Klein-Gordon波动方程多波传播的非线性特性

基于双波初值问题，讨论非线性对多波传播的影响。通过选取合适的多重尺度，对Klein-Gordon波动方程进行变形，得到方程的解的多尺度展式首项近似和三波传播时速度相互影响的定量关系，揭示了多波传播的非线性特性；最后，应用Mathematica对波动方程进行数值仿真。研究结果表明，另外多个波的存在会使波的传播速度（相速）超过独自传播时的速度（相速）。     

Inverse determinations of the parameters of three-layered plate using angle probe generated Lamb waves

The study on the inverse problems in the ultrasonic nondestructive testing (NDT) has a wide application field in various industries. An error function based inversion algorithm is introduced to determine the parameters of three-layered plates from the measured velocity of multi-mode Lamb waves. A mixed-spectral estimation is proposed to combine FFT with AR model for exact determination of the ultrasonic phase velocity. Experiments are performed using two conventional angle probes as transmitter and receiver on the same surface of three-layered laminates. Inverse analyses of one parameter (thickness) and two parameters (longitudinal and transverse wave velocities in a layer, or thickness of two layers) of three-layered laminates are made. The experimental results show that the inverse approach is in good agreement with the actual value.     

相速和群速的演示实验

本文介绍了演示相速和群速的演示实验装置和方法。     

径向气流上扰动的正压不稳定

本文研究了基本气流为经向气流的扰动的正压不稳定问题。得出了径向气流上扰动的正压不稳定的判据、增幅率的最大上限、复相速C的极限半圆,并从能量角度分析了扰动的不稳定发展所要求的基本流场与扰动场的特征。     

0.22 THz高效率行波管的互作用计算

利用CST Microwave Studio 计算双排矩形梳状慢波结构的色散并据此确定了0.22 THz左右频段（D波段）行波管用慢波结构的尺寸参数。将相速再同步技术应用于基于双排矩形梳状慢波结构的D波段行波管中,用CST PIC模拟计算了4例具有不同周期构型的D波段行波管。结果证实:对于无集中衰减器的D波段行波管,在218~232 GHz范围内,相速再同步技术使得输出功率从10~13 W提高到19~28 W,电子效率从1.4%~2.2%提高到2.6%~3.9%;对于具有集中衰减器D波段行波管,在218~232 GHz范围内,相速再同步技术使得输出功率从8~16.8 W提高到32~41 W,电子效率从1.5%~2.8%提高到4.4%~5.7%。此外,无论行波管有无集中衰减器,相速再同步技术都明显改善了行波管的增益平坦度。     

Rayleigh lamb waves in micropolar isotropic elastic plate

The propagation of waves in a homogeneous isotropic micropolar elastic cylindrical plate subjected to stress free conditions is investigated. The secular equations for symmetric and skew symmetric wave mode propagation are derived. At short wave limit, the secular equations for symmetric and skew symmetric waves in a stress free circular plate reduces to Rayleigh surface wave frequency equation. Thin plate results are also obtained. The amplitudes of displacements and microrotation components are obtained and depicted graphically. Some special cases are also deduced from the present investigations. The secular equations for symmetric and skew symmetric modes are also presented graphically.     

毫米波沟道梯型慢波结构行波管的线性理论

 在电子通道内引入一薄层空心电子注，对沟道梯型慢波结构行波管进行了线性理论研究，推导出了沟道梯型结构行波管的工作色散方程，计算了沟道梯型行波管的小信号增益和工作相速。计算结果表明：沟道梯型结构行波管每周期的增益高，带宽窄；当沟宽度由零增加到环内径的2倍时，增益减小量不足1%，这表明沟宽度对增益的影响不大；当脊高度增大10%时，增益增加62%，当环内径增大10%，增益减小57%，因此增益与脊高度正相关，与环内径负相关，且相关性十分明显。