新型列车侧墙内装板声学分析、优化及应用*

为了开发与应用新型列车车体降噪内装结构,基于混合FE-SEA法对轨道车辆用新型橡胶泡棉夹芯板进行隔声与声辐射预测建模,并进行了试验验证,进而利用该模型分析了橡胶泡棉孔隙率与芯皮厚度比对其隔声性能、声辐射性能的影响规律,并通过敷设阻尼层优化了其声学性能。最后,在侧墙组合结构的声学设计中评价了其实际应用效果。结果表明：随着孔隙率的逐步下降,橡胶泡棉夹芯板隔声量上升趋势较为明显,而辐射声功率持续降低;随着芯皮厚度比的逐步提高,夹芯板隔声量呈略微上升趋势,辐射声功率则相应降低。在远离声源一侧的橡胶泡棉蒙皮外侧敷设阻尼层的效果最优,优化后夹芯板计权隔声量提高0.7dB,总声功率级降低0.7dB;相较于传统木质胶合板和铝蜂窝板,橡胶泡棉夹芯板相较于传统内装板材在结构隔声设计中具有轻量化优势。     

纵向激发圆柱体超声频耦合振动的等效线路及其分析

本文利用表观弹性法的理论,得出了圆柱体耦合振动的一种等效线路,讨论了圆柱体耦合振动的频率方程及负载阻抗对振动频率的影响,计算了圆柱振动输入机械阻抗以及径向与纵向表观振速比随其几何尺寸变化的关系曲线.分析及计算结果表明,利用等效线路分析圆柱体的耦合振动,物理意义明显,计算简单,是分析及合理设计圆柱振动体的一种很方便的途径.     

非对称量子点中弱耦合极化子的相互作用能

采用改进的线性组合算符和幺正变换方法,研究非对称量子点中弱耦合极化子的性质.导出了非对称量子点中弱耦合极化子的振动频率和相互作用能随量子点的横向和纵向有效受限长度和电子-声子耦合强度的变化关系.数值计算结果表明:非对称量子点中弱耦合极化子的振动频率和相互作用能随量子点的横向和纵向有效受限长度的减小而迅速增大,表现出奇特的量子尺寸效应.     

磁场对非对称量子点中极化子性质的影响

采用线性组合算符和幺正变换方法研究磁场对非对称量子点中弱耦合磁极化子性质的影响.导出了非对称量子点中弱耦合磁极化子的振动频率、基态能量和基态结合能随量子点的横向和纵向有效受限长度、磁场和电子-声子耦合强度的变化关系.数值计算结果表明:非对称量子点中弱耦合磁极化子的基态能量和基态结合能随量子点的横向和纵向有效受限长度的增加而迅速增大.随回旋频率的增加而增大,随电子-声子耦合强度的增加而减小.     

飞秒脉冲非对称互相关绝对测距

光学频率梳是一种重复频率与偏置频率锁定的新型光源,在频域上为频率间隔稳定的频率梳齿,在时域上为相对距离稳定的飞秒脉冲激光.光学频率梳在测距中的应用广泛,能够实现远距离高精度的测量.本实验使用飞秒激光脉冲作为光源,基于谐振腔扫描光学采样测距原理得到非对称的互相关干涉条纹,实现了远距离高精度的绝对测距.非对称互相关条纹可通过色散补偿与调节光学频率梳的重复频率得到,并通过得到的非对称的互相关干涉条纹对测距结果进行补偿.实验结果表明测距系统能够实现在50 m范围内误差为2 μm的绝对测距,测量相对误差为1.9×10^-7.     

磁场对CsI非对称Gaussian受限势量子阱中强耦合极化子的影响（英文）

采用线性组合算符和幺正变换方法研究了磁场对非对称Gaussian受限势量子阱中强耦合极化子的振动频率、基态能量和基态结合能的影响.计算结果表明振动频率随磁场的回旋频率的增加而增大,基态能量的绝对值和基态结合能随回旋频率的增加而减少.振动频率是Gaussian受限势量子阱的范围的减函数,而基态能量的绝对值和基态结合能是其增函数.由此,我们得出磁场和Gaussian受限势量子阱的范围是研究非对称Gaussian受限势量子阱中磁极化子性质的重要因素.     

