Boryi A. Becerra-Patiño, Juan D. Paucar-Uribe, Carlos F. Martínez-Benítez
et al.
<b>Background</b>: Some studies have suggested that physical fitness and body composition may influence individual and collective performance. However, it is necessary to be able to define the relationships between these variables in soccer players of different ages. <b>Objective</b>: To determine the relation between physical fitness level, body composition, and somatotype in female youth soccer players in response to age. <b>Materials and methods</b>: A total of 56 players were evaluated: 19 early adolescents (EA–U13) with a body mass of 48.35 ± 5.67 kg and a height of 157.63 ± 5.55 cm, 21 middle adolescents (MA–U15) with a body mass of 54.02 ± 5.96 kg and a height of 160.37 ± 5.25 cm and 16 late adolescents (LA–U17) with a body mass of 55.37 ± 6.15 kg and a height of 162.39 ± 5.77 cm. The physical fitness tests were: Squat Jump (SJ), Countermovement Jump (CMJ), Countermovement Jump with Arms (CMJA), Single Leg Countermovement Jump, COD-Timer 5-0-5, COD-Timer 5+5, Speed 15 m, Hamstring Strength, and Running-Based Anaerobic Sprint Test (RAST). The International Society for the Advancement of Kinanthropometry (ISAK) protocols were used to determine anthropometric measurements (skinfolds, circumferences, bone diameters), and the Heath-Carter method was used to assess body composition and somatotype, with z-scores calculated using the Phantom strategy. <b>Results</b>: The analysis revealed that the most significant differences between groups were observed in general anthropometric measurements (ω<sup>2</sup> = 0.84), followed by sitting height (ω<sup>2</sup> = 0.51) and percentage of body fat according to Carter’s method (ω<sup>2</sup> = 0.24), all with large and statistically significant effect sizes (<i>p</i> < 0.05). Larger muscle and bone dimensions, especially in the hip, thigh, and calf, are closely related to better strength, power, and initial sprint speed performance in female soccer players. <b>Conclusions</b>: This study reaffirms that muscle mass is a key predictor of athletic performance, along with strength at high speeds, promoting improvements in power and sprinting in the initial meters. Adiposity is a limiting factor for youth soccer players. Age progression and biological maturation favor the development of the mesomorphic profile, optimizing strength and power.
Mechanics of engineering. Applied mechanics, Descriptive and experimental mechanics
This paper investigates the influence of airfoil parameters on the cavitation performance of water jet propulsion pumps through numerical simulation methods. The effects of a varying inlet pressure and different airfoil structures on the critical net positive suction head (NPSH), head, and efficiency were systematically studied. Subsequently, the impact pattern of the airfoil structure on the cavitation performance was analyzed. The results demonstrate that the NACA0009-16_0004-16 airfoil exhibited the lowest required NPSH and superior cavitation resistance relative to the other tested airfoils. Nevertheless, the NACA0009-13_0004-13 airfoil demonstrated an optimal comprehensive performance, balancing the efficiency, head, and cavitation resistance. By extracting a water velocity isosurface of 23.6 m/s, we further investigated the flow characteristics of the suction surfaces of different airfoils at different cavitation conditions and found that the cavitation mainly includes TIP cavitation and sheet cavitation. With an increasing cavitation intensity, the sheet cavitation region progressively develops axially from the blade tip towards the blade outlet, extends radially from the shroud to the hub, and eventually nearly extends over the entire blade surface. The area of the TIP cavitation also expands, spreading downward in the same direction as the impeller rotation. The velocity vector exhibits a significantly higher density near the shroud and blade tips, suggesting potential flow separation and complex vortex structures in these regions. Near the blade leading edge, the water velocity isosurface area contracts, whereas near the trailing edge, it expands. These alterations indicate that the cavitation development modifies the flow field velocity distribution and adversely affects the impeller performance. This study establishes a theoretical foundation and offers practical guidelines for the multi-objective collaborative design of water jet propulsion pumps.
Thermodynamics, Descriptive and experimental mechanics
Parthasarathy Rajesh Kanna, Yaswanth Sivakumar, G. V. Durga Prasad
et al.
