Acoustic Contribution Research Articles

Phonon engineering enabled reduction in thermal conductivity of SnS/Cu2Se composites: An experimental and numerical insights

SnS is a promising chalcogenide-based material that shows great potential for thermoelectric applications. Lattice thermal conductivity is the only independent parameter that can be modified without disrupting the complex relationship of parameters such as electrical conductivity and the Seebeck coefficient. Herein, Cu2Se x wt% (x = 1%, 3%, 5%, 7%) composited with SnS were synthesized by hydrothermal method. The addition of Cu2Se in SnS has resulted in a suppression of the intrinsic thermal conductivity from 0.891 W/mK to 0.447 W/mK for Cu2Se 5 wt% composited SnS at 753 K. Increasing Cu2Se% in the SnS matrix has led to decrease in crystallite size from 33 nm - 29 nm, while the dislocation density and microstrain showed an increasing trend. The different physical and microstructural factors were analysed to understand the influence on thermal conductivity using numerical techniques. Physical parameters like Cu2Se distribution, pelletizing temperature, pressure, volume fraction, and intrinsic material qualities are studied using effective thermal conductivity models and Maxwell Eurecken 2 shows the best fit. The Hasselman-Johnson model analyses interfacial thermal conductivity and shows an increasing trend from 0.31 × 10–6 to 6.2 10–6 m2K/W. In addition, the microstructural variables such as dislocations, stacking faults, and point defects are present in the samples. The phonon relaxation time for each mode of vibration determined using Raman spectroscopy also points towards the decrease in contribution from optical phonons by 30% from 7.71 × 10–13 to 5.31 × 10–13 s. The temperature-dependent and power-dependent Raman spectroscopy indicated lattice softening and anharmonic coupling leading to a red shift in the spectrum. A combination of optical and acoustic phonon contributions helped to reduce the thermal conductivity by about 50% for Cu2Se-composited SnS.

Noise generation and contribution of a single-gap bridge expansion joint: An experimental and numerical study

Noise generated from bridge expansion joints during vehicle passing has caused localized environmental problems around the world. The purpose of this paper is to investigate the vibration and noise radiation from the single-gap expansion joint induced by passing vehicles. First, a vibration and noise field test was performed for single-gap expansion joints in the highway ramps. Based on the tested results, two numerical models, involving a 3D tire-bridge expansion joint hybrid finite element model for the vibration analysis, as well as an acoustic boundary element model for the prediction of the noise radiation, were established and validated. The results of the numerical simulations and the field tests are well matched, which offers opportunities to predict the vibration and noise induced by vehicles passing through using the proposed methodology. Finally, the acoustic contribution and sound pressure distribution of different sound sources were discussed. The research showed that, for the single-gap expansion joint, the contribution of tire noise to the total noise level is dominant, and the contribution of structure-borne noise of the expansion joint and girder to the total noise level is insignificant. The findings emphasize the importance of tire noise and provide new ideas for noise control of single-gap expansion joints.

Investigation on Vibro-acoustic Characteristics of High-speed Railway Steel-concrete Composite Bridge Based on the Combined FE-BE-SEA Method

This paper presents a combined finite element-boundary element-statistical energy analysis (FE-BE-SEA) method to predict the vibro-acoustic characteristics of high-speed railway steel-concrete composite (SCC) bridge. The train-track coupling model is firstly introduced to accurately determine the forces transmitted to bridge, which are then imported into the established FE-BE model and SEA model. Among them, the former is adopted to calculate the vibration response in full frequency band and acoustic response at 20∼200 Hz, while for the noise part at 200∼2000 Hz, the latter is utilized for calculation. The on-site testing is carried out simultaneously to collect the measured results, which are compared with the predicted ones, validating the reliability and accuracy of the proposed method. Finally, a thorough discussion is conducted on the acoustic contribution and parametric analysis. The results indicate that the dominant frequency bands of deck and web radiated noise are below and above 200 Hz, respectively, ranking first and second in terms of overall acoustic contribution, followed by the diaphragm and flange. Reducing train speed, installing elastic fasteners, as well as increasing web thickness can significantly mitigate the vibro-acoustic responses from SCC bridge, but the effective frequency ranges for vibration and noise reduction are slightly different.

