微穿孔消声器在小型高速离心风机中的应用研究

小型高速离心风机的特点是体积紧凑、压力高、转速高,广泛应用于各类要求较高的特殊领域。在实际应用中,除了必须满足气动性能要求外,首要问题就是风机噪声控制,而小型高速离心风机与常规风机噪声特点又有所差别,以高频噪声为主。本文针对小型高速离心风机噪声特点,根据马大猷教授提出的微穿孔消声理论设计了风机进口微穿孔消声器,对该微穿孔板消声器的降噪效果进行了测试,试验结果表明该微穿孔消声器可以有效降低风机噪声。     

螺杆空压机用消声器的设计和优化

高转速的干式螺杆空压机的排气管路中的噪声都比较大,为了有效降低螺杆空压机的排气噪声,利用双层微穿孔板声学理论,建立了由微穿孔板的孔径、板厚、穿孔率、腔深等结构参数计算双层微穿孔板结构扩散场吸声特性的数学模型,设计了一种适合该类空压机用的消声器,并利用遗传算法对其结构参数进行优化,得到双层微穿孔板最佳的吸声特性。优化结果表明:优化后的双层微穿孔板消声器的吸声系数比优化前大大提高,更有利于高转速干式螺杆空压机减噪的需求。     

燃烧室结构-声耦合特性研究

声振耦合影响燃烧室燃烧稳定性,加剧火焰筒薄壁结构疲劳破坏,声振耦合特性研究对燃烧室燃烧稳定性设计与结构抗疲劳设计非常必要。利用有限元软件建立燃烧室结构-声三维模型,进行燃烧室封闭结构声振耦合特性研究,计算出结构的固有频率和模态振型。通过试验,测量燃烧室声振传递函数,得到燃烧室结构声振耦合固有频率和模态振型。研究表明,声场相当于给结构增加了附加质量,降低了结构固有频率,并产生了特殊的耦合频率。试验验证了有限元计算结果的正确性,从而为燃烧室薄壁结构设计提供了参考。     

Viscothermal fluid effects on vibro-acoustic behaviour of double elastic panels

This paper deals with the vibro-acoustic behaviour of two vibrating plates coupled to a viscothermal fluid cavity. The acousto-elastic model is established in dimensionless appropriate form including the effects of viscosity and thermal conductivity of fluid and taking into account the fluid–structure interaction. The finite element method is used for the discretization of the functional of energy, which gives after minimization a symmetrical coupled matrix system in which the acoustic matrices are frequency dependent. For this purpose, an iterative procedure is derived to determine the eigenmodes of the coupled system. The modal approach is adopted to determine the vibro-acoustic system's response which the numerical results show the importance of the viscothermal effects in the case of thin fluid layers.     

Two modelling techniques for the vibration and transmission loss of a nonlinear vibro-acoustic system

Fahy’s and Pretlove’s modelling techniques for a vibro-acoustic system have been employed in many research works. This is the first article addressing the differences between these modelling techniques for a nonlinear vibro-acoustic system. Pretlove’s technique is used for vibro-acoustic systems with one flexible panel only (or 2D enclosures); Fahy’s is applied to vibro-acoustic systems with multiple flexible panels (or 3D enclosures). The main difference between them is that all acoustic boundary conditions can be satisfied in the 2D modelling technique, while only rigid acoustic boundary conditions can be satisfied in the 3D modelling technique. The multi-level residue harmonic balance method, which was recently developed and modified from the classical harmonic balance method, is employed here. The advantage of this method is that it requires less computation effort when solving the nonlinear equations generated in the entire solution process. The comparisons between various transmission loss and nonlinear vibration results generated from the two models are investigated.     

