Acoustic Potential Energy Research Articles

Addressing cycle‐skipping in full‐waveform inversion using acoustic wave energy

AbstractLimitations in acquisition technologies lead to insufficient low‐frequency signals in field seismic data. Local optimization methods are the common approaches for full‐waveform inversion. Inaccurate initial velocity models and lack of low‐frequency signals in seismic data typically cause the local‐gradient‐based full‐waveform inversion to converge to a local minimum due to cycle‐skipping. The existing energy‐based objective functions can generate artificial low‐frequency signals successfully by squaring the pressure but overlook the law of energy conservation, which may mislead model updates. To overcome this issue, we combine acoustic wave potential energy and kinetic energy to develop a new objective function that fits the acoustic wave energy. The new acoustic‐wave‐energy‐based full‐waveform inversion considers the law of energy conservation. The new system creates low‐frequency signals to avoid cycle‐skipping and produce an accurate smooth background velocity model, which provides a sufficient starting model for conventional full‐waveform inversion. Numerical examples demonstrate that the combination of acoustic‐wave‐energy‐based full‐waveform inversion and conventional full‐waveform inversion can deliver more faithful and accurate final results than conventional full‐waveform inversion alone.

Mechanical Profiling of Biopolymer Condensates through Acoustic Trapping.

Characterizing the mechanical properties of single colloids is a central problem in soft matter physics. It also plays a key role in cell biology through biopolymer condensates, which function as membraneless compartments. Such systems can also malfunction, leading to the onset of a number of diseases, including many neurodegenerative diseases; the functional and pathological condensates are commonly differentiated by their mechanical signature. Probing the mechanical properties of biopolymer condensates at the single particle level has, however, remained challenging. In this study, we demonstrate that acoustic trapping can be used to profile the mechanical properties of single condensates in a contactless manner. We find that acoustic fields exert the acoustic radiation force on condensates, leading to their migration to a trapping point where acoustic potential energy is minimized. Furthermore, our results show that the Brownian motion fluctuation of condensates in an acoustic potential well is an accurate probe for their bulk modulus. We demonstrate that this framework can detect the change in the bulk modulus of polyadenylic acid condensates in response to changes in environmental conditions. Our results show that acoustic trapping opens up a novel path to profile the mechanical properties of soft colloids at the single particle level in a non-invasive manner with applications in biology, materials science, and beyond.

Directional active noise control for drones

Drones have become ubiquitous in various everyday applications, but their noise pollution remains an annoying issue. In this paper, we study the possibility of applying active noise control on drones with attached speakers. We propose the active noise control algorithms designed to iteratively calculate driving signals of speakers for canceling the outgoing noise from drones, specifically focusing on the blade passage frequencies within a directional spherical sector region. Two active noise control strategies are proposed: (i) minimizing the residual signal coefficients and (ii) minimizing the acoustic potential energy within the sector region. We derive update equations for two variables: (a) the loudspeaker weights and (b) secondary source spherical sector harmonics coefficients. Considering the power and loading limitations of drones, simulations are conducted under constraints of secondary source numbers to investigate the noise reduction performance with various secondary source setups. Simulation results demonstrate that the proposed method can effectively reduce the noise level over the directional sector region with a fast convergence speed.

Amplitude Matching for Multizone Sound Field Control

A multizone sound field control method, called amplitude matching, is proposed. The objective of amplitude matching is to synthesize a desired amplitude (or magnitude) distribution over a target region with multiple loudspeakers, whereas the phase distribution is arbitrary. Most of the current multizone sound field control methods are intended to synthesize a specific sound field including phase or to control acoustic potential energy inside the target region. In amplitude matching, a specific desired amplitude distribution can be set, ignoring sound propagation directions. Although the optimization problem of amplitude matching does not have a closed-form solution, our proposed algorithm based on the alternating direction method of multipliers (ADMM) allows us to accurately and efficiently synthesize the desired amplitude distribution. We also introduce the differential-norm penalty for a time-domain filter design with a small filter length. The experimental results indicated that the proposed method outperforms current multizone sound field control methods in terms of accuracy of the synthesized amplitude distribution.

