Attenuation Of Sound Waves Research Articles

Numerical Analysis of Damage to Retained Rock Mass of Dam Foundation Caused by Blasting Excavation

On basis of the existed TCK model, the establishment process of a new rock blasting damage model is discussed by considering the relationship of crack density Cd, which indicates the shock damage extent of rock, and sound wave attenuation coefficient ap. Then, this model is inserted into the user-defined material model library of ANSYS/LS-DYNA3D software to construct the new damage model. Numerical simulation of damage to retained rock mass of dam foundation caused by rock blasting excavation in dam region with this model. Calculation results show that: as far as the blasting parameters and geological conditions in this paper, the damage to retained rock mass below caused by rock blasting excavation above is basically limited to the scope of 1.5m below the bottom of blasthole, and damage degree gradually reduces from the bottom of blasthole to faraway. Meanwhile, blasting will not cause rock mass to open along soft layer inside, whose maximum calculation displacement is only 3mm. The calculation result can be referred by the practical engineering.

The Design of New Type Muffler Used For Steam Turbine’s Exhaust Device

The exhaust device of steam turbine usually establishes vacuum rapidly using steam injection. The gas of the nozzle of the exhaust mixing device emits at high speed. The noise is very large. The muffler is designed to reduce the noise of the steam turbine’s exhaust devices. Referring to the principle of the separated expansion chamber muffler and connecting with practical production, we present a new type muffler. The design considers fully the peak frequency of the jetting noise of the nozzle and the noise attenuation of sound waves in the pipeline transmission etc. The muffler is small, light, anti- high- temperature and high-speed gases, and easy to be installed. The effect of noise reduction is obvious.

Trade-offs in data acquisition and processing parameters for backscatter and scatterer size estimations

By analyzing backscattered echo signal power spectra and thereby obtaining backscatter coefficient vs. frequency data, the size of subresolution scatterers contributing to echo signals can be estimated. Here we investigate trade-offs in data acquisition and processing parameters for reference phantom-based backscatter and scatterer size estimations. RF echo data from a tissue-mimicking test phantom were acquired using a clinical scanner equipped with linear array transducers. One array has a nominal frequency bandwidth of 5 to 13 MHz and the other 4 to 9 MHz. Comparison of spectral estimation methods showed that the Welch method provided spectra yielding more accurate and precise backscatter coefficient and scatterer size estimations than spectra computed by applying rectangular, Hanning, or Hamming windows and much reduced computational load than if using the multitaper method. For small echo signal data block sizes, moderate improvements in scatterer size estimations were obtained using a multitaper method, but this significantly increases the computational burden. It is critical to average power spectra from lateral A-lines for the improvement of scatterer size estimation. Averaging approximately 10 independent A-lines laterally with an axial window length 10 times the center frequency wavelength optimized trade-offs between spatial resolution and the variance of scatterer size estimates. Applying the concept of a time-bandwidth product, this suggests using analysis blocks that contain at least 30 independent samples of the echo signal. The estimation accuracy and precision depend on the ka range where k is the wave number and a is the effective scatterer size. This introduces a region-of-interest depth dependency to the accuracy and precision because of preferential attenuation of higher frequency sound waves in tissuelike media. With the 5 to 13 MHz, transducer ka ranged from 0.5 to 1.6 for scatterers in the test phantom, which is a favorable range, and the accuracy and precision of scatterer size estimations were both within approximately 5% using optimal analysis block dimensions. When the 4- to 9-MHz transducer was used, the ka value ranged from 0.3 to 0.8 to 1.1 for the experimental conditions, and the accuracy and precision were found to be approximately 10% and 10% to 25%, respectively. Although the experiments were done with 2 specific models of transducers on the test phantom, the results can be generalized to similar clinical arrays available from a variety of manufacturers and/or for different size of scatterers with similar ka range.

Attenuation of shear sound waves in jammed solids

We study the attenuation of long-wavelength shear sound waves propagating through model jammed packings of frictionless soft spheres interacting with repulsive springs. The elastic attenuation coefficient, α(ω), of transverse phonons of low frequency, ω, exhibits power law scaling as the packing fraction ϕ is lowered towards ϕc, the critical packing fraction below which rigidity is lost. The elastic attenuation coefficient is inversely proportional to the scattering mean free path and follows Rayleigh’s law with α(ω) ∼ ω4(ϕ − ϕc)−5/2 for ω much less than ω* ∼ (ϕ − ϕc)1/2, the characteristic frequency scale above which the energy diffusivity and density of states plateau. This scaling of the attenuation coefficient, consistent with numerics, is obtained by assuming that a jammed packing can be viewed as a mosaic composed of domains whose characteristic size * ∼ (ϕ − ϕc)−1/2 diverges at the transition.

