Interior Noise Problem Research Articles

Analytical modelling techniques for efficient broadband noise prediction of high-speed trains

Analytical modelling techniques are presented for broadband noise prediction of high-speed trains. For interior noise problems, train body structures are modelled exactly by the dynamic stiffness method (DSM); whereas the interior acoustic cavities of the train body are modelled by the SDSM where the boundary conditions are described by modified Fourier series with a rapid convergence rate. Finally, the vibro-acoustic coupling model of the train body structures is constructed. For exterior noise problems, exterior train noise models are first formed by experimental data considering the Doppler effect; then both the DSM and theoretical attenuation formulas are used to build noise radiation models for different external environment conditions. The performance of the method is evaluated by predicting the interior sound field distribution of typical cross sections of the train body and the external radiated noise in a tunnel, or in an environment where the acoustic barrier or buildings along railways exist. Numerical results are in good agreement with the those obtained by the finite element method. Thus, the proposed methods can achieve broadband noise prediction highly accurately and efficiently, which can also serve as the benchmark for predicting the radiated noise generated by high‐speed trains.

Noise analysis of interior structure under powertrain excitation

To accurately identify the structural noise problem caused by vibration in the cockpit, an experimental study was conducted on a certain type of SUV under uniform acceleration conditions. Based on the planning of the multi-body system dynamics model, a transfer path model with secondary contributions is constructed, and the load is identified using the single degree of freedom model and multi-frequency bandwidth model under the OPAX method based on this path. The results indicate that the second-order vibration of the powertrain is transmitted to the entire suspension system through the X direction of the right suspension. The second-order vibration of the suspension system is then transmitted to the Z direction of the right rear bolt of the subframe, causing the entire subframe vibration and ultimately reaching the target point. This structural path has the greatest impact on the interior noise of the vehicle. This path research method can more accurately determine the main excitation points that cause interior noise problems on a certain path and better understand the overall energy transfer characteristics along the transmission path.

Bayesian inference for the interior noise problem of railway vehicles

Design and control of interior noise of transportation systems, such as rollingstock, is important from the standpoint of comfort. Therefore, a technical field called "NVH" has been established and various noise reduction methods have been developed. On the other hand, noise reduction measures conflict with other performances such as weight reduction and space saving. In many cases, there is a large uncertainty in the causal relationship between noise control measures and their effects. Therefore, the conventional deterministic method leads to designing on the overly safe side for achieving the noise target value, which is not desirable from the viewpoint of other performance. One solution to these problems is the introduction of probabilistic design decision making, which is used in such as the evaluation of the seismic resistance of nuclear power plants and the reliability of bearings. The authors have developed a Bayesian inference method for estimating the transfer function level , and contribution of noise source type, with the aim of introducing probabilistic decision making into interior noise design. The estimation accuracy was verified by applying the method to artificially generated data. As a result, it was confirmed that the estimation was possible at a practical level.

Multi-fidelity modeling using Gaussian processes for the frequency dependent Helmholtz equation

In scientific and engineering problems, accurate model predictions are generally accompanied with high resource and time expenses. In most applications, the data generation process can only be performed for a limited number of forward evaluations leading to insufficient model results. The concept of multi-fidelity modeling is to holistically evaluate data from different sources with varying complexity and costs. Ideally, the predictive quality of models with a high-fidelity can be combined with the efficiency of low-fidelity models. Usually, physical experiments and numerical simulations at large-scale are attributed to high-fidelity models, while analytical solutions or small-scale numerical models and experiments are considered as low-fidelity models. This contribution aims to develop a multi-fidelity model for an interior sound propagation problem. More specifically, a vehicle interior noise problem is investigated by using two boundary element models of different fidelity levels. The finer mesh corresponds to the high-fidelity model, whereas the coarser mesh is adopted as the low-fidelity model. As such, the multi-fidelity model is realized as a vector-valued Gaussian process.

Acoustic evaluation of a vehicle cabin by using energy-based surface contributions

Contribution analyses play a crucial role in the design process of vehicle cabins. In current implementations, however, surface contributions are only evaluated for single field points. The identification of surface contributions with regard to an entire cavity is accompanied with a cumbersome volume integral. This study aims to abridge this tedious volume integral by evaluating the surface contributions regarding a grid with regularly distributed field points. For this purpose, the boundary element method is used to solve the acoustic Helmholtz equation. In contrast to current techniques, the sound energy is deployed as the objective function. As the sound energy is sensitive to the sound pressure and the particle velocity, surface contributions can be also identified in regions with low sound pressure values. In order to validate the proposed framework, the vehicle interior noise problem is examined. Initial findings confirm the relevance of energy-based surface contributions, as entire volumes can be acoustically evaluated in an efficient way.

