Propagation Speed Of Acoustic Waves Research Articles

Investigation on effects of water-shale interaction on acoustic characteristics of organic-rich shale in Ordos Basin, China

The water-shale interaction affect the shale structure, leading to wellbore instability and increasing drilling costs. The extent of structural changes within the shale can be determined non-destructively by analyzing its acoustic characteristics. Experiments were conducted to investigate the acoustic properties of shale from the Yanchang Formation in the Ordos Basin before and after exposure to brines of varying types, soaking times, and salinities. The study investigated the effects of brine type, soaking time, and salinity on shale’s acoustic properties, including changes in acoustic wave propagation speed, P/S wave velocity ratio, and both time-domain and frequency-domain amplitudes. The results indicate that although the type of brine has a limited impact on the water-shale interaction, KCl exhibits a significant inhibitory effect. However, the soaking time and the brine salinity have a significant impact on the acoustic properties of shale. As the soaking time increases, the decrease in wave velocity increases, the P/S wave velocity ratio increases, and the decrease in time-domain amplitude increases. The amplitude of the main frequency in the frequency domain signal also decreases with the increase of reaction time, which is consistent with the analysis results of the time domain signal. As the salinity of brine increases, the decrease in wave velocity decreases, the P/S wave velocity ratio decreases, and the decrease in time-domain amplitude decreases. The amplitude of the main frequency in the frequency domain signal also decreases with the increase of brine salinity, which is consistent with the analysis results of the time domain signal. This work establishes the relationship between water-shale interaction and acoustic characteristics, which can quantitatively evaluate the degree of interaction between water and shale without damaging shale. Furthermore, this research provides new insights and guidance for predicting drilling collapse cycles and optimizing drilling fluid compositions.

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.

Vibrational, thermodynamic and acoustic properties of AgAlS2 crystal

First-principles calculations of vibrational properties of AgAlS2 crystal have been performed for the first time. The phonon dispersion and phonon density of states were calculated. Phonon dispersion curves disclose dynamical stability of the system. The group-theoretical classification of vibrational modes has been done and classification according to selection rules of modes active in infrared and Raman spectra has been performed. Raman and infrared spectra of AgAlS2 were calculated within the DFPT method. The LO-TO splitting of the infrared modes are reported. The effective Born charges for constituent atoms of the crystal were calculated and analyzed. Thermodynamic functions such as enthalpy, entropy, free energy and heat capacity at constant volume are obtained. The propagation velocities of longitudinal and transverse acoustic waves in the crystal were calculated for the (100) and (001) directions. The anisotropy coefficients are calculated and anisotropy of the propagation speed of acoustic waves in AgAlS2 crystal is analyzed.

Investigation on propagation mechanism of leakage acoustic waves in gas-liquid stratified flow

Propagation speed of acoustic waves is of vital importance in pipeline leakage detection using acoustic method. However, the wave front shape and thermodynamic process of leakage acoustic waves in gas-liquid stratified flow remain unclear, which restricts the proper calculation of sound speed in this flow pattern. This paper presents a simulation study using CFD software Fluent to investigate the propagation process of leakage acoustic waves in stratified flow. The leakage acoustic waves are generated in different fluid phases and small time-step simulation is implemented to study the pressure behavior during the wave propagation. The results show that leakage acoustic waves propagate as single plane wave in gas-liquid stratified flow and the propagation process is nearly adiabatic. The value of polytropic exponent when calculating the sound speed in gas phase should be 1.4. Further, experimental study is conducted to verify the simulation results. Influencing factors including pressure and void fraction are considered. The present results contribute to the proper selection of sound speed calculation model in stratified flow, which can improve the leakage detection accuracy in gas-liquid stratified flow pipelines.

Autonomous Machine Learning Algorithm for Stress Monitoring in Concrete Using Elastoacoustical Effect.

The measurement of stress in concrete structures is a complex issue. This paper presents a new measurement system called a self-acoustic system (SAS), which uses frequency measurements of acoustic waves to determine the condition of concrete structures. The SAS uses a positive feedback loop between ultrasonic heads, which causes excitation to a stable limit cycle. The frequency of this cycle is related to the propagation time of an acoustic wave, which directly depends on stresses in the test object. The coupling mechanism between acoustic wave propagation speed and stress is the elastoacoustic effect described in this paper. Thus, the proposed system enables the coupling between the limit cycle frequency and the stress degree of the concrete structure. This paper presents a machine learning algorithm to analyse the frequency spectrum of the SAS system. The proposed solution is a real-time classifier that enables online analysis of the frequency spectrum from the SAS system. With this approach, an autonomous system for stress condition identification of concrete structures is built and described.