驾驶室结构振动及其声固耦合噪声响应分析

利用有限元分析软件ANSYS和声学分析软件SYSNO ISE对卡车驾驶室的振动与内部声场耦合做了数值计算分析研究。介绍了振动频响分析方法,动力学计算与声学边界元模型耦合的具体步骤。通过计算分析,分别研究了驾驶室结构的声固耦合模型与非耦合模型对室内声场的影响,从而找出在不同的壁板厚度条件下,声固耦合作用对室内噪声的影响,以及驾驶室内声场的变化规律。     

微穿孔板消声器在风冷插箱噪声控制中的应用

雷达设备风冷插箱散热设计是雷达产品可靠性结构设计、热设计的重要内容。在实际应用中,强迫风冷被广泛使用,散热和噪声控制往往产生矛盾。如何控制噪声,对改善产品使用环境有着重要意义。文中针对风冷插箱噪声过大问题,运用微穿孔板近似吸声原理,设计了一种消声插件,对该微穿孔板消声器的降噪效果进行了测试,可以减低噪声3 dB(A)左右。从而说明该消声器有一定的降噪效果,在一定场合可以应用。     

An acoustic–structural interaction modelling for the evaluation of a gearbox-radiated noise

Gearbox power transmissions are widely used in the automotive industry. They have a complex vibro-acoustic behaviour that is influenced by the various acoustic–structural interaction mechanisms. This paper concentrates on modelling these systems using a three-dimensional finite-element (FE) approach for the structure combined with a Rayleigh integral (RI) method for the acoustic radiation process. A modal analysis method is used to evaluate the elasto-acoustic modal characteristics for the coupled system. Effect of the fluid inside the gearbox on the vibration response is discussed. The combined use of this FE/RI model enables evaluation of the acoustic response. A case study of a simplified gearbox internally excited with gear mesh stiffness fluctuation is presented. Vibratory analysis allows concluding that the vibro-acoustic coupling between elastic housing, air-cavity and free acoustic field have not to be neglected.     

Acoustic radiation from modal vibration of automotive brake drum

The vibro-acoustic characteristics of an automotive brake drum is studied by applying a hybrid approach, which combines a numerical vibration analysis with an analytical acoustic solution. Specifically, structural vibration of a drum is investigated with the numerical finite element analysis, and vibratory displacements of the outer surface of the drum is approximated by simple mathematical expressions. Then, radiation of sound from the drum vibration is calculated using well-known theoretical solutions based on the simplified modal displacements. Finally, the calculation results are compared with those obtained by full numerical analyses. The results show that the numerical-analytical hybrid method allows relatively accurate calculation of vibro-acoustic properties of a brake drum under realistic boundary conditions.     

基于板件贡献分析的装载机驾驶室低噪声设计

分别建立某装载机驾驶室及室内声腔有限元模型,通过单点输入多点输出(single input and multiple output,简称SIMO)法模态试验验证了声振耦合模型的准确性,测取悬置点激励进行频率响应分析及室内噪声预测。对驾驶室进行声学灵敏度分析,采用声传递向量法对驾驶室进行声学板件贡献度分析并对关键板件进行形貌优化,同时添加橡胶阻尼材料抑制壁板振动,进行二次声压虚拟预测。结果表明,声学灵敏度分析可得到多阶关键声振耦合频率,声传递向量法板件贡献度分析能准确定位产生噪声峰值的关键板件,形貌优化及添加阻尼材料的方案降噪效果显著,室内总声压级降低了4.43dB。此方案系统地为低噪声车身设计提供了技术路线,减少了传统方案的主观性和重复性,缩短了研发周期,降低了研发成本。     

薄板结构低噪声仿生拓扑优化方法

针对薄板结构的低噪声设计问题,以结构声辐射功率最小化为优化目标,借鉴植物脉序分枝结构的构型特征,提出了薄板结构加强筋布局的仿生拓扑优化方法。以结构应变能最小和释放局部最大剪应力作为加强筋主脉和次脉的生长准则,以广义Murray准则作为加强筋脉序的分歧准则,构造了具有脉序分级特征的加强筋自适应生长算法。以固支薄板结构的横向弯曲振动及声辐射问题为典型算例,对比分析了仿脉序分布加筋板结构的声辐射功率和振动功率流的分布特性。数值结果表明,与相同体积约束下的正交加筋布局方式相比,仿脉序分布加筋方法使薄板结构具有更优的声振特性,进而验证了薄板结构加强筋仿生布局降噪方法的有效性与可靠性。     