Dynamic reflectivity of an opto-acoustic three-layer transducer for picosecond ultrasonic measurements

We present an analysis of a three-layered structure used for both launching and detecting picosecond acoustic waves. To enhance the optical sensitivity to the acoustic disturbances, a cavity is designed, which acts as a Fabry–Perot interferometer. We use analytic modeling based on dual optical and acoustic transfer matrix formalism to analyze the coupled optical and acoustic wave propagation. Assuming a three-layer transducer made of an optical cavity sandwiched between two thin metallic layers, the model allows for mastering of the coupled optical and acoustic responses, which leads to an optimum design of the structure, and it highlights the various acoustic contributions to the reflectivity changes. The sensitivity of this three-layered structure to acoustic disturbances is compared to the numerical predictions we performed for the standard opto-acoustic transducer made of a single metallic layer.

Noise reduction mechanism of high-speed railway box-girder bridges installed with MTMDs on top plate

The issue of low-frequency structural noise radiated from high-speed railway (HSR) box-girder bridges (BGBs) is a significant challenge worldwide. Although it is known that vibrations in BGBs caused by moving trains can be reduced by installing multiple tuned mass dampers (MTMDs) on the top plate, there is limited research on the noise reduction achieved by this method. This study aims to investigate the noise reduction mechanism of BGBs installed with MTMDs on the top plate. A sound radiation prediction model for the BGB installed with MTMDs is developed, based on the vehicle–track–bridge coupled dynamics and acoustics boundary element method. After being verified by field tested results, the prediction model is employed to study the reduction of vibration and noise of BGBs caused by the MTMDs. It is found that installing MTMDs on top plate can significantly affect the vibration distribution and sound radiation law of BGBs. However, its impact on the sound radiation caused by vibrations dominated by the global modes of BGBs is minimal. The noise reduction achieved by MTMDs is mainly through changing the acoustic radiation contributions of each plate of the bridge. In the lower frequency range, the noise reduction of BGB caused by MTMDs can be more effective if the installation of MTMDs can modify the vibration frequency and distribution of the BGB to avoid the influence of small vibrations and disperse the sound radiation from each plate.

Study on Structure-Borne Noise Characteristics of Long-Span Steel Truss Bridge in Urban Rail Transit

The application of long-span steel bridge in urban rail transit is becoming more and more extensive, but the structure-borne noise of steel bridge induced by passing train is also prominent. Research on the structure-borne noise problem of long-span steel bridge in urban rail transit has positive significance in promoting the sustainable development of steel bridge, and improving the quality of sound environment along rail transit. In this work, dynamic receptance principle, finite element method and statistical energy method are combined to establish the structure-borne noise prediction model of the long-span steel bridge, and the rationality and validity of the model are verified based on field measurement results. Based on the prediction model, the noise radiation characteristics of large-span steel truss bridge in urban rail transit are studied, and the following conclusions are drawn: The bridge deck has the strongest acoustic contribution ability, with the contribution rate of 33–44%, followed by the longitudinal web and transverse web, with the contribution rate of 23–30%, followed by the truss chord, with the contribution rate of 5–8%, and the truss web, longitudinal wing and transverse wing have weak contribution ability, with the contribution rate of less than 2%. The acoustic radiation efficiency of steel truss bridge components reaches its peak at the critical frequency, and the critical frequency is determined by the thickness of steel bridge plate components when the material parameters are fixed. Under ordinary track structures, the middle-to-high frequency noise distribution characteristics of large-span steel truss bridge structure are obvious. Damping pad floating slab track can effectively suppress the high-frequency noise of steel bridge, and the overall sound level can be reduced by about 11–14[Formula: see text]dB.