Self-Organized Proactive Routing Protocol for Non-Uniformly Deployed Underwater Networks.

Electromagnetic (EM) waves cannot propagate more than few meters in sea water due to the high absorption rate. Acoustic waves are more suitable for underwater communication, but they travel very slowly compared to EM waves. The typical speed of acoustic waves in water is 1500 m/s, whereas speed of EM waves in air is approximately 3 × 108 m/s. Therefore, the terrestrial wireless sensor network (WSN) protocols assume that the propagation delay is negligible. Hence, reactive protocols are deemed acceptable for WSNs. Other important issues related to underwater wireless sensor networks (UWSNs) are determining the position of the underwater nodes and keeping a time synchronization among the nodes. Underwater nodes can neither determine their position nor synchronize using Global Navigation Satellite Systems (GNSS) because of the short penetration of EM waves in sea water. The limited mobility of UWSN nodes and variation in the propagation speed of acoustic waves make time synchronization a challenging task for underwater acoustic networks (UASNs). For all these reasons, WSN protocols cannot be readily used in UASNs. In this work, a protocol named SPRINT is designed to achieve high data throughput and low energy operation in the nodes. There is a tradeoff between the throughput and the energy consumption in the wireless networks. Longer links mean higher energy consumption. On the other hand, the number of relay nodes or hops between the source node and the final destination node is a key factor which affects the throughput. Each hop increases the delay in the packet forwarding and, as a result, decreases the throughput. Hence, energy consumption requires the nearest nodes to be chosen as forwarding nodes, whereas the throughput requires the farthest node to be selected to minimize the number of hops. SPRINT is a cross-layer, self-organized, proactive protocol which does not require positioning equipment to determine the location of the node. The routing path from the node to the gateway is formed based on the distance. The data sending node prefers to choose the neighbor node which is closest to it. The distance is measured by the signal strength between the two nodes.

Dual-Hop TDA-MAC and Routing for Underwater Acoustic Sensor Networks

This article investigates the application of underwater acoustic sensor networks (UASNs) for large scale monitoring of the ocean environment. The low propagation speed of acoustic waves presents a fundamental challenge for medium access control (MAC)—coordinating the access of multiple nodes to the shared acoustic communication medium. In this article, we propose sequential dual-hop transmit delay allocation MAC (SDH-TDA-MAC)—a centralized MAC and routing protocol that facilitates efficient dual-hop scheduling in UASNs without the need for clock synchronization among the sensor nodes. BELLHOP-based simulations of a 100 node network reveal that SDH-TDA-MAC can achieve full network connectivity with 16-dB lower transmit power, compared with the single-hop TDA-MAC protocol. This provides considerable energy savings, while still providing network goodput in excess of 50% of the channel capacity. We also present a method of incorporating routing redundancy into the SDH-TDA-MAC protocol that achieves a good tradeoff between the network throughput and reliability. For example, in a channel with 10% probability of link outage, incorporating double routing redundancy into SDH-TDA-MAC increases the packet delivery ratio from 81% to 95%, a significant improvement in network reliability, while still achieving the network goodput of 22% of the channel capacity, considerably higher than typical MAC protocols designed for UASNs. In summary, the high network goodput, low transmit power compared with the single-hop approach, no requirement for clock synchronization, and robust packet delivery via route diversity make SDH-TDA-MAC an efficient, reliable, and practical approach to data gathering in UASNs.

Slow sound laser in lined flow ducts.

This work considers the propagation of sound in a waveguide with an impedance wall. In the low frequency regime, the first effect of the impedance is to decrease the propagation speed of acoustic waves. Therefore, a flow in the duct can exceed the wave propagation speed at low Mach numbers, making it effectively supersonic. This work analyzes a setup where the impedance along the wall varies such that the duct is supersonic then subsonic in a finite region and supersonic again. In this specific configuration, the subsonic region acts as a resonant cavity, and triggers a laser-like instability. This work shows that the instability is highly subwavelength. Besides, if the subsonic region is small enough, the instability is static. This work also analyzes the effect of a shear flow layer near the impedance wall. Although its presence significantly alters the instability, its main properties are maintained. This work points out the analogy between the present instability and a similar one in fluid analogues of black holes known as the black hole laser.