两轴四框架结构光电稳瞄吊舱减振器谐振频率计算与试验

根据振动理论分析两轴四框架系统选择减振器的要点,对某型直升机内外框架刚性连接的吊舱进行扫频振动试验,测量了谐振频率和谐振点的扫频放大率,绘制了放大率曲线。通过使用放大率曲线计算内外框架刚性连接时系统的三向刚度。并根据减振器刚度值,利用弹簧串联刚度的计算方法计算了使用减振器系统的三向刚度和谐振频率。重新进行试验后,结果表明系统谐振频率和放大率都满足要求。该结构使用减振器的要点是：减振器放大段位于伺服带宽内,系统谐振频率避开外界扰动频率以及放大率应尽可能小。     

超导磁体螺栓结合面低温振动特性研究

振动特性对于超导磁体的各类工程应用具有重要意义, 螺栓法兰盘连接是超导磁体系统的一种常见的支撑结构类型, 然而螺栓结合面在低温条件下振动特性的相关研究目前尚少见报道. 本研究中设计加工了简化的连接结构, 在室温和液氮温度对其螺栓结合面进行振动特性的测试分析. 接下来, 采用集中质量法进行建模, 并利用振型、 频率与质量矩阵、 刚度矩阵的关系求解了不同螺栓预紧力情况下的刚度矩阵, 得到了系统总刚度和结合面刚度. 使用上述方法对振动测量数据计算发现, 该结构的系统总刚度与结合面刚度都随着预紧力增大而增大, 同时液氮低温条件可使系统总刚度和结合面刚度进一步增大.     

钢结构装配式住宅墙板连接方式对隔声性能的影响*

为提升其隔声性能,通过有限元法数值分析,比较了不同位置墙板的连接方式对房间隔声性能的影响。结果表明：(1)侧墙墙板柔性连接处理对侧向传声的抑制作用显著,当侧墙墙板采用柔性连接后,房间的隔声量在低频段平均可以提升3 dB左右;(2)公共隔墙墙板的柔性连接对房间低频段隔声量提升不明显,甚至在160 Hz、400 Hz、500 Hz等频率下隔声量有所降低。最后,基于模拟分析结果对装配式墙体连接方式提出了改进策略。     

基于非对称吸声器的发动机声学超表面声衬

为了解决发动机低频噪声问题,基于双端口非对称吸声器原理,设计了一种尺寸渐变的吸声超表面,用于发动机声衬降噪设计.首先,建立了非对称共振吸声器的理论分析模型和仿真分析模型,揭示了降噪机理,并分析了其降噪效果的影响因素.然后基于非对称共振吸声器设计了一种声学超表面声衬,用全模型理论计算、等效阻抗理论计算和COMSOL有限元仿真三种方法深入分析了声衬的降噪效果,并用全模型理论计算和等效阻抗理论计算方法考虑了流速对降噪效果的影响,然后对此结构进行了参数优化.研究结果表明,所设计的基于非对称吸声器的声学超表面声衬在厚度仅为2.5 cm (仅为252 Hz对应波长的1/54)的情况下,可实现252—692 Hz的频带范围内3 dB以上的降噪效果,为发动机降噪设计提供了一种新的设计思路.     

PREDICTION AND MEASUREMENT OF SOME DYNAMIC PROPERTIES OF SANDWICH STRUCTURES WITH HONEYCOMB AND FOAM CORES

Some dynamical properties of sandwich beams and plates are discussed. The types of elements investigated are three-layered structures with lightweight honeycomb or foam cores with thin laminates bonded to each side of the core. A six order differential equation governing the apparent bending of sandwich beams is derived using Hamilton's principle. Bending, shear and rotation are considered. Boundary conditions for free, clamped and simply supported beams are formulated. The apparent bending stiffness of sandwich beams is found to depend on the frequency and the boundary conditions for the structure. Simple measurements on sandwich beams are used to determine the bending stiffness of the entire structure and at the same time the bending stiffness of the laminates as well as the shear stiffness of the core. A method for the prediction of eigenfrequencies and modes of vibration are presented. Eigenfrequencies for rectangular and orthotropic sandwich plates are calculated using the Rayleigh-Ritz technique assuming frequency dependent material parameters. Predicted and measured results are compared.     

