Mean Value Of Velocity Research Articles

The Force-Velocity Relationship in Older People: Reliability and Validity of a Systematic Procedure.

This study compared the reliability and validity of different protocols evaluating the force-velocity (F-V) relationship and muscle power in older adults. Thirty-one older men and women (75.8±4.7 years) underwent two F-V tests by collecting the mean and peak force and velocity data exerted against increasing loads until one repetition maximum (1RM) was achieved in the leg press exercise. Two attempts per load were performed, with a third attempt when F-V points deviated from the linear F-V regression equation. Then, the subjects performed 2×3 repetitions at 60% 1RM to compare purely concentric and eccentric-concentric repetitions. The Short Physical Performance Battery was conducted to assess the validity of the different protocols. Significant differences were found in maximal power (Pmax) between mean and peak values and between protocols differing in the number of attempts per load (p<0.01). Registering mean values, a third attempt, and multiple loads (>3), was significantly more reliable (Pmax: CV=2.6%; ICC=0.99) than the other alternatives. Mean values were also observed to be more associated with physical function than peak values (R2=0.34 and 0.15, respectively; p<0.05). No significant differences were observed between concentric and eccentric-concentric repetitions. Thus, collecting mean force and velocity values against multiple loads, while monitoring the linearity of the F-V relationship, seemed to be the more adequate procedure to assess the F-V profile and muscle power in older adults.

Transcranial Doppler Screening in 50 Patients With Sickle Cell Hemoglobinopathies in Iran.

As previous studies had discordant results with regard to the correlation of transcranial Doppler (TCD) screening and brain MRI, the aim of this study was to find the correlation between TCD values and silent ischemia in sickle cell disease (SCD) patients. In this cross-sectional study, 50 patients with proven diagnosis of sickle cell hemoglobinopathies based on their hemoglobin electrophoresis were included. Demographic data, their physical exam, information with regard to crises history, and their laboratory data were recorded. Brain MRI and TCD were requested for all patients. The mean age of the patients was 10.2±5.8 years. Only 3 patients (6%) showed evidence of ischemia on brain MRI. Normal and ischemic patients were not significantly different with respect to TCD values, sex, splenomegaly, aplastic crisis, and laboratory test results (P-value >0.05). Only platelet count was significantly higher in the ischemic group compared with that in the normal group (P=0.002). The pain crisis was significantly associated with the mean velocity values of RMCA, LMCA, RV, and LV arteries (P-value <0.05). On the basis of our results, there was no significant difference in the mean velocity TCD values between patients with and without evidence of ischemic brain damage in brain MRI. The frequency of silent ischemia was much lower than expected. Further studies with larger sample sizes are needed to elucidate the positive predictive value of abnormal TCD in the prediction of silent ischemia in patients with sickle hemoglobinopathy in certain ethnic groups.

Experimental-laboratory study of the flow around mussel shocks

The productivity in an organized mussel culture area is closely related to the hydrodynamics in the area where the mussel units are located. The interaction between the hydrodynamics and mussel farming in Chalastra (NW Thessalonikigulf) has been investigated during last decades. In the framework of the study of optimizing the quality of mussels production in mussel farming areas, a laboratory channel was designed, where the flow around and possibly through the mussel shocks would be studied in physical scale. The experiments were designed in physical/natural scale and the relevant variables were determined. Moreover, the specific positions for the measurements, the depth of the flow and the velocity currents were also determined. The following three mean velocity values of entrance water velocity U were used in the experiment; 5 cm/sec, 7 cm/sec and 9cm/sec. A basic research parameter used in the experiment was the distance between the mussel shocks. Four cases were taken into account: 300mm, 500mm, 700mm and 900mm. The final goal was the determination of the velocity field in the areas around the shocks. The velocity field was studied with the modern Particle Image Velocimetry technique. According to the above presented experiments, for distances between the shocks greater than 500 mm the velocity field is almost restored. Furthermore the case of larger distance between the shocks (i.e. 90cm) present the largest percentage of the velocity class 5-10cm/sec(occurring for entrance current velocities 7 and 9 cm/s)which seem to be the best range for mussel's growth.