Richtmyer-Meshkov instability when a shock wave encounters with a premixed flame from the burned gas

We present a linear stability analysis of the Richtmyer-Meshkov instability that develops when a shock wave reaches a sinusoidally perturbed premixed flame from behind. In the hydrodynamic regime, when acoustic contributions dominate the flame growth rate, the problem is analytically addressed by the direct integration of the sound wave equations at both sides of the flame, which are bounded by the reflected and transmitted shock waves and the flame front that acts as a contact surface in the hydrodynamic limit. The resolution involves: a hyperbolic change of variables to modify the triangular spatio-temporal domain, a transformation in the Laplace variable, the resolution of the functional equations in the frequency domain, and the final inverse Laplace transform. The latter involves a novel resolution method that is proven beneficial for long-time dynamics. Asymptotic analysis is also carried out to describe the early time and late time hydrodynamic response. The nonuniform flow field resulting from distorted oscillating shocks is characterized by acoustic, rotational, and entropic disturbances, each of which exerts a substantial influence on flame dynamics. These disturbances contribute to the intricate interplay of factors shaping the behavior of the flame in response to the nonuniform flow. In particular, the sensitivity of local flame propagation to temperature disturbances is investigated. This work contributes to a deeper understanding of Richtmyer-Meshkov instability dynamics and offers insights into instability reduction through the modulation of temperature disturbances generated by the transmitted shock.

Thermal, optoelectronic and thermoelectric properties of inorganic double perovskites semiconductors Cs2(Sn, Pt, Te)I6 for application as intermediate-band solar cells

First-principle calculations using the Wien2k code and the GGA-mBJ exchange potential were used in the study of the thermodynamic, dynamic, chemical and elastic stability, as well as the electronic, optical and thermoelectric properties of Cs2(Sn, Pt, Te)I6. The presence of an intermediate band in Cs2(Sn, Pt, Te)I6 semiconductors confirmed by absorption peaks appeared at photon energy corresponding to the band gap enhances the efficiency of solar cells. The ideal band gap, high dielectric constants and optimal absorption make the double perovskites under study perform well in solar cells. The calculated minimum formation energy, Helmholtz free energy and phonon modes through the first Brillouin zone for the investigated Cs2(Sn, Pt, Te)I6 family confirm their thermal, thermodynamic and dynamic stability. The acoustic phonon contribution modes come from the Cs-6s and I-5p electrons, while the Pt-6s, Sn-5p, Te-5p and I-5p electrons participate in the optical phonon modes. The narrowness of the upper valence band and the band gap in the visible region for Cs2PtI6 advantage this double perovskite in energy harvesting. The geometric Goldschmidt tolerance factor value between 0.8 and 1.0 and octahedral factor 0.41 indicate that Cs2SnI6 double perovskite is more stable.

Human perception of impact sounds suggests auditory intuitive physics

Upon hearing objects collide, humans can estimate many of the underlying physical attributes, such as the objects’ material and mass. Although the physics of sound generation are well established, the inverse problem that listeners must solve – of inferring physical parameters from sound – remains poorly understood. In this work, we show that humans leverage an understanding of acoustical physics to constrain their perceptual inferences, allowing them to disambiguate multiple object properties from a single impact sound. We derived a linear generative model of impact sounds, combining theoretical acoustics with empirically measured statistics of object resonances. We used an analysis-by-synthesis algorithm to infer mode parameters from recorded object impulse responses. We then fit distributions to these parameters, from which object impulse responses could be sampled. Perceptual experiments demonstrated that humans could judge material and mass from sound alone, even when both of the underlying objects varied. However, performance with synthetic sounds was impaired if the simulated physical regularities were altered to be unnatural. The results suggest that listeners use internal physical models to separate the acoustic contributions of the objects that interact to create sound.

