Reynolds stress modelling of rectangular open‐channel flow

A Reynolds stress model for the numerical simulation of uniform 3D turbulent open‐channel flows is described. The finite volume method is used for the numerical solution of the flow equations and transport equations of the Reynolds stress components. The overall solution strategy is the SIMPLER algorithm, and the power‐law scheme is used to discretize the convection and diffusion terms in the governing equations. The developed model is applied to a flow at a Reynolds number of 77000 in a rectangular channel with a width to depth ratio of 2. The simulated mean flow and turbulence structures are compared with measured and computed data from the literature. The computed flow vectors in the plane normal to the streamwise direction show a small vortex, called inner secondary currents, located at the juncture of the sidewall and the free surface as well as the free surface and bottom vortices. This small vortex causes a significant increase in the wall shear stress in the vicinity of the free surface. A budget analysis of the streamwise vorticity is carried out. It is found that both production terms by anisotropy of Reynolds normal stress and by Reynolds shear stress contribute to the generation of secondary currents. Copyright © 2006 John Wiley & Sons, Ltd.     

Vortices in the Two-Dimensional Simple Exclusion Process

We show that the fluctuations of the partial current in two dimensional diffusive systems are dominated by vortices leading to a different scaling from the one predicted by the hydrodynamic large deviation theory. This is supported by exact computations of the variance of partial current fluctuations for the symmetric simple exclusion process on general graphs. On a two-dimensional torus, our exact expressions are compared to the results of numerical simulations. They confirm the logarithmic dependence on the system size of the fluctuations of the partial flux. The impact of the vortices on the validity of the fluctuation relation for partial currents is also discussed in an Appendix.     

A full-coupling model of PN junctions based on the global-domain carrier motions with inclusion of the two metal/semiconductor contacts at endpoints

A full-coupling model on the current-voltage(J-V) characteristics of PN junctions is put forward in the paper by taking into account both the whole junction and the two electrode regions consisting of metal/semiconductor(M/S) contacts. The depletion layer assumption proposed by the Shockley model is discarded. Gauss’ law on the electric potential and the electric field is applied in the whole junction region such that the majority-carrier currents inside and outside the P/N barrier region are ab...     

Shaft angular misalignment detection using acoustic emission

Shaft angular misalignment (SAM) is a common and crucial problem in rotating machinery. Misalignment can produce several shortcomings such as premature bearing failure, increase in energy consumption, excessive seal lubricant leakage and coupling failure. Vibration analysis has been traditionally used to detect SAM; however, it presents some drawbacks i.e. high influence of machine operational conditions and strong impact of the coupling type and stiffness on vibration spectra. This paper presents an extensive experimental investigation in order to evaluate the possibility of detecting SAM, using acoustic emission (AE) technique. The test rig was operated at under different operational conditions of load and speed in order to evaluate the impact on the AE and vibration signature under normal operating conditions. To the best of the author’s knowledge, this is the first attempt to use AE for the detection of SAM under varying operational conditions. A comparative study of vibration and AE was carried out to demonstrate the potentially better performance of AE. The experimental results show that AE technique can be used as a reliable technique for SAM detection, providing enhancements over vibration analysis.     

嵌入平行量子点的非平衡介观环路的极化电流

利用格林函数并借助于双杂质Anderson模型的哈密顿量，研究了嵌入平行耦合量子点的非平衡介观环路的磁极化电流性质. 结果表明：在零温环境中，随着双量子点耦合强度的增加，系统的Kondo效应被削弱.在低温环境中，人为控制和调节一定的电路参数，极化电流会发生方向的反转，从而可实现对介观环路的极化. 关键词： 极化电流 耦合量子点 Kondo效应 温度效应     

Extended Mild-Slope Equation

ＩｎｔｒｏｄｕｃｔｉｏｎＡｃｃｕｒａｔｅｍｏｄｅｌｌｉｎｇｏｆｓｕｒｆａｃｅｗａｖｅｄｙｎａｍｉｃｓｉｎｃｏａｓｔａｌｒｅｇｉｏｎｓｈａｓｂｅｅｎｔｈｅｇｏａｌｏｆｍｕｃｈｒｅｃｅｎｔｒｅｓｅａｒｃｈ ,ｗｈｉｃｈｈａｓｂｅｅｎｓｕｍｍａｒｉｚｅｄｉｎｓｕｒｖｅｙｓｂｙＤｉｎｇｅｍａｎｓ( 1 997) [1]ａｎｄＫｉｒｂｙ( 1 997) [2 ].Ｔｈｅｒｉｃｈｎｅｓｓｏｆｃｏａｓｔａｌｗａｖｅｄｙｎａｍｉｃｓａｒｉｓｅｓｆｒｏｍｔｈｅｓｔｒｏｎｇａｍｂｉｅｎｔｃｕｒｒｅｎｔｓａｎｄｔｈｅｗｉｄｅｖａｒｉａｔｉｏｎｓ…     

黄茅海波-流共同作用下的三维悬沙数值模拟

针对黄茅海河口区波流相互作用显著、三维空间结构明显及泥沙运动复杂等特点,联合第3代海浪模式SWAN,建立了波流共同作用下的三维悬沙数学模型.在水流计算中,考虑了波浪产生的辐射应力影响,波浪依赖的表面风应力影响及波浪影响下的底部剪切应力,并采用k-kl紊流闭合模型提供垂向涡粘系数和垂向扩散系数.悬沙扩散方程中的源函数利用切应力法确定,泥沙沉降速度考虑絮凝作用,从而提高黄茅海悬沙场数值模拟精度.通过含沙量实测资料验证,模拟值与实测值符合较好.在模型验证的基础上,讨论了不考虑波浪与考虑波浪两种情况下黄茅海的悬沙分布特征,为工程实际研究提供了依据.     

大同二电厂扩建厂址工程区活动构造评价

大同盆地西侧北北东-北东向鹅毛口-口泉断裂, 属正平移性质, 晚第四纪以来断裂继续活动, 但北东、南西两段活动有明显差异。盆地东侧北东-北东东向六棱山北麓断裂, 亦属正断层性质, 至今仍在活动。距大同二电厂扩建厂址最近的水峪断裂, 晚更新世末3～1.5万年以来已停止活动, 对厂址稳定性不会有影响。