Doppler Scaling Factor Estimation and Receiver Design for Underwater Acoustic Communication

Due to very low propagation speed of acoustic waves, underwater communication via acoustic waves observe a significant Doppler scaling in the received signal. In addition, due to severe frequency selective fading in underwater acoustic channel, the distinct multi-paths may induce different Doppler scaling factor. In this paper, we investigate a transmission strategy in which we append preamble and post-amble in the data frame to estimate the Doppler scaling factor. The frequency selective fading coefficients and additive noise in the system model are statistically characterized by Nakagami and Generalized Gaussian distribution, respectively. Further, the transmit data is assumed to be orthogonal frequency division multiplexing (OFDM) modulated to mitigate the frequency selective nature of underlying channel. In our analysis, we consider two scenarios: (1) multi-paths have common Doppler scaling factor and (2) multi-paths have different Doppler scaling factor. For both the scenarios, we propose receiver algorithms to detect OFDM symbols corrupted by multi-path propagation. We also discuss the improvement in bit error rate performance by exploiting maximal ratio combining scheme. Finally, we validate our approach in the proposed techniques by showing improvement in bit error rate performance via simulation under various signal to noise ratio and fading conditions.

Self-Organized Fast Routing Protocol for Radial Underwater Networks.

An underwater wireless sensor networks (UWSNs) is an emerging technology for environmental monitoring and surveillance. One of the side effects of the low propagation speed of acoustic waves is that routing protocols of terrestrial wireless networks are not applicable. To address this problem, routing strategies focused on different aspects have been proposed: location free, location based, opportunistic, cluster based, energy efficient, etc. These mechanisms usually require measuring additional parameters, such as the angle of arrival of the signal or the depth of the node, which makes them less efficient in terms of energy conservation. In this paper, we propose a cross-layer proactive routing initialization mechanism that does not require additional measurements and, at the same time, is energy efficient. The algorithm is designed to recreate a radial topology with a gateway node, such that packets always use the shortest possible path from source to sink, thus minimizing consumed energy. Collisions are avoided as much as possible during the path initialization. The algorithm is suitable for 2D or 3D areas, and automatically adapts to a varying number of nodes, allowing one to expand or decrease the networked volume easily.

Speed and attenuation of acoustic waves in snow: Laboratory experiments and modeling with Biot's theory

Monitoring acoustic emissions (AE) prior to imminent failure is considered a promising technique for assessing snow slope instability. Gaps in elastic wave propagation characteristics in snow hinder quantitative interpretation of AE signals. Our study focuses on characterizing the propagation of acoustic reference signals in the ultrasonic range across cylindrical snow samples with varying density (240–450kgm−3). We deduced the acoustic attenuation coefficient within snow by performing experiments with different column lengths to eliminate possible influences of the snow-sensor coupling. The attenuation coefficient was measured for the entire burst signal and for single frequency components in the range of 8 to 35kHz. The acoustic wave propagation speed, calculated from the travel time of the acoustic signal, varied between 300ms−1 and 950ms−1, depending on the density and hardness of snow. From the sound speed we also estimated the Young's modulus of our snow samples; the values of the modulus ranged from 30 to 340MPa for densities between 240 and 450kgm−3. In addition, we modeled the sound propagation for our experimental setup using Biot's model for wave propagation in a porous medium. The model results were in good agreement with our experimental results and suggest that our acoustic signals consisted of Biot's slow and fast waves. Our results can be used to improve the identification and localization of acoustic emission sources within snow in view of assessing snow slope instability.

Effects of accelerated aging on mechanical, thermal and morphological behavior of polyurethane/epoxy/fiberglass composites

Wind blades, an important application of polymeric composite materials, are subject to natural weathering. This study aims to evaluate mechanical, thermal and morphological behavior during accelerated aging in three thicknesses of epoxy and fiberglass polyurethane-coated composite plates used in wind turbines, in addition to testing with two acoustic emission techniques. An accelerated aging chamber simulated natural weathering mechanisms for 45, 90, 135 and 180 days. This degradation primarily reduced the mechanical properties of the thinner composites, with some damaged specimens exhibiting fiber-matrix debonding. Thermal properties deteriorated. There were no morphological changes on the polyurethane–epoxy interface; however, degradation occurred in the fiber-matrix interface on the surface exposed to radiation. The degree of chalking indicated coating deterioration on the external surface of the polyurethane. The acoustic wave propagation speed and attenuation coefficient measured prior to mechanical testing indicated the presence of damage areas.

