Combining hydro-acoustics and hydraulic modeling for evaluating fish entrainment risk

Individual fish may be involuntarily removed from hydropower reservoir populations due to dam operations, a phenomenon known as fish entrainment. Entrainment for two life stages (age-0 and age-1) of Kokanee salmon (Oncorhynchus nerka) was evaluated within the forebay of the Revelstoke Dam in the upper Columbia River, British Columbia, Canada. Intensive fish surveys using hydro-acoustics were conducted to estimate fish density in the forebay at two different times (day & night) and across three seasons (spring, summer and winter). The number of fish entrained into intakes was monitored using hydro-acoustics continuously over one year. Surveyed fish densities and entrainment numbers were combined with Computational Fluid Dynamic modeling of the velocity field around the penstock intakes to estimate the threshold velocity for entrainment where 50% of the fish within this volume of water would be entrained. Fish density decreased with increasing distance from the dam face and it also decreased with increasing water depths. Entrainment of age-0 kokanee was consistently higher compared to age-1 in all times and seasons evaluated. The threshold velocities resulting in entrainment of age-0 kokanee were consistently lower (range 0.24 to 0.59 m/s) compared to those estimated for age-1 kokanee (range 0.30 to 1.08 m/s). Additional modeled scenarios showed that fish entrainment risk increased both with increasing intake discharge and the number of intakes in operation. Results demonstrate combing computational fluid dynamics models with ecological information collected using hydro-acoustics allows age-specific entrainment risk to be evaluated for vulnerable species and warrants application to other species and hydropower facilities.

System modeling and simulation of flyer acceleration and explosive detonation in exploding foil initiator

In this theoretical study on an exploding foil initiator (EFI), the sequential events in an EFI system were numerically modeled and investigated from metallic bridge burst by ohmic heating and flyer acceleration by plasma expansion to explosive detonation by high-speed flyer impact. The EFI system modeling employed mass, momentum, and energy conservation coupled with the resistance–inductance–capacitance circuit equation of the initiation circuit and plasma property calculations of highly dense metallic plasma as well as a semi-empirical detonation model. The aim was to predict transient bridge behavior, flyer velocity, and detonation initiation threshold. Through comparisons and verifications with measured data from several existing EFI firing tests, the present system model was shown to predict bridge burst and flyer velocity very well. The numerical results indicated two different thresholds of charging voltage for flyer creation out of plastic film and impact detonation of explosive charge to be quite consistent with the measurements. The system behaviors in three different ranges of charging voltage were discussed in terms of discrete nature of this high-voltage explosive charge initiator.

Numerical simulation of the effect of embedded gap on impact initiation of explosive PBX-9502

ABSTRACT Aiming at the influence of the embedded gap on the impact initiation of the flat flyer of PBX-9502, the finite element simulation software LS-DYNA and the I-G model are used to establish the numerical calculation model of the cylindrical PBX-9502 with the embedded gap for the impact initiation of flat flyer, and analyze the influence of different impedance. The effect of the thickness and position of the large impedance gap on the reduction of the flyer initiation threshold is studied, the initiation velocity thresholds under different conditions are obtained, and the causes of abnormal detonation at the threshold velocity are analyzed. The results show that, under certain conditions, the small impedance gap will increase the impact initiation velocity threshold while the large impedance gap will decrease; the reduction effect of the position and thickness of the large impedance gap on the detonation velocity increased first and then decreased; both embedded gaps and deformed flying plates will produce Irregular reflection waves that affect the explosive initiated at a critical speed.