Development of composite plate for compact silencer design

A compact flow-through plate silencer is constructed for low frequency noise control using new reinforced composite plates. The concept comes from the previous theoretical study [L. Huang, Journal of the Acoustical Society of America 119 (2006) 2628–2638] which concerns a clamped supported plate enclosed by rigid cavities. When the grazing incident sound wave comes and induces the plate into the vibration, it will radiate sound and reflect sound. Such sound reflection causes a desirable noise reduction from low to medium frequency with wide broadband. The structural property of the very light plate with high bending stiffness is very crucial element in such plate silencer. In this study, an approach to fabricate new reinforced composite panel with light weight and high flexibility to increase the bending stiffness is developed in order to realize the function of this plate silencer practically. The plate silencer can be constructed in more compact size compared with the previous two-plate silencer with two rectangular cavities and the performance with the stopband of the range from 229 to 618 Hz, in which the transmission loss is higher than 10 dB over the whole frequency band without flow or with flow at the speed of 15 m/s, can be achieved. The experimental data also proves that the non-uniform clamped plates with thinner ends perform very well. To implement the use of such silencer practically in controlling noise at different dominant frequency ranges, a design chart has been established for searching the optimal bending stiffness and corresponding stopband at different geometries.     

Wave speeds of honeycomb sandwich structures: An experimental approach

In this study, the influence of different design parameters, such as core density, core material, and cell size on the wave speeds of honeycomb sandwich structures was experimentally analyzed. Bending and shear wave speeds were measured and related to the transmission loss performance for various material configurations. The shear modulus of the core showed maximum influence on the wave speeds of the samples, while cell size did not have a significant influence on the wave speeds or on the transmission loss. Skin material affected wave speeds only in the pure bending regime. Honeycomb sandwich structures with a subsonic core and reduced wave speed showed increased transmission loss compared to samples without a subsonic core.     

Sound transmission across lightweight all-metallic sandwich panels with corrugated cores

The transmission of sound through all-metallic sandwich panels with corrugated cores is investigated using the space-harmonic method. The sandwich panel is modeled as two parallel panels connected by uniformly distributed translational springs and rotational springs, with the mass of the core sheets taken as lumped mass. Based on the periodicity of the panel structure, a unit cell model is developed to provide the effective translational and rotational stiffness of the core. To check the validity of the model, it is used first to study the sound insulation properties of double-panel structures with air cavity, and the analytical predictions agree well with existing experimental data. The model is then employed to quantify the influence of sound incidence angle and the inclination angle between facesheet and core sheet on sound transmission loss （STL） across sandwich panels with corrugated cores. The results show that the inclination angle has a significant effect on STL and it is possible to avoid STL dips by altering the inclination angle. Moreover, it is found that sandwich panels with corrugated cores are more suitable for the insulation of sound waves having small incidence angles.     

Vibro-acoustic response and sound transmission loss analysis of functionally graded plates

This paper presents analytical studies on the vibro-acoustic and sound transmission loss characteristics of functionally graded material (FGM) plates using a simple first-order shear deformation theory. The material properties of the plate are assumed to vary according to power law distribution of the constituent materials in terms of volume fraction. The sound radiation due to sinusoidally varying point load, uniformly distributed load and obliquely incident sound wave is computed by solving the Rayleigh integral with a primitive numerical scheme. Displacement, velocity, acceleration, radiated sound power level, radiated sound pressure level and radiation efficiency of FGM plate for varying power law index are examined. The sound transmission loss of the FGM plate for several incidence angles and varying power law index is studied in detail. It has been found that, for the plate being considered, the sound power level increases monotonically with increase in power law index at lower frequency range (0–500 Hz) and a non-monotonic trend is appeared towards higher frequencies for both point and distributed force excitations. Increased vibration and acoustic response is observed for ceramic-rich FGM plate at higher frequency band; whereas a similar trend is seen for metal-rich FGM plate at lower frequency band. The dBA values are found to be decreasing with increase in power law index. The radiation efficiency of ceramic-rich FGM plate is noticed to be higher than that of metal and metal-rich FGM plates. The transmission loss below the first resonance frequency is high for ceramic-rich FGM plate and low for metal-rich FGM plate and further depends on the specific material property. The study has found that increased transmission loss can be achieved at higher frequencies with metal-rich FGM plates.     

