Identification of the nonlinear viscous properties of fluids by the vibrational method

Effects occurring in an oscillatory viscosimeter upon its filling with nonlinear viscous fluids whose rheological properties are described by the Ostwald-Weyl model have been revealed. The possibilities of the vibrational method for identification of the rheological belonging of media to nonlinear viscous ones with a power rheological law and of their nonlinear properties in the regime of free damped and forced vibrations have been discussed. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 5, pp. 70–77, September–October, 2005.     

Analytical method for estimating the nonlinear properties of liquids by a torsion viscosimeter

This paper considers the motion of a torsion viscosimeter that permits a conclusion about the rheological type of the liquid filling it. We have developed a theory of identification of nonlinear properties based on the use of the effective values of viscosity for each half-period and analytical solutions for linear liquids. The questions of the sensitivity that should be taken into account in planning an optimal experiment have been highlighted. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 3, pp. 518–523, May–June, 2008.     

Measurement of the Viscosity of a Liquid at High Pressures

A method of measuring the viscosity of a liquid over a wide range of pressures and temperatures and a rotation-type viscosimeter which employs this method are proposed. The possibility of determining and automatically regulating the flow of a liquid using the results of measurements of the viscosity in real time by employing two viscosimeters, placed in different sections of the channels, is pointed out. __________ Translated from Izmeritel'naya Tekhnika, No. 10, pp. 51–53, October, 2005.     

Numerical model of nonstationary flow of a viscoplastic fluid in a rotational viscosimeter

The results of numerical solution of the problem on flow of an incompressible viscoplastic fluid in the gap between two rotating cylinders have been presented. The criterion of formation of the boundaries of stagnant zones has been developed. A comparison of the results of numerical calculations to the analytical solution has been made. The time of establishment of stationary flow in the gap has been determined. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 1, pp. 12–14, January–February, 2007.     

Rheological properties of blood in the process of plasmapheresis

The rheological properties of the blood of donors and patients have been experimentally investigated on a rotational viscosimeter in the process of plasmapheresis at a temperature of 30°C and rates of shear ranging from 1.7 to 54.2 sec⁻¹. The efficiency of the plasmapheresis was increased when it was performed in combination with an extracorporeal autohemomagnetotherapy. The action of the plasmapheresis and the combined action of the plasmapheresis and the extracorporeal autohemomagnetotherapy on the rheological properties of blood were compared. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 5, pp. 24–26, September–October, 2005.     

Rheological changes in the blood and plasma of patients with myocardial ischemia and diabetes mellitus and dysfunction of their endothelium

The rheological properties of the whole blood and plasma of patients with myocardial ischemia and diabetes mellitus and of donors have been investigated using a Couette rotational viscosimeter at a temperature of 25°C in the range of rates of shear of 0.5–60 sec⁻¹. The rheological analysis was performed with the use of the Quemada relation. The functional state of the endothelium and some biochemical indices of the blood of these patients were investigated. It is shown that in patients with myocardial ischemia and diabetes mellitus, accompanied by dyslipemia and endocrine disturbances, rheological derangements and endothelial dysfunction develop. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 1, pp. 96–101, January–February, 2006.     

Dynamic instability of a pipe with internal mobile liquid blocks

We consider the problem of parametric vibrations of a rectilinear pipeline with internal mobile liquid blocks. As a result of its solution, we determine the influence of the size of the liquid blocks and their velocity on the character of the loss of stability of the pipe. Ukrainian Transport University, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 3, pp. 114–121, May–June, 1999.     

Exact solutions of problems on harmonic vibrations of a thermoelastic rod having a triangular cross section with account for the connectedness

Two exact solutions of the problem on harmonic vibrations of a thermoelastic rod with a cross section representing a right triangle have been obtained with the use of multiaction logic operations. The influence of the connectedness of the problem as well as the temperature and elastic properties of the indicated rod on the wave process of its deformation has been investigated. Expressions for the velocities of the temperature, longitudinal, and shear waves were obtained. A criterion M₀ for the expediency of taking into account the connectedness in the formulation of the problem was determined. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 6, pp. 18–29, November–December, 2007.     

Determination of the rheological properties of whole blood by the nonstationary method of pulsed changing of the rate of shear

Problems associated with the use of the nonstationary method of pulsed changing of the rate of shear for the measurement of important viscoplastic properties of whole blood — the critical shear stress τ₀ and the plastic viscosity μ_p — are considered. The indicated method was compared to the method of stationary rheometry. It is shown that the blood-flow curve obtained by this method, unlike that obtained by the stationary method, characterizes a viscoplastic medium. To calculate the parameters of this medium exactly, it is necessary to take into account the dependence of the rate of shear on the above-indicated parameters. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 5, pp. 176–179, September–October, 2005.     

