用等效参数法研究含球形空腔弹性体的吸声性能

复合弹性材料已广泛应用于水声吸声材料中。本文研究的对象是含有球形空气空腔、以均匀粘弹性介质为基材的复合吸声结构。文中以散射理论和可变形粘弹性介质力学的基本理论为基础，建立了该复合结构的物理模型，引入了等效参数的概念来研究它的声学特性，并且分析了结构参数对其声学性能的影响。     

狭缝空腔间粘弹性体中弹性波传播特性的研究

利用笛卡尔坐标下的Kelvin-Voigt线性粘弹性模型,研究了无限长粘弹性狭缝通道中波的传播和衰减。利用自适应绕数求根方法,针对具有狭缝形空腔周期性分布覆盖层的吸声问题,求得频散方程的根,并且得到无限长狭缝空腔中相速度频散曲线和衰减曲线。分析了各阶模式对无限长粘弹性狭缝结构中波传播的相速度和衰减的影响。通过引入复粘弹性模量,粘弹性波动方程具有弹性波动方程相对应的形式,计算中可用复值粘弹性模量代替相应的弹性模量。粘弹性狭缝结构中所有波传播模式均存在衰减,高阶波在某个频率以下衰减非常大,而在该频率以上逐渐减小;最低阶模式的相速度与材料无损耗的情况非常接近。粘弹性狭缝结构中波传播的衰减特性不仅与狭缝的结构参数有关,还与粘弹性材料本身的复弹性模量有关。     

饱和土中球形空腔稳态振动及其在基桩中的应用

利用Ｂｉｏｔ饱和土波动理论求解了饱和土中球形空腔内部受周期性动荷载作用下的动力响应，并分析了球形空腔表面排水条件和振动频率对位移和孔隙水压力的影响。利用上述结果分析了桩在稳态振动下桩端的刚度和阻尼。     

基于共振法的粘弹性材料动态力学参数测试方法研究

为了验证直接测量粘弹性材料共振参数来获得材料动态力学参数的可行性,用某种试验材料对共振法测试原理对进行了试验,结果表明:共振法的测试结果与粘弹仪的测试数据吻合较好,基于共振法的测试原理是可行的.     

局域共振型空腔覆盖层的低频吸声机理及调控规律研究

声学覆盖层的低频吸声特性对潜艇声隐身性能具有重要影响.综合考虑空腔型覆盖层结构和局域共振型薄膜材料的低频吸声性能,建立局域共振型空腔覆盖层的有限元模型,研究复合结构在10 Hz～2000 Hz频段内的吸声特性,并采用局域共振理论和模态分析揭示复合结构的吸声机理,进一步得到复合结构低频吸声性能的调控规律.研究结果表明:(...     

多孔材料对轮胎空腔共振降噪机理的研究EI北大核心CSCD

轮胎空腔共振噪声对汽车NVH性能有决定性影响。为研究轮胎内部添加多孔材料的降噪机理,从轮胎力传递率出发,通过试验验证了轮胎力传递率与空腔噪声的一致性;建立了轮胎力传递率模型,并验证了模型的准确性;通过该模型研究了多孔材料对轮胎空腔共振噪声的降噪机理。结果表明:多孔材料对轮胎空腔共振降噪效果是耦合结构振动与声学降噪共同作用的结果,选择多孔材料时要综合考虑多孔材料的物理参数与声学参数,研究结果为改善汽车NVH性能和提高低噪声轮胎设计水平奠定理论基础和方法指导。     

基于声管测量的粘弹性介质动态力学参数辨识方法

提出一种通过声管测量粘弹性覆盖层反射系数,识别粘弹性动态力学参数的方法。分别设计实心覆盖层和圆柱空腔覆盖层,测量实心覆盖层的反射系数可以计算得到粘弹性介质的复纵波声速,测量圆柱空腔覆盖层的反射系数、并结合求解粘弹性圆柱管的特征方程可以获得粘弹性介质的复剪切波声速,进而计算复杨氏模量和复泊松比。最后,对某种橡胶材料进行了声管测试,并对粘弹性动态力学参数的识别结果进行了分析和讨论。     

微观非均匀粘弹性材料吸声性能研究

橡胶类粘弹性材料作为吸声覆盖层时,可在内部加入空腔或掺杂其它材料改善其吸声特性.当大量分布的空腔尺度远小于波长时,这种微观非均匀的材料在宏观上看是均匀的,可以用一种均匀材料来等效.本文对含小球形空腔的橡胶材料,数值计算了等效介质参数及吸声系数.研究了腔大小、含量及橡胶材料参数对吸声的影响.     

