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提出一种求解二维功能梯度材料(FGMs)稳态热传导问题的重心Lagrange插值配点法.基于Chebyshev节点构造二维重心Lagrange插值函数及其偏导数,然后基于配点法将其直接代入FGMs热传导问题的控制方程和边界条件,得到系统离散方程.重心Lagrange插值配点法是一种真正的无网格方法,很好地融合了重心Lagrange插值和配点格式的优势,具有高效、稳定、高精度和易于数值实现的优点.采用重心Lagrange插值配点法分别对指数型、二次型和三角型FGMs热传导问题进行数值模拟.结果表明:该方法具有较高的计算效率和计算精度,对材料梯度参数的变化不敏感.可以进一步拓展到FGMs瞬态问题和FGMs的热力耦合分析. 相似文献
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受到电子二极管整流效应的启发,对单向声传播结构展开了一系列的理论与实验研究:将超晶格结构与非线性声学材料组合构成了可实现声整流效应的声二极管结构;通过将反对称弹性结构引入到复合结构板来产生Lamb波的不对称模式转化,设计了可实现Lamb波单向传播的线性声学结构;基于声子晶体的部分禁带特性,在有限尺度声学系统中设计并实现了单向声学波导结构;设计并实现了由纯板与声栅构成的声单向传播结构,具有小尺寸与高效率的特点,且声波出射角度可调;基于声学梯度材料设计了可在极宽频带内实现不对称声传播的声学结构。 相似文献
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基于双曲型热传导方程,采用镜像法和波函数展开法,求解了含亚表面异质圆柱缺陷的半无限功能梯度材料的表面温度场,给出了功能梯度材料中热波散射的一般解.分析了亚表面异质圆柱缺陷的几何参数(如埋藏深度)和热物理参数(如导热系数、热扩散长度、热扩散率及热弛豫时间等)对功能梯度材料表面温度场的影响.温度波由调制的超短脉冲激光在功能梯度材料表面激发,异质圆柱缺陷表面的边界条件为导热边界.研究结果可望为功能梯度材料的红外热波无损检测、导热反问题提供计算方法和参考数据. 相似文献
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在导波模式展开分析方法的基础上,提出激发效率参量来定量表征超声Lamb波积累二次谐波的发生效率。以P92钢板为例,理论计算得到了与频散曲线对应的理论激发效率参量分布图谱,从图谱中选择理论激发效率参量大小不同的两种基频Lamb波模式:纵波型S1模式和交点型A2/S2模式,分别测量这两种基频Lamb波模式在钢板中传播时产生的二次谐波信号。理论计算和实验测量结果表明,这两种基频Lamb波模式的理论和实验激发效率参量的比值基本一致,且激发效率参量较大的纵波型S1模式能激发出效率更高的二次谐波信号。研究结果表明激发效率参量可以有效的用于Lamb波二次谐波发生效率的表征及模式选择。 相似文献
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The importance of elastic wave propagation problem in plates arises from the application of ultrasonic elastic waves in non-destructive evaluation of plate-like structures. However, precise study and analysis of acoustic guided waves especially in non-homogeneous waveguides such as functionally graded plates are so complicated that exact elastodynamic methods are rarely employed in practical applications. Thus, the simple approximate plate theories have attracted much interest for the calculation of wave fields in FGM plates. Therefore, in the current research, the classical plate theory (CPT), first-order shear deformation theory (FSDT) and third-order shear deformation theory (TSDT) are used to obtain the transient responses of flexural waves in FGM plates subjected to transverse impulsive loadings. Moreover, comparing the results with those based on a well recognized hybrid numerical method (HNM), we examine the accuracy of the plate theories for several plates of various thicknesses under excitations of different frequencies. The material properties of the plate are assumed to vary across the plate thickness according to a simple power-law distribution in terms of volume fractions of constituents. In all analyses, spatial Fourier transform together with modal analysis are applied to compute displacement responses of the plates. A comparison of the results demonstrates the reliability ranges of the approximate plate theories for elastic wave propagation analysis in FGM plates. Furthermore, based on various examples, it is shown that whenever the plate theories are used within the appropriate ranges of plate thickness and frequency content, solution process in wave number-time domain based on modal analysis approach is not only sufficient but also efficient for finding the transient waveforms in FGM plates. 相似文献
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Experimental and numerical results are presented on the behavior of guided waves in elastic plates in plane strain that include a Gaussian variation of their section, located between two areas of constant thickness. The area of varying section is wide compared to the used wavelengths, which allows wave propagation inside this area. The experimental results show that an incident Lamb wave is indeed converted into an adiabatic wave inside the varying section domain. A trapped wave in the Gaussian domain is also observed, depending on the incident mode and on the Gaussian maximum height. Outside the varying section domain, conversion into different Lamb waves is observed. This conversion phenomenon is experimentally quantified by the measurement of the Lamb wave normal displacement and of its carried energy. A numerical study, based on the Finite Elements Method is performed, and successfully compared to the experimental results. 相似文献
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为了研究变壁厚结构中兰姆波的传播特性,以K9玻璃制成的台阶板为波导,运用动态光弹法实现了兰姆波在阶梯板中传播过程的可视化。使用MATLAB对兰姆波的理论应力分布进行了仿真,将仿真结果与光弹图像相对比以进行模式识别。此外,根据兰姆波的动态光弹图像计算了特定模式的相速度,并与相速度频散曲线相对比,以支持模式识别的结果。对4mm-3mm和4mm-2mm厚度差台阶板进行了对比分析。研究发现在激励目标模式的兰姆波时,可能会出现非目标模式,并且兰姆波的模态转换与频散程度与台阶处的厚度差有关。本文的结果可对具有相同性质类似结构材料的无损检测提供参考。 相似文献
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Souhail Dahmen Hassiba Ketata Mohamed Hédi Ben Ghozlen Bernard Hosten 《Ultrasonics》2010,50(4-5):502-507
A hybrid elastic wave method is applied to determine the anisotropic constants of Olive wood specimen considered as an orthotropic solid. The method is based on the measurements of the Lamb wave velocities as well as the bulk ultrasonic wave velocities. Electrostatic, air-coupled, ultrasonic transducers are used to generate and receive Lamb waves which are sensitive to material properties. The variation of phase velocity with frequency is measured for several modes propagating parallel and normal to the fiber direction along a thin Olivier wood plates. A numerical model based mainly on an optimization method is developed; it permits to recover seven out of nine elastic constants with an uncertainty of about 15%. The remaining two elastic constants are then obtained from bulk wave measurements. The experimental Lamb phase velocities are in good agreement with the calculated dispersion curves. The evaluation of Olive wood elastic properties has been performed in the low frequency range where the Lamb length wave is large in comparison with the heterogeneity extent. Within the interval errors, the obtained elastic tensor doesn’t reveal a large deviation from a uniaxial symmetry. 相似文献
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Time-domain analysis of second-harmonic generation of primary Lamb wave propagation in an elastic plate 下载免费PDF全文