Pola Arus Permukaan dan Kondisi Fisika Perairan di Sekitar Pulau Selayar pada Musim Peralihan 1 dan Musim Timur

&lt;strong&gt;Surface Current Pattern and Physics Condition of Waters Around Selayar Island in the First Transitional and Southeast Monsoons. &lt;/strong&gt; Seasonal observations of the flow of surface water and physics conditions around Selayar Island adjacent to Arlindo throughflow pathways of Makassar Strait have been conducted with a focus on the first transitional season and the southeast monsoon season. The purpose of this research is to obtain the pattern of seasonal surface current and physics characteristics of water column, i.e. temperature and salinity in Selayar Island waters during those seasons. The observations conducted on 22–27 May 2015 and 7–10 August 2015 illustrated the successive periods of the first transitional season and the southeast monsoon season. The methods used for taking oceanographic data such as temperature, salinity, and current were the stationary oceanographic measurement using CTD and currentmeter at 29 stations located in surrounding waters of Selayar Island. The surface current pattern generated from the interpolation process of the overall observation stations indicated that during the first transitional season the current moved eastward with an average velocity of 0.25 m/s. During the southeast monsoon season, the same pattern was still observed with a slightly higher average velocity of 0.26 m/s. The temperatures and salinity of Selayar Island waters during the southeast monsoon season were 2°C lower and 0.5 psu higher than during the first transitional season. Differences in mean current velocity values tended to be more affected by local tidal conditions. Different salinity was thought to be influenced by upwelling phenomena and local climatic factors such as rainfall, wind, and river flow discharge.

Comparative study of different subgrid-scale models for large eddy simulations of magnetohydrodynamic turbulent duct flow in OpenFOAM

Abstract Magnetohydrodynamic (MHD) turbulent duct flow has been numerically investigated using large eddy simulation (LES) method with different subgrid-scale models in OpenFOAM environment. Smagorinsky, dynamic Smagorinsky, and dynamic one equation eddy viscosity subgrid-scale models have been used to simulate MHD square duct flow with R e = 5681 . The results demonstrate that the average velocity and the turbulent kinetic energy obtained from the dynamic Smagorinsky subgrid-scale model agree well with those from direct numerical simulations (DNS). Furthermore, a MHD duct flow with R e = 29000 has been modeled using dynamic Smagorinsky subgrid-scale model. The results are compared with the results of coherent structure model. A good agreement in mean velocity values is observed. The agreement confirms that the dynamic Smagorinsky subgrid-scale model suitable for modeling MHD turbulent duct flows. Finally, LES with dynamic Smagorinsky subgrid-scale model has been used to simulate MHD flow in a square duct with electrically insulated walls with the same Reynolds number and different Hartmann number. The results for the mean velocity, velocity fluctuations and skin friction coefficient are presented. The laminar-turbulent transition parameters agree with the value given by Chaudhary's DNS results.

Numerical analysis of two experiments related to thermal fatigue

Abstract Jets in cross flow are of fundamental industrial importance and play an important role in validating turbulence models. Two jet configurations related to thermal fatigue phenomena are investigated: • T-junction of circular tubes where a heated jet discharges into a cold main flow and • Rectangular jet marked by a scalar discharging into a main flow in a rectangular channel. The T-junction configuration is a classical test case for thermal fatigue phenomena. The Vattenfall T-junction experiment was already subject of an OECD/NEA benchmark. A LES modelling and calculation strategy is developed and validated on this data. The rectangular-jet configuration is important for basic physical understanding and modelling and has been analyzed experimentally at CEA. The experimental work was focused on turbulent mixing between a slightly heated rectangular jet which is injected perpendicularly into the cold main flow of a rectangular channel. These experiments are analyzed for the first time with LES. The overall results show a good agreement between the experimental data and the CFD calculation. Mean values of velocity and temperature are well captured by both RANS calculation and LES. The range of critical frequencies and their amplitudes, however, are only captured by LES.

