声学黑洞梁的振动能量分布探讨

声学黑洞(Acoustic Black Hole,ABH)效应通过幂指数律剪裁厚度或者材料参数梯度变化等方式,来减小弯曲波速度并在末端实现能量聚集和吸收,一直是近年来的研究热点。本文从能量角度出发,基于半解析建模方法,建立一维声学黑洞梁的解析模型,选取Morlet小波为振型函数,对解析模型进行数值求解,分析能量密度的分布情况。研究表明:黑洞段的能量密度远大于均匀段能量密度,尖端部分对声学黑洞效应起到关键作用。理论分析结果对梁结构的振动控制和能量回收具有重要的参考价值。     

周期声学黑洞结构弯曲波带隙与振动特性

作为一种被动型波操控结构,声学黑洞能对弯曲波起到较好聚集作用,再结合阻尼层能更好抑制结构振动波的传播。从声子晶体角度通过周期性排列构造一种声学黑洞结构与基体结合的一维声子晶体结构,选取合适的晶胞,采用有限元法对周期排列的声学黑洞结构弯曲波带隙特性进行研究,对比分析8周期声子晶体梁与等长度的恒定截面梁及周期楔形梁的振动位移传递函数,讨论黑洞区域材料变化对带隙的影响。结果表明:该声学黑洞结构具有较好弯曲波带隙,在对应带隙及附近频带区间振动位移响应出现较大衰减,表明其抑制振动效果明显;在黑洞区域选择合适的材料可以使带隙向低频移动,同时使得带隙区间增多。     

板结构中声学黑洞参数优化及其阵列的能量汇集效应分析

声学黑洞结构是一种可实现板内弯曲波操控和振动能量汇聚的新结构,在振动和噪声控制领域具有应用 前景,因此对内嵌于板结构的二维声学黑洞及其阵列的动力学特性和设计方法进行研究十分必要。首先给出描述声 学黑洞汇集效果的定量参数,然后通过正交试验得出内嵌于板结构的单二维声学黑洞几何参数在一定范围内的最优 值;最后,基于这些参数设计声学黑洞并组成包含两声学黑洞的阵列,在频域内研究板结构具有不同排布方式声学黑 洞阵列时的能量汇集效应。结果表明,在一定频带范围内两个声学黑洞组成的阵列的能量汇聚效应比单声学黑洞更 为明显,且横向排列的声学黑洞阵列结构具有更好的能量汇聚效果。对于声学黑洞阵列和阻尼减振的设计具有一定 参考价值。     

板结构中声学黑洞参数优化及其阵列的能量汇集效应分析

声学黑洞结构是一种可实现板内弯曲波操控和振动能量汇聚的新结构，在振动和噪声控制领域具有应用 前景，因此对内嵌于板结构的二维声学黑洞及其阵列的动力学特性和设计方法进行研究十分必要。首先给出描述声 学黑洞汇集效果的定量参数，然后通过正交试验得出内嵌于板结构的单二维声学黑洞几何参数在一定范围内的最优 值；最后，基于这些参数设计声学黑洞并组成包含两声学黑洞的阵列，在频域内研究板结构具有不同排布方式声学黑 洞阵列时的能量汇集效应。结果表明，在一定频带范围内两个声学黑洞组成的阵列的能量汇聚效应比单声学黑洞更 为明显，且横向排列的声学黑洞阵列结构具有更好的能量汇聚效果。对于声学黑洞阵列和阻尼减振的设计具有一定 参考价值。     

动力吸振器在声黑洞单元中的放置位置对减振效果的影响

声黑洞(ABH)效应是通过将板结构厚度按特定规律改变以逐渐降低振动波在板内的传播速度,从而实现将能量聚集于某特定区域的现象;ABH近年来在控制结构振动和噪声方面得到较多的研究。以排列有(2×2)个声黑洞单元的板结构为研究对象,通过射线声学理论建立了在其等效二维板结构中弯曲波传播的轨迹模型;探讨了不同入射角度下声黑洞结构对弯曲波的聚焦位置;发现当声黑洞单元最小厚度不为0时,其聚焦位置可能不在声黑洞单元的几何中心;对此类声黑洞单元板使用多个动力吸振器(DVA)进行振动控制并采用数值搜索技术对其进行参数优化;在此基础上,研究了动力吸振器的放置位置对减振效果的影响。通过对比发现,参数优化后的动力吸振器在峰值处及其附近宽频带范围内均有非常显著的减振效果。     