Dynamic Receptance Analysis Combined with Hybrid FE-SEA Method to Predict Structural Noise from Long-Span Cable-Stayed Bridge in Urban Rail Transit

In this study, dynamic receptance analysis (DRA) is proposed and combined with hybrid finite element (FE)-statistical energy analysis (SEA) method to accurately predict structural noise from long-span cable-stayed bridge (LSCB) with steel box composite girder (SBCG) in urban rail transit (URT). To begin with, a vertical vehicle–track coupling model in frequency domain is established based on DRA, in which the rail is represented by an infinite Timoshenko beam supported by a series of fasteners that are regarded as springs with complex stiffness. The floating slab is regarded as the Euler beam with both ends free supported by steel springs. Using this model, the spectrums of the wheel–rail force and the forces transferred to the bridge can be efficiently obtained by taking rail roughness as the excitation. Due to the low modal density of the concrete deck, the hybrid FE-SEA method is introduced to establish the noise prediction model, in which the discontinuity caused by using distinct models for different frequency bands is avoided. Then the on-site noise tests of a LSCB with SBCG in URT are carried out to verify of the proposed method. Finally, based on the prediction method, the acoustic contributions of the bridge components are analyzed in detail. The force transfer characteristics as well as the noise reduction effects of different track structures are thoroughly investigated, so as to provide reference for the future research on bridge-borne noise control.

Role of phonon scattering and bonding in resolving lattice thermal conductivity ambiguities of β-Ga2O3.

Understanding the lattice thermal conductivity (κl) of β-Ga2O3 is very intriguing owing to its advantages in high-voltage and high-temperature applications. Despite several attempts, the underlying mechanism and causes of the notable discrepancies found in the κl values of β-Ga2O3 along [100] and [001] directions calculated using first principles remained unresolved. We demonstrate that the understanding of the nature of chemical bonding is crucial to overcome the inconsistency in theoretically reported κl values. In low-symmetry structures such as β-Ga2O3, the nature of the interactions is primarily long-range; therefore, a sufficiently large supercell inclusive of various bonding characteristics is required to capture relevant phonon wavelengths. Bonding nature-aware structure modeling allows precise estimation of acoustic and optical mode contributions towards κl. Additionally, phonon mean free path analysis confirms that considering only third-order interaction terms is adequate to determine the κl of β-Ga2O3. The calculated κl values are in excellent agreement with experimentally reported values in all three directions. Our results establish that the bonding nature and its influence on phonon scattering are essential to consider in calculating κl accurately.

Acoustic transmission across the interface in impulsive stimulated Brillouin microscopy

Brillouin microscopy, an emerging mechanical imaging technology, has made rapid development in recent years. The Brillouin imaging signal is not only determined by acoustic waves in the optical focus volume but also by acoustic waves outside the focus volume. Here, we study how acoustic propagation across the polydimethylsiloxane (PDMS)–ethanol interface affects the heterodyne impulsive stimulated Brillouin scattering (ISBS) signal. When the acoustic direction is perpendicular to the interface, a frequency component corresponding to the PDMS Brillouin shift appears in the signal although the probe focus is in the ethanol. The transmitted wave from PDMS appears when the acoustic wave propagates to the probe focus. To discuss the acoustic contribution of spatial resolution and the acoustic mode propagation distance, it is necessary to consider the acoustic properties of the medium. The influence of transmitted waves on the interference signal is observed in about 100 μm (phonon mean free path in ethanol). Since ISBS analyzes the signal in the time domain, it is possible to distinguish the transmitted wave from the local signal in a single pixel. Different spatial resolutions are obtained by the time-domain method and frequency-domain method. Using mechanical information outside the optical focus volume, ISBS has the potential to image with fewer pixels, which is more flexible and faster than point-by-point scanning.

Numerical simulation and coupling mechanism study of acoustic-inertial micromixer

Acoustic-inertial micromixers exhibit a wider operating range and higher mixing efficiency than conventional mixers. We have carried out experimental studies and numerical simulations of acoustic-inertial micromixers. It is found that the acoustic streaming will be changed in morphology and intensity by the background flow, and the coupling mechanism between them is obtained. Specifically, we developed the numerical model of acoustic-inertial micromixer by using perturbation theory and the Generalized Lagrangian Mean (GLM) theory. By dividing the flow variables into zero-order, first-order and second-order variables, we obtained the control equations representing background flow, acoustic response and time-averaged streaming flow. Then realized the decoupling analysis of the acoustic-inertial coupling phenomenon. It is found that in terms of acoustic streaming flow, the intensity extreme of it increases as the background flow rate increases. The flow velocity at 5Vpp can reach 0.46 m/s under 500 μL/min, which is 30 times for the same condition under 10 μL/min. However, the streaming morphology no longer behaves as a symmetric vortex distributed on both sides of the sharp edge, which is stretched and twisted by the background flow and structure at a high flow rate. The percentage of acoustic contribution at different working conditions is also investigated quantitatively, and the acoustic contribution index (ACI) will generally decrease to less than 0.5 after the background flow dominates the flow field. The results of the study can provide a reference for the design of acoustic-inertial micromixers with larger flow ranges and higher efficiencies.

