Hollow cylinders often exhibit backward propagation modes whose group and phase velocities have opposite directions, these a minimum possible frequency at which the velocity vanishes nonzero wavenumber. These zero-group-velocity (ZGV) points are associated with resonant conditions in medium. On basis of ZGV resonances, non-contact laser ultrasound technique has been developed to measure elastic constants hollow pipes. This paper provides theoretical numerical investigation influence...

It is known that modes in axially uniform waveguides exhibit backward-propagation characteristics for which group and phase velocities have opposite signs. For elastic plates, of backward Lamb waves depend only on Poisson's ratio. This paper explores ways to achieve a large velocity mode hollow cylinders by changing the outer inner radius ratio, order such with strong may be used acoustic logging tools. Dispersion spectra guided varying radii are numerically simulated explore existence...

Abstract For soil liquefaction prediction from multiple data sources, this study designs a hierarchical machine learning model based on deep feature extraction and Gaussian Process with integrated domain adaption techniques. The proposed first combines fisher discriminant analysis (DDA) (GP) in unified framework, so as to extract features enhance the performance for classification. To deliver fair evaluation, classifier is validated approach of repeated stratified K -fold cross validation....

Temperature has a complex effect on acoustic dispersion in dilute gases. In this paper, the of temperature gases is analyzed theoretically and experimentally. Theoretically, Navier–Stokes (NS) equation Greenspan's theory, which includes rotational-relaxation correction, are applied to calculate dispersive sound speed. It concluded that affects molecular translational relaxation rotational by influencing average collision frequency number, respectively, thus, change amplitude dispersion....

This paper considers the propagation of Stoneley modes along interfaces three-layered concentric cylindrical solid media in order to assist design ultrasonic transmission rods. The phase velocity dispersion curves and amplitude distributions are numerically analyzed. analogous non-dispersive waves confined vicinities two at high frequency. A key finding is that peak location for each mode transfers between as a function simplified model introduced, giving locations different frequency ranges...

We investigate the guided waves in a multi-layered cylindrical elastic solid medium. The dispersion function of is usually complex and curves all modes are not conveniently obtained. Here we present an effective method to obtain modes. First, transformed into real function. then calculated for by bisection method. with orders n = 0, 1, 2 analysed two- three-layer media. existence condition Stoneley wave discussed. also investigated two-layer medium, which velocity shear outer layer less than...

Guided waves in plates and cylinders exhibit the backward propagation that group phase velocities have opposite directions. Backward might be used to control acoustic energy flux. The existence of waveguides has been well established, but direct visualization modes not widely reported. dynamic photoelastic method is able present stress distribution inside a solid material. In this paper, photoelasticity measure backward-wave motions plates, order obtain better understanding characteristics waves.

Experimental data on the sound speed in rarefied air are limited. We employed an environmental simulator to realise a low-pressure (200-10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> Pa) environment. The pressure control precision of reached ± 10 Pa, and temperature uniformity is ±5 °C. Transducers three different frequencies (21 kHz, 34 40 kHz) used measure speed. results demonstrated increasing trend experimental as decreased air....

On 13–15 January 2022, the Hunga Tonga–Hunga Ha'apai underwater volcano erupted. This powerful eruption generated infrasonic waves with amplitudes of thousands Pascals in near field. The ground stations China, located approximately 10 000 km from volcano, also received frequencies 0.01 to 0.05 Hz. However, amplitude reached 17 Pa, which is higher than predicted using absorption model without considering dispersion effect thin thermosphere. At high altitudes, exists and sound speed depends on...

This paper presents an investigation into the dispersion of guided waves in cylindrical multi-layered solid media. will aid design ultrasonic transmission rods, consisting a metal rod surrounded by sheath, used liquid cleanliness measurements. The aim is to understand material parameters which define regions normal and anomalous dispersion, such that sheath transmitted frequency range can be designed improve measurement surrounding medium. Three models were created for infinite length rods:...

