热声回热器结构频率的数值研究

介绍了声波在结构中的几种表现形式,综合考虑结构声传播过程中的色散现象会影响结构和流体的声耦合,将结构声理论运用于热声系统回热器内结构振动的分析。通过采用Ansys软件对回热器中薄板建立模型并分析其振动模态。结果显示:(1)回热器中薄板结构主要受弯曲波作用,振动时发生弯曲变形;(2)薄板振动模态的固有频率随板厚度减小而降低,随长度减小而增加;(3)薄板振动模态随阶数升高而趋于复杂,相应的固有频率值由数十赫兹发展到数千赫兹,包含热声系统谐振频率的工作区间。     

双激励纵弯耦合宽带复合棒水声换能器

为研究进一步拓宽双激励复合棒水声换能器的工作带宽方法。利用等效电路法和有限元方法研究了双激励换能器的振动模态,分析了中间质量块的材料、长度对换能器发射电压响应的影响,提出结合较低工作频段的纵向振动和较高工作频段的纵向振动与径向振动耦合引起的弯曲振动进一步展宽带工作频带的方法。根据优化参数后的仿真模型制作的样品工作频带为14 kHz～47 kHz。采用这种纵弯振动模态耦合的方法可以有效拓宽双激励宽复合棒换能器的工作带宽。     

随钻声波测井四极子发射换能器的设计*

提出一种基于金属基片结构的随钻四极子发射换能器,其一阶弯曲模式可用于随钻四极子声源。利用有限元法对该换能器进行了设计分析,结果表明在5kHz附近存在一阶弯曲振动模态,其径向位移分布及发射电压级响应均优于单纯的瓦片状压电阵子,非常适合随钻四极子工作频率及声场的测量需求。针对一阶弯曲振动模态,数值模拟了几何尺寸对换能器性能参数的影响。换能器谐振频率随着陶瓷片厚度、陶瓷片高度、陶瓷片张开角度、金属基片厚度的增大而升高。最大发射电压级幅值随着陶瓷片高度、陶瓷片张开角、金属片厚度的增大而升高;随着陶瓷片厚度的增大,最大发射电压级幅值先升高后逐渐降低。金属基片采用铝片可以使换能器有较大的发射功率。数值模拟结果可以对随钻声波测井仪四极子发射换能器的设计起到良好的指导作用。     

基于标准格子的低马赫可压缩Boltzmann模型及应用于气体谐振的模拟

提出一种基于D2Q9标准格子的低马赫数可压缩格子Boltzmann模型,模拟了管内一维气体谐振。气体振荡由位于谐振管左端的活塞振动引起,传播至右端并反射回来。利用本文模型捕捉到了谐振频率附近不同频率下的激波现象,得到了谐振频率下不同位置处轴向速度、密度和温度随时间和沿轴向的变化规律。模拟结果和理论分析及前人文献结果相一致,验证了本文所提出的基于标准格子的低马赫数可压缩格子Boltzmann模型的有效性。     

扬声器锥壳的全频段强迫振动解

解析和数值研究了扬声器锥壳全频段的轴对称强迫振动。给出了典型低频段、典型转点频段和典型高频段的显式位移解析解、特征频率方程和轴向导纳表达式。解析结果与数值计算和实验结果结果非常吻合。在典型低频段,振动完全是纵波型的。在典型转点频段,全域的纵波运动和转点外侧域的横波运动共存,谐振和反谐振频率方程相应呈现出无矩解和弯曲解的耦合特性。在典型高频段,全域的纵波运动和横波运动互相独立,相应出现2组独立的纵波和横波固有频率。      

基于金属线阵列嵌入的低频宽带电路模拟吸波体设计

由于等效电阻谐振条件限制, 传统的单层电路模拟吸波体(CA)结构在低频段不能形成多个谐振点. 为了突破这个限制, 本文提出了一种金属线阵列嵌入的单层CA结构. 该结构在低频段形成了双谐振峰吸收, 拓展了吸波频带. 采用准静态模型, 分析金属线阵列嵌入的单层CA结构内的电磁波的散射. 分析结果表明, 金属线阵列的嵌入使结构的介质层在低频激发等离子体谐振. 在该谐振频率点, 结构形成额外吸收峰, 该吸收峰和单层CA结构原有的吸收峰一起实现了双峰吸收. 实验和FDTD数值计算结果相符合, 结果表明该结构在不增加厚度的前提下, 扩展了低频段的吸波频段. 关键词： 金属线阵列 宽带吸波 电路模拟吸波体 电阻型频率选择表面     

