The nonlinear propagation of acoustic waves in a viscoelastic medium containing cylindrical micropores

Based on an equivalent medium approach, this paper presents a model describing the nonlinear propagation of acoustic waves in a viscoelastic medium containing cylindrical micropores. The influences of pores＇ nonlinear oscillations on sound attenuation, sound dispersion and an equivalent acoustic nonlinearity parameter are discussed. The calculated results show that the attenuation increases with an increasing volume fraction of micropores. The peak of sound velocity and attenuation occurs at the resonant frequency of the micropores while the peak of the equivalent acoustic nonlinearity parameter occurs at the half of the resonant frequency of the micropores. Furthermore, multiple scattering has been taken into account, which leads to a modification to the effective wave number in the equivalent medium approach. We find that these linear and nonlinear acoustic parameters need to be corrected when the volume fraction of micropores is larger than 0.1%.

Dynamic anti-plane characteristic on an infinite piezoelectric medium with a movable rigid cylindrical inclusion

Scattering and dynamic stress concentrations of time harmonic SH-wave in an infinite elastic piezoelectric medium with a movable rigid cylindrical inclusion are studied in this paper with the help of complex variable and wave function expansion method. The relations that a movable rigid cylindrical inclusion depends on intensity of incident wave and electric field are revealed. The expressions of dynamic stress at the edge of the inclusion are obtained. Numerical calculations are made with different wave numbers and different piezoelectric characteristic parameters. The calculating results show that dynamic stress concentrations at the edge of the inclusion have linear dependence on the incident electric field. And dynamic analyses are very important for an infinite piezoelectric medium with a movable rigid cylindrical inclusion at larger piezoelectric characteristic parameters.

On the higher-order thermal vibrations of FG saturated porous cylindrical micro-shells integrated with nanocomposite skins in viscoelastic medium

Since the multi-layered structures are widely used nowadays, and due to interesting applications of cylindrical shells, this study is dedicated to analyzing free vibrational behaviors of functionally graded saturated porous micro cylindrical shells with two nanocomposite skins. Based on Biot's assumptions, constitutive relations for the core are presented and effective properties of the skins are determined via the rule of mixture. A sinusoidal theory is used to capture the shear deformation effects, and to account for the scale effects, the modified couple stress theory is employed which suggests a material length-scale parameter for predicting the results in small-dimension. With the aid of extended form of Hamilton's principle for dynamic systems, differential equations of motion are extracted. Fourier series functions are used to obtain natural frequencies and after validating them, a set of parametric studies are carried out. The results show the significant effects of porosity and Skempton coefficient, pores placement patterns, CNTs addition and distribution patterns, temperature variations, material length-scale parameter and viscoelastic medium on the natural frequencies of the microstructure. The outcomes of this work could be used to design and manufacture more reliable micro cylindrical structures in thermo-dynamical environments.

In-plane dynamic Green's functions for inclined and uniformly distributed loads in a multi-layered transversely isotropic half-space

The dynamic stiffness method combined with the Fourier transform is utilized to derive the in-plane Green’s functions for inclined and uniformly distributed loads in a multi-layered transversely isotropic（TI）half-space.The loaded layer is fixed to obtain solutions restricted in it and the corresponding reactions forces,which are then applied to the total system with the opposite sign.By adding solutions restricted in the loaded layer to solutions from the reaction forces,the global solutions in the wavenumber domain are obtained,and the dynamic Green’s functions in the space domain are recovered by the inverse Fourier transform.The presented formulations can be reduced to the isotropic case developed by Wolf（1985）,and are further verified by comparisons with existing solutions in a uniform isotropic as well as a layered TI halfspace subjected to horizontally distributed loads which are special cases of the more general problem addressed.The deduced Green’s functions,in conjunction with boundary element methods,will lead to significant advances in the investigation of a variety of wave scattering,wave radiation and soil-structure interaction problems in a layered TI site.Selected numerical results are given to investigate the influence of material anisotropy,frequency of excitation,inclination angle and layered on the responses of displacement and stress,and some conclusions are drawn.

RECONSTRUCTION OF ONE DIMENSIONAL MULTI-LAYERED MEDIA BY USING A TIME DOMAIN SIGNAL FLOW GRAPH TECHNIQUE

A novel inverse scattering method to reconstruct the permittivity profile of one-dimensional multi-layered media is proposed in this paper.Based on the equivalent network ofthe medium,a concept of time domain signal flow graph and its basic principles are introduced,from which the reflection coefficient of the medium in time domain can be shown to be a series ofDirac δ-functions(pulse responses).In terms of the pulse responses,we will reconstruct both thepermittivity and the thickness of each layer will accurately be reconstructed.Numerical examplesverify the applicability of this

中型AUV锂离子电池系统设计研究

中型AUV具有续航力强、载荷量大等优势,在长航程科学观测、大载荷搭载等任务领域有较好的应用前景。本文根据某中型AUV的任务需求和指标进行锂离子电池系统设计,基于21700圆柱电芯,对电池成组方案、焊接工艺、电路设计和BMS设计等进行研究,并进行了相关性能测试和分析。试验结果表明,21700圆柱电池在中型AUV锂离子电池系统中具有较好的适用性。

