Times Of Velocity Research Articles

1216 固気二相粒子クラスター流動に及ぼす粒径の影響(離散粒子シミュレーションと実験による検証)(OS-3 分散相・連続相流れの相互作用問題(2))

Particle clusters formed in gas-solid flows in risers of circulation fluidized beds or pipes of pneumatic transport systems have much influence on various kinds of transport phenomena. In the present study, the structure of flow with particle clusters is investigated numerically. Especially effects of particle diameter on the cluster structure and the intensity of fluctuating velocity are studied. As a result, it was found that the scale of particle clusters increases with increasing particle diameter and that the intensity of streamwise fluctuating velocity is 0.5 to 1.3 times of the terminal velocity.

Effect of Key Process Variables on Microstructure of Injection Molded Microcellular Polystyrene Foams

The effect of control factors as key process variables on injection molds of microcellular plastics were investigated experimentally in this paper. The continuous foam processing system was constructed using screw preplasticating type injection mold machine, which is capable of supplying blowing agent, plasticity, kneading and keeping of retention time for gas/polymer solution. The propriety of foam processing system constructed in this study was verified. Control factors that affect cell nucleation and growth by injection molding were classified and some of them were considered in this study. In order to investigate cell morphology and cell structure, microcellular polystyrene samples were produced under various ranges in control factors by using the above processing system. In particular, the effect of injection velocity, mold temperature, retention time, plunger stroke and dwelling pressure on cell morphology of microcellular polystyrene were examined and discussed. It was found that cell size decreases and cell density increases with an increase in injection velocity. Cell size decreases about linearly with an increase in injection velocity and becomes about half size for five times of velocity. An increase rate of cell density is about ten times to five times of injection velocity.

1318 アブレシブウォータージェットの PIV 法による速度計測

Experimental studies are conducted to clarify the flow structure and velocity distribution of the abrasive water injection jet (AWIJ). The water velocity is obtained by the PIV method. It is shown that the water velocity decreases steeply with the slight addition of the abrasive. When the abrasive flow rate is relatively large, the water velocity is 0.2 to 0.4 times of the theoretical velocity calculated by Bernoulli's equation.

Analysis of plate wave propagation in anisotropic laminates using a wavelet transform

A new approach is presented for the analysis of transient waves propagating in anisotropic composite laminates. The wavelet transform (WT) using the Gabor wavelet is applied to the time-frequency analysis of dispersive flexural waves in these plates. It can be shown that the peaks of the magnitude of WT in a time-frequency domain is related to the arrival times of the group velocity. Experiments were performed using a lead break as the simulated acoustic emission source on the surface of unidirectional and quasi-isotropic laminates. A method was developed to obtain the group velocity of the flexural mode as a function of frequency. Theoretical predictions were made using the Mindlin plate theory, which includes the effects of shear deformation and rotatory inertia. Our predictions on the dispersion of the flexural mode showed good agreement with the experimental results.

Structure of High Intensity Turbulent Premixed Flames.

Direct numerical simulations of hydrogen-air turbulent premixed flames propagating in two-dimensional homogeneous isotropic turbulence are conducted to investigate the effects of turbulence intensity on the structure of turbulent premixed flames. Detailed kinetic mechanism including 12 reactive species and 27 elementary reactions is used to simulate H2-O2-N2 reaction in turbulence. DNS are conducted for the cases of turbulent intensities of 10.0, 20.0 and 30.0 times of the laminar burning velocity. Turbulent burning velocity increases with the increase of turbulence intensity. The flame fronts for the case of lowest turbulence intensity can be classified in the regime of 'wrinkled laminar flame', whereas those for the cases of higher turbulence intensities show the characteristics of 'distributed reaction zone'. The mean flame thickness increases and the mean heat release rate decreases with the increase of turbulence intensity. However, for the higher intensity cases, variances of local flame thickness and heat release rate become large where the minimum local flame thickness decreases and the maximum local heat release rate increases with the increase of turbulence intensity. The local flame thickness and local heat release rate are well correlated with the tangential strain rate at the flame front.

