变参数分空腔单层微穿孔板低频降噪性能研究

由于微穿孔板结构在低频噪声下无法实现高效宽带的吸声效果,为了提高低频吸声性能,需要优化吸声器的结构参数以达到需要的降噪水平。本研究优化和测试了变参数分空腔单层微穿孔板结构,该结构在低频的吸声系数高且吸声频带宽。首先,通过声电类比法建立变参数分空腔单层微穿孔板结构理论模型,分析吸声系数与结构参数之间的关系;其次,确定优化变量和约束条件,利用布谷鸟算法优化理论模型,得到最佳吸声系数的结构参数;最后,对微穿孔板结构的吸声系数进行有限元仿真,加工微穿孔板结构样品,在驻波管中进行了吸声性能测试。结果表明,3组结构参数分空腔单层微穿孔板结构和4组结构参数分空腔单层微穿孔板结构能够在400~2 000 Hz的频率范围内保证高吸收（恒定超过80%）。     

复杂机械系统多维耦合振动传递矩阵分析

以特性传递矩阵描述复杂机械系统中子结构输入、输出力与速度矢量关系,提出了复杂振源激励、多弹性支承与基础板结构三维耦合隔振系统传递矩阵力学模型。考虑隔振支承多维波动效应,推证了弹性支承耦合振动传递矩阵,为复杂系统功率流特性及隔振器多维驻波效应研究确立了有效途经。数值模拟计算表明,基础板结构的前两阶弯曲共振模态是高频域系统功率流提高的主要原因。振源力矩或垂向激振力诱发的隔振器纵向谐振使系统功率流明显提高:增大基础板厚度,驻波共振峰值提高。     

微穿孔板的吸声特性研究

微穿孔板是一种防火性能强,吸声效果好的共振吸声体,由于其吸声性能好,结构简单,所以被广泛的应用到吸声降噪领域,但是目前对其特性的研究还不够完善,因此研究微穿孔板的吸声特性是很有必要的。采用传递函数法利用声望SW系列驻波管通过测量微穿孔板不同参数下的吸声系数,得出了微穿孔板在不同孔径和孔间距以及在不同的空腔深度下的吸声系数,并结合实验数据分析说明了孔径、孔间距及空腔深度对微穿孔板吸声特性的影响。结果对微穿孔板性质的研究有一定的指导意义,为吸声材料的研发提供了参考,有利于降低噪声污染,改善环境。     

固-流掺杂结构声子晶体中弹性波的缺陷模

为了研究弹性波在固-流掺杂结构声子晶体中缺陷模的特性,推导出了弹性波斜入射固-流掺杂结构声子晶体的转移矩阵。研究了固-流掺杂结构声子晶体中弹性波的透射系数,得到了由于掺杂在禁带的中央出现了一条狭长的缺陷模透射峰的结论。当杂质厚度固定时,缺陷模随入射角的增加向高频方向移动。当入射角固定时,缺陷模的中心频率随杂质厚度的增加近似呈线性减小。     

新型空心结构阻振质量的阻振性能实验

分析了薄板结构-刚性阻振质量的振动传递特性,研究了一种空心结构阻振质量的阻振性能,发展了薄板结构的阻振技术;设计了带近似等质量的空心与实心阻振质量的薄板结构实验模型,通过测试板结构的平均振动加速度,得到了阻振质量的阻振损失;对比研究了空心与实心阻振质量的阻振损失,分析了空心+实心二级阻振质量的减振效果,探讨了空心阻振质量填充颗粒阻尼对阻振性能的影响。结果表明:同等质量的空心阻振质量比实心阻振质量的阻振损失更大,且有效阻振频率向低频移动;空心+实心二级阻振质量仅略高于单级阻振质量的阻振损失;空心阻振质量内部填充颗粒阻尼,可有效提高减振效果,其阻振损失优于空心+实心二级阻振质量。     

吸声蜗壳在离心风机降噪中的应用研究

在标准进气风管测试装置上,对某离心风机及在风机蜗壳周向板、前盖板、后盖板等部位分别加装吸声材料后,测试了不同结构形式下风机性能和噪声特性。试验结果表明:相比原风机,蜗壳周向板与后盖板同时加装吸声材料效果最好,设计工况下A声级能够降低7.2dB(A),在小流量工况下,吸声蜗壳的降噪效果变差;根据风机噪声频谱,穿孔板加玻璃棉吸声蜗壳的吸声性能中高频好于低频,风机基频噪声在设计点能够降低12.5dB(A);加装吸声材料后风机气动性能会略有下降,压力和效率都有不同程度的降低。     

