多孔吸声材料声学模型及其特征参数测试方法研究进展

噪声是载人航天器的重要环境因素之一,航天器环境噪声升高会直接影响航天员工作和休息,进而影响空间科学任务.然而,以往在轨运行的载人航天器存在较多噪声过大的问题,多孔吸声材料已经在国际空间站应用并取得良好的降噪效果,我国空间站预计2022年底建成,了解声学多孔材的声学模型以及吸声机理对我空间站运营阶段的降噪具有重要的意义.基于刚性框架假设,多孔吸声材料声学等效模型分为经验模型和唯像模型,Delany-Bazley是常用的经验模型,采用此模型不能对多孔材料吸声的性能提供精确的预测,唯象模型考虑了声波在材料孔隙和空腔中的传播,可以准确预测吸声性能,因此Johnson-Champoux-Allard唯象模型被众多学者应用.流阻、孔隙率、曲率、粘胶特征长度和热特性长度等多孔材料声学特性参数是准确建立多孔材料Johnson-Champoux-Allard模型的关键,流阻测试方法包括直接气流法、声学阻抗管法、交流法和比较法;孔隙率的测试方法分为直接测试方法和声学阻抗管测试方法;曲率、粘性特征长度和热特性长度可以通过超声波进行直接测试,直接测量通常比较复杂、不太可靠并且具有破坏性,反演优化方法是获得多孔材料曲率、粘性特征长度和热特性长度的常用方法.本文概述了多孔吸声材料在国际空间站的应用情况,综述了多孔吸声材料声学等效模型的研究进展,介绍了多孔吸声材料吸声原理、声学扰动基本方程以及声学属性参数的测试方法,重点介绍了多孔吸声材料声学等效模型中的经验模型和唯像模型,进而对多孔材料声学等效模型中的声学特征参数的测试方法进行详细论述.     

梯度弹性多孔材料吸声性能分析与优化设计

梯度孔隙率结构对多孔材料吸声性能有着很大的影响,可以拓宽多孔材料的吸声频带。以具有梯度孔隙率的弹性多孔材料为研究对象,基于Biot理论及传递矩阵法研究了常见梯度结构以及梯度差对吸声系数的影响,并利用多岛遗传算法(MIGA)寻求梯度结构的最优厚度分布。研究表明:通过对孔隙率和层厚的合理设计,可以提高期望频段的吸声性能,其中,孔隙率由高到低再到高的梯度结构可以明显提高宽频吸声系数,这对弹性多孔材料的设计及其在声学包上的应用具有重要的指导意义。     

结构因素对多孔材料吸声性能的影响

多孔吸声材料由于具有比重小、取材范围广、加工制造工艺相对简单等优点而在吸声降噪领域显示出了广阔的应用前景.为了更好的研究与设计多孔吸声材料,总结和分析了多孔材料中孔隙率、孔隙形貌、孔径、厚度和空腔等结构因素对材料吸声性能的影响.发现孔隙率和孔径过大或过小均不利于吸声性能的提高,可能存在一最佳值;而厚度和空腔的增加能有效...     

纤维对硅酸盐基多孔材料吸声性能的影响

以硅酸盐水泥为主要原料,通过原位自组装技术制备了硅酸盐基多孔材料.通过改变纤维的添加量,制备了含有不同种类和不同纤维添加量的多孔材料,并分析了纤维对多孔材料的吸声性能的影响.采用驻波管法测试多孔材料的吸声性能,通过立体显微镜(SM)分析材料形貌.结果表明,PP纤维和玻纤对材料吸声性能影响显著:当PP纤维长度为19mm时,材料的吸声效果最好;随着PP纤维掺量的增加,材料的中低频吸声性能提高,中高频吸声性能降低;随着玻纤掺量的增加,材料的中低频吸声性能提高,中高频吸声性能降低.     