Evaluation of wind load effects on solar panel support frame: A numerical study

Ground-mounted solar systems utilize huge agricultural land because of their high demand. The application/installation of Solar Panels on high rooftop structures can help save agricultural land. However, rooftop structures are vulnerable to high wind-loading conditions. There is no clear guidance available in the literature for finding additional stresses, which are produced by high roof-mounted solar panels due to strong wind loading. This simulation study comprises computational fluid variant (CFX) testing of solar panels and structural analysis of high rooftop structures at different wind velocities of ±7.53, ±15, ±25, ±35, and ±45 m/s. In this simulation study factors of safety (FoS) and displacement against these velocities for all elements of the structure are computed and presented. The truss is the most vulnerable even at the minimum wind load. The FoS for the truss is 0.41 and the displacement is 51.6 mm at a velocity of 7.53 m/s. The mounting structure fails at the velocity of -15 m/s as the resulting FoS and displacement are 0.72 and 58.26 mm, respectively. Based on the analysis, it has been determined that the Channel and Column structures can withstand speeds of up to ±25 m/s without exceeding the threshold limit. The Factor of Safety (FoS) for the Channel and Column at +25 m/s are 15 and 14.27, respectively, while the corresponding deformations are 0.43 mm and 4.59 mm. At -25 m/s, the FoS for the Channel and Column are 1.26 and 4.8, respectively. Overall, these results indicate that the Channel and Column structures have a good margin of safety and can withstand typical wind loads without failure. Meanwhile, deformations are 13.02 mm and 4.59 mm, respectively. Further, results give that the new proposed design of the mounting structure and truss can withstand up to the threshold velocity level of 25 m/s. Hence, investing in an existing structure can save useful agricultural land.

A practical evaluation of micro-hydrokinetic power potential for the Continental United States

Study regionContinental United States (CONUS) Study focusMicro-hydrokinetic turbines are hydropower turbines that can utilize the current of the river to generate power without constructing a dam. Recent advances in micro-hydrokinetic turbine technology have made their use an attractive alternative to traditional hydropower systems that require the construction of a dam. In this paper, we introduce a novel and practical analysis of continental to global scale hydrology and hydraulics that we use to assess continental United States (CONUS) stream locations with optimum hydraulic characteristics for an example micro-hydrokinetic turbine (Volturnus). We then utilize the boundaries of CONUS military installations to determine installations possessing the greatest potential to utilize the Volturnus. New hydrological insights for the regionFor the Volturnus, our results indicate that although less than 1% of CONUS stream locations possess the hydraulic characteristics necessary for the Volturnus to function optimally, this translates into roughly 224–544 million kWh per week, considerably less than previous estimates of CONUS theoretical and recoverable power but substantial, nonetheless. Around 26–40 CONUS military installations possess streams that are sometimes capable of producing hydropower with the Volturnus and 12–20 of those military installations possess optimum hydraulic conditions for the Volturnus year round. In our analysis, reducing either the minimum velocity or minimum depth threshold of the Volturnus nearly double the proportion of CONUS locations with optimum Volturnus hydraulic characteristics.

Settling dynamics of circular particles in vibrating tanks filled with a yield-stress liquid

The effect of sinusoidal vibration is numerically investigated on the settling dynamics of a heavy particle of circular shape immersed in a viscoplastic fluid obeying the regularized Bingham–Papanastasiou (BP) model. Having modeled the solid particle as a highly viscous Newtonian droplet, we have relied on the finite element method for solving the equations of motion for the particle and the surrounding fluid. Our numerical results could closely recover the theoretical critical Bingham number of 0.0658 for circular particles settling in Bingham materials. Using a very small threshold velocity to decide whether a particle is stuck or unstuck, it is shown that stuck particles can be excited to fall in the BP liquid provided that, for any given frequency, the amplitude is larger than a minimum value. An increase in the size of the particle or its density is predicted to reduce the threshold amplitude. In general, vibration is found to have an accelerating effect on particle settling in the BP liquid although the effect is non-monotonic. The accelerative effect of vibration is attributed to the enlarged size of the yielded zone, while the non-monotonic behavior is attributed to the effect of the sidewalls. At high density ratios, a phase lag is predicted to arise between the particle and the vessel. A comparison between the obtained numerical results with published experimental data for spherical particles suggests that, in settling flows, circular particles can be used as a good paradigm for spherical particles.

