Heat transfer of an oscillating cylinder in a viscous incompressible fluid flow

Unsteady flow and heat transfer of the heated cylinder with transverse and longitudinal oscillations in unbounded flow of viscous incompressible heat conducting fluid are considered. Influence of amplitude, frequency and direction of harmonic oscillations of the cylinder on the near-wake structure and heat transfer are investigated.     

Screening of the Coulomb field in a magnetized electron gas of a quantum cylinder

The quantum theory is constructed for screening of the Coulomb field of a point charge in a magnetized electron gas of a quantum cylinder. The asymptotics of the screened potential are calculated for both degenerate and Boltzmann electron gases. It is demonstrated that, in the degenerate case, apart from the known quasi-classical monotonic part, the result contains the quantum oscillating part, which corresponds to Friedel oscillations. The Aharonov-Bohm oscillations of the screened Coulomb interaction of electrons on a cylindrical surface are described analytically. It is shown that the Friedel oscillations can be represented as a superposition of oscillations with different frequencies which are determined by the macroscopic properties of the nanotube.     

Laminar incompressible viscous flow past a cylinder performing rotary oscillations

The numerical simulation of the laminar viscous flow past a cylinder performing rotary oscillations around its axis is carried out. The Navier–Stokes equations are solved by finite volume method using the program package OpenFOAM. The values of the amplitude and frequency of forced oscillations are found, at which the maximum reduction of the drag coefficient of the cylinder is achieved.     

Electron-phonon interaction and electrical conductivity of a nanotube in an external magnetic field

A contribution of the electron-phonon scattering to the conductivity of a quantum cylinder in a magnetic field is calculated. It is demonstrated that the nanotube conductivity undergoes the Aharonov–Bohm oscillations with changes of the magnetic flux through the nanotube cross section.     

Handling of temperature dependence of viscosity in problems of incompressible medium flow around a cylinder

The viscous incompressible medium (water, air) flow past a circular cylinder is considered with regard for the temperature T dependent viscosity v. The influence of different boundary conditions for temperature on flow structure, the drag coefficient and its components due to the pressure and viscosity is investigated in the problem of the flow past a cylinder at rest for the (diameter-based) Reynolds number Re_D = 40. A relation between the viscosity gradient along a normal to the body surface and the integral vorticity flux from the body surface into the boundary layer is discussed. Unlike the constant viscosity case the vorticity flux may be different from zero, which must lead because of the integral conservation law for the vorticity to an alteration of the far-field boundary conditions for the velocity. In the same connection, the problem is analysed on the heat spot entry into the computational region under consideration for the flow past a circular cylinder. The examples of the symmetrization of separated flow past a cylinder performing rotation oscillations in a uniform free stream (the Taneda problem) are considered. A comparison with flow computations for low Mach numbers M « 1 for the flow of a medium past a cylinder at rest is carried out. At the computation of the equation for heat transfer under the assumption of incompressibility of such media as air, it is proposed to retain the pressure derivative, which is typical of gases. In this case, a better agreement with the computations of compressible flows (for M « 1) is achieved, for example, at the determination of the sizes of a symmetric zone of flow separation past a circular cylinder. An unsteady flow in the neighborhood of the point of joining the zero streamline bounding a closed region of separated flow (the cavity) in a wake of the cylinder at rest is obtained by a numerical simulation at the Reynolds number equal to 40.     

Exchange interaction and oscillations of the magnetization of the electron gas in a quantum cylinder

The exchange energy of the electron gas on a cylindrical surface in a constant magnetic field has been calculated. Analytical formulas describing the contribution of the exchange interaction into oscillations of the magnetization of the electron gas in a quantum cylinder have been obtained. It is shown that the magnetic response of the system exhibits Aharonov-Bohm oscillations for both degenerate and Boltzmann electron gases.     

Combustion process in a spark ignition engine: dynamics and noise level estimation

We analyze the experimental time series of internal pressure in a four cylinder spark ignition engine. In our experiment, performed for different spark advance angles, apart from the usual cyclic changes of engine pressure we observed additional oscillations. These oscillations are with longer time scales ranging from one to several hundred engine cycles depending on engine working conditions. Based on the pressure time dependence we have calculated the heat released per combustion cycle. Using the time series of heat release to calculate the correlation coarse-grained entropy we estimated the noise level for internal combustion process. Our results show that for a larger spark advance angle the system is more deterministic.     

Quantum and semiclassical oscillations in the organic metal (BEDO-TTF)2Clx(H2O)y

We study quantum (Shubnikov-de Haas and de Haas-van Alphen) oscillations and angular oscillations of the reluctance in the organic quasi-two-dimensional metal (BO)₂Cl_x(H₂O)_y. We show that the Fermi surface in this compound consists of a slightly corrugated cylinder with its axis perpendicular to the conducting plane. The cross section of the cylinder in this plane is a perfect circle of radius k _F≃3×10⁷ cm⁻¹. The effective carrier mass associated with this cylinder is m*=(1.65–2.0) m ₀ in the conducting plane, while the Dingle temperature is T _D=3–4 K. Zh. éksp. Teor. Fiz. 114, 1137–1146 (September 1998)     

Vibration and waves in a cylinder with screw anisotropy

On the basis of the three-dimensional theory of elasticity, we consider the features of propagation of harmonic waves in a hollow cylinder with screw anisotropy. The main attention is focused on studying axisymmetrical oscillations. To describe low-frequency long-wavelength longitudinal-torsional oscillations by perturbation theory methods, we construct an applied theory and evaluate the area of its applicability. To analyze high-frequency oscillations, a numerical method of determining the critical frequencies and dispersion curves is developed and implemented. It is shown that in the axisymmetrical case, screw anisotropy generates a relation between longitudinal and torsion oscillations, which is mathematically described by the amplitude coefficients of homogeneous waves.     

