Velocity Vector Distribution Research Articles

Thermal Fluid Flow Transport Phenomenon in Unsteady Rotating Drumduring Spin‐Down Process

Numerical analysis is performed on unsteady‐state thermal fluid flow transport phenomena in a rotating drum heated at constant wall temperature during a spin‐down process. Emphasis is placed on the effect of aspect ratio of the drum on the velocity and temperature fields. The governing equations are discretized by means of a finite‐difference technique and numerically solved to determine the distributions of velocity vector and fluid temperature in the drum. It is disclosed from the study that (i) the formation of Ekman boundary layers on both sidewalls of the drum results in a pair of recirculating flows, and (ii) an attenuation of the flow velocity is affected by the aspect ratio of a drum. Results may be used to develop a method to achieve uniform mixing in an enclosed vessel.

Measurement of the spatial distribution of fluvial bedload transport velocity in both sand and gravel

AbstractMaps are presented of the spatial distribution of two‐dimensional bedload transport velocity vectors. Bedload velocity data were collected using the bottom tracking feature of an acoustic Doppler current profiler (aDcp) in both a gravel‐bed reach and a sand‐bed reach of Fraser River, British Columbia. Block‐averaged bedload velocity vectors, and bedload velocity vectors interpolated onto a uniform grid, revealed coherent patterns in the bedload velocity distribution. Concurrent Helley‐Smith bedload sampling in the sand‐bed reach corroborated the trends observed in the bedload velocity map. Contemporaneous 2D vector maps of near‐bed water velocity (velocity in bins centered between 25 cm and 50 cm from the bottom) and depth‐averaged water velocity were also generated from the aDcp data. Using a vector correlation coefficient, which is independent of the choice of coordinate system, the bedload velocity distribution was significantly correlated to the near‐bed and depth‐averaged water velocity distributions. The bedload velocity distribution also compared favorably with variations in depth and estimates of the spatial distribution of shear stress. Published in 2004 by John Wiley & Sons, Ltd.

Thermal characterisation of a direction dependent flow sensor

A calorimetric sensor for detection of gas velocity and flow direction was constructed by sacrificial porous silicon micromachining technique. The sensing element contains four temperature sensing resistors arranged symmetrically around a central filament heater. Finite volume flow simulations (FVM) for velocity vector and temperature distribution around the system elements led to the conclusion that the laminar flow conditions, essential for accurate calorimetric sensing, can be maintained by adequate selection of device dimensions and channel depth. Predictions by the flow and thermal simulations were aimed at defining the optimum geometric design. The results of functional tests performed on the fabricated structure were interpreted in terms of changes of parameters in the thermal equivalent circuit of the device.

足圧中心動揺の簡便な評価方法の提案

The aim of this study is to examine a method to evaluate the center of foot pressure (CFP) during a static upright posture using the following 4 body-sway factors: unit time sway, front-back sway, left-right sway and high frequency band power. Four body-sway factors were interpreted in a previous study by applying factor analysis to a correlation matrix consisting of 32 parameters representing 6 domains of distance, distribution of amplitude, area, velocity, power spectrum, and body sway vector. Data was gathered from 220 healthy young males and females. The CFP measurement for 1 min was carried out twice with 1 min rest. The measurement device was an Anima's stabilometer G5500. The data sampling frequency was 20 Hz.It was confirmed that 4 body-sway factors follow a normal distribution and their reliability is very high (ICC=0.89-0.95). After the distribution of each body-sway factor was divided into 4 domains (0-25% (A), 25-50% (B1), 50-75% (B2), and 75-100% (C)), each domain was subdivided into 4 categories. Boundary domains were made up between A and B (1), B (1) and B (2), and B (2) and C (AB, BB and BC). In analyzing trial-to-trial change for each factor, it was confirmed that 74% of the subjects (F3)-97% (Fl) belonged to the same domain. As a result of expanding the range of AB, BB and BC domains to determine each individual's pattern, 95% or more of the subjects could be placed by their positions on 2 trials. Based on the above-stated domain decision method, as a result of examining the change of body-sway for 20 subjects before and after alcohol intake, 65-75% of the subjects showed a domain change in each factor, and all had a body-sway pattern change.From the above, the convenient evaluation method of body-sway developed in this study was considered to have high reliability and validity, and can synthetically and simply evaluate individual body-sway.