Massive Protostellar Disks as a Hot Laboratory of Silicate Grain Evolution

Typical accretion disks around massive protostars are hot enough for water ice to sublimate. We here propose to utilize the massive protostellar disks for investigating the collisional evolution of silicate grains with no ice mantle, which is an essential process for the formation of rocky planetesimals in protoplanetary disks around lower-mass stars. We, for the first time, develop a model of massive protostellar disks that includes the coagulation, fragmentation, and radial drift of dust. We show that the maximum grain size in the disks is limited by collisional fragmentation rather than by radial drift. We derive analytic formulae that produce the radial distribution of the maximum grain size and dust surface density in the steady state. Applying the analytic formulae to the massive protostellar disk of GGD27-MM1, where the grain size is constrained from a millimeter polarimetric observation, we infer that the silicate grains in this disk fragment at collision velocities above ≈10 m s−1. The inferred fragmentation threshold velocity is lower than the maximum grain collision velocity in typical protoplanetary disks around low-mass stars, implying that coagulation alone may not lead to the formation of rocky planetesimals in those disks. With future measurements of grain sizes in massive protostellar disks, our model will provide more robust constraints on the sticking property of silicate grains.

Fitting Cumulus Cloud Size Distributions From Idealized Cloud Resolving Model Simulations

AbstractWhereas it is now widely accepted that cumulus cloud sizes are power‐law distributed, characteristic exponents reported in the literature vary greatly, generally taking values between 1 and >3. Although these differences might be explained by variations in environmental conditions or physical processes organizing the cloud ensembles, the use of improper fitting methods may also introduce large biases. To address this issue, we propose to use a combination of maximum likelihood estimation and goodness‐of‐fit tests to provide more robust power‐law fits while systematically identifying the size range over which these fits are valid. The procedure is applied to cloud size distributions extracted from two idealized high‐resolution simulations displaying different organization characteristics. Overall, power‐laws are found to be outperformed by alternative distributions in almost all situations. When clouds are identified based on a condensed water path threshold, using power‐laws with an exponential cutoff yields the best results as it provides superior fits in the tail of the cloud size distributions. For clouds identified using a combination of water content and updraft velocity thresholds in the free troposphere, no substantial improvement over pure power‐laws can be found when considering more complex two‐parameter distributions. In this context however, exponential distributions provide results that are as good as, if not better than power‐laws. Finally, it is demonstrated that the emergence of scale free behaviors in cloud size distributions is related to exponentially distributed cloud cores merging as they are brought closer to each other by underlying organizing mechanisms.

Aerobic adaptations following two iso-effort training programs: an intense continuous and a high-intensity interval.

The intensity of the training stimulus and the effort exerted (regarded as an index of internal load) to complete an exercise session are driving forces for physiological processes and long-term training adaptations. This study compared the aerobic adaptations following two iso-effort, ratings of perceived exertion (RPE)-based training programs, an intense continuous (CON) and a high-intensity interval (INT). Young adults were assigned to a CON (n=11) or an INT (n=13) training group to perform 14 training sessions within 6 weeks. The INT group performed running bouts (9.3±4.4 repetitions) at 90% of peak treadmill velocity (PTV) with bout duration equal to 1/4 of time to exhaustion at this speed (134.2±27.9 s). The CONT group ran (1185.0±487.6 s) at a speed corresponding to -2.5% of critical velocity (CV; 80.1%±3.0% of PTV). Training-sessions were executed until RPE attained 17 on the Borg scale. VO2max, PTV, CV, lactate threshold velocity (vLT), and running economy were assessed pre-, mid-, and post-training. Both CONT and INT methods increased (p<0.05) VO2max (INT: 57.7±8.1-61.41±9.2; CONT: 58.1±7.5-61.1±6.3 mL kg-1 min-1), PTV (INT: 14.6±1.8-15.7±2.1; CONT: 15.0±1.7-15.7±1.8 km h-1), CV (INT: 11.8±1.4-12.8±1.8; CONT: 12.2±1.6-12.9±1.7 km h-1), and vLT (INT: 9.77±1.1-10.8±1.4; CONT: 10.4±1.4-11.0±1.8 km h-1) with no differences (p>0.05) between them; running economy remained unchanged. The continuous training method, when matched for effort and executed at relatively high intensity at the upper boundaries of the heavy-intensity domain (∼80% of PTV), confers comparable aerobic adaptations to those attained after a high-intensity interval protocol following a short-term training period.

