Acoustic Boundary Element Model Research Articles

Prediction and experimental study of radiated noise of rotating vane compressor under compound effects of multiple sources excitations

Aiming at the problem that it is difficult to accurately predict the radiated noise of rotary vane compressor under multi-source excitation, in this paper, the rigid body dynamics model and the dynamics model of airflow pulse excitation of the suction-compression-exhaust process of the rotary vane compressor were established, and the mechanism of multi-body contact excitation and airflow pulsation excitation for rotating vane compressor is expounded. Meanwhile, a flexible multibody finite element mesh model including a rotor, blades, cylinder, end cover and shell was established, and mechanical excitation and airflow pulse excitation were taken as mechanical boundary conditions to calculate the vibration response characteristics of the rotary vane compressor. To estimate the radiated noise of the rotary vane compressor, a compressor acoustic boundary element model was established, and a noise test bench system was built in a semi-anechoic chamber to compare and analyze the calculated noise value. At constant speed and acceleration, the rear sound pressure value is larger, followed by the right part, which is close to the exhaust port, and the front sound pressure is obviously lower than other points. The maximum relative error of sound pressure levels at four field points is 4.8%, and the average relative error of all measured points is 2.4%. The measured values are in good agreement with the calculated values, which verifies the accuracy of the radiated noise prediction model of rotary vane compressor.

Reliability analysis of composite sandwich structure for fuselage skin based on surrogate model

Composite structures are characterized by multiple source uncertainties in mechanical properties, geometric dimension, etc., and multiple failure modes, which bring challenges to their design and application. In order to explore the reliability analysis method of composite sandwich structures with multi-source uncertainties and multi-failure modes, a parametric finite element model and an acoustic boundary element model were established for deterministic analysis of a fuselage skin sandwich structure. Considering the randomness of the mechanical properties of composite materials and the laminate thickness, the structural reliability models were established for three typical failure modes of sandwich structures: static strength failure, global buckling and vibration noise. In order to reduce the computational effort, the Kriging surrogate models of failure modes were constructed, and the subset simulation method was used to predict the system failure probability of the sandwich structure of fuselage skin. The proposed computational framework provides support and tool for the fine design of composite sandwich structure.

Modelling of vibration and noise behaviour of embedded tram tracks using a wavenumber domain method

Tracks with rails embedded in a layer of rubber are commonly used for tramways. The vibration and sound radiation behaviour of these tracks differs from that of conventional railway tracks. This is studied here using coupled wavenumber finite element and boundary element models. A detailed analysis is carried out for an embedded rail with a narrow embedding material and comparisons are made with field measurements. The rail, embedding material and surrounding concrete are modelled with finite elements, whereas the support conditions due to the underlying ground are modelled with structural boundary elements coupled to the base of the track model. The sound radiation is calculated using a wavenumber acoustic boundary element model in which it is assumed that there is only one-way coupling with the structure. At low frequencies, vibration of the concrete slab also contributes to the noise radiation. Consequently, the radiated sound is increased compared with that produced by the rail alone at low frequencies but it is reduced above 300 Hz, where the rail and concrete vibrate out of phase with one another; at frequencies above 500 Hz the concrete has negligible effect. The track decay rate has a broad minimum between 500 and 1000 Hz; the noise radiation therefore has a peak in this important frequency region. However, the decay rate increases strongly above 1000 Hz due to the influence of the embedding material. The track considered has a grass in-fill between and outside the rails and allowing for the absorptive effect of the grass leads to a small reduction in the sound radiation. In addition, the attenuation effect of the fairings around the bogie region is estimated taking account of the absorptive effect of the grass surface. The embedded rail models are coupled with a model of a tram wheel and used to predict the rolling noise during the passage of a tram, showing good agreement with field measurements. Finally, various alternative embedded rail designs are compared, including different shapes of the embedding material and different rail profiles. Differences of up to 3 dB are found between the various designs.

Joint parameter identification, vibration and noise analysis of gearbox

A certain type of gearbox is investigated for the problem that the stiffness and damping of bearings are difficult to be accurately determined and then affect the analysis of vibration and noise of gearbox. Firstly, a coupled dynamic lumped parameter model of three-stage helical gear system with consideration of bearing stiffness, bearing damping, and transmission error is established. The modal parameters of gear system are obtained by using the experimental modal analysis method with single-input and multiple-output. The equation for joint parameter identification of gearbox is established which is based on the experimental modal analysis theory and the dynamic lumped parameter model, and subsequently the parameters of the joint are obtained by the least square method. Then, a gear-shaft-bearing- housing coupled dynamic finite element model is developed on the basis of the identified parameters, and after that the dynamic response results of gearbox are solved by using the modal superposition method and compared with the vibration test results. Finally, an acoustic boundary element model of gearbox is established by taking the dynamic response results as the acoustic boundary condition, and the surface sound pressure and radiation noise of gearbox are solved by the boundary element method (BEM), and then the results are compared with the noise test. The results show that the simulation laws and test laws are in good agreement, and thus the method of joint parameter identification, vibration and noise analysis of gearbox is feasible.

