Computer simulation of the drift of solid particles caused by resonance gas oscillations in the open channel

Computer simulation methods are used to study the drift of solid spherical particles suspended in the open channel due to longitudinal oscillations of the gas column. The gas velocity field consists of periodic nonlinear waves and an acoustic flow. The particles move under the action of the Stokes force. Particle distributions in the wave field of the open channel are obtained in the vicinity of the first, second and third eigen-frequencies of the gas column. The particle’s spatial distribution features attributed to the particle’s drift under the action of acoustic radiation are revealed.     

Hydrodynamics of resonance oscillations of columns of inelastic particles

We study oscillations of a one-dimensional (1D) column of N slightly inelastic particles, produced by a piston vibrating at one end of a closed tube. It is found that for large enough vibrational amplitudes of the piston, the column oscillates periodically with the period equal to the vibrational period. The oscillation patterns are governed by the shock waves propagating across the column. The averaged kinetic energy per particle is shown to be proportional to the square of the vibrational frequency, omega. This energy also strongly depends on the vibrational amplitude. The maximal value of this kinetic energy achievable by these external vibrations is found to be of order omega(2)L(2), where L is the total volume (length) of the tube free of particles. The above results on the column resonance oscillations are also predicted by a 3D hydrodynamic model of an inelastic granular gas.     

Sound waves generated due to the absorption of a pulsed electron beam in gas

The results of an experimental investigation of acoustic vibrations (their frequency, amplitude, and attenuation coefficient) generated in a gas mixture as a result of the injection of a high-current pulsed electron beam into a closed reactor are presented. It is shown that the change in the phase composition of the initial mixture under the action of the electron beam leads to a change in the frequency of the sound waves and to an increase in the attenuation coefficient. By measuring the change in frequency, it is possible to evaluate with sufficient accuracy (about 2%) the degree of conversion of the initial products in the plasmochemical process. Relations describing the dependence of the sound energy attenuation coefficient on the size of the reactor and on the thermal and physical properties of the gases under study are derived. It is shown that a simple experimental setup measuring the parameters of acoustic waves can be used for monitoring the plasmochemical processes initiated by a pulsed excitation of a gas mixture.     

Forced flexural vibrations of a pipe with a liquid flow

The effect of a liquid flow on the forced vibrations of a pipe under an external driving force is studied both theoretically and experimentally. The analytic dependences of the displacement field on the frequency, the liquid flow velocity, the force application point, and the parameters of the pipe and the liquid are determined by means of the small perturbation method. Experimental results agree well with theoretical dependences. It is shown that the effect of the liquid flow on the pipe vibrations is maximal in the vicinity of the resonance of the second vibration mode.     

Acoustic power measurements of a damped aeroacoustically driven resonator

Strong self-sustained acoustic oscillations may occur in a gas pipe network under certain gas flow velocities within the network. The pipe network under consideration consists of a main pipe, with a variable mean airflow, with two closed coaxial side branches of variable but equal length joined to the main pipe. Coupling between resonant acoustic standing waves and instabilities of the shear layers separating the flow in the main pipe from the stagnant gas in the closed side branches leads to strong acoustic oscillations at a frequency corresponding to the half-wavelength acoustic mode defined by the total side-branch length. An acoustic damper consisting of a variable acoustic resistance and compliance is used to dissipate power from the resonating mode. The response of the aeroacoustically driven resonator to variable damping will be examined for different fluid flow regimes as well as side-branch geometries.     

Stability of the one-dimensional precession regime of a domain wall under a dc magnetic field in a uniaxial ferromagnet

The conditions for parametric excitation of flexural vibrations of a domain wall (DW) are determined in the case where the DW moves under the action of a uniform dc magnetic field whose strength exceeds the Walker critical value (in the spin precession regime). Vibrations are excited when uniform precession caused by the magnetic field during DW translational motion breaks down. Using numerical methods, it is shown that steady-state large-amplitude vibrations can occur and that these vibrations significantly affect the average DW velocity     

The possibility of an isochoric phase transition

The possibility of modifying the equation of state of a gas in a closed, thermally insulated capacitor filled with a nonpolar gas and changing the temperature and pressure under the action of an electrostatic field is considered.     