Exploration of playa surface crusts in Qehan Lake, China through field investigation and wind tunnel experiments

Globally, many lakes are drying up, leaving exposed lakebeds where wind erosion releases dust and sand rich in salt and harmful heavy metals into the atmosphere. Therefore, understanding the characteristics and spatial distribution of playa surface crusts is important to recognize the manifestation of salt dust storms. The objective of this study was to explore the playa surface crust types as well as their spatial distribution and evolution of Qehan Lake in Inner Mongolia Autonomous Region, China to understand the salt dust release potential of different types of playa surface crusts. Various crust characteristics were investigated by field sampling in Qehan Lake, and playa surface crusts were further divided into five types: vegetated areas, salt crusts, clay flats, curly crusts, and margins. It should be noted that curly crusts were distributed in clay flats and covered only a small area in Qehan Lake. The spatial distribution characteristics of playa surface crust types were obtained by supervised classification of remote sensing images, and the salt dust release potential of crusts was explored by the wind tunnel experiments. The field investigation of Qehan Lake revealed that playa surface crust types had a circum-lake band distribution from the inside to the outside of this lake, which were successively vegetated areas, clay flats, salt crusts, and margins. The spatial distribution patterns of playa surface crust types were mainly controlled by the hydrodynamics of the playa, soil texture, and groundwater. There was a significant negative correlation between crust thickness and electrical conductivity. The results of the wind tunnel experiments showed that the initial threshold of friction wind velocity for the salt dust release was higher in clay flats (0.7–0.8 m/s) than in salt crusts (0.5–0.6 m/s). Moreover, the particle leap impact processes occurring under natural conditions may reduce this threshold value. Salinity was the main factor controlling the difference in the initial threshold of friction wind velocity for the salt dust release of clay flats and salt crusts. This study provides a scientific reference for understanding how salt dust is released from a lakebed, which may be used for ecological restoration of dry salt lakes.

Optimal Minimum Velocity Threshold to Estimate the 1-Repetition Maximum: The Case of the Smith Machine Bench Press Exercise.

To compare the accuracy in the estimation of the Smith machine bench press 1-repetition maximum (1RM) when using a novel minimum velocity threshold (MVT) called optimal MVT (MVT that minimizes the differences between the actual and predicted 1RM in a preliminary session) with respect to using the 2 standard MVTs (general and individual MVTs). A total of 126 young men (Smith machine bench press 1RM = 80.7 [13.6]kg) completed 2 identical sessions consisting of an incremental loading test until reaching the 1RM load. Four individual load-velocity relationships were modeled in each session considering all loading conditions until reaching the load that showed the closest mean velocity to 0.60, 0.50, 0.40, and 0.30m·s-1. The first testing session was used to determine the preindividual MVT and 4 optimal MVTs (1 for each final test velocity), while the second testing session was used to estimate the 1RM using 4 types of MVT (general MVT, preindividual MVT, actual-individual MVT, and optimal MVT). The absolute errors in the prediction of the 1RM were significantly lower for the optimal MVT (2.94 [2.40]kg) compared to the general MVT (3.66 [2.99]kg), preindividual MVT (3.80 [3.15]kg), and actual-individual MVT (4.02 [3.21]kg). The optimal MVT (intraclass correlation coefficient [ICC] ranged from .56 to .62) was always more reliable than the individual MVT (ICC = .34). The optimal MVT provides more accurate estimates of the Smith machine bench press 1RM than the standard MVTs previously used in scientific research (general and individual MVTs).