Influence of web plate holes on the radiation noise characteristics of wheels of the high speed train

The finite element model of wheels without holes was established to compute its free modal and compare with the experimental result. The relative error was controlled within 5 %, which indicated that the finite element model in this paper was reliable. Based on the finite element and geometric model, the acoustic boundary element model of wheels was established to compute the radiation noise of wheels under the action of radial and normal excitation forces. Results showed that the change trend and value of radiation noises of wheels were similar under the action of two kinds of excitation forces when the analyzed frequency was lower than 1421 Hz. However, the radiation noise of wheels under the action of two kinds of excitation forces was significantly different and presented obvious directivity in three planes with the increase of the analyzed frequency. Then, models of wheels with 5, 6, 9 and ellipse holes were established to compute radiation noises and conduct comparative analysis. Results showed that the radiation noise of wheels with 6 holes was relatively minimum under radial and normal excitations and did not decrease with the increase of the hole number. The radiation noise of wheels with circular holes made certain improvement, compared with the radiation noise of wheels with ellipse holes. Distribution curves for the directivity of radiation noises of various wheels were highly symmetrical in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>Z</mml:mi></mml:math> plane and radiation noises had relatively maximum in the position of multiples of 30°. The curve for the directivity of radiation noises of wheels with 5 holes was clearly different from that of other structures in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>Y</mml:mi></mml:math> plane.

Development of a model to assess acoustic treatments to reduce railway noise

Porous materials have recently been used in absorptive treatments around railway tracks to reduce noise emissions. To investigate the effect of porous materials, a finite element model has been developed. 2D models for porous materials have been considered either as an equivalent fluid or as a poroelastic material based on the Biot theory. The two models have been validated and compared with each other to check the effect of the skeleton vibration. The poroelastic FE model has been coupled with a 2D acoustic boundary element model for use in railway applications. The results show that it may be necessary to include the frame vibration, especially at low frequencies where a frame resonance occurs. A method for the characterization of porous materials is also discussed. From this it is shown that the elastic properties of the material determine the resonance frequency and the magnitude.

Simulation Analysis of an Ambulance Carriage Interior Noise

Based on the theory of multi-body system dynamics, the analytical method of finite element and boundary element, the finite element model of vehicle body, the rigid-flexible coupled model of vehicle and the acoustic boundary element model of carriage were established by applying a variety of simulation software. Road roughness was simulated and the SPL of field point in carriage under the excitation was computed at the frequency range of 20-150Hz. Considering the size and the positive /negative nature of panels acoustic contribution at SPL peak of field point, damping treatments were taken on different combinations of panels to decrease multiple field points SPL peak and the optimal treatment was finally confirmed. The results showed that noise reduction measures can generally decrease the SPL peak around the crew.

Interior structure-borne noise reduction by controlling the automotive body panel vibration

The adoption of a numerical method to perform vibration and acoustic analyses is attracting increasing attention because of its merits in saving costs and time. The analysis flow chart of structure-borne noise reduction by controlling the vehicle body panel vibration is proposed. A finite element analysis of a body in white is performed according to this flow chart, using MSC. Nastran, and the experimental modal analysis of a body in white is also carried out. To verify the finite element model, a correlation analysis between the test and the finite element results is performed. After the acoustic boundary element model with seats has been constructed, the acoustic transfer vector is calculated using LMS software. A transfer path analysis is performed to estimate the powertrain and exhaust pipe operational forces at idle. Then the forces are input into the acoustic boundary element model to calculate the body panel velocity. By combining the acoustic transfer vector and the body panel velocity, the interior acoustic response can be obtained. The simulation results are verified by tests. To determine the main contribution panels for the interior sound pressure level, a panel acoustic contribution analysis is based on the boundary element method. Finally, constrained damping treatments are adopted to control the main panel vibration based on the results of the panel acoustic contribution analysis. The test results indicate that the sound pressure level of the interior noise at idle is reduced obviously before and after treatments, which has proved the correctness of the results from the panel acoustic contribution analysis. Therefore it is believed that the proposed analysis method is feasible for reducing interior structure-borne noise.

Vehicle Interior Low Frequency Noise Optimum Using Substructure Modal Synthesis Method

Combined with the structural dynamic model of a car set up with the substructure modal synthesis method, body panels acoustic contribution was analyzed to reduce the in-car structural noise in low frequency range. The driver-right-ear position was selected as acoustic response point, with the operational vibration response of the dynamic model as boundary condition for acoustic BEM (boundary element model), the panels that attribute most to the in-car noise were located according to ATV (acoustic transfer vector) results. After the vibrational restraint of the crucial panels by corresponding experimental measurement, in idling, the most decrease of main peaks is 5.7dB; the overall level of in-car noise is reduced by 3.89dB. It indicates that the substructure mode synthesis method can provide proper suggestion for optimizing in-car structural noise.

