Showing papers on "Velocity gradient published in 1973"

A Velocity Analogue of Brightness Contrast

Abstract: A velocity illusion is reported which is analogous to results obtained in the case of brightness contrast. When two targets move with the same velocity against a background of smaller moving dots which have a velocity gradient, the target which is moving faster than its immediate surround appears to move faster than the target which is moving slower than its immediate surround. Apparent velocity of a target therefore depends strongly on its velocity in relation to its immediate surround; we interpret this in terms of motion-sensitive cells which have center–surround antagonisms analogous to the physiological interpretation of brightness contrast.

On a finite strain theory of elastic-inelastic materials

Abstract: An attempt is made to develop a theory of inelastic behavior of crystalline materials subjected to arbitrary deformation. The introduced concept of elastic motion leads to a simple decomposition rule: the total velocity gradient is the sum of the elastic velocity gradient and the inelastic velocity gradient. The important role of rotations and relevant constitutive relations is discussed and illustrated by an example of a tensile test of a single crystal. The assumption usual in plasticity that plastic deformation does not change the volume of the body follows in the present theory as a consequence of the second law of thermodynamics and material symmetry.

Prediction of the Monin-Obukhov Similarity Functions from an Invariant Model of Turbulence.

Abstract: The second-order, invariant modeling technique for turbulent flows as developed by Donaldson is applied to the atmospheric surface layer. The steady, high-Reynolds number equations reduce to a universal set when the variables are scaled by the shear stress and vertical heat flux as suggested by Monin and Obukhov. Numerical integration of these equations yields results for the mean velocity gradient, mean temperature gradient, Richardson number, rms vertical velocity and temperature fluctuations, and horizontal heat flux which agree favorably with experimental observations over the complete range of stability conditions.

Large‐scale dynamical effects upon the solar wind flow parameters

Abstract: The Vela 3 proton data have been examined to determine the extent to which interplanetary compressions and rarefactions affect the large-scale nonshock statistics of the solar wind temperature T and density n. Considered as a joint function of velocity V and velocity gradient ΔV/Δt, the temperature is found to be much more strongly related to the velocity. The density shows significant V dependence, but ΔV/Δt appears to be more important. Simple analytic functions are derived from flow parameter values obtained during times of little velocity change (|ΔV/Δt| ≤ 1 km sec−1 hr−1) to describe the average T-V and n-V dependencies. Fluctuations about these norms in both n and T are demonstrated to be positively correlated with ΔV/Δt on a time scale of 9–12 hours. However, more rapid (≤6-hour) variations in T during periods of high V, low n, and negative ΔV/Δt (corresponding to the rarefaction phase of interacting stream events) lack this association. The large-scale compressional perturbation of n and T is not limited in importance to the relatively infrequent large interacting streams, but should be regarded as a fundamental and widely occurring solar wind process. The implication is that much, perhaps most, nonshock solar wind activity can be viewed as a steady succession of interacting streams of varying intensities. This circumstance limits the usefulness of the average relations in identifying the physical processes dominating the flow in the acceleration region of the corona.

Theory of Flocculation for Continuous Flow System

Abstract: The Smoluchowski equation for orthokinetic equation is applied to the case of a couette-type flocculator with continuous flow. With the inner cylinder tapered to provide a decreasing principal velocity gradient in the direction of flow, a three-dimensional velocity gradient field is established. Based on a mathematical model, flocculation is compared with such a tapered flocculator, and one in which the velocity gradient is uniform. The importance of the limitation of the floc size by fluid shear is established, but the mode of floc particle breakup is not so significant. With both initially monodispersed and polydispersed suspensions, the tapered flocculation is better, judged by the number of fine particles remaining as the suspension leaves the flocculator. The relative efficiency of the tapered flocculator increases with increased values of velocity gradient and with initial concentration of particles.

