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Long time series of velocity profiles collected by up-looking acoustic profilers in the westernmost sill of the Strait of Gibraltar show an unexpected pattern in the deepest ∼80 m of the water column, consisting in an appreciable diurnal weakening of the measured horizontal velocity. A harmonic analysis performed on long time series reveals a surprising magnitude of S1 constituent (exactly 1 cpd of frequency) in the horizontal velocity and echo amplitude, which prevails over the rest of diurnal constituents within this depth range, including K1, despite being around 200 times smaller than it in the tide generating potential. High resolution echograms collected by a new instrument recently installed in the mooring line, point at the diel vertical migration of living acoustic scatterers (zooplankton) as the most reasonable cause. It provokes a nightly depletion of scatterers availability near the bottom, which is registered by the instrument as a nighttime weakening of the velocity, as well as an increase of its uncertainty, at the deepest part of the profile. Newly acquired high spatial resolution measurements of the velocity near the seafloor report intense currents which are incompatible with the ones produced by the scatterers scarceness. This result indicates an overall underestimation of the Mediterranean current in previous works of approximately 17% within the depth range of 280–360 m, which in turn translates into an underestimation of previously computed outflow of ∼5%. These new findings make it necessary the re-computation of all the near-20-year long (to date) series of Mediterranean outflow based on the observations collected at this sill of the Strait of Gibraltar. [ABSTRACT FROM AUTHOR]

Large roughness elements (LREs) play a crucial role in river and stream restoration, influencing flow patterns, inducing turbulence and enhancing habitat suitability. Despite their widespread use, uncertainties exist in the literature concerning the spatial variation of three-dimensional (3D) mean flow characteristics. This study attempts to address this gap by conducting a comparative analysis of three simplified LREs—quasi-spherical boulder, artificial vegetation patch, and wooden log—focusing on their effects on downstream mean flow characteristics. The findings of this research reveal notable deviations in streamwise, transverse, and vertical downstream velocity profiles for each LRE compared to reference velocity profiles. These deviations eventually tend to realign with the reference velocity profiles. Each LRE exhibited a distinctive trend for downstream depth-averaged velocity in each direction. The reach averaged shear velocity downstream of the boulder was the highest among the three LREs, followed by the wooden log and then the vegetation patch. The streamwise velocity profiles for each LRE do not adhere to the typical logarithmic velocity distribution of von Karman–Prandtl. Particularly, the wooden log generates the largest wake zone and exhibits a higher streamwise velocity deficit compared to other LREs. Moreover, it demonstrates the highest divergence from reference transverse velocity, resulting in an extended recirculation zone. These observations suggest that the use of wooden logs has the potential to enhance habitat diversity in natural streams and can be effectively integrated into stream restoration projects aimed at improving aquatic ecosystems, thereby contributing to the sustainable management of river environments. [ABSTRACT FROM AUTHOR]

Estimation of velocity profile within mud depth is a long-standing and essential problem in debris flow dynamics. Until now, various velocity profiles have been proposed based on the fitting analysis of experimental measurements, but these are often limited by the observation conditions, such as the number of configured sensors. Therefore, the resulting linear velocity profiles usually exhibit limitations in reproducing the temporal-varied and nonlinear behavior during the debris flow process. In this study, we present a novel approach to explore the debris flow velocity profile in detail upon our previous 3D-HBP-SPH numerical model, i.e., the three-dimensional Smoothed Particle Hydrodynamic model incorporating the Herschel-Bulkley-Papanastasiou rheology. Specifically, we propose a stratification aggregation algorithm for interpreting the details of SPH particles, which enables the recording of temporal velocities of debris flow at different mud depths. To analyze the velocity profile, we introduce a logarithmic-based nonlinear model with two key parameters, that a controlling the shape of velocity profile and b concerning its temporal evolution. We verify the proposed velocity profile and explore its sensitivity using 34 sets of velocity data from three individual flume experiments in previous literature. Our results demonstrate that the proposed temporal-varied nonlinear velocity profile outperforms the previous linear profiles. [ABSTRACT FROM AUTHOR]

This article presents an experimental study about boundary slippage on the film thickness of hydrodynamic lubrication (HL) using a custom‐made slider‐on‐disc bearing testing apparatus. The interfaces with different affinity were obtained by surface energy modification of sliders with various oleophobic coatings, which are characterised by their contact angle (CA) and contact angle hysteresis (CAH). To study the mechanism of interfacial slip on HL under different wettability constraints, the film thickness and velocity profiles under shear were measured using interference and fluorescence photobleached method, respectively. The results showed that the CAH could better characterise the influence of interface effect on the film thickness of HL, which was explained by the correlation between CAH and the interface potential barrier. Furthermore, it was found that the slip velocity increased with lubricant viscosity and shear rate, which can be explained by the spatial heterogeneity of the flow in conformal contact and the critical shear stress slip model. [ABSTRACT FROM AUTHOR]

Abstract The presence of particles on the surface of a tunnel slope renders it susceptible to erosion by water flow, which is a major cause of soil and water loss. In this study, a nonlinear mathematical model and a mechanical equilibrium model are developed to investigate the distribution of flow fields and particle motion characteristics of tunnel slopes, respectively. The mathematical model of flow fields comprises three parts: a runoff region, a highly permeable soil layer, and a weakly permeable soil layer. The Navier‒Stokes equation controls fluid motion in the runoff region, while the Brinkman‐extended Darcy equation governs fast and slow seepage in the highly and weakly permeable soil layers, respectively. Analytical solutions are derived for the velocity profile and shear stress expression of the model flow field under the boundary condition of continuous transition of velocity and stress at the fluid‒solid interface. The shear stress distribution shows that the shear stress at the tunnel‐slope surface is the largest, followed by the shear stress of the soil interface, indicating that particles in these two locations are most vulnerable to erosion. A mechanical equilibrium model of sliding and rolling of single particles is established at the fluid‒solid interface, and the safety factor of particle motion (sliding and rolling) is derived. Sensitivity analysis shows that by increasing the runoff depth, slope angle, and soil permeability, the erosion of soil particles will be aggravated on the tunnel‐slope surface, but by increasing the particle diameter, particle‐specific gravity, and particle stacking angle, the erosion resistance ability of the tunnel‐slope surface particles will be enhanced. This study can serve as a reference for the analysis of surface soil and water loss in tunnel‐slope systems.