A study of the dissipative properties of homogeneous materials deposited as coatings. Part 2. Copper condensates with different microstructural characteristics

The dependence of dissipative properties of copper condensates on the grain size has been studied. Condensates with a grain size of 0.9–3.7 μm were obtained by electron-beam vapor deposition of copper as coatings on a titanium substrate. The oscillograms of damped bending vibrations of the substrate-coating system were recorded at a frequency of 140–150 Hz in the temperature range 20–350°C. The values of true logarithmic vibration decrement for copper condensates were determined by the self-consistent calculation of energy loss factors of the substrate and coating by the method proposed in the part 1. It has been shown that the amplitude dependences of the true logarithmic vibration decrement of copper condensates at room and elevated temperature are largely determined by their structure. __________ Translated from Problemy Prochnosti, No. 2, pp. 149–158, March–April, 2008.     

Influence of nozzle vibrations on the aerodynamic characteristics of a jet

The results of investigations of the aerodynamic characteristics of turbulent jets issuing from nozzles and subjected to the action of various kinds of low-frequency vibrations — transverse, longitudinal, and torsional (during axisymmetric vibrations of the nozzle around the longitudinal axis) — are presented. Data on the laws governing changes in the average and pulsation velocities along the jet axis, as well as on the spectra of velocity pulsations in the zone of jet mixing, have been obtained. It has been established that at low-frequency vibrations of the nozzle a noticeable intensification of jet mixing is attained. The same effects as on acoustic excitation of a jet are observed. The experiments were carried out at Reynolds numbers Re = 2∙10⁴–8∙10⁴.     

Electrical conductivity, thermoelectric power and viscosity of liquid Sn-based alloys

Shear viscosity of liquid Sn–Ag, Sn–Cu and Sn–Ag–Cu eutectics from melting temperature up to 1100 K and their electrical conductivity and thermoelectric power up to 850 K have been investigated. The electrical properties of liquid Sn with additions of Fe and Ni have also been studied. It is shown that small amounts of metal admixtures affect noticeably the behavior of the physical properties of liquid Sn.     

The effect of quenching medium on the wear behaviour of a Ti–6Al–4V alloy

The aerospace alloy, Ti–6Al–4V is a difficult material to machine, and, in general, shows poor wear resistance due to the soft, ductile properties of the alloy. In this study, the Ti–6Al–4V alloy has been heat treated to a temperature above and below the β-transus temperature and then quenched using a medium of oil, water or liquid nitrogen to change the surface wear behaviour of the alloy. The results showed that no significant change in microstructure and surface properties was achieved when the alloy was heated to 750 °C and then quenched in liquid nitrogen. However, when the alloy was heated to 1,000 °C (above the β-transus), the hardness of the titanium alloy significantly increased from 400 VHN to about 800 VHN, but the wear resistance of the alloy did not improve. In fact, the wear resistance of the alloy decreased as the surface hardness increased, and this change in wear behaviour was attributed to a change in the mechanism of wear from plastic deformation to brittle-fracture of the surface.     

Temperature-Induced Reversible Change of Electrical Resistivity in Sn–Bi Melts

Using a dc four-probe method, the temperature dependence of the electrical resistivity of liquid Sn–Bi alloys has been investigated. The results show that there are clear turning points both on heating and cooling for several experimental cycles. Since the electrical resistivity is one of the physical properties sensitive to structure, the unusual change of the resistivity indicates that liquid–liquid transitions (LLT) probably take place in Sn–Bi melts. Moreover, the transitions are reversible. Compared with the experimental results for pure Sn and Bi, it is assumed that Sn plays an important role in the reversible liquid–liquid transitions.     

High-speed imaging and CFD simulations of a deforming liquid metal droplet in an electromagnetic levitation experiment

Electromagnetic levitation of a liquid metal droplet is of great interest to study gas–liquid metal reactions. An important prerequisite for the evaluation of the overall mass transfer between the gas and metal is to characterize the geometry of the deforming molten droplet, which determines the interfacial reaction area. In this article, the free surface shape and dynamics of a molten 80%Ni–20%Cr droplet is investigated both experimentally and numerically. The frequencies associated to the oscillatory translational motions of the drop and to the vibrations of its free surface are measured using high-speed video image analysis. A 2D transient model is then presented, in which three interacting phenomena are considered: electromagnetic phenomena, the turbulent flow of liquid metal in the drop and the change in the drop shape. The numerical results presented demonstrate the capabilities of the model.     

