External Acoustic Field Research Articles

Inhibiting Shuttle Effect and Dendrite Growth in Sodium-Sulfur Batteries Enabled by Applying External Acoustic Field.

The room-temperature sodium-sulfur (RT Na-S) battery is a promising alternative to traditional lithium-ion batteries owing to its abundant material availability and high specific energy density. However, the sodium polysulfide shuttle effect and dendritic growth pose significant challenges to their practical applications. In this study, we apply diverse disciplinary backgrounds to introduce a novel method to stimulate polarized BaTiO3 (BTO) nanoparticles on the separator. This approach generates more charges due to the piezoelectric effect under stronger driving forces produced by applying a controllable acoustic field at the outer edge of the cell. The acoustically stimulated BTO attracts more polysulfides, thus reducing the shuttling effect from the cathode to the anode and ultimately enhancing the battery performance. Meanwhile, the acoustic waves create additional streaming flows, improving the uniformity of the sodium ion dispersion, enhancing the sodium ion transport and reducing the possibility of sodium dendrite development. We believe that this work offers a new strategy for the development of high-performance Na-S batteries.

Comparative numerical investigation of flow-induced noise characteristics of high-speed trains using high-resolution compressible Large Eddy Simulation

The South Korean Ministry of Land, Infrastructure and Transport has developed a “Comprehensive Plan for 400km/h High-Speed Rail” aimed at enhancing the operational speed of the high-speed railways, currently running up to 300km/h. A short-term goal is to elevate the operating speed of high-speed trains to 370 km/h, up from 320 km/h. Because aerodynamic noise proportionally escalates with the 6th powers of the speed, aerodynamic noise becomes more significant at higher speeds. Consequently, there's a pressing need for design solutions that reduce aerodynamic noise in high-speed trains. This study involves an aeroacoustic analysis using real-scale models of the current model and the preliminary design targeting 370 kph operation. Each model's 8-car formation has been simplified to a 5- car setup. A challenge in predicting aerodynamic noise is the generation of detailed sound sources in the near field and precise noise propagation in the acoustic field. For that, a three-dimensional compressible Large Eddy Simulation technique is employed, utilizing high-resolution grids. This allows for concurrent computation of the external flow and acoustic fields for a real-scale, high-speed train in an open environment. The analysis comprehensively examines the aerodynamic and aeroacoustic properties of each train car, including the major contributors to aerodynamic noise in high-speed trains. The radiated noise is predicted using the Ffowcs Williams and Hawkings equation and is further examined in relation to vortex sound sources.

Prediction and analysis of flow-induced noise of a real-size high-speed train using compressible Large Eddy Simulation and vortex sound source

As technology advances, high-speed trains have become faster, and the aerodynamic noise generated by their exterior flow fields has become a critical consideration in the design process. Accurately predicting the flow-induced noise of high-speed trains requires high-resolution sound source generation in the near-field and noise propagation in the acoustic field without numerical dissipation. This necessitates the appropriate design of the grids from the point of aerodynamic noise generation and propagation in association with the length scales of the relevant components of an actual train. To address this challenge, this research study employs a three-dimensional compressible Large Eddy Simulation (LES) technique with high-resolution grids to simultaneously calculate the external flow and acoustic fields of a real-size high-speed train consisting of five cars running in open field. Further analysis is carried out to evaluate the contribution of major components, including the cap, pantograph, bogie, intercoach, and HVAC cover, which are known to be significant contributors to high-speed train flow noise. The study also employs the vortex sound source to analyze the generation mechanism of flow-induced noise for each component, providing insights for reducing aerodynamic noise.

Programmable Modular Acoustic Microrobots.

Microrobots have emerged as promising tools for biomedical and in vivo applications, leveraging their untethered actuation capabilities and miniature size. Despite extensive research on diversifying multi-actuation modes for single types of robots, these tiny machines tend to have limited versatility while navigating different environments or performing specific tasks. To overcome such limitations, self-assembly microstructures with on-demand reconfiguration capabilities have gained recent attention as the future of biocompatible microrobotics, as they can address drug delivery, microsurgery, and organoid development processes. Reversible modular reconfiguration structures require specific arrangements of particles that can assume several shapes when external fields are applied. We show how magnetic interaction can be used to assemble cylindrical microrobots into modular microstructures with different shapes. The motion actuation of the formed microstructure happens due to an external acoustic field, which generates responsive forces in the air bubbles trapped in the inner cavity of the robots. An external magnetic field can also steer these structures. We illustrate these capabilities by assembling the robots into different shapes that can swim and be steered, showing the potential to perform biomedical applications. Furthermore, we confirm the biocompatibility of the cylindrical microrobot used as the building blocks of our microstructure. Exposing Chinese Hamster Ovary cells to our microrobots for 24 hours demonstrates cell viability when in contact with the microrobot.