On the impact of non-Gaussian wind statistics on wind turbines – an experimental approach

Abstract. The effect of intermittent and Gaussian inflow conditions on wind energy converters is studied experimentally. Two different flow situations were created in a wind tunnel using an active grid. Both flows exhibit nearly equal mean velocity values and turbulence intensities but strongly differ in their two point statistics, namely their distribution of velocity increments on a variety of timescales, one being Gaussian distributed, and the other one being strongly intermittent. A horizontal axis model wind turbine is exposed to both flows, isolating the effect on the turbine of the differences not captured by mean values and turbulence intensities. Thrust, torque and power data were recorded and analyzed, showing that the model turbine does not smooth out intermittency. Intermittent inflow is converted to similarly intermittent turbine data on all scales considered, reaching down to sub-rotor scales in space. This indicates that it is not correct to assume a smoothing of intermittent wind speed increments below the size of the rotor.

Open Channel Flow Friction Factor: Logarithmic Law

ABSTRACT Lim, H.S., 2018. Open channel flow friction factor: Logarithmic law. The friction factor in open channel flow is considered to increase proportionally with wall roughness compared to that of pipe flow because of undulation at the free surface. The undulation is considered to be driven from the bottom and side walls. The increment factor associated with free surface undulation, shape distortion, and meandering is related to the Manning coefficient, and the incremented friction factor is substituted into the friction factor of circular pipe smooth (stretching) turbulent flow so as to yield the friction factor for open channel flow. The new equation for friction factor or mean velocity provides similar results to the Manning equation and the Ganguillet-Kutter (GK) equation for small streams. However, it is found that the Manning equation results in larger values of mean velocity in wide rivers compared with the GK equation and the new logarithmic equation based on the concept termed as “smooth turbu...

Automated Generation of Reliable Blood Velocity Parameter Maps from Contrast-Enhanced Ultrasound Data.

Objectives The purpose of this study was the automated generation and validation of parametric blood flow velocity maps, based on contrast-enhanced ultrasound (CEUS) scans. Materials and Methods Ethical approval for animal experiments was obtained. CEUS destruction-replenishment sequences were recorded in phantoms and three different tumor xenograft mouse models. Systematic pixel binning and intensity averaging was performed to generate parameter maps of blood flow velocities with different pixel resolution. The 95% confidence interval of the mean velocity, calculated on the basis of the whole tumor segmentation, served as ground truth for the different parameter maps. Results In flow phantoms the measured mean velocity values were only weakly influenced by the pixel resolution and correlated with real velocities (r2 ≥ 0.94, p < 0.01). In tumor xenografts, however, calculated mean velocities varied significantly (p < 0.0001), depending on the parameter maps' resolution. Pixel binning was required for all in vivo measurements to obtain reliable parameter maps and its degree depended on the tumor model. Conclusion Systematic pixel binning allows the automated identification of optimal pixel resolutions for parametric maps, supporting textural analysis of CEUS data. This approach is independent from the ultrasound setup and can be implemented in the software of other (clinical) ultrasound devices.

Transition to turbulent heat transfer in heated vertical channel - Scaling analysis

A thermally driven flow in a vertical channel with heated walls is studied through a scaling analysis and results are compared with the experimental data reported in [1]. As the geometry is symmetrical with respect to the vertical axis, the half-channel is considered. The domain is split into seven zones in which the flow behaviour results from a balance between several phenomena. This zonal analysis exhibits the main phenomena that drive the flow in each zone. The study leads to an expression of the wall temperature profile below and above the transition. An expression is given for the driving pressure that is found to increase along the channel. The increase rate is much more important above the transition due to the fluid heating in the center of the channel. Finally, The maximum Reynolds stress is expressed in terms of the mean velocity values and is found to fit well with the experimental data.