基于半解析法的一维圆锥形声学黑洞梁能量聚集效应研究

声学黑洞(Acoustic Black Hole,ABH)效应是弯曲波在楔形结构中传播时波速逐渐减小至零从而不发生反射的现象。由于弯曲波在理想黑洞结构中不发生反射,这就意味着能量被集中在楔形结构的尖端部分,这一现象使得黑洞结构在减振降噪,能量回收等领域中具有极大的应用潜力。为了对截面呈幂率变化的杆结构进行动力学分析,首先建立相应的物理模型,然后利用小波函数拟合杆振动时的挠度曲线并结合拉格朗日方程建立系统的动力学方程;通过对其进行求解得到系统的振动响应。分析计算结果可知,相较于均匀杆结构,截面呈幂律变化的杆结构能够有效的抑制其振动;进一步比较楔形梁和圆杆的振动响应表明,黑洞结构对两者振动响应的抑制效果相似,但锥形杆的尖端聚能效果要优于楔形梁结构。     

基于高斯展开法的周期声学黑洞宽频能量回收特性研究EI北大核心CSCD

声学黑洞(acoustic black hole,ABH)效应是遵循幂变规律对梁或薄板结构的厚度进行剪裁,使弯曲波在结构尖端波速降至为零而无法发生反射的现象,从而能够在结构末端实现能量的聚集与高效回收。针对单一声学黑洞结构在实现峰值回收时对外界激励频率敏感的问题,提出基于周期声学黑洞的宽频压电能量回收系统。首先,基于高斯展开法,建立了耦合压电层的声学黑洞压电俘能半解析模型,并在频域范围内结合能带理论分析了周期数、幂指数、中心截断厚度以及黑洞半径对能量回收特性的影响;最后,通过压电能量回收试验,验证了周期声学黑洞对于实现宽频能量回收的有效性。研究结果表明:声学黑洞的各结构参数会通过影响峰值个数、峰值区间长度以及能带结构等因素,对系统的输出功率以及采集效率产生影响。分析结果对实现周期声学黑洞梁的宽频能量回收优化设计具有重要的参考价值。     

含周期声学黑洞梁的板架结构振动特性

声学黑洞结构通过使结构厚度按幂率渐变,改变结构阻抗从而调控弯曲波在结构中的波长和波速,可实现能量在黑洞区域的聚集和耗散。目前关于声学黑洞结构的研究主要是针对嵌入式声学黑洞,基于周期声学黑洞结构在部分频带良好的减振特性,将带阻尼层的周期声学黑洞梁贴敷在薄板上,提升薄板的减振效果并起到加强板刚度的作用。采用有限元法研究带周期声学黑洞梁的板架结构的减振效果,并将其基于敷设阻尼层和黑洞梁材料进行对比分析。结果表明,含声学黑洞梁能明显削弱振动速度传递响应,较好抑制板的振动;敷设阻尼层能增强对板减振效果,且适当增加黑洞梁数量能提升结构抑振性能;钢质梁较铝质梁刚度更大,能进一步增加板架结构的抑制带宽和增强抑制效果。     

椭圆柱空腔吸声覆盖层的声学特性

采用波导有限元方法（WFEM）分析了共振腔型吸声覆盖层内轴向波的传播和损耗特性,以椭圆柱空腔吸声层为例,在保持穿孔系数不变的前提下,分别从轴向波传播和波型转换的角度分析了空腔形状改变吸声覆盖层声学特性的机理。在此基础上,结合波导有限元方法和传递矩阵（TM）建立了变截面空腔吸声覆盖层的分析模型,以圆台空腔吸声层为例,与二维解析方法对比验证了WFEM-TM方法的正确性,并讨论了椭圆台空腔吸声层的声学特性。     

典型船舶结构中振动波传递特性研究

摘要：以波动理论为基础,根据不均质结构中波型转换、阻抗特性,系统地分析了典型船舶结构中振动波的传递特性,推导并给出了平面弯曲波入射时的隔声量公式。在此基础上人为构造了阻抗失配基座,分析了阻抗失配基座的隔振性能。结果表明,十型结构对弯曲波有较强的阻抑作用,弯曲波在突变截面处的能量再分配关系主要由两块板的特性阻抗所决定;┻┳型构件的连接处机械阻力较大,其隔振效果超过十型结构; 型结构隔振性能随突变截面阻抗失配程度增大显著提高,采取多次截面突变的办法能够得到较大的隔声量;阻抗失配基座加剧了振动波在船体板架中的波型转换、散射和反射,使总的隔振效果显著提高。本文旨在为船舶结构声学设计提供参考。     

