Instantaneous Velocity Data Research Articles

Effects of submergence ratio on flow around a circular pier in combined wave–current flows using particle image velocimetry

The present study illustrates an experimental investigation of flow hydrodynamics in the vicinity of a submerged circular pier across various submergence levels under only current and wave–current combined flow conditions. The instantaneous velocity data are collected using particle image velocimetry for three distinct frequencies of waves to determine the influence of wave superimposition on the current-induced turbulence parameters. The distribution of phase averaged turbulence quantities, such as mean velocities, Reynolds shear stress, turbulent kinetic energy, flow patterns, and vorticity analysis by Q-criterion, are presented. The results provide insight into the impacts of wave frequency and submergence ratio on the formation of horseshoe vortices, trailing vortex, and reverse flow zones. From the results it is observed that a decrease in the submergence level of the structure causes the formation of strong horseshoe vortices and reverse flow zones in the absence of waves. Also, an increase in wave frequency intensifies the turbulence kinetic energy at the upstream of the pier and eddy generation behind the pier. The present findings highlight the effects of pier submergence and wave characteristics, such as frequency, wave height, and wave period, on flow patterns and turbulent flow characteristics and aid in the design of marine structures. Furthermore, experimental data serve as a valuable resource for validating theoretical or mathematical models related to combined wave–current environments.

Between-rater reliability for using radar technology to quantify maximal horizontal deceleration performance in NCAA division 1 American football and female lacrosse athletes.

With recent increases in the popularity of studying the physical construct of horizontal deceleration performance in team-sport athletes, the aim of the present study was to assess the inter-rater and intra-rater reliability of processing and quantifying horizontal deceleration ability using radar technology. Data from 92 NCAA Division 1 athletes from two different athletic teams (American football and Lacrosse) were used for the present investigation. All athletes performed two trials of the modified acceleration to deceleration assessment (ADA), which consisted of a maximal 10 m sprint acceleration, followed by a rapid deceleration. Four individual raters manually processed raw, radar-derived instantaneous velocity data for the ADA, and an automated script was used to calculate metrics of interest. Primary study findings suggest moderate to excellent levels of agreement (ICC = 0.56-0.91) for maximal horizontal deceleration metrics between the four individual raters. The intra-rater analyses revealed poor to excellent consistency (ICC = 0.31-0.94) between ADA trials, with CV%'s ranging from 3.1% to 13.2%, depending on the respective metric and rater. Our data suggests that if a foundational understanding and agreement of manual data processing procedures for radar-derived data is given between raters, metrics may be interpreted with moderate to excellent levels of confidence. However, when possible, and when using the Stalker ATS radar technology, authors recommend that practitioners use one trained individual to manually process raw data. Ideally, this process should become fully automated, based on selected filters or algorithms, rather than the subjectivity of the rater.

Characteristics of very-large-scale motions in natural rivers based on large eddy simulation

Exploring very-large-scale motions (VLSMs) in open channel flows (OCFs) is crucial for comprehensively understanding material transport and energy exchange. While previous studies focused on OCFs in ideal flumes with simple boundaries, this paper presents large eddy simulation (LES) results on the existence and scale characteristics of VLSMs in complex river morphologies with the Minjiang River in southwestern China as a case study. This research demonstrates that the OpenFOAM-based LES model is capable of accurately reconstructing the time-averaged flow field and providing instantaneous velocity data that capture VLSMs with sufficient resolution. Spectrum analysis of the streamwise fluctuating velocity shows that VLSMs are present in the straight segment of the river, with streamwise wavelengths approximately (16–22) times the water depth but are absent in the bend and confluence segments due to the suppression by secondary currents. This article validates the effectiveness of LES in examining the characteristics of VLSMs in natural rivers, thereby laying a good foundation for further studies on the impacts of such structures on sediment transport and pollutant dispersion.

Validation of Automatically Quantified Swim Stroke Mechanics Using an Inertial Measurement Unit in Paralympic Athletes.