Prediction and analysis of aeroacoustic characteristics of a real-size high-speed train running in open field using compressible Large Eddy Simulation and vortex sound source

With the rapid advancement of technology, high-speed trains have been requested to increases their speeds. Aerodynamic noise generated from the external flow fields around these trains has become a critical factor to be addressed during a design phase. Accurate prediction of flow-induced noise in high-speed trains requires high-resolution sound source generation in the near-field and precise noise propagation analysis in the acoustic field without numerical dissipation. This necessitates the appropriate design of grids, taking into account aerodynamic noise generation and propagation in conjunction with the length scales of the relevant components of a real-size train. To tackle this challenge, the present research employs a three-dimensional compressible Large Eddy Simulation (LES) technique with high-resolution grids to simultaneously calculate the external flow and acoustic fields of a real-size high-speed train consisting of five cars running in an open field. A comprehensive analysis is conducted to evaluate the contributions of major components, namely, a cap, pantograph, bogie, intercoach, and HVAC cover, which are well-known as significant contributors to high-speed train flow-induced noise. The study utilizes the vortex sound source approach to analyze the generation mechanism of flow-induced noise for each component, providing valuable insights that could potentially aid in reducing aerodynamic noise.

Numerical Analysis of Wind Noise Transmission through BEV Underbody

In electrified automobiles, wind noise significantly contributes to the overall noise inside the cabin. In particular, underbody airflow is a dominant noise source at low frequencies (less than 500 Hz). However, the wind noise transmission mechanism through a battery electric vehicle (BEV) underbody is complex because the BEV has a battery under the floor panel. Although various types of underbody structures exist for BEVs, in this study, the focus was on an underbody structure with two surfaces as inputs of wind noise sources: the outer surface exposed to the external underbody flow, such as undercover and suspension, and the floor panel, located above the undercover and battery. In this study, aero-vibro-acoustic simulations were performed to clarify the transmission mechanism of the BEV underbody wind noise. The external flow and acoustic fields were simulated using computational fluid dynamics. The vehicle structural vibration and sound fields of the interior and exterior cabin were analyzed using vibroacoustic models consisting of three subsystems modeled by the finite-element or boundary-element method: The first is an underbody structure finite-element model containing a white body, suspension, battery, and undercover; the second is the interior cabin space boundary-element model; the third is the exterior cabin space finite-element model for analyzing acoustic radiation resulting from vehicle structural vibration for the small space between the floor panel and battery, the motor room and the under-vehicle space between the ground and undercover. The analysis results using the vehicle model reveal that the pressure fluctuations acting on the floor panel are more-dominant inputs for cabin noise than those acting on the outer surface. The pressure fluctuation acting on the floor panel is affected by the acoustic mode of the space between the battery and the floor panel.

Identification of Aerodynamic Tonal Noise Sources of a Centrifugal Compressor of a Turbocharger for Large Stationary Engines

The aerodynamics of centrifugal compressors is a topical issue, as the vibrations and noise reduce the comfort of people who are in proximity to the compressor. The current trend in rotating machinery research is therefore not only concerned with performance parameters but also increasingly with the effect on humans. An analysis of aerodynamic noise based on external acoustic field measurements may be a way to assess the nature of aerodynamic excitation. In this research, the experimental measurements at 20 operating points covered the entire characteristic operating range of the selected centrifugal compressor. The dominant noise arising at blade-passing frequency (BPF) was identified at all the operational points, and the dominant effect of the buzz-saw noise was identified at the maximum rotor speed. The determination of the total sound pressure level LPA showed a trend towards an increasingly higher rotor speed and compressor surge line. In the amplitude-frequency characteristics, the sound pressure was found to be dependent on the rotor speed for BPF. On the other hand, non-monotonicity was detected between the operational points at given speed lines, confirming the complexity of the aerodynamics of rotating machines. The metric chosen to identify prominent tones determined by the tonality of individual tones in the frequency spectrum showed a clear effect of integer multiples of the rotational frequency on the overall noise. Thus, the results presented here confirm the dominant influence of BPF in terms of the psychoacoustic impact on humans.