Wavelet analysis of plate wave propagation in composite laminates

A new approach is presented for the analysis of transient waves propagating in composite laminates. The wavelet transform (WT) using the Gabor wavelet is applied to the time–frequency analysis of dispersive plate waves. It is shown that the peaks of the magnitude of WT in the time–frequency domain are related to the arrival times of group velocity. Experiments are performed using a lead break as the simulated acoustic emission source on the surface of quasi-isotropic and unidirectional graphite/epoxy laminates. For predictions of the dispersion of the flexural mode, Mindlin plate theory is shown to give good agreement with the experimental results. The planar source location based on the flexural wave is performed using a triangulation method. The use of frequency-dependent arrival time of output signal and angular dependence of group velocity provides accurate results of source location for anisotropic laminates.

Pulsed discharge of a two-phase medium from a bounded duct capable of longitudinal motion

The regularities of the initial stage of discharge of a two-phase disperse medium from a bounded duct capable of longitudinal motion are established. Numerical results obtained within the framework of a medium with nonequilibrium for velocities and temperatures are compared with analytical solutions of the equilibrium mechanics of disperse systems for the case where the characteristic time of the process is of the order of the characteristic times of velocity and thermal relaxation or smaller.

Anisotropy of MHD Homogeneous Turbulence. 2nd Report. Coherent Fine Scale Eddies and Lorentz Force.

Fine scale structure in MHD homogeneous turbulence is investigated to clarify the relationship between anisotropy and coherent fine scale structure in turbulence. In MHD turbulence, mean diameter of the coherent fine scale eddy is about 10 times of Kolmogorov micro scale and maximum azimuthal velocity is about 0.7 times of umrs, which coincide with those in homogeneous isotropic turbulence, turbulent mixing layer and turbulent channel flows without magnetic field. Effect of magnetic field appears in angle distribution of axis of the coherent fine scale eddy. The coherent fine scale eddy perpendicular to the mean magnetic field decays fast due to strong Lorentz force, which results in anisotropic behaviors of MHD homogeneous turbulence.

Some aspects of the decay of convective turbulence

The decay of temperature and velocity fluctuations in a convective turbulent boundary layer over a heated surface in response to cooling at the surface was studied using a laboratory experiment. The time scale associated with cooling was greater than the relaxation time scale of turbulence, whereupon the convective layer responds to the changes of thermal forcing in a series of quasi-stationary steps. It was found that, when the cooling rate |d T s/d t| is maintained constant, the decay times of turbulent velocity and temperature fields, from the initiation of cooling, scale with Δ T 0/|d T s/d t|, where Δ T 0 is the temperature difference between the cooling surface and the mixed layer, irrespective of the Prandtl number. Mechanistic explanations are provided to describe the experimental observations. Geophysical relevance of the results is also discussed by considering the dissolution of the atmospheric convective boundary layer.

Velocity, acceleration and vorticity under a breaking wave

The fluid particle velocities in the overturning jet of a breaking wave have been measured by the Particle Image Velocimetry (PIV) technique. Monochromatic waves with wave height of 14.5 cm and wavelength of 121 cm were generated in the water depth of 20 cm. The measured fluid particle velocity at the tip of the overturning jet reached 1.68 times of the phase velocity calculated from the linear wave theory. Fluid particle accelerations were estimated from the velocity data with the following results: The overturning jet enters the horizontal water surface with an acceleration of 1.1 g at an angle of 88° downward. The PIV technique was also used to measure the instantaneous vertical vorticities generated by breaking waves. The number and locations of the vortices on the horizontal plane appear to be random. The maximum instantaneous vorticity was in the order of magnitude of 20–30 s−1, whereas the ensemble-averaged vorticity was quite small.

Human neutrophil motility: time-dependent three-dimensional shape and granule diffusion.