Biomechanics and training load monitoring are important for performance evaluation and injury prevention in elite swimming. Monitoring of performance and swim stroke parameters is possible with inertial measurement units (IMU) but has not been validated in para-swimmers. The purpose of this study was to validate a single IMU-based system to accurately estimate pool-swam lap time, stroke count (SC), stroke duration, instantaneous stroke rate (ISR), and distance per stroke (DPS). Eight Paralympic athletes completed 4 × 50 m swims with an IMU worn on the sacrum. Strokes cycles were identified using a zero-crossing algorithm on the medio-lateral (freestyle and backstroke) or forward-backward (butterfly and breaststroke) instantaneous velocity data. Video-derived metrics were estimated using Dartfish and Kinovea. Agreement analyses, including Bland-Altman and Intraclass Correlation Coefficient (ICC), were performed on all outcome variables. SC Bland-Altman bias was 0.13 strokes, and ICC was 0.97. ISR Bland-Altman biases were within 1.5 strokes/min, and ICCs ranged from 0.26 to 0.96. DPS Bland-Altman biases were within 0.20 m, and ICCs ranged from 0.39 to 0.93. A single-IMU system can provide highly valid performance and swim stroke monitoring data for elite para-swimmers for the majority of strokes, with the exception of backstroke. Future work should improve bilateral stroke detection algorithms in this population.

Reliability of a semi-tethered front crawl sprint performance test in adolescent swimmers.

This study aimed to evaluate the test-retest reliability of a sprint performance test with semi-tethered front crawl swimming to indirectly assess the current potential to perform at maximal anaerobic effort in adolescent swimmers. Eight adolescent swimmers participated in this study (gender: females (n = 4) aged 13.0 ± 0.8 years, body height 1.6 ± 0.0m, body mass 50.1 ± 4.5kg; and males (n = 4) aged 13.3 ± 1.3 years, body height 1.7 ± 0.1m, body mass 59.0 ± 8.2kg. The testing protocol consisted of two trials of 25m semi-tethered front crawl swimming with maximal effort and with 1kg resisted isotonic load. Velocity data were recorded automatically by the 1080 Sprint device for 15m (between 3m and 18m). The Fast Fourier Transform algorithm filtered raw instantaneous swimming velocity data in distance (time) function. A third-degree polynomial was used to extract the individual velocity profile, from which the following variables were chosen for test-retest reliability and the assessment of sprint performance: ttrial15, vmax, vmin, tvto max, tvat max, Dto vmax, Dat vmax, fatigue index. Parameters such as vmax, vmin, and ttrial15 were estimated from swimming velocity profiles and considered as reliable. The CV showed low variance <5%; while ICC2,1 demonstrated respectively good (ICC2,1: 0.88), very good (ICC2,1: 0.95), and excellent (ICC2,1: 0.98) rate of relative reliability; and the Bland-Altman index revealed an acceptable agreement (LoA ≤5%) between two measurements. The sprint performance test based on semi-tethered front crawl swimming confirmed that ttrial15, vmax, and vmin were reliable variables to indirectly indicate a potential to perform the maximal anaerobic effort among adolescent swimmers. The evaluation of the swimming velocity profiles allows coaches to monitor the adaptive changes of performance during the training process.

Effect of filament length on the flow field of a rotationally oscillating cylinder with an attached filament

Experimental studies are conducted to examine the effect of filament length on the flow field and forces in the flow past a rotationally oscillating cylinder with an attached filament. The diagnostics are flow visualization through planar laser-induced fluorescence technique and characterization of the velocity and vorticity field using planar particle image velocimetry measurements. The streamwise force is estimated through control volume analysis, using an improved expression, described in Sunil et al., J. Fluid Mech. 930, A3 (2022). With an increase in the filament length, the wake structure transitions from a Kármán wake to a reverse Bénard–Kármán wake and subsequently to an asymmetric wake. This happens at a Strouhal number of StA = 0.25 and 0.6, respectively. The transition from a Kármán wake to a reverse Kármán wake precedes the drag-to-thrust transition. Thrust generation is observed to be a function of both the cylinder forcing parameters and the filament length. Shorter filaments (L/D = 0.5 and 1) produce drag, whereas longer filaments (L/D = 2, 3, and 4) produce thrust at FR≥ 2.5. Normalized values of circulation scale well with the filament length, L, and the filament tip velocity, VTE, in the case of longer filaments. The effect of filament length on vortex dynamics and thrust generation is examined through a time evolution of the instantaneous vorticity, velocity, and kinetic energy data. Maximum momentum and kinetic energy content is observed in the flow field near the instants when the vortices are shed in the wake.

