Smart Phase Tuning in Microwave Photonic Integrated Circuits Toward Automated Frequency Multiplication by Design

The author investigates the monitoring methods for fine adjustment of the previously proposed on-chip architecture for frequency multiplication and translation of harmonics by design. Digital signal processing (DSP) algorithms are utilized to create an optimized microwave photonic integrated circuit functionality toward automated frequency multiplication. The implemented DSP algorithms are formed on discrete Fourier transform and optimization-based algorithms (Greedy and gradient-based algorithms), which are analytically derived and numerically compared based on the accuracy and speed of convergence criteria.     

A shock dynamics theory based analytical solution of double Mach reflections

The shock-dynamics based governing equations of double Mach reflection (DMR) wave configurations were developed and solved. The analytical results were compared to experimental results from various sources. Very good to excellent agreement was evident.     

Numerical and analytical study of transverse supersonic flow over a flat cone

Quasisteady supersonic flow over a flat cone on a plane surface is studied. A formula is derived for the angle through which the flow lines turn at the cone. The results are used to justify the use of two-dimensional simulations of the flow. Peak pressures and total impulses are obtained numerically for various cone angles.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1990.     

后掠激波诱导分离特性的马赫数影响

利用壁面压力测量和表面油流显示技术对后掠压缩角产生的激波与湍流边界层干扰进行了实验研究。主要研究了来流马赫数对干扰分离特性和起始分离条件的影响，实验的马赫数为１．７９，２．０４和２．５０，相应的雷诺数为２．４２—２．４７×１０￣７／ｍ．实验模型共１５个，其后掠角变化范围是０°—６０°，流向压缩角变化范围是１０°—３０°，实验结果表明，与二维干扰不同，对于大后掠角的三维干扰来说，分离线上的压比和起始分离时的无粘激波压比近似相等，且是一个与马赫数无关的常数。     

Analysis of the shock structures in a regular detonation

Time-dependent two-dimensional numerical simulations have been used to investigate the detailed shock structures and patterns of energy release in the regions of the triple points and transverse waves in a planar detonation. As the system of shock triple points evolves between collisions, they trace a well shaped cellular pattern characteristic of detonations in argon-diluted, low-pressure mixtures of hydrogen and oxygen. In the region of the triple points, the shock structure evolves continuously from a single Mach structure to a double Mach structure and finally to a complex Mach structure characteristic of spinning detonations. Most of the energy released in the region of the triple points. The amount of energy release increases as the triple point comes closer to a collision with a wall or another triple point. Just before the collision, there is a large region of energy release that covers the length of the interacting transverse waves. The result is a rectangular high-energy region which boosts the propagation of the new detonation cell.     

Internal streamwise action of saw-tooth sound waves on turbulent jets

The results of an experimental investigation of the acoustic field produced by turbulent subsonic jets under internal acoustic excitation are presented. It is shown that under the action of saw-tooth finite-amplitude waves the turbulent jets can radiate Mach waves into the ambient medium due to compact acoustic disturbances traveling along the jet at a velocity greater than the speed of sound in the surrounding space.Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 5, 2004, pp. 153–158. Original Russian Text Copyright © 2004 by Pimshtein.     

Multiple-scale modelling of acoustic sources in low Mach-number flow

The main difficulty in the calculation of sound generated by fluid flow at low Mach numbers is the occurrence of different scales. The fluid flow is characterized by small spatial structures containing a large amount of energy that may propagate with a small convective velocity, such as small vortices in a turbulent flow. The radiated acoustic waves have small amplitudes and carry a small amount of energy, but have a long wavelength due to their fast propagation velocity. In this paper a perturbation method is used to calculate noise generation and propagation in combination with fluid flow based on the incompressible equations. The idea for the numerical modelling is to introduce a fine grid for the resolution of the fluid flow that is embedded into a larger acoustical domain with a coarse grid adapted to the long wavelength acoustics. To get an appropriate restriction of the acoustic source terms from the fine CFD-grid to the coarse CAA-grid, a multi-scale expansion with one time and two space scales is introduced. To cite this article: C.-D. Munz et al., C. R. Mecanique 333 (2005).     

气相爆轰在T形管中传播新现象的实验研究

对2H2/O2/Ar系统爆轰波在T形管(截面为40mm×40mm)中传播现象进行了实验研究.用烟迹片记录了T形管中爆轰波的胞格结构,用压电传感器记录了分叉口附近指定点压力时间曲线,得到了爆轰波在分叉口附近的平均速度和胞格图案演变.结果表明:初压P0≥2.67kPa,在水平和垂直支管下游区域(距离分叉口约3.5—6倍方管截面边长),分叉口影响消失,爆轰波恢复稳定,且强度基本保持不变.在分叉口绕射过程中,爆轰波在膨胀区中衰减,诱导激波阵面弯曲.两个支管中发生马赫反射,三波点迹线清晰可见.该传播特性是爆轰波的诱导激波和横波共同作用的结果.分叉口附近的胞格结构先消失再恢复,在无胞格和平衡胞格之间的区域存在细密胞格的过渡区,表征了在诱导激波与化学反应阵面分离后的区域中出现二次点火.P0=2.00kPa,水平支管中稳定自持爆轰能重建,垂直支管中爆轰熄灭.P0<2.00kPa,分叉口上游已不能形成稳定爆轰.还对胞格结构中的几个特征参数进行了测量,并初步分析了P0对这些参数的影响.     

Perturbation method for the second-order nonlinear effect of focused acoustic field around a scatterer in an ideal fluid

Two nonlinear models are proposed to investigate the focused acoustic waves that the nonlinear effects will be important inside the liquid around the scatterer. Firstly, the one dimensional solutions for the widely used Westervelt equation with different coordinates are obtained based on the perturbation method with the second order nonlinear terms. Then, by introducing the small parameter (Mach number), a dimensionless formulation and asymptotic perturbation expansion via the compressible potential flow theory is applied. This model permits the decoupling between the velocity potential and enthalpy to second order, with the first potential solutions satisfying the linear wave equation (Helmholtz equation), whereas the second order solutions are associated with the linear non-homogeneous equation. Based on the model, the local nonlinear effects of focused acoustic waves on certain volume are studied in which the findings may have important implications for bubble cavitation/initiation via focused ultrasound called HIFU (High Intensity Focused Ultrasound). The calculated results show that for the domain encompassing less than ten times the radius away from the center of the scatterer, the non-linear effect exerts a significant influence on the focused high intensity acoustic wave. Moreover, at the comparatively higher frequencies, for the model of spherical wave, a lower Mach number may result in stronger nonlinear effects.     

The measurement of the diameter change of a piezoelectric transducer cylinder with the white-light interferometry

The measurement of the diameter change of a piezoelectric transducer (PZT) cylinder with the white-light interferometry is proposed and experimentally demonstrated. One arm of a Mach–Zehnder interferometer (MZI) is wrapped on the PZT cylinder, and the phase change of the interferogram of the MZI is used to determine the diameter change when a DC voltage is applied on the PZT cylinder. The Fourier transform white-light interferometry is used for recovering the phase change of the interferometer. The experimental results show that the diameter change resolution of 0.8 nm for the PZT cylinder with diameter of 40 mm is achieved.