The locomotion of human polymorphonuclear leukocytes (PMNs) was studied with two complementary methods: Three-dimensional shapes were reconstructed from time series of optical sectioning microscopy using differential interference contrast (DIC) optics, and the diffusion of cytoplasm granules within individual cells was measured using quasielastic laser light scattering (QELS). The three-dimensional cell edges outlined in the optical sections were analyzed qualitatively in time-lapse film strips and quantitatively from morphometry. The fastest locomotion occurred in chemotactic gradient with cell velocity that oscillated between 10 and 30 microns/min with a period of 50-55 seconds. Within the periodic bursts of speed, a fibroblast-like locomotory cycle was observed, with leading lamella extended and contacts formed with the substrate surface, followed by rapid motion of the cell body and nucleus over the immobile contacts. Consistent with this apparent staged motion, correlation analysis revealed a phase lag of 2-3 seconds in velocities between the bottom (ventral) and the top layers of the cell. In addition there was a tendency to a lower cell profile at times of higher velocity. The diffusion of natural cytoplasmic granules within resting PMNs was not affected by cytoskeleton disrupting drugs. During the stage of most rapid motion, when cytoplasmic streaming could be seen, diffusion of the granules decreased two- to 2.5-fold, and then returned to resting levels. These observations suggest that PMN locomotion consists of extensions near the surface to form forward contacts and then stiffening or possibly contraction of the cytoskeleton when the body of the cell is moved forward. Three-dimensional movies of PMN cells are included in the video supplement.

Efficient robot arm modeling for computer control

AbstractThis article presents a comparative study of the required number of arithmetic operations necessary for computing robot arm models using the Denavit‐Hartenberg symbolic notation and a proposed one. The proposed notation is based on the idea of describing the motion of a robot joint by a pair matrix and the geometry of a link by a shape matrix. This notation needs the use of two coordinate systems for each joint or link. The results prove that the proposed notation reduces the computation time of robot models. For a 6‐degrees of freedom robot arm, the computation times of kinematic position, velocity, and dynamic models are reduced respectively by 20%, 5%, and 2%, respectively. The two notations have the same effects on computing the inverse models. © 1993 John Wiley & Sons, Inc.

Wind velocity and algal crusts in dune blowouts

In two saucer-shaped blowouts wind velocity was measured at 0.18 m height and compared to the wind velocity data from the nearest standard meteorological station at Valkenburg about 3.5 km to the northeast. In blowout 1 relative velocities are highest when the wind blows from directions between E and SSE. In blowout 2 winds blowing from directions between S and WSW are relatively stronger. In general the wind speed increases as its moves along the surface inside the blowout, because the aerodynamic roughness of the blowout surface is less than that of the surrounding area. Less important are the influence of the configuration of the terrain surrounding the blowout and the influence of the slopes within the blowout. The frequency distribution of the general wind at Valkenburg is analysed and combined with the horizontal wind velocity pattern within blowouts. A simulation model, producing the spatial distribution of the wind power shows that the prevalence of algal crusts at the SW side of blowouts agrees well with the location which reaches the lowest wind power values. In other parts of the blowouts algal crusts are damaged by moving sand at times of high wind velocity.

Kinematic description of variability of fast movements: analytical and experimental approaches

Analysis of variability of fast aimed movements predicts the properties of trajectory variance. The analysis is based on a kinematic model with nonlinear changes in "internal time". The purpose of the work was to identify different sources of variability and their influence on the trajectory variance. An analytical expression for the speed-accuracy trade-off is introduced. Experiments were performed with subjects making single-joint elbow flexion movements over different distances as fast as possible with their eyes closed to memorized targets. Standard deviation of movement trajectory increased during the first part of the movement and subsequently decreased. The variance peaked after the time of peak velocity, close to the time of peak deceleration. A dependence of the trajectory variance on movement distance (speed-accuracy trade-off) was seen during the movement (at times of peak velocity and peak deceleration) but not after the movement termination. We conclude that the previously reported drop in the variability of movement trajectory during the deceleration phase does not necessarily mean a compensation by the control system but may result from purely kinematic properties of the movement. The importance of the time of measurement for analysis of the speed-accuracy trade-offs is emphasized.