We present a numerical study for Poiseuille and Couette as well as Taylor- Couette swirling flows. The governing equations of momentum and energy are transformed into coupled and nonlinear ordinary differential equations using similarity transformation and then solved numerically. We critically evaluate the effect of dimensionless pressure gradients on fluid velocity and observed that the velocity increases as the dimensionless pressure gradient increases. Couette flows are simulated in different scenarios, including top plate moving, bottom plate moving, and top plate moving in adverse pressure gradient conditions. In a third scenario, the flow velocity profile revealed a backflow regime (BFR). A simple schematic model is, therefore, proposed to explain the presence of BFR in the flow’s profile. Numerical and analytical solutions around the circular cylinder are presented. The marginal discrepancy between the analytical and numerical profiles is maximum at ~ 900 and 2700 degrees, which indicates that the chosen method is suitable and capable of reproducing engineering problems. Velocity magnitude and vector diagrams show that the cylinder shape was found to have a significant effect on the flow field. The velocity at the top and bottom of the cylinder is twice the velocity that seen away from the cylinder.

Introduction: While maximum strength diagnostics are applied in several sports and rehabilitative settings, dynamic strength capacity has been determined via the one-repetition maximum (1RM) testing for decades. Because the literature concerned several limitations, such as injury risk and limited practical applicability in large populations (e.g., athletic training groups), the strength prediction via the velocity profile has received increasing attention recently. Referring to relative reliability coefficients and inappropriate interpretation of agreement statistics, several previous recommendations neglected systematic and random measurement bias. Methods: This article explored the random measurement error arising from repeated testing (repeatability) and the agreement between two common sensors (vMaxPro and TENDO) within one repetition, using minimal velocity thresholds as well as the velocity = 0 m/s method. Furthermore, agreement analyses were applied to the estimated and measured 1RM in 25 young elite male soccer athletes. Results: The results reported repeatability values with an intraclass correlation coefficient (ICC) = 0.66-0.80, which was accompanied by mean absolute (percentage) errors (MAE and MAPE) of up to 0.04-0.22 m/s and =7.5%. Agreement between the two sensors within one repetition showed a systematic lower velocity for the vMaxPro device than the Tendo, with ICCs ranging from 0.28 to 0.88, which were accompanied by an MAE/MAPE of =0.13 m/s (11%). Almost all estimations systematically over/underestimated the measured 1RM, with a random scattering between 4.12% and 71.6%, depending on the velocity threshold used. Discussion: In agreement with most actual reviews, the presented results call for caution when using velocity profiles to estimate strength. Further approaches must be explored to minimize especially the random scattering. [ABSTRACT FROM AUTHOR]

A set of exact solutions is suggested for the Poisson equation in a plane region of a certain form for describing a flow of Newtonian incompressible liquid in a channel at low Reynolds numbers. The motion of an ideal liquid in a region bounded by a rotating contour, torsion of a rod, deflection of a membrane at zero displacement on the boundary of its region, and heating of a rod under certain conditions are equivalent to a mathematically formulated problem of such a flow. A possibility is demonstrated to construct approximate solutions to the said problem for certain sections of a channel, having a parabolic segment of the contour, using exact solutions to this problem. Examples are given for the construction of flow regions in a prismatic channel resting on a parabolic contour. [ABSTRACT FROM AUTHOR]

Recently, capacitive micromachined ultrasound transducers (CMUTs) with long rectangular membranes have demonstrated performance advantages over conventional piezoelectric transducers; however, modeling these CMUT geometries has been limited to computationally burdensome numerical methods. Improved fast modeling methods, such as equivalent circuit models, could help achieve designs with even better performance. The primary obstacle in developing such methods is the lack of tractable methods for computing the radiation impedance of clamped rectangular radiators. This paper presents a method that approximates the velocity profile using a polynomial shape model to rapidly and accurately estimate radiation impedance. The validity of the approximate velocity profile and corresponding radiation impedance calculation was assessed using finite element simulations for a variety of membrane aspect ratios and bias voltages. Our method was evaluated for rectangular radiators with width:length ratios from 1:1 up to 1:25. At all aspect ratios, the radiation resistance was closely modeled. However, when calculating the radiation reactance, our initial approach was only accurate for low aspect ratios. This motivated us to consider an alternative shape model for high aspect ratios, which was more accurate when compared with FEM. To facilitate the development of future rectangular CMUTs, we provide a MATLAB script that quickly calculates radiation impedance using both methods. [ABSTRACT FROM AUTHOR]

This paper proposes a method for solving the path planning problem for a collaborative robot. The time-optimal, smooth, collision-free B-spline path is obtained by the application of a nature-inspired optimization algorithm. The proposed approach can be especially useful when moving items that are delicate or contain a liquid in an open container using a robotic arm. The goal of the optimization is to obtain the shortest execution time of the production cycle, taking into account the velocity, velocity and jerk limits, and the derivative continuity of the final trajectory. For this purpose, the velocity profiling algorithm for B-spline paths is proposed. The methodology has been applied to the production cycle optimization of the pick-and-place process using a collaborative robot. In comparison with point-to-point movement and the solution provided by the RRT* algorithm with the same velocity profiling to ensure the same motion limitations, the proposed path planning algorithm decreased the entire production cycle time by 11.28% and 57.5%, respectively. The obtained results have been examined in a simulation with the entire production cycle visualization. Moreover, the smoothness of the movement of the robotic arm has been validated experimentally using a robotic arm. [ABSTRACT FROM AUTHOR]