Optimal design of acoustical sandwich panels with a genetic algorithm

An optimization study is performed to design a sandwich panel with a balance of acoustical and mechanical properties at minimal weight. An acoustical model based on higher-order sandwich beam theory is used with mechanical analysis of the maximum deflection at the center of the sandwich panel under a concentrated force. First, a parametric study is performed to determine the effects of individual design variables on the sound transmission loss of the sandwich panel. Next, by constraining the acoustical and mechanical behavior of the sandwich panel, the area mass density of the sandwich panel is minimized using a genetic algorithm. The sandwich panels are constructed from eight face-sheet and sixteen core materials, with varying thicknesses of the face sheets and the core. The resulting design is a light-weight, mechanically efficient sound insulator with strength and stiffness comparable to sandwich structures commonly used in structural applications.     

Assessment of sandwich models for the prediction of sound transmission loss in unidirectional sandwich panels

The consistent higher-order approach and the two-parameter foundation formulation are used for the derivation of sound transmission loss in symmetric unidirectional (infinitely wide) sandwich panels with isotropic face sheets. In both models, transmission loss is calculated using decoupled equations representing symmetric and anti-symmetric motions of a sandwich panel. The closed-form expressions for impedances and transmission coefficient of a symmetric sandwich panel with an isotropic core are derived for the two-parameter foundation model. A comparison between the numerical predictions based on the two sandwich models and available experimental data shows that the consistent higher-order formulation can be used to predict the transmission loss in symmetric sandwich panels with both honeycomb and isotropic cores. For prediction of transmission loss of symmetric sandwich panels with an isotropic core, the two-parameter foundation model is more convenient, while the consistent higher-order approach is more accurate.     

Low frequency sound insulation using stiffness control with honeycomb panels

A new honeycomb core design has been used to increase the stiffness of the panel and applied to improve the noise transmission loss at frequencies between 100 and 200 Hz. A model is presented to predict the transmission loss of the honeycomb panels based on the structural modal parameters. A new test specimen with fiber reinforced plastic cores and face sheets had been used to investigate the effect of stiffness and damping on noise transmission loss. The measurements of noise transmission loss have been compared with data for common structural panels. The results show that the new core fabrication techniques using moulding to improve the noise transmission are effective. In comparison to a cement panel of the same mass, the honeycomb panels have higher TL at low frequencies between 100 and 200 Hz due to higher stiffness and damping. The honeycomb panels have more significant vibration responses above 500 Hz but these are limited by damping.     

压电网络复合板的波动特性与隔声性能分析

在压电网络复合板机电耦合波动方程基础上,首先对在其中传播的弯曲波的波动特性进行了分析,发现压电网络复合板中同时存在两种不同频散特性的弯曲波,电感电阻并联型压电网络复合板中存在的两种弯曲波的频散曲线具有频率转向现象;在频率转向区,弯曲波的衰减常数或达到最大或迅速增大这一结论为压电网络复合板的减振降噪设计提供了参考。对压电网络复合板中的能量分析给出了这一结论的机理:即在频率转向区板中的机械能与电能能够进行最大的能量交换;在波动分析的基础上对压电网络复合板的隔声特性进行了分析,发现压电网络复合板隔声曲线上的低谷随外界电感值的变化能够发生移动或者消失,最后结合压电网络复合板的波动频散特性对复合板的隔声机理进行了分析,为设计压电网络复合板的隔声性能提供了理论参考。      

The effect of external mean flow on sound transmission through double-walled cylindrical shells lined with poroelastic material

Sound transmission through a system of double shells, lined with poroelastic material in the presence of external mean flow, is studied. The porous material is modeled as an equivalent fluid because shear wave contributions are known to be insignificant. This is achieved by accounting for the energetically most dominant wave types in the calculations. The transmission characteristics of the sandwich construction are presented for different incidence angles and Mach numbers over a wide frequency range. It is noted that the transmission loss exhibits three dips on the frequency axis as opposed to flat panels where there are only two such frequencies—results are discussed in the light of these observations. Flow is shown to decrease the transmission loss below the ring frequency, but increase this above the ring frequency due to the negative stiffness and the damping effect added by the flow. In the absence of external mean flow, porous material provides superior insulation for most part of the frequency band of interest. However, in the presence of external flow, this is true only below the ring frequency—above this frequency, the presence of air gap in sandwich constructions is the dominant factor that determines the acoustic performance. In the absence of external flow, an air gap always improves sound insulation.