消声器中频声学性能的计算测量方法

传统的消声器声学性能计算和实验测量都是在消声器进出口管道作为平面波声场的条件下进行,当进出口管道内出现有高阶模态激发的三维声场时,这些计算方法和实验测量方法就不再适用。由此,采用消声器进出口管道内加径向隔板的方法来计算消声器的声学性能,当原来管道声场中出现高阶模态时,仍然可以用平面波方法计算消声器的传递损失。应用该方法对进气滤清消声器进行传递损失数值计算,在原来进出口管道的平面波声场范围内,计算结果与传统方法计算结果均接近实验的测量结果,验证了该方法预测消声器声学性能的可行性。进而在所设计的消声器中频声学性能实验测试台架上,用声波分解法对阻性消声器进行传递损失测试,实验测量结果和有限元仿真结果也吻合良好。     

穿孔管阻性消声器横向模态和声学特性计算与分析

应用二维有限元法计算穿孔管阻性消声器的横向模态,利用数值模态匹配法计算其传递损失,推导了相应的公式并编写了计算程序。对于圆形同轴穿孔管阻性消声器的传递损失,数值模态匹配法计算结果与三维有限元法计算结果以及实验值吻合良好,表明了二维有限元法计算穿孔管阻性消声器横向模态和数值模态匹配法预测消声性能的准确性。进而分析孔径、穿孔率、吸声材料的密度和穿孔管偏移对圆形直通穿孔管阻性消声器横向模态和消声特性的影响。结果表明,孔径减小、穿孔率增大,或者穿孔管偏移量增大均能使消声器有效的平面波区域变宽,高频消声效果变好,但中频消声效果变差;增加吸声材料的填充密度则能提高消声器中高频的消声量。     

基于管道声模态的消声器传递损失计算

传递损失是评价消声器声学性能的一个重要指标。提出了一种方法—管道声模态法代替传统方法估算传递损失。对进出口截面积较小的消声器进行计算和检验,与传统方法比较,结果基本吻合,且过程简单,提高传递损失的计算效率。对进出口截面积较大的消声器,中高频段由于大量高次波的出现,传统方法失效;但低频段管中声波以平面波为主,其结果与传统法一致。因此可以采用管道声模态法快速估算传递损失。     

双腔结构消声器声学性能计算子域耦合方法

提出基于子域划分的耦合方法求解双腔结构消声器声学性能。据结构特点或材料属性将消声器分为不同子域,用数值模态匹配法或三维解析方法求解规则等截面子域结构传递矩阵,用三维数值方法求解非规则渐变截面子域结构传递矩阵,用子域连续条件求得消声器整体矩阵,进而获得消声器传递损失。分别用基于子域划分的耦合方法、三维有限元方法及数值模态匹配法计算典型双腔结构消声器的传递损失。结果表明,基于子域划分的耦合方法适用预测双腔结构消声器声学特性,与数值模态匹配法相比计算效率较高。     

运用模态叠加法研究扩张式消声器的传递损失

采用声学模态叠加法建立单腔扩张式消声器传递损失计算模型,然后通过Matlab编程实现单腔扩张式消声器传递损失的数值计算。在此基础上,比较声学模态叠加法、有限元法和基于平面波假定的经典公式法在计算单腔扩张式消声器传递损失上的差别,研究单腔扩张式消声器膨胀段尺寸对传递损失的影响。结果表明,对于平面入射波,声学模态叠加法可用于单腔扩张式消声器各频段传递损失的计算;增大膨胀段的半径能有效提高低频段的传递损失,但对高频段的影响较小;随着膨胀段宽度的增大,传递损失的峰值向低频移动,传递损失最大的频段向高频移动。     

抗性消声器传递损失预测的三维时域计算方法

将三维时域计算方法应用于计算无流和有流条件下抗性消声器的传递损失,具体过程为:首先在消声器进口施加压力脉冲信号,然后通过三维非定常流体动力学计算获得消声器上游和下游的压力波动,最后由快速傅里叶变换将时间域的入射压力信号和透射压力信号转化到频率域,从而计算得到消声器的传递损失。使用该方法计算了无流和有流条件下抗性消声器和穿孔管消声器的传递损失,数值计算结果与文献中的实验测量结果吻合良好。     

