Fluid flow in a rotating curved rectangular duct

The fluid flowing in a rotating curved duct is subjected to both the Coriolis force due to a rotation and the centrifugal force due to a curvature. In this paper, the combined effects of the two forces on the flows in rotating curved rectangular ducts are examined numerically. According to the aspect ratio of the cross-section, the rectangular ducts are divided into three types: η>1, η=1, η<1, where η is the aspect ratio. The variations of the flow structures with the force ratio F (the ratio of the Corislis force to the centrifugal force) are studied in detail and many hitherto unknown flow patterns are found. The effects of the force ratio and the aspect ratio of the cross-section on the friction factor are also examined. Present results show both the characteristics of the secondary flow, axial flow and the natures of the friction factor.     

风浪因素对海洋波导雷达回波作用机理的研究

采用文氏谱模型描述近海海洋动力环境海面的粗糙特征, 并运用海浪谱理论得到风速和均方根高度偏差的关系. 进而应用修正的离散混合傅里叶变换方法和改进的雷达散射系数模型分别计算了电磁波传输损耗和雷达散射系数. 在此基础上, 通过数值计算分析了风浪因素对海洋波导环境雷达回波功率值的影响. 结果表明, 风浪因素对不同观测高度处的传输损耗的影响均不大; 风浪因素对雷达回波功率有显著影响, 并且相对于传输损耗, 雷达散射系数项受风浪因素影响较大因而导致较大的雷达回波功率的变化.     

Evaluation of one‐ and two‐equation low‐Re turbulence models. Part II—Vortex‐generator jet and diffusing S‐duct flows

This second segment of the two‐part paper systematically examines several turbulence models in the context of two flows, namely a vortex flow created by an inclined jet in crossflow, and the flow field in a diffusing S‐shaped duct. The test cases are chosen on the basis of availability of high‐quality and detailed experimental data. The tested turbulence models are integrated to solid surfaces and consist of: Rodi's two‐layer k–ε model, Wilcox's k–ω model, Menter's two‐equation shear–stress‐transport model, and the one‐equation model of Spalart and Allmaras. The objective of the study is to establish the prediction accuracy of these turbulence models with respect to three‐dimensional separated flows with streamline curvature. At the same time, the study establishes the minimum spatial resolution requirements for each of these turbulence closures, and identifies the proper low‐Mach‐number preconditioning and artificial diffusion settings of a Reynolds‐averaged Navier–Stokes algorithm for optimum rate of convergence and minimum adverse impact on prediction accuracy. Copyright © 2003 John Wiley & Sons, Ltd.     

Analysis and design of mechanical crack arrestors for gas pipeline

Mechanical arrestors are frequently used in gas transmission pipelines to prevent the possibility of long running cracks. These arrestors have the effect of reducing the pipe from opening as the crack passes. This decreases the available crack driving force and, as a result, crack arrest may take place. This essentially is a second line of defence against catastrophic failure in the event crack initiation cannot always be prevented. A novel analyzing method presented in this paper has been developed to investigate the suitability of these crack arrestors. This is based on a fluid/structure/fracture interaction package, PFRAC. A dynamic finite element approach has been developed for a three dimension curved beam with initial plane curvature, which has been implemented in PFRAC to simulate the behaviour of the arrestor. The contact conditions between the pipe wall and the arrestor, along with the various computational procedures, are described. Several numerical results for a cracked pipe with arrestors are presented and compared with those for pipes without arrestors.     

自然弯扭梁的非线性分析

研究了两端边界均为完全约束的自然弯扭梁在小应变，大位移和大转动情况下的非线性性质，并考虑了横向剪切变形和扭转翘曲变形的影响，分析中还包括了拉伸，弯曲和扭转的各种弹性耦合。由最小势能原理可以导出所给问题的平衡方程。这里欧拉角可以用来表示任意大的转动。该方法还可方便地推广到其他各种不完全约束边界的情况。此外，利用上述结果还可以得到该梁在小位移理论中的基本方程和有关公式。     

ICF靶腔曲面光场计算

传统的衍射计算方法都是针对衍射场为平面的计算,对于ICF靶腔衍射场为曲面时,计算困难。通过比较常用衍射计算方法的优缺点,基于层析成像的思想,提出采用快速傅里叶变换分层计算,并根据最相邻原则拟合曲面衍射场光场分布的快速计算方法。该方法可以计算出任意给定空间曲面上的光场分布,且具有计算快速、结果精确的优点。模拟分析表明,当分层数足够大时,采用该方法可有效解决ICF靶腔内壁曲面光场的计算问题。     

脉冲离子束作用下靶面次级电子的抑制

论述了离子束作用下固体表面次级电子产生的机制,介绍了特种真空器件中次级电子抑制的各种方法及其优缺点,提出了脉冲离子束作用下靶面次级电子抑制的自偏势法和曲面靶法等设计思路,并在实验上进行了初步验证。实验结果表明,自偏势电压大于80 V后,次级电子得到很好的抑制。在相同束流情况下,曲面靶较平面靶的次级电子产额少。利用实验结果进行估算得到了近似的次级电子产额约为0.67,比文献中的结果(0.58)偏大。对实验中自偏势法抑制反峰电子电流的效果进行了分析和讨论,结果表明：自偏势法不但能够有效抑制离子打靶产生的次级电子,还能抑制由功率源不稳定带来的入射反峰电子流。     

弹性支承圆弧梁内力分析

以现代桥梁及房屋结构为工程背景,提出弹性支承曲线梁计算模型,按结构力学方法推导出弹性支承圆弧梁的内力计算公式,分析讨论了竖向和抗扭弹性支承对内力的影响．     

Conductivity of a two-dimensional curved microconstriction

The quantum conductance of a long two-dimensional curved microconstriction has been considered theoretically. It is shown that over-the-barrier-reflection of electrons at points in which the curvature of the surface is changed, results in fine structure of quantum steps of the conductance. The observation of this structure would be a demonstration of the influence of the curvature on the quantum properties of two-dimensional electrons.     

Numerical modelling of subcritical open channel flow using the K-ε turbulence model and the penalty function finite element technique

A numerical model has been developed that employs the penalty function finite element technique to solve the vertically averaged hydrodynamic and turbulence model equations for a water body using isoparametric elements. The full elliptic forms of the equations are solved, thereby allowing recirculating flows to be calculated. Alternative momentum dispersion and turbulence closure models are proposed and evaluated by comparing model predictions with experimental data for strongly curved subcritical open channel flow. The results of these simulations indicate that the depth-averaged two-equation k-ε turbulence model yields excellent agreement with experimental observations. In addition, it appears that neither the streamline curvature modification of the depth-averaged k-ε model, nor the momentum dispersion models based on the assumption of helicoidal flow in a curved channel, yield significant improvement in the present model predictions. Overall model predictions are found to be as good as those of a more complex and restricted three-dimensional model.