Sound energy-based surface contribution analysis for the vehicle interior noise problem

Booming noise is a major comfort problem in vehicle cabins occurring in lower frequencies. The method of panel or surface analysis serves as a viable tool to trace the sound emitting components on the enveloping chassis. Traditional techniques evaluate the surface contributions with respect to the sound pressure level at the driver’s position. However, using the sound pressure level as the control objective implies two major drawbacks: Firstly, the local sound pressure is highly sensitive to the position of the evaluation point. As a consequence, the predictions of the surface contributions become unreliable at frequencies or areas with low sound pressure levels. Secondly, surface contributions in existing techniques can be positive or negative, which facilitates the event of acoustic shortcircuits. This talk presents an accurate and robust contribution analysis method for the vehicle interior noise problem. For this purpose, the sound energy density is used as the control objective. A quadratic form yields energy-based contributions, which are always non-negative and thus avoiding acoustic shortcircuits. These findings demonstrate that contributing surface are effectively identified even in regions with sound pressure levels. As such, the evidence from this study suggests that the sound energy density provides an accurate and robust control objective.

Multi‐fidelity Gaussian processes for an efficient approximation of frequency sweeps in acoustic problems

AbstractThis paper presents a multi‐fidelity model for the acceleration of frequency sweep analyses in acoustics. In traditional analyses, the frequency‐dependent Helmholtz equation is repetitively solved at each frequency. Using the boundary element method requires then a plethora of evaluations resulting in high computational costs. In the proposed method, the fidelity levels are realized as Gaussian processes, which are conditioned on observations obtained by boundary element simulations. A coarse boundary element mesh is considered as the low‐fidelity model, whereas a fine mesh is adopted as the high‐fidelity model. To validate the proposed framework, the vehicle interior noise problem is investigated. The results demonstrate that multi‐fidelity Gaussian processes efficiently accelerate the frequency sweep analysis, as they provide accurate and fast predictions across the entire frequency range of interest. As a beneficial side effect, the present method takes uncertainties into account. This allows to consider limited information on the model, which is particularly important in early design phases.

Development of a Metasilencer Considering Flow in HVAC Systems

Although the driving noise of electric vehicles has been reduced compared with that of internal combustion engine vehicles, a new interior noise problem is emerging. It is crucial to reduce the noise of the heating, ventilation, and air conditioning (HVAC) system, which is one of the main causes of interior noise. Therefore, in this study, a metasilencer with an acoustic metasurface structure is presented. The metasilencer was designed to restrain the travel direction of the sound wave of the target frequency into a U-shaped configuration using an acoustic metasurface while considering the flow noise effect of the HVAC system. Acoustic analysis confirmed the noise reduction frequency range and refraction effect of the metasurface. The speaker test confirmed the noise reduction effect of the silencer. The same was also confirmed via HVAC tests, even in the presence of a flow.

Mechanism Study and Reduction of Minivan Interior Booming Noise during Acceleration

Interior booming noise during acceleration has been one of the most significant NVH problems for minivans. However, the generation mechanism of the interior booming noise remains unclear, so the access to reduce the booming noise is blocked. To solve the booming noise problem, a Source‐Path‐Receiver‐Model‐based approach is established to study the generation mechanism of the booming noise. Based on the generation mechanism, several modifications are proposed to reduce the minivan booming noise. In the established approach, the transfer path of the booming noise energy is figured out by the vehicle body and cavity experimental TPA, rear suspension dynamic analysis, and drivetrain torsional vibration analysis. Meanwhile, the vibroacoustic energy in the transfer processes is analyzed quantitatively. The identified generation mechanism is validated by the comparison of the test results of minivan interior noise and the simulation results from the established approach. During the minivan acceleration, the 5th torsional vibration mode (50.5 Hz) of the driveline is excited by the engine torsional vibration around 1500 r/min. Then, the driveline torsional resonance energy is transferred to the body and cavity through the rear suspension and finally leads to the interior booming noise. Based on the validated mechanism, several modifications are proposed to reduce the frequency response function of the driveline, the rear suspension, and the vehicle body around 50 Hz. With these modifications applied to the minivan, it is shown in the experimental results that the interior booming noise is reduced around 1500 r/min engine speed during acceleration. The mechanism study provides effective assistance with minivan interior booming noise reduction and the study approach also could be extended to explore the mechanism of other complex interior noise problems in automobiles.