Non-linear gas oscillations in a pipe

The results of an experimental study of non-linear longitudinal gas oscillations in a closed tube are presented. Forced oscillations greater than in other experiments to date are obtained. A brief representation of the theory holding for excitation frequencies near and equal to the natural frequencies of a gas column is given. The experimental amplitude and the periodic shock wave form are compared with the calculated values. Oscillations whose excitation frequencies are twice as small as the first natural frequency are also studied.     

液氮中单管加注二氧化碳气体的实验研究

向饱和液氮中加注常温二氧化碳气体时,为形成细小而分散的固体二氧化碳颗粒以及充分且均匀的固液混合物,通过实验分别采用不锈钢盘管、大管径塑料管以及金属毛细管往液氮中加注一定流量下的常温二氧化碳气体,研究固液混合过程、凝固颗粒大小以及管路的堵塞状况。结果表明,不管是否经过预冷,大直径管道加注时,经过一段时间后管道必定发生堵塞;而毛细管加注则不会堵塞,但是气体流量会发生脉冲性变化。     

Magnetodeformation of ferrogels and ferroelastomers. Effect of microstructure of the particles’ spatial disposition

The work deals with the theoretical study of ferrogel/ferroelastomer deformations under the action of a homogeneous magnetic field. The compositions with linearly magnetizable non-Brownian particles are considered. Under the field action the ferrogel/ferroelastomer samples can either elongate or contract in the field direction. The type of deformation is determined by the sample shape and microstructure of the particles’ spatial disposition. Two kinds of systems are studied. The first one is the composition with the particles homogeneously distributed, like in an ideal gas, in the polymer matrix. The second kind is the system of linear chain-like aggregates of densely situated particles. The results show that the particles’ spatial disposition in the matrix is crucially important for the type of macroscopical deformation of the magnetopolymer compositions. The systems with the gas-like distribution of particles, depending on the sample shape, can either elongate or contract, whereas the chains stimulate the sample elongation.     

Detection of dust grains vibrations with a laser heterodyne receiver of scattered light

We present the results of measurement of grains vibrations under external action in gas and liquid with a laser heterodyne receiver of scattered radiation. For investigation of dynamic characteristics of particles we made the laser heterodyne receiver with sensitivity about 2×10⁻¹⁷ W/Hz and source of probing with radiation power 1 mW. In our pilot experiments, measurement of vibration amplitude of nanoparticles in gas (cigarette smoke) and microparticles in fluid (toothpaste in water) was made. We measured values of vibration amplitudes about 20–30 nm.     

Light-induced cross transport phenomena in a single-component gas

The cross transport processes that occur in a single-component gas in a capillary and are caused by resonance laser radiation and pressure and temperature gradients are studied. An expression for entropy production is derived using a system of kinetic Boltzmann equations in a linear approximation. The kinetic coefficients that determine the transport processes are shown to satisfy the Onsager reciprocal relations at any Knudsen numbers and any character of the elastic interaction of gas particles with the capillary surface. The light-induced baro- and thermoeffects that take place in a closed heat-insulated system in the field of resonance laser radiation are considered. Analytical expressions are obtained for the Onsager coefficients in an almost free-molecular regime. The light-induced pressure and temperature gradients that appear in a closed heat-insulated capillary under typical experimental conditions are numerically estimated.     

Unusual electromechanical effects in glycine

Unusual piezoresponse signals have been observed in glycine aminoacid powder at a frequency near 10 MHz, which exhibited a regular pattern in time determined by a periodic phase variation in the elastic vibrations of individual powder particles. This phenomenon results from the formation of spatial structures in glycine powder under the action of a strong rf field. Fiz. Tverd. Tela (St. Petersburg) 40, 1086–1089 (June 1998)     

Influence of wall vibrations on the sound of brass wind instruments

The results of an experimental and theoretical investigation of the influence of wall vibrations on the sound of brass wind instruments are presented. Measurements of the transmission function and input impedance of a trumpet, with the bell both heavily damped and freely vibrating, are shown to be consistent with a theory that assumes that the internal pressure causes an oscillation of the diameter of the pipe enclosing the air column. These effects are shown to be most significant in sections where there are flaring walls, which explains why damping these vibrations in cylindrical pipes normally produces no measurable effects.     