Many Body Aspects on the Lattice Vibrational Properties of Germanene and Silicene along Highly Symmetry Directions

The investigation of lattice vibrational properties in monolayer two-dimensional honeycomb lattices comprising 2D group-IV semiconductor materials such as Germanene and Silicene (Low Buckled structure) holds immense significance in the realm of research, owing to their potential integration into the forthcoming electronic sector for information technology. The ductile nature of 2D group-IV semiconductor materials enables seamless integration with existing semiconductor technology on substrates, setting them apart from Graphene. Our primary objective revolves around comprehending the lattice vibrational properties of Germanene and Silicene (LB) through the examination of their honeycomb and buckled lattice structures. We use the Adiabatic Bond Charge Model with a Python program to derive vibrational frequencies at the Г points along highly symmetrical directions. Moreover, we extensively analyze the acoustical and optical contributions to the lattice vibrational frequencies. We anticipate that the phonon frequencies along the Г‒M direction for 2D atomically thin Germanene and Silicene will yield reasonably similar outcomes to those other research groups achieve.

Acoustic Radiation Prediction Model Rationality and Mechanism of Steel-Spring Floating-Slab Tracks on Bridges

In the actual operation of urban rail transit (URT), the vibrations of steel-spring floating-slab tracks (SSFSTs) are amplified, and the track structure has strong low-frequency acoustic radiation; therefore, it is necessary to study the acoustic radiation of SSFSTs. In addition, multi-block short track structures are often laid within the URT lines; however, many researchers studying the reduction of vibration track service performance problems only select one or several block tracks to study. In reality, many short track structures will become sound sources when a train passes, and different sound sources will have various acoustic effects during the propagation process; therefore, it is necessary to study the rationality of any track acoustic model that analyzes the acoustic radiation problem. In order to more accurately predict the acoustic characteristics of steel-spring short floating-slab tracks (SSSFSTs) on a one-span bridge, train-track-bridge interaction theory and the acoustic boundary element method (BEM) were adopted to study the acoustical differences and mechanism of the float-slab number in the acoustic model. The results showed that with the increase in the floating-slab number in the acoustic model, the acoustic radiation ability of SSSFSTs and the sound pressure in the sound field increased; however, it was not a simple linear increase. Thus, the floating-slab number in the acoustic model not only affected the acoustic radiation ability but also caused acoustic effects during the propagation process, which affected the predicted results. The vibration characteristics of each floating-slab were different, and the acoustic input conditions of different numbers of floating-slabs in the acoustic model led to significant differences in the acoustic analysis. There was also obviously a different acoustic contribution of each floating-slab to the same sound field point, which led to the significant influence of the sound pressure at the sound field points when using different acoustic models. Therefore, using acoustic models with different floating-slab numbers had a significant effect on the acoustic analysis of SSSFSTs. In order to study the acoustic characteristics of SSSFSTs on a one-span bridge, it was necessary to establish a complete acoustic model.

