scholarly journals Measurements and numerical simulations of snow-particle saltation

1998 ◽  
Vol 26 ◽  
pp. 184-190 ◽  
Author(s):  
K. Nishimura ◽  
K. Sugiura ◽  
M. Nemoto ◽  
N. Maeno
Keyword(s):  
Friction Velocity ◽  
Laser Sheet ◽  
Impact Angle ◽  
Wind Tunnel Experiments ◽  
Mean Velocity ◽  
Measured Probability ◽  
The Mean ◽  
Snow Particle ◽  
The Relationship ◽  
Particle Saltation

First, wind-tunnel experiments were carried out to measure the trajectories of saltating snow particles with varying friction velocity. Trajectories of saltating particles were recorded by a video system with a laser sheet and trajectory statistics, such as ejection and impact velocities and angles, were obtained for each particle. Parabolic trajectories are considerably elongated with an increase in the friction velocity; impact angle was approximately the same but ejection angle decreased with increasing friction velocity. Furthermore, it should be noted that the gradient of flux decay with height decreased with friction velocity. In the experiments, a snow-particle counter, which can sense not only the number of particles but also their diameters, was introduced. The flux distribution and the transport rate obtained as a function of the particle size gave a new insight into the relationship with the friction velocity.Trajectories of saltating grains were computed, using the measurements of the initial ejection velocities, angles and the mean velocity profile of the air. The results agreed reasonably with our measurements. Using the measured probability distribution of the ejection velocities, an ensemble of trajectories was computed and thence the vertical profiles of stream-wise fluxes. The exponential decay of the flux on height was obtained in all cases and it supports the basic validity of the model, although agreement is less than expected.

scholarly journals Measurements and numerical simulations of snow-particle saltation

1998 ◽  
Vol 26 ◽  
pp. 184-190 ◽  
Author(s):  
K. Nishimura ◽  
K. Sugiura ◽  
M. Nemoto ◽  
N. Maeno
Keyword(s):  
Friction Velocity ◽  
Laser Sheet ◽  
Impact Angle ◽  
Wind Tunnel Experiments ◽  
Mean Velocity ◽  
Measured Probability ◽  
The Mean ◽  
Snow Particle ◽  
The Relationship ◽  
Particle Saltation

First, wind-tunnel experiments were carried out to measure the trajectories of saltating snow particles with varying friction velocity. Trajectories of saltating particles were recorded by a video system with a laser sheet and trajectory statistics, such as ejection and impact velocities and angles, were obtained for each particle. Parabolic trajectories are considerably elongated with an increase in the friction velocity; impact angle was approximately the same but ejection angle decreased with increasing friction velocity. Furthermore, it should be noted that the gradient of flux decay with height decreased with friction velocity. In the experiments, a snow-particle counter, which can sense not only the number of particles but also their diameters, was introduced. The flux distribution and the transport rate obtained as a function of the particle size gave a new insight into the relationship with the friction velocity.Trajectories of saltating grains were computed, using the measurements of the initial ejection velocities, angles and the mean velocity profile of the air. The results agreed reasonably with our measurements. Using the measured probability distribution of the ejection velocities, an ensemble of trajectories was computed and thence the vertical profiles of stream-wise fluxes. The exponential decay of the flux on height was obtained in all cases and it supports the basic validity of the model, although agreement is less than expected.

Experimental Investigation of a Turbulent Boundary Layer Subjected to an Adverse Pressure Gradient

2011 ◽  
Author(s):  
Takanori Nakamura ◽  
Takatsugu Kameda ◽  
Shinsuke Mochizuki
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Friction Velocity ◽  
Adverse Pressure Gradient ◽  
Turbulent Intensity ◽  
Mean Velocity ◽  
Law Of The Wall ◽  
Velocity Scale ◽  
The Mean ◽  
The Law

Experiments were performed to investigate the effect of an adverse pressure gradient on the mean velocity and turbulent intensity profiles for an equilibrium boundary layer. The equilibrium boundary layer, which makes self-similar profiles, was constructed using a power law distribution of free stream velocity. The exponent of the law was adjusted to −0.188. The wall shear stress was measured with a drag balance by a floating element. The investigation of the law of the wall and the similarity of the streamwise turbulent intensity profile was made using both a friction velocity and new proposed velocity scale. The velocity scale is derived from the boundary layer equation. The mean velocity gradient profile normalized with the height and the new velocity scale exists the region where the value is almost constant. The turbulent intensity profiles normalized with the friction velocity strongly depend on the nondimensional pressure gradient near the wall. However, by mean of the local velocity scale, the profiles might be achieved to be similar with that of a zero pressure gradient.