In natural river systems, layered vegetation like grass, shrubs, and tall bushes greatly affects the biodiversity, morphological process, and distribution of nutrients and pollutants. Previously, the effects of uniform one-layered vegetation on the flow structure and hydrodynamics have been extensively studied. However, due to the complexity of flow dynamics in the vegetated channel, multiple-layered vegetation has rarely been investigated. This paper presents a novel experiment to show the effect of three-layered vegetation on open channel flow. It contributes to our understanding of the impact of vegetation locations and heights on the velocity and discharge distributions for a mixed vegetated channel flow. Velocities at different positions along a half cross-section were measured using a mini propeller velocimetry. Observed results showed that the velocity has a distinct profile directly behind vegetation and behind the vegetation gap. The overall trend has two specific inflections about one quarter below (0.75 z/h) or near the top of short vegetation (h): the velocity remains nearly constant in the bottom layer (z/h < 0.75) and then rapidly increases until the top of short vegetation; after a gradual increase, the velocity rapidly rises to the water surface. The velocities directly behind the vegetation in the middle-after-short vegetation arrangement increase much faster than those directly behind the vegetation in the short-after-tall arrangement. The results showed that the maximum zonal discharge for a channel with mixed-height vegetation is situated at the mid-section of each half-channel, i.e., the area from 1/6 to 1/3 width of channel away from the wall. This research will attain significant importance to the engineers and practitioners defining the ecological and riverine flow pattern in the presence of riparian vegetation disseminating nutrients, pollutants, and sediments. [ABSTRACT FROM AUTHOR]

In this study, the friction factor of a turbulent pipe flow for dried rice malt extract solutions was experimentally reduced to that of a Newtonian fluid. The friction factor was measured for four types of solutions at different culture times and concentrations. The results indicate that the experimental data points of the test solutions diverged from the maximum drag reduction asymptote at and above Re√f ≅ 200~250 and aligned parallel to those of Newtonian fluids. This drag reduction phenomenon differed from that observed in artificial high-molecular-weight polymer solutions, called Type A drag reduction, in which the drag reduction level is dependent on the Reynolds number in the intermediate region. This is classified as a Type B drag reduction phenomenon in biopolymer solutions and fine solid particle suspensions. The order of drag reduction corresponded to approximately 5–50 ppm xanthan gum solutions, as reported previously. Furthermore, the velocity profile in a turbulent pipe flow was predicted using a semi-theoretical equation in which the friction factors were determined using the difference between the experimental results of the tested solutions and Newtonian fluids. The results indicate considerable thickening of the viscous sublayer in the turbulent pipe flow of the test solutions compared with that of Newtonian fluids.

It is proposed to determine the main parameters of the structure of flows in objects by velocity profile without taking response curves using the indicator method in heat and mass transfer apparatuses and reactors. A formula is derived for calculating the variance (central moment of the second order) and the flow structure function for a half-open vessel. An algorithm is also proposed for calculating the average residence time, the Peclet number of longitudinal diffusion for a one-parameter diffusion model, the number of cells and the differential response function of a combined model with a sequential connection of ideal displacement and mixing zones for a cell model. Moreover, calculation of the distribution density of the differential and integral response curves corresponding to a given velocity profile is provided. [ABSTRACT FROM AUTHOR]

We present a numerical study for Poiseuille and Couette as well as Taylor- Couette swirling flows. The governing equations of momentum and energy are transformed into coupled and nonlinear ordinary differential equations using similarity transformation and then solved numerically. We critically evaluate the effect of dimensionless pressure gradients on fluid velocity and observed that the velocity increases as the dimensionless pressure gradient increases. Couette flows are simulated in different scenarios, including top plate moving, bottom plate moving, and top plate moving in adverse pressure gradient conditions. In a third scenario, the flow velocity profile revealed a backflow regime (BFR). A simple schematic model is, therefore, proposed to explain the presence of BFR in the flow's profile. Numerical and analytical solutions around the circular cylinder are presented. The marginal discrepancy between the analytical and numerical profiles is maximum at ~ 900 and 270° degrees, which indicates that the chosen method is suitable and capable of reproducing engineering problems. Velocity magnitude and vector diagrams show that the cylinder shape was found to have a significant effect on the flow field. The velocity at the top and bottom of the cylinder is twice the velocity that seen away from the cylinder. [ABSTRACT FROM AUTHOR]

This study delves into the characteristics of a water jet impacting a stationary target, employing Computational Fluid Dynamics (CFD) simulations conducted with ABAQUS/CFD 6.14. Inspired by an orthogonal cutting configuration of a Ti6AL4V alloy during high-pressure water jet-assisted machining, the paper investigates the effect of nozzle inclination angles ranging from 6° to 81°. Utilizing the Finite Volume (FV) method, the jet impacts the target with an initial velocity of 223 m/s through a 0.7 mm diameter nozzle, positioned 6 mm away from the target center. Additionally, simulations were conducted for a 23° inclined jet to analyze the influence of nozzle diameter 'D' across a range of 5 values from 0.3 mm to 1.1 mm, with a step of 0.2 mm. Turbulence phenomena are addressed using the K-ε model. Results indicate that a 23° inclination yields significant pressure values, enhancing chip fragmentation. Furthermore, recirculation phenomena intensify with inclination, highlighting the importance of nozzle diameter reduction for achieving a more laminar jet and precise injection, albeit with reduced cutting edge pressure. Moreover, the study introduces a novel approach to construct a new equivalent jet with modified boundary conditions to tackle fluid-structure coupling limitations, mitigating speed drops and turbulence phenomena. While thermal effects are excluded in this study, acknowledging the importance of sufficient cooling in machining operations, the findings provide valuable insights into the mechanical dynamics of machining processes. Additionally, the paper serves as a guideline for researchers, particularly those engaged in computational fluid dynamics within machining, shedding light on the underexplored area of numerical modeling of High-Pressure Lubrication (HPL) using software like Abaqus/CFD [ABSTRACT FROM AUTHOR]