Heat stress has an effect on motility and metabolic activity of rabbit spermatozoa

In the warm months the function of the spermatozoa can be affected by the temperature of the reproductive tract of the female exposed to hyperthermic conditions. The aim of this study was to evaluate the impact of heat stress on sperm parameters in an in vitro model and to determine if there were seasonal effects on sperm heat tolerance. Sperm samples from 32 New Zealand White rabbits were collected in two seasons and incubated at scrotal (32.5°C), body (37°C) or hyperthermic (42°C) temperatures for 3h. Sperm viability and morphology were evaluated using nigrosin-eosin staining. Motility and metabolic activity parameters were determined using computer-assisted sperm analysis and the QBlue cell viability test, respectively. The incubation of spermatozoa at 42°C decreased (P<0.05) the mean values of total motility, curvilinear (VCL) and mean velocity (VAP) as well as the metabolic activity with respect to the incubation at 32.5°C and 37°C.No seasonal effects were observed except for the highest percentages of bent and coiled tails in the cold season, and the highest mean values of VCL, linear velocity and VAP in the warm season (P<0.01). The interaction between in vitro heat stress and season was significant for metabolic activity (P=0.02). Our results suggest that rabbit spermatozoa parameters are largely modified by a short exposure to hyperthermic conditions, in terms of metabolic activity and motility parameters. Thus, a short exposure of spermatozoa to an environment of 42°C in temperature for only 3h may compromise sperm functionality. Additionally, sperm metabolic activity is influenced by season.

Visualization of CSF Flow with Time-resolved 3D MR Velocity Mapping in Aqueductal Stenosis Before and After Endoscopic Third Ventriculostomy : AFeasibility Study.

The aim of this study was to evaluate timed-resolved three-dimensional (3D) magnetic resonance (MR) velocity mapping as amethod for investigation of cerebrospinal fluid (CSF) flow changes in patients with aqueductal stenosis (AS) treated by endoscopic third ventriculostomy (ETV). The MR velocity mapping was performed in 12AS patients before and after ETV and in 10 healthy volunteers by using a3-Tesla MR system. Time-resolved 3D MR velocity mapping data were acquired with astandard 3D phase contrast (PC) sequence with cardiac triggering. Values of mean (vmean) and maximum (vpeak) velocity were measured at several ventricular structures using dedicated software. Of the patients 11 showed asatisfactory clinical improvement after ETV, whereas one patient needed subsequent shunt implantation. All AS patients showed significant hypomotile CSF flow dynamics in the third ventricle when compared to healthy subjects before surgery (p< 0.05). In contrast, CSF flow velocity was increased within the Foramen of Monro in AS patients. After ETV, all AS patients showed adecrease of CSF flow dynamics within the third ventricle. Mean and peak CSF flow velocities through the ventriculostomy were 1.72± 0.59cm/s (vmean) and 3.53± 0.79cm/s (vpeak), respectively after ETV. The patient who needed shunt implantation after ETV had the lowest flow velocities through the ventriculostomy. This study demonstrates that timed-resolved 3D MR velocity mapping is auseful imaging investigation for diagnostics and follow-up in patients with AS. This new technique provides an insight into the physiological CSF flow changes related with AS and its treatment.

Heat transfer and flow structure of an impinging jet with upstream flow

In the present study, Particle Image Velocimetry and infrared thermography are used to investigate a jet issuing from a perforation with a crossflow on both sides of the perforated plate. This type of injection is typical of industrial applications such as combustion chamber or turbine blade cooling. The influence of five different parameters (Reu, e/D, Rej, Rec, H/D) has been considered. Due to the upstream flow influence, the injection flow is not axisymmetric: the highest mean velocity values are present in the lower part of the injection and on its sides forming a crescent shape jet with high velocity fluctuations in the jet core. The jet has global upward movement and its velocity rapidly decreases. Heat transfer rates resulting from its impingement are relatively low, compared to those of an academic jet issuing from a long tube. Moreover, Nusselt number distribution is not axisymmetric for low injection-to-plate spacing H/D. The injection Reynolds number and the injection-to-plate distance are the parameters with the greatest influence on heat transfer rates. Finally, correlations are deduced from heat transfer measurements.

