scholarly journals Функциональные возможности электромагнитно-акустических преобразований в токовом режиме в металлическом расплаве

2021 ◽  
Vol 57 (6) ◽  
pp. 60-71
Author(s):  
В. Н. Цуркин ◽  
◽  
А. В. Иванов ◽  
Keyword(s):  
Acoustic Field ◽  
Discharge Current ◽  
Source Parameters ◽  
Good Reason ◽  
Skin Layer ◽  
Magnetic Pressure ◽  
Sound Waves ◽  
Entire Volume ◽  
Frequency Spectra ◽  
Acoustic Disturbances

The paper deals with a symmetric problem on the base of physically substantiated estimates of the processes of electromagnetic-acoustic transformations (EMAT) of energy during the flow of an electric current through a melt, the key parameters of the open problem of the system "Power source parameters – Parameters of the magnetic field and magnetic pressure of the skin layer – Parameters of acoustic disturbances". It was shown that the key parameter when formulating the EMAT problem in technological applications is the geometry of the container with the object of processing and the material of the form. And when solving the problem, they are the parameter of the skin layer and the time dependence of the discharge current. It was established that a part of energy during the formation of the magnetic pressure in the skin layer from the amount of the energy stored in the capacitor bank of the pulse current generator is on the order of 10-4–10-2. The value of this part depends on the period of the discharge current and is proportional to the T1/2. When acoustic disturbances propagate in a melt, the main share of energy losses is determined by the difference in the acoustic stiffness of the melt and the shape of materials. The frequency spectra of the pressure of sound waves at the parameters selected for the analysis can cover the range of up to hundreds kHz, which is a good reason for the realization of resonance effects and the active formation of dissipative structures. Attention is focused on the fact that EMAT effects are manifested in the melt not only under the influence of an acoustic field, but also under that of an electromagnetic one in the skin layer. They are separated in time, but the acoustic field can occupy the entire volume of the melt and its effect is longer in time.

scholarly journals On the acoustic disturbances produced by small bodies in plane waves transmitted through water, with special reference to the single-plate direction finder

1921 ◽  
Vol 100 (704) ◽  
pp. 261-288
Keyword(s):  
Special Reference ◽  
Plane Waves ◽  
Maximum Amplitude ◽  
Sound Waves ◽  
Small Bodies ◽  
Acoustic Disturbances ◽  
Sense Of Direction ◽  
Single Plate ◽  
Direction Finder ◽  
Metal Diaphragm

The experiments to be described were carried out for the Board of Invention and Research, under the direction of Sir William Bragg, between October 1916 and February 1917, on the Cullaloe Reservoir, near Aberdour, Fifeshire, and are now published with the permission of the Admiralty. A form of directional hydrophone has already been described by Sir William Bragg. It consists of a metal diaphragm, A, about four inches in diameter, mounted in a heavy ring, B, and open to the water on both sides ( vide Chart 9). In the centre of the diaphragm is a small metal box, C, carrying a carbon granule microphone of the button type. The microphone is connected into an ordinary telephone circuit. If the instrument is rotated about a vertical diameter in water through which sound waves are passing the sound heard in the receivers passes through a number of maxima and minima. When the diaphragm is turned “edge-on” to the source of sound it is obvious that the pressure pulses will reach the two faces of the diaphragm symmetrically and the diaphragm will fail to vibrate. As, however, either face is turned toward the source this symmetry ceases to exist and the diaphragm is thrown into vibration, which reaches a maximum amplitude when the instrument is “broad-side” on to the source. The instrument, therefore, indicates the line of propagation of the sound, but owing to the existence of two positions of maximum or minimum its indications are ambiguous as regards the sense of direction.

Source Parameters and Excitation in a Spark Discharge

1972 ◽  
Vol 26 (1) ◽  
pp. 17-40 ◽  
Author(s):  
J. P. Walters
Keyword(s):  
Mass Transport ◽  
Time Dependence ◽  
Discharge Current ◽  
Transport Model ◽  
Source Parameters ◽  
Excitation Condition ◽  
Mass Transport Model ◽  
Simple Mass ◽  
Excitation Processes ◽  
Parameter Dependent

Experiments are reported for two key lines of aluminum, sparked in nitrogen against graphite for a variety of discharge current waveforms, that suggest that changes in spark source parameters do not fundamentally change the excitation processes in the spark. A straightforward, “either-or” excitation condition is imposed on a simple mass transport model, calculated from measured velocities of electrode vapor in the spark, to predict the time dependence of a primary feature of radiation emitted in the Al II spectrum. The data combine to suggest that parameter-dependent excitation indices require re-examination in terms of the manner in which radiation emitted from the discharge is viewed by the spectrometer.