This paper presents a discrete element method (DEM) study of confined shear flow to explore its nonlinear behavior. As a supplement to the analog experiments, the DEM simulation facilitates to capture of the behavior of confined shear flow and allows a detailed analysis of the microscopic mechanisms of granular matter. Using DEM, we perform a series of simulations with different boundary conditions applied during the shear processes. We first extend our understanding of the side friction effect in the confined shear flow, and the physical friction parameter of the sidewall is also evaluated to ensure the efficiency of simulation and its viability in subsequent studies. We then demonstrate how the velocity profile of the particle assemblage depends on the level of the overlying pressure and applied shear velocity. It is found that the linearized velocity profile is mainly generated by the enhancement of uniformity of the normal stress network in the spatial distribution. We specifically investigate the dilation within the particle assemblage and two distinct mechanisms emerged, which depend on the overlying pressure and the applied shear velocity, that is, the rate-dependent dilation and the rolling-induced densification. As a consequence, strong links have been built to demonstrate the underlying microscopic mechanisms that trigger the macroscopic nonlinear behaviors, including the velocity profile and the dilation. [ABSTRACT FROM AUTHOR]

The drag reduction of high molecular polymer solutions is well known as the Toms effect. The drag reduction can be divided into two types: Type A and B. Type A corresponds to the solutions of synthetic polymers such as polyethylene oxide or polyacrylic amide. In contrast, Type B corresponds to the solutions of biopolymers such as xanthan gum, guar gum, and polysaccharide. Experiments were performed to measure the friction factor and heat transfer coefficient for the aqueous suspensions of graphene oxide thin-plate particles. The results show that the complex fluids exhibit a Type B drag reduction phenomenon in the turbulent flow range. The onset point of the drag reduction was found to be R e f ≅ 260 for Cw = 0.1 wt%. This point increased compared to the experimental results for Cw = 0.5 wt% graphene oxide solutions that have been reported on drag reduction. The velocity profiles of the aqueous suspensions of graphene oxide thin-plate particles and the dried malted rice culture solutions classified as biopolymer were estimated from the experimental data of the friction factor. In general, aqueous suspensions of fine particles are characterized by an increase in the friction factor and the heat transfer coefficient as compared to water. However, the aqueous suspension of the graphene thin-plate particles produces the drag reduction of the friction factor and increases the heat transfer coefficient. Therefore, the experimental results obtained in this study show that graphene oxide shin-plate particle suspensions become a useful carrier for the cooling pipeline system. [ABSTRACT FROM AUTHOR]

In this study, flow behavior in a meandering channel was investigated experimentally and numerically. The experiments were carried out for nine different cases on a channel consisting of 180° and 120° angle bends following successively. Measurements were conducted employing Acoustic Doppler Velocimetry (ADV) at 13 different points in the inner, middle, and outer bends of the sections located at significant bends along the channel. Depth-averaged velocity, velocity profiles, bed shear stress, and turbulence kinetic energy parameters were considered to understand the flow behavior in the meandering channel. A 1:1 scale numerical model of the experimental setup was generated using the Computational Fluid Dynamics (CFD) method through the verified FLOW-3D software (HYDRO 2022R1). It was found to be successful in estimating all parameters and was capable of investigating the flow behavior in the meandering channel. Additionally, a mesh independence study was performed, and four different turbulence models were compared. As a result, as the flow encountered the first meander in the channel, secondary flow occurred, and lateral momentum transfer took place. Therefore, velocity increased by approximately 30% from the first meander of 180° angles to the second meander of 120° angles. Therefore, the most critical zone was the inner bend of the 120-angle meander. [ABSTRACT FROM AUTHOR]

In this study, the friction factor of a turbulent pipe flow for dried rice malt extract solutions was experimentally reduced to that of a Newtonian fluid. The friction factor was measured for four types of solutions at different culture times and concentrations. The results indicate that the experimental data points of the test solutions diverged from the maximum drag reduction asymptote at and above Re√f ≅ 200~250 and aligned parallel to those of Newtonian fluids. This drag reduction phenomenon differed from that observed in artificial high-molecular-weight polymer solutions, called Type A drag reduction, in which the drag reduction level is dependent on the Reynolds number in the intermediate region. This is classified as a Type B drag reduction phenomenon in biopolymer solutions and fine solid particle suspensions. The order of drag reduction corresponded to approximately 5–50 ppm xanthan gum solutions, as reported previously. Furthermore, the velocity profile in a turbulent pipe flow was predicted using a semi-theoretical equation in which the friction factors were determined using the difference between the experimental results of the tested solutions and Newtonian fluids. The results indicate considerable thickening of the viscous sublayer in the turbulent pipe flow of the test solutions compared with that of Newtonian fluids. [ABSTRACT FROM AUTHOR]

Approved medical face masks have been shown to prevent the spread of respiratory droplets associated with coronavirus transmission in specific settings. The primary goal of this study was to develop a new strategy to assess the filtering and transmissibility properties of medical- and non-medical-grade face masks. In this study, we designed and assessed the filtering efficiency of particles through six different masks with a diverse set of fabrics, textures (woven and non-woven), fiber diameters, and porosity. The filtering and transmissibility properties of face mask layers individually and in combination have been assessed using mathematical analyses and new experimental data. The latter provided velocity profiles and filtration efficiencies for which the data were shown to be predictable. The filtration efficacy and pressure drop across each fabric have been tested using an aerosol particle spray and scanning electron microscopy. To assess clinical significance, the temperature and humidity of the masks were tested on a group of healthy volunteers spanning various age ranges (9–79 years old), utilizing an embedded temperature sensor disc. Also, a mask filter model was developed using fluid dynamic simulations (Solidworks Flow) to evaluate the aerodynamic dispersion of respiratory droplets. Overall, the FFP2 and FFP3 masks demonstrated the highest filtration efficiencies, each exceeding 90%, a feature of multi-layered masks that is consistent with simulations demonstrating higher filtering efficiencies for small particles (<5 µm). The velocity and temperature simulations of all six masks revealed a low air velocity (~1 m/s) inside the mask and a temperature variation of approximately 3 °C during the breathing cycle. [ABSTRACT FROM AUTHOR]

