Sound Power Radiation Research Articles

On application of sound power radiation of rolling tyre measured using CPX-based methodology

The present paper provides a comprehensive account of sound power radiation measurement from a rolling tyre, utilising a methodology that employs an advanced PolyU Mark III Close-Proximity (CPX) trailer enclosure which is aimed to provide CPX measurement per relevant ISO stsandard with suppressed background noise within the interior. The interior walls and ceiling of the enclosure are equipped with diffuser panels, creating a reverberant environment suitable for sound power measurement using the comparison method. The optimal design of the enclosure, which minimizes acoustic resonance and ensures a uniform distribution of acoustic energy, is determined through extensive numerical simulations. During tyre/road sound power measurements, the spatially averaged sound pressure level (SPL) distributions within the enclosure are obtained with a reference sound source (RSS) of known sound power. The relationships between the RSS SWLs and the corresponding SPLs are established at all vehicle speeds. These relationships can then be utilised to deduce the total SWL, as well as its 1/3-octave spectrum, from the captured averaged SPL radiated by a tyre rolling at any vehicle speed. The effectiveness of the CPX-based sound power measurement are illustrated. Additionally, the potential of utilising the measured SWLs for predicting pass-by noise radiation to roadside is discussed.

Acoustic characteristics of composite structures with 2D acoustic black holes and stiffened plates

Acoustic black hole (ABH) structure, a novel technology for modulating flexural waves, offers promising solutions for controlling noise caused by structural vibrations. In this paper, we introduce acoustic black holes into traditional stiffened plate structures and design a new type of ABH stiffened plate structure, which combines the wave manipulation ability of ABH with the load-bearing capacity of the stiffened structures. We establishes finite element models for calculating the free space sound field and closed cavity sound field of an ABH stiffened plate, builds corresponding experimental platforms, and tests them under point load excitation. The results show that ABH stiffened plate has great vibration and noise reduction effects, with a 5–10 dB reduction in sound radiation power above the cut-on frequency and a maximum noise reduction of about 30 dB. Through quantitative analysis from multiple perspectives, it is shown that ABH have an inherent mechanism of increasing damping level and reducing coupling between structure and sound field. Studying the influence of different media on the acoustic radiation of ABH stiffened plates, results further reveal that ABH have noise reduction effects in water media, and increasing the application scenarios of the ABH stiffened plate structures.

Vibro-acoustic performance of graded piezoelectric metamaterial plates

This work investigates the vibro-acoustic performance of graded piezoelectric metamaterial plates. A piezoelectric layer with electrodes segmented in a regular lattice is attached over a rectangular, simply-supported panel to realize the electromechanically coupled metamaterial plate, rendering a geometrically periodic structure. The grading is achieved in the electric domain, as each unit cell’s inductive shunt resonant frequency can be tuned independently. We investigate two first-order grading patterns based on linear variations along one and both dimensions of the plate and evaluate their impact on vibration attenuation, sound power, kinetic energy, and acoustic radiation efficiency. The graded metamaterial plates outperform the periodic locally resonant counterparts in vibration and radiated sound power attenuation. Moreover, sound radiation efficiency may increase within the attenuation band for steep grading patterns related to the vibration localization phenomenon. The results show that piezoelectric metamaterial plates with reconfigurable properties are an interesting alternative for enhanced vibro-acoustic performance.

Internal sound pressure and power radiation from a submerged cylindrical enclosure with interior acoustic excitation

This paper presents the modelling and analysis of the effect of an interior acoustic excitation on a submerged cylindrical enclosure. The enclosure has ring stiffeners and acoustic absorption material on the internal wall. The acoustic excitation generates an incident and scattered sound field inside the enclosure. The incident and scattered sound forms the internal pressure which induces a structural response and, thus, the radiated sound. The previous work (James 1985) with an internal noise source located on the vertical axis is expanded to allow forces and interior acoustic sources at arbitrary locations. The formulation of the internal pressure is developed by solving the unknown coupling term between the internal fluid and the hull. The coupling term was neglected by James (1985). However, this term is significant in magnitude for the internal pressure and must, therefore, be included. The analytical results are compared with numerical finite element/boundary element models with good agreement.

