Evolution Of Acoustic Waves Research Articles

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.

A comparison of the factorization approach to temporal and spatial propagation in the case of some acoustic waves

The evolution of acoustic waves can be evaluated in two ways: either as a temporal, or a spatial propagation. Propagating in space provides the considerable advantage of being able to handle dispersion and propagation across interfaces with remarkable efficiency; but propagating in time is more physical and gives correctly behaved reflections and scattering without effort. Which should be chosen in a given situation, and what compromises might have to be made? Here the natural behaviors of each choice of propagation are compared and contrasted for an ordinary second order wave equation, the time-dependent diffusion wave equation, an elastic rod wave equation, and the Stokes’/ van Wijngaarden’s equations, each case illuminating a characteristic feature of the technique. Either choice of propagation axis enables a partitioning the wave equation that gives rise to a directional factorization based on a natural ‘reference’ dispersion relation. The resulting exact coupled bidirectional equations then reduce to a single unidirectional first-order wave equation using a simple ‘slow evolution’ assumption that minimizes effect of subsequent approximations, while allowing a direct term-to-term comparison between exact and approximate theories.

Large Eddy Simulation of Self-Sustained Cavity Oscillation for Subsonic and Supersonic Flows

The primary objective is to perform a large eddy simulation (LES) using shear improved Smagorinsky model (SISM) to resolve the large-scale structures, which are primarily responsible for shear layer oscillations and acoustic loads in a cavity. The unsteady, three-dimensional (3D), compressible Navier–Stokes (N–S) equations have been solved following AUSM+-up algorithm in the finite-volume formulation for subsonic and supersonic flows, where the cavity length-to-depth ratio was 3.5 and the Reynolds number based on cavity depth was 42,000. The present LES resolves the formation of shear layer, its rollup resulting in large-scale structures apart from shock–shear layer interactions, and evolution of acoustic waves. It further indicates that hydrodynamic instability, rather than the acoustic waves, is the cause of self-sustained oscillation for subsonic flow, whereas the compressive and acoustic waves dictate the cavity oscillation, and thus the sound pressure level for supersonic flow. The present LES agrees well with the experimental data and is found to be accurate enough in resolving the shear layer growth, compressive wave structures, and radiated acoustic field.

Evolution of Acoustic Waves in Homogeneous Media with Different-Modulus Nonlinearity and Relaxation

We present the results of analytical and numerical studies of propagation and evolution of the initially harmonic acoustic waves in homogeneous media with different-modulus nonlinearity and relaxation. The solutions for the profiles of nonlinear waves and their spectral characteristics are obtained.

Simulation of the Transient Behavior of Matter with Characteristic Geometrical Variations & Defects Irradiated by Nanosecond Laser Pulses Using FEA

The thermomechanical transient response of matter illuminated by nanosecond laser pulses is modeled and simulated using the Finite Element Analysis (FEA). Matter’s behavior is numerically described by a three-dimensional (3D) multiphysics, coupled thermal structural, transient FEA, experimentally validated, model. FEA offers substantial insights into the materials’ micro-mechanical behaviour providing detailed information for the spatiotemporal evolution of acoustic waves. In this computational approach the impact of the geometric characteristics of the modeled metallic films to the generation and propagation of the ultrasonic waves, in relation to temperature, is investigated. The study is expanded to the dynamic reactions of matter in the presence of surface and solid volume defects and enclosures e.g.: gaps, holes or bubbles. The transient behavior of matter in the time and the space solution domains is obtained by the FEA model and presented.

The sensitivity of BAO dark energy constraints to general isocurvature perturbations