Visualization of acoustic streaming produced by lithotripsy field using a PIV method

We visualized the acoustic streaming produced in water by an experimentallithotripter using a particle image velocimetry (PIV) method. Streaming generatedaround the beam focus has been optically visualized using light scattering particlesand was easily noticeable even with naked eye for all electrical settings of thelithotripter. Spatial distributions of velocity vectors are complicated and several localpeaks and vortices are observed. Measured streaming velocities are found to be inranges of 1.5 - 3 cm/s. It should be noted that the measured velocity was averagedover 1/30 sec, the time resolution limited by video frame rate, and the true velocity isexpected to be at least 10 times higher. Despite such an underestimation, it was shownthat the streaming velocity increased with voltage settings and, as predicted by theory,is proportional to intensity and closely related to the shock-wave pressures generated.In particular, the velocity has almost a linear correlation with peak-negative pressures(r = 0.98683, p = 0.0018). This suggests that the streaming velocity measured using thePIV technique can be used to estimate the generated peak-pressures without disturbingthe field.

Numerical analysis and experimental estimation of a low-leakage injection technique for capillary electrophoresis.

This paper presents an experimental and numerical investigation into the use of low-leakage injection techniques to deliver sample plugs within electrophoresis microchips. The study addresses the principal material transport mechanisms such as electrokinetic migration, fluid flow, and diffusion and gives detail analyses to the double-L injection technique, which employs electrokinetic manipulations to avoid sample leakage within the microchip. Electrical potential contour, velocity vector, and streamline distribution in the micro CE chip are successfully developed. Experimental and numerical testing results show the double-L injection technique is capable of reducing sample leakage within cross-form microfluidic chips. The current study confirms the double-L injection technique has an exciting potential for use in high-quality, high-throughput chemical analysis applications and in many other applications throughout the field of micro total analysis systems.

静的立位姿勢における足圧中心動揺変数相互の関係の検討―領域別及び性差の観点から―

This study examined the interrelationships between various parameters evaluating body sway from the center of foot pressure (CFP) during a static standing posture, and gender difference by domain. The subjects were 220 healthy young males and females. CFP was measured 3 times with a 1 min rest, and the mean of trials 2 and 3 was used for the analysis. The measurement device was Anima's stabilometer G-5500. Data sampling frequency was 20Hz. Sixty parameters with higher reliability were selected from the following 7 domains: distance, center average, distribution of amplitude, area, velocity, power spectrum, and body sway vector.Several parameters showed a significant gender difference, but the degree was not large. The correlation coefficients between parameters in each domain of distance, center average, distribution of amplitude, area, velocity, and body sway vector were very high, and they tended to relate closely to some parameters in the other domains. Gender difference in the correlation coefficient was insignificant. Therefore, the relationship between parameters in both genders was judged to be very similar.After examining the interrelationship between parameters, 36 parameters were selected. We judged that the body sway can be synthetically evaluated by these rather than 60 parameters.

Oblique Impact of a Spherical Projectile on Spherical Particulate Aggregation of Two-Dimensional Arrangement.

The dynamic response of two-dimensional particulate aggregation subjected to the oblique impact of a spherical projectile less than 15 m/s are investigated experimentally and also numerically by using discrete element method. The particulate aggregation is modeled by the 329 nylon spheres arranged regularly and two-dimensionally in a rectangular container. When the damping coefficient between particles is assumed to be in proportion to the contact force between particles, the numerical simulations agree well with the results measured by a high-speed video camera. The asymmetrical behavior of the particulate aggregation is explained by the distribution of velocity vector of individual particle and normal direction component of contact force between particles. The scattering behavior of particulate aggregation depends on the impact position of particulate aggregation and incident angle of projectile. It is found that the normal direction component of contact force between the base plate and the lowest layer of particulate aggregation shows dynamic M-shaped distribution under impact point.

B308 感染対応病室内の風速分布のニューラルネットベースト推定

Air conditioning in a hospital room must be very important to prevent infection. To design the air conditioning system, it is necessary to measure air flow distributions all over the room. The whole flow field measurement, however, is very difficult in a real space such as a hospital room. Air flow distributions are usually measured with some sensors whose measurement points are limited in a large space. It is required, therefore, to estimate an entire flow velocity vector field from limited measured vectors. One promising approach for the estimation is to make an appropriate model of the field by using measured information. In this paper the entire velocity vector distribution is reconstructed using an artificial neural network from the measured data. The concentration distribution in the room is calculated from the estimated velocity vectors and then is compared with the concentration data measured by using smoke.

Three-Dimensional Analysis of Flow and Heat Transfer of Thermal Plume in Stably Stratified Ambient (Flow Field)

The flow field of a three-dimensional, time-dependent thermal plume in stably stratified ambient above a heated square plate was elucidated by solving numerically governing equations. Phenomena characterizing this plume are as follows : (a) Velocity vectors on a horizontal plane above the heated plate have a X-shape distribution at any stratification. (b) The local Nusselt number distribution on the plate was affected by the X-shape distribution. (c) In Velocity vectors on the vertical plane, a V-shape occurred near the plate, and a horizontal imterface occurred between inward and outward flows. Time-dependency in the plume is resulted from instability near the front with negative buoyancy, and became weak with increasing stratification. At the extremely strong stratification, flow became steady state. The flow at strong stratification differed clearly from that at medium stratification as follows : At the medium stratification, the upward flow interfered with the stratified air, and a Π-shape of the velocity vector distribution occurred near the front. However, at strong stratification, the stratification effect is more dominant than the upward flow effect, and a Λ-shape occurred. With increasing stratification, the flow velocity near the plate became small, and the mean Nusselt number decreased.