Simulation Analysis of Acoustic Radiation from Force Excitation of Foam-Filled Stiffened Sandwich Panels

To tackle the influence of foam filling on the sound radiation performance of reinforced sandwich panels, this study employs a combined approach of experiments and simulations to investigate the factors that impact the sound radiation performance in the 1–2000 Hz mid–low frequency range. The aim is to determine how the parameters of foam impact the sound radiation performance of foam-filled reinforced sandwich panels. The results indicate that changes in the acoustic parameters of the foam have a weak effect on the frequency corresponding to the peak sound radiation power and the non-peak frequency range sound radiation performance of the sandwich panel, while significantly impacting the peak sound radiation power. Among them, porosity has the least influence on sound radiation performance, whereas static flow resistivity and tortuosity factors have a greater influence on peak sound radiation performance. The reduction in thermal characteristic length and the increase in static flow resistivity can both enhance the sound radiation performance of the panel, while the impact of tortuosity factor and viscous characteristic length on panel sound radiation performance depends on the frequency range.

Sound transmission characteristics of a plate backed by an irregular cavity

The study of the coupling cavity provides an effective theoretical reference for the acoustic design. However, most of the previous studies are based on idealized models and there is little research on the sound radiation power about the irregular shapes. The work in this paper achieves the generalization of the model and explores the impact of irregular back cavities on the sound radiation of the plate structures. The influence on the results of the sound insulation performance testing of the plate is also investigated when irregular cavities involved. The displacement of the plate and the sound pressure inside the cavities are expressed as multidimensional Fourier series with additional terms, which will contribute to maintaining the continuity of pressure and velocity at the boundaries. The sound field of the irregular cavity is considered as a unit cubic one in a new coordinate system by coordinate transformation method. The arbitrary boundary of the cavities is realized by adding the energy terms of impedance into the Lagrange equation. The Hamilton’s principle is employed to realize the complete coupling between the plate and the sound fields on both sides. The sound radiation power of the plate can be obtained by using the Rayleigh integral. By using Fast Cosine Transform, the quadruple integrals of the radiation power are simplified to improve accuracy and efficiency of the calculation. Numerical results from the analytical approach are compared with those given by Finite Element Analysis (FEM) to guarantee the rightness and validity of the models. Moreover, experimental results are also given to discuss the reasons of the bias between theory and practice.

Vibration and Sound Radiation of Cylindrical Shell Covered with a Skin Made of Micro Floating Raft Arrays Excited by Turbulence

To reduce the vibration and sound radiation of underwater cylindrical shells, a skin composed of micro floating raft arrays and a compliant wall is proposed in this paper. A vibroacoustic coupling model of a finite cylindrical shell covered with this skin for the case of turbulence excitation is established based on the shell theories of Donnell. The model is solved with the modal superposition method to investigate the effects of the structural parameters of micro floating raft elements on the performance of reducing vibration and sound radiation of the cylindrical shell of this skin. The results indicate that increasing the stiffness ratio, damping ratio, mass ratio, or decreasing the interval between micro floating raft elements can improve the vibration and sound radiation reduction performance of this skin over the frequency range 0~2000 Hz. Moreover, the mean quadratic velocity level and sound radiation power level of the finite cylindrical shell with this skin can be reduced by 12.00 dB and 9.65 dB respectively compared to the finite cylindrical shell with homogeneous viscoelastic coating in the frequency range from 0~2000 Hz, implying a favorable performance of this skin for reducing the vibration and sound radiation of cylindrical shells.

Analytical Investigation of Sound Radiation from Functionally Graded Thin Plates Based on Elemental Radiator Approach and Physical Neutral Surface

This paper analyzes the sound radiation behavior of a clamped thin, functionally graded material plate using the classical plate theory and Rayleigh Integral with the elemental radiator approach. The material properties of the plate are assumed to vary according to the power-law distribution of the constituent materials in the transverse direction. The functionally graded material is modeled using a physical neutral surface instead of a geometric middle surface. The effects of the power-law index, elastic modulus ratio, different constituent materials, and damping loss factor on the sound radiation of functionally graded plate are analyzed. It was found that, for the considered plate, the power-law index significantly influences sound power level and radiation efficiency. There exists a critical value of the power-law index for which the corresponding peak of sound power level is minimum. In a wide operating frequency range, approximately 500–1500 Hz, this research suggests that the radiation efficiency is lower for the power-law index equal to 0 and 1. However, for very low frequencies (less than 250 Hz), the power-law index does not affect radiation efficiency significantly. Further, as the modulus ratio increases, the sound power peak decreases for a given power-law index. For the given material constituents of the functionally graded plate, the different values of damping loss factors do not significantly influence radiation efficiency. However, the selection of material constituents affects the radiation efficiency peak.