Liquid-filled pipes that are widely used in industries must be regularly inspected for the structure integrity. Elastic guided waves suitable long-range pipe inspections. In this paper, influences of flowing speed and temperature fluid flow on propagation properties filled with high liquid metals investigated. The dispersion equation is theoretically derived applying coordinate transformations, then simplified to get its approximation form, finally numerically solved obtain curves. aim...

In this paper, the dispersion characteristics and excitation mechanisms of guided waves propagated in a cylindrical multi-layered elastic solid medium are investigated. The equation is generally plural function for real axial propagation velocity. We transform it into employ bisection technique to find all roots, order give curves waves. All modes two-, three-, four-, five-layered models studied. intensities excited by symmetric point source, radial force sources They highly relied on both...

At present, Mars acoustic detection is gradually becoming an important new tool for understanding and exploring Mars. To explore the sources of sound, it necessary to study sound speed attenuation in thin low-temperature Martian atmosphere, model propagation stratified atmosphere. According extremely low pressure large variation gas composition with altitude, we propose a simulation method based on Navier-Stokes (NS) equation mixed-gas calculate vertical profiles atmosphere at 0–250 km...

For an elastic circular hollow-pipe, a backward wave possesses only one zero-group-velocity (ZGV) point at which the group velocity vanishes non-zero wavenumber. Based on ZGV resonance, non-contact laser technique has been developed to measure material properties and wall-thickness of hollow pipes. In this paper, dispersion, excitation properties, mode structures waves associated modes in liquid-filled pipes are investigated, order explore whether ZGV-resonance could be applied for...

For acoustic logging, the estimation of rock properties from Stoneley waves is considerable importance. wave interfacial propagating on interface between borehole liquid and formation. In majority cases in physics, phase velocity decreases with frequency, so that this type dispersion referred to as normal dispersion. On other hand, increases frequency. It happens less frequently it anomalous However, dispersions are commonly encountered for waves. We studied influences formation existence...

Acoustical well logging is a widely used technique in oil fields to investigate the formation outside wells and quality of wells. The knowledge acoustical behavior important has been studied. are usually modeled as fluid filled cylindrical borehole an infinite solid medium. This structure with section, sometimes called open waveguide, more difficult study than typical waveguide finite section free or rigid boundaries. In this presentation studied coupled vibration system consisted cylinder...

Backward Lamb waves, which exhibit a group velocity that propagates in the opposite direction to their phase velocity, have recently garnered considerable attention for potential applications nondestructive testing. Herein we present theoretical study on backward waves elastic plate subject prestresses. We demonstrate of first antisymmetric wave, A3b, decreases with tensile stress, whereas symmetric S2b, increases. Notably, sensitivity A3b prestress is approximately ten times greater than...

Theoretical and numerical analyses of propagating properties non-asymmetric flexural modes in a three-layered cylindrical transmission rod model are presented this paper. The first order mode segments the higher behaving assemble to Stoneley waves along inner outer interfaces, respectively. Investigations coupling between assist understand exhibition characteristics infinite number separated wave segments.

Future China mission to explore the planet Mars may carry acoustic probes. Because sound interacts with matter intimately, they could be used in measure wind speed directly, record possible ambient sounds, and assist safety of a travelling Lander by inspecting obstacles detecting soft subsurface soil which might cause being trapped. All these Martian anemometer, microphone, ultrasound inspector need designed specifically adapt low-pressure, low-temperature, mainly CO <inf...

The variation of sound speeds air and nitrogen gas at temperatures from 15 to -80 °C, pressures 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> 150 Pa have been measured in a KM2G space simulator. objective is provide the primary acoustic parameters set up proper multi-layered near-space atmosphere model, so that simulate propagation paths waves. From experimental data, both decrease with decreasing temperature °C pressure about 5000...

At present, Mars acoustic detection is gradually becoming an important new tool for the knowledge and exploration of Mars. To explore sources sound, it necessary to study sound speed attenuation in thin low-temperature Martian atmosphere, model propagation stratified atmosphere. Based on extremely low pressure large variation gas composition with altitude, we proposed a simulation method based Navier-Stokes (NS) equation mixed-gas calculate vertical profiles atmosphere at 0~250 km altitude...