Numerical and experimental investigation of turbulent three separated jets

In this work three-dimensional turbulent and separated jets are numerically studied and compared with experimental data. The basic idea of the separated jet burner consists in separating fuel and oxidizer injection to dilute reactants with combustion products before the reactants mix. The computation is achieved using the finite-volume numerical method. The turbulence is modeled using a second order Reynolds Stress Model (RSM) by Launder–Reece–Rodi. A non uniform grid is applied and particularly tightened close to the exit jets in order to capture the near field mechanisms. The validation of the numerical tools is done by comparison with experimental data of the non ventilated jets. Ventilated jets are investigated only numerically. The obtained results show that mixing is improved using three jets compared to the single jet. A comparison between computed ventilated and non ventilated jets is presented. It yields a larger velocity mean value, but a decreasing of the corresponding root mean square of the turbulent velocity fluctuations (rms).

Development of a tunable diode laser absorption sensor for online monitoring of industrial gas total emissions based on optical scintillation cross-correlation technique.

We report the first application of gas total emission using a DFB diode laser for gas concentration measurements combined with two LEDs for gas velocity measurements. In situ gas total emissions and particle density measurements in an industrial pipeline using simultaneous tunable diode laser absorption spectroscopy (TDLAS) and optical scintillation cross-correlation technique (OSCC) are presented. Velocity mean values obtained are 7.59 m/s (OSCC, standard deviation is 1.37 m/s) and 8.20 m/s (Pitot tube, standard deviation is 1.47 m/s) in a steel plant pipeline for comparison. Our experiments demonstrate that the combined system of TDLAS and OSCC provides a new versatile tool for accurate measurements of total gas emissions.

Use of cerebrospinal fluid flow rates measured by phase-contrast MR to differentiate normal pressure hydrocephalus from involutional brain changes

AimThe aim of our study was to assess the value of cerebrospinal fluid flow rates measured by phase-contrast MR in cases of normal pressure hydrocephalus (NPH) and to differentiate it from brain atrophy. Material and methodsA total of 26 participants were enrolled into this study, consisting of 15 patients considered to have NPH, 6 patients with atrophic dilatation of the ventricular system not proportional with cerebral sulci, and 5 control cases. All cases were studied using 1.5 T MRI scanner between January 2012 and June 2014. ResultsIn NPH patients with high stroke volume, we reported marked elevation of the systolic peak and mean velocity as well as stroke volume in comparison with healthy volunteers, indicating a hyperdynamic CSF circulation.On the other hand we studied six patients with involutional brain changes who were found to have non-statically significant lower systolic peak velocity, systolic mean velocity and stroke volume values in comparison with healthy volunteers indicating a hypodynamic CSF circulation and a diagnosis of atrophy. ConclusionThe mean CSF flow rate may be useful in the diagnosis and differential diagnosis, and the prediction of the potential benefits of surgical intervention for patients considered to have NPH.

An All-Time-Domain Moving Object Data Model, Location Updating Strategy, and Position Estimation

To solve the problems from the existing moving objects data models, such as modeling spatiotemporal object continuous action, multidimensional representation, and querying sophisticated spatiotemporal position, we firstly established an object-oriented all-time-domain data model for moving objects. The model added dynamic attributes into object-oriented model, which supported all-time-domain data storage and query. Secondly, we proposed a new dynamic threshold location updating strategy. The location updating threshold was given dynamically in accordance with the velocity, accuracy, and azimuth positioning information from the GPS. Thirdly, we presented several different position estimation methods to estimate the historical location and future location. The cubic Hermite interpolation function is used to estimate the historical location. Linear extended positioning method, velocity mean value positioning method, and cubic exponential smoothing positioning method were designed to estimate the future location. We further implemented the model by abstracting the data types of moving object, which was established by PL∖SQL and extended Oracle Spatial. Furthermore, the model was tested through the different moving objects. The experimental results illustrate that the location updating frequency can be effectively reduced, and thus the position information transmission flow and the data storage were reduced without affecting the moving objects trajectory precision.