Vibration and critical pressure analyses of functionally graded combined shells submerged in water with external hydrostatic pressure

This paper describes a unified nondestructive semi-analytical formulation for the critical pressure of underwater functionally graded combined shells subjected to external hydrostatic pressure. The structural model of combined shells is constructed from the first-order shear deformation theory, Voigt mixing law, and virtual spring technology. The admissible displacement functions are uniformly expressed with Legendre polynomials along the generatrix direction and Fourier series along the circumferential direction. The Kirchhoff-Helmholtz boundary integral equation is discretized by using the Legendre-Gauss spectral boundary element method, and the external acoustic field model is derived by expanding the Green's function, sound pressure, and displacement of combined shells with one-dimensional Fourier transformation. The linear elastic material theory is applied to deduce the work done by the hydrostatic pressure. The key technology to predict the critical pressure is to create an accurate equivalent model of the hydrostatic pressure. Through solving the final coupled governing equation, the critical pressure is obtained from the linear relationship between the hydrostatic pressure and the square of natural frequency. The convergence and correctness are verified by comparison with the results from published papers and numerical methods. The effects of different hydrostatic pressures, power-law exponents, geometric parameters, and boundary conditions on the critical pressure are investigated in several examples. Computed results can provide security guidance for the nondestructive prediction of underwater functionally graded combined shells at the beginning of engineering application design.

Surfactant sorption on a single air bubble in an ultrasonic standing acoustic wave field

Ultrasound application presents a promising non-intrusive way to enhance and facilitate mass transfer in aqueous systems. This enhanced mass transfer can influence the sorption processes in multiphase flows. Previous studies investigating the impact of ultrasound on sorption, have reported an increase in either desorption due to the rise in liquid temperature or adsorption due to the additional convective mass transfer resulting from acoustic streaming. In this study, low intensity ultrasound with a frequency of 36kHz was deployed to evaluate the sorption process of Triton X-100 on the surface of a single bubble, placed along the standing acoustic wave using profile analysis tensiometry. Furthermore, microscopic particle image velocimetry was used to understand the role acoustic streaming might play during different stages of the sorption process. Contrary to expectations, the results showed no considerable change in surface tension and sorption dynamics after sonicating both fresh and surfactant-loaded bubbles. The results of this study suggest that the observations from previous studies may be attributed to the additional energy input of the acoustic wave into the system rather than the presence of an external acoustic field.

An ACA-BM-SBM for 2D acoustic sensitivity analysis

<abstract> <p>In this paper, we present a novel computational approach (named ACA-BM-SBM) for the calculation of 2D acoustic sensitivity by combining the Burton-Miller-type singular boundary method (BM-SBM) with the adaptive cross-approximation (ACA) algorithm. The BM-SBM circumvents the source singularities of the fundamental solutions by introducing the origin intensity factors, and it eliminates the fictitious frequency problem in external acoustic fields by introducing the Burton-Miller formula. As a semi-analysis meshless method, the BM-SBM can accurately solve the external acoustic problem governed by the Helmholtz equation. Nevertheless, the computational inefficiency introduced by the dense coefficient matrix renders this method suboptimal, particularly for large-scale simulations. As the number of nodes increases, the computation time and store memory increase dramatically. ACA is a purely algebraic method based on hierarchical matrices which can be used to partition the coefficient matrix step by step. By employing ACA, the BM-SBM can be effectively accelerated, and this results in less computation time, as well as fewer memory requirements. Numerical experiments, including Dirichlet and Neumann boundary conditions, illustrate that the proposed approach is an accurate, efficient and fast numerical method for acoustic sensitivity analysis.</p> </abstract>

Electrothermal sound receivers

An analysis of the physical processes occurring during the emission of sound waves by electrothermal sound sources (thermophones) showed that a thermophone is a reversible physical system. This made it possible to determine the conditions under which the convertion of an acoustic signal into an alternating electric current can be carried out on the thermophone active element and, hence, the system will respond to an external acoustic field. Keywords: acoustic signal, active element, metal film, electric current, electrothermal receiver.