Double-averaged turbulence statistics of wave current flow over rough bed with staggered arrangement of hemispherical blocks

Double-average turbulence characteristics of combined wave-current flow are studied over a rough bed comprising hemispheres arranged in a staggered pattern with different spacing (p/r = 4, 6, and 8; p = pitch length, r = height). The instantaneous velocity data was collected by Acoustic Doppler Velocimetry for the evaluation of double-average (DA) velocity, turbulence intensity, form-induced intensity, Reynolds stress, and form-induced stresses. The smallest DA velocity was obtained for p/r = 4 at the bottom region, signifying that p/r = 4 offered the maximum resistance to the flow among the tested cases. DA Reynolds stress is decreased for the entire flow depth due to superimposed waves. The advection of momentum-flux of normal stress in stream-wise and bottom-normal directions is increased at the outer layer and decreased at the near-bed region after wave-imposition. Maximum TKE production and diffusion are obtained just above the interfacial sub-layer and the middle of the form-induced sub-layer respectively. The turbulence structure is strongly anisotropic at the bottom region for p/r = 4 and near the outer layer, the tendency towards the return to isotropic state is dominant while with the increase in roughness spacing, a decrease in anisotropy is observed. Furthermore, an increase in wave-frequency decreased the tendency for the return to isotropy at the free surface.

INVESTIGATION OF HYDRODYNAMICS AND SCOUR AROUND BRIDGE PIERS UNDER THE COMBINED WAVE AND CURRENT EFFECTS

Bridges piers and other marine structures in coastal regions are affected by water currents and waves. These structures may collapse due to scour induced by water currents or waves, leading to huge economic and life losses. The problem worsens when surface waves are superimposed on current. The superposition of the wave further modifies the flow field around the bridge pier. A thorough understanding of turbulent flow under these circumstances will be crucial for the cost-effective and ideal design of the pier. This study experimentally investigates the effect of the superposition of surface wave on the flow hydrodynamics and the local scour around a circular pier over a gravel bed. It also presents the comparison of turbulence characteristics under only current condition and combination of wave and current. Laboratory experiments were performed in a 15 m long rectangular flume. A surface wave with frequency of 0.5 Hz was superimposed in the direction of current. The instantaneous velocity data for evaluating turbulent kinetic energy was recorded using particle image velocimetry (PIV). The analysis of the result showed that the superposition of surface wave significantly increased the turbulence strength which leads to approximately 30% increase in the local scour depth. This study will be helpful in optimal design of bridge piers and other coastal structures by improving the relationship for the scour prediction in coastal area and provide a data set for the numerical simulation of the problem as well.

Bulk Cavitation in Model Gasoline Injectors and Their Correlation with the Instantaneous Liquid Flow Field

It is well established that spray characteristics from automotive injectors depend on, among other factors, whether cavitation arises in the injector nozzle. Bulk cavitation, which refers to the cavitation development distant from walls and thus far from the streamline curvature associated with salient points on a wall, has not been thoroughly investigated experimentally in injector nozzles. Consequently, it is not clear what is causing this phenomenon. The research objective of this study was to visualize cavitation in three different injector models (designated as Type A, Type B, and Type C) and quantify the liquid flow field in relation to the bulk cavitation phenomenon. In all models, bulk cavitation was present. We expected this bulk cavitation to be associated with a swirling flow with its axis parallel to that of the nozzle. However, liquid velocity measurements obtained through particle image velocimetry (PIV) demonstrated the absence of a swirling flow structure in the mean flow field just upstream of the nozzle exit, at a plane normal to the hypothetical axis of the injector. Consequently, we applied proper orthogonal decomposition (POD) to analyze the instantaneous liquid velocity data records in order to capture the dominant coherent structures potentially related to cavitation. It was found that the most energetic mode of the liquid flow field corresponded to the expected instantaneous swirling flow structure when bulk cavitation was present in the flow.