金属纤维多孔材料复合结构的声学性能

针对精密电子元器件等领域在受限空间内的噪声处理难题,以纤维直径为8μm~20μm的316L不锈钢纤维为原料,首先采用真空烧结技术制备了厚度为2 mm,孔隙率为55%~76%的不锈钢纤维多孔材料,然后将其与穿孔板、金属薄板复合并采用真空烧结技术制备了厚度为3~4 mm的复合结构,利用4206型声学阻抗管测试了金属纤维多孔材料及其复合结构的吸声系数和隔声量。系统分析了不锈钢纤维多孔材料的孔隙率与纤维直径、穿孔板结构参数及金属薄板对复合结构的吸声性能和隔声性能的影响规律。研究表明:当金属纤维多孔材料的厚度为2 mm时,宜选择单层复合结构进行噪声处理,其吸声系数稳定在0.3~0.4;当声波频率超过3000 Hz时,宜选择梯度复合结构进行噪声处理,其吸声系数最高可达0.75。穿孔板显著提高了复合结构的吸声系数。相对于穿孔板吸声结构而言,复合结构将第一共振频率向低频方向移动且将共振频率附近的吸声频带变宽。在梯度金属纤维多孔材料层间添加金属薄板后,可进一步提高其吸声系数。     

多孔吸声材料的吸声特性研究

多孔吸声材料具有吸声系数高、吸声频带宽等优点,采用多孔吸声材料的圆管理论模型,并对此进行数学编程计算与分析,结合工程实际,研究多孔材料孔隙率、孔径、厚度以及结构因子对多孔材料吸声性能的影响,对实际的设计有一定参考价值。     

轻质多孔陶瓷的制备及吸声性能研究

通过模压法成功制备轻质多孔陶瓷吸声材料, 采用JTZB吸声系数测试系统研究造孔剂粒径、含量以及样品厚度对多孔陶瓷材料吸声性能的影响。结果表明: 造孔剂含量为50vol%时, 大孔径多孔陶瓷吸声性能优于小孔径多孔陶瓷; 随着造孔剂含量的增加, 第一吸收峰从低频向高频移动, 峰值从0.41增加到0.82, 孔隙率过高和过低都不利于提高材料吸声性能; 样品厚度从10 mm增加到30 mm, 第一吸收峰逐渐向着低频方向移动; 造孔剂含量为60vol%, 样品厚度为20 mm时, 样品整体具有优异吸声性能, 并逐层在其背后加入空腔发现, 随着空腔层数的增加, 样品的第一吸收峰从高频向低频移动, 平均吸声系数逐渐增大。     

FeCrAl纤维混合毡的吸声性能

通过分散机将3种不同丝径的FeCrAl纤维均匀分散后,由铺毡机铺制出混合毡,将该单层混合毡制成一定厚度的多孔纤维吸声材料。测定结果表明,不同材质、同一丝径的两种纤维多孔材料,具有相似的吸声性能;利用混合毡所制成的纤维多孔材料具有与其它纤维多孔材料一样的吸声性能变化规律;无论怎么样改变单层材料的内部结构,其吸声性能均差于正梯度结构的吸声性能。     

金属橡胶材料双层结构吸声特性研究

理论研究了金属橡胶材料双层结构吸声特性。根据金属橡胶材料声学特性参数计算式,推导出两种基本双层吸声结构—置于刚性墙和带有空气层吸声结构的声阻抗率和吸声系数计算式。确定了流阻率是决定金属橡胶材料声学特性的基本参数。分析了各层材料厚度、流阻率及空气层厚度对两种吸声结构吸声性能的影响关系,对比分析了双层吸声结构与单层吸声结构的吸声性能。研究结果表明:通过合理设计双层吸声结构,可使其在很宽的频率范围内具有良好的吸声性能。     

低温环境对多孔材料声学性能的影响研究EI北大核心CSCD

针对低温环境对船舶多孔舾装材料声学性能的影响,阻抗管吸/隔声性能测试研究是被开展。基于传递函数法进行不同环境影响下玻璃棉材料的声学性能测试,试验给出了温度和含水率对玻璃棉材料声学性能的影响规律;在此基础上,以内河破冰船为例分析了低温环境下玻璃棉材料声学性能变化对舱室噪声的影响。研究表明,低温环境下玻璃棉的高频吸声系数将随含水率增加而显著下降,插入损失随含水率增加而增加,但低温环境导致玻璃棉材料声学性能的变化不会提高舱室噪声的超标风险。     

Material selection for the torque tubes of large superconducting rotating machinery

This report identifies properties to be considered when selecting materials used in construction of torque tubes for rotating superconducting field windings in electrical machinery.The main design requirements are stated and the groups of material properties that influence directly the mechanical and thermal performance of a torque tube are derived. Most desirable is a low thermal conductivity to modulus of elasticity ratio which governs the refrigeration expenses and the tube wall aspect ratio (thickness/length). Numerical examples point out that fibre-reinforced plastics are potential candidates for use in torque tubes.     