Proper Orthogonal Decomposition Method for the Prediction of Fan Broadband Interaction Noise

The turbulent wake generated by a rotor interacting with outlet guide vanes (OGVs) is one of the dominant broadband noise sources in a turbofan engine. An accurate representation of the rotor wake turbulence is therefore important for the reliable prediction of the rotor–OGV interaction noise. This paper presents a turbulence synthesis method based on a spectral proper orthogonal decomposition (POD) representation of the turbulent wake that aims to reproduce the desired velocity cross-spectrum along the OGV leading edges where noise is emitted due to turbulence–OGV interaction. The method is first developed in the frequency domain based on a superposition of vortical modes with the appropriate amplitudes. Fourier modes and POD modes are proposed to represent the two-point velocity spectrum. The POD modes will be shown to be highly efficient in reconstructing the flowfield near the tip region where a large-scale coherent structure is present. An extension of the POD synthetic turbulence method to the time domain is also presented by means of a white noise filtering technique to allow the generation of time-varying velocity signals with the desired cross-spectral characteristics. The results show that both the one- and two-point statistics can be closely reproduced. The proposed frequency-domain POD synthetic turbulence method for fan broadband noise prediction for a realistic fan–OGV configuration is illustrated by the use of a frequency-domain linearized Navier–Stokes solver to predict the sound power radiation due to each vortical mode. Overall sound power levels at a number of discrete frequencies are predicted and compared against measured noise data. Agreement is found to be within the uncertainty of the noise sound power measurement.

Analytical coupled vibro-acoustic modeling of tensioned membrane backed by the rectangular cavity

This paper proposes a unified approach to establish the analytical vibro-acoustic coupled model consisting of the tensioned membrane and the closed cavity. A 2-D Fourier cosine series with auxiliary functions is used to derive the displacement of the membrane structure. The sound pressure inside the cavity is expressed as a 3-D Fourier series with additional terms by the method of wave acoustics. Then, the vibro-acoustic coupled model between the membrane and the closed cavity is established based on the Hamilton's principle, which is suitable for different boundary conditions. The program developed by this method can be used to study the sound radiation power and sound transmission loss of coupled systems with various parameters. To demonstrate the accuracy of the proposed method, the free and forced responses of the coupled model are compared with results obtained by finite element method. The membrane with general boundary conditions is well investigated. Besides, the acoustic characteristics of the coupled model are analyzed by adjusting membrane thickness, membrane tension, cavity depth, membrane mounting position and source position, including sound radiation power and sound transmission loss. And the findings have been interpreted appropriately.

Acoustic Radiation Characteristics from Shell Structure for Different Depth State

As a naval warship, submarine is a typical complex combined system. The excitation source of its vibration has the characteristics of large amplitude and wide frequency spectrum, and the prediction of vibro-acoustic radiation needs to be carried out in a wide frequency band. How to accurately predict the vibro-acoustic radiation of submarines in the whole frequency band has become a problem of practical significance. Elastic cylindrical shell is the typical structure of underwater vehicle. Studying acoustic radiation characteristics from shell structure for different depth state has a certain significance for studying submarine acoustic stealth characteristics. As an important acoustic performance metrics, the radiation sound power of underwater structure is significant for researching vibration and sound radiation characteristics. In this article, based on the FEM and BEM method, by using ANSYS and SYSNOISE software shell structure for different depth state is modeled and its vibration and radiation characteristics are researched. Numerical calculation shows that with immersed depth increasing, the vibration response and sound radiation power from shell structure gradually tend to the ones from under free field.

Reducing underwater radiated noise of a SUBOFF model propelled by a pump-jet without tip clearance: Numerical simulation