Accurate simulation of the evolution of freak waves by the wave phase focusing method requires accurate linear and nonlinear properties, especially in deep-water conditions. In this paper, we analyze the ability to simulate deep-water focused waves of a two-layer Boussinesq-type (BT) model, which has been shown to have excellent linear and nonlinear performance. To further improve the numerical accuracy and stability, the internal wave-generated method is introduced into the two-layer Boussinesq-type model. Firstly, the sensitivity of the numerical results to the grid resolution is analyzed to verify the convergence of the model; secondly, the focused wave propagating in two opposite directions is simulated to prove the symmetry of the numerical results and the feasibility of the internal wave-generated method; thirdly, the limiting focused wave condition is simulated to compare and analyze the wave surface and the horizontal velocity of the profile at the focusing position, which is in good agreement with the measured values. Meanwhile the simulation of focused waves in very deep waters agrees well with the measured values, which further demonstrates the capability of the two-layer BT model in simulating focused waves in deep waters. [ABSTRACT FROM AUTHOR]

IntroductionWhile maximum strength diagnostics are applied in several sports and rehabilitative settings, dynamic strength capacity has been determined via the one-repetition maximum (1RM) testing for decades. Because the literature concerned several limitations, such as injury risk and limited practical applicability in large populations (e.g., athletic training groups), the strength prediction via the velocity profile has received increasing attention recently. Referring to relative reliability coefficients and inappropriate interpretation of agreement statistics, several previous recommendations neglected systematic and random measurement bias.MethodsThis article explored the random measurement error arising from repeated testing (repeatability) and the agreement between two common sensors (vMaxPro and TENDO) within one repetition, using minimal velocity thresholds as well as the velocity = 0 m/s method. Furthermore, agreement analyses were applied to the estimated and measured 1RM in 25 young elite male soccer athletes.ResultsThe results reported repeatability values with an intraclass correlation coefficient (ICC) = 0.66–0.80, which was accompanied by mean absolute (percentage) errors (MAE and MAPE) of up to 0.04–0.22 m/s and ≤7.5%. Agreement between the two sensors within one repetition showed a systematic lower velocity for the vMaxPro device than the Tendo, with ICCs ranging from 0.28 to 0.88, which were accompanied by an MAE/MAPE of ≤0.13 m/s (11%). Almost all estimations systematically over/ underestimated the measured 1RM, with a random scattering between 4.12% and 71.6%, depending on the velocity threshold used.DiscussionIn agreement with most actual reviews, the presented results call for caution when using velocity profiles to estimate strength. Further approaches must be explored to minimize especially the random scattering.

Abstract This study proposes an empirical model for preliminary wind‐resist design of downburst flow. Existing empirical models were compared with field data and found to underpredict horizontal wind speed below the height corresponding to the maximum radial velocity, due to the neglect of viscous effects and the evolution of vertical wind profiles along radial direction. To address these deficiencies, semi‐empirical piecewise functions including wall shear effects in the local turbulent boundary layer and interpolation functions were proposed to improve the accuracy of existing models. The wind profile based on Coles' theory was found to agree well with field data, with the parabola interpolation function being the most desirable. Using the proposed method, the vertical profile of horizontal wind speed at different local radial locations can be predicted for wind resist design given the inlet wind speed of the downburst flow. Overall, this model improves upon existing empirical models and allows for more accurate wind‐resist design.

As a typical nonlinear wave, forward-leaning waves can be frequently encountered in the near-shore areas, which can impact coastal sediment transport significantly. Hence, it is of significance to describe the characteristics of the boundary layer beneath forward-leaning waves accurately, especially for the turbulent boundary layer. In this work, the linearized turbulent boundary layer model with a linear turbulent viscosity coefficient is applied, and the novel expression of the near-bed orbital velocity that has been worked out by the authors for forward-leaning waves of arbitrary forward-leaning degrees is further used to specify the free stream boundary condition of the bottom boundary layer. Then, a variable transformation is found so as to make the equation of the turbulent boundary layer model be solved analytically through a modified Bessel function. Consequently, an explicit analytical solution of the turbulent boundary layer beneath forward-leaning waves is derived by means of variable separation and variable transformation. The analytical solutions of the velocity profile and bottom shear stress of the turbulent boundary layer beneath forward-leaning waves are verified by comparing the present analytical results with typical experimental data available in the previous literature. [ABSTRACT FROM AUTHOR]

This study proposes an empirical model for preliminary wind‐resist design of downburst flow. Existing empirical models were compared with field data and found to underpredict horizontal wind speed below the height corresponding to the maximum radial velocity, due to the neglect of viscous effects and the evolution of vertical wind profiles along radial direction. To address these deficiencies, semi‐empirical piecewise functions including wall shear effects in the local turbulent boundary layer and interpolation functions were proposed to improve the accuracy of existing models. The wind profile based on Coles' theory was found to agree well with field data, with the parabola interpolation function being the most desirable. Using the proposed method, the vertical profile of horizontal wind speed at different local radial locations can be predicted for wind resist design given the inlet wind speed of the downburst flow. Overall, this model improves upon existing empirical models and allows for more accurate wind‐resist design. [ABSTRACT FROM AUTHOR]