Biophysical characteristics of skin in diabetes: a controlled study

Cutaneous complications are common in diabetes. Previous assays suggest that hyperglycemia and decreased insulin signal are involved in the impairment of skin function. The aim of this study was to evaluate the biophysical characteristics of skin in patients with diabetes mellitus and compares them with healthy non-diabetic controls. To measure biophysical characteristic of skin including transepidermal water loss (TEWL), water content, sebum and skin elasticity in patients with diabetes mellitus and compare them with healthy non-diabetic controls. This case-control study was conducted on 38 patients with diabetes and 40 age- and sex-matched healthy people. The biophysical properties of skin including stratum corneum (SC) hydration, sebum content, TEWL and skin elasticity were measured and compared between the two groups at three different locations of the body. The measurement of SC hydration and TEWL showed no significant difference between diabetics and controls. The skin surface lipids on the forehead but not other sites were significantly lower in the diabetics than in the controls. Acoustic wave propagation speed, a measurement related to skin elasticity, was significantly lower in forearm and forehead of diabetics. Diabetes affects some functional properties of epidermis and dermis that may responsible for many cutaneous manifestations of diabetes. These results suggest that patients with diabetes mellitus tend to show a normal hydration state of the SC together with decreased sebaceous gland activity and impaired skin elasticity, without any impairment of the SC barrier function.

Correction for longitudinal mode vibration in thin slender beams

This letter reports on a correction to the theoretical prediction of longitudinal mode vibration in thin, slender beams. Thin magnetostrictive strips were fashioned from Metglas™ and subjected to a modulated magnetic field to determine resonant frequency and acoustic wave propagation speed. The results indicated that current analytical solutions were not adequate to predict behavior. Numerical simulations were performed that adjusted Poisson’s ratio until the acoustic wave speed matched that measured in the experiments. The results indicated that the current equations, formulated using the plane-strain modulus, should be modified by using the plane-stress or biaxial modulus.

Airborne synthetic aperture acoustic imaging

This paper presents a system model and inversion for airborne synthetic aperture acoustic (SAA) imaging. The system model accurately represents the intercation of the acoustic source and the target region at near range values. Moreover, the model incorporates the fact that the relative speed of the vehicle's (transmitter/receiver) with respect to the target region is comparable to the acoustic wave propagation speed. The inversion utilizes the principle of spectral decomposition of spherical phase functions to develop a wavefront reconstruction method from SAA data. Processing issues and selection of appropriate acoustic FM-CW sources are discussed. Results are provided that exhibit the superior accuracy of the proposed SAA system model and inversion over their synthetic aperture radar (SAR) counterpart in which the vehicle's speed is assumed to be much smaller than the wave propagation speed.

Determination of velocity profiles in oscillating pipe-flows by using laser Doppler velocimetry and ultrasonic measuring devices

The velocity profiles measured with a recently built ultrasonic velocity profile (UVP) sensor based on ultrasound (US) pulsed echography are compared with laser Doppler velocimetry (LDV) measurements. The results from the experiments show that both techniques are well suited to measurements in oscillating, piston-driven pipe-flows. LDV has a higher spatial resolution in the region of high-velocity gradients, but requires considerably greater effort to obtain a complete velocity profile than the UVP sensor, which can obtain the complete profile information simultaneously. However, in the near-wall regions, reflections of the US beam degrade the quality of the UVP measurements. This problem may be reduced by matching the wall material and the fluid so as to minimize the difference in the propagation speed of acoustic waves in both media.

Interferometric phase and frequency measurements of the propagation speed of acoustic waves

It is shown that direct measurements of the phase and frequency of the electrical signal at the interferometer output yield an increase in the sensitivity and accuracy with which the propagation speed of acoustic waves in a medium can be determined.

Extension of synthetic aperture radar (SAR) technique to undersea applications

This paper presents results on the extension of synthetic-aperture radar (SAR) technique to underwater mapping applications. Due to the modest propagation speed of acoustic waves in water, the areal-mapping rate is found to be limited. A number of approaches are discussed in the paper which have the potential of significantly increasing the mapping rate. The map resolutions, both in azimuth and range, are derived for a synthetic array system employing multiple elements. The digital processing requirements, such as the complex multiplication rate and memory size are determined. It was found that the digital signal-processing requirements for many viable mapping systems are within the capability of existing processing hardware.