A pump-jet without tip clearance is proposed to propel a scaled SUBOFF model. The hydrodynamic performance of the pump-jet behind the SUBOFF, modal characteristics and vibro-acoustic responses of the SUBOFF – pump-jet under unsteady excitations are reported and compared with those by the pump-jet with a 2 mm tip clearance. The hydrodynamics are obtained by CFD (Computational Fluid Dynamics) and vibro-acoustic responses are predicted by coupled FEM (Finite Element Method) and direct BEM (Boundary Element Method). The CFD model of the pump-jet without tip clearance is validated by experimental results in a cavitation tunnel through steady hydrodynamics. Fluctuation pressure, standard deviation of fluctuation pressure and spectra of the new pump-jet behind SUBOFF are demonstrated. It is shown that fluctuation pressure on a single blade and fluctuation force of the rotor are suppressed remarkably, as well the amplitudes at BPF (blade passing frequency) and its multiples is greatly attenuated for the monitoring points on the rotor and duct. Since a shroud is added for rotor blades and stiffness is presented between the shroud and the duct due to hydrodynamic lubrication, a new mode of coupled rotor and duct deformation is borne and modal frequency at longitudinal mode of shaft is increased due to change of the cantilever supporing state of rotor blades. New force transmission paths for the rotor via the duct to excite the hull, and that for the duct via the shafting to excite the hull are presented, which will transmit part of vibration energy when applying excitation forces on the rotor or duct. The sound radiation power level is greatly suppressed after eliminating the tip clearance. Especially at the characteristic structural modes due to combined effect of alternating the structural modes to be far away from the characteristic frequencies of excitation forces and suppressing fluctuation pressures on the rotor and duct.

Passive, remote and omnidirectional suppression of sound source radiation via an acoustic superscatterer

Effective direct control of the sound source is the fundamental solution to the problem of noise. Herein, we propose a passive, non-closed and remote scheme for omnidirectional reduction of the sound power radiated from vibrating sources. The physical mechanism of this scheme is to design an acoustic superscatterer based upon the idea of transformation media so that the virtual boundary of the acoustic superscatterer can overlap with the radiation boundary of the sound source to construct drastic multiple scattering effects. Through theoretical analyses and numerical simulations, we confirm the effectiveness of adopting an acoustic superscatterer to significantly suppress the sound radiation power generated by some typical dipolar sources in air. Our study shows that by arranging no more than two acoustic superscatterers at designated positions away from a dipolar thin rod, about 90% of the sound radiation power, i.e. 10 dB, can be suppressed in all directions of the dipole axis. This preliminary work could aid research into the use of passive methods to achieve non-contact omnidirectional noise control of vibrating sources.

Effects of annular acoustic black holes on sound radiated by cylindrical shells

While most acoustic black hole (ABH) designs are intended to reduce vibrations in beams and plates, annular ABHs have been recently proposed for cylindrical shells. The key to achieve the ABH effect in a structure consists in embedding an indentation on it such that it slows down incident waves and concentrates their energy at the center of the ABH. There, it can be typically dissipated by means of a viscoelastic layer. Many studies exist on the vibration of structures with ABH indentations but only a few address the topic of sound radiation. In this work, we evaluate the impact that an annular ABH has on the sound radiated by a baffled cylindrical shell. The vibration of the cylinder is computed using Gaussian basis functions in the Rayleigh-Ritz method. Once determined the surface velocity of the ABH cylinder, a Green's function approach is employed to obtain its surface acoustic pressure and then the sound power level, radiation efficiency and supersonic intensity. The dependency of the latter on the ranges determined by the ring and critical frequencies is analyzed for the case of a thick acoustic shell. Beyond the critical frequency, supersonic flexural waves entering the ABH become subsonic, substantially reducing the radiation efficiency and therefore, the emitted sound. Further reduction is achieved once passed the ring frequency.

Vibro-acoustic characteristics of a coupled pump-jet – Shafting system – SUBOFF model under distributed unsteady hydrodynamics by a pump-jet

This study presents the unsteady hydrodynamics of the excitations from a pump-jet running in the wake of a SUBOFF model and the vibro-acoustic characteristics of a coupled pump-jet – shafting system – SUBOFF model under unsteady excitations. The excitations of the pump-jet are obtained by CFD and the vibro-acoustic responses are predicted by coupled FEM/BEM. A mapping method based on radial basis function is established between CFD and structural mesh to apply the distributed pulsation forces on the wet surface of the pump-jet. The effect of the method used to apply the excitation forces on vibro-acoustic responses is investigated by applying distributed or equivalent pulsation forces at different areas of the pump-jet. Modal shapes, transmitted forces, sound radiation power, radiation directivity pattern and panel contributions are reported to illustrate the characteristics of the vibro-acoustic responses and the influence of the method used to apply the excitation forces on the responses. It is seen that the shaft frequency and the longitudinal mode resonant frequency of the shafting system are the typical characteristic frequencies with large magnitude in vibro-acoustic responses of the coupled system. Compared with applying concentrated forces applied at hub or 0.7 R, the responses produced by applying distributed forces on the whole pump-jet present modes and excitation characteristics with more reasonable magnitudes, illustrating the importance of applying distribute forces instead of concentrated forces. Besides, the contribution of the distributed forces on rotor is dominant since the responses of applying distributed forces on the pump-jet and applying distributed forces on rotor are similar.