Active noise control for global broadband noise attenuation in a cylindrical cavity using Modal FxLMS algorithm

Noise reduction is very important for cavities such as long ventilation ducts, and train and airplane cabins. This paper seeks to develop, design, and implement an active noise control system to globally reduce narrowband and broadband acoustic noises inside a cylindrical cavity using the Modal FxLMS algorithm along with canceling the feedback effect of the actuator on the reference microphone. In addition, the efficiency of the proposed algorithm is compared to the conventional FxLMS algorithm for broadband noises in terms of acoustic potential energy and energy consumption of the actuators. To this end, the natural frequencies and mode shapes are derived using experimental methods and finite element simulation, and the results are compared. The modal data are used to design and implement a modal filter. The filter output is fed to the Modal FxLMS algorithm as the error signal for updating controller coefficients. Due to the presence of a reference microphone for the proposed algorithm and the effect of the control loudspeaker, it is required to remove the feedback effect. An experimental setup is developed, and an FPGA board and LabVIEW software are adopted to implement and verify the effectiveness of the proposed algorithm. The results indicate that the controller could effectively attenuate the narrowband and broadband acoustic noises globally. Furthermore, although the conventional FxLMS algorithm can suppress the noise around acoustic modes, it produces a larger control signal than the Modal FxLMS algorithm and consumes more energy.

Vibro-acoustic characteristics analysis of the rotary composite plate and conical–cylindrical double cavities coupled system

PurposeThe purpose of the study is to obtain and analyze vibro-acoustic characteristics.Design/methodology/approachA unified analysis model for the rotary composite laminated plate and conical–cylindrical double cavities coupled system is established. The related parameters of the unified model are determined by isoparametric transformation. The modified Fourier series are applied to construct the admissible displacement function and the sound pressure tolerance function of the coupled systems. The energy functional of the structure domain and acoustic field domain is established, respectively, and the structure–acoustic coupling potential energy is introduced to obtain the energy functional. Rayleigh–Ritz method was used to solve the energy functional.FindingsThe displacement and sound pressure response of the coupled systems are acquired by introducing the internal point sound source excitation, and the influence of relevant parameters of the coupled systems is researched. Through research, it is found that the impedance wall can reduce the amplitude of the sound pressure response and suppress the resonance of the coupled systems. Besides, the composite laminated plate has a good noise reduction effect.Originality/valueThis study can provide the theoretical guidance for vibration and noise reduction.

Influence of the inclination angle on the sound field in an irregular enclosure containing two elastic walls

The sound field model of an irregular enclosure with two elastic walls and an inclined wall is established by the modal theory. The modal parameters of the irregular enclosure are obtained by the envelope rectangular technique. The influence of the inclination wall angle on the sound field in the irregular enclosure is discussed. When the inclination angle is increased from 0° to 45°, the resonance frequencies of the acoustic enclosure are basically reduced in the frequency range of 0∼250 Hz. When the inclination angle is increased from 0° to 45° every 15° interval, the amplitude of a certain acoustic mode itself decreases, while the amplitudes of the acoustic modes coupled to it basically increase. The acoustic potential energy peaks in the enclosure basically shift to the low frequency with the increase of the inclination angle. Furthermore, the change trend of the acoustic potential energy is regular in the low-order modes, but relatively chaotic in the high-order modes. In addition, in order to verify that the accurate description of the primary sound field is the basis of effective noise control, the two-elastic plate model is deliberately treated as one-elastic plate model, and its influence on the performance of active noise control is discussed. Also, if the multi-elastic plate model is regarded as a simplified automobile cab, the research results can be used for the preliminary acoustic design of the cab; that is, the research results can be used for the acoustic design of similar models.

Optimization of secondary source configuration in enclosure using plane wave decomposition

The optimization of secondary source configuration for an active noise control (ANC) system in its enclosed space generally focuses on noise reduction requirements at discrete points only. This may lead to the poor noise reduction performance in the whole spatial region, and it is necessary to know the information on error sensor positions in advance. To address this problem, a cost function for spatial-region-oriented noise reduction is proposed. The plane wave decomposition of the enclosed sound field is used to obtain the primary field plane waves and the unit secondary field plane wave of each candidate secondary source as the prior knowledge for configuration optimization, so as to formulate a wave-domain ANC cost function. The optimization method adopts the simulated annealing search. Taking a rigid-walled rectangular cavity as an example, the optimization method is firstly compared with two space-domain methods by using analytic values of the wave-domain prior knowledge. The comparison results show that the better reduction of spatial acoustic potential energy can be achieved independent of the error sensor configuration information. Then the estimated values of the wave-domain prior knowledge through measuring randomly distributed microphones are used to optimize the configuration of the ANC system. The optimization results suggest that the noise reduction of spatial acoustic potential energy of the optimized configuration can be better than that of the space-domain method, but the microphone positions have a great influence on the noise reduction performance.

