Propagation Characteristics Of Acoustic Waves Research Articles

Analysis of Influence of Excitation Source Direction on Sound Transmission Loss Simulation Based on Alloy Steel Phononic Crystal

As a type of locally resonant phononic crystal, alloy steel phononic crystals have achieved notable advancements in vibration and noise reduction, particularly in the realm of low-frequency noise. Their exceptional band gap characteristics enable the efficient reduction of vibration and noise at low frequencies. However, the conventional transmission loss (TL) simulation of finite structures remains the benchmark for plate structure TL experiments. In this context, the TL in the XY-direction of phononic crystal plate structures has been thoroughly investigated and analyzed. Given the complexity of sound wave incident directions in practical applications, the conventional TL simulation of finite structures often diverges from reality. Taking tungsten steel phononic crystals as an example, this paper introduces a novel finite element method (FEM) simulation approach for analyzing the TL of alloy steel phononic crystal plates. By setting the Z-direction as the excitation source, the tungsten steel phononic crystal plate exhibits distinct responses compared to excitation in the XY-direction. By combining energy band diagrams and modes, the impact of various excitation source directions on the TL simulations is analyzed. It is observed that the tungsten steel phononic crystal plate exhibits a more pronounced energy response under longitudinal excitation. The TL map excited in the Z-direction lacks the flat region present in the XY-direction TL map. Notably, the maximum TL in the Z-direction is 131.5 dB, which is significantly lower than the maximum TL of 298 dB in the XY-direction, with a more regular peak distribution. This indicates that the TL of alloy steel phononic crystals in the XY-direction is closely related to the acoustic wave propagation characteristics within the plate, whereas the TL in the Z-direction aligns more closely with practical sound insulation and noise reduction engineering applications. Therefore, future research on alloy steel phononic crystal plates should not be confined to the TL in the XY-direction. Further investigation and analysis of the TL in the Z-direction are necessary. This will provide a novel theoretical foundation and methodological guidance for future research on alloy steel phononic crystals, enhancing the completeness and systematicness of studies on alloy steel phononic crystal plates. Simultaneously, it will advance the engineering application of alloy steel phononic crystal plates.

The acoustic Galton board

Phononic crystals are a class of materials with periodic structures that influence the propagation characteristics of acoustic waves through periodically arranged structural units. Here, we have developed the acoustic Galton board (AGB), a groundbreaking apparatus that serves as a cost-effective and user-friendly tool for demonstrating phononic crystal properties such as band gaps, Bragg scattering, and local resonance. The device comprises an elastic wave signal generator, an enhanced Galton board featuring a sophisticated pillar-nail array, and a signal receiver. The experimental results we have obtained demonstrate the significant impact of the AGB on elastic wave dispersion, effectively creating bandgaps that impede wave transmission within specific frequency ranges while allowing unhindered propagation in others. Furthermore, the AGB can simulate phononic crystals using both the Bragg scattering mechanism, achieved through the design of periodic rigid pillar-nail arrays, and the locally resonant mechanism, facilitated by the design of pillar-nail arrays with composite material structures. Additionally, the AGB can extend its applications to serve as a simulation tool for elastic metamaterials.

Impact of acoustic wave propagation characteristics on aerodynamic damping of rotor blades in a transonic axial compressor

The aeroelastic stability associated with the acoustic wave propagation characteristics of transonic rotor blades was numerically investigated in this study. The influence of the vibration frequency on the aerodynamic damping of the first bending mode was primarily considered at different speeds, including both work and stall points. We found that the state of acoustic wave propagation associated with aeroelastic instability is closely related to rotational speed. At low speeds near stall points, the risk of aeroelastic instability is confined to the upstream cut-off state. However, at high speeds near stall points, aeroelastic instability may occur in both the downstream cut-off state and the acoustic wave propagation state of the upstream cut-off frequency, further expanding the range of the acoustic wave propagation state in which aeroelastic instability can arise. The research findings show that for suction surfaces, aerodynamic work is affected not only by acoustic wave propagation characteristics, but also by shock waves, radial flow, and reflux in the flow field. However, for pressure surfaces, the acoustic wave propagation characteristics play a significant role. When aeroelastic instability occurs, negative damping predominantly arises from the pressure surface. To investigate why lower-order modes are more prone to aeroelastic instability, specific simulations were conducted for the first bending and twisting modes under different operating conditions in the downstream cut-on state. When the vibration frequency significantly exceeds the downstream cut-off frequency, the blade phase is minimally influenced by acoustic wave propagation characteristics, and the rotor is aeroelastically stable in these phases. Simultaneously, there is an approximately linear increase in the unsteady pressure amplitude with increasing vibration frequency, and the aerodynamic work is predominantly influenced by the unsteady pressure amplitude.