柱形装药土介质爆炸成坑效应的数值模拟研究

本文指出在爆炸案件中,为便于携带、掩人耳目,犯罪分子采用的炸药包装物常为瓶、罐等柱形物体;土体是爆炸现场的常见介质,土介质爆炸成坑效应的研究对爆炸案的现场重建等技术工作具有重要意义。为了研究柱形装药土介质爆炸成坑效应,通过量纲分析得出了一定条件下炸坑比例直径、炸坑比例深度是柱体比例半径和比例埋深的二元函数,并通过LS-DYNA模拟了不同柱体比例半径、比例埋深的爆炸成坑过程,根据模拟实验数据拟合出了该函数关系,最终得到了爆炸抛掷作用直径、炸坑真实深度与装药半径、炸药埋深之间的关系。

Polar interface and surface optical vibration spectra in multi-layer wurtzite quantum wires： transfer matrix method

The polar interface optical （IO） and surface optical （SO） phonon modes and the corresponding Froehlich electron phonon-interaction Hamiltonian in a freestanding multi-layer wurtzite cylindrical quantum wire （QWR） are derived and studied by employing the transfer matrix method in the dielectric continuum approximation and Loudon＇s uniaxial crystal model. A numerical calculation of a freestanding wurtzite GaN/AlN QWR is performed. The results reveal that for a relatively large azimuthal quantum number m or wave-number kz in the free z-direction, there exist two branches of IO phonon modes localized at the interface, and only one branch of SO mode localized at the surface in the system. The degenerating behaviours of the IO and SO phonon modes in the wurtzite QWR have also been clearly observed for a small kz or m. The limiting frequency properties of the IO and SO modes for large kz and m have been explained reasonably from the mathematical and physical viewpoints. The calculations of electron-phonon coupling functions show that the high-frequency IO phonon branch and SO mode play a more important role in the electron phonon interaction.

The Scattering of SH Wave in a Nano Hole Embedded the Infinite Inhomogeneous Medium

Scattering of the shear waves by a nano-sized cylindrical hole embedded the inhomogeneous is investigated in this study. The Helmholtz equation with a variable coefficient is transformed the standard Helmholtz equation by the complex function method and the conformal mapping method. By wave function expanding method, the analytical expressions of the displacement field and stress field in the inhomogeneous medium are obtained. Considering the surface effect and using the generalized Young-Laplace equation, we obtain the boundary conditions at nano arbitrary-shaped hole, then the field equations satisfying boundary conditions are attributed to solving a set of infinite algebraic equations. Numerical results show that when the radius of the cylindrical cavity shrinks to nanometers, surface energy becomes a dominant factor that affects the dynamic stress concentration factor (DSCF) around the cylindrical cavity. The influence the density variation of the inhomogeneity on the DSCF is discussed at the same time.

非饱和多孔弹性介质中圆柱形衬砌洞室对平面波散射的解析解

采用波函数展开法求解了非饱和多孔弹性介质中无限长圆柱形衬砌洞室对平面波的二维散射问题。将非饱和孔隙弹性介质视为利用界面混合物理论建立的孔隙弹性模型,并将控制方程解耦为4个亥姆霍兹方程。衬砌结构视为单相弹性介质,并解耦为两个亥姆霍兹方程。利用边界条件求解波函数中待定系数,分别得到平面P波和SV波在非饱和多孔弹性介质中圆柱形衬砌洞室周围散射问题的解析解。利用该解析解,考虑饱和度对剪切模量的影响,数值计算分析了不同入射频率下饱和度对洞室周围动应力集中系数的影响。

钻铤对随钻电磁波测井电压信号影响分析

随钻电磁波测井仪器的发射及接收线圈缠绕在钻铤上,利用圆柱状分层介质模型可以模拟线圈电压信号随井眼参数和地层参数的变化特征,分析钻铤对电压信号的影响规律。针对随钻电磁波测井仪器轴向发射-倾斜接收线圈结构,给出计算倾斜接收线圈电压的解析算法,通过对谱域中背景场与反射场分别积分,增加了算法的稳定性。模拟了倾斜接收线圈的电压信号随源距、发射频率及地层电导率变化特征,对比分析了钻铤、井眼泥浆对电压信号的影响。数值模拟结果表明,钻铤对倾斜接收线圈电压信号强度及曲线形态的影响远大于井眼泥浆的影响,为后期随钻测井资料处理校正或标定提供了理论基础。

Determining a Multi-layered Fluid-solid Medium from the Acoustic Measurements

Consider the inverse problem of recovering a multi-layered fluid-solid medium from many acoustic measurements corresponding to time-harmonic acoustic plane waves.We prove that both the supports of the embedded solid obstacle and the surrounding layered fluid medium can be uniquely identified by means of acoustic far-field pattern for all incident wave fields at a fixed frequency.Our proof is based on the constructions of some well-posed partial differential equation systems in sufficiently small domains combined with the a priori estimates for the solutions of the forward scattering problem.