In-plane manipulation of single particle based on phase-modulating acoustic tweezer

The acoustic radiation force allows acoustic tweezers to suspend and move tiny particles. The horizontal movement is one of the common forms in which acoustic tweezers manipulate particles. In this paper, the direct relationship between acoustic radiation force and sound pressure is derived theoretically. The results show that there is a corresponding relationship between the maximum point of sound pressure (focus point) and the minimum point of acoustic radiation force potential energy. A model for focused acoustic field in acoustic tweezers is established based on the principle of phase modulating. In the numerical simulation, taking the double-sided 16-element acoustic tweezers device for example, the method of controlling the horizontal movement of particles and its stability are analyzed. Owing to the influence of gravity, the balance in the vertical direction must be considered in the horizontal movement of particles. Horizontal movement shows different stabilities at different positions in acoustic filed. The closer to the center of the array the particle is, the more stably it moves. The step length (accuracy) also has an important influence on the moving stability. In general, the shorter the step size is, the higher the stability is. In this model, when moving step length is reduced by one-half, the stability is improved by nearly 40%. The research results have theoretical significance for designing acoustic tweezers, planning particle movement paths, and promoting the application of acoustic tweezers technology.

Spatial Active Noise Control Based on Kernel Interpolation of Sound Field

An active noise control (ANC) method to reduce noise over a region in space based on kernel interpolation of sound field is proposed. Current methods of spatial ANC are largely based on spherical or circular harmonic expansion of the sound field, where the geometry of the error microphone array is restricted to a simple one such as a sphere or circle. We instead apply the kernel interpolation method, which allows for the estimation of a sound field in a continuous region with flexible array configurations. The interpolation scheme is used to derive adaptive filtering algorithms for minimizing the acoustic potential energy inside a target region. A practical time-domain algorithm is also developed together with its computationally efficient block-based equivalent. We conduct experiments to investigate the achievable level of noise reduction in a two-dimensional free space, as well as adaptive broadband noise control in a three-dimensional reverberant space. The experimental results indicated that the proposed method outperforms the multipoint-pressure-control-based method in terms of regional noise reduction.

Active Control of Sound Transmission in Ship Cabins Through Multiple Independently Supported Flexible Subplates

The vibration and noise produced by the powertrain and waves inside ship cabins limit working efficiency and crew and passengers’ accommodation quality. This paper simplifies ship cabins as cavities and explores active control techniques to attenuate sound transmission via multiple parallel-supported flexible subplates. The theoretical formulations of the interaction between multiple subplates and cavities were performed and the coupling relationships between them were analyzed. Based on the multiple subplates and the cavity coupling models, numerical simulations were performed using the derived optimal controller to minimize the transmission of sound into the cavities through two and nine parallel-supported subplates. The various control strategies were explored to minimize the coupling system’s acoustic potential energy, and the control performances were compared and discussed. The mechanism of reducing sound transmission through multiple supported subplates into a cavity is revealed. The simulation results showed that the vibration pattern of the controlled subplate is changed after it is regulated, which increases its radiation to subdue the other subplates’ radiation, while increasing vibration of the controlled subplate. The more subplates a cavity has, the more kinetic energy the controlled subplate possess. Furthermore, the noise reduction performance of a cavity with fewer subplates is better than that with more subplates.

Particle Patterning by Ultrasonic Standing Waves in a Rectangular Cavity

By means of the acoustic radiation force, standing waves of ultrasound can form a two-dimensional microarray to hold dispersed particles or cells in solution. This phenomenon can be used in lab-on-a-chip technology for single-cell analysis and analytical chemistry, though the physics behind ultrasound patterning is not fully understood. This study provides an analytical expression for the acoustic potential energy that traps cells, and reveals that the trapping points at pressure nodes, antinodes, and internode midpoints depend on a cell's size and mechanical properties. This theoretical approach should help to engineer acoustic-patterning devices, especially for ``one cell per well'' analysis.