Theoretical and numerical study on transient acoustic wave propagation across ice layers in the Arctic Ocean.

The study of transient acoustic wave propagation across the Arctic Ocean ice layer provides theoretical guidance for the design of trans-ice acoustic communication systems. In this study, the Arctic Ocean was modeled as an ice-water composite structure, where the ice and water are regarded as an elastic solid and liquid, respectively. An analytical transient solution for acoustic wave propagation in this structure was derived using the eigenfunction expansion method. Further, the numerical procedures were presented and used to analyze the acoustic wave propagation characteristics across the ice layer. The results show that waveforms corresponding to the radial displacements are more severely distorted than the axial displacements. The amplitudes of the radial and axial displacements decreased rapidly with increasing propagation distance. The ice thickness had a greater impact on the radial displacement than axial displacement; the thicker the ice, the greater the distortion for both radial and axial displacements.

Propagation Characteristics of Acoustic Emission Waves in Three Different Asphalt Pavement Materials

Propagation Characteristics of Acoustic Emission Waves in Three Different Asphalt Pavement Materials

Propagation characteristics of nonlinear dust acoustic solitary waves in complex plasma with nonthermal electrons and trapped ions

The propagation characteristics of nonlinear dust acoustic solitary waves in a complex plasma system with nonthermal electrons and trapped ions are investigate in this work. The nonlinear dispersion relation of dust acoustic waves is obtained by using the linear method, and the two-dimensional autonomous system governing the motion of nonlinear dust acoustic waves is derived by using the Sagdeev potential method. At the same time, the specific expression of the Sagdeev potential function is obtained based on the Sagdeev potential equation. The numerical simulations are used to analyze the phase portraits of the two-dimensional autonomous system, revealing the linear periodic wave orbits, nonlinear periodic wave orbits, and homoclinic orbits co-existing in the complex dusty plasma system with nonthermal electrons and trapped ions. Furthermore, from the variations of the Sagdeev potential function with different system parameters it follows that only the compressive solitary waves exist in this complex plasma system. The significant influences of various system parameters on the amplitude, width, and waveform of the nonlinear dust acoustic solitary wave in the complex plasma system are discussed in detail. The results demonstrate that the Mach number, the nonthermal electrons and trapped ions, undisturbed dust particle number density, temperature, and charge have important effects on the propagating characteristics of the nonlinear dust acoustic solitary waves in a complex plasma with nonthermal electrons and trapped ions.

Surface acoustic wave digital microfluidics with surface wettability gradient.

This paper reports a digital microfluidic technology that combines surface wettability gradient and surface acoustic waves. The technology enables selection of the driven object, facilitating reactions among multiple droplets and improving the precision of droplet control. Octagonal patterns with a wetting gradient and orthogonally distributed interdigital transducers were created on the surface of a LiNbO3 wafer by photolithography. Leveraging the propagation characteristics of surface acoustic waves on different wetting models, the latter serve as a switch for microfluidic motion, successfully achieving selection of the driven object and demonstrating sequential reactions among multiple droplets. Also, under the excitation of standing surface acoustic waves, droplets on the wetting gradient surface move slightly in the direction of wetting gradient descent, significantly enhancing the positional accuracy of the droplets to the micrometer level. With the advantages of surface acoustic wave digital microfluidics, this technology addresses the challenges of multi-droplet digital manipulation and improved droplet positional accuracy.

Experimental study on the acoustic wave propagation characteristics of bedding shales under changes in temperature and pressure

To determine the acoustic wave propagation characteristics of bedded shales under different confining pressures and temperatures, shales from the Longmaxi Formation in the Sichuan Basin are taken as research objects. Based on ultrasonic experiments, the acoustic wave propagation properties of shales with different bedding angles are investigated. The effects of the confining pressure, temperature, and bedding angle on the acoustic velocity, attenuation coefficient, and acoustic anisotropy coefficient are analyzed. Based on the results, an acoustic velocity prediction model for bedded shales considering the confining pressure, temperature, and bedding angle is established. The experiments show that, for confining pressures from 0 to 50 MPa and temperatures from 20 to 100 °C, the acoustic velocity of the shales increases with increasing confining pressure and decreases with increasing temperature and bedding angle. The attenuation coefficient of the shales exhibits a decreasing trend with increasing confining pressure, but increases with increasing temperature and bedding angle. The acoustic anisotropy coefficient of shale gradually decreases with increasing confining pressure, but increases with increasing temperature and bedding angle. The acoustic velocity prediction model for in-situ bedded shales established in this study has a high level of accuracy. The relationship between the acoustic anisotropy coefficient and the bedding angle is satisfied by a binomial equation. The relationship between the acoustic anisotropy coefficient and the confining pressure and temperature follows a binary linear logarithmic equation.