Development of a noise prediction software NASEFA and its application in medium-to-high frequency ranges

For the analysis of noise problems in medium-to-high frequency ranges, the energy flow boundary element method (EFBEM) has been studied. EFBEM is numerical analysis method of energy flow analysis (EFA), and solves energy governing equations using a boundary element method in complex structures. Based on EFBEM, a noise prediction software, “noise analysis system by energy flow analysis” (NASEFA), was developed. For effective maintenance, NASEFA is composed of three main modules: the translator, the model converter, and the main solver. The translator changes the FE model to the NASEFA BE model, and the model converter changes the BE model to an EFBE model, including various data, such as structural materials, medium properties, sources, and boundary conditions. NASEFA then solves the acoustic energy density and intensity on boundary and in the field. Moreover, it analyzes interior and exterior noise problems for single and multiple domains in two and three dimensions. Finally, for the validation of the software developed, interior and exterior noise predictions of various structures were performed. The results obtained with NASEFA were compared with those of the commercial SEA program and experiment. From these comparative studies, the usefulness of NASEFA was established.

Investigation on Technology of Automobile Vibration and Noise Reduction Based on Body-In-White Structure

The automotive body system is not only a source for directly radiating noise into the vehicle interior space, but also a key component for transmitting various vibrations and noise. The optimization of the modes for body-in-white has significant meanings for improving the reliability and NVH (Noise, Vibration and Harshness) performance of the whole vehicle. Based on the current situation that there is more severe interior vibration and noise problem occurring in driving for a light passenger vehicle, a hybrid modal analysis method combined with experiment and simulation methods is applied to investigate the vibration and noise characteristics of the whole vehicle body. By performing such modal analysis, the modal frequencies of the auto-body are improved effectively by strengthening the vibration sensitive regions in the body structure. The experiment for measuring interior vibration and noise levels under cruise condition is conducted to validate that the structural optimization for body-in-white has significant contribution for improving the whole vehicle NVH performance.

3차원 파워흐름유한요소법을 이용한 인접한 두 실내에서의 진동음향 해석

Power flow analysis(PFA) methods have shown many advantages in noise predictions and vibration analysis in medium-to-high frequency ranges. Applying the finite element technique to PFA has produced power flow finite element method(PFFEM) that can be effectively used for analysis of vibration of complicated structures. PFADS(power flow analysis design system) based on PFFEM as the vibration analysis program has been developed for vibration predictions and analysis of coupled structural systems. In this paper, to improve the function of vibro-acoustic coupled analysis in PFADS, the PFFEM has been extended for analysis of the interior noise problems in the vibro-acoustic fully coupled systems. The vibro-acoustic fully coupled PFFEM formulation based on energy coupled relations is extended to structural system model by using appropriate modifications to structural-structural, structural-acoustic and acoustic-acoustic joint matrices. It has been applied to prediction of the interior noise in two room model coupled with panels, and the PFFEM results are compared to those of statistical energy analysis(SEA).

Identification of noise modes for automobile operational modal analysis

In rotating machinery, the input excitation does not meet the requirement of operational modal analysis (OMA). In this article, an effective and improved method of distinguishing forced harmonic response from measured vibration signal is presented based on the differences of the statistical properties of a stochastic signal and a harmonic signal. It makes the OMA applicable to the situation of existing periodic excitation. In order to prove the effectiveness of the proposed method, a modal experiment of a steel plate excited by a motor is performed. Then, an OMA is performed to solve the vehicle interior noise problem. Combining the projection channel technique with the advanced method, most noise modes, especially harmonic modes are successfully separated. Precise modal parameters of the car are obtained in typical working conditions which provide guidance of the dynamic modification and show that the harmonic identification method has great practical value.

Finite Element Simulation of Smart Structures for Active Vibration andAcoustic Control

AbstractThe design process of engineering smart structures using piezoelectric patches as distributed sensors and actuators requires a virtual overall model, which includes the main functional parts. In the paper a suitable software tool based on the FEM is presented to simulate coupled electro‐mechanical‐acoustical problems regarding interior noise problems. The modal truncation technique is used to design a LQ‐controller as well as to study the time‐depending behaviour of a clamed smart plate.

New analysis methods for the calculation of interior noise

Recently developed analysis methods applicable to the prediction of aircraft interior noise are described. Analytical-numerical matching (ANM) and Local-global homogenization (LGH) are methods for the low- to mid-frequency range. Energy-intensity boundary elements are applicable for high frequencies. ANM is a method that replaces the effect of structural discontinuities (ribs, stringers, attachments) with dynamically equivalent smooth force distributions, thereby removing the need for high-resolution numerics in the overall computational problem. LGH, which applies for periodic and quasiperiodic structures, provides a means to solve directly for the long wavelength spatial content of the structure. This part of the structural motion is strongly coupled most to the interior sound field. Energy-intensity boundary elements provide a very efficient means to predict high-frequency broadband sound fields in a fundamentally correct manner. Current research on this boundary element method involves its extension to handle coupling with structural surfaces vibrating at high frequency. The strengths and limitations of each of the above methods is discussed in the context of the interior noise problem. Innovative methods for the reduction of interior noise, as suggested by these approaches, are also mentioned.