Spectral line formation in non-LTE expanding atmospheres

Abstract: The local transfer equation is formulated for an optically thick atmosphere in which a linear velocity field is present, in order to obtain an integral equation for the line source function. The study and solution of this equation compared with that for the static case'' makes clear the effect of the shift of the absorption coefftcient, due to the velocity gradient, upon the photons emitted in the line, in the continuum, and coming from the exterior (incident intensity). In some cases, the line source function in presence of a velocity gradient can be greater than in the static case''. The variation of emergent intensity with direction is grenter than in the static case''; consequently the geometric effect produced on the flux by this variation is very important. Emergent intensities and fluxes have also been computed. Some calculated line-profiles have the shape of P Cygni'' or Wolf Rayet'' profiles. On the other hand, quasi-symmetrical lineprofiles have been produced, which can be erroneously attributed to microturbulence'' or rotational broadening. (auth)

Velocity gradients and microturbulence in Cepheids.

Abstract: Variations of the microturbulent velocity with phase and height in the atmosphere were reported in classical Cepheids. It is shown that these effects can be understood in terms of variations of the velocity gradient in the atmospheres of these stars.

Effects of a drag-reducing polymer on the turbulent boundary layer

Abstract: Data are presented showing the time effects caused by polymer solution drag-reduction degradation on the mean velocity and axial fluctuating velocity profiles. Velocity profiles obtained in the study at high drag reduction using a time-study technique demonstrate that the polymer molecules affect not only the near wall region, as shown by the change in viscous sublayer velocity gradient and sublayer thickness, but that the turbulent core is affected as well, as evidenced by the fact that the slope of the turbulent core velocity profile differs substantially from the Newtonain value of 5.75.

A study of momentum transport in turbulent flow

Abstract: The eddy viscosity and the representative mixing time and length, which are the most indispensable basic informations in studying turbulent mixing phenomena, are investigated theoretically and experimentally. The new eddy viscosity is defined as the product of kinematic viscosity and coefficient which relates the turbulence energy dissipation through fluctuating motion with that through mean motion. The turbulent flow field being looked upon as the flow field in which the turbulent elements move transverse to the mean flow, new representative mixing time and length are proposed. The representative mixing time is applied to relate the above eddy viscosity with the mean velocity gradient. Being different from the conventional eddy viscosity, the newly defined eddy viscosity is determined uniquely on the notice point if there is only one mean velocity gradient to any direction at that point. In the transitional region from laminar to turbulent flow of liquid in a circular pipe, experimental values of the newly defined eddy viscosity and the representative mixing length are obtained by measuring the liquid velocity fluctuations by an electro-chemical technique based on an electro-chemical reaction controlled by diffusional mass transfer rate.

The Effect of Sand Movement on the Surface Wind

Abstract: WE can now examine the changes which occur in the wind when it blows over a mobile surface of loose sand; and compare the new velocity distribution with that which would be produced by the same sand if it were prevented from moving. It may be clearest to begin with the experiment by which these changes were discovered.

Methods of investigating the rheological behaviour of concentrated polymer solutions in rotary devices with a cone-disc gap in connection with flow instability☆

Abstract: A study was made of the instability of the solution flow of two polyisobutylenes and aluminium naphthenate of different concentrations in an elasto-viscometer with a cone-disc operating pair. Instability was recorded according to tangential stress and visually through the transparent parts of the device. It was shown that, according to molecular weight and polymer concentration in solution, flow instability may be accompanied or not by polymer degradation: the velocity gradient and shear stress, at which instability occurs, are in some cases close to, and in others, far from, the range of highest Newtonian viscosity.

Electro-optical measurement of longitudinal dispersion in turbulent pipe flow

Abstract: An attempt was made to correlate light beam absorption with the longitudinal dispersion of ink in turbulent pipe flow. Ink was injected into water flowing in a 2.22 cm ID pipe and the light beam produced by a laser traversed the pipe through transparent sections. Light beam attenuation by the ink pulse was measured with a photodiode and recorded by various means. Attenuation was measured at two locations downstream of the injection point. Since the attenuation was calibrated for ink density, theoretical prediction of the ink density distribution and the resulting light attenuation at the points of laser traverse was produced. The theoretical density distribution was based on only the first order source of longitudinal dispersion: the velocity gradient. The comparison between theory and experiment shows that, over a wide range of turbulence, dispersion was almost entirely due to velocity gradient and can be conveniently measured by the light beam absorption technique.