Acoustic agglomeration characteristics of fine solid particles under effect of additional droplets

Agglomeration of fine solid particles under the excitation of external acoustic field has potential applications in the field of ultra-low emission of combustion pollutants. It is expected that the performance of particle agglomeration can be improved by adding large sized liquid droplets. According to the dynamic process of acoustic agglomeration, including the particle motion, collision, agglomeration and rebound, a model of acoustic agglomeration for gas-liquid-solid three phase system with coexistence of liquid droplets and solid particles in gas phase is developed by using the direct simulation Monte Carlo (DSMC) method. Using this model, numerical simulations are performed to investigate the process and performance of acoustic agglomeration of fine solid particles under the effect of additional droplets. The numerical results are compared with experimental data, and the proposed model is validated. On this basis, the dynamic behaviors of acoustic agglomeration of fine particles in the case with additional droplets are explored. Furthermore, the influences of the diameter and number concentration of additional droplets on the performance of acoustic agglomeration of fine particles are examined. The results show that rapid agglomeration among the solid fine particles and additional droplets can be achieved by adding droplets into the acoustic field, yielding large sized liquid-solid mixed-phase particles. In this process, the agglomeration efficiency of fine particles increases significantly. It is also found that the diameter and number concentration of additional droplets are important factors that affect the acoustic agglomeration of fine particles. The agglomeration efficiency of fine particles rises, while the magnitude of increase tends to decrease with the droplet diameter and number concentration increasing. The research results can provide both theoretical basis for modeling the agglomeration process of complex particle systems and method guidance for achieving the ultra-low emission of fine particles from combustion sources.

Электротермические приемники звука

An analysis of the physical processes occurring during the emission of sound waves by electrothermal sound sources - thermophones, showed that a thermophone is a reversible physical system. This made it possible to determine the conditions under which the process of converting an acoustic signal into an alternating electric current can be carried out on the active element of the thermophone, and, consequently, the system will respond to an external acoustic field.

High-Precision Numerical Research on Flow and Structure Noise of Underwater Vehicle

This paper presents the results of research on the noise generated by an underwater vehicle in the operational state. The study combines the large eddy simulated turbulence model and Lighthill’s acoustic analogy theory and extracts the transient flow field data as the excitation conditions for acoustic calculations. The results of the numerical calculations of the external acoustic field were obtained under vehicle wall pressure pulsation condition, Lighthill volume excitation condition, and the vibration excitation condition of the underwater vehicle. It is found that the noise is concentrated at the front and tail of underwater vehicle, and its level is closely related to the form of vortex shedding. The peak frequency of structural radiation noise of underwater vehicle is consistent with its peak frequency of mean square vibration velocity. The basis for selecting the boundary conditions of the sound field according to the incoming flow conditions is also evaluated. The research results provide a reference for the noise reduction design of underwater vehicles, thus improving their concealment in combat.

Fast and Simple Fabrication of Multimaterial Hierarchical Surfaces Using Acoustic Assembly Photopolymerization (AAP)

AbstractMultimaterial surfaces with hierarchical features have many potential applications in self‐cleaning, droplet manipulation, microfluidics, and biomedicine, owing to their wide range of functionalities induced by structural and material contrasts. Here, a fast and sustainable manufacturing method, acoustic assembly photopolymerization (AAP), is presented for productions of such surfaces. In the novel AAP process, an external acoustic field is used to assemble microparticles to microsized patterns, while the photocuring is combined with the acoustic assembly to produce multilevel hierarchical features, such as cones and wrinkles ranging from nanometer to micrometer. The mechanism underlying the proposed multimaterial surface structuring technique is discussed, and the relationship between process parameters and surface structures is modeled. Effects of surface material composition patterns and surface topology on the hydrodynamic properties are studied. To demonstrate potential applications, three microreactors are designed and automated droplet manipulations are demonstrated. The application of the proposed surface manufacturing approach is further extended to fog harvesting. The AAP technology and the fabricated multimaterial hierarchically‐structured surfaces demonstrated in this study can be employed in many other advanced applications in microfluidics, tissue engineering, and also potentially many other fields such as mechanical systems and battery systems.