排气消声器传递损失的实验测量与分析

介绍消声器传递损失的测量方法,包括声波分解法、两负载法、两声源法和脉冲法。在消声器声学性能试验台上采用两负载法测量无流和有流时简单膨胀腔和直通穿孔管消声器的传递损失。测量结果表明：穿孔率对穿孔管消声器低频消声性能影响较小,对中高频消声性能影响较大,增加穿孔率能够拓宽穿孔管消声器的有效消声频率范围;气流对直通穿孔管消声器的声学性能有一定影响,穿孔率越低影响越大,随着流速的增加,低频段传递损失变化不大,高频段的传递损失显著增加。     

穿孔管消声器的数值分析

为降低穿孔管消声器模型的复杂性,采用Mechel公式,通过施加阻尼边界条件对穿孔管进行模拟。运用SYSNOISE软件对消声器的传递损失进行有限元计算,同J．W．Sullivan和M．J．Crocker获得的结果（实验测量和预测）进行分析比较,取得较好的一致性。计算分析相同孔径不同穿孔率下消声器传递损失的特点,并同理论结论进行比较,其结果进一步验证该方法的可行性。     

基于无网格的数值模态匹配法求解消声器声学特性

应用全局弱式无网格方法求解消声器的横向模态,使用模态匹配技术求解其传递损失。计算了圆形穿孔管阻性消声器的横向模态和传递损失,计算结果与解析方法和有限元方法计算结果吻合较好,且节省计算时间。     

多穿孔管板阻性消声器的声学特性研究

应用包含高阶模态声波的二维解析法研究多穿孔管板阻性消声器的声学性能,消声器传递损失的计算结果和实验结果吻合良好.分析了穿孔率和吸声材料的流阻率对阻性消声器声学性能的影响,并且研究了具有组合式阻抗及组合流阻率吸声材料的多穿孔管板消声器的声学特性.结果表明:不同类型的组合式阻抗及组合流阻率的吸声材料对消声器在不同频段的消声性能产生一定影响.     

大型客机机舱内饰板隔声性能计算与试验

结合单层板与夹层板隔声理论，推导了应用于计算典型飞机机舱内饰板隔声量的分析方法。根据所推导的计算公式，将真实环境条件与内饰板材料参数代入其中，获得地面与飞行状态下的隔声量计算结果。与实测数据对比之后，发现在特定频率区域内饰板计算量值与趋势都与试验吻合较好，但在共振频率、吻合频率和压缩频率上，计算值与试验测量值有较大起伏。对比飞行与地面两种条件，飞机状态下的隔声量普遍大于地面状态。     

Loss Angle and Permittivity Determination of a Dielectric Rod Using a Three-Wire Cage-Shape System

A simple innovative measurement system is proposed for the simultaneous determination of the loss angle and permittivity of a cylindrical dielectric rod at high-frequency regimes (megahertz band). The measurement method, based on multiconductor transmission-line (MTL) theory, explores the frequency-domain resonant features of the new proposed structure, which consists of three equally spaced wires where the cylindrical rod is tightly caged inside. The wires are bonded together at the far end of the MTL structure, while at the sending end, only two are bonded. The input impedance of the transmission line is measured against the frequency, with sharp peaks being observed when the length of the structure comes close to an odd multiple of a quarter wavelength. A theory is developed showing how the propagation parameters of the MTL device depend on the dielectric rod properties, and based on that, a measuring technique is devised for retrieving the loss angle and permittivity of the rod from the critical resonance frequencies and input impedance maximum values. Experimental results are presented to show the effectiveness of the method.      