Experimental study on characteristics of turbulence and sediment transport produced by wind-induced water waves

Many researchers and engineers have shown great interest in mass transfer processes produced by wind-induced waves. Such waves contribute significantly to the transfer of environmental materials, such as sediment and marine debris, and the turbulence occurring beneath the waves further complicates wave-induced mass transport. The phase cycle of wave motion is generally considered to be a key determinant of mean flow and turbulence. In aqueous environmental engineering, this relationship is a crucial one to investigate, since turbulence is closely related to mass transport. To address this question, we measured the time-series of instantaneous velocity vectors by means of particle image velocimetry in a laboratory flume to reveal the turbulence structure induced by wave motion. By using a wavelet analysis free of specific assumptions, we were able to decompose the instantaneous velocity data into mean current, wave motion, and turbulence components. This analysis allowed for the objective evaluation of the shear stresses related to wave energy and turbulence energy production. Furthermore, we found significant phase characteristics of energy transfer among mean velocity, wave, and turbulence components. In order to examine the diffusion and convection properties induced by wind waves, we also conducted tracking analysis of imaginary sediment markers. Our results support the conclusion that mass transfer induced by wind waves impacts the entire range of water depths, at least in relatively shallow aqueous environments.

Three-dimensional wake structures over a short cylinder having a fore angled hole

The complex three-dimensional (3D) flows around a short cylinder on the wall, acted by a flow exiting from a fore angled hole (FAH) that penetrates the cylinder from the fore to the top end, were experimentally investigated. The 3D instantaneous velocity distributions were measured based on tomographic particle image velocimetry (Tomo-PIV). The 3D flow structures behind the FAH and no-hole cylinders are compared in terms of the measured 3D velocity and vorticity distributions, Q-criterion, and tip vortices. A 3D W-type arch vortex, which shows a larger peak or convexity on the horizontal part center than for the no-hole cylinder, is found around the FAH short cylinder. The exiting flow from the FAH increases the separation zone, and FAH height effectively controls the eddy structures. The instantaneous 3D velocity data obtained from Tomo-PIV are decomposed using 3D wavelet multiresolution analysis and proper orthogonal decomposition. With the FAH cylinder, the large-scale streamwise wake vortices are smaller than with the no-hole cylinder, and this exhibits more evident as increasing the FAH height. The time-mean 3D large-scale arch vortical structures, however, become stronger. Proper orthogonal decomposition indicates that the energetic flow structures of the FAH cylinders are stronger than those of the no-hole cylinder.

Changing gears: data-driven velocity zones to support monitoring and research in men’s rugby league

ABSTRACT Objectives The study aimed to (1) apply a data-mining approach to league-wide microtechnology data to identify absolute velocity zone thresholds and (2) apply the respective velocity zones to microtechnology data to examine the locomotor demands of elite match-play. Methods League-wide microtechnology data were collected from elite male rugby league players representing all National Rugby League (NRL) teams (n = 16 teams, one excluded due to a different microtechnology device; n = 4836 files) over one season. To identify four velocity zones, spectral clustering with a beta smoothing cut-off of 0.1 was applied to each players’ instantaneous match-play velocity data. Velocity zones for each player were calculated as the median while the overarching velocity zones were determined through an incremental search to minimise root mean square error. Results The velocity zones identified through spectral clustering were 0–13.99 km · h−1 (i.e., low velocity), 14.00–20.99 km · h−1 (i.e., moderate velocity), 21.00–24.49 km · h−1 (i.e., high velocity) and >24.50 km · h−1 (i.e., very-high velocity). Conclusions The application of spectral clustering (i.e., a data-mining method) to league-wide rugby league microtechnology data yielded insights into the distribution of velocity data, thereby informing the cut-off values which best place similar data points into the same velocity zones. As the identified zones are representative of the intensities of locomotion achieved by elite male rugby league players, it is suggested that when absolute zones are used, the consistent application of the identified zones would facilitate standardisation, longitudinal athlete monitoring as well as comparisons between teams, leagues and published literature.