The Effects of Surface Roughness on the Mean Velocity Profile in a Turbulent Boundary Layer

2002 ◽  
Vol 124 (3) ◽  
pp. 664-670 ◽  
Author(s):  
Donald J. Bergstrom ◽  
Nathan A. Kotey ◽  
Mark F. Tachie
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Turbulent Boundary Layer ◽  
Velocity Profile ◽  
Friction Velocity ◽  
Outer Region ◽  
Stream Velocity ◽  
Mean Velocity ◽  
Outer Flow ◽  
The Mean

Experimental measurements of the mean velocity profile in a canonical turbulent boundary layer are obtained for four different surface roughness conditions, as well as a smooth wall, at moderate Reynolds numbers in a wind tunnel. The mean streamwise velocity component is fitted to a correlation which allows both the strength of the wake, Π, and friction velocity, Uτ, to vary. The results show that the type of surface roughness affects the mean defect profile in the outer region of the turbulent boundary layer, as well as determining the value of the skin friction. The defect profiles normalized by the friction velocity were approximately independent of Reynolds number, while those normalized using the free stream velocity were not. The fact that the outer flow is significantly affected by the specific roughness characteristics at the wall implies that rough wall boundary layers are more complex than the wall similarity hypothesis would allow.

scholarly journals Snow particle characteristics in the saltation layer

2014 ◽  
Vol 60 (221) ◽  
pp. 431-439 ◽  
Author(s):  
Christof Gromke ◽  
Stefan Horender ◽  
Benjamin Walter ◽  
Michael Lehning
Keyword(s):  
Particle Size ◽  
Particle Number ◽  
Particle Diameter ◽  
Wind Tunnel Experiments ◽  
Scale Parameters ◽  
Particle Characteristics ◽  
Maximum Particle ◽  
The Mean ◽  
Snow Particle ◽  
Measurement Area

AbstractShadowgraphy was employed to study snow saltation in boundary-layer wind tunnel experiments with fresh, naturally deposited snow. The shadowgraphy method allowed for a temporally and spatially high-resolution investigation of snow particle characteristics within a measurement area of up to 50 mm × 50 mm. Snow particle size and number characteristics, and their variation with height in the saltation layer, were analysed. The following observations and findings were made for the saltation layer: (1) the particle number decreases exponentially with height, (2) the mean particle diameter is fairly constant, with a very slight tendency to decrease with height, (3) the maximum particle diameter decreases linearly with height, and (4) the snow particle size distribution can be adequately described by gamma probability density functions. The shape and scale parameters of the gamma distribution were found to vary systematically, though only slightly, with height over ground and between experiments with different snowpack characteristics.

scholarly journals Relación entre la potencia y velocidad en press de banca y la velocidad de lanzamiento de balón en jugadores profesionales de balonmano (Relationship between barbell power and velocity in bench press exercise and ball throwing velocity in professional ha

Retos ◽  
2020 ◽  
pp. 53-59
Author(s):  
Iker Javier Bautista ◽  
Juan Vicente-Mampel ◽  
Luis Baraja-Vegas ◽  
Isidoro Martínez
Keyword(s):  
Bench Press ◽  
Average Power ◽  
Mean Velocity ◽  
Specific Performance ◽  
Relevant Variables ◽  
The Mean ◽  
Incremental Protocol ◽  
The One ◽  
The Relationship ◽  
Correlation Range