软包装液体体积测量技术

目的实现软包装内液体体积的快速、非侵入测量。方法在研究亥姆霍茨共振器原理的基础上,分析共振腔体积改变对声学系统的影响;采用Virtual Lab软件对所设计的测试系统进行仿真计算,求取传递损失最大值频率与被测液体体积的关系;搭建软包装液体体积声学测试系统,采用Labview软件对管道入口、出口处的声音信号进行采集;采用声波分解法对信号进行分析,得到声学系统的传递损失。结果测试结果表明,软包装内液体体积由25增大至200 m L时(即共振腔腔体体积减小),测试系统传递损失的峰值所对应的频率由256上升至278 Hz。实验结果与仿真结果具有相同的趋势;系统的灵敏度为7.4 m L/Hz。结论所设计的基于亥姆霍茨共振器理论的声学测试装置可以实现对软包装液体体积的测量。     

梁模型三明治板的隔声预报

提出一种针对有限大三明治蜂窝板的隔声预报方法。在一定条件下,三明治蜂窝板被看成是正交各向异性的,通过对蜂窝板正交方向上切割下来梁的简单测 试,可以得到三明治蜂窝板的等效刚度,结合正交各向异性板的振动方程,把板的振动展开成模态叠加的形式并求解,最终可以得到一块有限大三明治蜂窝板的理论隔声公式,理论预报结果与实验室测量结果对比良好。     

Microwave-absorbing properties of silver nanoparticle/carbon nanotube hybrid nanocomposites

Silver (Ag) nanoparticles fabricated by chemical reduction process were grafted onto the surface of carbon nanotubes (CNTs) to prepare hybrid nanocomposites. The Ag/CNT hybrid nanomaterials were characterized using transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. The Ag/CNT hybrid nanomaterials were then loaded in paraffin wax, and pressed into toroidal shape with thickness of 1 mm to evaluate their complex permittivity and complex permeability by scattering parameters measurement method in reflection mode using vector network analyzer. The reflection loss of the samples was calculated according to the transmission line theory using their measured complex permittivity and permeability. The minimum reflection loss of the Ag/CNT hybrid nanocomposite sample with a thickness of 1 mm reached 21.9 dB (over 99 % absorption) at 12.9 GHz, and also exhibited a wide response bandwidth where the frequency bandwidth of the reflection loss of less than ?10 dB (over 90 % absorption) was from 11.7 to 14.0 GHz. The Ag/CNT hybrid nanocomposite with thickness of 6 mm showed a minimum reflection loss of ~?32.1 dB (over 99.9 % absorption) at 3.0 GHz and was the best absorber when compared with the other samples of different thickness. The reflection loss shifted to lower frequency as the thickness of the samples increased. The capability to modulate the absorption band of these samples to suit various applications in different frequency bands simply by manipulating their thickness indicates that these hybrid nanocomposites could be a promising microwave absorber.     

宽带在片SOLT校准件研制及表征

针对在片S参数校准,设计制作GaAs衬底SOLT校准组件,通过计算方法对校准组件中直通、开路、短路和负载校准件中偏置传输线的时延和损耗进行定义,运用基于NIST multiline TRL校准的测量方法对校准组件中开路校准件电容和短路校准件电感参数进行提取,结合直流电阻测试法测试负载阻值大小,实现对SOLT校准组件的完整表征。最后用自行研制并表征的SOLT校准组件校准在片S参数测试系统,通过测量无源器件验证校准效果,将测量结果与NIST multiline TRL校准后的测量结果比较,在20 GHz内传输幅度最大偏差0.1 dB,传输相位最大偏差3.5°。     

Comparison of cutoff wavelength measurements for single-mode waveguides

The intrinsic cutoff wavelength of the LP11 mode is investigated using three different types of measurement for an ITT single-mode fiber. Characterization of the far-field pattern of the LP01 mode gives a cutoff value approximately 660 nm, a near-field transmission experiment gives approximately 690 nm, and a refracted power measurement gives approximately 830 nm. We conclude that the refracted power technique is the best experimental method for the determination of the intrinsic cutoff wavelength of a fiber sample. The effect of the loss of coupling efficiency into the LP11 mode as cutoff is approached on the transmission and refracted power experiments is noted.