穿孔管阻性消声器横向模态和声学特性计算与分析

应用二维有限元法计算穿孔管阻性消声器的横向模态,利用数值模态匹配法计算其传递损失,推导了相应的公式并编写了计算程序。对于圆形同轴穿孔管阻性消声器的传递损失,数值模态匹配法计算结果与三维有限元法计算结果以及实验值吻合良好,表明了二维有限元法计算穿孔管阻性消声器横向模态和数值模态匹配法预测消声性能的准确性。进而分析孔径、穿孔率、吸声材料的密度和穿孔管偏移对圆形直通穿孔管阻性消声器横向模态和消声特性的影响。结果表明,孔径减小、穿孔率增大,或者穿孔管偏移量增大均能使消声器有效的平面波区域变宽,高频消声效果变好,但中频消声效果变差;增加吸声材料的填充密度则能提高消声器中高频的消声量。     

Cased Hole Flexural Modes in Anisotropic Formations

Based on the perturbation method, for flexural wave in cased hole in anisotropic formation, the alteration in the phase velocity caused by the differences in elastic constants between anisotropic formation of interest and a reference, or unperturbed isotropic formation is obtained. Assuming the cased hole is well bonded, the Thomson-Haskell transfer matrix method is applied to calculate the dispersion relation of flexural wave in cased hole in unperturbed isotropic formation. Both the cases of a fast and slow formation are considered where the symmetry axis of a transversely isotropic (TI) formation makes an angle with the cased hole axis, the dispersion of the phase velocity of the flexural mode in cased holes is studied. The corresponding dispersion curves of flexural wave in open hole are presented simultaneously for comparison. The computational results indicate that because of the influence of the casing, the flexural wave dispersion curves in cased hole in both fast and slow TI formations all almost tend toward an identical Stoneley wave velocity at higher frequency. The casing and the cement affect the form as well as the cut-off frequency of flexural wave dispersion curves more greatly in slow TI formation than in fast TI formation. At a frequency high enough, the flexural and the Stoneley waves reach the appropriate Scholte wave velocity in both the open hole and cased hole situation.     

Finite element simulation and visualization of leaky Rayleigh wavesfor ultrasonic NDE

The generation and propagation properties of transient leaky Rayleigh waves are characterized by a two-dimensional finite element model. The displacement vector is used as the primary variable for the solid medium and a potential scalar, which is a replacement for the pressure, is taken as the fundamental variable for the fluid medium. The coupled system of finite element equations are solved in the time domain by direct integration through the central difference scheme. Three configurations are considered: the conversion of a Rayleigh surface wave into a leaky Rayleigh wave, a focused beam probing a fluid/solid interface at the Rayleigh angle, and the interaction of a defocused wave with the interface. The wave velocity in the fluid (water) is lower than the Rayleigh wave velocity in the solid (aluminum). The wave propagation profile in each case is predicted by the model. The finite element model proves to be an effective tool for surface acoustic device design and ultrasonic NDE     

Air-Coupled Nondestructive Evaluation Dissected

This work develops a two-dimensional theoretical model to simulate the behavior of a fully non-contact air-coupled nondestructive evaluation system for a thin isotropic plate. The model is divided into transmission, guided wave propagation and reception phase. The validation of the complete model was carried out by modeling the same system by means of finite element method using a Multiphysics software. In addition, the dependency of the generated Lamb waves on different transmitter’s parameters and incidence angle is thoroughly investigated. The results of the acoustic pressure excited by the transducer, the out-of-plane velocity amplitudes for the generated first antisymmetric Lamb wave mode, and the radiated pressure from the plate caused by the leaky Lamb wavefield were all compared between the two models and a reasonable degree of similarity was found.     

基于声学黑洞现象的结构波操纵及其在振动噪声控制中的应用

Acoustics Black Holes(ABH)effects can be achieved through manipulations of bending wave propagation inside a thin-walled structure with its thickness tailored according to a power-law variation.In doing so,the phase velocity of the bending wave gradually reduces alongside thickness thinning,eventually to zero in the ideal scenario at the wedge tip/indentation center,resulting in zero wave reflection and high energy concentration within a small localized area.The phenomenon attracts increasing attentions as a promising passive vibration control method because vibration energy can be channeled and only a very small amount of damping material is required within the energy focalization region to achieve efficient damping to flexural waves.In addition,the wave slowing phenomenon allows the creation of a subsonic region inside a supersonic structure,thus reducing the its overall sound radiation efficiency.These unique features point at a great potential of the ABH technology for various applications such as vibration control,sound radiation reductions and energy harvesting.This talk summarizes some of the recent progress made in the study of the ABH.Topics cover the semi-analytical modelling of the ABH structures;design and analysis of a double-layer compound ABH beam for improved static and dynamic properties;combination of locally resonant and Bragg scattering for broadband stopband creation as well as some examples of ABH for vibration and sound noise control applications.     