Nonlinear attenuation of sound waves by inertial cavitation bubbles

Acoustic cavitation fields generally involve clouds of inertial bubbles, expanding to many time their initial radius, and then collapsing. A correct estimation of the wave attenuation in such media requires a realistic estimation of the power dissipated by the oscillation of each bubble. This power loss originates mainly from thermal diffusion in the gas and viscous friction in the liquid, and is calculated numerically for a single inertial bubble, by solving the bubble dynamics in a typical parameter range at 20 kHz, using a convenient model accounting for the thermal behavior of the gas. These estimations are then injected in the nonlinear Caflish equations, which describe wave propagation in a bubbly media, conveniently recast in an energy conservation equation. A nonlinear attenuation coefficient is deduced and found to be several orders of magnitude higher than the linear prediction.

The effects of rigid polystyrene particles on the glass transition characteristics and mechanical wave attenuation of styrene-butadiene rubber: Particle size and acoustic mismatch

Glass transition characteristics and mechanical wave attenuation of the neat and filled styrene-butadiene rubber (SBR) containing 10 wt % of rigid monosize polystyrene particles of various diameters from several hundred microns down to several tens of nanometers were investigated by dynamic mechanical thermal analysis, impedance tube, and ultrasonic spectroscopy. The results showed the matrix damping capacity and the breadth of glass transition increase by reducing the size of rigid particles due to the matrix-particles interfacial area increase as the major governing parameter. Matrix glass transition broadening toward higher temperatures was attributed to the increased dynamic heterogeneity induced by fillers, whereas the damping capacity increase was assigned to contribution of interfacial friction loss mechanism. The proposed postulation was confirmed based on the calculated temperature distribution of the relaxing matrix volume fraction. Sound wave attenuation by the matrix and PS particles filled systems led to a broad absorption peak for the former and appearance of a secondary absorption peak at lower frequencies for the latter. Intensity of this secondary peak was highest for the system containing PS nanoparticles. Finally, ultrasonic attenuation enhanced by the PS particle size to wavelength ratio increase according to α sca ∼ (d/λ) 0.38 scaling law and declined by replacing the dense particles with larger hollow PS particles. Comparison of the normalized attenuation of the PS particle filled SBR in various mechanical wave attenuation regimes implied low sensitivity to particle size in vibration, mild differentiation in the sound, and finally severe differentiation in the ultrasound regimes.

Extension of the pressure correction method to zero-Mach number compressible flows

In the present paper, the classical pressure correction method was extended into low Mach number compressible flow regime by integrating equation of state into SIMPLE algorithm. The self-developed code based on this algorithm was applied to predicting the lid-driven cavity flow and shock tube problems, and the results showed good agreement with benchmark solutions and the Mach number can reach the magnitude of as low as 10−5. The attenuation of sound waves in viscous medium was then simulated. The results agree well with the analytical solutions given by theoretical acoustics. This demonstrated that the present method could also be implemented in acoustics field simulation, which is crucial for thermoacoustic simulation.

Sound waves in (2+1) dimensional holographic magnetic fluids

We use the AdS/CFT correspondence to study propagation of sound waves in strongly coupled (2+1) dimensional conformal magnetic fluids. Our computation provides a nontrivial consistency check of the viscous magneto-hydrodynamics of Hartnoll-Kovtun-Müller-Sachdev to leading order in the external field. Depending on the behavior of the magnetic field in the hydrodynamic limit, we show that it can lead to further attenuation of sound waves in the (2+1) dimensional conformal plasma, or reduce the speed of sound. We present both field theory and dual supergravity descriptions of these phenomena. While to the leading order in momenta the dispersion of the sound waves obtained from the dual supergravity description agrees with the one predicted from field theory, we find a discrepancy at higher order. This suggests that further corrections to HKMS magneto-hydrodynamics are necessary.

COUPLED DOUBLE-DISTRIBUTION-FUNCTION LATTICE BOLTZMANN MODEL WITH AN ADJUSTABLE BULK VISCOSITY

A coupled double-distribution-function (DDF) lattice Boltzmann method was recently developed for the compressible Navier–Stokes equations. In this method, the specific-heat ratio and the Prandtl number can be easily adjusted. However, the ratio between the bulk and shear viscosities is fixed at a value related to the specific-heat ratio. In order to obtain a bulk viscosity satisfying the Stokes' hypothesis or an adjustable bulk viscosity in the recovered momentum and energy equations, correction terms, which are proportional to the divergence of macroscopic velocity, are incorporated into the microscopic evolution equations. The constraints imposed on these correction terms can be derived from the Chapman–Enskog analysis. With these constraints, the forms of the correction terms can be determined, and then a coupled DDF lattice Boltzmann model with adjustable specific-heat ratio, Prandtl number, and bulk viscosity can be obtained. Numerical simulations are performed for the attenuation of sound waves. The numerical results are found to be in good agreement with the theoretical solutions.

