在含气孔粘弹媒质中非线性声传播特性

1引言: 共振型消声是实现水下吸声的一种基本形式.结构共振消声是通过在基底粘弹(通常为橡胶类粘弹材料)材料中嵌入声学结构--各种类型和大小的空腔,利用空腔的共振吸收增加损耗.本文运用等效媒质法,着重对含气孔粘弹材料的二阶非线性声场做了研究.     

粘弹性材料覆盖层对于声波透射及反射的衰减作用

本文采用Thomson Haskell方法计算了在钢板上覆盖橡胶和高分子聚合物对于反射及透射声波所产生的影响 ,并且研究了在橡胶层下填充不同厚度的粘弹性高分子聚合物对于压力声波的衰减作用。本文还给出了具有不同空洞体积比的填充材料的减噪效果。     

声波在低声速海底上的反射

用爆炸声源进行了海底反射特性的测量,获得了掠射角2°到85°之间的海底反射系数.应用一个多层的海底模型对海底反射系数进行了理论计算,在这个模型中,把最下层看成为固体的半无限空间.假设这些层是具有吸收的,而且各层之间有一个相互平行的分界面.对现场采集的底质样品测量了沉积物的声速,并应用于理论计算中,表明这一海区的海底是低声速沉积物,中间夹杂着一些薄的高声速层.在理论预言的一些角度上,示波器记录到的海底反射信号相对于入射波相位发生反转.将反射系数的理论值与实验值在1、2、和4千赫兹的频率上做了比较,一般说来,在整个范围内符合的较好.在贯穿角附近,发现测得的反射系数随着频率有一个奇异的增加,这大约可以用下层反射体的存在来解释.     

结构阻尼与高分子粘弹材料

一、前言 随着现代科学技术的飞速发展,火箭,卫星、飞船、舰艇、火车、汽车等的功率和速度都有很大提高,这必然会带来宽频带的随机振动和噪声,並将激发起结构和仪器的许多共振峰,导致结构破坏、仪器失灵。这类振动和噪声的控制就成了必要的先决条件。另外,振动和噪声会对人们的正常生活、工作甚至身体健康带来不良的影响,因此许多国家都拟定了噪声标准並以法律形式固定下来。     

电流变液复合层的声波透射行为

对夹于两柔性电极间的淀粉硅油电流变液进行了声波透射实验研究。结果表明: 电流变液的声波透射有较强的频率选择性。淀粉体积分数为31 %时, 在100～160 Hz 频率范围内, 随电场强度E 增加, 相对透射率T出现增强峰, 其它频率段T 基本不随E 变化。当E = 2. 0 kV/ mm 时, 在130 Hz 处透射峰的相对透射率约为零电场时的7 倍。透射波相位随E 增大, 入射波频率为105 Hz 时, 李萨如图椭圆主轴随E 增加顺时针转动45°。电场强度加大, 增强峰的幅值和相位表现出可调节的特征。随颗粒体积分数从16 %增大到31 % , 电流变液中声波最大相对透射率( E = 2. 0 kV/ mm) 从1. 8 变为7 , 增强峰的响应频带向高频移动。分析认为, 电流变液中场致微结构与声波的相互作用可能是出现这些现象的原因。      

高分子材料粘弹性能测定方法

本方法列出了高聚物动态试验的一些定义。利用受控频率，受控振幅及受控形式的周期性变化的作用力或形变，采用一定的参数条件，用法国ＭＥＴＲＡＶＩＢ的ＭＡＫ－０４型粘弹分析仪测定高分子材料的粘弹性能。     

水下压电/弹性材料复合层球壳声波反射的数值研究

采用有限单元计算软件ANSYS对无限水域中压电/弹性材料复合层球壳的声波反射进行了数值研究.研究表明,在压电层中加载适当的电压可以在一个圆锥形的流体区域内有效地减小壳体对于外来声波的反射,并且有可能完全消除任意选定空间点上的反射.     

