Experimental investigation of coupling effects of passenger compartment and trunk of a car on coupled system natural frequencies using noise transfer function

The parcel shelf of a car has several holes for speakers and electrical devices. In addition, air ventilation holes are installed on the trim that covers the parcel shelf. The effect of the holes between the two cavities, passenger compartment and the trunk, and the natural frequencies of double cavities connected by the neck (parcel shelf) are very vital and useful to noise–vibration–harshness engineers, as the low frequency resonances contribute to the booming noise inside the car. In the present study, the coupling effect of the passenger compartment and the trunk connected through the holes on the parcel shelf in between, has been investigated experimentally using noise transfer function. The first and second coupled system modes are measured at around 40 Hz and 70–80 Hz respectively. By increasing the effective size of the holes on the parcel shelf, the first and second natural frequencies of coupled modes can be shifted to higher values. The current study has verified that holes act as point sources in the low frequency ranges. It was concluded that the coupled acoustic modes, in the low frequency range, are strongly controlled by fluid–structure interaction as well as changes in the panels mass and stiffness in the car interior space. The shift in the natural frequencies of connected cavities can be useful in the prediction of the interior noise in an automobile as well as provide a verification tool for conventional numerical techniques such as finite element methods.     

Coupled FEM/BEM for control of noise radiation and sound transmission using piezoelectric shunt damping

In this paper, we present a coupled finite element/boundary element method (FEM/BEM) for control of noise radiation and sound transmission of vibrating structure by passive piezoelectric techniques. The system consists of an elastic structure (with surface mounted piezoelectric patches) coupled to external/internal acoustic domains. The passive shunt damping strategy is employed for vibration attenuation in the low frequency range. The originality of the present paper lies in evaluating the classically used FEM/BEM methods for structural–acoustics problems when taking account smart systems at the fluid–structure interfaces.     

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.     

Research on the interior noise contributed from a local panel's vibration of an elastic thin-walled cavity

A theoretical algorithmic method about the interior noise contributed from a local structural panel of an elastic thin-walled cavity is put forward based on the reciprocity of the acoustic system and the finite-element analysis. An example for a passenger compartment is given in order to validate the correctness of the method, and the source of error is also discussed briefly.     

Effect of coupling between passenger compartment and trunk of a car on coupled system natural frequencies using acoustic frequency response function

Conventional numerical techniques, used to study the acoustics of a car passenger cabin, treat the cabin as an isolated cavity excited by the cavity boundaries. Realistically, other cavity volumes such as the trunk communicate with the cabin through the holes in the parcel shelf of the car. An extended acoustic model of a car is formed by the cavity volumes of the passenger compartment and the trunk as well as air leakages through the holes provided for electrical devices and ventilation on the parcel shelf. In this study, the dynamic influence of air leakages between the passenger and trunk compartments on the first and second coupled system modes was investigated experimentally using acoustic frequency response function. The response to the acoustic excitation was measured for four different configurations of trim and holes of the parcel shelf. The natural frequencies of the first and second coupled system modes increased with increasing holes size with and without the trim of the parcel shelf. The experimental results were in good agreement with the reported results of coupling effects of double cavities connected by a neck. In the low frequency region since the wavelength is longer compared to the holes dimension, these holes act as point sources.     

微穿孔板和小孔喷注——马大猷教授对声学的特殊贡献

微穿孔板吸声体是马大猷教授提出的一项特殊的设计技术,自上世纪80年代以来被广泛地应用在音质处理和噪声控制中。微穿孔板吸声体是一种无纤维的宽带吸声材料,它不仅能够应用在传统的建筑声学和噪声控制等领域中,更有意义的是它适用于高温、高速气流、高洁净、需要透明采光等一些极端条件下。当微穿孔板后面有一定的空腔时,它可以在低频的几个频程内具有很高的吸声系数。在喷注噪声控制理论方面,马教授根据小孔喷注噪声与其压力和直径的关系,根据人的听觉生理和心理特性,提出了在气流或者蒸汽出口的颈部处设计合适的小孔结构,可以大大减少气流噪声对人的干扰作用可听声频段内的声辐射,降噪量一般来说可以达到20~60 dBA的降噪量。这就是小孔喷注理论。本文回顾了马大猷教授在他学术生涯第二个春天里结出的这两颗硕果——微穿孔板和小孔喷注,关于微穿孔板在声场和声源噪声控制中的声学特性理论,主要回顾和讨论了微穿孔板结构的研究进展及其在噪声控制中的实际应用,以及小孔喷注噪声的主要能量转移到超声波频段内的物理概念,这一概念对现代喷注噪声控制的发展依然具有重要意义。      