Effect of S-shaped guardrails on pedestrian crowd flows in bottleneck areas

The influence of obstacle effects on personnel traffic flow is a hot topic in the evacuation field. However, research is lacking on the use of S-shaped guardrails in daily life. Based on previous studies, we placed two S-shaped guardrails in front of an exit. Thereafter, a real person evacuation experiment was designed, and 97 volunteers were recruited to the application of this structure in terms of crowd management and evacuation. The evacuation time, visual trajectory, spatial and instantaneous velocity, regional density, and other data were studied in detail. The study found that in the 97-person experiment, the addition of the S-shaped guardrails prolonged the evacuation time. Considering speed and density, the average instantaneous velocity of pedestrians in the structure was higher and maximum area density smaller. In addition, a phenomenon was observed in the study that large angle turns eradicated the zipper effect generated by a narrow channel width, preventing the accumulation of high density and pressure. This, is expected to provide some reference for channel design in real life.

Experimental Study of Flow Hydrodynamics Around Circular Cylinder Arrangements Using Particle Image Velocimetry

AbstractThis study investigates the turbulent flow properties experimentally in the vicinity of two side-by-side circular cylinders, along with the influence of the third cylinder of the same dimension placed in the upstream and successively in the downstream forming an equilateral triangle. Three-dimensional stereoscopic particle image velocimetry (PIV) was employed to collect the instantaneous velocity data around the arrangements. The study highlights the prime parameters of turbulence such as the mean velocities, Reynolds stresses, turbulent kinetic energy (TKE), quadrant analysis, and Q-criteria for vortices, which are responsible for the development of various problems such as scour-hole around the cylindrical pier arrangements, disturbance around industrial and marine structures. The spectral analysis was performed to examine the energy distributions, vortex-shedding frequencies with corresponding Strouhal numbers. Dominant vorticity locations were identified from the contours of Q-criteria. The magnitude of turbulence characteristics was reduced by 15–20% (turbulence intensity reduced by 20% and TKE by 15%) when the third cylinder was placed the upstream of side-by-side cylinder group. Streamlines are also studied to visualize the flow patterns for a better understanding of physics in the presence of the third cylinder. The maximum energy of vortices obtained from the spectrum analysis showed that the vortices generated were less when the third cylinder is placed upstream.

How fast is fast? Defining velocity zones in women’s rugby league

ABSTRACT Objectives The study aimed to: 1) apply a data-mining approach to identify velocity zone thresholds for female rugby league players and 2) apply these velocity zones to examine the locomotor demands of match-play. Methods Microtechnology data were collected from elite female rugby league players representing all National Rugby League Women’s teams (n = 85 players; n = 224 files) over one season. Spectral clustering with a beta smoothing cut-off of 0.1 was applied to each player’s instantaneous match-play velocity data for the identification of four zones. To account for outliers within repeated data-points, the velocity zones for each player were calculated as the median. The overarching velocity zones were determined through an incremental search to minimise the root mean square error. Results Through a data-mining approach, four velocity zones were determined. Rounded to the nearest 0.5 km.h−1 the velocity values across each zone were classified as low (<11.49 km.h−1), moderate (11.50 to 17.49 km.h−1), high (17.50 to 20.99 km.h−1) and very-high (>21.00 km.h−1). Practical application of the zones demonstrated positional group differences in the absolute (effect size (ES): 0.03 to 1.77) and relative (ES: 0.04 to 1.60) locomotor demands of match-play. The back positional group covered greater absolute and relative distances at a very-high velocity than all other positions. Conclusions This work informs the velocity zones that could be applied consistently to women’s rugby league data within practical (i.e., in the training and monitoring of players) and academic (i.e., as a model for future research to analyse locomotor demands) settings.