粘弹材料复弹性模量的全频段表征与测量

1引言 声学上常用的吸声材料多为高阻尼的有机材料,这类材料在力学性能上表现为恒应力加载下的蠕变行为和恒应变加载下的应力松弛行为,在声学性能上表现为材料响应比激励明显滞后,即损耗角较大,并且材料的性质强烈依赖于激励频率.     

高分子材料粘弹过程的混沌运动

从混沌学的角度，讨论了高分子材料的粘弹行为，首先讲座了非晶高分子分子运动的混沌性，其次以混沌学的观点重新认识了玻璃化转变和熔体破裂等主要粘弹性质，最后介绍了混沌应用与控制。     

二层粘弹阻尼复合结构的优化设计

构造二节点八自由度有限元模型对二层粘弹弱约束阻尼复合结构的动力学特性进行了数值分析，其计算结果与实验结果基本一致．利用此有限元模型研究了各层阻尼材料的几何及物理参数对复合结构阻尼性能的影响．     

有阻尼负载时圆柱壳的声传递特性分析

摘要 本文分析研究有阻尼负载圆柱壳的声波透射问题,从经典薄壳理论出发,给出有阻尼负载的圆柱壳振动微分方程,结合均匀流场中的波动方程,利用流-固耦合边界条件,给出了声波传递损失的公式,并计算了相应的算例,研究了有阻尼负载圆柱壳中的声波传递特性。分析了声波入射角度、阻尼厚度、壳体厚度等对声波传递损失的影响,得到了有意义的结论,旨在为工程设计提供参考。     

Dynamic characteristics of cylindrical hybrid panels containing viscoelastic layer based on layerwise mechanics

The viscoelastic damping model of the cylindrical hybrid panels with co-cured, free and constrained layers has been developed and investigated by using the refined finite element method based on the layerwise shell theory. The transverse shear and normal strains and the curved geometry are exactly taken into account in the present layerwise shell model, which can depict the zig-zag in-plane and out-of-plane displacements. The damped natural frequencies, modal loss factors and frequency response functions of cylindrical viscoelastic hybrid panels are compared with those of the base composite panel without a viscoelastic layer. The difference in the free vibration and damping of the thin and thick composite laminates and the viscoelastic sandwiched beam between full and partial layerwise theories is verified by comparison with the published results. Various damping characteristics of cylindrical hybrid panels with free viscoelastic layer, constrained layer damping, and co-cured sandwich laminates are investigated. Present results show that the full layerwise damping model accurately predicted the vibration and damping of the cylindrical hybrid panels with viscoelastic layers.     

Gas-storage ice grown from water containing microbubbles

Gas-storage ice is the ice that contains various functional gas pores, and can be produced by freezing water in which a desired gas is dissolved. In this conventional method, however, the gas content in the ice is limited by the gas solubility in water. To overcome this limitation, we developed a method to produce gas-storage ice from water in which microbubbles of a desired gas are dispersed, and then obtained images of the structural features of pores formed in the ice prepared using this microbubble method. The images clarified the interaction between a microbubble arriving at an ice–water interface and an existing pore already formed in the ice. The air content in ice prepared using the microbubble method was higher than that prepared using the conventional method, and was about three times higher than the solubility of air in water.     

Acoustic and effective material parameters of heterogeneous viscoelastic bodies

Summary Acoustic waves propagating through a special class of random viscoelastic bodies are considered. These media are assumed to be composed ofM (M=1, 2, 3, ...) distinct and linearly viscoelastic materials (phases). All these phases are randomly dispersed in the volume of the body in the form of grains, perfectly bonded together. Assuming the mean displacement field to be in the form of attenuated plane waves, the equations for the fluctuating part of the displacement were solved formally for the case of small, moderate and large inhomogeneities. Subsequent to this, equations and formulae determining the effective complex moduli tensor of the heterogeneous body as well as the propagation velocity and attenuation coefficient are derived for the mean displacement field propagating through such media in the form of acoustic plane waves.     