结构参数对偶极声波换能器谐振频率的影响

偶极横波远探测技术在我国复杂地质结的构油气勘探中具有十分广阔的应用前景。换能器的工作频率直接影响声波测井的探测深度。本文对正交偶极声波测井换能器弯曲模态的谐振频率进行了解析计算,并利用有限元方法研究了其结构参数对谐振频率的影响。计算结果表明:当压电陶瓷片的长度增加时,换能器一阶谐振频率先降低后升高,三阶谐振频率先升高再降低之后又上升;当金属基片厚度增加时,换能器一阶与三阶谐振频率均升高;当压电陶瓷片厚度增加时,换能器谐振频率的变化方向与幅度还与压电陶瓷片长度等其他参数相关,有可能升高或降低。     

空间遥感器调焦机构组件动特性分析

为了研究某种空间遥感器调焦机构组件的动特性,对其进行了锤击法模态试验。通过采用有限元分析软件MSC/NASTRAN对空间遥感器调焦机构组件进行模态分析,得到了空间遥感器调焦机构组件的低阶固有振动频率和主振型。对空间遥感器调焦机构组件试验模态与计算模态进行了对比,并进行了相关性分析和评估。通过空间遥感器调焦机构组件试验模态与计算模态的对比可知:前四阶的固有频率相对误差均在5%以内;模态置信准则判据(MAC)的值均在0.95左右;模态贡献因子(MPF)的值均在0.9左右。说明空间遥感器调焦机构组件计算模态与试验模态具有比较好的相关性,有限元模型比较准确地反映了实际的空间遥感器调焦机构组件的动特性,并为空间遥感器调焦机构的进一步设计提供了依据。     

偶极声波换能器振动特性计算

利用ANSYS有限元软件计算了声波测井中使用的偶极子换能器在不同机械边界条件下的振动模态和频率响应。计算结果显示,偶极子换能器在一定的频率范围内有多个振动模态,不同的机械边界条件不仅影响振动模态的个数而且还影响同一振动模态的谐振频率;从频率响应曲线上还可以看出此结构的偶极子换能器在做弯曲振动时的频带较窄,这对在不同地层井眼中进行的偶极子声波测井非常不利。通过多个不同主频的偶极子换能器组合工作可以从根本上拓宽偶极声波换能器的频带宽度。     

DMD和POD对超燃冲压发动机凹腔流动的稳定性分析

开式凹腔作为超燃冲压发动机中增加掺混和稳焰的装置, 其流动稳定性的研究对深入理解凹腔增加掺混和稳焰机理以及凹腔的设计有着重要的学术意义和工程应用价值.基于大涡模拟方法对超燃冲压发动机开式凹腔流动进行数值模拟, 分别采用动力学模态分解(dynamic mode decomposition, DMD)和本征正交分解方法(proper orthogonal decomposition, POD)对自激振荡流动进行稳定性分析. DMD方法可准确提取凹腔的振荡频率, 与Rossiter模型以及压力脉动FFT分析得到的频率吻合较好, 且DMD中对应Rossiter前3阶频率的模态在流动中的主导作用顺序也与FFT分析结果一致, 自激振荡中RossiterⅢ模态占据主导作用, 同时DMD方法对Rossiter 3阶以上模态频率的预测能力明显强于FFT分析方法.在对低频的提取方面, DMD方法比Rossiter模型更具有优势.与前6阶Rossiter模态对应DMD模态均缓慢收敛, 主要表现为剪切层中的分离涡结构和中部及下游区域中的涡结构.前3阶不稳定模态中的分离涡结构主要集中在中部剪切层以及后缘附近区域. POD方法中较少的模态包含流场绝大部分的能量.但是, 通过POD方法提取的模态频率在分辨率上效果不佳, 提取到最低频率为Rossiter 3阶模态对应的频率, 且模态中均存在次频, 次频与主频之间的耦合导致模态的形态相差较大.另外, 与DMD方法相比POD方法无法判断所提取的模态的稳定性.      