A general concept for design modification of shell meshes in structural-acoustic optimization — Part II: Application to a floor panel in sedan interior noise problems

The second part of this paper is dedicated to the application of the new concept that was outlined in the first part. Using this concept, one manipulates the geometry of a finite element shell mesh directly. Part of a sedan floor structure is chosen for this application. A plane rectangular domain of the floor panel is defined as modification domain. The number of 33 design variables consists of nine defining the global modification function and 24 that altogether define four local modification functions. It will be demonstrated in this paper that combination of global and local modification functions allows a great variety of new shapes. In the particular case of design optimization, the root mean square value of the noise transfer function is decreased by about two decibel. Contribution analysis allows to detect reasons for decrease and increase of the optimum's noise transfer function at certain frequencies in comparison to the original model. Finally, this result is discussed and compared with other results of structural-acoustic optimization.

Sensitivity Analysis of Engine Mount System using FRF-based Substructuring Method

A general procedure for the design sensitivity analysis of structural dynamic problems has been presented in frame of the FRF-based substructuring formulation. For a system response function, the proposed method gives a parametric design sensitivity formula in terms of the partial derivatives of the connection element properties and the transfer matrix of the subsystems. The derived design sensitivity formula is applied to an engine mount system. An interior noise problem in the passenger car is analyzed using the FRF-based substructuring method and the proposed formulation is adopted to study the response variations with respect to the dynamic characteristics of the engine mounts and the bushes. To obtain the FRFs, a finite element model is built for the engine mount structures, and test data is used for the trimmed body including cabin cavity. The comparison of sensitivities derived by the proposed method and the finite difference method shows that the proposed method is efficient and accurate. The proposed sensitivity analysis method indicates effectively the most sensitive location to the interior noise among the engine mounts and the bushes.

Automotive panel noise contribution modeling based on finite element and measured structural-acoustic spectra

The radiated noise contributions of automotive body panels to the interior sound pressure levels are modeled using an approximate spectral formulation that applies the theoretical interior acoustic sensitivity terms derived from a finite element model and measured spatial-averaged structural-acoustic spectra. The finite element calculation is validated by comparison to a set of experimental acoustic transfer functions. A measurement set-up for the sound intensity and structural-acoustic response is applied to acquire the cross and auto power spectra needed to predict the relative mean-squared velocity term of each control plane near the panel surface, and to obtain the individual panel contribution function. The proposed approach also computes the noise spectra in 1/12 octave band form at selected positions in the passenger compartment, which matches well with the overall experimental results. Through an actual passenger car application, the approximate computational scheme is proven to be generally quite robust and effective for analyzing higher frequency interior noise problems.

A combined experimental/FEM model for predicting vehicle panel acoustic noise contribution

Radiated acoustic noise contributions from the structural panels that form the inner shell of the vehicle body to the interior sound pressure response are modeled using an approximate spectral formulation. The approach essentially utilizes the theoretical interior acoustic sensitivity terms derived from a finite element model and measured spatial-averaged structural-acoustic spectra. The finite element calculation is validated by comparison to a set of experimental acoustic transfer functions. In addition, an experimental setup for measurement of the sound intensity and structural-acoustic response is used to acquire the cross and auto power spectra needed to predict the relative mean-squared velocity term of each control plane near the panel surface. These velocity functions are then combined with the acoustic sensitivity terms to compute the individual panel contribution function. The proposed approach is applied to a specific case of a passenger car to compute the acoustic noise spectra in 1/12 octave band form at selected positions in the passenger compartment. The calculations show excellent match with the overall experimental results. Also through this example, the approximate computational scheme is proven to be generally quite robust and effective for analyzing higher frequency interior noise problems.

Application of Hybrid Frequency Domain Substructuring for Modelling an Automotive Engine Suspension

A practical application of hybrid FRF-coupling (Frequency Response Function) in the development of a passenger car is presented. First, a short review is given about FRF-coupling in general. Next, some problems are discussed which may be encountered when both analytical and experimental FRF-data is used in FRF-coupling. This is also known as hybrid modelling. The main part of this paper presents a successful application of hybrid FRF-coupling to analyze and solve an interior noise problem of a passenger car. Both analytical and experimental FRFs were used to create a hybrid dynamic model of a complete passenger car. The engine and its suspension system were modelled using finite elements, while the remainder of the car was modelled by experimentaly derived FRFs. This hybrid model was then used to compute the response of the vehicle due to the engine excitation. Measured noise transfer function were used next to compute the interior sound pressure level using forced response results of the hybrid car model. Subsequently, the hybrid model was used to analyze the problem, and to predict the effects of an alternative design of the engine suspension on interior noise. Numerical results indicated that the alternative design would have a significant positive effect on noise. This was confirmed by verification measurements on a car.