Vibro-acoustic characteristics of an annular disk with narrow radial slots

Analytical solutions for vibro-acoustic characteristics of a thin annular disk containing narrow radial slots have been proposed with numerical and limited experimental verifications. Structural characteristics of split and repeated modes of the disk are expressed in terms of eigensolutions for the corresponding uniform disk that has same geometric configuration. Sound radiations due to the modal vibrations are calculated using pre-developed analytical solution based on the structural data obtained above. Structural and acoustic responses of the disk for a stationary concentrated harmonic force have been studied using the modal expansion technique. Based on these results, the effects of relative location of the excitation to the slots on the vibro-acoustic responses as well as interactions between sound radiations for two split modes are investigated. The results demonstrate that the introduced procedure has reasonable accuracy obtaining vibro-acoustic characteristics of a thin annular disk containing narrow radial slots.     

Widening the sound absorption bandwidths of flexible micro-perforated curved absorbers using structural and acoustic resonances

In this paper, the sound absorptions of flexible curved micro-perforated panels that are backed by an air cavity are studied in detail. A theoretical model that is based on the classical plate equation coupled with an acoustic wave equation is developed for the prediction of sound absorption. This model considers both symmetrical and antisymmetrical structural acoustic responses. Using the electro-acoustic analogy approach, another model is developed that only considers single structural and acoustic modes. It is proposed to make use of panel and cavity resonances to widen the absorption bandwidth of a single/double perforated absorber. The absorption of a flexible micro-perforated panel can be further enhanced by adjusting its curvature to bring the resonant frequencies closer together. The effects of various parameters such as boundary condition, incidence angle, and curvature on the absorption are studied. Predicted results for the single and double layer absorbers show good agreement with measurements.     

APPLICATION OF DOMAIN DECOMPOSITION IN ACOUSTIC AND STRUCTURAL ACOUSTIC ANALYSIS

Conventional element based methods for modeling acoustic problems are limited to low-frequency applications due to the huge computational efforts. For high-frequency applications, probabilistic techniques, such as statistical energy analysis (SEA), are used. For mid-frequency range, currently no adequate and mature simulation methods exist. Recently, wave based method has been developed which is based on the indirect TREFFTZ approach and has shown to be able to tackle problems in the mid-frequency range. In contrast with the element based methods, no discretization is required. A sufficient, but not necessary, condition for convergence of this method is that the acoustic problem domain is convex. Non-convex domains have to be partitioned into a number of (convex) subdomains. At the interfaces between subdomains, specific coupling conditions have to be imposed. The considered two-dimensional coupled vibro-acoustic problem illustrates the beneficial convergence rate of the proposed wave based prediction technique with high accuracy. The results show the new technique can be applied up to much higher frequencies.     

Dynamic and acoustic characteristics of bell type structure using finite element method

Dynamic and acoustic characteristics of the bell type structure were analyzed numerically. The finite element method with 3-D general shell element was used to identify the natural frequencies and mode shapes of the structure. Mode shapes and stress distributions of a transient dynamic analysis were effectively displayed by using computer graphic technique. The results of this numerical study were in good agreement with those obtained from the experimental test of fast Fourier transform analyer. Vibrational modes, which effect the acoustic characteristics of the typical bell-type structure were found to be the first flexural mode (4-0 mode) and the second flexural mode (6-0 mode). Asymmetric effects by Dangjwas and acoustic holes gave rise to beat frequencies, and the Dangjwa was found to be most effective. When the impact load was applied to the bell, the stress concentration occured at the rim part of the bell. It was found that the bell type structure should be designed thickly at the rim part in order to prevent failure from impact loads.     