Baryon Acoustic Oscillation (BAO) surveys will be a leading method for addressing the dark energy challenge in the next decade. We explore in detail the effect of allowing for small amplitude admixtures of general isocurvature perturbations in addition to the dominant adiabatic mode. We find that non-adiabatic initial conditions leave the sound speed unchanged but instead excite different harmonics. These harmonics couple differently to Silk damping, altering the form and evolution of acoustic waves in the baryon-photon fluid prior to decoupling. This modifies not only the scale on which the sound waves imprint onto the baryon distribution, which is used as the standard ruler in BAO surveys, but also the shape, width and height of the BAO peak. We discuss these effects in detail and show how more general initial conditions impact our interpretation of cosmological data in dark energy studies. We find that the inclusion of these additional isocurvature modes leads to a decrease in the Dark Energy Task Force figure of merit (FoM) by 46% i.e., FoMISO = 0.54 × FoMAD and 53% for the BOSS and ADEPT experiments respectively when considered in conjunction with PLANK data. We also show that the incorrect assumption of adiabaticity has the potential to bias our estimates of the dark energy parameters by 2.7σ (2.2σ) for a single correlated isocurvature mode (CDM isocurvature), and up to 4.9σ (5.7σ) for three correlated isocurvature modes in the case of the BOSS (ADEPT) experiment. We find that the use of the large scale structure data in conjunction with CMB data improves our ability to measure the contributions of different modes to the initial conditions by as much as 95% for certain modes in the fully correlated case.

On the possibility of acoustic probing of gas wells

The possibility of probing the critical areas of gas wells using acoustic signals is analyzed. The results of investigations on the evolution of acoustic waves in cylindrical channels with permeable portions surrounded by a porous space are presented. The quantitative and qualitative features of the dynamics of waves as a function of the state of an inhomogeneous porous medium are established. Results showing that the state of the reservoir characteristics of rocks has a substantial influence on the evolution of acoustic signals are obtained.

Evolution of acoustic waves in microinhomogeneous media with quadratic elastic nonlinearity and relaxation

A nonlinear wave equation for the velocity “relaxator” is derived in the framework of the rheological model and the corresponding equation of state of a microinhomogeneous medium containing viscoelastic defects with quadratic nonlinear elasticity. The equation is qualitatively analyzed, and numerical solutions to it are presented for a stationary symmetric shock wave and the evolution of initially harmonic waves.

Acoustical wave propagator for time-domain flexural waves in thin plates.

In this paper, an explicit acoustical wave propagator technique is introduced to describe the time-domain evolution of acoustical waves in two-dimensional plates. A combined scheme with Chebyshev polynomial expansion and fast Fourier transformation is used to implement the operation of the acoustical wave propagator. Through this operation, the initial wave packet at t = 0 is mapped into the wave packet at any instant t > 0. By comparison of the results of the exact analytical solution and the Euler numerical method, we find that this new Chebyshev-Fourier scheme is highly accurate and computationally effective in predicting the acoustical wave propagation in thin plates. This method offers an opportunity for future study of dynamic stress concentration and time-domain energy flow in coupled structures.

Acoustical wave propagator technique for time‐domain analysis of dynamic stress in a step plate

In this paper, we introduce an explicit acoustical wave propagator technique to describe the time‐domain evolution of acoustical waves in two‐dimensional plates. This technique uses a combined scheme with Chebyshev polynomial expansion and fast Fourier transformation for implementation of the operation of the acoustical wave propagator. We also apply the acoustical wave propagator for studying dynamic stress in a step plate in time‐domain.

Evolution of acoustic waves in channels with permeable-wall regions in an inhomogeneous porous medium

The evolution of acoustic waves that propagate in cylindrical channels containing permeable regions and surrounded with a porous medium is studied. The quantitative and qualitative features of the wave dynamics are determined in relation to the condition of the inhomogeneous porous medium. In particular, cases when the channel is surrounded with radial fractures or with a low-permeability mudcake are considered.

Transient acoustic processes in a low-Mach-number shear flow

A systematic perturbation procedure, based on a small mean flow Mach number and large duct Reynolds number, is employed to formulate and solve an initial-boundary-value problem for acoustic processes in a shear flow contained within a rigid-walled parallel duct. The results describe the general transient evolution of acoustic waves driven by a plane source located at a given duct cross-section. Forced bulk oscillations near the source and oblique wave generation are shown to result from refraction of the basic planar axial disturbance by the shear flow. Refraction also causes the axial waves to exhibit higher-order amplitude variations in the transverse direction. As the source frequency approaches certain critical values, specific refraction-induced oblique waves evolve into amplifying purely transverse waves. As a result, the magnitude of the refraction effect increases with time, and quasi-steady solutions do not exist. The analysis is extended to the thin acoustic boundary layer adjacent to the solid walls to examine the shear-layer structure induced by the variety of acoustic waves in the core flow. Nonlinear effects and acoustic streaming are shown to be negligibly small on the scale of a few axial wavelengths.