Vibration Characteristics and Location of Buried Gas Pipeline under the Action of Pulse Excitation

In this paper, the attenuation of sound waves in underground gas pipelines and the vibration characteristics of pipelines are studied, and the feasibility and effectiveness of acoustic measurement of PE pipelines are verified. In this paper, the attenuation equation of sound waves in an underground gas transmission pipeline is derived based on the propagation characteristics of gas and the vibration characteristics of the pipeline itself. In order to verify the experimental results, we conducted an experimental test on the air pipeline model and verified the feasibility and effectiveness of the acoustic measurement of the PE pipeline through the test under the action of pulse excitation. Then, we detect the background noise, design the test scheme according to the characteristics of the buried pipeline, and select the test site for field test. In the test process, we collected the test data and obtained the spectrum diagram of the test data by fast Fourier transform (FFT). By analyzing the results of the spectrogram, we find that the pulse signal can penetrate the medium composed of the pipe formation, but the amplitude of the sound will be sharply attenuated. At the same time, according to the size of the peak in the spectrum, we can determine the location of the pipe. In summary, the feasibility and effectiveness of acoustic measurement of the PE pipeline are verified through experimental tests, and attenuation equations based on acoustic wave propagation characteristics and pipeline vibration characteristics are proposed. It has important practical application value for the safety monitoring and positioning of the buried gas pipeline.

Effects of confining pressure and pore pressure on multipole borehole acoustic field in fluid-saturated porous media

In-situ stress is a common stress in the exploration and development of oil reservoirs. Therefore, it is of great significance to study the propagation characteristics of borehole acoustic waves in fluid-saturated porous media under stress. Based on the acoustoelastic theory of fluid-saturated porous media, the field equation of fluid-saturated porous media under the conditions of confining pressure and pore pressure and the acoustic field formula of multipole source excitation in open hole are given. The influences of pore pressure and confining pressure on guided waves of multipole borehole acoustic field in fluid-saturated porous media are investigated. The numerical results show that the phase velocity and excitation intensity of guided wave increase significantly under the confining pressure. For a given confining pressure, the phase velocity of the guided wave decreases with pore pressure increasing. The excitation intensity of guided wave increases at low frequency and then decreases at high frequency with pore pressure increasing, except for that of Stoneley wave which decreases in the whole frequency range. These results will help us get an insight into the influences of confining pressure and pore pressure on the acoustic field of multipole source in borehole around fluid-saturated porous media.

Research on Conditions and Influence Factors of an Acoustic Wave Acting as a Plane Wave in Tire Acoustic Cavity

Tire acoustic cavity resonance noise (TACRN) contributes significantly to the interior noise of electric cars and passenger cars with lower powertrain noise, which affects the comfort of the ride. To suppress TACRN effectively, it is crucial to clarify the characteristics of TACRN. In previous studies, the acoustic wave in the tire acoustic cavity is straightforwardly assumed to be the plane wave for convenience. In fact, there exist strict conditions for the acoustic wave propagating in the pipeline to act as a plane wave. The aim of this paper is to make the characteristics and evolution of acoustic waves in tire acoustic cavities clear. To do so, a simplified model of the tire cavity is established, and the sound field distribution and the acoustic wave propagation characteristics in the tire cavity are analyzed based on the theory of acoustic waveguide. Then, the existence ranges of higher-order waves (non-plane waves), the conditions of an acoustic wave evolving into a plane wave, and the frequency range of a plane wave are investigated. Finally, the characteristics and evolution law of an acoustic wave in a tire acoustic cavity are obtained. The work in this paper may deepen the understanding of the characteristics and mechanism of acoustic waves in the tire cavity and be helpful and meaningful for analyzing and suppressing TACRN. Therefore, it is of practical significance to reduce TACRN transmitted to the vehicle and improve the sound quality inside the vehicle.