Thermophysical Properties of a Quaternary Refrigerant Mixture: Comparison of Dynamic Light Scattering Measurements with a Simple Prediction Method

Dynamic light scattering (DLS) has been used for the measurement of several thermophysical properties of a quaternary refrigerant mixture R-125/143a/32/134a in its liquid phase under saturation conditions. The thermal diffusivity and sound speed have been obtained by light scattering from bulk fluids over a temperature range from about 293 K up to the liquid–vapor critical point. By applying the method of DLS to a liquid–vapor interface, also called surface light scattering (SLS), the saturated liquid kinematic viscosity and surface tension can be determined simultaneously. These properties have been measured from about 243 to 343 K. The results are discussed in comparison with literature data and with a simple prediction method based on the mass-weighted properties of the pure components, expressed as functions of the reduced temperature. Once again, the simple prediction method was shown to be applicable for the calculation of different transport and other thermophysical properties of multicomponent refrigerant mixtures and this with sufficiently high accuracy for technical practice. Moreover, the input data for the simple prediction scheme can be reduced without loss of accuracy by treating binary or ternary mixtures as a subset of the multicomponent mixture.     

Investigation into nonlinear vibrations of composite plates using the <Emphasis Type="Italic">R</Emphasis>-function theory

We have developed an effective approach to the solution of problems on geometrically nonlinear vibrations of orthotropic multilayer plates of irregular shapes in a classical statement based on the use of the R-function theory, Ritz variational method and Bubnov-Galerkin method. Using the proposed method, problems of vibrations of both multilayer rectangular plates and plates of complex geometries have been solved. The effect of the domain geometry and boundary conditions on the amplitude-frequency characteristics has been investigated. __________ Translated from Problemy Prochnosti, No. 5, pp. 101–113, September–October, 2007.     

On vibration-convective flows in a Hele-Shaw cell

The influence of high-frequency horizontal vibrations on convective flow conditions in a Hele-Shaw cell located in a homogeneous gravitational field and heated from below has been studied theoretically and experimentally. The linear problem of stability of mechanical quasi-equilibrium in the case of model boundary conditions has been solved analytically. The supercritical conditions of vibrational convection have been investigated numerically by the finite-difference method. It has been shown that at small values of the thermal and vibration Rayleigh numbers in a fluid a state close to quasi-equilibrium is realized. The critical values of the thermal and vibration Rayleigh numbers at which a change of different stationary and nonstationary convective regimes takes place have been determined. A stability map of vibration-convective flows has been generated. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 4, pp. 712–720, July–August, 2008.     

Micromechanically Established Constitutive Equations for Multiphase Materials with Viscoelastic–Viscoplastic Phases

A model for viscoelastic–viscoplastic solids is incorporated in a micromechanical analysis of composites with periodic microstructures in order to establish closed-form coupled constitutive relations for viscoelastic–viscoplastic multiphase materials. This is achieved by employing the homogenization technique for the establishment of concentration tensors that relate the local elastic and inelastic fields to the externally applied loading. The resulting constitutive equations are sufficiently general such that viscoelastic, viscoplastic and perfectly elastic phases are obtained as special cases by a proper selection of the material parameters the phase. Results show that the viscoelastic and viscoplastic mechanisms have significant effect on the global stress-strain, relaxation and creep behavior of the composite, and that its response is strongly rate-dependent in the reversible and irreversible regimes.     

Computation of the equilibrium position of a liquid with surface tension inside a tank of complex geometry and extension to sloshing dynamic cases

To study the vibrations of a tank partially filled with a liquid in low-gravity environment, we first have to find the static position of the liquid. In this paper, we present a three-dimensional finite element approach to find this equilibrium configuration for any tank geometry. Both gravity and capillary effects are taken into account. The nonlinear equations of this problem are derived from the differentiation of the total potential energy of the system, then the problem is transformed into a liquid free surface form-finding. The well-known singularity of this kind of problems is regularized using the updated reference strategy. The equations of the regularized problem are discretized using the finite element method and solved by the Newton–Raphson algorithm. Several examples illustrate the effectiveness of this method, even for complex cases, and two validation tests are presented. The linear sloshing vibrations of the liquid are finally studied near this equilibrium position and two validation cases are proposed for the eigenvalue dynamic problem.