Roughness sub-layer investigation of a turbulent boundary layer

ABSTRACTParticle image velocimetry (PIV) measurements at relatively low Reynolds numbers in a turbulent boundary layer over a three-dimensional roughened surface, consisting of pyramidal rows, have been presented. Measurements have been taken in a streamwise wall-normal plane intercepting the apex of a row of pyramids and the diagonal of the square base. The results shown in this paper point out the non-homogeneity of the flow in the roughness sub-layer. The different flow behaviour along the ascendant and the descendent part of the pyramids and in the region between two consecutive pyramids has been visualised. Low values of the streamwise component of the mean velocity and high values of the streamwise and wall-normal component of the Reynolds normal stresses, turbulent kinetic energy and Reynolds shear stresses are present in the downstream part of the pyramids, near their base. The mean representation of the flow shows swirling patterns in correspondence of the top of the pyramids. It is suggested that this representation is produced mainly by vortical structures travelling along the wall, retarded and intensified when interacting with the flow around the roughness element and by swirling patterns originating from the interaction of the incoming flow with the pyramids. In order to understand the origin of the high turbulence activity observed downstream the pyramids, near their base, a conditional analysis based on the quadrant method has been performed. It has been shown that sweep events are the major contributor to the very high values of the Reynolds shear stresses observed in this region and are due to the combination of the vortical flow at the top of the pyramid and a large scale (with respect to the roughness element) inflow motion.

Effect of temperature-dependent viscosity variation on fully developed laminar microconvective flow

The effects of temperature-dependent viscosity variation on fully developed flow through a micro-channel are numerically investigated in this work. The effects of μ(T) variation are able to couple the velocity and temperature fields. Therefore, the velocity and temperature profiles vary qualitatively along the micro-flow. Due to μ(T) variation, the concept of flow undevelopment (the reverse process of flow development) is observed in the flow regime. Four different flow regions have been observed in the flow regime and possible path is, developed → undeveloping → undeveloped → developing. In the vicinity of the inlet, the hydrodynamic undevelopment of flow (the reverse process of hydrodynamic development of flow) is represented by the distortion in axial velocity profile which is confirmed from ∂/∂z¯(∂u¯/∂r¯)w>0. The thermal undevelopment of flow (the reverse process of thermal development of flow) is expressed by the rapid enhancement in the convective heat transfer coefficient (h) along the flow due to significant flattening of the axial velocity profile. This study also investigates the Chilton–Colburn analogy for variable viscosity fluid at different mean velocities. The direct proportionality between the Chilton–Colburn j-factor for heat transfer, jH(=St·Pr2/3) and the skin friction coefficient (cf) is studied which shows the validity of the Chilton–Colburn analogy for variable viscosity fluid. It is observed that the Chilton–Colburn analogy is largely valid for lower values of mean velocity, but progressively fails as the mean velocity of the fluid increases. Additionally, the role of a modified non-dimensional parameter “ΠSμT” in flow friction is also investigated in this research.

Effects of Hand Placement Technique on the Video Head Impulse Test (vHIT) in Younger and Older Adults.

To investigate the effects of hand placement techniques on the video head impulse test (vHIT) responses (i.e., gain, velocity) in older and younger adults and to determine intra-rater and inter-rater reliability of the horizontal vHIT. Descriptive, reliability study. University research laboratory. Forty healthy adults grouped by age with negative history of current or previous vestibular diseases between the ages of 20 and 88 years (mean = 46.60, standard deviation 23.20). Three examiners each used two hand placement techniques (chin and head) to elicit the horizontal vHIT responses. Both the examiner and hand placement orders were counterbalanced to account for order and fatigue effects. The outcome measures of interest were vHIT gain and velocity. A two-way between-subject factorial analysis of variance revealed a significant main effect for hand placement technique and gain response. Mean values for vHIT gain were higher for head technique. Significant main effects were observed for the velocity response for hand placement technique and age group. Mean velocity values were higher for chin technique and lower velocities were observed in the older age group. Intra- and inter-rater reliability scores were consistent for gain values; however, poor to fair inter-rater reliability scores were observed for velocity values. It is suggested that clinical sites select one hand placement technique for the measure to provide consistency of protocol. Establishing clinical norms using the one selected method to verify reliability within and across clinicians is suggested before examination with a disordered population.