 Los objetivos de este estudio fueron (a) analizar la relación existente entre la una repetición máxima (1-RM) en press de banca y la velocidad de lanzamiento en jugadores de balonmano U18 de nivel internacional y, (b) analizar qué variables del ejercicio del press de banca son más relevantes en el rendimiento específico (velocidad de lanzamiento del balón) durante el test de velocidad de lanzamiento (T3-Step). Dieciséis jugadores de la Selección Española de Balonmano Juvenil participaron en la presente investigación. Todos los sujetos realizaron un protocolo incremental en el ejercicio del press de banca, además del T3-Step de velocidad de lanzamiento del balón. Por un lado, se analizó la relación existente entre la velocidad media (Velmedia), velocidad media de la fase propulsiva (VelMFP), velocidad pico (Velpico), potencia media (Potmedia), potencia media de la fase propulsiva (PotMFP), y potencia pico (Potpico) en todo el espectro de cargas en relación con la velocidad de lanzamiento. También se realizaron los mismos análisis con la carga en donde se obtuvo la máxima potencia media (CargaMP). Los resultados mostraron, por un lado que el rango de correlación de la CargaMP, PotmediaMP, PotMFPMP y PotpicoMP y la velocidad de lanzamiento fueron de .61 (p= .012), .702 (p< .01), .734 (p< .01) y .63 (p< .01), respectivamente. El coeficiente de correlación de Pearson entre la 1-RM y la velocidad de lanzamiento fue de r = .61 (p < .01). En conclusión, las variables relevantes a nivel de rendimiento específico con la velocidad de lanzamiento fueron la 1RM, la CargaMP, la PotMFPMP y la VelMFPMP. Todas estas analizadas en función del 60% de la 1-RM.  Abstract. The objectives of this study were (a) to analyze the relationship between one repetition maximum (1-RM) in free bench press exercise and ball throwing velocity in handball players U18 of international level and, (b) to analyze which variables of bench press exercise are more relevant in the specific performance during the ball throwing velocity test (T3-Step). Sixteen (n = 16) players of the Spanish Youth Handball Team participated in the present investigation. All subjects included performed an incremental protocol bench press exercise, in addition to the T3-Step. On the one hand, it analyzed the relationship between the mean velocity (Velmean), the mean velocity of propulsive phase (VelmeanPP), peak velocity (Velpeak), the average power (Powermean), the average power of the propulsive phase (PowermeanPP), and peak power (Powerpeak) over the entire spectrum of charges in relation to the launch speed. The same analyzes were also obtained with the load where the maximum average power (LoadMP). The results obtained, on the one hand that the correlation range of the LoadMP, PowermeanPP, PowerMPPMP and PowerpeakPP and ball throwing velocity were .61 (p = .012), .70 (p < .01), .73 (p < .01) and 0.63 (p < .01), respectively. The correlation coefficient between the 1-RM and ball throwing velocity was r = 0.61 (p< .01). In conclusion, the relevant variables at the specific performance level with the ball throwing velocity were 1-RM, LoadMP, PowerMFPMP and VelMFPMP. All these analyzed according to 60% of the 1-RM.

Analysis and modelling of anisotropies in the dissipation rate of turbulence

1997 ◽  
Vol 344 ◽  
pp. 155-180 ◽  
Author(s):  
CHARLES G. SPEZIALE ◽  
THOMAS B. GATSKI
Keyword(s):  
Transport Equation ◽  
Dissipation Rate ◽  
Algebraic Model ◽  
Scalar Dissipation ◽  
Mean Velocity ◽  
Production Term ◽  
New Model ◽  
Symmetry Properties ◽  
The Mean ◽  
The Relationship

The modelling of anisotropies in the dissipation rate of turbulence is considered based on an analysis of the exact transport equation for the dissipation rate tensor. An algebraic model is systematically derived using integrity bases methods and tensor symmetry properties. The new model differs notably from all previously proposed models in that it depends nonlinearly on the mean velocity gradients. This gives rise to a transport equation for the scalar dissipation rate that is of the same general form as the commonly used model with one major exception: the coefficient of the production term is dependent on the invariants of both the rotational and irrotational strain rates. The relationship between the new model and other recently proposed models is examined in detail. Some basic tests and applications of the model are also provided along with a discussion of the implications for turbulence modelling.