Structural-borne acoustics analysis and multi-objective optimization by using panel acoustic participation and response surface methodology

This paper is aimed to investigate the structural-borne acoustics analysis and multi-objective optimization of an enclosed box structure by using the panel acoustic participation (PAP) and response surface methodology (RSM). The acoustic frequency response function is applied to achieve the critical frequency of interest under each excitation. The PAP analysis is then carried out at all critical frequencies and the remarkable acoustic panels are identified. The correlation coefficient matrix method is proposed for reselecting and grouping the positions of acoustic panels identified to paste damping layer to control noise. With the help of faced central composite design, an efficient set of sample points are generated and then the second-order polynomial functions of sound pressure response at each critical frequency are computed and verified by the adjusted coefficient of multiple determination. The functional relationships between sound pressure responses and the thicknesses of damping layers are investigated, and multi-objective optimization of the thicknesses of damping layers is developed. The results indicate that, by using the PAP and RSM, the structural-borne acoustics at critical frequencies are calculated conveniently and controlled effectively. The optimization process of the explicit optimization model proposed in this paper is simple and the computational time is saved.     

Comparison of various decentralised structural and cavity feedback control strategies for transmitted noise reduction through a double panel structure

This paper compares various decentralised control strategies, including structural and acoustic actuator–sensor configuration designs, to reduce noise transmission through a double panel structure. The comparison is based on identical control stability indexes. The double panel structure consists of two panels with air in between and offers the advantages of low sound transmission at high frequencies, low heat transmission, and low weight. The double panel structure is widely used, such as in the aerospace and automotive industries. Nevertheless, the resonance of the cavity and the poor sound transmission loss at low frequencies limit the double panel's noise control performance. Applying active structural acoustic control to the panels or active noise control to the cavity has been discussed in many papers. In this paper, the resonances of the panels and the cavity are considered simultaneously to further reduce the transmitted noise through an existing double panel structure. A structural–acoustic coupled model is developed to investigate and compare various structural control and cavity control methods. Numerical analysis and real-time control results show that structural control should be applied to both panels. Three types of cavity control sources are presented and compared. The results indicate that the largest noise reduction is obtained with cavity control by loudspeakers modified to operate as incident pressure sources.     

某型振动轮噪声数值模拟及优化分析

空中声源的辐射噪声谱包括宽带连续谱和窄带线谱,线谱能量高于连续谱。与水下声源相比,空中声源的运动速度普遍较高,线谱多普勒频移明显,可用于进行水下对空中声源的运动参数估计。首先通过时频分析提取接收信号的瞬时频率,而后利用非线性最小二乘法将瞬时频率提取值与预测值相拟合,进而估计声源的运动参数(声源的运动速度、静止频率、与接收器最小水平距离及经过最近点时刻)。仿真与实验均能较为准确地估计出声源运动参数,同时在实验中实现了水下对空中运动声源的测距和定位,测距误差小于15.8%。在满足一定信噪比和保证足够多普勒信息的情况下,该参数估计方法具有很好的适用性。     

薄膜型声学超材料的结构设计与隔声特性*

为探讨薄膜型声学超材料用于汽车前围声学包、提高其中低频隔声能力的可行性,设计一种米字摆臂多质量块薄膜型声学超材料,构建其隔声分析有限元模型 ,分析其隔声特性及影响因素,开展结构优化及其在汽车前围声学包上的应用探索。研究表明,所设计的薄膜型声学超材料单胞在中低频区域具有较宽的隔声频带;增加薄膜上质量块半径或厚度会使传声损失曲线整体向低频区域移动,且质量块半径的增加还会拓宽高频区域的隔声频带;增加薄膜厚度或预应力会使传声损失曲线整体向高频区域移动;优化后的薄膜型声学超材料与钢板组合应用于汽车前围板,可明显提高其中低频隔声能力。     

Active vibration control for structural-acoustic coupling system of a 3-D vehicle cabin model

This paper presents an active vibration control system for use with structural-acoustic coupling system using piezoelectric actuators and piezoelectric sensors. For modelling a complicated 3-D vehicle cabin model, the structural-acoustic coupling system is analyzed by combining the structural data from modal testing with the acoustic data from the finite element method. Through the structural-acoustic analysis program, the control plate and the control modes are selected, which are most effective for attenuating its noise. A robust LQG controller with two sensor signal filters is designed to remove the experimental problems such as the spillover effect due to uncontrolled modes. The robust LQG controller for the structural-acoustic coupling system can reduce the interior noise of the cavity as well as the structural vibration of the cabin.     

