Interior Noise Problem Research Articles

Development of an analysis method for acoustic–structural coupling systems using the BEM for the acoustic field: The validity of the method developed and comparison with the FEM acoustic field

A formulation is developed for the analysis of coupled acoustic–structural systems using the boundary element method (BEM) in order to apply the coupled method to the open field in addition to the closed field. In this formulation the most general mode superposition method by Ma-Hagiwara, namely, the high- and low-order truncatable mode superposition method, is used where the higher and the lower modes are truncated. The propriety of this formulation is verified by comparing it with a theoretical solution in a one-dimensional problem and with the solution by a method in an interior noise problem, which was developed using the finite-element method (FEM).

Component Mode Synthesis Method for Large-Scale Coupled Structure-Acoustic Fluid Interaction Problem.

In order to analyze frequency response problems in the higher frequency range, we have developed a component mode synthesis method, based on the mode superposition technique, which is capable of simulating a higher frequency range using fewer modal degrees of freedom. In this paper, it is expanded to the solution of a coupled structure-acoustic fluid interaction problem, and it is applied to the interior noise problems of the vehicle cabin. In the cases of analysis of higher frequency range, the required mesh size in the FEM models of the vehicle body becomes much finer than that in the acoustic model, in order to obtain sufficient accuracy. A technique based on the least square method is presented to connect the fine structural mesh with a coarse acoustic one on the interface having noncoincident nodal points of the structure and acoustic field. Several numerical examples are analyzed to verify the effectiveness of the present method.

Development of New Mode-Superposition Technique for Truncating Lower- and/or Higher-Frequency Modes : Application to Eigenmode Sensitivity Analysis

A new mode-superposition technique with higher accuracy and efficiency was proposed by the authors in Ref. (1). This paper applies the technique to eigenmode sensitivity analysis for a structural system and a coupled acoustic-structural system. It will be shown that the use of a new mode-superposition technique greatly improves the convergency of a modal sensitivity analysis, and makes it possible to calculate the sensitivity with better efficiency than Fox and Kapoor's modal method and Wang's modified modal method, and also with better efficiency than Nelson's method. The theoretical results are verified through application of the method to a box structure and a practical vehicle interior noise problem.

The development of eigenmode sensitivity analysis methods for coupled acoustic-structural systems and their application to reduction of vehicle interior noise

Reducing the noise and vibration of a vehicle is an important issue from the standpoints of improving its sales potential as a product and of preventing noise pollution problems. So researchers have used finite element methods or boundary element methods to make predictions of noise and vibration. But what is required at the design stage is to find body structures which will reduce the predicted noise and vibration to the target values. The use of sensitivity analysis makes it easy to determine how the analytical model should be modified or the structure optimized for the purpose of reducing vibration and noise of the structural-acoustic systems. The present work focused on a structural-acoustic coupling problem. As the coefficient matrices of a coupled structural-acoustic system are not symmetrical, the conventional orthogonality conditions obtained in structural dynamics generally do not hold true for the coupled system. To overcome this problem, the orthogonality and normalization conditions of a coupled system were derived by us. In this paper, the new sensitivity analysis methods are applied to an interior noise problem of a cabin model. It will be shown how a sensitivity analysis process is performed, and how vibration and noise can be reduced.

Development of New Mode-Superposition Technique for Truncating the Lower and/or Higher Frequency Modes. 5th Report. Accuracy Confirmation of the New Method for the Vehicle Model and the Investigation of the Utilization Method for Vehicle Interior Noise Reduction Design.

Since interior noise has a strong effect on vehicle salability, it is particularly importart to be able to estimate noise levels accurately by means of simulation in the design stage. The use of sensitivity analysis makes it easy to determine how the analytical model should be modified or the structure optimized for the purpose of reducing vibration and noise of the structural-acoustic systems. The present work focuses on a structural-acoustic coupling problem. As the coefficient matrices of a coupled structural-acoustic system are not symmetrical, the conventional orthogonality conditions obtained in structural dynamics generally do not hold true for the coupled system. To overcome this problem, we derived the orthogonality and normalization conditions of a coupled system. In this paper, our sensitivity analysis methods are applied to the interior noise problem of a vehicle cabin model. It will be shown how a sensitivity analysisprocess is performed, and how vibration and noise can be reduced.

Development of Eigenmode and Frequency Response Sensitivity Analysis Methods for Coupled Acoustic-Structural Systems.

