Optimization procedure for pulse separation in cross-correlation PIV

In PIV, the optimal time separation (t) between successive laser pulses is influenced by a number of parameters. In the present paper, only two kinds of error affecting the choice of t are studied: (i) random error arising from noise during recording of the flow seeded with tracer particles and subsequent interrogation of the particle images, and (ii) acceleration error arising from approximation of the local Eulerian velocity based on small (but non-zero) particle displacements. These two kinds of error place conflicting requirements on t. A model to optimize t with respect to these errors is described, and the model is confirmed by the results of a Monte Carlo simulation. This model for optimal t is extended to various acceleration distributions. An estimate for the spatial resolution of the velocity field resulting from cross-correlation PIV is proposed.We wish to thank the University of Delaware and the Department of Mechanical Engineering for providing a graduate fellowship to support this work.     

Influence of the surface layer on the phase transition process in an inhomogeneous medium with account of heat flux relaxation

Moscow Institute of Physical Engineering, Moscow 115409. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 36, No. 3, pp. 116–121, May–June, 1995.     

Stability of vertical oscillations in an electrodynamic suspension system with a discrete guideway structure

Conclusions 1. The coupling of the vehicle oscillation equation and the equations for the currents in the guideway structures must be taken into account in the stability analysis of vertical oscillations in an electrodynamic suspension system with a discrete guideway structure.2. The reported calculations indicate that vertical oscillations are unstable over a wide range of travel velocities. Consequently, the execution of steady-state vehicle motion requires vertical stabilization of the system.3. Effective stabilization can be achieved by means of a dynamic vibration damper. Even for a small relative mass =0.025 of the optimally tuned damper the perturbed motion decays rapidly.Physicotechnical Problems Branch of the Institute of Geotechnical Mechanics, National Academy of Sciences of Ukraine, Dnepropetrovsk. Translated from Prikladnaya Mekhanika, Vol. 31, No. 7, pp. 88–93, July, 1995.     

Hydrodynamical modeling of the development of non-homogeneous oil reservoirs

Results of mathematical modeling of two-phase flow in non-homogeneous (layered) reservoirs are reported. Characteristic patterns of flow in reservoirs with high layer permeability contrast are investigated. It is shown that in such reservoirs crossflow between layers must be taken into account. Specific features of the use of hydrodynamic methods of improving oil recovery in such reservoirs based upon flow pattern control are studied. The possibility of using rational flow management to improve oil recovery partially blocking the reservoir in the neighborhood of the wells is demonstrated.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 6, pp. 87–94, November–December, 1995.     

Triaxial force measurement at specific positions on a soil-cutting blade

In order to create a mathematical model of a soil-cutting blade, it is necessary to understand thoroughly the behavior of a soil slice and its interaction with the blade surface. The triaxial force transducer was developed to serve as one of the various tools to verify the proposed mathematical model. The prototype model transducer was fabricated, calibrated and tested with a soil slice on a flat cutting blade. The calibration results have indicated high sensitivity and the capability of simultaneous measurement in three directions. As a technological refinement, the detecting part of this triaxial force transducer was tapered to solve the problem of soil clogging in the opening clearance. Furthermore, the effects of the clearance configurations between the bore on the soil-cutting blade and the detecting part which is embedded in this bore were investigated to determine the most desirable configuration. The comparative results indicated that by tapering both the detecting part and the bore, the tangential stress measurement gained the highest value, and provided the most satisfactory condition for three-dimensional stress management.     

Studying heat exchange of dispersion-drop gas-liquid flow in granular layer

Conclusions Experimental procedure has been developed for physical modeling of monopropellant decomposition in a catalytic packet upon limiting stage of the process, i.e., during evaporation of a liquid in drop conditions. Heat exchange of liquid drops in a catalyst layer heated to high temperatures has been analyzed. Experimental dependence of a volume heat transfer coefficient on grain diameter, liquid flow rate and catalyst material has been obtained. It has been shown that within parameter variations this coefficient is practically independent of the gas velocity and drop diameter. Evaporation mechanism of drops in a heated granular layer has been discussed and carried out. For a more comprehensive examination of the interaction mechanism between the drops and the catalyst layer, a further experimental investigation is necessary in a wider range of change of the basic parameters of the process and use of mathematical modeling in analyzing experimental data. Novosibirsk. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, No. 4, pp. 118–123, July–August, 1994.     

Circular punch on the unstretchable Westergaard-type subgrade

Summary Horizontally unstretchable continuum of the Westergaard's type is modelled by elastic layers of finite thicknesses interconnected with very thin, flexible but unstretchable sheets. For the regular layered structure, the finite difference equations are formulated and their closed solutions is presented. The resulting formulase are used when the contact problem solution is sought in a form of series of spherical functions. The unknown series coefficients are determined via Galerkine method, the formulae for punch settlement and inclination are presented and a numerical procedure is developed and used to study the influence of the Westergaard's subgrade material parameters (subgrade reinforcement intensity) and (Poisson's ratio of the basic material).