An experimental investigation of flow-induced acoustic resonance and flow field in a closed side branch system using a high time-resolved PIV technique

Abstract  

Systems with closed side branches are liable to an excitation of sound known as cavity tone. It may occur in pipe branches leading to safety valves or to boiler relief valves. The outbreak mechanism of the cavity tone has been ascertained by phase-averaged pressure measurements in previous research, while the relation between sound propagation and the flow field is still unclear due to the difficulty of detecting the instantaneous velocity field. It is possible to detect the two-dimensional instantaneous velocity field using high time-resolved particle image velocimetry (PIV). In this study, flow-induced acoustic resonance in a piping system containing closed side branches was investigated experimentally. A high time-resolved PIV technique was used to measure the gas flow in a cavity. Airflow containing oil mist as tracer particles was measured using a high-frequency pulse laser and a high-speed camera. The present investigation on the coaxial closed side branches is the first rudimentary study to visualize the fluid flow two-dimensionally in a cross-section using high time-resolved PIV, and to measure the pressure at the downstream side opening of the cavity by microphone. The fluid flows at different points in the cavity interact, with some phase differences between them, and the relation between the fluid flows was clarified.     

Study of Features of the Diffraction of X Rays in a Quartz Crystal Modulated by Longitudinal and Transverse Ultrasonic Vibrations

JETP Letters - Features of the simultaneous action of longitudinal and transverse ultrasonic vibrations in the quartz crystal on the parameters of reflected X-rays are studied. It is shown that...     

Self-Similar Solution of Spherical Shock Wave Propagation in a Mixture of a Gas and Small Solid Particles with Increasing Energy under the Influence of Gravitational Field and Monochromatic Radiation

Similarity solution for a spherical shock wave with or without gravitational field in a dusty gas is studied under the action of monochromatic radiation. It is supposed that dusty gas be a mixture of perfect gas and micro solid particles. Equilibrium flow condition is supposed to be maintained and energy is varying which is continuously supplied by inner expanding surface. It is found that similarity solution exists under the constant initial density. The comparison between the solutions obtained in gravitating and non-gravitating medium is done. It is found that the shock strength increases with an increase in gravitational parameter or ratio of the density of solid particles to the initial density of the gas, whereas an increase in the radiation parameter has decaying effect on the shock waves.     

Self-Similar Solution of Spherical Shock Wave Propagation in a Mixture of a Gas and Small Solid Particles with Increasing Energy under the Influence of Gravitational Field and Monochromatic Radiation

Similarity solution for a spherical shock wave with or without gravitational field in a dusty gas is studied under the action of monochromatic radiation. It is supposed that dusty gas be a mixture of perfect gas and micro solid particles. Equilibrium flow condition is supposed to be maintained and energy is varying which is continuously supplied by inner expanding surface. It is found that similarity solution exists under the constant initial density. The comparison between the solutions obtained in gravitating and non-gravitating medium is done. It is found that the shock strength increases with an increase in gravitational parameter or ratio of the density of solid particles to the initial density of the gas, whereas an increase in the radiation parameter has decaying effect on the shock waves.     

Dynamic gas anisotropy under optomechanical parametric resonance

An approximate kinetic equation describing a gas of two-or three-level atoms in an external laser field is found under conditions of optomechanical parametric resonance, which causes atomic oscillations along the field wave vector. The approximation is applicable to a gas of cylindrical particles whose axes retain their spatial orientation, making the gas anisotropic. The closed set of equations for macroparameters allows for a numerical solution. Expressions for direction-dependent transfer coefficients such as diffusion, viscosity, and thermal conductivity are derived phenomenologically. A two-temperature medium is shown to arise if a fluid consists of several gases with the optomechanical parametric resonance conditions satisfied for one of them.     

Dust particles in a thermophoretic trap in a plasma

The feasibility of confining dust particles in a plasma by thermophoretic forces was demonstrated. An extended dust structure in a positive glow discharge column was experimentally obtained at liquid nitrogen temperature. The dust structure was confined in an electrostatic-thermal trap, in which vertical stability was provided by the summed action of longitudinal electrostatic field and thermophoretic forces. Traps of this kind can be analyzed in terms of the general principles developed for confining particles in traps with the use of electric and magnetic multipole fields. We were able to change the shape and volume of the structure and even separate it into parts by varying temperature fields.