带空腔尖劈吸声器吸声性能的研究

本文研究带有空腔的锥形主声器的吸声性能。文给出了一种计算该吸声器的吸声系数的方法，并对吸声系数与频率的关系进行计算机仿真。仿真结果表明：带有空腔的尖劈吸声器相对普通尖壁吸声器，除保持高频段较好上性能外，在低频段吸声系数有显著提高；通过改变「空腔结构可以改善吸声器的低频吸声性能。     

球形石墨空腔电离室内部电场的研究

国际上辐射剂量计量基标准电离室多采用球形或圆柱型空腔电离室,其腔室自身几何对称。不同形状的收集极置于腔室中,会影响腔室内部的几何对称性,进而对其内部电场的均匀性和电荷的收集产生一定的影响,作为绝对测量需要对电离角响应方向性进行修正。该文采用Ansoft Maxwell 2D程序建立一个石墨空腔电离室灵敏体积内的静电场模型,分别计算含有3种不同形状收集杆腔室内的电势分布;并对同系列大体积电离室收集杆是否产生放电现象进行了分析,对同类型电离室相关指标的优化设计提供一定的参考。     

分数导数黏弹性准饱和土中球空腔振动特性

在频率域内用解析方法研究分析了简谐轴对称荷载和流体压力作用下分数导数黏弹性准饱和中球空腔的稳态响应问题。将土骨架等效为具有分数阶导数本构关系的黏弹性体,基于Biot两相饱和介质模型,通过势函数推导求得了边界部分透水时分数导数粘弹性准饱和土中球空腔的位移、应力和孔压等的解析解。根据界面连续性条件,确定了待定系数的表达式。在此基础上,考察了准饱和土各参数对动力响应的影响,结果表明：轴对称荷载和流体压力两种情况时,相对渗透系数对动力响应的影响有较大的差异。分数导数本构模型更合理地描述了准饱和土中球空腔的振动特性。     

Random response of a viscoelastic dielectric elastomer spherical balloon

The viscoelastic behavior of the dielectric elastomers (DEs) plays an important role in the time-dependent mechanical deformation. The increasingly demands to precise utilities and controls of the DEs are motivating the researchers to insight into the influence of the viscoelasticity on the dynamical response. In this paper, the random response of a DE spherical balloon subjected to electrical and/or mechanical disturbances is analytically studied. Based on a rheological model of two parallel units, the governing equations of the stretch ratio of the deformed and undeformed radius of the spherical balloon are derived from the Lagrange equation. Firstly, the influences of the pressure in balloon and the voltage on the membrane on the equilibrium positions are discussed. The big pressure and high voltage will both induce static instability. Then, by expanding the motion equations around the static equilibrium position, the relation of the resonant frequency with the viscoelasticity are revealed. Finally, an approximation procedure is adopted, which pave the way to adopt the stochastic averaging. The probabilistic density function (PDF) of the stretch ratio around the equilibrium position is obtained. The influences of system parameters, i.e., viscoelasticity, voltage, pressure, on the probability distribution are investigated in detail. The accuracy of the proposed procedure are also been evaluated by the Monte-Carlo simulation (MCS).     

Propagation of transient pules from a spherical cavity in a viscoelastic medium

The problem of an impulsively applied pressure acting on the surface of a spherical cavity in a linear viscoelastic medium is solved by an approximate inversion of the Fourier transform. The method can be applied to general models of viscoelasticity described by the Boltzmann superposition principle, with relaxation or creep functions given analytically or numerically in the time or the frequency domain.     