Non-Parametric Nonlinear Parameter-Varying Parallel-Cascade Identification of Dynamic Joint Stiffness.

The paper presents a method to identify ankle joint dynamic stiffness during functional tasks where intrinsic and reflex stiffness change with a time-varying scheduling variable (SV), such as joint position or torque. The method models joint stiffness with two pathways: (1) A parameter-varying (PV) impulse response function (IRF) describing intrinsic stiffness; and (2) a reflex stiffness model comprising a PV static nonlinearity followed by a PV linear element. Monte-Carlo simulations demonstrated that the method accurately estimated all elements of the intrinsic and reflex pathways as they changed with a SV. Experimental results with a healthy individual subjected to large, imposed ankle movements demonstrated that: (a) Intrinsic stiffness changed substantially as a function of ankle position; elasticity was lowest near the mid-position and increased with either dorsiflexion or plantarflexion. (b) Reflex gain increased and the velocity threshold for reflex excitation decreased monotonically with ankle dorsiflexion. (c) Reflex dynamics resembled a second-order, low-pass system that was invariant with ankle position. (d) The identified PV Parallel-Cascade (PC) model accurately predicted the torque response to novel trajectories of ankle movement. The PV-PC method can accurately and reliably estimate how intrinsic and reflex stiffness change with a time-varying SV. The method is novel with multiple advantages: (a) It provides a unified algorithm that characterizes the changes in the parameters of all joint stiffness elements needed to understand their role in postural/movement control; (b) It is efficient requiring only two trials; (c) The models identified can predict the joint stiffness response to novel movements informing orthoses and prostheses design.

ОДНОМЕРНАЯ ДИНАМИКА ДОМЕННОЙ ГРАНИЦЫ В СЕМИСЛОЙНОЙ ФЕРРОМАГНИТНОЙ СТРУКТУРЕ

The dynamics of the domain boundary is considered using the example of a seven-layer ferromagnetic structure with three thin and four wide magnetic layers. The structure of the domain boundary is represented as a kink solution of the sine-Gordon equation. The equation of motion for magnetization was solved numerically using an explicit scheme. The discretization of the equation was carried out according to a standard five-point scheme of the "cross" type. The paper shows the features of the dynamics of the domain boundary in a multilayer magnetic system in the presence of thin magnetic layers with an increased value of the magnetic anisotropy constant. Thin layers with an increased value of the magnetic anisotropy constant compared to the homogeneous state represent potential barriers to the moving domain boundary. Thin layers with an increased magnitude of magnetic anisotropy compared to a homogeneous state represent potential barriers to a moving domain boundary. A diagram of possible scenarios of the dynamics of the domain boundary is constructed depending on the initial velocity of its movement and the distance between three thin magnetic layers. The maximum value of the kink velocity for reflection from all potential barriers, depending on their size, is obtained. With an increase in the height and width of the barrier, the value of such a threshold maximum reflection velocity of the domain boundary increases nonlinearly. With a sufficiently high barrier height, there is already an almost linear dependence on the width of this threshold velocity. With a slight increase in the speed of movement of the domain boundary, the kink can pass through the first barrier, but it is reflected from the second barrier. There is also a case of kink oscillation between the second and third potential barriers. Such fluctuations are clearly inharmonious. The dependence of the threshold velocity on the distance between the barriers is obtained. As the distance between the barriers increases, the threshold speed value tends to a value equal to the threshold speed for one barrier. In the work, the minimum value of the speed of the domain boundary of the passage of all layers, depending on the parameters of potential barriers, is obtained. It is also found that there is a critical distance separating the dynamics of the domain boundary into two regions with qualitatively different behavior of the system.