On attenuation of plane sound waves in turbulent mean flow

Plane sound waves in a smooth pipe turbulent boundary layer are known to be more strongly damped when the acoustic boundary layer becomes thicker than the viscous sublayer. The attenuation constants that govern this phenomenon are accurately predicted by the mathematical model proposed by M.S. Howe [The damping of sound by wall turbulent shear layers. Journal of the Acoustical Society of America 98(3) (1995) 1725–1730. Also in: Acoustics of Fluid– Structure Interactions, Cambridge University Press, Cambridge, 1998]. This model assumes uniform mean core flow. The present paper proposes a variant of this model which is based on the assumption of parallel sheared mean core flow. Predictions of the two approaches are compared.

Reflection of sound from a forest: comparison of experimental data to scattering theory

Reflection of sound by a forest has been investigated by means of measurements near Thun in Switzerland. Sound pulses were generated at 50 and 150 m from the forest, and reflected sound was recorded at distances of 100, 200, and 300 m from the forest. By comparison with numerical calculations of reflection of sound from a hard wall, using a parabolic‐equation model for sound propagation in an atmosphere with wind and temperature as recorded during the measurements, the attenuation of sound waves upon reflection at the forest was determined. It was found that the reflection attenuation decreases from about 20 dB at low frequency to about 10 dB at high frequency. The experimental results for the reflection attenuation are compared with results of a theoretical model for scattering of spherical sound waves by a single row of cylinders. The model employs an effective spacing between the cylinders, to account for trees that are not at the edge of the forest, i.e., inside the forest. The model results are in good agreement with the experimental results. The comparison indicates that the effective spacing decreases with decreasing frequency, as low‐frequency waves penetrate deeper into a forest than high‐frequency waves do.

ON THE NON-ISENTROPIC SOUND WAVES PROPAGATION OF A STATIONAY OR FLOWING FLUID IN A CYLINDERICAL TUBE FILLED WITH POROUS MEDIA

ABSTRACTIt is shown that the five parameters governing the propagation of sound waves in a fluidcontained in rigid cylindrical tubes filled with a saturated porous media are the shearwave number s = R ρω / μ , ratio of specific heats γ , the Prandtl number σ , porosityeand the Darcy number Da = R2 K . A variational solution of the problem with nonisentropicwave’s propagation in a cylindrical tube in the presence and absence of aconvective steady flow is presented. The manner in which the flow influences theattenuation and the phase velocity of the forward and backward propagating acousticwaves is deduced. It is found that the inclusion of the solid matrix or the increasing ofDarcy number increases the attenuation and decreases the phase velocities of theforward, backward and hydrodynamic sound wave’s; this is due to favorable retardingeffect of the solid matrix. The increasing of porosity is found to decrease attenuationand increases phase velocities of the forward, backward and hydrodynamic soundwaves; this is due to absent role of solid matrix in damping sound waves. The effect ofincreasing Mach numbers is found to increase attenuation and decrease phasevelocities for the backward sound waves; this is due favorable retarding steady flowvelocities and decrease attenuation and increase phase velocities of the forward andhydrodynamic sound waves; this is due to favorable steady flow velocities in drivingthese two sound waves.

Dehydration Process of Protein Crystals by Micro-Brillouin Scattering

Polymorphism and dehydration process have been studied by the micro-Brillouin scattering technique in hen egg white lysozyme crystals without cross-linking. Two types of crystal with tetragonal and monoclinic systems have been successfully grown by the two-liquid interface method. The dehydration processes of tetragonal and monoclinic crystals have been investigated by the exposure of crystals to open air. Sound velocity increases markedly owing to the increase in intermolecular interaction between lysozyme molecules, while the attenuation of sound wave decreases markedly owing to the decrease in friction generated by mobile water. The time dependences of sound velocity in two crystals have been discussed on the basis of the Avrami–Erofe'ev model. It is found that a monoclinic crystal dehydrates much faster than a tetragonal one.

Role of heterogeneity for sound speed and attenuation in unconsolidated ocean sediments

Although ocean sediments may have many types and degrees of heterogeneity, it has been determined that two-component models are tractable for poroelastic, thermoelastic, and thermoporoelastic studies. We have found in particular that a substantial part of the increased sound wave attenuation observed in both ocean sediments and laboratory glass-bead experiments above 50 kHz can be explained by such a two-component poroelastic model. Furthermore, the inclusion of thermal expansion and entropy effects into a generalized binary thermoporoelastic model provides an additional attenuation enhancement (though not as large --- by itself --- as the poroelastic enhancement) of a mathematically very similar type that is also relatively easy to model and understand. The paper will present this extended model as well as comparisons to available data.