Noise Control in an Industrial Hall

2013 ◽  
Vol 430 ◽  
pp. 251-256
Author(s):  
Vasile Bacria ◽  
Nicolae Herisanu
Keyword(s):  
Acoustic Field ◽  
Noise Control ◽  
Human Beings ◽  
Characteristic Parameters ◽  
Noise Mitigation ◽  
Frequency Spectra ◽  
Mitigation Methods

nside the industrial halls one can find different noisy machines and equipments. During their work these ones generate noise and vibrations which affect human beings inside or outside the hall. In this paper we present the results obtained in the investigation of the acoustic field generated by sources within an industrial hall emphasizing the frequency spectra, characteristic parameters, propagation way and some effects generated. A description of measurements is included together with an analysis of obtained results as well as the establishment of noise mitigation methods consisting in acoustical arrangement of the hall in order to eliminate the unpleasant effects.

scholarly journals Low-frequency sound radiated by a nonlinearly modulated wavepacket of helical modes on a subsonic circular jet

2009 ◽  
Vol 637 ◽  
pp. 173-211 ◽  
Author(s):  
XUESONG WU ◽  
PATRICK HUERRE
Keyword(s):  
Acoustic Field ◽  
Low Frequency ◽  
Base Flow ◽  
Matched Asymptotic Expansion ◽  
Sound Waves ◽  
Mean Flow ◽  
Flow Distortion ◽  
Experimental Conditions ◽  
Modulation Equation ◽  
Instability Modes

A possible fundamental physical mechanism by which instability modes generate sound waves in subsonic jets is presented in the present paper. It involves a wavepacket of a pair of helical instability modes with nearly the same frequencies but opposite azimuthal wavenumbers. As the wavepacket undergoes simultaneous spatial–temporal development in a circular jet, the mutual interaction between the helical modes generates a strong three-dimensional, slowly modulating ‘mean-flow distortion’. It is demonstrated that this ‘mean field’ radiates sound waves to the far field. The emitted sound is of very low frequency, with characteristic time and length scales being comparable with those of the envelope of the wavepacket, which acts as a non-compact source. A matched-asymptotic-expansion approach is used to determine, in a self-consistent manner, the acoustic field in terms of the envelope of the wavepacket and a transfer factor characterizing the refraction effect of the background base flow. For realistic jet spreading rates, the nonlinear development of the wavepacket is found to be influenced simultaneously by non-parallelism and non-equilibrium effects, and so a composite modulation equation including both effects is constructed in order to describe the entire growth–attenuation–decay cycle. Parametric studies pertaining to relevant experimental conditions indicate that the acoustic field is characterized by a single-lobed directivity pattern beamed at an angle about 45°–60° to the jet axis and a broadband spectrum centred at a Strouhal number St ≈ 0.07–0.2. As the nonlinear effect increases, the radiation becomes more efficient and the noise spectrum broadens, but the gross features of the acoustic field remain robust, and are broadly in agreement with experimental observations.

A Discussion on the measurement and interpretation of changes of strain in the Earth - Derivation of source parameters from low-frequency spectra

1973 ◽  
Vol 274 (1239) ◽  
pp. 369-371 ◽  
Keyword(s):  
Focal Mechanism ◽  
Moment Tensor ◽  
Source Parameters ◽  
Low Frequency ◽  
Frequency Spectra ◽  
Isotropic Part ◽  
The Earth ◽  
Double Couple ◽  
The Moment ◽  
Deviatoric Part

By recording several components of tilt, strain and acceleration at one location, one can determine the focal mechanism, or moment tensor, of an earthquake. Alternatively, recordings made at several locations can be used. The moment tensor can be decomposed into its isotropic part and its deviatoric part. When the eigerrvalues of the deviator are in the sequence (— 1, 0, 1) the equivalent double couple can be found.