Does jumping conducted before the swimming start elicit underwater enhancement?

The effects of pre-activation exercises on undulatory underwater swimming (UUS) have not been studied. This research aimed to: 1) assess the effects of a jumping-exercise strategy upon UUS performance and kinematics variables; 2) test the different effects on males and females, and; 3) to explore if stronger participants exhibit greater post-activation performance enhancement (PAPE). Ninety-two age-group national level swimmers randomly assigned into control (17 males and 18 females) and experimental groups (27 males and 30 females) took part in a cross-sectional study designed to test two maximal 15-m UUS performance efforts. The experimental group performed four maximal tuck jumps before the first or the second UUS effort. Performance and kinematics variables were analyzed using instantaneous velocity data via speedometer. Maximal lower-limbs force was obtained during a countermovement jump through a linear-encoder. Two-way repeated measures ANOVA test and linear regression analysis were used to explore variable interactions between baseline and PAPE, and the association between the PAPE response and strength of the swimmers, respectively. Despite trends toward improvements in push-off velocity (Δ = 1.33%; d = 0.12), the results did not show enhancements nor deterioration in UUS performance and kinematics after the tuck jumps. No specific PAPE responses modulated by sex or by the strength level of the swimmers were observed for this age-group (p &lt; 0.05). Four tuck jump repetitions executed prior to diving could be insufficient to acutely enhance UUS performance. The fact that the exercise performed during warm-up was a body-weight based exercise, was possibly not enough to evoke PAPE.

Quantification of turbulent flow anisotropy in an alluvial channel mining pit

In this paper, turbulence anisotropy over a mining pit is studied. Laboratory experiment is performed in a flume with non-cohesive sand under steady flow condition. Two different geometric shaped mining pits, namely trapezoidal pit and irregular pit were excavated and instantaneous velocity data along the flow depth are taken at upstream, downstream and inside the mining pit. Turbulent anisotropy at various locations of the pit are compared. Stream-wise turbulence anisotropy is more in the upstream flow and nearly constant over the flow depth as compared to the other sections. For near bed flow in the pit, span-wise and vertical anisotropic contribution is more prominent as compared to the other components. Anisotropic invariant map (AIM) explains presence of two dimensional anisotropy near the bed for all the sections. It further illustrates the occurrence of two dimensional anisotropy in the outer flow zone in the pit. Mostly cigar shaped turbulence is observed in the upstream of the pit that changes to pancake shaped for near bed flow in the pit. At downstream of the pit, two dimensional anisotropy occurs near the bed and further it inclines to the three dimensional isotropy in the upper flow region.

Swimming Phase-Based Performance Evaluation Using a Single IMU in Main Swimming Techniques.

Comprehensive monitoring of performance is essential for swimmers and swimming coaches to optimize the training. Regardless of the swimming technique, the swimmer passes various swimming phases from wall to wall, including a dive into the water or wall push-off, then glide and strokes preparation and finally, swimming up to the turn. The coach focuses on improving the performance of the swimmer in each of these phases. The purpose of this study was to assess the potential of using a sacrum-worn inertial measurement unit (IMU) for performance evaluation in each swimming phase (wall push-off, glide, stroke preparation and swimming) of elite swimmers in four main swimming techniques (i.e. front crawl, breaststroke, butterfly and backstroke). Nineteen swimmers were asked to wear a sacrum IMU and swim four one-way 25 m trials in each technique, attached to a tethered speedometer and filmed by cameras in the whole lap as reference systems. Based on the literature, several goal metrics were extracted from the instantaneous velocity (e.g. average velocity per stroke cycle) and displacement (e.g. time to reach 15 m from the wall) data from a tethered speedometer for the swimming phases, each one representing the goodness of swimmer’s performance. Following a novel approach, that starts from swimming bout detection and continues until detecting the swimming phases, the IMU kinematic variables in each swimming phase were extracted. The highly associated variables with the corresponding goal metrics were detected by LASSO (least absolute shrinkage and selection operator) variable selection and used for estimating the goal metrics with a linear regression model. The selected kinematic variables were relevant to the motion characteristics of each phase (e.g. selection of propulsion-related variables in wall push-off phase), providing more interpretability to the model. The estimation reached a determination coefficient (R2) value more than 0.75 and a relative RMSE less than 10% for most goal metrics in all swimming techniques. The results show that a single sacrum IMU can provide a wide range of performance-related swimming kinematic variables, useful for performance evaluation in four main swimming techniques.