Thermocapillary instability of a viscoelastic liquid layer

Summary The stability of a layer of viscoelastic fluid heated from below is studied in the case that the instability is driven by surface-tension gradients at the upper surface. The operative parameter for instability is the Marangoni number and the critical value of this parameter is calculated as a function of Prandtl number, heat-transfer coefficient and elasticity parameters. It is shown that when the elasticity is very small instability sets in as steady convection, as for a Newtonian fluid, but at larger elasticities oscillatory convection is the first mode of instability to appear.With 5 Figures     

中高频段下的粘弹性材料声学参数测量

为了实现粘弹性材料在高频段上的声学参数测量,提出一种自由场测量方法,通过测量目标的水下散射声场指向性,计算目标散射场声压的前几阶勒让德系数,建立以目标的材料声学参数为变量的数学模型,并运用遗传算法进行参数反演.仿真结果表明以铝球的杨氏模量(E)为例,不存在声场误差的情况下反演精度可达0.0014%,铝球散射场的实验数据也提供了较高的参数反演精度.将此方法应用于中高频段上某种成分的粘弹性材料参数测量,成功地获取了其在此频段上的声学参数.提高目标散射场的测量精度有利于目标材料反演精度的提高.此方法避免了对声压相位的测量,减少了影响精度的因素.     

Pressure and flow pulses in viscoelastic arterial models with reflection sites

Summary Herein we develop a linear one-dimensional model for impulse propagation in fluidfilled tubes. Area changes are related to pressure changes by means of convolution integrals of the creep or relaxation function for the tube wall material. The model is employed to study the propagation of pressure and flow pulses along initially uniform tubes and their subsequent interaction with various junctions characteristic of the arterial system.With 2 Figures     

Acoustic remote sensing of the boundary layer

An acoustic echo sounder (called sodar) has been developed, designed and fabricated. This equipment has been operating successfully for several years and has been shown to have important applications in the areas of air pollution control/studies, microwave and millimetre wave radio communication including troposcatter, aviation and micrometeorology. Work on the development of the sodar was taken up at the National Physical Laboratory (npl) in 1972. At that time, this was one of the few equipment of its kind in the world. It has been designed in the laboratory and has been built with indigenous components. The equipment currently probes the thermal structure of the atmosphere upto a height of 700 m but can be extended to a kilometre. Two sodars are in operation-one at the National Physical Laboratory, Delhi and the other at the Micrometeorological Laboratory, Tarapur in collaboration with barc, Bombay. The design criteria of the npl sodar and experiments with it are described in this paper. We believe that the technique will soon become an important tool in the areas of micrometeorology, radio communication, aviation and air pollution studies.     

Transformation of hydrogen trapped onto microbubbles into H platelet layer in SI

Features of a process of delamination of a crystalline silicon layer from a silicon wafer along a hydrogen platelet layer formed by r.f. plasma hydrogenation are described. The process involves first making a buried layer of nuclei for hydrogen platelets. Ion implantation of inert or low-soluble gases is used to form the layer. The nuclei are microbubbles that appear along the R_p plane of implanted ions. Results for argon are presented. Wafers implanted with a dose of 10¹⁵ cm^–2 are then hydrogenated with an r.f. plasma. During hydrogenation, atomic hydrogen diffuses into the silicon wafer and collects onto internal surfaces of the microbubbles. Then the hydrogen increases the internal surface of the microbubbles by growing platelet-type extensions to the microbubbles. The extensions grow preferentially along the buried-layer plane. A silicon layer above the layer of grown platelets was delaminated through a pre-bonding/cut/post-bonding sequence as in a standard layer-transfer process. The plasma hydrogenation of the trap layer may be used as a step in a process of fabricating of SOI wafers with a very thin top crystalline silicon layer. Also, implant doses needed to form the microbubble trap layer are much lower than doses of direct implantation of hydrogen in the layer-transfer process.