Propeller-shaft-hull coupling acoustic radiation characteristics induced by friction self-excitation of the stern bearing

This paper focuses on the practical engineering problem of excessive propeller-shaft-hull coupling vibration noise, which is caused by poor lubrication contact of water-lubricated stern bearings in the ship propulsion shaft system. Firstly, based on the three-dimensional sono-elasticity theory of ships, calculation models for the propeller-shaft-hull coupling acoustic radiation transfer function are established separately, considering the propeller excitation and friction excitation of the stern bearing. Secondly, by analyzing the acoustic radiation contribution of each mode, the vibration mode with the highest contribution to the typical acoustic radiation transfer function peaks of the propeller-shaft-hull coupling under the friction excitation of the stern bearing is separated. The spatial distribution and pointing characteristics of the sound field corresponding to the propeller-shaft-hull coupling acoustic under friction excitation of the stern bearing are given. Finally, a quantitative evaluation model of propeller-shaft-hull coupling acoustic radiation caused by friction self-excitation of the stern bearing is established. The mechanism behind the typical acoustic radiation peaks of propeller-shaft-hull coupling under friction excitation of the stern bearing is revealed, which provides methodological guidance for the quantitative evaluation of friction vibration noise and the separation of vibration noise components in ship stern structures.

Low noise optimization of two-stage gearbox housing structure based on acoustic contribution analysis and topology optimization

Low noise optimization of two-stage gearbox housing structure based on acoustic contribution analysis and topology optimization

Structure-borne Noise Differences of Metro Vehicle Running on Different Tracks

A floating-slab track (FST) increases the interior noise and reduces the passenger's acoustic comfort. A study combining experimental measurement and numerical simulation was conducted to reveal the characteristics of internal structure-borne noise on different tracks and improve riding comfort. A field measurement was taken to analyze the essential interior noise characteristics on different tracks with different speeds. A noise prediction model was built by combining a vehicle-track coupling model, the structural finite element method and the acoustic boundary element method to predict the interior noise and study the panel contribution for noise control. The results show that the sound pressure level (SPL) of FST is 5 – 10 dB higher than the ordinary monolithic track (OMT). The curve section is 1 – 4 dB larger than the straight section. In the range of 90 – 110 Hz and 135 – 150 Hz, the SPL of FST condition is higher than that of OMT condition, with a maximum difference of 12 dB. And the SPLs at five ISO positions all have peaks at 30 Hz and 90 Hz frequencies, and the sound pressure fluctuates wildly at 100 Hz. The vibration at 90 Hz is relatively violent, which leads to more significant noise, but at 110 Hz, that is small. At different frequencies, the contribution of the panels to the sound pressure in the carriage is different, and the acoustic contribution of these panels may be the opposite.

Experimental and numerical investigation on the vibro-acoustic characteristics of periodic rib stiffened plate based on band gap theory

This study presents a novel method for analyzing the vibration and noise from the periodic rib stiffened plate (PRSP). For the first time, the band gap theory was combined with hybrid finite element-boundary element method (FE-BEM) to predict the vibro-acoustic characteristics of this structure and guide its vibration and noise reduction design from the perspective of bending wave propagation. The excitation test was carried out simultaneously to verify the rationality and accuracy of the proposed method. Then, the acoustic contribution analysis was conducted and the influence of structural design parameters on bending wave bandgap and noise reduction effect was discussed in detail. The results show that there are alternating passbands and stopbands for bending waves propagating in PRSP, making the vibro-acoustic responses in different frequency bands exhibit distinct differences as well. Increasing the base plate thickness and decreasing the rib spacing are conducive to widen the bandgaps and reduce the noise radiation, which are the decisive factors affecting the vibro-acoustic characteristics of PRSP. While the rib thickness has little effect, this provides a new approach for vibration mitigation and acoustic optimization in steel bridges.

High-frequency crossover from vortex-mass enhancement to pinning

Starting from lattice dynamics, Ginzburg Landau Theory is used to study phonon contributions to the effective vortex mass of a moving Abrikosov lattice driven by a small driving force, in this case circularly polarized light. A general expression is obtained of dynamical additional mass, which is capable of including both acoustic and optical phonon contributions. At the level of linear response, this frequency-dependent mass increases with driving frequency. After reaching a maximum at the frequency corresponding to the eigenvalue of the wave vector matching the coherence length, the mass begins to decrease, and eventually changes sign crossing to an effective pinning regime at high frequency. These calculations are applied to experimental results of YBCO (Teasř et al 2021 Sci. Rep. 11 21708).