風向正面の場合の通風気流に関する予測精度検証と流管分析 : LESと風洞実験による建物通風気流構造の解明に関する研究(第1報)

Airflow structure of a cross-ventilated model building for normal wind angle case was analyzed using Large Eddy Simulation. Simulated results were in close agreement with experimental observations in view point of flow rate, distribution of velocity vector and turbulence kinetic energy and wind pressure coefficients. Simulated results were analyzed, and it was elucidated that the downfall of the inflow specific to cross-ventilation is strongly affected by pressure gradient due to recirculation on the lower portion on the windward surface of the building. Further analysis was then made to identify shape of streamtube passing through windward opening. Spatial change of static, dynamic and total pressure along the identified streamtube indicated that strong acceleration and deceleration of the airflow does not exert significant change in total pressure at the upstream side of the opening, although energy is exchanged between static and dynamic pressure. This means that flow energy of the streamtube is virtually conserved at the upstream side of the opening, while energy loss occurs after passing through the opening due to the production of turbulence kinetic energy.

Numerical Analysis on Flow and Heat Transfer in an Axially Rotating Flow Passage with a Concentric Orifice

This paper deals with numerical analysis on steady-state incompressible laminar flow transfer in an axially rotating passage with a concentric orifice. Consideration is given to rotational effects on secondary flow and heat transfer in rotating flow passages. The governing equations are discretized by means of a finite-difference technique and numerically solved for the distributions of velocity vector and fluid temperature subject to constant wall temperature and uniform inlet velocity and fluid temperature. The Reynolds number and rotation rate are varied to determine their effects on both the formation of vena contracta and the heat-transfer performance behind the orifice. It is disclosed that: (i) for a laminar flow through a concentric orifice in a pipe, axial rotation causes the vena contracta in the orifice to stretch and amplifies the heat-transfer performance in the downstream region, and (ii) the elongation of the vena contracta and heat-transfer performance are enhanced with an increase in both the rotation rate and the Reynolds number. Results may find applications in automotive and rotating hydraulic transmission lines.

Impact Phenomenon of a Spherical Projectile on Particulate Aggregation. Simulation by Using Discrete Element Method and Experiment of Two-Dimensional Arrangement.

The dynamic responses of two-dimensional granular material subjected to the oblique impact and side impact of a spherical projectile are investigated experimentally and also numerically by using discrete element method. The granular material is modeled by the 329 nylon spheres arranged regularly and two-dimensionally in a rectangular container. The numerical simulations are carried out at the impact velocities less than 10 m/s. The numerical simulations are compared with the results of measurements using high-speed video camera. It is ascertained that the motion of each particle can be well simulated by discrete element method. The dynamic response of the particulate aggregation is elucidated by probing the distribution of velocity vectors of individual particle and normal direction component of contact forces between particles in detail. The effect of wave propagation on the shattering behavior of granular materials is manifested. It is found that the dynamic arching in granular material is formed just under impact point.

Discrete element simulation and experiment for dynamic response of two-dimensional granular matter to the impact of a spherical projectile

The dynamic response of two-dimensional granular matter subjected to the impact of a spherical projectile is investigated experimentally and also numerically using discrete element method (DEM). The granular matter is modeled by the mono-disperse aggregation of nylon spheres arranged regularly and two-dimensionally in a rectangular container. The numerical simulations are compared with the experiments using high-speed video camera for the impact velocity of about 10 m/s. It is shown that the motion of each particle can be well simulated by discrete element method. Also, the dynamic response of the particulate aggregation is elucidated in detail by inspecting the distribution of velocity vectors of individual particles and contact forces between particles, and very distinctive behaviors are found.

3-D Velocity Measurement of Natural Convection Using Image Processing.

This paper describes quantitative three-dimensional measurement method for flow field of a rotating Rayleigh-Benard convection in a cylindrical cell heated below and cooled above. A correlation method for two-dimensional measurement was well advanced to a spatio-temporal correlation method. Erroneous vectors, often appeared in the correlation method, was successfully removed using Hopfield neural network. As a result, calculated 3-D velocity vector distribution well corresponded to the observed temperature distribution. Consequently, the simultaneous three-dimensional measurement system for temperature and flow field was developed.