Global active noise control in vibro-acoustic cavities using acoustic sensing

This paper proposes a method for global active noise control in vibro-acoustic cavities using acoustic sensing under the presence of both structural and acoustic disturbances. Global active noise control has earlier been carried out by minimizing the acoustic potential energy in the cavity expressed as the sum of squares of the acoustic pressures at discrete microphone locations. However, this approximation though holds well for a rectangular box cavity, is not applicable for the cavities of other shapes. This calls for development of an active noise control method based on the estimation of the acoustic potential energy applicable to the cavities of arbitrary shapes as encountered in practice. Virtual sensing of the acoustic potential energy has been reported in the literature based on measurement of vibration by the structural sensors. However, such approaches are applicable when only the structural disturbances act on the cavity, but cannot be used if the acoustic disturbances are also present in the cavity. This paper presents development of a global active noise control method based on virtual sensing of the acoustic potential energy in the cavity under the presence of structural and acoustic disturbances. Minimisation of the estimated acoustic potential energy through a feedforward control law is developed. Numerical studies on an irregular-shaped vibro-acoustic cavity and a car cavity are presented to evaluate the performance of the proposed technique. The results are also compared with the maximum possible reduction in the acoustic potential energy obtained using the optimal control inputs. The levels of reduction in the acoustic potential energy obtained with the proposed method are found to be close to the maximum possible reduction using the optimal control inputs. The proposed method is then also validated through an experimental study on a rectangular box cavity.

Tuning of vibration absorbers and Helmholtz resonators based on modal density/overlap parameters of distributed mechanical and acoustic systems

This paper presents a study on the tuning of vibration absorbers and Helmholtz resonators used to control at target resonance frequencies respectively the flexural response of lightly damped distributed structures and the acoustic response of lightly damped cavities subject to broadband stochastic excitations. The vibration and acoustic control effects of these two devices are assessed considering the broadband flexural response and acoustic response of typical structures and enclosures encountered in practical applications, that is: beam, thin plate and thin walled cylinder structures and one-dimensional duct, two-dimensional slender volume, three-dimensional volume enclosures. The herein proposed multi-mode tuning approaches are based on the H2 cost functions of the total flexural kinetic energy of the three structures and of the total acoustic potential energy of the three enclosures. The H2 cost functions are defined within finite frequency bands centred at the target structural or acoustic resonance frequencies respectively. A comprehensive overview of the modal density and modal overlap functions for the flexural response of the three structures and for the acoustic response of the three enclosures is also presented to provide physical interpretations and practical guidelines on the performance and applicability of classical single-mode and the proposed multi-mode tuning approaches. The study shows that classical tuning laws can be straightforwardly employed to control the response at low resonance frequencies such that the modal overlap is not greater than one, whereas to control the response at higher resonance frequencies, where the modal overlap is significantly greater than one, the proposed multi-mode tuning approach should be adopted.

Global active control of harmonic noise in a vibro-acoustic cavity using Modal FxLMS algorithm

The Modal FxLMS algorithm is recently proposed for reduction of global level of noise in vibro-acoustic cavities. The algorithm minimizes acoustic potential energy expressed in modal domain which allows a choice of acoustic modes whose modal amplitudes are desired to be minimized. The working of the algorithm and its effectiveness has been demonstrated previously through a numerical study and an experimental study is required to test the effectiveness of the algorithm in practice. To meet this objective this paper presents an experimental study of this algorithm for global active noise control in a rectangular box cavity. The algorithm utilizes modal filtered reference signals and modal amplitudes of the selected acoustic modes of the cavity. To identify modal filtered reference signals, modal secondary paths are utilized. In the present study, modal secondary paths are identified using experimentally identified physical secondary paths and acoustic mode shapes. Modal amplitudes of the acoustic modes are identified on the basis of acoustic pressure measurements from eight microphones suitably placed throughout the cavity. The performance of the algorithm is studied under the presence of acoustic and structural disturbances using one or two control loudspeakers. The active control is carried out at harmonic frequencies coinciding with cavity-controlled resonances and panel-controlled resonances. It is found from the experimental results that the Modal FxLMS algorithm is successful in reducing modal amplitudes of the selected acoustic modes. When all the significantly contributing acoustic modes are chosen, a reduction in global level of noise is observed at cavity as well as panel controlled resonances.

Global feedforward active noise control in vibro-acoustic cavities without increasing structural vibrations.