A hybrid SEA/modal technique for modeling structural-acoustic interior noise in rotorcraft

This paper describes a hybrid technique that combines Statistical Energy Analysis (SEA) predictions for structural vibration with acoustic modal summation techniques to predict interior noise levels in rotorcraft. The method was applied for predicting the sound field inside a mock-up of the interior panel system of the Sikorsky S-92 helicopter. The vibration amplitudes of the frame and panel systems were predicted using a detailed SEA model and these were used as inputs to the model of the interior acoustic space. The spatial distribution of the vibration field on individual panels, and their coupling to the acoustic space were modeled using stochastic techniques. Leakage and nonresonant transmission components were accounted for using space-averaged values obtained from a SEA model of the complete structural-acoustic system. Since the cabin geometry was quite simple, the modeling of the interior acoustic space was performed using a standard modal summation technique. Sound pressure levels predicted by this approach at specific microphone locations were compared with measured data. Agreement within 3 dB in one-third octave bands above 40 Hz was observed. A large discrepancy in the one-third octave band in which the first acoustic mode is resonant (31.5 Hz) was observed. Reasons for such a discrepancy are discussed in the paper. The developed technique provides a method for modeling helicopter cabin interior noise in the frequency mid-range where neither FEA nor SEA is individually effective or accurate.     

STRUCTURE-BORNE NOISE AND VIBRATION OF CONCRETE BOX STRUCTURE AND RAIL VIADUCT

In this study, the vibration and acoustic resonance, and dominant frequency range of simple concrete box and viaduct are examined from the measurement results. A narrow band analysis—fast Fourier transform (FFT) method is used to analyze the measurement results and finite element method (FEM) is used to validate resonance frequencies for noise and vibration. The experiment of the concrete box structure is a preliminary study of analyzing resonance frequency radiated from the vibrating concrete structure since railway viaduct is a concrete box structure too. According to their noise and vibration spectra, it shows that the vibration resonance is more significant than the acoustics resonance.Based on the measurement results of the rail viaduct structure-borne noise and vibration, the relationship in terms of transfer function and coherence between noise and vibration are evaluated. They show that the dominant frequency range for noise and vibration of concrete viaduct is between 20 and 157 Hz, the resonance frequencies are 43 and 54 Hz and have significant tonal noise characteristics. The experimental results are in good agreement with the theoretical relationship between sound and vibration.     

汽车车内噪声主动控制系统仿真

摘要：降低汽车空腔的振动,是抑制汽车车内噪声的有效途径之一。以激振器、作动器和控制器等为主要部件,搭建了简化的汽车车内噪声主动控制系统,该系统通过将汽车空腔模型简化为板件,以减弱板件振动为目标,实现了汽车车内噪声主动控制。采用简谐正弦及余弦信号作为激振器发出的激励,用于模拟板件的初始振动,控制器通过采用模糊控制算法直接控制压电陶瓷作动器的振动,压电陶瓷作动器的振动用于抑制板件的振动,完成了汽车车内噪声主动控制系统仿真。仿真结果表明,研究采用的汽车车内噪声主动控制系统,使汽车空腔振动降低23%,为解决由汽车发动机和动力总成的振动所引发的汽车车内噪声问题提供了一个有效途径。     

Passive and active interior noise control of box structures using the structural intensity method

This paper presents passive and active vibro-acoustic noise control methods for attenuating the interior noise level in box structures which can be an analogy of cabins of vehicle and aircraft. The structural intensity (SI) approach is adopted to identify the predominant vibration panels and interior noise sources for box structures. In the study, the finite element method is used to determine the structural vibration and structural intensity in the box surfaces. According to structural intensity vectors plot and structural intensity stream lines presentation, the possible effective control positions where the dampers may be attached and the active control forces may act to reduce vibration and interior noise, are identified. From the study, it can be demonstrated that the structural intensity approach and stream line presentation are possible methods for identifying the vibro-acoustic interior noise source and predominant panels which may be modified to reduce the interior noise level. The structural intensity methodology, passive and active noise control results can be extended to the further study of the vibration and interior noise control of actual cabins of vehicles and aircraft.     

