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本文对超换能器时域、频域声场及它们之间的关系进行了分析,从理论上说明二者间由傅低变换相联系。 相似文献
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Besides their other obvious advantages over conventional ultrasonic sensors, laser interferometers offer optical diffraction limited apertures that are far smaller than the acoustic wavelength in the specimen under inspection. This unique feature can be exploited for the purposes of super-resolution near-field acoustic microscopy, which detects the rapidly decaying evanescent vibrations produced by surface and near-surface scatterers such as small fatigue cracks, pores, anomalous grains, etc. However, higher resolution also means higher sensitivity to inherent microscopic material inhomoge-neities. In this paper, experimental results are presented for the incoherent material noise in 2024 aluminum and Ti-6Al-4V titanium alloys at two different nominal frequencies of 5 and 10 MHz. It is shown that the incoherent grain noise significantly increases as the illuminated spot size decreases. Above the acoustic wavelength, the observed phenomenon is mainly due to the increasing sensitivity of the receiver to propagating scattered waves generated in the interior of the specimen. Below the acoustic wavelength, the further increasing material noise is mainly due to evanescent vibrations caused by nearby scatterers. 相似文献
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Xue T. Lord W. Udpa S. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1996,43(1):78-87
Radiated fields of a circular transducer and a time-delay spherically focused transducer array are analyzed and compared using classical impulse response method and finite element analysis. In the first approach, the velocity potential at an observation point is expressed as the convolution of the excitation velocity and the impulse response, while the pressure is obtained by the differentiation of the velocity potential. The impulse response for an array is expressed as the superposition of those of a series of circular pistons and is dependent on the observation point and piston/array structure. The finite element method starts with the formulation for elastic waves, and the pressure fields are obtained through the pressure analog method. No paraxial or farfield approximation is needed and excellent agreement is observed between results from the two methods 相似文献
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ANSYS是通常用于分析和设计声学换能器的有限元软件之一,通过实例给出分析声学换能器的处理过程,包括建模、施加载荷、设置求解选项、使用后处理器、以及获得换能器振动辐射参数的一般过程,并涉及宽带换能器、矢量换能器的发射与接收问题,对ANSYS有限元软件模拟换能器的一些经常遇到的问题细节的处理方法做了较全面的概括。还简要讨论了流体中结构模态分析的一般处理方法,对结果数据进行数学运算操作并获得换能器的特性参数等等。 相似文献
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An overview is given of finite element analysis and its application to the modeling of ultrasonic nondestructive evaluation phenomena. Following a discussion of the underlying weighted residual methodology, a mass-lumping technique is described which results in an efficient computer implementation for 2D geometries. Code predictions are compared with both analytical and experimental results, and data from studies of attenuation, anisotropy, defect interactions, and surface waves are given. Initial results from a full 3D formulation are also shown. 相似文献
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Issam Doghri 《International journal for numerical methods in engineering》1995,38(20):3403-3431
This paper deals with a class of rate-independent metal plasticity models which exhibit non-linear isotropic hardening, non-linear kinematic hardening (Chaboche-Marquis model) and ductile damage (Lemaitre-Chaboche model). The backward Euler scheme is used to integrate the rate constitutive relations. The non-linear equations obtained are solved by the Newton method. The consistent tangent operator is obtained by exact linearization of the algorithm. Despite the complexity of the constitutive equations, closed-form expressions are derived, without any approximations. Analytical, numerical and experimental results are presented and discussed. 相似文献
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A. A. Trofimov 《Measurement Techniques》2008,51(12):1347-1350
The main problems of unification that arise in the development of special purpose displacement transducers are formulated.
Ways are considered for resolving these problems, and the main concepts and definitions used in unification and standardization
of transducer equipment are provided.
Translated from Izmeritel’naya Tekhnika, No. 12, pp. 56–58, December, 2008. 相似文献
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The strength of austenitic welds will be considerably reduced if cracks are present. To guard against this possibility good workmanship is essential; quality is monitored by inspecting the welds after manufacture. Ultrasound is the favored method of inspection but there are difficulties associated with this in the coarse-grained columnar weld structures often associated with austenitic materials. We present two different approaches to modeling such inspections: ray tracing and full numerical solution of the governing wave equation. We show that the two approaches, although very different in physical nature and numerical method, give similar and consistent results. 相似文献
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Guoyu Lin Yun-Jae Kim Alfred Cornec Karl-Heinz Schwalbe 《International Journal of Fracture》1998,91(4):323-347
Ductile failure of an interleaf tension specimen consisting of a metal interleaf bonded between two elastic substrates, with
a crack located in the centre of the metal, is studied by means of detailed finite element (FE) analyses. The rate-independent
version of the Gurson model is used. This accounts for ductile failure mechanisms of micro-void nucleation, growth and coalescence
within the framework of a finite deformation plasticity theory. Also, the rapid evolution of void density due to coalescence,
which leads to ultimate failure, is considered. The effect of the interleaf thickness on failure (crack initiation and limited
amount of crack growth) is investigated. The results show that the interleaf thickness affects crack initiation only slightly.