Interior noise in vibro-acoustic cavities may be generated due to acoustic and structural disturbances. Earlier studies have shown that for global control, the maximum reduction in acoustic potential energy can be realised by using an optimum combination of acoustic and structural actuators. However, it is observed that this reduction in interior noise may also be accompanied with an increase in kinetic energy of the cavity structure. This paper presents the development of a feedforward technique for active noise control in vibro-acoustic cavities ensuring that the noise reduction does not lead to an increase in kinetic energy. The problem is formulated as a constrained minimisation problem to minimise the acoustic potential energy subject to a constraint that the kinetic energy does not increase. Through a numerical study, it is shown that the optimum solution of the above problem indeed is favourable in terms of reduction in acoustic potential energy in the cavity and kinetic energy of the structure. The paper further proposes a method for solution of this constrained minimisation problem using a penalty function method and solution of sequential unconstrained problems. The proposed method is validated through a numerical study on a car-like cavity for single- and multi-tonal noise.

Active control of sound transmission into an enclosure using structural modal filters

This paper deals with active control of sound transmission through a flexible structure into an enclosed space. The control system consists of sensors and actuators used to measure and control the vibration of a flexible structure for reducing sound transmission. However, since the structural modes mutually contribute to the acoustic potential energy in the enclosure, evaluating the contribution of each structural mode independently is not straightforward. Hence, it is not clear which structural modes should be measured and controlled. In this paper, a formulation for expressing the contribution from each structural mode to the acoustic potential energy via interaction between structural modes is developed. Though the formulation is not a closed form, it enables one to evaluate the contribution of each structural mode independently. Once the highly contributive structural modes are identified, these structural modes can be measured and controlled independently without spillover to other structural modes by using structural modal filters. It is found that the proposed control method can effectively reduce the acoustic potential energy and can avoid an increase in the vibration of the flexible structure. The theory is developed for an arbitrarily-shaped enclosure. A numerical simulation for a rectangular enclosure is also conducted to verify the theory.

Vibro-acoustic analysis of a trapezoidal cavity with a clamped flexible wall

The coupled model between trapezoidal cavity and its clamped flexible wall is developed using classical modal coupling theory. Based on the coupled model, the resonance frequencies of coupled system are obtained and compared with the corresponding uncoupled one. Meanwhile, the reason for the variation of resonance frequencies of coupled system modes is analyzed in detail. Then, the response of coupled system is investigated using the acoustic potential energy in the cavity and panel vibration kinetic energy when it is excited by an incident plane wave outside of the cavity. Coupling coefficient between trapezoidal cavity and its clamped flexible wall is proposed to assess the modal matching degree between them. It is shown that the coupling selection is not satisfied except in the axis direction which is parallel to the inclined wall. In addition, a rectangular cavity with a clamped flexible wall is also considered and compared with that of the trapezoidal one.

Active Noise Control Over Space: A Wave Domain Approach

Noise control and cancellation over a spatial region is a fundamental problem in acoustic signal processing. In this paper, we utilize wave-domain adaptive algorithms to iteratively calculate the secondary source driving signals and to cancel the primary noise field over the control region. We propose wave-domain active noise control algorithms based on two minimization problems: first, minimizing the wave-domain residual signal coefficients, and second, minimizing the acoustic potential energy over the region, and derive the update equations with respect to two variables, the loudspeaker weights and wave-domain secondary source coefficients. Simulation results demonstrate the effectiveness of the proposed algorithms, more specifically the convergence speed and the noise cancellation performance in terms of the noise reduction level and acoustic potential energy reduction level over the entire spatial region.

Modal filtered-x LMS algorithm for global active noise control in a vibro-acoustic cavity

Abstract This paper proposes an algorithm called as 'Modal filtered-x LMS algorithm' for global active noise control in vibro-acoustic cavities. The proposed algorithm is a formulation of the conventional filtered-x least mean square algorithm in modal domain to reduce acoustic potential energy in a cavity. The formulation leads to a concept of what has been called as 'modal secondary path' in the paper. The active control method makes use of the reference signal filtered using modal secondary paths instead of the reference signal filtered using physical secondary paths as done in the conventional FxLMS algorithm. The method requires knowledge of acoustic modal pressures which in the present paper are estimated using acoustic pressure measurements at a discrete number of points in the cavity. The proposed method allows a modal based control of acoustic potential energy in the cavity. The proposed method also has an advantage that it reduces the computational burden associated with filtering of the reference signal with secondary paths for global control. A numerical study to actively control noise due to structural and acoustic disturbances acting on a car-like cavity is presented. Results of modal based control are compared with maximum reduction that is possible for given disturbances and control sources. It is found that the noise reduction obtained using the modal based approach is close to the maximum possible but at a lower computational cost.