Near-surface characteristics of velocity profile and momentum transport after wave-breaking in deep water

Wave-breaking plays an important role in the process of mixing in the upper ocean, which can cause wave momentum and energy flux loss, enhance near-surface turbulence, and adjust the distribution of the momentum flux at the air-sea interface. In this paper, wave-breaking was generated using a laboratory method of controllable deep water breaking waves, and flow field characteristics after wave-breaking were measured and analyzed using PIV technology and the ensemble average method. The velocity threshold was proposed for the effective influence of wave-breaking on the flow field, then the EID (Effective-Influenced-Depth) of wave-breaking, which is Dv in the paper, was quantified, and the quantitative relationship between Dv and energy loss induced by breaking was established. Velocity characteristics of the near-surface flow field and transport characteristics of horizontal momentum induced by wave-breaking were analyzed, which can contribute to the parameterization of wave-breaking. The results show that the energy injected by wave-breaking is transported downstream along the direction of wave propagation. The vertical-influenced range of wave-breaking is about 1–2 times the wave-breaking height. The time integral of horizontal momentum flux increases significantly in the depth of about 1 time the wave-breaking height near the surface and decays significantly with depth. Mass transport of the fluid near the surface induced by wave-breaking mainly occurs in the depth where momentum flux increases significantly. After about 29 times the SWWP (spectrally weighted wave period) after breaking, fluid near the surface is no longer under the action of horizontal stress induced by wave-breaking, so no mass transport occurs anymore. For parameterization of wave-breaking in circulation models, the research can provide a reference in time and space scale, as well as experimental data support for the establishment of a new influence mode.

Droplets impact on rotating cylinders

In the present work, the impact dynamics of oil droplets on curved surfaces is reported. The influences of curvature, surface roughness, rotating speed, and wetting conditions on the impact dynamics are investigated. It is found that the deformation of droplets on rotating cylinders is more significant than that on static ones. An interesting bouncing phenomenon on rotating, pre-wetted, and curved surfaces is reported, and bouncing dynamics under different conditions are highlighted. Numerical simulation indicates that the sunken of liquid film on the cylinder surface generates a liquid camber there and seals compressed air, providing a cushion effect for droplets bouncing. Critical conditions are given to identify the velocity thresholds of droplets bouncing and depositing. This work provides a basic understanding of droplets impact dynamics on curved surfaces and design concepts for applications in modern industry, such as mist lubrication systems.

Paper 22: Ulnar Collateral Ligament Tear in Elite Baseball Pitchers: Do High School Showcase Exposures Predict Injury™

Paper 22: Ulnar Collateral Ligament Tear in Elite Baseball Pitchers: Do High School Showcase Exposures Predict Injury™

Probabilistic impact fragility analysis of bridges under Barge collision and local scour

Vessel collision is a common cause of structural failure to bridges crossing navigable waterways. Although numerous efforts focus on the safety evaluation of bridge structures under vessel impact, very few jointly consider a more threatening situation that involves a scoured bridge colliding with a vessel (e.g., a barge). In this work, an impact fragility analysis (IFA) process is proposed to understand a bridge's failure probability under the combined hazards. To achieve high-fidelity modeling of material behavior during the collision process, scaled pier-foundation models subjected to pendulum impacts are experimentally studied. Nonlinear material models and an explicit dynamic simulation procedure are verified, which are further adopted to develop a high-resolution finite-element model for a full-scale three-span bridge. The resulting impact-fragility models conditional upon impact velocities at different scour depths reveal essential insights into the failure modes of the bridge. The findings include that: (1) scour has a minor effect on the probability of slight and moderate damage at various impact velocities; (2) at a high impact velocity (when higher than an impact fragility velocity threshold), scour can significantly increase the probability of major damage and collapse; (3) barge-tonnage has a significant influence on the threshold value reflecting the significant scour effects.