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Kreisförmiger Stempel auf unausdehnbarer Unterlage Westergaard'schen Typs

Übersicht Horizontal unausdehnbares Kontinuum Westergaard'schen Typs wird über elastische Schichten endlicher Dicke, die mittels sehr dünner und biegsamer, aber nichtdehnbarer Membranen verbunden sind, modelliert. Für den Fall regulärer Schichtstrukturen werden die Finite-Differenzen-Gleichungen aufgestellt und die geschlossene Lösung formuliert. Diese Lösung wird dann benutzt, wenn das Kontaktproblem in der Form von sphärischen Funktionenreihen dargestellt wird; die unbekannten Koeffizienten der Reihe werden über die Galerkin-Methode bestimmt. Für den Fall einer senkrechten Belastung und einer Momentenbelastung werden die Setzung und Verdrehung bestimmt. Dafür wird ein numerisches Verfahren entwickelt und verwendet, um den Einfluß der Materialparameter und des Westergaard'schen Kontinuum zu untersuchen.

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Presented at the GAMM Seminar Kontakt fester Körper, Stuttgart 18.–19. March 1993

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Dedicated to Prof. H. Bufler upon the occasion of his 65th birthday anniversary     

Time-dependent interaction of two fluid flows separated by a semi-infinite non-rigid plate

In this paper the following problem is solved in the linear approximation. Let a flat plate separate two uniform inviscid fluid flows with different steady-state densities and velocities. These flows are subject to small time-dependent disturbances due to plate deformation. This problem is solved for arbitrary deformations as well as in the case of the angular harmonic oscillations of a flapping mover. The time-dependent forces acting on the plate are determined, together with the dynamic characteristics of the mover and the position of the fluid-fluid interface. Kazan'. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 55–64, January–February, 1994.     

Columnar vortices in isotropic turbulence

The structure of the intense vorticity regions is studied in numerically simulated homogeneous, isotropic, equilibrium turbulent flow fields at four different Reynolds numbers, in the rangeRe =35–170, and is found to be organized in coherent, cylindrical or ribbon-like, vortices (worms). At the Reynolds numbers studied, they are responsible for much of the extreme intermittent tails observed in the statistics of the velocity gradients, but their importance seems to decrease at higherRe . Their radii scale with the Kolmogorov microscale and their lengths with the integral scale of the flow, while their circulation increases monotonically withRe . An explanation is offered for this latter scaling, based in the assumed presence of axial inertial waves along their cores, excited by a random background strain of the order of the root mean square vorticity. This explanation is consistent with the presence of comparable amounts of stretching and compression along the vortex cores.

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Sommario La struttura di regioni ad intensa vorticità in campi di flusso turbolento omogenei, isotropi ed in equilibrio, simulati numericamente, viene studiata per quattro differenti numeri di Reynolds nell'intervalloRe =35÷170, e si trova che tali regioni si organizzano in vortici coerenti, cilindrici o a forma di nastro (vermi). Con rifermento ai numeri di Reynolds studiati, si vede che tali vortici sono responsabili per gran parte delle code estreme ed intermittenti, osservate nelle statistiche dei gradienti di velocità, ma la loro importanza sembra decrescere a più altiRe . I loro raggi scalano con la microscala di Kolmogorov e le loro lunghezze con la scala integrale del flusso, mentre la loro circolazione cresce monotonicamente conRe . Per quest'ultimo riscalamento viene offerta una spiegazione basata sull'assunzione della presenza di onde inerziali assiali lungo i loro nuclei, eccitate da una deformazione di fondo casuale dell'ordine della radice quadrata della velocità media. Questa spiegazione è consistente con la presenza di incrementi paragonabili di allungamenti e compressioni lungo i nuclei dei vortici.

     

Chemoconcentration capillary effect associated with the motion of a drop in a liquid

The effect of a surface chemical reaction involving a weak soluble surface active substance on the motion of a drop in a liquid is investigated. It is shown that as a result of the Marangoni effect the non-uniformity in the distribution of the substance along the surface associated with the proper motion of the drop and the chemical reaction has an important influence on the nature of the motion of the drop and on the force exerted by the surrounding Liquid. Under certain conditions this Leads to the development of a thrust proportional to the velocity of the drop (chemoconcentration capillary effect). The condition of occurrence of the thrust is obtained, together with its dependence on various physical parameters.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 147–154, January–February, 1988.