结构型吸波材料电磁特性的设计计算

结构型吸波材料兼具吸波与承载的双重功能,且具有可设计性,是一个重要的吸波材料的研究方向。夹芯结构吸波复合材料因其质轻、强度高,又能较好地吸收电磁波而广泛应用于飞机的机翼、尾翼和机身等部位。应用时域有限差分法(FDTD)建立正六边形蜂窝夹芯结构和波纹板型夹芯结构的电磁散射模型,通过数值仿真手段,计算了两种夹芯吸波结构和全金属结构的RCS值,对不同结构形状的夹芯结构的吸波性能进行了分析。     

Dynamic modeling and analysis of axial vibration of a coupled propeller and shaft system

The dynamic and acoustic characteristics of a coupled propeller and shaft system which is modeled by the transfer matrix method are studied. The elasticity of the propeller is taken into consideration by employing the equivalent reduced modeling method. Thus the influence of the elastic propeller on the vibro-acoustic responses of the coupled system is investigated. To reduce the axial vibration of the coupled propeller-shaft system, the influence and location of the vibration isolator on the structural and acoustic responses is presented. Simulation results demonstrate that utilizing the relationship between the natural frequency of the propeller and the resonance frequency range of the shaft can control the vibration of the coupled system without other vibration control method. Utilizing a vibration isolator is another effective way to control vibration. The optimal position for the isolator installed between the shaft and the thrust bearing is investigated.     

Vibro-acoustic Radiation Characteristics Analysis of Railway Vehicle Wheel with Damping Ridges Based on Modal Strain Energy

The existing researches on the damping wheel mainly focus on investigating the influence of damping structure change on the vibro-acoustic control.The changes include the geometric size of the damping structure,the damping material parameters,and the placement,and so on.In order to further understand the mechanism in reducing the acoustic radiation of railway wheel with layer damping treatment,in this paper,the wheel is simply modified by a full-sized circular plate.The circle plate side has stuck circumference constrained damping ridges and radial constrained damping ridges on it.Based on a hybrid finite element method-boundary element method(FEM-BEM),the paper develops a vibro-acoustic radiation model for such a distributed constrained damping structure.The vibration and acoustic radiation of the circular plate is analyzed.In the analysis,the dynamic response of the system is obtained by using the 3D finite model superposition method.The obtained vibration response is used as the initial boundary condition in solving Helmholtz boundary integral equation for the sound radiation analysis.In the procedure,firstly,the modal analysis of the circular plate is performed to get the distribution of the system modal strain energy.Secondly,the vibro-acoustic radiation characteristics of the plate with different kinds of circumference damping ridges and radial damping ridges are compared in order to try to find the best effective damping ridge structure.Thirdly,using the distribution of the plate modal strain energy investigates the effect of the ridge distribution locations on the circular plate on its vibro-acoustic radiation.The calculation and analysis research results show that,the sticking circumference and radial damping ridges on the plate can control the vibro-acoustic radiation of the plate effectively in different frequency range.The distribution of the constrained damping ridge has an effect on reduction in vibro-acoustic radiation of the circular plate.The present research is very useful in the design of railway wheel with low noise level.     

基于声-固耦合模型的车内噪声响度参数的预测与分析研究

针对传统A计权声压级评价指标对噪声低频成分衰减较大,常常出现车内声压级达标,声品质不合格的问题。引入心理声学参数的响度参量,利用虚拟仿真技术分析评价车内声学特性。建立驾驶室声-固耦合有限元模型,结合试验激励数据,进行基于模态的声学响应计算。在Matlab平台上,建立车内声品质客观心理声学参数响度的计算模型,对比预测驾驶室内场点的声压级和响度分布,结合声压级和响度结构板块贡献量分析,研究声压级和响度参量评价驾驶室结构特性的差别并识别驾驶室主要噪声源。以此为基础指导优化驾驶室结构阻尼铺设位置,综合提高车内声学品质。