A numerical simulation of the circular cylinder as an obstacle in a double forward-facing (DFFS) step was performed. The size and position of the upstream cylinder (<i>c</i><sub>1</sub>) and downstream cylinder (<i>c</i><sub>2</sub>) were varied to explore their role in heat transfer in both laminar and turbulent conditions. Comparative results of the upper and lower half of the downstream cylinder were plotted as results to understand the heat transfer and flow characteristics around the downstream cylinder due to the effect of the upstream cylinder’s dimension and position. For <i>Re</i> = 800, when the <i>c</i><sub>1</sub> is placed near the bottom of the wall, it results in a pair of rear-side symmetrical vortices, and the <i>c</i><sub>2</sub> cylinder vortices become larger when the <i>c</i><sub>1</sub> is shifted towards the top wall. Additional flow separation happens adjacent to the steps when <i>c</i><sub>1</sub> is greater than <i>c</i><sub>2</sub>. These vortices strongly influence the convection heat transfer from the step. However, when Reynolds number (<i>Re</i>) is increased from 800 to 80,000, these vortices’ size is decreased. When <i>c</i><sub>1</sub> moves from 0.375<i>H</i> to 0.75<i>H</i>, the average Nusselt number is increased significantly. Moreover, a hike in <i>Re</i> results in a higher average Nusselt number irrespective of the position of obstacles. The upstream cylinder significantly enhances the Nusselt number when it is placed near the top wall rather than the bottom wall.
Thermodynamics, Descriptive and experimental mechanics
The triply periodic minimal surface (TPMS) is receiving much interest among researchers. The advantage of using this TPMS structure is the ability to design a structure based on engineering need. In the present context, experimental measurement was conducted and compared with numerical models using a foam porous medium and TPMS porous structure, leading to an accurate calibration of the model. A porous medium, metal foam, was heated experimentally at the bottom, and forced convection was investigated for different heating conditions. Then, the porous foam was replaced with a TPMS, and the experiment was repeated under similar conditions. The experimental data were compared with the numerical model using COMSOL software. Besides the model’s accuracy, the TPMS showed a uniform heating condition contrary to the metal foam case. At a later stage, the numerical model was used to investigate the importance of flow direction (two flow directions) in cooling hot surfaces. The first flow was parallel to the hot surface, and the second perpendicular to the hot surface. The TPMS structure was located on the top of the hot surface and acted as a fin in both cases. The Nusselt number exceeded 80 in the presence of the TPMS. As the porosity of the TPMS decreases below 0.7, a more considerable pressure drop is observed. The performance evaluation criterion was found to be greater than 70 when the porosity of the TPMS structure was 0.8.
Thermodynamics, Descriptive and experimental mechanics
Experimental and numerical investigations are conducted on a rotating disk from the perspective of convective heat transfer to understand the effect of heating on the stability of flow. A non-invasive approach with a thermal camera is employed to determine local Nusselt numbers for different rotational rates and perturbation parameters, i.e., the strength of the heat transfer. A novel transient temperature data extraction over the disk radius and an evaluation method are developed and applied for the first time for the air on a rotating disk. The evaluation method utilizes the lumped capacitance approach with a constant heat flux input. Nusselt number distributions from this experimental study show that there is a good agreement with the previous experimental correlations and linear stability analysis on the subject. A significant result of this approach is that by using the experimental setup and developed approach, it is possible to qualitatively show that instability in the flow starts earlier, i.e., an earlier departure from laminar behavior is observed at lower rotational Reynolds numbers with an increasing perturbation parameter, which is due to the strength of heating. Two experimental setups are modeled and simulated using a validated in-house Python code, featuring a three-dimensional thermal model of the disk. The thermal code was developed for the rotating disks and brake disks with a simplified geometry. Experimentally evaluated heat transfer coefficients are implemented and used as convective boundary conditions in the thermal code. Radial temperature distributions are compared with the experimental data, and there is good agreement between the experiment and the model. The model was used to evaluate the effect of radial conduction, which is neglected when using the lumped capacitance approach to determine heat transfer coefficients. It was observed that the radial conduction has a slight effect. The methodology and approach used in this experimental study, combined with the numerical model, can be used for further investigations on the subject.
Thermodynamics, Descriptive and experimental mechanics
The study of valve asymmetry represents an important avenue for modern cardiac surgery. The correct choice of leaflet reconstruction may indicate a new path in the quality and long-term survival of patients. A systematic investigation was performed with a total of 25 numerical simulations using a healthy ventricle and an ideal valve with varying degrees of valve asymmetry. An overall assessment is made in terms of vorticity, kinetic energy, dissipated energy, and hemodynamic forces. The results indicate that the optimal asymmetry to consider for a valve repair or prosthetic design is between 0.2 and 0.4 with an optimal point of about 0.3. Out of this range, the heart is subjected to an excessive workload, which can only worsen the patient’s state of health.
Thermodynamics, Descriptive and experimental mechanics
This study aims at numerically exploring the behavior of flow fields and nonlinear hydrodynamic coefficients of a horizontal cylinder beneath the free surface flow considering the effects of nonlinear surface waves and various cylinder shapes. The computational model is based on two-dimensional incompressible Navier-Stokes solvers along with the treatment of the free surface flow using the volume of fluid method. The effect of the turbulent flow is also considered by using the shear stress transport turbulence model. The simulation result of a benchmark case study of the submerged cylinder is first validated with available experiment data, where a mesh convergence analysis is also performed. Afterward, the flow fields and hydrodynamic force coefficients around the cylinder surface are analyzed, and the influences of various cylinder shapes and Reynolds numbers on the hydrodynamic coefficients are investigated. A state diagram representing the hydrodynamic behavior including stable and unstable stages is finally proposed; this is an important criterion for the practice design of submerged civil structures under the free surface flow.