A comprehensive understanding of velocity distribution is the fundamental information hydraulic engineers need to estimate an alluvial channel's discharge and stage characteristics. This study examines the Tsallis entropy approach for estimating streamwise velocity patterns in open channels. Entropy, which quantifies system uncertainty, has been applied in hydraulic research to account for variables such as shear strength, silt content, and flow velocities. However, its applicability to non-uniform channel sections remains unexplored. In the current work, the velocities estimation under various experimental conditions was calculated using the Tsallis entropy approach, wherein the random variable employed for constructing the velocity estimations was the time-averaged normalised velocity. This study considered two experimental conditions: (1) channels with attached spurs under seepage and non-seepage conditions and (2) channels with a 31-degree bank slope with and without an upstream pit. The velocity pattern obtained closely corresponds to the experimental data, exhibiting significant accuracy. However, it should be noted that the accuracy of the velocity pattern is slightly diminished in the region near the spur field when the y / D value is below 0.3. The difference can be caused by factors such as the area's non-uniform cross-section, sediment interaction along the bed, and secondary currents, which ultimately affect the velocity profile. [ABSTRACT FROM AUTHOR]

The steady pipe flow of thixotropic yield stress fluids has been investigated theoretically based on a modified isotropic kinematic hardening (mIKH) model. Analytical solution is derived for a specific case (m = n = 1) and a general semi-analytical solution is put forward as well. The effect of thixotropic yield stress on shear rate and velocity profiles is illustrated by comparing to other well-known solutions. Moreover, the influences of model parameters are examined. It is worth noting that shear banding may occur at the yielded surface in case of a sufficiently large Bingham number, thixotropic number, and flow index, but a sufficient small value of structure-related exponent. [ABSTRACT FROM AUTHOR]

ABSTRACTTriangular plan form weirs are one type of long-crested weirs. Therefore, they can pass more discharge capacity than weirs at the given channel width. This study aims to investigate the effects of different number of teeth (3, 4, and 5 teeth), angle of the weir tip (90, 60, 120, and 150 degrees), and the amount of different discharges (0.009–0.0063 m3/s) of sharp-crested triangular plan form weirs on the hydraulic parameters by using the Finite Volume Method (FVM). It was found that, increasing the effective length of the crest, increases the discharge coefficient up to 95% in the case with 5 teeth (L/B = 4.14 and h/W = 0.128), 45% in the case with 4 teeth (L/B = 3.71 and h/W = 0.168) and 39% for 3 teeth (L/B = 3.28 and h/W = 0.188) compared to the simple triangular plan weir (without teeth). Also, Results indicated that the discharge coefficient has an inverse relationship with the h/w ratio. In contrast, the investigations showed that the velocity in the flow jet is affected by the effective length of the triangular plan crest, and the increase in the effective length results in a decrease in the average velocity of the flow jet. So that these disturbances caused the highest dissipation of energy to occur in the triangular plan crest with 5 teeth (27% compared to the upstream section (Section 1) and 37% compared to the downstream section (Section 2)).

Hydraulic jump is used for dissipation of kinetic energy downstream of hydraulic structures such as spillways, chutes, and gates. In the present study, the experimental measurements and numerical simulation of the free hydraulic jump by applying Flow-3D software in six different conditions of adverse slope, roughness, and positive step were compared. It should be noted that two turbulence models including k-ε and RNG were used for numerical simulation. Based on the results, simulation accuracy using the RNG model was more than the k-ε model. The statistical indices of NRMSE, ME, NS, and R2 for comparing the water surface profile were obtained at 34.3, 0.0052, 0.995, and 983 for the application of the RNG model, respectively. Also, using the RNG model, the values of these indices for the velocity profile were obtained at 14.92, 0.127, 0.9982, and 962, respectively. In general, the error of the simulated water surface and velocity profile were obtained at 5.31 and 12.4 percent, respectively. Moreover, the maximum error of the numerical simulation results of D2/D1, Lj/D2, and Lr/D1 was ±12, ±12, and 16%, respectively. Therefore, the use of Flow-3D software with the application of the RNG turbulence model is recommended for numerical simulation of the hydraulic jump in different situations.

The aerodynamic interaction between the wake flow structure behind a single spire with a smooth wall boundary layer at a long streamwise location was observed in a wind tunnel experiment. The application of a single spire is intended to generate a wake flow similar to the one generated behind a skyscraper. A quarter elliptic wedge spire was used and a long streamwise distance of up to 26 times the spire’s height was adopted to ensure the development of the boundary layer and the wake recovery. To grasp how the smooth wall boundary layer interacts with the wake as well as how the wake recovers downstream, vertical and lateral velocity profiles were examined. Despite only one spire being utilized, it was found that the role of the spire as a vortex generator was confirmed the boundary layer height in the with-spire case increased compared to that of the without-spire case. Moreover, the velocity deficit recovery process was observed vertically and streamwise. However, within the boundary layer, the recovery rate in the streamwise direction was lower compared to the above it. This finding indicates that within the boundary, the turbulence generated can sustain the wake caused by the spire, reducing the recovery rate. Based on the current lateral velocity analysis, the final streamwise distance required by the wake to fully recover could not be predicted due to the large velocity deviation of 2.15% at the end of the streamwise distance.