Ultrasonic measurement of residual wall thickness during gas assisted injection molding

AbstractUltrasonic technology provides a powerful and noninvasive method of in‐process measurement during injection molding and extrusion. Changes in the velocity, attenuation and reflection coefficients of high frequency sound waves can be related to the state and conditions of the materials through which they propagate. The velocity of an ultrasonic wave changes with density and elastic moduli; this allows information on solidification and material properties to be collected during the molding cycle. The time of flight of the wave is a function of velocity and path length. This paper shows that it can be correlated with the residual wall thickness of polymer in the mold during gas assisted injection molding. POLYM. ENG. SCI., 47:1730–1739, 2007. © 2007 Society of Plastics Engineers

Effective kinematic viscosity of turbulentHeII

The temperature dependence of the effective kinematic viscosity of turbulent He II, nu(eff)(T) , is deduced from second sound attenuation data using the late stage of decay of thermally induced counterflow He II turbulence in two channels of square cross section. It is shown to qualitatively agree with the published data for nu(eff)(T) calculated based on experiments on decaying-grid-generated He II turbulence [Niemela, J. Low Temp. Phys. 138, 537 (2005)]. Corrections to these data due to the "sine squared" law that describes attenuation of the second sound wave propagating along an arbitrary direction with respect to the direction of the core of a quantized vortex in turbulent He II are discussed and applied.

Sound propagation in the mixtures of liquid and solid aggregate; similarities at micro- and nanoscales.

Sound propagation phenomena in certain liquid and solid aggregate mixtures, at micrometer scales, in some cases resemble the wave propagation behaviors of materials observed at nanometer and atomic scales. For example, it can be shown that the sound wave dispersion, attenuation, and cutoff-frequency effects depend on the same structural parameters as those observed at nano or atomic levels and are similar at both scales. Therefore, to investigate theoretical models of wave and matter interactions it is more convenient to use, as experimental tools, the readily analyzable models of wave propagation, in mixtures of solid and liquid, constructed at micrometer scales. Theoretical findings on sound propagation in the mixtures of liquid and solid particles at micrometer scales will be discussed. These results show the resemblance to the behavior of acoustic phonons, the lattice thermal vibrations of crystalline structures, at radically different scales. Experimental data on wave dispersion, attenuation, band-pass, and cutoff frequency effects, measured for sound propagation, in inhomogeneous materials consisting of mixtures of solid and liquid will be presented, showing the similarities of wave propagation behaviors at micro- and nanoscales.

Frequency dependences of absorption and scattering components of attenuation for water‐saturated sands

Frequency dependences of attenuation of sound waves in water‐saturated marine sands are discussed. Measured attenuation includes a scattering component, and this makes it difficult to understand the frequency dependences of attenuation. By removing the scattering component from the measured attenuation, the Kramers‐Kronig (K‐K) relationship gives the correct sound speed dispersion. Consequently, the intrinsic attenuation extracted from the data collected during SAX99 experiments follows the Biot theory for overall frequencies. This suggests that the attenuation coefficient of sound waves for water‐saturated sands is not linear in f. The sound speeds recalculated via the K‐K relationship are also in excellent agreement with the Biot theory at high frequencies.

Generalized linear transport theory in dilute neutral gases and dispersion relation of sound waves

The transport processes in dilute neutral gases are studied by using the kinetic equation with a collision relaxation model that meets all conservation requirements. The kinetic equation is solved keeping the whole anisotropic part of the distribution function with the use of the continued fractions. The conservative laws of the collision operator are taken into account with the projection operator techniques. The generalized heat flux and stress tensor are calculated in the linear approximation, as functions of the lower moments, i.e., the density, the flow velocity and the temperature. The results obtained are valid for arbitrary collision frequency nu with the respect to kv(t) and the characteristic frequency omega, where k(-1) is the characteristic length scale of the system and v(t) is the thermal velocity. The transport coefficients constitute accurate closure relations for the generalized hydrodynamic equations. An application to the dispersion and the attenuation of sound waves in the whole collisionality regime is presented. The results obtained are in very good agreement with the experimental data.

Hydrodynamics of Sakai–Sugimoto model in the quenched approximation

Abstract We study transport properties of the finite temperature Sakai–Sugimoto model. The model represents a holographic dual to ( 4 + 1 ) -dimensional supersymmetric SU ( N c ) gauge theory compactified on a circle with anti-periodic boundary conditions for fermions, coupled to N f left-handed quarks and N f right-handed quarks localized at different points on the compact circle. We analytically compute the speed of sound and the sound wave attenuation in the quenched approximation. Since confinement/deconfinement (and the chiral symmetry restoration) phase transitions are first order in this model, we do not see any signature of these phase transitions in the transport properties.