A rate-dependent algebraic stress model for turbulence

Based on the stress transport model, a rate-dependent algebraic expression for the Reynolds stress tensor is developed. It is shown that the new model includes the normal stress effects and exhibits viscoelastic behavior. Furthermore, it is compatible with recently developed improved models of turbulence. The model is also consistent with the limiting behavior of turbulence in the inertial sublayer and is capable of predicting secondary flows in noncircular ducts. The TEACH code is modified according to the requirements of the rate-dependent model and is used to predict turbulent flow fields in a channel and behind a backward-facing step. The predicted results are compared with the available experimental data and those obtained from the standard k-ε and algebraic stress models. It is shown that the predictions of the new model are in better agreements with the experimental data.     

显像管调制特性的测量与分析

测试了显象管调制特性曲线，并分析了特性曲线与显像管工作原理．     

Interfacial dynamics‐based modelling of turbulent cavitating flows,Part‐2: Time‐dependent computations

The interfacial dynamics‐based cavitation model, developed in Part‐1, is further employed for unsteady flow computations. The pressure‐based operator‐splitting algorithm (PISO) is extended to handle the time‐dependent cavitating flows with particular focus on the coupling of the cavitation and turbulence models, and the large density ratio associated with cavitation. Furthermore, the compressibility effect is important for unsteady cavitating flows because in a water–vapour mixture, depending on the composition, the speed of sound inside the cavity can vary by an order of magnitude. The implications of the issue of the speed of the sound are assessed with alternative modelling approaches. Depending on the geometric confinement of the nozzle, compressibility model and cavitation numbers, either auto‐oscillation or quasi‐steady behaviour is observed. The adverse pressure gradient in the closure region is stronger at the maximum cavity size. One can also observe that the mass transfer process contributes to the cavitation dynamics. Compared to the steady flow computations, the velocity and vapour volume fraction distributions within the cavity are noticeably improved with time‐dependent computations. Copyright © 2004 John Wiley & Sons, Ltd.     

压电陶瓷压电特性的激光调制法测量研究

介绍可测量压电陶瓷压电特性的激光干涉调制测量方法.采用相干检测原理对信号进行提取,不仅可以抑制噪声对干涉信号的影响,而且还可以大大降低光电探测器和电路的1/f噪声.与通常干涉仪测量方法相比,这种方法具有测量灵敏度高等优点.利用该方法对压电陶瓷压电特性进行了测量,讨论了激励电压信号的频率、幅度对压电陶瓷压电常数d₃₁的影响,并对其压电迟滞曲线进行了测量.     

调制不稳定性对级联放大光纤传输系统信噪比的影响

在考虑光纤损耗和级联放大器的情况下，推导了调制不稳定性的产生条件和增益的普适解析表达式，分析了调制不稳定性对信噪比的影响，给出了一个新的计算信噪比的表达式。     

波导调制器的光束传播法设计

以光束传播法分析马赫－陈德尔型波导电光强度调制器的波导宽度，Ｙ型分支角、调制电压等参量与器件特性之间的关系，有利于Ｍ－Ｚ波导电光调制器的优化设计。     

A Pseudo-Random Frequency Modulation Continuous Wave Coherent Lidar Using an Optical Field Correlation Detection Method

We propose a new detection method for a pseudo-random frequency modulation continuous wave (RM-CW) coherent lidar. The feature of this method is modulation of local beam with a time delayed pseudo-random sequence. Heterodyne detection and correlation detection between the received beam and the local beam are simultaneously carried out in an optical field. In the RM-CW coherent lidar using the optical field correlation detection method, the received equipment is greatly simplified. We carried out preliminary experiments and demonstrated that the new method is effective for detection of a CW coherent lidar.     

光纤加速度传感器研究进展

光纤加速度传感器与传统加速度传感器相比，不但能抗电磁干扰，而且体小、质轻、动态范围宽、精度高、能在恶劣环境下工作，因此受到各先进国家军事与商业领域的极大重视，各种实用的光纤加速度传感器不断涌现。主要有光强调制型和相位调制型两大类。光强调制式有反射式、透射式和偏振式等等。相位调制式有Ｍａｃｈ－Ｚｅｎｄｅｒ干涉仪、Ｍｉｃｈｅｌｓｏｎ干涉仪和Ｆａｂｒｙ－Ｐｅｒｏｔ干涉仪。有一维的，也有二维的；有与水听器组合在一起的，也有与光纤陀螺仪组合的光纤加速度传感器。最小的已经做到２．５ｃｍ长，直径仅０．２５ｍｍ；测量精度已能达到１μｇ；共振频率可达到１０ｋＨｚ。为了克服温度不稳定性对测量精度的影响，人们采用了３×３耦合器解调法，双光路法，由单臂式改成推挽式等。一旦关键技术得以克服，光纤加速度传感器将会在惯性导航和其它领域发挥更重要的作用。本文将分别介绍目前各种类型光纤加速度传感器的结构、特点、走向实用化存在的问题。