A Comparative Study between Sand- and Gravel-Bed Open Channel Flows in the Wake Region of a Bed-Mounted Horizontal Cylinder

In nature, environmental and geophysical flows frequently encounter submerged cylindrical bodies on a rough bed. The flows around the cylindrical bodies on the rough bed are very complicated as the flow field in these cases will be a function of bed roughness apart from the diameter of the cylinder and the flow velocity. In addition, the sand-bed roughness has different effects on the flow compared to the gravel-bed roughness due to differences in the roughness heights. Therefore, the main objective of this article is to compare the mean velocities and turbulent flow properties in the wake region of a horizontal bed-mounted cylinder over the sand-bed with that over the gravel-bed. Three experimental runs, two for the sand-bed and one for the gravel-bed with similar physical and hydraulic conditions, were recorded to fulfil this purpose. The Acoustic Doppler Velocimetry (ADV) probe was used for measuring the three-dimensional (3D) instantaneous velocity data. This comparative study shows that the magnitude of mean streamwise flow velocity, streamwise Reynolds normal stress, and Reynolds shear stress are reduced on the gravel-bed compared to the sand-bed. Conversely, the vertical velocities and vertical Reynolds normal stress are higher on the gravel-bed than the sand-bed.

Is the metabolic power paradigm ecologically valid within elite Gaelic football?

To examine the association between the metabolic power paradigm during training and match-play and objective aerobic fitness measures within elite Gaelic football players. Twenty-five elite Gaelic football players completed objective physiological testing for VO2max, vVO2max, Peak treadmill Velocity (PTV), Running economy (RE) and selected blood lactate concentrations of 2 mmol L−1 (S2) and 4 mmol L−1 (S4). Aerobic testing was performed at the start of the season and at the halfway point of the season. Training and match-play running performances were recorded across the period with global positioning system technology (GPS; 4-Hz; VX Sport, Lower Hutt, New Zealand). Instantaneous raw velocity data were obtained from the GPS and exported to a customised spreadsheet which provided estimations of total distance (m), high-speed running distance (m; 17 km h−1), very-high-speed running distance (m; 22 km h−1), total accelerations (n), acceleration distance (m), peak and mean velocity (km h−1). Furthermore, changes in velocity were analysed which allowed for the assessment of the metabolic power paradigm during these training and match-play events. Players average metabolic power (Pmet; W Kg−1) observed to have a large association with VO2max (r = 0.76–0.88) and velocity at VO2max (r = 0.72–0.91) in training and match situations. Interestingly, peak treadmill velocity showed a moderate association with training and match-play high metabolic power distance (r = 0.56–0.76). Large associations were observed between high power distance during match and training categories and velocity at VO2max (r = 0.76–0.89). Furthermore, high power distance was observed to have a large association with peak treadmill velocity (r = 0.72–0.91) in training and match situations with lactate variables showing a small to moderate association with metabolic power variables. The current investigation is the first to provide evidence towards the ecological validity of the metabolic power paradigm to assess aerobic fitness within elite Gaelic football. Practitioners should consider the association between aerobic fitness and specific metabolic load paradigm variables within their monitoring system as a potential means to understand the impact of training plans within elite Gaelic football players.