Elastic stress transmission in cellular systems—Analysis of wave propagation

A closely packed array of thin-walled rings constitutes an idealisation of a cellular structure. Elastic waves propagating through such structures must do so via the ring (cell) walls. A theoretical investigation into the propagation of elastic stresses in thin-walled circular rings is undertaken to examine the nature of wave transmission. Three modes of motion, corresponding to shear, extensional and flexural waves, are established and their respective velocities defined by a cubic characteristic equation. The results show that all three waves are dispersive. By neglecting extension of the centroidal axis and rotary inertia, explicit approximate solutions can be obtained for flexural waves. Employment of Love's approach for extensional waves [Love AEH. A treatise on the mathematical theory of elasticity, 4th ed. New York: Dover Publications; 1944. p. 452–3] enables approximate solutions for shear waves to be derived. The three resulting approximate solutions exhibit good agreement with the exact solutions of the characteristic equation over a wide range of wavelengths. The effects of material property, ring wall thickness and ring diameter on the three wave modes are discussed, and the results point to flexural waves as the dominant means of elastic energy transmission in such cellular structures. Wave velocities corresponding to different frequency components determined from experimental results are compared with theoretical predictions of group velocity for flexural waves and good correlation between experimental data and theory affirms this conclusion.     

相控聚焦超声与圆孔交互作用的散射特性研究

相较于传统超声检测,相控阵技术的声束聚焦控制能力使得相控超声检测的分辨率、信噪比和灵敏度等性能得到有效提升。但针对相控超声与缺陷的交互作用认识不足,导致目前检测技术无法对缺陷进行准确定性和精确定量。为此,建立了一维线阵相控超声检测圆孔缺陷的有限元模型,重点研究相控聚焦波束与圆孔缺陷交互作用的声场散射特性。结果表明,圆孔散射L模态的能量主要集中于正反射区和正透射区,且在透射区的能量大于反射区的能量,而在与入射声束垂直的方向上能量极其微弱,几乎没有散射能量;散射L模态沿入射方向呈轴对称分布;对于不同直径的圆孔缺陷,直径越大,在相同方向上散射波的能量越大;对于相同直径的圆孔,聚焦波与平面波入射时,散射波的分布规律相同,但聚焦波散射的能量明显高于平面波入射时散射的能量。     

套管井中泄漏弯曲型Lamb波声场的模拟与分析

基于套管中传播的最低阶泄漏弯曲型Lamb波(以下简称弯曲型Lamb波)对套管后介质尤其是低阻抗慢速水泥声学参数的敏感性,通过建立多层介质模型并利用实轴积分方法,数值模拟了有限尺寸定向辐射探头激发的声场和定点接收的全波波列。结果表明,在声源辐射到套管内壁上的入射角度约为33°时,在套管中主要激发弯曲型Lamb波。声场快照显示弯曲型Lamb波在沿着套管传播时,还会向与套管耦合的泥浆或水泥中泄漏比它速度低的波。若套管后介质是纵横波速度均低于弯曲型Lamb波相速度的慢速水泥,则套管中弯曲型Lamb波的衰减较大。利用弯曲型Lamb波对套管后耦合不同参数介质时的敏感性,可以有效地区分声阻抗接近的固体和液体,提高低阻抗水泥固井质量评价的效果。     

梁撞击弹塑性波传播的动态子结构方法的研究

该文针对简支梁横向弹塑性撞击问题,建立动态子结构模型,推导了相应的动力学控制方程,并采用Newmark隐式积分法进行求解,将动态子结构方法应用于撞击激发弹塑性波传播问题的研究。考虑局部弹塑性接触变形,通过对撞击激发的弹塑性波传播,包括弯矩波、挠曲波、速度波和应力波传播过程的计算,研究动态子结构法分析弹塑性波的传播特征,弯曲波的弥散特征,以及塑性铰形成机理等的合理性。经过与三维动力有限元计算结果的比较表明,动态子结构方法可以合理地应用于柔性梁中弹塑性撞击瞬态波传播问题的研究。