Experimental and Numerical Study on a Straight Exhaust Pipe

2011 ◽  
Vol 27 (4) ◽  
pp. 597-605
Author(s):  
S.-M. Liang ◽  
C.-J. Wang
Keyword(s):  
Acoustic Field ◽  
Gas Flow ◽  
Numerical Study ◽  
Flow Speed ◽  
Exhaust Pipe ◽  
Sound Waves ◽  
Expansion Waves ◽  
Numerical Result ◽  
Inclination Angles ◽  
Euler Solver

ABSTRACTIn this study, radiated noise is investigated by experimental and numerical methods for a straight exhaust pipe of diameter 23mm that replaces the original exhaust pipe of a motorcycle of EZ 125cc provided by Kwang Yang Motor Co. In experiment, temperature, pressure and flow speed of the exhausted gas have been measured for different engine speeds ranging from 3000-5000rpm without loading. Sound pressure levels (SPL) at a distance of 0.5m from the exhaust pipe exit for different inclination angles (0° ∼ 90°) were recorded and compared with the result of simulation. In numerical simulation, a high-resolution 5th-order Euler solver was used and conducted on a parallel computation system with a cluster of 4 personal computers with dual processors. It is found that the back-and-forth reflection of expansion waves inside the pipe due to the shock wave diffraction around the pipe exit is the mechanism of radiating sound waves from the exhaust pipe. The numerical result shows the exhausted-gas flow with complicated vortex rings and its associated acoustic field. The acoustic field indicates that there are three sound lobes with different directivities for the engine speed of 4000rpm.

scholarly journals Fully compressible simulations of waves and core convection in main-sequence stars

2020 ◽  
Vol 641 ◽  
pp. A18 ◽  
Author(s):  
L. Horst ◽  
P. V. F. Edelmann ◽  
R. Andrássy ◽  
F. K. Röpke ◽  
D. M. Bowman ◽  
...  
Keyword(s):  
Temporal Frequency ◽  
Wave Theory ◽  
Stellar Model ◽  
Pressure Waves ◽  
Linear Wave ◽  
Sound Waves ◽  
Frequency Spectra ◽  
Linear Wave Theory ◽  
Stellar Oscillations ◽  
Hydrodynamical Simulations

Context. Recent, nonlinear simulations of wave generation and propagation in full-star models have been carried out in the anelastic approximation using spectral methods. Although it makes long time steps possible, this approach excludes the physics of sound waves completely and requires rather high artificial viscosity and thermal diffusivity for numerical stability. A direct comparison with observations is thus limited. Aims. We explore the capabilities of our compressible multidimensional Seven-League Hydro (SLH) code to simulate stellar oscillations. Methods. We compare some fundamental properties of internal gravity and pressure waves in 2D SLH simulations to linear wave theory using two test cases: (1) an interval gravity wave packet in the Boussinesq limit and (2) a realistic 3 M⊙ stellar model with a convective core and a radiative envelope. Oscillation properties of the stellar model are also discussed in the context of observations. Results. Our tests show that specialized low-Mach techniques are necessary when simulating oscillations in stellar interiors. Basic properties of internal gravity and pressure waves in our simulations are in good agreement with linear wave theory. As compared to anelastic simulations of the same stellar model, we can follow internal gravity waves of much lower frequencies. The temporal frequency spectra of velocity and temperature are flat and compatible with the observed spectra of massive stars. Conclusion. The low-Mach compressible approach to hydrodynamical simulations of stellar oscillations is promising. Our simulations are less dissipative and require less luminosity boosting than comparable spectral simulations. The fully-compressible approach allows for the coupling of gravity and pressure waves in the outer convective envelopes of evolved stars to be studied in the future.

scholarly journals Plume Divergence and Discharge Oscillations of an Accessible Low-Power Hall Effect Thruster

2021 ◽  
Vol 11 (4) ◽  
pp. 1973
Author(s):  
Matthew Baird ◽  
Thomas Kerber ◽  
Ron McGee-Sinclair ◽  
Kristina Lemmer
Keyword(s):  
Hall Effect ◽  
Discharge Current ◽  
Electric Propulsion ◽  
Low Voltage ◽  
Discharge Voltage ◽  
Operating Conditions ◽  
Low Flow ◽  
Divergence Angle ◽  
Frequency Spectra ◽  
Plume Divergence