带阀消声器阀体开度变化的声学特性分析及应用

低频阶次噪声对排气噪声声品质有着重要的影响,带阀消声器成为消除排气低频噪声的手段之一。对带阀消声器进行试验分析和三维数值仿真,发现随着阀体开度的增加,共振器的共振频率向高频移动。进一步从实际带阀消声器结构中提取出一种可调声质量抗共振器子结构单元,采用三维数值方法和集总阻抗传递矩阵模型计算出不同开度下的阀体结构的声质量抗,建立共振器的集总阻抗模型。结果显示,阀体开度变化改变了共振器的声质量抗,而声质量抗是影响共振频率的关键因素,揭示出带阀消声器消除低频阶次噪声的机理。将带阀消声器和对比消声器进行实车测试。结果表明,带阀消声器起到跟踪消减低频阶次噪声的作用。     

基于2.5维有限元-边界元的高速列车车体铝型材声振特性研究

铝型材作为高速列车车体层状复合结构的主要部件，声振性能的优劣直接影响车内声学环境和乘车舒适度。由于铝型材尺寸庞大、结构复杂，解析模型和传统的有限元/边界元法对其声振特性的预测存在一定的局限。铝型材截面几何特征和材料属性沿纵向均匀一致分布，当结构波长远大于结构尺寸时，可视为典型的波导结构，2.5维有限元-边界元法被广泛认为是研究其声振特性最合适的方法之一。因此，基于2.5维有限元法建立了铝型材的波动模型，研究了铝型材的波传播特征；基于2.5维边界元法建立了铝型材两侧声场的预测模型，同时，结合结构与声场的边界耦合条件，建立了铝型材的2.5维有限元-边界元声辐射和隔声模型，分析了力激励位置对结构振动响应、辐射声功率及辐射效率的影响，讨论了混响声场激励下边界条件对结构隔声性能的影响，提出了一种基于频散特性的将铝型材等效为均质板的方法。研究结果表明，在低频和高频，结构振动分别以截面的整体变形和局部变形的特征波为主；等效均质板的弯曲波频散与铝型材的整体弯曲波频散吻合很好；力激励位置对结构的振动响应和辐射声功率影响显著，对辐射效率影响很小；声激励下，边界条件只对结构在刚度控制区的隔声影响显著，约束约...     

电流变液在结构振动抑制中的应用研究

根据结构抑振的应用要求,研制出了几种零场粘度低、有场粘度变化梯度大的电流变液,并设计制作了电流变液静态屈服应力测试仪,测试出了所研制的电流变液的静态屈服性能随电场强度和液体组份比变化的曲线。利用自制的电流变液,对含电流变液的夹层板振动进行了单模态抑制,由此得出电流变液对振动机理在于：一方面通过电流变阻尼效应降低结构振动响应的幅值,特别是共振峰的幅值;另一方面通过电流变刚度效应使结构的有效刚度增加,结构的共振点发生移动,从而使结构在共振频率激励下的振幅大大降低。对本文的夹层板模型,在３ｋＶ／ｍ ｍ 的电场强度下,第三阶模态的响应幅值降低了９０％ 。     

孔结构对多孔铝空气声吸收性能的影响

对多孔铝的空气声吸收性能进行了研究。结果表明：多孔铝具有较高的空气声吸收系数，并且与孔结构密切相关。声吸收系数在低频端（〈1kHz）较低，高频端（〉1kHz）则可达到0．85以上。随着孔隙率、孔径的减小，多孔铝的共振吸声系数有所下降，吸声频谱曲线向低频方向移动，且频带宽度展宽。     

Whistling behavior of periodic systems: Corrugated pipes and multiple side branch system