A smoothing technique for discrete delta functions with application to immersed boundary method in moving boundary simulations

The effects of complex boundary conditions on flows are represented by a volume force in the immersed boundary methods. The problem with this representation is that the volume force exhibits non-physical oscillations in moving boundary simulations. A smoothing technique for discrete delta functions has been developed in this paper to suppress the non-physical oscillations in the volume forces. We have found that the non-physical oscillations are mainly due to the fact that the derivatives of the regular discrete delta functions do not satisfy certain moment conditions. It has been shown that the smoothed discrete delta functions constructed in this paper have one-order higher derivative than the regular ones. Moreover, not only the smoothed discrete delta functions satisfy the first two discrete moment conditions, but also their derivatives satisfy one-order higher moment condition than the regular ones. The smoothed discrete delta functions are tested by three test cases: a one-dimensional heat equation with a moving singular force, a two-dimensional flow past an oscillating cylinder, and the vortex-induced vibration of a cylinder. The numerical examples in these cases demonstrate that the smoothed discrete delta functions can effectively suppress the non-physical oscillations in the volume forces and improve the accuracy of the immersed boundary method with direct forcing in moving boundary simulations.     

Galvanomagnetic phenomena in organic layered conductors

Galvanomagnetic phenomena in organic conductors with a quasi-two-dimensional energy spectrum of an arbitrary form in the presence of several groups of charge carriers whose states belong to Fermi surface sheets with different topological structures are considered. The dependences of magnetoresistance, Shubnikov-de Haas oscillations, and Hall field on the intensity and orientation of a strong magnetic field with respect to the normal to layers n are analyzed for a Fermi surface consisting of a weakly corrugated cylinder and a plane weakly corrugated along the p _z=pn plane.     

A contribution from exchange interaction to magnetization of a degenerate electron gas in a quantum cylinder

The exchange energy of an electron gas on a cylindrical surface in a constant magnetic field is calculated. Analytical formulas describing the contribution from exchange interaction to magnetization of a quantum cylinder are derived. It is shown that the magnetic response of the system undergoes the Aharonov-Bohm oscillations. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 51–54, December, 2006.     

A mathematical model of Helmholtz resonator type gas oscillation discharges of two-stroke cycle engines

For the example of a one cylinder, 3·7 in³ two-stroke cycle engine, it is shown that combustion engines discharge combusted gas in oscillatory bursts whose primary frequency is independent of engine speed. The superposition of a Helmholtz resonator model and a thermodynamic model of the combustion process is used to predict pressure oscillations and sound radiation. It is shown that the elastic and inertial characteristics of the gas in the combustion chamber and the exhaust port have to be considered in the model. Theoretical and experimental results compare well.     

绝热气缸-导热活塞系统的振动特性

用计算机模拟的方法研究了绝热气缸中导热活塞的振动特性。在自由振动或受迫振动的情况下，系统在总体上都是和一个普通的阻尼振子相似的。与此同时，本也指明并分析了该热力学系统的一些独特而有趣的性质。     

Force acting on a cylinder under ultrasonically induced cavitation

To elucidate mechanisms of cavitation action on a surface with microcapillary discontinuity and refine the model of the sonocapillary effect, the force acting on a cylinder is correlated with the height of a liquid in the capillary under cavitation, both quantities being measured at the same point of the ultrasonic field. It is found that the force acting on the cylinder is directed toward a cavitation cluster stabilized at the end face of the cylinder. This force can be enhanced with another cylinder placed on the side of the cluster coaxially with the first one. The dynamics of the cavitation cluster depending on the cylinder spacing is investigated in the case when one of the cylinders is on a pendulum suspension. The conditions for self-sustained oscillations of the pendulum are found. The dependence of the attracting force between the cylinders on the ultrasonic frequency and cylinder spacing is derived. The end-face-averaged pressure exerted on a cylinder of diameter 1.2 mm may reach 0.16 kPa, and the intracapillary pressure attains 0.89 kPa. Thus, the sonocapillary effect may be explained, at least partially, by a counterpressure arising from cluster-capillary interaction. This effect can be used in designing cavitation sensors and ultrasonic sources.     

Giant oscillations of energy levels in mesoscopic superconductors

The interplay of geometrical and Andreev quantization in mesoscopic superconductors leads to giant mesoscopic oscillations of energy levels as functions of the Fermi momentum and/or sample size. Quantization rules are formulated for closed quasiparticle trajectories in the presence of normal scattering at the sample boundaries. Two generic examples of mesoscopic systems are studied: (i) one-dimensional Andreev states in a quantum box and (ii) a single vortex in a mesoscopic cylinder.     

Electron-phonon scattering and conductivity of a quantum cylinder in a magnetic field

The contribution of electron-phonon scattering to conductivity of a quantum cylinder in a longitudinal magnetic field has been studied. It has been shown that the conductivity of the nanotube undergoes Aharonov-Bohm oscillations with variations in the magnetic flux through the nanotube cross section. The formulas describing the temperature dependence of the resistance of the nanostructure both in the case of an isotropic phonon spectrum and with allowance for the effects of phonon confinement have been obtained in the analytical form.     

Dynamics of three-tori in a periodically forced navier-stokes flow

Three-tori solutions of the Navier-Stokes equations and their dynamics are elucidated by use of a global Poincare map. The flow is contained in a finite annular gap between two concentric cylinders, driven by the steady rotation and axial harmonic oscillations of the inner cylinder. The three-tori solutions undergo global bifurcations, including a new gluing bifurcation, associated with homoclinic and heteroclinic connections to unstable solutions (two-tori). These unstable two-tori act as organizing centers for the three-tori dynamics. A discrete space-time symmetry influences the dynamics.