穿孔管阻性消声器消声性能计算及分析

一维解析法和三维子结构边界元法被用于计算和分析穿孔管阻性消声器的消声性能，以及考查消声器内非平面波对消声特性的影响。直通穿孔管阻性消声器传递损失的预测结果与实验测量结果比较表明：一维解析法只适合于消声器的低频声学性能计算，对于高频声学性能的精确预测需使用三维计算方法。边界元法进而被用于研究吸声材料的填充密度（流阻率）和几何参数对穿孔管阻性消声器消声性能的影响。增加吸声材料的填充密度、穿孔管的穿孔率和穿孔长度、以及吸声材料的厚度，均能有效地改善阻性消声器的中高频声学性能，而对消声器的低频消声效果影响较小。     

Oxygen barrier properties of thermoformed trays manufactured with different drawing methods and drawing depths

A comparison was made of oxygen barrier properties and wall thickness distribution of different thermoformed trays. The thermoformed trays were manufactured with three drawing depths and two different thermoforming methods; with and without plug‐assist. Four different polymer combinations were evaluated. The oxygen transmission rate (OTR) [cm³/(package/day)] was measured at three conditions (23°C/50% relative humidity (RH) with 0% RH inside, 6°C/80% RH with 0% RH inside, and 6°C/80% RH with 100% RH inside. Wall thickness was measured at five different positions in the trays. In general, temperature had more influence on the oxygen transmission rate (OTR) than the humidity. The OTR in the packages increased with increasing drawing depth, but the increase was not linear. Other effects besides thinning, such as orientation, may have influenced the OTR, since the relationship between OTR, given as cm³/(m²/day), and the drawing depth was not linear. Plug‐assisted thermoforming only had an effect on the OTR in trays with 70 mm drawing depth made of 600 µm thick laminate of PP/PE, which was probably due to exceeding the maximum drawing depth of this material. There was no correlation between the OTR value in the packages and the wall thickness in either of the positions, but a quite high correlation between the drawing depth and the relative wall thickness in all measured positions was observed. Copyright © 2004 John Wiley & Sons, Ltd.     

Characterization and humidity sensing of ZnO/42° YX LiTaO3 Love wave devices with ZnO nanorods

Love mode surface acoustic wave devices based on ZnO/42° YX LiTaO₃ were characterized with the thickness of the sputtered ZnO guiding layer varied from 250 nm to 1.18 μm. Phase velocity, temperature coefficient of resonant frequency, sensitivity, electromechanical coupling coefficient and humidity sensing of the Love mode SAW devices were studied as a function of the ZnO layer thickness. With increasing ZnO thickness over the range of thickness values we have examined, the sensitivity of 42° YX LiTaO₃ to liquid loading increased and the values of electromechanical coupling coefficient decreased. The device with a thickness of 250 nm showed the best humidity response. ZnO nanorods were grown on this device and its humidity sensing performance has been further improved due to their large surface-to-volume ratio of the ZnO nanorods.     

无菌包装袋的透氧性研究

目的研究无菌包装袋的透氧率与其厚度、材质及温湿度的关系。方法用厚度测试仪测量无菌包装袋厚度,用红外光谱仪检测材质、用氧气渗透测试仪测试透氧率,并比较厚度、材质和温湿度对透氧率的影响。结果无菌包装袋的透氧率随厚度的增加而减小;材质对无菌包装袋的透氧率影响较大;无菌包装袋的透氧率随着温度的增加而增加,阻氧性能下降。结论无菌包装袋的厚度、材质和环境温度对其透氧率均有影响,而相对湿度对透氧率无显著影响。     

Effects of stacking thickness on the damage behavior in CFRP composite cylinders subjected to out-of-plane loading