FREE VIBRATIONS OF SELF-STRAINED ASSEMBLIES OF BEAMS

This paper examines the natural frequencies and modes of transverse vibration of two simple redundant systems comprising straight uniform Euler-Bernoulli beams in which there are internal self-balancing axial loads (e.g., loads due to non-uniform thermal strains). The simplest system consists of two parallel beams joined at their ends and the other is a 6-beam rectangular plane frame. Symmetric mode vibration normal to the plane of the frame is studied. Transcendental frequency equations are established for the different systems. Computed frequencies and modes are presented which show the effect of (1) varying the axial loads over a wide range, up to and beyond the values which cause individual members to buckle (2) pinning or fixing the beam joints (3) varying the relative flexural stiffness of the component beams. When the internal axial loads first cause any one of the component beams to buckle, the fundamental frequency of the whole system vanishes. The critical axial loads required for this are determined. A simple criterion has been identified to predict whether a small increase from zero in the axial compressive load in any one member causes the natural frequencies of the whole system to rise or fall. It is shown that this depends on the relative flexural stiffnesses and buckling loads of the different members. Computed modes of vibration show that when the axial modes reach their critical values, the buckled beam(s) distort with large amplitudes while the unbuckled beam(s) move either as rigid bodies or with bending which decays rapidly from the ends to a near-rigid-body movement over the central part of the beam. The modes of the systems with fixed joints change very little (if at all) with changing axial load, except when the load is close to the value which maximizes or minimizes the frequency. In a narrow range around this load the mode changes rapidly. The results provide an explanation for some computed results (as yet unpublished) for the flexural modes and frequencies of flat plates with non-uniform thermal stress distributions.     

A distributed-mass approach for dynamic analysis of Bernoulli-Euler plane frames

The exact dynamic analysis of plane frames should consider the effect of mass distribution in beam elements, which can be achieved by using the dynamic stiffness method. Solving for the natural frequencies and mode shapes from the dynamic stiffness matrix is a nonlinear eigenproblem. The Wittrick-Williams algorithm is a reliable tool to identify the natural frequencies. A deflated matrix method to determine the mode shapes is presented. The dynamic stiffness matrix may create some null modes in which the joints of beam elements have null deformation. Adding an interior node at the middle of beam elements can eliminate the null modes of flexural vibration, but does not eliminate the null modes of axial vibration. A force equilibrium approach to solve for the null modes of axial vibration is presented. Orthogonal conditions of vibration modes in the Bernoulli-Euler plane frames, which are required in solving the transient response, are theoretically derived. The decoupling process for the vibration modes of the same natural frequency is also presented.     

自由端盖Ⅲ型宽带弯张换能器的设计

提出了一种利用多模耦合实现低频、宽带、大功率特性的新结构Ⅲ型弯张换能器。通过在压电陶瓷堆内部嵌入与凹型弯张壳体相连的弹性辅助弯曲梁结构,并用弯曲圆盘作为顶部自由端盖,增加有效工作模态。利用有限元方法对换能器进行了设计优化,分析结果显示换能器在低频段存在4个主要工作模态。根据优化结果,加工制作了换能器样机,水池实验的测试结果表明:在1.5～5.5 kHz范围内,换能器样机的发送电压响应均大于135 dB;1.5～4 kHz内的最大发送电压响应大于142 dB,响应起伏小于6 dB。研究结果表明自由端盖Ⅲ型弯张换能器不仅能够在小尺寸设计下实现大功率工作,还能获得低频宽带发射性能。      

Experimental study of coupled vibration in a finite periodic dual-layered structure with transverse connection

The analytical equations of the transfer matrix method are further derived for the multi-coupled vibration of flexural and longitudinal waves in a periodic dual-layered beam structure with connection branches, with full consideration given to the flexural and longitudinal motions that are tri-coupled at each connection. Measurements of mobilities at the junctions on the uni-layered beam and the cross-layered beam are made. The numerical results agree well with the experimental results at all frequencies from 10 to 2000 Hz, which verifies the theoretical methodology for the multi-coupled vibration in a finite dual-layered beam. The cross-layer energy transmission is calculated, which reveals that the transmitted longitudinal energy is enhanced not only at the longitudinal resonant modes but also at the flexural resonant modes of the connection branches due to the structural wave coupling. The flexural energy is excited by wave coupling and becomes stronger at the longitudinal resonant modes and the flexural resonant modes of the connection branches. The cross-layer vibration motions from coupled waves in the branches can be effectively controlled by the attached cantilevers with mass at the resonance modes. This method can be used to control the structure-borne sound transmission in multi-layer beam structures.     