Verification of Fully Developed Flow Entering Diffuser and Particle Image Velocimetry Procedures

2013 ◽  
Vol 465-466 ◽  
pp. 1352-1356 ◽  
Author(s):  
Normayati Nordin ◽  
Zainal Ambri Abdul Karim ◽  
Safiah Othman ◽  
Vijay R. Raghavan
Keyword(s):  
Particle Image ◽  
Abrupt Change ◽  
Laser Sheet ◽  
Settling Chamber ◽  
Mean Velocity ◽  
Fully Developed Flow ◽  
3 Dimensional ◽  
Image Velocimetry ◽  
The Mean ◽  
Good Agreement

3-Dstereoscopic PIV is capable of measuring 3-dimensional velocity components. Itinvolves a very sophisticated routine during setup, calibration, measurementand data processing phases. This paper aims to verify the 3-D stereoscopic PIVmeasurement procedures and to prove that the flow entering thediffuser is a fully developed flow. A diffuser inlet of rectangularcross-section, 130 mm x 50 mm is presently considered. For verification, thevelocities from PIV are compared with the velocities from pitot static probeand theory. The mean velocity obtained using pitot static probe is 2.44 m/s,whereas using PIV is 2.46 m/s. It thus gives the discrepancy of 0.8%. There isalso a good agreement between the mean velocity measured by PIV and theoreticalvalue with the discrepancy of 1.2%. This minor discrepancy is mainly due touncertainties in the experiments such as imperfect matching of coordinatesbetween the probe and laser sheet, unsteadiness of flow, variation in density andless precision in calibration. Basically, the operating procedures of 3-Dstereoscopic PIV have successfully been verified. Nevertheless, the flowentering diffuser is not perfectly developed due to the imperfect joining ductand the abrupt change of inlet cross-section introduced. Therefore, improvementto the existing rig is proposed by means of installing settling chamber withmultiple screens arrangement and contraction cone.

Mean-flow scaling of turbulent pipe flow

1998 ◽  
Vol 373 ◽  
pp. 33-79 ◽  
Author(s):  
MARK V. ZAGAROLA ◽  
ALEXANDER J. SMITS
Keyword(s):  
Friction Factor ◽  
Friction Velocity ◽  
Outer Region ◽  
Reynolds Numbers ◽  
Velocity Profiles ◽  
Mean Velocity ◽  
Velocity Scale ◽  
The Mean ◽  
Log Law ◽  
High Reynolds

Measurements of the mean velocity profile and pressure drop were performed in a fully developed, smooth pipe flow for Reynolds numbers from 31×103 to 35×106. Analysis of the mean velocity profiles indicates two overlap regions: a power law for 60<y+<500 or y+<0.15R+, the outer limit depending on whether the Kármán number R+ is greater or less than 9×103; and a log law for 600<y+<0.07R+. The log law is only evident if the Reynolds number is greater than approximately 400×103 (R+>9×103). Von Kármán's constant was shown to be 0.436 which is consistent with the friction factor data and the mean velocity profiles for 600<y+<0.07R+, and the additive constant was shown to be 6.15 when the log law is expressed in inner scaling variables.A new theory is developed to explain the scaling in both overlap regions. This theory requires a velocity scale for the outer region such that the ratio of the outer velocity scale to the inner velocity scale (the friction velocity) is a function of Reynolds number at low Reynolds numbers, and approaches a constant value at high Reynolds numbers. A reasonable candidate for the outer velocity scale is the velocity deficit in the pipe, UCL−Ū, which is a true outer velocity scale, in contrast to the friction velocity which is a velocity scale associated with the near-wall region which is ‘impressed’ on the outer region. The proposed velocity scale was used to normalize the velocity profiles in the outer region and was found to give significantly better agreement between different Reynolds numbers than the friction velocity.The friction factor data at high Reynolds numbers were found to be significantly larger (>5%) than those predicted by Prandtl's relation. A new friction factor relation is proposed which is within ±1.2% of the data for Reynolds numbers between 10×103 and 35×106, and includes a term to account for the near-wall velocity profile.

