排序方式: 共有9条查询结果,搜索用时 0 毫秒
1
1.
Piezoelectric transducer parameter selection for exciting a single mode from multiple modes of Lamb waves
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Excitation and propagation of Lamb waves by using rectangular and circular piezoelectric transducers surface-bonded to an isotropic plate are investigated in this work. Analytical stain wave solutions are derived for the two transducer shapes, giving the responses of these transducers in Lamb wave fields. The analytical study is supported by a numerical simulation using the finite element method. Symmetric and antisymmetric components in the wave propagation responses are inspected in detail with respect to test parameters such as the transducer geometry, the length and the excitation frequency. By placing only one piezoelectric transducer on the top or the bottom surface of the plate and weakening the strength of one mode while enhancing the strength of the other modes to find the centre frequency, with which the peak wave amplitude ratio between the S0 and A0 modes is maximum, a single mode excitation from the multiple modes of the Lamb waves can be achieved approximately. Experimental data are presented to show the validity of the analyses. The results are used to optimize the Lamb wave detection system. 相似文献
2.
Improved confinement of tokamak plasma with central negative shear
is checked against the resistive ballooning mode. In the negative
shear regime, the plasma is always unstable for purely growing
resistive ballooning mode. For a simplest tokamak equilibrium model,
the s--α model, characteristics of this kind of instability
are fully clarified by numerically solving the high n resistive
magnetohydrodynamic ballooning eigen-equation. Dependences of the
growth rate on the resistivity, the absolute shear value, the
pressure gradient are scanned in detail. It is found that the growth
rate is a monotonically increasing function of α while it is not
sensitive to the changes of the shear s, the initial phase \ta0
and the resistivity parameter \vaR. 相似文献
3.
K.-W.Chow 《Acta Mechanica Sinica》2011,27(5):620-626
Exact doubly periodic standing wave patterns of the Davey-Stewartson (DS) equations are derived in terms of rational expressions of elliptic functions.In fluid mechanics,DS equations govern the evolution of weakly nonlinear,free surface wave packets when long wavelength modulations in two mutually perpendicular,horizontal directions are incorporated.Elliptic functions with two different moduli (periods) are necessary in the two directions.The relation between the moduli and the wave numbers constitutes the dispersion relation of such waves.In the long wave limit,localized pulses are recovered. 相似文献
4.
5.
提出了用波模的频率偏移求矩形管道中沉积层厚度的方法。在已知无沉积层矩形管道内横截面的情形下,将测量的波模频率与用有限元计算得到的波模频率进行比对,确定沉积层的厚度。给出了有限元计算结果以及实验结果(长15m,截面为449mm×425mm的矩形管道,沉积层厚度分别为40mm和60mm)及其相对误差。实验和有限元计算的结果有很好的一致性,验证了本方法的正确性。 相似文献
6.
7.
在托卡马克等离子体中,由于极向对称被破坏,剪切阿尔芬波(sAw)连续谱有间断特征。在低频情形,当|ω|〈〈|ωA|=νA/qR时,已经证明有限离子温度梯度使SAW连续谱变得不稳定。这里,νA是阿尔芬波速度,q和R分别表示安全因子和通量面大半径。最近,用多尺度渐进技术又证明,由于托卡马克等离子体中有限离子拉摩半径和漂移轨道宽度的影响,在不稳定剪切阿尔芬连续谱中可能存在离散模对理想磁流体动力学(MHD)不稳定是稳定的。 相似文献
8.
A simple magnetic modulation structure of the exchange-coupling FePt/FeNi bilayer film is fabricated and studied for its magnetization dynamics using time-resolved magneto-optical polar Kerr spectroscopy. It is found that two spin-wave modes can be excited. One is fixed at -3.2 GHz in frequency for any external field and may serve as a frequency-stabilized spin-wave filter, while the other is external field dependent. In contrast, only the external field-dependent mode is excited in single-layer FeNi, supporting the localized origin of the mode at -3.2 GHz, which is confined to a thin exchange-coupling region. The other external field-dependent mode in frequency is attributed to the Kittel mode. 相似文献
9.
1