Sensitivity analysis methods applicable to the eigenmodes and frequency responses of coupled acoustic-structural systems are proposed for the purpose of reducing vehicle interior noise. The concept of the left and right eigenvectors is introduced for treating coupled acoustic-structural problems, and four propositions concerning this concept are presented and proven. Based on these propositions, formulations are derived for conducting modal sensitivity and modal frequency response sensitivity analyses. The theoretical results and computation equations are verified through the application of the methods to a coupled acoustic-box structure and a practical vehicle interior noise problem.

Sensitivity Analysis Methods for Coupled Acoustic-Structural Systems Part I: Modal Sensitivities

An analytical is proposed for calculating the sensitivities of the eigenvalues and eigenvectors of coupled acoustic-structural systems for the purpose of reducing vehicle interior noise. The concept of the left and right eigenvectors with regard to the eigenvalue problems of coupled systems is presented first, and four propositions concerning this concept are then proved. Based on these propositions, the formulations for the eigenvalue and eigenvector sensitivity analysis of coupled systems are obtained. It is shown that the new provides better convergence than the method and modified modal method (extensions of these methods to coupled systems), and it achieves better calculation efficiency than the extended Nelson's when more than one eigenvector is being considered. The theoretical results and computation equations are verified through application of the to a coupled acoustic-box structure and an actual vehicle interior noise problem.

Technical development of eigenmode and frequency response sensitivity analysis for coupled acoustic-structural systems.

Sensitivity analysis methods of the eigenmodes and frequency responses of coupled acoustic-structural systems are proposed for the purpose of reducing vehicle interior noise. The concept of the left and right eigenvectors with regard to coupled acoustic-structural eigenvalue problems is presented first and four propositions concerning this concept are then proven. Based on these propositions, the formulations for the modal sensitivity and modal frequency response sensitivity analyses are obtained. The theoretical results and computation equations are verified through the application of the methods to a coupled acoustic-box structure and a practical vehicle interior noise problem.

Development of New Mode-Superposition Technique for Truncating The Lower-and/or Higher Frequency Modes. 2nd Report, An Application for Eigenmode Sensitivity Analysis.

A new mode-superposition technique with higher accuracy and efficiency was proposed by the authors in Part 1. This paper applies the technique to eigenmode sensitivity analysis for a structural system or a coupled acoustic-structural system. It would be shown that the use of a new mode-superposition technique greatly improves the convergence of a modal sensitivity analysis, and makes it possible to calculate the sensitivity with better efficiency than Fox-Kapoor's modal method and Wang's modified modal method and also with better efficiency than Nelson's Method. The theoretical results are verified through application of the method to a box structure and a practical vehicle interior noise problem.

Technical development of eigenmode sensitivity analysis.

An sensitivity analysis method for the eigenproblem of coupled acoustic-structural systems is proposed, which is to be applied for reducing the vehicle interior noise. At first the conception of the left eigenvector and right eigenvector with regard to coupled acoustic-structural eigenproblems is introduced, and four propositions concerning this conception are then proved. On the basis of these propositions, the formulation of the eigenmode sensitivity analysis is obtained. The eigenmode sensitivity formulations are applicable to the change of structural parameters, acoustic parameters and acoustic-structural coupling conditions respectively. By estimating the calculation error of this method theoretically, a guideline of the design variable change limit is shown. The theoretical results and computation formulations are demonstrated through a cubic shell interior noise problem.

Field-incidence noise transmission loss of general aviation aircraftdouble-wall configurations

Theoretical formulations have been developed to describe the transmission of reverberant sound through an infinite, semi-infinite and a finite double panel structure. The model incorporates the fundamental resonance frequencies of each of the panels, the mass-air-mass resonances of the structure, the standing wave resonances in the cavity between the panels and finally the coincidence resonance regions, where the exciting sound pressure wave and flexural waves of each of the panels coincide. It is shown that phase cancellation effects of pressure waves reflected from the cavity boundaries back into the cavity allows the transmission loss of a finite double panel structure to be approximated by a finite double panel mounted in an infinite baffle having no cavity boundaries. Comparison of the theory with high quality transmission loss data yields good agreement in the mass-controlled frequency region. It is shown that the application of acoustic blankets to the double panel structure does not eliminate the mass-air-mass resonances if those occur at low frequencies. It is concluded that this frequency region of low noise transmission loss is a potential interior noise problem area for propeller driven aircraft having a double panel fuselage construction.