Quantitative detection of crack depth in V-groove weld using laser-generated surface acoustic waves

Thick-walled structures are widely used in kinds of high-end equipment. As the most conventional method adopted to manufacture large-scale structures, multi-pass butt-welds are one of the most critical areas prone to defects. In this paper, we focus on the quantitative detection of crack depth in a V-groove weld using laser-generated surface acoustic waves. A two-dimensional finite-element method with Q345 steel is adopted to reveal the complicated propagation characteristics of laser-generated surface acoustic waves with surface cracks. The displacement fields are discussed to show the wave transmission, reflection, and mode-conversion phenomena. The main propagating wave modes—P, R, R′, R′r, and R′t waved—are distinguished with the help of the out-of-plane displacement under different crack depths in the time domain. It is found that R′r can be used to locate the cracks and R′t can be used to quantify the depth of the cracks.

Observations of the Roots of Plasma Bubbles: Are They Sometimes Foamy?

AbstractDramatic irregularities in the plasma density of the ionosphere, first discovered by their effects on radio wave propagation in 1938, despite decades of investigation, still remain puzzling. Their deleterious effects on radio wave communication, satellite command and control, and GPS navigation strongly motivate better understanding of their nature. Many aspects of such irregularities are now understood, but the mechanism(s) of their formation and their detailed nature remain a topic of great interest. In this work, detailed time resolved measurements of lightning generated waves sometimes show dispersionless, strongly attenuated propagation with substantial propagation delays. These characteristics of the electromagnetic wave propagation in the hypothetical two‐phase bubble/non‐bubble lower ionosphere parallel the characteristics of acoustic wave propagation through two‐phase liquid/vapor foams. This motivates the suggestion that the bottomside layer of the ionosphere may sometimes be foamy.

Theoretical investigation of Rayleigh surface acoustic wave propagation characteristics in c-axis-zigzag ScAlN film/silicon substrate structure

Surface acoustic wave (SAW) resonators are key components of mobile communication systems, and the development of wideband SAW resonators is especially required because next-generation mobile communication systems require high-speed data transmission using wide frequency bands. In this study, two layered structures—(i) a c-axis-tilted ScAlN bilayer film/silicon substrate and (ii) a c-axis-zigzag ScAlN film/silicon substrate—are proposed for highly coupled SAW resonators, and the electromechanical coupling coefficient K2 of the non-leaky Rayleigh-mode SAW propagating in these structures is investigated theoretically. With a proper c-axis tilt angle and thickness selection of the ScAlN film, the first-mode Rayleigh SAW in the c-axis-tilted ScAlN bilayer film/silicon substrate and c-axis-zigzag ScAlN film/silicon substrate offers high K2. The maximum K2 was 9.56%, obtained in the c-axis-zigzag ScAlN film/silicon substrate structure, which was 2.5 times the maximum K2 in the c-axis-tilted ScAlN monolayer film/silicon substrate structure; this is because the c-axis-zigzag ScAlN films increase the shear vertical component of the SAW particle displacement, most of which is concentrated in the c-axis-zigzag ScAlN film on the silicon substrate. It is also important that the second-mode SAW (Sezawa wave) in the c-axis-zigzag ScAlN film/silicon substrate structure is not excited when the K2 value of the first-mode SAW is maximized. The techniques for fabricating a c-axis-tilted ScAlN film and a c-axis-zigzag ScAlN film have been reported, and well-established micromachining technology related to silicon semiconductors offers significant advantages in the manufacturing and processing of SAW resonators. Therefore, the c-axis-zigzag ScAlN film/silicon substrate structure has significant potential for SAW device applications.

Experimental Study on Downhole Acoustic Wave Propagation Characteristics in Curved Drill String

Aiming at the problem of the unclear sound wave attenuation in the signal transmission of the load-bearing drill string, an experimental device for the sound wave propagation characteristics in the curved drill string was set up. The influence of the drill string structure and acoustic excitation parameters on the sound propagation characteristics in the drill string under different loads is different. The results show that the curvature of the drill string has an influence on the propagation of the sound wave in the drill string, and its rule is related to the curvature of the drill string and the frequency of the sound wave. The pulse repetition rate, excitation voltage, and pulse width only affect the passband amplitude, and the effect is significantly greater than the curvature of the drill string. The main influencing factor of its sound transmission characteristics is the degree of drill string curvature. The low-frequency signal should be preferentially selected as the carrier of downhole information transmission after considering the influence of drill string bending on acoustic transmission.