多振子梁弯曲振动中的局域共振带隙

从梁的弯曲振动方程出发,利用传递矩阵法,给出了无限周期结构的一维多振子声子晶体梁的弯曲振动能带结构,并利用有限元方法计算了有限周期结构梁的弯曲振动频率响应.建立了多振子声子晶体梁的简化模型,推导出带隙起始截止频率公式.结果表明:一维多振子声子晶体梁具有比单振子声子晶体梁更宽更丰富的振动带隙,可应用于呈倍频关系的减振降噪中;振动在带隙频率范围内频率响应具有明显的衰减;所建立的简化模型与理论模型结果符合较好.研究工作为梁类结构的减振提供一种新的思路.     

对一端固定钢条弯曲振动共振的分析

对一端固定钢条弯曲振动的共振进行了分析,指出它有一系列的振动模式,满足一定条件的策动力若频率接近其某一振动模式的频率时,则可以激发钢条共振．     

固体材料拉伸波速的共振法测量

文章系统论述了利用弯曲共振和纵向共振两种方式测量拉伸波速的方法，作者改进了传统的纵向共振测试装置，指出了两种方式各自的适用性．在理论上纵向共振方法更为严谨，且误差来源较少，从而具有较高测量精度，实验上测量操作更为方便．     

Dynamic identification of beam axial loads using one flexural mode shape

In the last decades, various methods have been proposed for the experimental evaluation of tensile forces acting in tie-beams of arches and vaults. Moreover, static and dynamic approaches have been formulated to evaluate critical compressive axial forces and flexural stiffness of end constraints. Adopting Euler–Bernoulli beam model, this paper shows that, if bending stiffness and mass per unit length of a beam with constant cross-section are known, the axial force and the flexural stiffness of the end constraints can be deduced by one vibration frequency and three components of the corresponding mode shape. Finally, data conditions are given to assess a physically admissible identification of the unknown parameters.     

Sensitivity analysis of scanning near-field optical microscope probe

In this paper, we study the dynamic modes of a scanning near-field optical microscope (SNOM) which uses an optical fiber probe; and the sensitivity of flexural and axial vibration modes for the probe were derived and the closed-form expressions were obtained. According to the analysis, as expected each mode has a different sensitivity and the first mode is the most sensitive mode of flexural and axial vibration for the SNOM probe. The sensitivities of both flexural and axial modes are greater for a material surface that is compliant with the cantilever probe. As the contact stiffness increases, the high-order vibration modes are more sensitive than the lower-order modes. Furthermore, the axial contact stiffness has a significant effect on the sensitivity of the SNOM probe, and this should be noted when designing new cantilever probes.     

Effect of interactive damping on vibration sensitivities of a scanning near-field optical microscope probe

The effect of interactive damping on the sensitivity of flexural and axial vibration modes of scanning near-field optical microscope (SNOM) with a tapered optical fiber probe has been analyzed. The interaction of the SNOM probe with a sample surface is modeled by a combination of a spring and a dashpot in the flexural direction and a similar combination in the axial direction. An approximate form for the sensitivities of both modes was derived by using the Rayleigh–Ritz method. The results show that the interactive damping will decrease the sensitivities of both flexural and axial vibration modes when the contact stiffness is low. The more the damping effect, the lower the sensitivities are. In addition, when the contact stiffness was low, the flexural sensitivity of the tapered probe slightly increased as the tapered angle decreased. However, the axial sensitivity apparently decreased as the tapered angle decreased. When the contact stiffness became higher, the sensitivities of both flexural and axial vibration modes increased as the tapered angle increased. PACS 68.35.Ja; 07.79.Fc; 61.16.Ch