柱形装药爆炸破坏混凝土的数值模拟分析

利用LS-DYNA有限元程序建立计算模型,对有无预制孔的半无限混凝土介质中柱形装药的爆炸破坏过程进行了数值模拟研究,得出了不同埋深时的爆腔半径和爆破漏斗半径以及毁伤混凝土的最佳埋深范围,结果与理论计算吻合较好。同时,计算分析了在一定埋深处正向起爆与反向起爆的破坏状态,并对计算结果进行理论分析,结果表明反向起爆更有利于混凝土的破坏。

黏弹性饱和多孔介质中圆柱孔洞的频域响应

研究了无限黏弹性饱和多孔介质中圆柱孔洞(有衬砌)表面受轴对称简谐荷载和流体压力作用下的频域响应问题.引入carcione提出的本构模型来描述介质的流变和松弛性质.考虑衬砌和介质的相对渗透性,孔洞处于半封闭状态,边界半透水.引入两个势函数,在频域中得到了应力、位移和超孔隙水压力响应解答.并进行了算例分析,讨论了反映介质黏弹性性质的最小质量因子,反映孔洞边界半透水性质的渗透性参数及衬砌和介质的相对刚度对问题的影响.分析结果表明:以上参数对圆柱孔洞的频域响应有很大影响.

聚磁介质对高梯度磁选效果的影响

为了给高梯度磁选机聚磁介质的选择提供参考,以国外某微细粒赤铁矿石和广东某褐铁矿石的强磁扫选尾矿为对象,在SSS-II型水平磁场周期式高梯度磁选机上研究了棒状聚磁介质的形式和直径对高梯度磁选效果的影响。介质形式试验结果显示：表面具环状尖突起的异形棒介质与普通圆棒介质相比,可使国外矿样的精矿回收率提高3.17-6.17个百分点,说明异型棒介质对磁性颗粒的吸引力更强。介质直径试验结果显示：Ф4 mm异型棒介质与Ф3 mm和Ф5 mm异型棒介质相比,可使国外矿样的精矿回收率提高1.18-5.52个百分点,使广东矿样的精矿回收率提高2.14-2.98个百分点,说明适当增大介质直径有利于磁性物的回收,但介质直径过大时反而会降低对磁性物的捕捉能力。

端泵Nd：YAG高功率复合棒三维热应力分布的计算模拟

采用有限差分方法分析模拟了高功率端泵Nd:YAG复合棒的三维热应力分布,并与不含端帽的情况作了对比。研究了非对称泵浦、端帽厚度、冷却边界条件、激光介质尺寸和材料特性等参数对三维热应力分布的影响。计算结果表明:采用复合棒结构能够改善介质的热分布,减小介质表面的张应力(由无端帽时的136MPa减少到8.6MPa),因此这种结构允许激光器获得大功率的激光输出。数值计算结果与Anasys软件模拟的结果一致,与已知实验结果定性相符。文中采用的有限差分方法避免了超大型矩阵运算,提高了计算精度和运算速度,对高功率固体激光器的优化设计有实际价值。

偶极子在径向非均匀介质中的电磁场分布

提出了柱状多层介质中的磁偶极子在任意介质层中的电磁场的递推算法,给出了磁偶极子产生的电磁波在柱状多层介质中的反射、透射系数和广义反射系数,从而得到了任意介质层中满足各层界面边界条件的电磁场解析表达式.

含刚性圆柱夹杂压电介质的动力反平面特性

利用复变函数和波函数展开法对稳态SH波在含刚性可移动圆柱夹杂的无限线弹性压电介质中的散射与动应力集中问题进行研究.获得压电介质中刚性圆柱夹杂周边动应力的表达式,并对具有不同压电特征参数和不同波数情况下的夹杂边界动应力集中系数进行了数值计算.计算结果表明,边界动应力集中对外加电场压电参数具有线性依赖关系。

考虑横向弯曲振动的轮胎圆柱薄壳模型

建立了充分考虑带束层宽度和厚度及侧向正应变和切、侧向预应力的轮胎三维等效圆柱薄壳模型,提出了一组适合不同频段的轮胎带束层切向、径向和横向振动的位移函数。该模型不仅能够准确计算中低频(0-300 Hz)的轮胎面内、外振动固有频率,还能够预测带束层截面方向发生的中、高频弯曲振动(300-500 Hz)。通过瑞利-里兹法求解低频振动并简化计算过程,通过模态展开法求解中高频弯曲振动。使用锤击法试验验证了模型的准确性。

筒形件热态颗粒介质压力成形自由变形区失稳分析（英文）

采用热态固体颗粒介质成形工艺对金属板材筒形件成形展开研究,得到板材变形过程中的应力分布函数,并结合板材破裂失稳理论给出自由变形区冲头临界破裂成形压力的解析表达式。研究结果表明,颗粒介质所具有的主动摩擦效应和内压非均匀分布特征能显著提高板材的成形性能;冲头临界破裂成形压力随颗粒介质与板材间摩擦因数和材料塑性应变比的增加而上升,随材料硬化指数的增加而下降。各因素对冲头临界破裂成形压力影响由大到小的顺序为塑性应变比、摩擦因数和硬化指数。最后,采用AZ31B镁合金板材HGMF工艺试验对失稳理论进行验证。