First clinical experience using a novel automated mapping algorithm for mapping of ventricular arrhythmias

A new automated vector-based mapping algorithm (AMA) for 3-dimensional (3D) mapping has been introduced. The aim of this study was to present our experience using AMA to recognize additional catheter ablation targets in patients with ventricular arrhythmias (VA). A total of 16 patients (ICM; ischemic cardiomyopathy, n = 6; NICM; non-ischemic cardiomyopathy n = 10) suffering from VA underwent catheter ablation. Following bipolar voltage mapping, AMA was utilized to reveal zones of decelerated conduction velocity vectors (CVV) and this information was superimposed onto the 3D reconstructions and compared with the presence of scar. Mapping time was 28.1 ± 10 min for the endocardial reconstruction of the left ventricle (LV) and 17 ± 5.4 min for the epicardium (n = 6 patients). The mean area of LV low voltage was 13.9 ± 15% (endocardial) and 11.9 ± 5.7% (epicardial). Decelerating CVV zones were revealed in all patients (mean conduction velocity threshold of 39.3 ± 13%). Sustained VA have been terminated through ablation and substrate modification was performed in all patients. Correlation between the presence of CVV deceleration zones and areas of abnormal low voltage from bipolar mapping was revealed in only 37.5% of patients, but there was good correlation between scar from unipolar voltage mapping and the presence of CCV deceleration zones (94%; p = 0.008). The novel AMA may improve the understanding of individual VA substrates due to the visualization of decelerated CVV zones and their correlation with abnormal low voltage predominantly from unipolar mapping.

High-speed running and sprinting in professional adult soccer: Current thresholds definition, match demands and training strategies. A systematic review.

The aims of this systematic review were (1) to summarize the evidence on absolute velocity thresholds used to classify high-speed running and sprinting, (2) to examine the existing evidence about the individualized thresholds approach, (3) to describe high-speed and sprint running distance match demands, and (4) to provide training strategies for eliciting HSR and sprinting during training sessions in professional adult soccer. This systematic review was conducted following the PRISMA 2020 guidelines. After the authors' screening, 30 studies were included in this review. This review found that, to date, there is no consensus on the absolute thresholds defining high-speed and sprint running in adult soccer players. Until international standards are defined, it is reasonable to set absolute thresholds considering the range of values found in the literature collected in this review. Relative velocity thresholds could be considered for specific training sessions whose goal is to reach near maximal velocity exposure. During official matches, high-speed and sprint running distances ranged from 911 to 1,063 m and 223-307 m, respectively, in professional female soccer players, while ranges from 618 to 1,001 m and 153-295 m, respectively, in professional male soccer players. During training, game-based drills designed in formats using relative areas per player greater than 225 m2 and 300 m2 appear to be adequate for achieving high-speed running and sprinting exposure, respectively, for male players. The combination of game-based, running exercises and soccer circuit-based drills is advisable to ensure adequate high-speed and sprint running exposure both at a team and individual level.

Novel Feature Extraction and Locomotion Mode Classification Using Intelligent Lower-Limb Prosthesis

Intelligent lower-limb prosthesis appears in the public view due to its attractive and potential functions, which can help amputees restore mobility and return to normal life. To realize the natural transition of locomotion modes, locomotion mode classification is the top priority. There are mainly five steady-state and periodic motions, including LW (level walking), SA (stair ascent), SD (stair descent), RA (ramp ascent), and RD (ramp descent), while ST (standing) can also be regarded as one locomotion mode (at the start or end of walking). This paper mainly proposes four novel features, including TPDS (thigh phase diagram shape), KAT (knee angle trajectory), CPO (center position offset) and GRFPV (ground reaction force peak value) and designs ST classifier and artificial neural network (ANN) classifier by using a user-dependent dataset to classify six locomotion modes. Gaussian distributions are applied in those features to simulate the uncertainty and change of human gaits. An angular velocity threshold and GRFPV feature are used in the ST classifier, and the artificial neural network (ANN) classifier explores the mapping relation between our features and the locomotion modes. The results show that the proposed method can reach a high accuracy of 99.16% ± 0.38%. The proposed method can provide accurate motion intent of amputees to the controller and greatly improve the safety performance of intelligent lower-limb prostheses. The simple structure of ANN applied in this paper makes adaptive online learning algorithms possible in the future.