The purpose of this study is to evaluate effects of stacking thickness on the microscopic damage behavior in a filament wound carbon fiber reinforced plastics (FW-CFRPs) composite cylinder subjected to impact or quasi-static out-of-plane loading. From both tests, thicker CFRP improved the stiffness of the cylinder and decreased the resultant plastic deformation due to indentation. From the cross-sectional observation, it is clarified that fiber breakages were localized for the specimens with impact tests more than 10-layers and specimens with quasi-static tests more than 15-layers. In order to discuss the relation between the damage and the absorbed energy, damage depth ratio was defined as fiber damage depth per unit CFRP thickness. To normalize the effect of thickness, absorbed energy ratio was also defined as absorbed energy per unit CFRP thickness. Absorbed energy ratio as a function of absorbed energy ratio was expressed as one master curve regardless of loading conditions.     

Low frequency acoustic microscopy and pattern recognition for studying damaged and anisotropic composites and material defects

In recent years, acoustic microscopy has been found to be very useful for characterizing engineering as well as biologic materials. With the present state of knowledge on acoustic microscopy, one can obtain the surface wave velocity of a homogeneous specimen or coating thickness of a coated material and produce images of near surface internal defects and inhomogeneities in a specimen. Applications of acoustic microscopy for obtaining material properties of anisotropic specimens and detecting material defects at a greater depth are meager because commercially available acoustic microscopes are insensitive to direction-dependent material properties and they, in general, have poor penetration properties because of high operating frequencies. Recently at the University of Arizona an unconventional low frequency (0.5–2.5 MHz) acoustic microscope has been fabricated where the microscope lens has been replaced by two ultrasonic transducers with cylindrical concave faces; one works as a transmitter and the other one works as a receiver. Using this arrangement, it has been found that it is possible to detect internal damages in a material and identify material anisotropy in fiber-reinforced composite plates. These capabilities of the microscope are demonstrated in this paper by presenting some experimental results along with theoretical justifications. Then pattern recognition techniques are used to solve the inverse problem, that is, to predict the type of material defect from reflected acoustic signals.     

消声器气流再生噪声测试技术研究

摘 要：基于双传声器传递函数法,发展了一种采用传声器间距组合的消声器气流再生噪声测量方法。通过对三种取样管声场和流场分析,重点比较了其导流透声效果,分析表明选取的取样管能真实反映主管道内的声压,且导流透声结构对主管道内声场和流场的影响较小。在无气流条件下,试验验证了声场仿真计算的结果。在设计的试验台上对一穿孔管消声器测试表明：研究的测量方法以及研制的试验台能够较准确的测试消声器在不同气流速度下的气流再生噪声。     

室外环境参数对空气源热泵翅片管蒸发器动态结霜特性的影响

对一台空气源热泵空调器在不同环境条件下室外换热器的动态结霜性能进行了实验研究，分析了进风温、湿度对热泵空调器结霜量及霜层厚度的影响。实验中考虑了结霜引起的热泵系统蒸发温度及风机流量的变化，采用显微照相法测量翅片表面霜层厚度，结霜量则通过测量蒸发器进出口含湿量的方法来获得。实验结果表明，室外换热器结霜量随时间线性增长，而翅片表面霜层厚度则分为初始段、匀速增长段和快速增长段三个阶段；在结霜循环的最后20％～30％的快速增长段内霜层生长速率大大加快，可达匀速生长段霜层生长速率的2．4，3．3倍。对于不同的工况，蒸发器均在进风温度0～3℃附近时结霜最为严重，且相对湿度对霜层厚度的影响要大于对结霜量的影响。     

Dependence of sonoluminescence intensity on the geometrical configuration of a reactor cell

Dependence of sonoluminescence (SL) intensity on the geometrical configuration of a reactor cell is studied theoretically and experimentally. The model is a rectangular glass cell set in a water-cooling bath. Ultrasound is irradiated from the bottom of bath into the cell. Theoretical analysis of transmitted acoustic energy assuming a plane acoustic wave clarified the influences of distance between the transducer and the cell bottom, thickness of the cell bottom, and water depth in the cell. The theory is examined through intensity measurement of SL emitted in the cell using a photomultiplier tube. Dependence of SL intensity on the above parameters agreed with the theory very well. Distributions of SL are also observed using a high sensitivity CCD camera and are compared with optically visualized sound fields to show the relationship between the sound field and the SL