Within the second-order perturbation approximation,this paper investigates the physical process of generation of the time-domain second harmonic by a primary Lamb wave waveform in an elastic plate.The present work is performed based on the preconditions that the phase velocity matching is satisfied and that the transfer of energy from the primary Lamb wave to the double frequency Lamb wave is not zero.It investigates the influences of the difference between the group velocities of the primary Lamb wave and the double frequency Lamb wave,the propagation distance and the duration of the primary Lamb wave waveform on the envelope shape of the time-domain second harmonic.It finds that the maximum magnitude of the envelope of the second-harmonic waveform can grow within some propagation distance even if the condition of group velocity matching is not satisfied.Our analyses also indicate that the maximum magnitude of the envelope of the second-harmonic waveform is kept constant beyond a specific propagation distance.Furthermore,it concludes that the integration amplitude of the time-domain second-harmonic waveform always grows with propagation distance within the second-order perturbation.The present research yields new physical insight not previously available into the effect of generation of the time-domain second harmonic by propagation of a primary Lamb wave waveform. 相似文献
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Behnam Ghodrati Afshin Ghanbar Zadeh Hamid Mohammad-Sedighi 《Waves in Random and Complex Media》2018,28(1):15-34
In this paper, Lamb wave propagation in a homogeneous and isotropic non-classical micro/nano-plates is investigated. To consider the effect of material microstructure on the wave propagation, three size-dependent models namely indeterminate-, modified- and consistent couple stress theories are used to extract the dispersion equations. In the mentioned theories, a parameter called ‘characteristic length’ is used to consider the size of material microstructure in the governing equations. To generalize the parametric studies and examine the effect of thickness, propagation wavelength, and characteristic length on the behavior of miniature plate structures, the governing equations are nondimensionalized by defining appropriate dimensionless parameters. Then the dispersion curves for phase and group velocities are plotted in terms of a wide frequency-thickness range to study the lamb waves propagation considering microstructure effects in very high frequencies. According to the illustrated results, it was observed that the couple stress theories in the Cosserat type material predict more rigidity than the classical theory; so that in a plate with constant thickness, by increasing the thickness to characteristic length ratio, the results approach to the classical theory, and by reducing this ratio, wave propagation speed in the plate is significantly increased. In addition, it is demonstrated that for high-frequency Lamb waves, it converges to dispersive Rayleigh wave velocity. 相似文献
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An important material property in the paper industry is the anisotropic stiffness distribution due to the fibrous microstructure of paper and to processing procedures. Ultrasonic methods offer a means of determining the stiffness of sheets of paper from the anisotropic propagation characteristics of elastic Lamb waves along the machine direction and the cross direction. That is, along and perpendicular to the direction of paper production. Currently, piezoelectric ultrasonic methods are employed in the industry to measure the elastic polar diagram of paper through multiple contacting measurements made in all directions. This paper describes a new approach utilizing the INEEL Laser Ultrasonic Camera to provide a complete image of the elastic waves traveling in all directions in the plane of the paper sheet. This approach is based on optical dynamic holographic methods that record the out of plane ultrasonic motion over the entire paper surface simultaneously without scanning. The full-field imaging technique offers great potential for increasing the speed of the measurement and it ultimately provides a substantial amount of information concerning local property variations and flaws in the paper. This report shows the success of the method and the manner in which it yields the elastic polar diagram for the paper from the dispersive flexural or antisymmetric Lamb wave. 相似文献
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L. Samek 《Czechoslovak Journal of Physics》1998,48(1):45-56
In the article the analysis of a monochromatic elastic surface wave in an unlimited plate of limited thickness whose opposite
surfaces are planar and mutually parallel, made of an elastic isotropic material of a constant density is described. Equations
are calculated for the wave number calculation — speed of surface wave propagation, and an equation for the calculation of
the vector components deformation (component trajectory) of the elastic medium. 相似文献
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In this paper, free vibration response of stepped beams made from functionally graded materials (FGMs) is investigated. The beams are supported by various types of elastically end constraints. The differential transformation method (DTM) is employed to solve the governing differential equations of such beams in order to obtain natural frequencies and mode shapes. The power law distribution is used and modified to describe material compositions across the thickness of the beams made of FGMs. Two main types of the stepped FGM beams in which their material compositions can be described by using the modified power law distribution are selected to investigate their vibration behaviour. The significant parametric studies such as step ratio, step location, boundary conditions, spring constants and material volume fraction are taken into investigation. 相似文献