Abstract Background Thermal diffusion of dusty fluids has valuable interference in various fields, including waste-water treatment, oil transportation, and power plant pipes. Dusty fluids are used in lots of industrial fields as a result of their improved heat transfer and heat management capabilities. These industries range from renewable energy systems to aerobic plastic sheet extrusion, manufacturing, and rolling and reaching metal sheet cooling. Results The work embodied in this paper presents the analytical solution performed to predict the effects of thermal diffusion on dusty, viscous, incompressible fluid flows between two porous, parallel vertical plates with a heat source or a heat sink. The mathematical equations are solved by the separation of variables and Laplace transform techniques. The influence of temperature is investigated for various values of Prandtl number and heat source or heat sink parameters. Also, the influences of various coefficients like the thermal diffusion coefficient, Schmidt number, Prandtl number, and heat source or heat sink coefficient on the concentration are observed. The fluid velocity distribution is graphically obtained. The solutions are discussed and exhibited graphically. The influences of the thermal diffusion parameter and chemical reaction parameter on fluid and dust particles’ velocities are examined. A parametric study on the effect of time on temperature and concentration is made. Conclusions The exact expressions for temperature, concentration, and velocity variation for fluid and dusty particles are obtained analytically. The temperature is inversely proportional to both the Prandtl number Pr and the heat source or heat sink parameter $$H_s$$ H s . The concentration of the fluid is inversely proportional to the thermal diffusion parameter Td and the heat source or heat sink parameter $$H_s$$ H s .

One of the challenges in using Manning’s equation lies in accurately determining Manning’s roughness coefficient, especially due to sediment transport. The condition of sediment transport within a specific section of a river can be in equilibrium, meaning that the amount of sediment entering and exiting the segment is balanced or it can be in non-equilibrium, where there is an imbalance between the sediment entering and leaving the segment. Experiments were carried out in the laboratory to simulate both transport conditions, one involving sediment feeding (equilibrium condition) and the other without sediment feeding (non-equilibrium condition). A total of 180 mean velocity profiles were measured using an acoustic doppler velocimeter (ADV) in fixed and movable bed flows. The present experiment was combined with theoretical approaches to evaluate Manning’s coefficient in open channels under sediment transport-flow conditions and reach conclusive results. The shape of the velocity profile, u/U, for flows over a movable bed with sediment feeding is “slender” compared to those without sediment feeding. The presence of sediment transport affects the shape of the velocity profile, especially in the inner region, influencing Manning's roughness coefficient. This coefficient can be determined from two-point velocity measurements at z/H = 0.1 and 0.2 for fixed and movable bed flows with and without sediment feeding, respectively. On average, sediment feeding increases the coefficient by 19% compared to the non-sediment feeding case. [ABSTRACT FROM AUTHOR]

The aerodynamic interaction between the wake flow structure behind a single spire with a smooth wall boundary layer at a long streamwise location was observed in a wind tunnel experiment. The application of a single spire is intended to generate a wake flow similar to the one generated behind a skyscraper. A quarter elliptic wedge spire was used and a long streamwise distance of up to 26 times the spire's height was adopted to ensure the development of the boundary layer and the wake recovery. To grasp how the smooth wall boundary layer interacts with the wake as well as how the wake recovers downstream, vertical and lateral velocity profiles were examined. Despite only one spire being utilized, it was found that the role of the spire as a vortex generator was confirmed the boundary layer height in the with-spire case increased compared to that of the without-spire case. Moreover, the velocity deficit recovery process was observed vertically and streamwise. However, within the boundary layer, the recovery rate in the streamwise direction was lower compared to the above it. This finding indicates that within the boundary, the turbulence generated can sustain the wake caused by the spire, reducing the recovery rate. Based on the current lateral velocity analysis, the final streamwise distance required by the wake to fully recover could not be predicted due to the large velocity deviation of 2.15% at the end of the streamwise distance. [ABSTRACT FROM AUTHOR]

The paper elaborates on experimental testing of the effect of the mixing chamber length of the cylindrical flow conditioner on the shape of velocity profiles in the downstream pipeline section. The study estimates the parameters of the assembly consisting of the cylindrical flow conditioner and the pipe section connecting it to the flow meter from the standpoint of its compactness. [ABSTRACT FROM AUTHOR]

The task of modeling the surface atmospheric boundary layer (ABL) in the wind turbine zone at the location of the Ulyanovsk wind farm is set. Reliable and accurate prediction of the evolution of ABL interacting with a wind farm over a wide range of spatial and temporal scales provides valuable quantitative information about its potential impact on the local meteorological situation and is of great importance for optimizing both the design (placement of turbines) and the operation of wind farms. The main problems of modeling and numerical investigation of the atmospheric boundary layer in combination with a wind turbine are considered. The main modeling problems include: multiscale, accounting for a highly rough inhomogeneous surface, wind irregularity in amplitude, direction and frequency, accounting for convection, solar radiation, stratification and phase transitions and precipitation, turbulence generation, and choice of modeling method and tool. The problem of multiscale research of the ABL-wind turbine system is considered and an overview of computational technologies for solving aerodynamic problems on the scale of one installation and wind farms is given. An analytical review of methods for modeling ABL and its interaction with a wind turbine is carried out. Approaches to the study of ABL based on systems of equations averaged by Reynolds, eddy-resolving models, and direct numerical modeling are considered; their advantages and limitations are given for solving the problem of studying the ABL–wind generator system. The mathematical model of the ABL–wind turbine system is described. The results of mathematical modeling and numerical study of the aerodynamics of the ABL–wind turbine system of the Ulyanovsk wind farm are presented, and numerical data on the attenuation of the aerodynamic wake behind the wind turbine and the restoration of the velocity profile, as well as on the friction resistance on the surface of the wind turbine blade, are obtained and analyzed. The analysis of the results of mathematical modeling of ABL in the wind turbine zone is carried out. [ABSTRACT FROM AUTHOR]