Acoustic Radiation Simulation of Marine Sliding-Thrust Bearing Shell Based on SYSNOISE

This paper takes marine Kingsbury sliding thrust bearing as the research object and conducts the finite element dynamic analysis with the aid of ANSYS software. On this basis, the acoustic boundary element model of a sliding thrust bearing shell is established with the ANSYS dynamic analysis results as the boundary excitation conditions. Besides, the radiated sound power of the shell is calculated by indirect boundary element method in SYNOSISE software. The influence of different condition parameters on the radiated sound power of the shell is perceived through the analysis of several rotation-thrust conditions. As for the special structure of this kind of sliding-thrust bearing, this paper states the impact of the supporting structure performance parameters, the pad number and damp of shell on the shell radiated sound power. The optimized measure for the supporting structure and the plan concerning the pad number’s selection lays the theoretical basis for damping and noise-reducing research on marine sliding-thrust bearing and its rotor system.

Experimental validation of finite element–boundary element model dynamic strain model under diffuse acoustic field loading.

Structural finite element (FE) models naturally output displacement or acceleration response data. However, they can also be used to compute stress, internal forces, and strain response. When coupled with a boundary element model (BEM) of the fluid surrounding the structure, a fully coupled analysis can be performed. Modeling a diffuse acoustic field in the BEM fluid provides an excitation like that found when the structure is placed in a reverberation chamber. Fully coupling the structural FE model to the acoustic BEM model provides a means to predict not only the acceleration response of the panel to diffuse field loading but also the ability to predict the dynamic stress and strain response. This type of model has been available with current predictive tools, but experimental validation of the prediction of dynamic stress or strain is difficult to find. An aluminum panel was instrumented with accelerometers and strain gauges and hung in a reverberation room and subjected to a diffuse acoustic field. Th...

Experimental and Computational Models for Simulating Sound Propagation Within the Lungs

An acoustic boundary element model is used to simulate sound propagation in the lung parenchyma and surrounding chest wall. It is validated theoretically and numerically and then compared with experimental studies on lung-chest phantom models that simulate the lung pathology of pneumothorax. Studies quantify the effect of the simulated lung pathology on the resulting acoustic field measured at the phantom chest surface. This work is relevant to the development of advanced auscultatory techniques for lung, vascular, and cardiac sounds within the torso that utilize multiple noninvasive sensors to create acoustic images of the sound generation and transmission to identify certain pathologies.

Elimination of a non-oscillatory instability in a retarded potential integral equation

This paper deals with the unstable behaviour of an acoustic boundary element model. The model, based on a marching on time (MOT) algorithm, uses a hypersingular derivative Green method. It is able to cope with open or closed diffracting objects. These objects are rigid or can be deformed. When a long enough computation is carried out, the pressure magnitude shows an exponential growth, which is an unrealistic behaviour. In the paper we show that we are faced with a numerical instability of the static pressure in closed cavities. A simple processing method using the eigenelement decomposition of an ‘ad hoc’ matrix suffices to correct the problem without damage to other components of the result. The method is related to a more general method dedicated to instability problems.

Hull Disturbing Forces Due to Propeller Sources

An acoustic boundary element model of a modern twin-screw cruise liner is used to show how fluctuating pressures above the propeller, and hull forces that cause ship vibration, change relative to each other with the nature of propeller sources. The low frequency effects of fluctuating loads on the propeller in different directions are compared with the effects of unsteady cavitation. The implications of the results for specification of ship requirements and estimation of ship vibration are discussed.

Computational and experimental models for sound transmission in the pulmonary system and chest to aid in medical diagnosis

Acoustic wave propagation in the pulmonary system and torso is simulated by coupling a numerical acoustic boundary element model that predicts sound propagation throughout the solid tissues with a proven comprehensive analytical model for sound wave propagation in the airways of the bronchial tree that is valid up to at least 2 kHz. This approach enables modeling various pathologies that result in structural changes in the lung and/or changes in breath sound source and strength. The model may be also used to predict the resulting acoustic changes measured by acoustic sensors, e.g., stethoscopes, accelerometers, or other skin-contact sensors. Experimental studies in a novel lung phantom model are used to partially validate the computational model. This study focuses on low audible frequencies, i.e., less than 2 kHz. This range encompasses naturally generated respiratory sounds that have been shown to have diagnostic value, as well as externally-introduced vibro-acoustic stimuli used for diagnosis. [Work supported by NIH EB 003286-01.]