Mechanical engineering and machinery, Descriptive and experimental mechanics
Alexey Savitskii, Aleksei Lobasov, Dmitriy Sharaborin
et al.
The present paper reports on the combined stereoscopic particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF) measurements of turbulent transport for model swirl burners without combustion. Two flow types were considered, namely the mixing of a free jet with surrounding air for different swirl rates of the jet (Re = 5 × 10<sup>3</sup>) and the mixing of a pilot jet (Re = 2 × 10<sup>4</sup>) with a high-swirl co-flow of a generic gas turbine burner (Re = 3 × 10<sup>4</sup>). The measured spatial distributions of the turbulent Reynolds stresses and fluxes were compared with their predictions by gradient turbulent transport models. The local values of the turbulent viscosity and turbulent diffusivity coefficients were evaluated based on Boussinesq’s and gradient diffusion hypotheses. The studied flows with high swirl were characterized by a vortex core breakdown and intensive coherent flow fluctuations associated with large-scale vortex structures. Therefore, the contribution of the coherent flow fluctuations to the turbulent transport was evaluated based on proper orthogonal decomposition (POD). The turbulent viscosity and diffusion coefficients were also evaluated for the stochastic (residual) component of the velocity fluctuations. The high-swirl flows with vortex breakdown for the free jet and for the combustion chamber were characterized by intensive turbulent fluctuations, which contributed substantially to the local turbulent transport of mass and momentum. Moreover, the high-swirl flows were characterized by counter-gradient transport for one Reynolds shear stress component near the jet axis and in the outer region of the mixing layer.
Thermodynamics, Descriptive and experimental mechanics
As fish swim through a fluid environment, they must actively use their fins in concert to stabilize their motion and have a robust form of locomotion. However, there is little knowledge of how these forces act on the fish body. In this study, we employ a 3D immersed boundary model to decode the relationship between roll, pitch, and yaw of the fish body and the driving forces acting on flexible fish bodies. Using bluegill sunfish as our representative geometry, we first examine the role of an actuating torque on the stability of the fish model, with a torque applied at the head of the unconstrained fish body. The resulting kinematics is a product of the passive elasticity, fluid forces, and driving torque. We then examine a constrained model to understand the role that fin geometry, body elasticity, and frequency play on the range of corrective forces acting on the fish. We find non-monotonic behavior with respect to frequency, suggesting that the effective flexibility of the fins play an important role in the swimming performance.
Thermodynamics, Descriptive and experimental mechanics
We present an overview of a modern, efficient approach for uncoupling groundwater–surface water flows governed by the fully evolutionary Stokes–Darcy equations. Referred to as non-iterative partitioned methods, these algorithms treat the coupling terms explicitly and at each time level require only one Stokes and one Darcy sub-physics solve, thus taking advantage of existing solvers optimized for each sub-flow. This strategy often results in a time-step condition for stability. Furthermore, small problem parameters, specifically those related to the physical characteristics of the porous media domain, can render certain time-step conditions impractical. Despite these obstacles, researchers have made significant progress towards efficient, stable, and accurate partitioned methods. Herein, we provide a comprehensive survey and comparison of recent developments utilizing these non-iterative numerical schemes.
Thermodynamics, Descriptive and experimental mechanics
An analysis of 2D subsonic flow over an NACA 0015 airfoil with a 30% trailing edge flap at a constant Reynolds number of 106 for various incidence angles and a range of flap deflections is presented. The steady-state governing equations of continuity and momentum conservation are solved combined with the realizable k-ε turbulence model using the ANSYS-Fluent code (Version 13.7, ANSYS, Inc., Canonsburg, PA, USA). The primary objective of the study is to provide a comprehensive understanding of flow characteristics around the NACA 0015 airfoil as a function of the angle of attack and flap deflection at Re = 106 using the realizable k-ε turbulence model. The results are validated through comparison of the predictions with the free field experimental measurements. Consistent with the experimental observations, the numerical results show that increased flap deflections increase the maximum lift coefficient, move the zero-lift angle of attack (AoA) to a more negative value, decrease the stall AoA, while the slope of the lift curve remains unchanged and the curve just shifts upwards. In addition, the numerical simulations provide limits for lift increment Δ C l and Cl, max values to be 1.1 and 2.2, respectively, obtained at a flap deflection of 50°. This investigation demonstrates that the realizable k-ε turbulence model is capable of predicting flow features over an airfoil with and without flap deflections with reasonable accuracy.
Thermodynamics, Descriptive and experimental mechanics