Accurate and reliable river discharge evaluation at a river station is an essential piece of information to obtain. This work modifies a power-law (PL)-based model and a single point velocity measurement (SPM) method for calculating channel discharge. Specifically, modifications are proposed for the constant shear velocity assumption, water surface effects, the underlying velocity distribution, and the number of measurements. A coefficient of water surface (cw) is proposed to consider the impact of water surface on distribution of velocity. Additionally, a power-wake-law (PWL) method is proposed to cope with the velocity dip phenomenon, where the maximum velocity occurs below the water surface. A critical assessment of the performance of the modifications using laboratory and field data is introduced. A trial-and-error procedure is applied to the laboratory data to obtain the value of the proposed coefficient cw and the parameters of PWL velocity distribution, α and β. It is found that cw=0.3 , α=1.5/m , and β=0.6 are the most appropriate values that produce minimum errors in most cases. A combination approach is applied to the field data to demonstrate the performance of the modifications and the impact of increasing the number of measurements. It is found that considering a water surface effect has significantly improved the accuracy. Also, it is found that the modified PL- and PWL-based models can estimate discharge with a reasonable accuracy using five measured velocimetry points in most tested cross-sections. In most studied rivers, the five-point combinations reduce the mean absolute percentage error (MAPE) value to less than 5%. [ABSTRACT FROM AUTHOR]

Since the existence of dunes in fluvial channels significantly alters near-bed flow structures, the related velocity profile is complex and different from that over a plane bed. To understand its average characteristics over a dune length, velocity distribution is analyzed preferably in a spatiotemporal or double-averaging manner. In this study, turbulent flow velocities over two-dimensional fixed dunes with smooth and rough surfaces are measured using particle image velocimetry (PIV). The data analysis shows that the double-averaged velocity profile generally comprises two layers, the first being linear near the bed and the second being logarithmic away from the bed. The two-layer velocity profile can be described using a unified formula, which is proposed by combining the linear and logarithmic laws in a power-sum fashion. The new formula is finally validated using the experimental data. As a prevalent bedform in fluvial and coastal environments, dunes have been a subject of research for decades. To appreciate the average characteristics of the flow over a dune-covered bed, it would be better to perform a proper average of measurements of flow fields in both time and space domains. Such an effort was made in the present study. With the measured data, we are able to develop a new approach for unifying the velocity distribution from the dune trough to the free water surface. This is done by combining logarithmic and linear laws in a power-sum form. Although conducting fine-scale field measurements of flows over dunes is still not easy at present, the formula proposed in this paper would be of great significance in estimating dune-affected flow velocity distributions, and thus helpful for understanding flow resistance, sediment transport, and river and coastal management. [ABSTRACT FROM AUTHOR]

The most popular way to transport natural gas is to use pipelines. However, complex spatial configuration of pipeline systems, as well as regulating devices and gate valves, break the uniformity and symmetry of the velocity profile, induce swirling flows, generate acoustic disturbance, and promote amplification of acoustic noise. It is almost impossible to estimate and take into account all these effects in gas metering. Therefore, the measurement uncertainty in complex conditions can be as high as 20%. It is reasonable to employ flow conditioners (FC) in order to increase the measurement accuracy. Their function is to form the flow with known characteristics. The existing FC models, however, were designed to deal with a limited set of flow histories and typically require calibration in combination with a flow meter. There are almost no FCs able to deal with a wide spectrum of flow histories and mitigate the effect of acoustics on the measurement accuracy. The study submits an approach to the design of the flow passage inside FC that addresses the described problems. The proposed FC has a cartridge containing a set of coaxial perforated streamwise cylinders nested within one another with a varied pitch along the diameter. An experimental model of the device demonstrated its effectiveness in velocity profile conditioning and reproducibility of profiles in steady and unsteady flows in pipelines of different spatial configurations. The Reynolds number range considered in the study spans from the lower threshold, at which the majority of flow meters operate, to the values at which the flow becomes self-similar. The acoustic efficiency was estimated for the frequency range of 5 Hz to 120 kHz. In general, the experimental model met all challenges successfully. At the same time, the shape of velocity profiles downstream of the device is somewhat different from the developed velocity profile in straight pipes. This problem will require optimization of the device geometry, which will be addressed in the future research. [ABSTRACT FROM AUTHOR]

Flow resistance in rivers with vegetation patches is one of the challenging parameters in river engineering. This study aimed to investigate the effect of vegetation patches on flow resistance in Shapur, Fahlian, and Dalaki rivers. The data measured in this study include velocity measurement, surveying, and bed sampling. In this study, considering the simplifying assumptions, the equation for the flow resistance due to vegetation patches was derivated. Accordingly, the flow resistance due to vegetation patches was obtained by the difference in the flow resistance due to bed from the value of the total flow resistance for each section. The results show that the average percentage of vegetation patches’ contribution from the total flow resistance is 44%, which shows the significant effect of vegetation patches on flow resistance. In addition, an investigation of 71 measured velocity profiles showed the phenomenon of Dip in the velocity profiles near the vegetation patches, and by moving away from the vegetation patches, the effect of this phenomenon is reduced and the profiles become S-shaped.

Approved medical face masks have been shown to prevent the spread of respiratory droplets associated with coronavirus transmission in specific settings. The primary goal of this study was to develop a new strategy to assess the filtering and transmissibility properties of medical- and non-medical-grade face masks. In this study, we designed and assessed the filtering efficiency of particles through six different masks with a diverse set of fabrics, textures (woven and non-woven), fiber diameters, and porosity. The filtering and transmissibility properties of face mask layers individually and in combination have been assessed using mathematical analyses and new experimental data. The latter provided velocity profiles and filtration efficiencies for which the data were shown to be predictable. The filtration efficacy and pressure drop across each fabric have been tested using an aerosol particle spray and scanning electron microscopy. To assess clinical significance, the temperature and humidity of the masks were tested on a group of healthy volunteers spanning various age ranges (9–79 years old), utilizing an embedded temperature sensor disc. Also, a mask filter model was developed using fluid dynamic simulations (Solidworks Flow) to evaluate the aerodynamic dispersion of respiratory droplets. Overall, the FFP2 and FFP3 masks demonstrated the highest filtration efficiencies, each exceeding 90%, a feature of multi-layered masks that is consistent with simulations demonstrating higher filtering efficiencies for small particles (