The nucleus of the optic tract. Its function in gaze stabilization and control of visual-vestibular interaction.

1. Electrical stimulation of the nucleus of the optic tract (NOT) induced nystagmus and after-nystagmus with ipsilateral slow phases. The velocity characteristics of the nystagmus were similar to those of the slow component of optokinetic nystagmus (OKN) and to optokinetic after-nystagmus (OKAN), both of which are produced by velocity storage in the vestibular system. When NOT was destroyed, these components disappeared. This indicates that velocity storage is activated from the visual system through NOT. 2. Velocity storage produces compensatory eye-in-head and head-on-body movements through the vestibular system. The association of NOT with velocity storage implies that NOT helps stabilize gaze in space during both passive motion and active locomotion in light with an angular component. It has been suggested that "vestibular-only" neurons in the vestibular nuclei play an important role in generation of velocity storage. Similarities between the rise and fall times of eye velocity during OKN and OKAN to firing rates of vestibular-only neurons suggest that these cells may receive their visual input through NOT. 3. One NOT was injected with muscimol, a GABAA agonist. Ipsilateral OKN and OKAN were lost, suggesting that GABA, which is an inhibitory transmitter in NOT, acts on projection pathways to the brain stem. A striking finding was that visual suppression and habituation of contralateral slow phases of vestibular nystagmus were also abolished after muscimol injection. The latter implies that NOT plays an important role in producing visual suppression of the VOR and habituating its time constant. 4. Habituation is lost after nodulus and uvula lesions and visual suppression after lesions of the flocculus and paraflocculus. We postulate that the disappearance of vestibular habituation and of visual suppression of vestibular responses after muscimol injections was due to dysfacilitation of the prominent NOT-inferior olive pathway, inactivating climbing fibers from the dorsal cap to nodulouvular and flocculoparafloccular Purkinje cells. The prompt loss of habituation when NOT was inactivated, and its return when the GABAergic inhibition dissipated, suggests that although VOR habituation can be relatively permanent, it must be maintained continuously by activity of the vestibulocerebellum.

Rayleigh–Taylor stability for a normal shock wave–density discontinuity interaction

The solution for the perturbation growth of a shock wave striking a density discontinuity at a material interface is developed. The Laplace transformation of the perturbation results in an equation which has a simple solution for weak shock waves. The solution for strong shock waves may be given by a power series. It is assumed that the equation of state is that of an ideal gas. The four independent parameters of the solution are the ratio of specific heat for each material, the density ratio at the interface, and the incoming shock strength. Properties of the solution which are investigated include the asymptotic behavior at large times of the perturbation velocity at the interface, the vorticity near the interface, and the rate of decay of the solution at large distances from the interface. The last is much weaker than the exponential decay in an incompressible fluid. The asymptotic solution near the interface, in addition to a constant term, consists of a number of slowly decaying discrete frequencies. The number is roughly proportional to the logarithm of the density ratio at the surface for strong shocks, and decreases with shock strength. For weak shocks the solution is compared with results for an incompressible fluid. Only interface perturbation velocities which tend to zero at large times lead to a limited deformation of the interface. It is found that these are possible only for density ratios less than about 1.5.

Mechanisms of reduced left ventricular filling rate in coronary artery disease.