Minimizing the radiated sound power from vibrating plates by using in-plane functionally graded materials

This paper presents a method for decreasing sound radiation from vibrating plates. The method uses Functionally Graded Materials (FGM) for building the plates instead of isotropic material. The graded pattern of material composition is characterized within the in-plane directions based on a two-dimensional trigonometric law. In the proposed method, the finite element method (FEM) is utilized for estimating the dynamic response of the plates. Then, the Lumped Parameter Model (LPM) is used for calculating sound radiation power. A genetic algorithm is applied as an optimization tool for determining the best distribution of the FGM. The efficacy of the proposed method is demonstrated by three design problems; minimizing the radiated sound from vibrating FGM plate at a particular excitation frequency, over a frequency band, and at a particular natural frequency. The design problems show that a considerable decrease of sound power can be accomplished with the optimal design of FGM plates in comparison with the isotropic plates.

Vibro-acoustic performance of acoustic metamaterial plate with periodic lateral local resonator

Based on the Bloch theory and the flexural wave propagation theorem, the model for calculating the vibration response, sound radiation power and radiation efficiency of an acoustic metamaterial plate is established. The modal analysis of a bare pate and the plate attached to periodical lateral local resonators are developed to investigate the vibration regulation. In addition, the patterns of the sound radiation power and radiation efficiency of the plate attached to periodical lateral local resonators versus frequency are studied. The results show that 1) in a specific frequency range, the mean square velocity and the sound radiation power are far lower than those of the bare plate, which is due to the resonance of the lateral local resonator; 2) unlike the vibration response and sound radiation power, the radiation efficiency of the plate attached to periodical lateral local resonator is higher than that of the bare plate. The investigation of the plate attached to lateral local resonator in this paper lays a solid foundation for the practical engineering in the field of vibration suppression and noise reduction.

Метод оптимизации демпфирования на основе анализа рабочих режимов для подавления низкочастотных шумов оборудования

Aiming at the reduction of low-frequency noise problem for large equipment, a damping optimization method based on the OMA (Operational Mode Analysis) is proposed. Due to the stability of the mode frequencies and shapes, damping application could make efficient noise reduction without bringing new problems compared with structural optimizations, which makes it one of the most important means for finalized products. Taking the engine compartment of an excavator as the study object, a damping optimization method based on the OMA test is proposed in this article, which makes a more efficient optimization for large equipment by its feasible modal test. Through simulation and experimental verification, the method is effective. The test results show that based on the OMA damping application method, the low-frequency sound power level has been significantly reduced, and after the damping application, the sound radiation power level defined by the national standard has also been reduced.

Sound radiation from the plate backed by the rectangular cavity

The radiation sound field of the plate with general boundary conditions backed by the acoustic cavity is investigated theoretically. The displacement function of the plate is generally expressed as a 2-D Fourier cosine series with additional terms. The addition terms could be used to accelerate the convergence rate of the present method and to account for the discontinuity of the displacement at the boundaries. The vibro-acoustic coupling between the vibration of the plate and the sound field on both sides of the plate is fully taken into consideration by adopting the Hamilton's principle. The sound pressure in the cavity is expressed as a 3-D Fourier series with additional terms which is used to account for the continuity between the velocity of the plate and the sound pressure on the plate. The sound radiation power of the plate can be obtained by using the Rayleigh integral. By means of Fast Cosine Transform, the quadruple integrals of the sound radiation power of the plate is reduced to several single integrals, which effectively avoids the time-consuming calculation. The influence of parameters on sound radiation power, such as boundary conditions, the sizes of the cavity, acoustic medium inside the cavity and the mounting position of the plate, are studied.

Wave Superposition Method Applied To Calculate the Radiation Sound Power of a Stiffened Plate

An indirect boundary element method using discrete sound field of virtual sound source is used to calculate the acoustic and vibration coupling response of the stiffened plate in water. In this paper, the relationship between the structural vibration mode coefficient and the virtual sound source intensity is established by using the superposition principle through Fourier transform using structural dynamics equations and boundary compatibility condition satisfying the function of virtual sound source intensity. Once the virtual sound source intensity is obtained, the radiation power can be determined. Taking the simply supported rectangular thin plate as an example, the sound radiation power is calculated on the condition that surface velocity is unknown, and the results are compared with the results of the analytical method, which shows that the method has high accuracy.