Reduction of sound transmission into a circular cylindrical shell using distributed vibration absorbers and Helmholtz resonators

A modal expansion method is used to model a cylindrical enclosure excited by an external plane wave. A set of distributed vibration absorbers (DVAs) and Helmholtz resonators (HRs) are applied to the structure to control the interior acoustic levels. Using an impedance matching method, the structure, the acoustic cavity, and the noise reduction devices are fully coupled to yield an analytical formulation of the structural kinetic energy and acoustic potential energy of a treated cylindrical cavity. Lightweight DVAs and small HRs tuned to the natural frequencies of the targeted structural and acoustic modes, respectively, result in significant acoustic and structural attenuation when the devices are optimally damped. Simulations show that significant interior noise reduction can only be achieved by adding damping to both structural and acoustic modes, which are resonant in the frequency bandwidth of interest. In order to be independent of the azimuth angle of the excitation and to avoid unwanted modal interactions, the devices are distributed evenly around the cylinder in rings. This treatment can only achieve good performance if the structure and the acoustic cavity are lightly damped.     

DESIGN SENSITIVITY ANALYSIS AND OPTIMIZATION OF AN ENGINE MOUNT SYSTEM USING AN FRF-BASED SUBSTRUCTURING METHOD

The FRF-based substructuring method is one of the most powerful methods in analyzing the responses of complex built-up structures with high modal density. In this paper, a general procedure for the design sensitivity analysis of a vibro-acoustic system has been presented using the FRF-based substructuring formulation. For an acoustic response function, the proposed method gives a parametric design sensitivity expression in terms of the partial derivatives of the connection element properties and the transfer functions of the substructures. The derived noise sensitivity formula is combined with a non-linear programming module to obtain the optimal design for the engine mount system of a passenger car. The objective function is defined as the area of the interior noise graph integrated over a concerned r.p.m. range. The interior noise variations with respect to the dynamic characteristics of the engine mounts and bushings have been calculated using the proposed sensitivity formulation and transferred to a non-linear optimization software. To obtain the FRFs, a finite element analysis was used for the engine mount structures and experimental techniques were used for the trimmed body including the cabin cavity. The optimization based on the sensitivity analysis gives the ideal stiffness of the engine mount and bushings. The resultant interior noise in the passenger car shows that the proposed method is efficient and accurate.     

Experimental investigation of different active noise control concepts applied to a passenger car equipped with an active windshield

The main purpose of this work is the implementation and experimental investigation of different active structural acoustic control (ASAC) concepts for the reduction of interior noise in an automobile passenger compartment. For the control experiments, a medium-class test car was used, which had been equipped with an active windshield. The active windshield consists of the serial-production laminated glass pane augmented with piezoceramic patch-transducers applied to the blackened rim of the windshield. A multi-reference test provided measurement data for the identification of a local discrete-time state-space model (SSM). The subsequent acquisition of frequency response functions (FRF) by way of using the same actuators but measuring on a much finer grid provided the database for the formulation of a least-squares problem to derive a global system model. Based on the local and global discrete-time SSMs, different controllers were designed and experimentally realized. The comparison of the vibration levels in open- and closed-loop showed a global reduction of 5–7 dB in the acoustically relevant frequency band containing the second and third structural resonance of the windshield system. The occurrence of complex operational deflection shapes (ODS) was identified as the main limitation concerning the disturbance rejection of the active system. The acoustic performance of the ASAC system is reflected in a reduction up to 15 dB in sound pressure level (SPL).     

有限元-统计能量分析法的拖拉机驾驶室噪声研究*

对某拖拉机驾驶室内中频噪声进行预测,建立了拖拉机驾驶室FE-SEA(有限元统计能量分析)混合模型,通过理论计算和试验方法获取驾驶室结构内损耗因子等数据；加载振动和噪声激励后进行有限元-统计能量分析联合仿真,将仿真获取的驾驶室声压级与实测数据进行对比,分析对比表明该模型在中频段利用FE-SEA混合法分析所得结果与试验测试值拟合程度较高,分析各子系统对驾驶室声腔的能量贡献度,确定对驾驶室噪声贡献较大的子系统,针对性对驾驶室声学包进行整改,获得一定降噪效果。     

基于球形压电陶瓷的耐压水听器

利用球形压电陶瓷自身所具有的耐压能力,采用径向极化空气背衬压电球壳换能器作为声学接收敏感元件,设计并制作了一种球形耐压水听器。首先对其低频开路接收灵敏度和谐振频率等声学特性进行了分析和有限元仿真,然后对其强度和稳定性等耐压性能进行了分析和有限元仿真,最后对其声学性能和耐压能力进行了测试。测试表明,该球形耐压水听器的直径为36 mm,工作频段为50 Hz～10 kHz,低频接收灵敏度为-198.4 dB (0 dB=1 V/μPa),等效自噪声谱级为46.5 dB@1 kHz,其耐压深度可达3000 m。该耐压水听器为大深度水听器设计提供了参考,在深水声学领域具有重要的应用价值。