For all specimens considered, crack initiation takes place at the crack tip. However, after crack initiation, the interleaf
thickness affects stress and strain distributions significantly. Reducing the interleaf thickness significantly increases
the load-carrying capacity. Moreover, reducing the interleaf thickness increases the maximum hydrostatic stress in the interleaf,
which is no longer developed at the crack tip but at a distance far away from the crack tip. The resulting fracture toughness
thus decreases as the interleaf thickness decreases. The shielding of the crack tip due to constrained plasticity is observed
at higher load levels for interleaf specimens.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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Jos R. Fernndez Rebeca Martínez Georgios E. Stavroulakis 《International journal for numerical methods in engineering》2009,77(2):261-284
In this paper, we analyze an algorithm for the quasistatic evolution of the mechanical state of an elasto‐piezoelectric body with damage. Both damage, caused by the development and the growth of internal microcracks, and piezoelectric effects, are included in the model. The mechanical problem is expressed as an elliptic system for the displacement field coupled with a non‐linear parabolic partial differential equation for the damage field and a linear partial differential equation for the electric potential. The variational formulation leads to a coupled system composed of two linear variational equations for the displacement field and the electric potential, and a non‐linear parabolic variational equation for the damage field. The existence of a unique weak solution is stated. Then, a fully discrete scheme is introduced by using the finite element method to approximate the spatial variable and an Euler scheme to discretize the time derivatives. Error estimates are derived on the approximate solutions, from which the linear convergence of the algorithm is deduced under suitable regularity conditions. Finally, some numerical simulations are performed, in one, two and three dimensions, to demonstrate the accuracy of the scheme and the behaviour of the solution. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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超声换能器广泛应用于声学测量,其工作性能主要取决于它的振动与声特征。然而,多数研究中的换能器被认为是经典的活塞或高斯型,经典与常用的真实换能器之间的差异容易被忽视。基于此,首先用激光测振和传声器测声方法测量了某厂家换能器产品的表面振动与声场特征。然后设计有限元方案,分别仿真经典与真实换能器的声场。最后从辐射面振速分布、声场声压和相关系数等方面,综合比较经典与真实超声换能器之间振动与声场的异同。结果表明,换能器间的辐射面振速分布差别明显,所研究的真实换能器的声场特征接近于活塞,而与高斯型差别较大。 相似文献
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Y. M. A. Hashash S. Jung J. Ghaboussi 《International journal for numerical methods in engineering》2004,59(7):989-1005
Neural network (NN) based constitutive models can capture non‐linear material behaviour. These models are versatile and have the capacity to continuously learn as additional material response data becomes available. NN constitutive models are increasingly used within the finite element (FE) method for the solution of boundary value problems. NN constitutive models, unlike commonly used plasticity models, do not require special integration procedures for implementation in FE analysis. NN constitutive model formulation does not use a material stiffness matrix concept in contrast to the elasto‐plastic matrix central to conventional plasticity based models. This paper addresses numerical implementation issues related to the use of NN constitutive models in FE analysis. A consistent material stiffness matrix is derived for the NN constitutive model that leads to efficient convergence of the FE Newton iterations. The proposed stiffness matrix is general and valid regardless of the material behaviour represented by the NN constitutive model. Two examples demonstrate the performance of the proposed NN constitutive model implementation. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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采用有限元法分析了声表面波换能器电极上的激励问题。从声场波动方程、麦克斯韦方程以及压电本构方程出发,利用哈密顿原理,推导了在压电介质中声表面波有限元方程,然后采用Newmark法对有限元方程进行时域变换。分析了换能器电极上的静态电荷分布和动态电荷分布。对压电介质中声表面波振动振幅进行计算并分析了质点振动振幅随深度的变化情况。 相似文献
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研究了频率为20 kHz的超声作用在圆柱形料腔中出现声流现象时超声空化效应的空间分布特性。结合大振幅声源条件下的声辐射力,对声场内的声流现象进行了仿真分析,获取了不同超声功率和液位高度下的声流速度场分布,初步探究了声流条件下空化气泡的运动分布规律。采用超声空化效应的声致化学发光实验,对比研究了有、无声流条件时超声空化效应的空间分布特性。结果表明:功放电流高于80 mA(电功率为17.6 W)时,超声场可形成稳定的声致流动现象且可有效提高其声能辐射效率,大大增加了空化效应的作用区域,进而提高了声化学反应效率;声流条件下料腔内超声空化效应的分布区域与超声功率(振幅)、料腔液位高度相关,功放电流从40 mA(电功率为8.8 W)增加至120 mA(电功率为26.4 W)时,空化面积占比提高了100.86%,液位高度为60 mm时的空化面积占比较50 mm和70 mm时分别提高了13.11%和73.91%,提高超声功率及选择合理的料腔液位高度,可有效提高空化气泡扩散距离,增大空化分布面积;对于固定形状及尺寸料腔中的声场,声流速度达到一定阈值时,会出现空化效应增强,空化效应增强区域位于大于声流速... 相似文献