The spherical problem for a linear viscoelastic material with environment-dependent properties

This paper is concerned with linear viscoelastic materials whose mechanical properites are affected by environmental factors such as temperature, and by ageing. Solutions are given for mixed and unmixed boundary value problems in a thickwall spherical shell. The environment fields are radially symmetric, but arbitrarily time-dependent. The solutions may be calculated to any required degree of accuracy by considering a sufficient number of terms in the solution series.     

球形LiFePO4材料碳包覆的研究

主要研究了采用不同碳源和掺碳量包覆对液相共沉淀-碳热还原法制备的球形LiFePO4材料性能的影响.结果表明,采用过量5%葡萄糖作碳源制备的材料在0.1C下,首次放电比容量达到了154.6mAh/g,并且循环性能良好.     

敷设空腔覆盖层水下复杂目标的声散射特性研究

研究敷设空腔覆盖层水下复杂目标的声散射特性具有重要的意义。首先通过建模软件构建目标模型，然后利用分层近似法，结合多层介质的传递矩阵方法，将含有变截面空腔的吸声覆盖层分为多个可视为圆柱空腔结构的薄层，进而实现复合结构的声反射系数的求解，最后利用基于戈登(Gordon)积分的板块元方法对目标强度进行预报，并针对复杂目标提出基于光线投射的可见面元判别方法。在此基础上，以BeTSSi Ⅱ标准模型为例，研究敷设空腔覆盖层的水下复杂目标的声散射方位特性和频率特性。结果表明：文中提出的基于光线投射的可见面元判别方法可以快速有效地提供板块元方法所需的可见面元；板块元方法对BeTSSi Ⅱ标准模型的预报结果可以很好地反映其目标强度的特征及其变化规律；模型敷设空腔覆盖层可以有效降低目标强度，与敷设等厚均匀覆盖层时相比，复合结构声反射系数曲线的第一谷值频率降低，在频率较低时敷设空腔覆盖层的吸声效果更好，可以进一步减小目标强度。该研究有助于实际工程中实现对水下平台散射特性的快速预报。     

Determination of the relaxation modulus of a linearly viscoelastic material

In this paper, a numerical method for computing the relaxation modulus of a linearly viscoelastic material is presented. The method is valid for relaxation tests where a constant strain rate is followed by a constant strain. The method is similar to the procedure suggested by Zapas and Phillips. Unlike Zapas-Phillips approach, this new method can be also applied for times shorter than t ₁/2, where t ₁ denotes time when the maximum strain is achieved. Therefore this method is very suitable for materials that experiences fast relaxation. The method is verified with numerical simulations. Results from the simulations are compared with analytical solution and Zapas-Phillips method. Results indicate that the presented approach is suitable for estimating the relaxation modulus.     

Large-strain dynamic cavity expansion in a granular material

The dynamic problem of the symmetric expansion of a cylindrical or spherical cavity in a granular medium is considered. The constitutive behaviour of the material is governed by a hypoplasticity relation for granular soils capable of describing both monotonic and cyclic deformation. The problem is solved numerically by a finite-difference technique. A nonreflecting boundary condition used at the outer boundary of the computational domain makes it possible to model a continuous multi-cycle loading on the cavity wall. The solution is illustrated by numerical examples. Possible geomechanical applications to the modelling of the vibratory compaction and penetration in granular soils are discussed.     

Large-strain dynamic cavity expansion in a granular material

The dynamic problem of the symmetric expansion of a cylindrical or spherical cavity in a granular medium is considered. The constitutive behaviour of the material is governed by a hypoplasticity relation for granular soils capable of describing both monotonic and cyclic deformation. The problem is solved numerically by a finite-difference technique. A nonreflecting boundary condition used at the outer boundary of the computational domain makes it possible to model a continuous multi-cycle loading on the cavity wall. The solution is illustrated by numerical examples. Possible geomechanical applications to the modelling of the vibratory compaction and penetration in granular soils are discussed.