To identify mechanisms underlying slow left ventricular filling in coronary artery disease, left ventriculograms from 93 patients and 18 normal subjects were digitised frame by frame and global and regional function analysed. In 54 patients peak normalised filling rates were above the lower 95% confidence limit of normal (2 X 9s-1) and in 39 they were below. Patients with slow filling had a lower ejection fraction, a higher end systolic volume, and less overall shape index change, although a larger percentage occurred during isovolumic relaxation owing to asynchronous relaxation. Stroke volume was not significantly different. Slow outward wall motion was associated with increased cavity volume and systolic hypokinesis. Wall motion was also appreciably asynchronous, with wide spreads in the times of peak outward velocity and termination of rapid outward movement between regions. Early outward movement usually started in the anterior region, with peak velocity occurring before mitral valve opening, and significantly earlier than that in the apex or the inferior region. Ventricular oscillations occurred during filling in 23 patients. This asynchronous wall movement was unrelated to the distribution of coronary artery disease, systolic hypokinesis, or Q waves on electrocardiograms but was similar to that occurring in mitral stenosis. The main causes of slow left ventricular filling in patients with coronary artery disease appear to be (a) failure to achieve a normal low end systolic volume, with associated loss of physiological changes in left ventricular cavity shape, and (b) incoordinate wall motion during isovolumic relaxation which dissipates energy normally coupled to rapid ventricular filling. The resulting slow and asynchronous wall motion may have clinical implications especially when the time available for left ventricular filling is short.

Steady reflection, absorption and transmission of small disturbances by a screen of dusty gas

An analytical solution of a system of linearized equations for a gas–particle mixture is obtained for steady periodic motions. A finite volume fraction of particles and a continuous distribution of particle sizes are taken into consideration. It is shown that the effect of a continuous distribution of particle radii on the acoustic motions of a dusty gas is incorporated through only four integral quantities containing the relaxation times of the particle velocity and temperature, integrated over all particle sizes. This solution is applied to the problem of acoustic reflection, absorption, and transmission by a screen of dusty gas.

The Uplift of Unteraargletscher at the Beginning of the Melt Season—A Consequence of Water Storage at the Bed?

AbstractResults of systematic movement studies carried out by means of an automatic camera on Unteraargletscher since 1969 are discussed together with supplementary theodolite measurements made at shorter intervals and over a longer section of the glacier. In addition to the typical spring/early summer maximum of velocity known from other glaciers, an upward movement of up to 0.6 m has been recorded at the beginning of the melt season. It was followed, after a few fluctuations of the vertical velocity, by an equal but slower downward movement which continued at an almost constant rate for about three months. Possible explanations of the uplift are discussed, the most satisfactory explanation being water storage at the bed. The observations then suggest that this storage system is efficiently connected with the main subglacial drainage channels only during times of very high water pressure in the channels. Detailed measurements showed that the times of maximum horizontal velocity coincided with the times of maximum upward velocity rather than with the times when the elevation of the surveyed poles had reached a maximum. On the basis of the hypothesis of water storage at the bed this finding means that the sliding velocity is influenced mainly by the subglacial water pressure and the actual, transient stage of cavity development, while the amount of stored water is of lesser influence.

The Uplift of Unteraargletscher at the Beginning of the Melt Season—A Consequence of Water Storage at the Bed?

Abstract Results of systematic movement studies carried out by means of an automatic camera on Unteraargletscher since 1969 are discussed together with supplementary theodolite measurements made at shorter intervals and over a longer section of the glacier. In addition to the typical spring/early summer maximum of velocity known from other glaciers, an upward movement of up to 0.6 m has been recorded at the beginning of the melt season. It was followed, after a few fluctuations of the vertical velocity, by an equal but slower downward movement which continued at an almost constant rate for about three months. Possible explanations of the uplift are discussed, the most satisfactory explanation being water storage at the bed. The observations then suggest that this storage system is efficiently connected with the main subglacial drainage channels only during times of very high water pressure in the channels. Detailed measurements showed that the times of maximum horizontal velocity coincided with the times of maximum upward velocity rather than with the times when the elevation of the surveyed poles had reached a maximum. On the basis of the hypothesis of water storage at the bed this finding means that the sliding velocity is influenced mainly by the subglacial water pressure and the actual, transient stage of cavity development, while the amount of stored water is of lesser influence.