scholarly journals A Comparison of Critical Velocity Estimates to Actual Velocities in Predicting Simulated Rowing Performance

2000 ◽  
Vol 25 (4) ◽  
pp. 223-235 ◽  
Author(s):  
Michael D.J. Kennedy ◽  
Gordon J. Bell
Keyword(s):  
Oxygen Consumption ◽  
Critical Velocity ◽  
Critical Speed ◽  
Critical Power ◽  
Aerobic Power ◽  
Maximal Oxygen Consumption ◽  
Mean Velocity ◽  
Rowing Performance ◽  
The Mean ◽  
The Relationship

The most accurate critical velocity (CV) estimate for the prediction of velocity during a simulated 2,000-m rowing race and the relationship to aerobic power were studied. Sixteen male rowers completed randomized maximal exertion trials (200, 400, 600, 800, 1,000, and 1,200 m), a maximal oxygen consumption [Formula: see text] on a Concept II rowing machine, and an actual 2,000-m simulated rowing race. Three mathematical models were applied to 4 rowing distance combinations producing 12 CV estimates. Seven of the 12 possible CV estimates were not significantly different from actual 2,000-m velocity. Comparison of the 3 CV models using all 6 trial distances revealed that the nonlinear model produced a CV estimate lower than the 2 linear CV models. CV was significantly correlated to [Formula: see text] (r = 0.91) and the mean velocity achieved during the 2,000-m simulated rowing race (r = 0.97). [Formula: see text] was significantly correlated to 2,000-m simulated rowing race velocity (r = 0.93). Key words: maximal oxygen consumption, critical power, critical speed

FIBRINOGEN DAN TRANSCRANIAL DOPPLER DI STROK ISKEMIK AKUT

2016 ◽  
Vol 21 (3) ◽  
pp. 280
Author(s):  
Hafizah Soraya Dalimunthe ◽  
Adi Koesoema Aman ◽  
Yuneldi Anwar
Keyword(s):  
Ischemic Stroke ◽  
Transcranial Doppler ◽  
Pearson Correlation ◽  
Control Group ◽  
Mean Velocity ◽  
Diastolic Velocity ◽  
Stroke Group ◽  
The Mean ◽  
And Control ◽  
The Relationship

Elevated fibrinogen levels is related to the blood hyperviscosity, that causes low blood velocity. Non-contrast-enhanced transcranial Doppler (TCD) is used to evaluate blood flow from the cerebrovascular system. To know the relationship between fibrinogen levels and examination of TCD in acute ischemic stroke through evaluation. A cross sectional study was admitted from July 2012-Juny 2013. The researchers determined the differences between fibrinogen and TCD in the stroke group and control. The researchers examined the relationship between fibrinogen and TCD examination in the stroke group. The fibrinogenwas measured with Clauss method. The TCD was examined due to middle of the cerebral artery (MCA) and the Internal Carotid one Artery (ICA). The patients were diagnosed as ischemic stroke from head CT-scan. Statistical analyses employed the Independent T test, Anova test and Pearson correlation. The researchers had 24 patients and 24 controls that the Fibrinogen levels in stroke group is 549.16±104.84 mg/mL and in the control group is 385.64±16.80 mg/mL. The researchers examined MCA in the stroke as well as the control and found the mean velocity 43.12±21.03and 56.97±6.22 (p=0.05), the peak velocity 74.17±32.58 and 94.55±14.11 (p=0.05) end diastolic velocity 23.27±12.66 and 35.30±7.34 (p=0.00). In ICA, the stroke group and control and found the mean velocity 31.40±8.86 and 43.07±8.06 (p=0.00), thepeak velocity 54.99±11.50 and 75.04±16.04 (p=0.00) end diastolic velocity 18.23±7.67 and 25.64±5.24 (p=0.00). The correlation between fibrinogen and TCD in the stroke group was not significant on MCA and ICA, P>0.05. It can be concluded that the differences between fibrinogen levels and TCD in the stroke group and control are significant. But there is no correlation between the fibrinogen and TCD in the stroke group.

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