Hall effect thrusters (HETs) are an increasingly utilized proportion of electric propulsion devices due to their high thrust-to-power ratio. To enable an accessible research thruster, our team used inexpensive materials and simplified structures to fabricate the 44-mm-diameter Western Hall Thruster (WHT44). Anode flow, discharge voltage, magnet current, and cathode flow fraction (CFF) were independently swept while keeping all other parameters constant. Simultaneously, a Faraday probe was used to test plume properties at a variety of polar coordinate distances, and an oscilloscope was used to capture discharge oscillation behavior. Plasma plume divergence angle at a fixed probe distance of 4.5 thruster diameters increased with increasing anode flow, varying from 36.7° to 37.4°. Moreover, divergence angle decreased with increasing discharge voltage, magnet current, and CFF, by 0.3°, 0.2°, and 8°, respectively, over the span of the swept parameters. Generally, the thruster exhibited a strong oscillation near 90 kHz, which is higher than a similarly sized HET (20–60 kHz). The WHT44 noise frequency spectra became more broadband and the amplitude increased at a CFF of less than 1.5% and greater than 26%. Only the low flow and low voltage operating conditions showed a quiescent sinusoidal discharge current; otherwise, the discharge current probability distribution was Gaussian. This work demonstrates that the WHT44 thruster, designed for simplicity of fabrication, is a viable tool for research and academic purposes.

Measurement of Acoustic Receptivity at Leading Edges and Porous Strips

1990 ◽  
Vol 43 (5S) ◽  
pp. S167-S174 ◽  
Author(s):  
R. W. Wlezien ◽  
D. E. Parekh ◽  
T. C. Island
Keyword(s):  
Boundary Layer ◽  
Wave Velocity ◽  
Acoustic Field ◽  
Laminar Boundary Layer ◽  
Leading Edge ◽  
Porous Surface ◽  
Instability Wave ◽  
Relative Importance ◽  
Acoustic Disturbances ◽  
Tollmien Schlichting

The receptivity of a laminar boundary layer to acoustic disturbances in the vicinity of a leading edge and a narrow porous surface is investigated experimentally. The relative importance of the receptivity mechanisms is explored for leading edge and porous surface configurations. Several methods to decouple the acoustic and instability wave velocity perturbations are discussed, and consistent estimates of the Tollmien-Schlichting modes are achieved when the acoustic field is directly estimated from profiles of the total fluctuating velocity. A 24:1 leading edge produces negligible Tollmien-Schlichting response when interacting with symmetric acoustic disturbances and is used to confirm the porous-surface receptivity mechanism.

scholarly journals Application of partial areas method in the problem of sound radiation by a sphere in a waveguide with soft acoustically boundaries

2021 ◽  
Vol 5 (5 (113)) ◽  
pp. 62-79
Author(s):  
Oleksii Korzhyk ◽  
Sergey Naida ◽  
Tetiana Zheliaskova ◽  
Oleksander Chaika ◽  
Nikita Naida
Keyword(s):  
Boundary Conditions ◽  
Acoustic Field ◽  
Practical Importance ◽  
Experimental Studies ◽  
Fourier Method ◽  
Liouville Problem ◽  
Source Surface ◽  
Sound Waves ◽  
Spherical Source ◽  
Working Space

The paper considers the features of the formation of an acoustic field by a spherical source with complicated properties in a regular plane-parallel waveguide, which is of practical importance in marine instrumentation and oceanographic research. The calculation algorithm is based on the use of the Helmholtz equation and the Fourier method for each partial region and the conjugation conditions on their boundaries. The presented calculation allows one to get rid of the idealized boundary conditions on the source surface, with the subsequent determination of the excitation coefficients of the waveguide modes within the framework of the Sturm-Liouville problem. In this case, the attraction of the boundary conditions on the surface and the bottom of the sea, as well as the Sommerfeld conditions, makes it possible to obtain the real distribution of the field in the vertical sections of the waveguide. The obtained frequency dependences of the pressure and vibrational velocity components show their amplitude-phase differences, which reach 90 degrees, which partially explains the appearance of singular points in the intensity field in a regular waveguide. It has been determined that multiple reflections of sound waves from the boundaries of the working space and the space of the waveguide cause oscillations of the pressure components with a change in the amplitude level up to 6 dB. It was found that with an increase in the size of the source, a kind of resonance is formed in the working space, the frequency of which depends on the depth of the sea and corresponds to the region kr=x=5.8. It was found that when the acoustic field is formed in the working space, the frequency response of the impedance components is represented as a multiresonant dependence formed on the basis of the frequency characteristics of the lower modes and their combinations. Experimental studies have shown that the results of calculations of the mode composition of the acoustic field of the emitter, obtained in the conditions of the pool, correspond to the spatial characteristics of the mode components of the acoustic field with an error of up to 3 dB

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