Whistling behavior of two geometrically periodic systems are investigated: corrugated pipes and a multiple side branch system. In both systems frequency (Helmholtz number) is a non-decreasing piecewise constant function of the Mach number, whose increase on average is approximately linear. The plateaus, lock-in frequencies, of this piecewise constant function correspond to the longitudinal acoustic pipe modes. In both systems pressure fluctuation amplitude changes non-monotonically with Mach number with local maxima that correspond to the lock-in frequencies. A characteristic length, equal to cavity width plus upstream edge radius, yields the smallest discrepancy in the measured peak whistling Strouhal number for both corrugated pipes and multiple side branch system. For both systems the upstream edge radius of the cavity has a strong effect on pressure fluctuation amplitudes. Whistling amplitudes increase by a factor of 3-5 upon rounding off the upstream cavity edges. The radius of the downstream edge has a less pronounced effect on the sound amplitude and frequency. The geometric parameters of the multiple side branch system can easily be modified. This makes the multiple side branch system a convenient tool for making experiments on the effects of various geometric parameters. A number of aspects are addressed with the multiple side branch system such as the effect of pipe termination geometry, source localization, side branch depth to diameter ratio, a gradient in depth along the pipe and hysteresis upon change in the acceleration or deceleration of the flow.     

微穿孔板的主动吸声研究

提出用微穿孔板进行主动吸声的方法。用微穿孔板作为主动吸声的材料，检测出入射声波的频率，得到微穿孔板的共振频率，从而得到微穿孔板背后空腔的深度，移动微穿孔板背后的刚性壁以满足空腔深度的要求，使得吸声系数达到最大，从而达到主动吸声的目的。最后，进行了数值计算与实验，计算结果与实验结果能很较好的吻合，说明了该主动吸声方法的可行性。     

Bi-modes alternation stepping ultrasonic motors

Based on the principle of alternative operation of two bending vibration modes in an annular stator, this paper presents a standing-wave stepping ultrasonic motor characterized by no accumulative errors driven by an open-loop control circuitry. The driving forces are generated from the motions of projections on the stator in two modes. The positioning of the motor is achieved by the cooperation between the stator projections and rotor teeth, and the number of the rotors determines the stepping angle of the motor. Two-phase sinusoidal signals corresponding to the two modal frequencies drive the motor bi-direction stepping rotation via a switch unit. The prototype runs steadily without miss-step on trial. The single-step angle displacement of the motor is 2.5°. __________ Translated from Journal of Nanjing University of Aeronautics and Astronautics, 2006, 38(5): 600–604 [译自: 南京航空航天大学学报]     

Frequency-domain computation of inflow broadband noise due to interaction of a rectilinear cascade of flat plates with incident turbulence

This paper deals with the broadband noise due to the interaction between convected turbulent gusts and a rectilinear cascade of flat plates bounded by two parallel walls. An analytic formulation for the acoustic power spectrum due to this turbulence-cascade interaction is derived, which can be used to assess the effects of the span-wise wavenumber components of ingesting turbulent gust on the overall acoustic power spectrum. This three-dimensional theory is based on the two-dimensional theory of Cheong et al. (2006, 2009). The three-dimensional model is shown to provide a close fit to the measured spectrum of rotor-stator interaction. The predictions using this three-dimensional model are also compared with those using the previous two-dimensional model by Cheong et al. (2006; 2009). Through this comparison, it is found that the contributions to the acoustic power of the span-wise wavenumber components of incident turbulent gust are increased as the frequency is augmented, which is mainly due to three-dimensional dispersion-relation characteristics of acoustic waves. This implies that the number of incident turbulent gust modes directly involved in generating cut-on acoustic waves increases as the frequency increases. Therefore, in the lower frequency range, three-dimensional acoustic power is less than its corresponding two-dimensional one, whereas, as the frequency increases, the three-dimensional acoustic power spectrum closely follows those of two-dimension. The formulation is also used to make a parametric study about the effects on the power spectrum of the blade number, stagger angle, gap-chord ratio, and Mach number.     

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。     

Three-dimensional effects of supersonic cavity flow due to the variation of cavity aspect and width ratios