Analyzing the acoustic wave propagation characteristics in discontinuous bifurcated waveguide

This article examines the dispersion characteristics and energy distribution in different regions of the bifurcated waveguide with vertical step discontinuities. In this research study, we have considered mathematical model of noise reduction devices, specifically analyzing the acoustic wave propagation problem in a bifurcated waveguide with elastic membrane outer plates and rigid inner plates. Mode-matching (MM) technique is employed to match the eigenfunctions at the interface and analyzed the reflection and transmission amplitudes in all regions. Through MM scheme an infinite system of equations has been obtained for these boundary conditions by dividing the structure into three regions and finding dispersion relations and eigenfunctions using separation of variables and the corresponding orthogonality relations. Because of the flexible nature of the boundary surfaces, the acquired eigenfunctions and the dispersion relation do not satisfy the standard orthogonality relation. To resolve this difficulty, we have established a modified orthogonality relation to take into account the flexible nature of the boundary surfaces. With the implication of physical connections, the uniqueness of the problem has been ensured, and zero displacement and zero gradient edge conditions on bending surfaces have been considered to present results. Energy expressions are obtained showing how the energy is distributed in different sections of the waveguide, which is consistent with the energy conservation law. Finally, the numerical discussion illustrates the quantitative behavior of the physical parameters and summarizes the significant contribution of the study by presenting graphical data.

Stability of dust-acoustic solitary waves in magnetized dusty plasmas: effect of polarization force and degenerate electron temperature

The influence of polarization force, trapped degenerate electrons, and nonthermal ions on the propagation characteristics of dust acoustic solitary waves (DASWs) in a magnetized dusty plasma is investigated. The reductive perturbation approach has been adopted to derive the extended Zakharov-Kuznetsov (eZK) equation and the solitary pulse solution is obtained to investigate the characteristics of DASWs. Pulse stability has also been analysed following the method proposed by Allen and Rowlands. Influence of different relevant plasma parameters on the growth rate of DASWs is studied. It is also found that the relevant plasma parameters have significant impact on the instability criteria of DASWs. This investigation is useful in explaining the nonlinear structures in ultra-dense degenerate plasma media which may exist in astrophysical compact objects (e.g., white dwarfs, neutron stars, etc.) and high density plasma experiments in which plasma degeneracy and relativistic effects play an important role.

Experimental study on leakage location of branched pipelines based on acoustic propagation characteristics

In order to study the principle of leakage location for branched pipeline based on acoustic propagation characteristics, an acoustic propagation model of branched pipelines is established, and the propagation characteristics of acoustic waves in branched pipeline are obtained by analyzing the continuous acoustic signals generated by pipe leakage, a new leakage location method of branched pipelines based on acoustic propagation characteristics is proposed. Experimental results show the leakage position in branched pipeline system is accurately located with an average relative error of 3.2%. It is proved that the new location method for the leakage location of branched pipelines has wide applicability and improved accuracy, which can contribute great significance to expanding application scenarios of leakage location method based on acoustic propagation characteristics as well.

Finite element analysis on the propagation characteristics of laser-generated surface acoustic wave in V-groove weld

Thick-walled structures, such as marine engineering and rail transportation, are widely used in modern society. V-groove welding is a common welding method in thick structures. At the same time, the V-groove weld is also the area of a thick-walled structure in which defects are most easily formed. Laser-generated surface acoustic waves are a promising non-destructive testing method in most fields. This study examined the propagation characteristics of laser-generated surface acoustic waves in a V-groove weld. A two-dimensional finite element model with Q345 steel was constructed. A thermoelastic mechanism was adopted to generate the wave. The temperature and displacement fields were analyzed in detail. The results showed that wave transmission, reflection, and mode conversion are generated with an R wave at the junction, and the dispersion phenomenon of the R wave occurred in the welded area.

Influencing mechanisms of gas bubbles on propagation characteristics of leakage acoustic waves in gas-liquid two-phase flow

Propagation speed of acoustic waves in liquid can be significantly degraded when gas bubbles exist. To reveal the influence of gas bubbles on propagation characteristics of leakage acoustic waves in liquid pipelines, numerical simulation is utilized in the present paper. It can be divided into three stages when leakage acoustic waves propagate through a single gas bubble and the influence of each stage on propagation characteristics of acoustic waves is discussed. In gas-liquid two-phase flow, there are two basic mechanisms of gas resistance on wave propagation: elastic resistance effect and drag resistance effect. The results show that the influence of elastic resistance effect on sound speed is much greater than that of drag resistance effect. When propagating through a long gas bubble with the radius of 2 mm and the length of 7 mm, the elastic resistance effect causes a time delay of 0.00038 s while the drag resistance effect only causes a time delay of 0.00002 s. The results of this paper contribute to better understanding of the differences in acoustic wave propagation characteristics between different flow patterns in gas-liquid two-phase flow, and lay a foundation for the utilization of acoustic leakage detection methods in gas-liquid two-phase flow pipelines.