VIDEO IMAGE ANALYSIS OF OPEN CHANNEL TURBULENT FLOW

A longitudinal vertical cross-section of unsteady open channel flow was visualized by video camera. The 120 frames during 4 seconds in rising stage and the 120 frames during 4 seconds in falling stage were analyzed by cross-correlation method to obtain velocity vector distribution. The structure of large scale turbulence which drives longitudinal spiral motions were examined by using the obtained data.

Computer Simulation of Strong Ground Motion near a Fault Using Dynamic Fault Rupture Modeling: Spatial Distribution of the Peak Ground Velocity Vectors

Computer Simulation of Strong Ground Motion near a Fault Using Dynamic Fault Rupture Modeling: Spatial Distribution of the Peak Ground Velocity Vectors

Particle pairing using genetic algorithms for PIV

This paper presents a new particle pairing algorithm using "Genetic Algorithms" for DPIV (Digital Particle Image Velocimetry), which are searching algorithms for obtaining an optimal solution based on the mechanism of evolution. The particle pairing between two tracer images with a constant time interval is needed to obtain a velocity vector field. Since the algorithm adopts a fitness function which totally evaluates the similarity between respective small particle patterns in the two tracer images over the field, it promises to give a more correct velocity vector distribution than the conventional PTV (Particle Tracking Velocimetry) which identifies each particle based on its local information. In addition, a particle pattern matching for the similarity is performed after correcting fluid rotation. It therefore is robust against a high particle density and an increase in the time interval. The algorithm is applied to the PIV standard images distributed through the Internet (http://www.vsj.or.jp/piv). It gives a correct velocity vector distribution as a result even if a pair of the successive images has a large time interval.

Gas-flow measurements in a jet flame using cross-correlation ofhigh-speed-particle images

Temporal variations of a two-dimensional distribution of velocitiesin a nitrogen jet and a methane-jet flame are measured by cross-correlationparticle-image velocimetry (PIV). Two different approaches to investigatingthe turbulence characteristics are demonstrated. One gives the distribution ofensemble-averaged velocities and turbulence intensities by means of repetitivePIV measurements using a double-pulse laser for a longer period. The otherprovides the detailed motion of velocity profiles for a shorter duration,allowing one to analyse the characteristic scale of turbulence using ahigh-power continuous laser.The accuracy of measurements of the time-averaged velocity and turbulenceintensity is quantitatively assessed on the basis of the agreement with theresults from hot-wire-anemometry (HWA) measurement. This indicates thefeasibility of the PIV measurement, which may supply information aboutturbulence characteristics. From the measured results for a jet and a jettingflame, it is shown that the velocity gradient in the shear layer in thereacting zone is increased due to the local acceleration caused by buoyancy,resulting in higher turbulence intensities than those in a non-reacting jet.Also, from the change in the distribution of velocity vectors with time, it isclear that the turbulence eddies are carried downstream along the gas motionwith little transformation. The time scale of turbulence at each location inthe flow is obtained from the autocorrelation function of the velocityfluctuations. Furthermore, this can afford an estimate of the turbulencelength scale if one assumes that the Taylor hypothesis is valid and multipliesthe time scale and the time-average velocity. It is shown that thecharacteristic length scales of a flaming jet are about 1.5 times greater thanthose of a non-flaming jet. The effects of combustion on the turbulence in aflaming jet are discussed in detail on the basis of these experimentalresults.

Continuity-based and discontinuity-based segmentation in transparent and spatially segregated global motion

The mechanisms underlying the parsing of a spatial distribution of velocity vectors into two adjacent (spatially segregated) or overlapping (transparent) motion surfaces were examined using random dot kinematograms. Parsing might occur using either of two principles. Surfaces might be defined on the basis of similarity of motion vectors and then sharp perceptual boundaries drawn between different surfaces (continuity-based segmentation). Alternatively, detection of a high gradient of direction or speed separating the motion surfaces might drive the process (discontinuity-based segmentation). To establish which method is used, we examined the effect of blurring the motion direction gradient. In the case of a sharp direction gradient, each dot had one of two directions differing by 135°. With a shallow gradient, most dots had one of two directions but the directions of the remainder spanned the range between one motion-defined surface and the other. In the spatial segregation case the gradient defined a central boundary separating two regions. In the transparent version the dots were randomly positioned. In both cases all dots moved with the same speed and existed for only two frames before being randomly replaced. The ability of observers to parse the motion distribution was measured in terms of their ability to discriminate the direction of one of the two surfaces. Performance was hardly affected by spreading the gradient over at least 25% of the dots (corresponding to a 1° strip in the segregation case). We conclude that detection of sharp velocity gradients is not necessary for distinguishing different motion surfaces.