Unlike the steady closed-type supersonic cavity flow, open-type cavity flow is divided into internal and external flows by turbulent shear layer. The cavity flow may cause resonance phenomena due to pressure oscillation, depending on the cavity geometry and the flow conditions. These phenomena may induce noise generation, structural damage, and aerodynamic instability. In this research, the flow characteristics of three-dimensional supersonic cavity flow of Mach number 1.5 were analyzed with the variations of aspect ratio and width ratio. Three-dimensional unsteady compressible Reynolds-averaged Navier-Stokes (RANS) equations were used with a turbulence model. For numerical calculations, the 4th-order Runge-Kutta method and the FVS method with van Leer’s flux limiter were applied. The numerical calculations were performed by using a parallel processing program with 16 CPUs. The sound pressure level (SPL) spectra of pressure variations were analyzed at the point of cavity leading edge. The correlation of pressure distribution (CPD) was also analyzed for the propagation of dominant oscillation pressure waves with respect to the reference point of the cavity leading edge. The dominant oscillation frequency was compared with the oscillation modes of Rossiter’s formula. Oscillation Mode 2 appeared as a dominant oscillation frequency regardless of the aspect ratio of cavity in the two-dimensional flow. Oscillation Modes1 and 2 appeared in three-dimensional cavities of small aspect ratios. However, as the aspect or the width ratio increases, only the mode 2 or 3 frequency appeared as a dominant oscillation frequency.     

Analysis of two dimensional and three dimensional supersonic turbulence flow around tandem cavities

The supersonic flows around tandem cavities were investigated by two-dimensional and three-dimensional numerical simulations using the Reynolds-Averaged Navier-Stokes (RANS) equation with thek-ω turbulence model. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves, and the acoustic effect transmitted from wake flow to upstream. The upwind TVD scheme based on the flux vector split with van Leer’s limiter was used as the numerical method. Numerical calculations were performed by the parallel processing with time discretizations carried out by the 4th-order Runge-Kutta method. The aspect ratios of cavities are 3 for the first cavity and 1 for the second cavity. The ratio of cavity interval to depth is 1. The ratio of cavity width to depth is 1 in the case of three dimensional flow. The Mach number and the Reynolds number were 1.5 and 4.5 × 10⁵, respectively. The characteristics of the dominant frequency between twodimensional and three-dimensional flows were compared, and the characteristics of the second cavity flow due to the first cavity flow was analyzed. Both two dimensional and three dimensional flow oscillations were in the ‘shear layer mode’, which is based on the feedback mechanism of Rossiter’s formula. However, three dimensional flow was much less turbulent than two dimensional flow, depending on whether it could inflow and outflow laterally. The dominant frequencies of the two dimensional flow and three dimensional flows coincided with Rossiter’s 2nd mode frequency. The another dominant frequency of the three dimensional flow corresponded to Rossiter’s 1st mode frequency.     

考虑声振耦合下结构阻尼板降噪拓扑优化设计

弹性板-声腔系统声振耦合研究不仅要计算结构-声场耦合的频率以及振型,还要计算耦合后系统对设计变量的灵敏度.本文采用伴随法得到弹性板上节点位移对阻尼层单元的灵敏度,并使用变密度优化方法对阻尼材料敷设位置予以优化.同时,引入Sigmund提出的过滤公式,抑制优化过程中出现的棋盘格现象.分析表明,敷贴约束阻尼层后控制点位置的声压明显减低.与均匀敷贴阻尼相比,阻尼材料敷设位置优化后的结构能有效地抑制声腔内控制点的声压级和减轻结构重量.     

重卡驾驶室的声固耦合模态分析

利用有限元法建立某重卡驾驶室车身结构和车室空腔模型,并建立了考虑结构与空气之间相互作用的车室声固耦合系统模型。使用Nastran软件对三个模型的模态进行仿真计算,对结构的模态频率和变形部位、空腔声学模态频率和声压分布情况以及耦合系统中结构和声学空腔模态频率和振型的变化进行了详细分析,为下一步的车身设计和改进提供了依据。     

一种新型单元的频率选择表面

本文通过对传统的十字单元进行改进，设计了一种新型单元的频率选择表面（FSS）。利用模式匹配法，对传统十字单元FSS和这种新型单元FSS从理论上进行了对比分析，对TE波入射时角度变化和大角度入射时极化方式变化对中心频率的影响两个方面进行了研究，并采用镀膜和光刻技术制备了新型单元FSS的实验样件，在微波暗室中进行测试，得到的实验曲线与理论仿真曲线基本一致。结果表明：传统十字单元FSS不能实现中心频率的角度稳定性，TE波0°到45°时中心频率漂移300MHz，并且45°入射时中心频率的极化稳定性很差，漂移量为800MHz，而新型单元FSS具有中心频率的角度稳定性，TE波０°到45°入射中心频率漂移量仅为100MHz，同时对于大的入射角度，具有中心频率的极化稳定性。