Aerodynamic Noise Simulation of a Car Side Mirror at Hight Speed

Airflow around the car side mirrors is one of the sensitivity zones in which the airflow is separated and detached from the mirror flat side. The turbulence created by this flow detachment can affect the airflow to the main body of the car which lies behind the mirror. The turbulent structures of airflow exert directly on the lateral panels that causes the reduction of the car performance due to the increased drag, the source of noise and vibration, and so on. Consequently, the analysis of airflow structure allows for better understanding of the aerodynamic phenomena that is the origin of noise source and provides design information to improve and optimize the side mirrors. In this paper, the focus lies on the aerodynamic noise simulation by analyzing the turbulent flow structure and predict the external acoustic field using k-ε and LES turbulent modeling approaches. The numerical results are compared to the experimental results with only 6.7% error in static pressure on the mirror surfaces. The simulation results showed that the spectra of sound pressure level with LES model is close to experimental data than that with k-ε model.

Physical impact of a surfactant on the nonlinear oscillations of a microbubble considering a dynamic surface tension and subject to an external acoustic field

In this work, we study the transport of surfactant molecules to the surface of an oscillating microbubble when an acoustic pressure is used as driving force to promote the nonlinear oscillation. We consider a dynamic surface tension as a function of the surfactant concentration and a large diffusive P\'eclet number, as occurs in several applications. The surfactant concentration equation is solvable by using a similarity transformation which simplifies the problem, whereas the equation for the radius evolution is solved by the 4th order Runge-Kutta method.

The Degassing Processes for Oil Media in Acoustic Fields and Their Applications.

Numerous experiments on the effect of acoustic fields on oil media have shown the changing nature of oil physicochemical properties. In the present paper, we present a concept of internal airlift for oil medium with dissolved gas which could be propelled by external acoustic field. The mechanism determining gas bubble size as a function of pressure change is discussed. Model of interaction for the growing bubbles with acoustic fields is presented. Relationships specifying the characteristics of both the required acoustic field and oil medium are derived. The use of these relations makes it possible to define the available range of parameters for the system under consideration where one can obtain the expected effect on oil medium. It is demonstrated how the change in pressure and oil saturation (namely, the density of oil particles in the entire flow) of the medium is associated with temperature fields in the system. In particular, it is shown that the maximum deviation between the temperature change in oil and gas and gas–liquid media reaches a significant value, namely 10−2 K for a gas–liquid medium, while this difference is −0.1 K in an oil-and-gas medium. Using this approach, thermograms of oil producing wells have been analysed at a qualitative level.

Far field acoustic radiation and vibration analysis of combined shells submerged at finite depth from free surface

A completely submerged underwater vehicle is modeled as a conical-cylindrical-spherical combined shell, the vibro-acoustic response near free surface of which is rarely analyzed in existing studies. In this paper, a Ritz-Legendre spectral method is proposed to analyze the vibro-acoustic response of combined shells under different submerged depths from the free surface. A theoretical structural model is established based on the Love shell theory, virtual spring technology and coordination relationship between displacements and rotation angle of adjacent subshells. The half-space external acoustic field model with the free surface is formulated by the Legendre spectral method, image method and Kirchhoff–Helmholtz boundary integral equation. The unified displacement admissible function of each subshell is expanded as Legendre orthogonal polynomial along generatrix direction and Fourier series along circumferential direction. The free surface treated as an ideal infinite acoustic soft boundary is substituted into acoustic wave equation and the half-space Green's function is obtained. The key technology to construct final coupled governing equation is how to expand the half-space Green's function with two-dimensional Fourier transform. Computed results are compared with those of the references and finite element method. The convergence, applicability, and correctness of the present method are verified. Influence of the free surface on the vibration and far-field acoustic radiation of combined shells under different submerged depths is analyzed, providing engineering significance for predicting external acoustic radiation of complicated combined shells with free surface.

Radiation force on a bubble located near an interface.

The presence of a boundary produces marked changes in the oscillation amplitudes and types of bubble distortion modes excited by an external acoustic field. In the majority of cases, the radiation force can be determined based on the linearized equations of motion. Bispherical coordinates are used to obtain an analytical description of linearized bubble dynamics at distances from the interface comparable to those of the bubble size. In the limit of weak dissipation, explicit formulas have been derived that describe the dependence of the radiation force on the separation distance between the bubble and the interface, the material parameters of the contacting media, and the angle of incidence of the incoming wave. The component of the radiation force directed to the interface has been shown to exhibit qualitative changes when the direction of the incoming field passes through the angle of the total internal reflection.