信号源内置式球形偶极子天线

为实现30MHz～1GHz频率范围内的机箱机柜电磁屏蔽效能测量,研制了直径为100mm的信号源内置式球形偶极子天线。该天线采用具有陡峭上升沿与下降沿的30MHz方波信号作为信号源,信号源和电源部分均置于天线内部。对天线幅值动态范围的测试结果表明:在与接收天线相距1m的条件下,该天线在30MHz～1GHz频率范围内的动态范围都在50dB以上,大多数谱线的动态范围达到60dB。所研制天线体积小、可连续工作5小时以上,解决了体积较小机箱机柜的电磁屏蔽效能测试难题。     

铸件中缩孔缺陷成因分析

通过对铸铁材料的概述，详细分析了铸件中常见缺陷——缩孔的特征、危害以及形成原因，从而探讨抑制此类缺陷的对策。     

Biomimetic Formation of 2‐Tropolones by Dioxygenase‐Catalysed Ring Expansion of Substituted 2,4‐Cyclohexadienones

Substituted 2‐tropolone natural products are found in plants and fungi. Their biosynthesis is thought to occur by ring expansion from a cyclohexadienone precursor, but this reaction has not previously been demonstrated experimentally. Treatment of 6‐hydroxy‐6‐hydroxymethylcyclohexa‐2,4‐dienone with the non‐haem iron(II)‐dependent extradiol catechol dioxygenase MhpB from Escherichia coli results in the formation of the 2‐tropolone ring‐expansion product through a pinacol‐type rearrangement. Three further substituted cyclohexa‐2,4‐dienone analogues were prepared, and treatment of each analogue was found to give the substituted 2‐tropolone ring‐expansion product. This ring expansion could also be effected nonenzymatically by treatment with 1,4,7‐triazacyclononane and FeCl₂. This is a novel transformation for non‐haem iron‐dependent enzymes, and this is the first experimental demonstration of the proposed ring‐expansion reaction in tropolone biosynthesis.     

Strengths of horseshoe vortices around a circular cylinder with an upstream cavity

Horseshoe vortices are formed at the junction of an object immersed in fluid-flow and endwall plate as a result of three-dimensional boundary layer separation. This study presents the variation of the strengths of such horseshoe vortices around a circular cylinder with a cavity (slot) placed upstream. Through the cavity, no mass flow addition (blowing) or reduction (suction) is applied. With the upstream cavity, adverse pressure gradient is weakened upstream of the cavity whereas it is strengthened downstream of the cavity. Furthermore, a single vortex system is found to form immediately upstream of the cylinder instead of a typical two vortex (primary and secondary vortices) system observed in the absence of the upstream cavity. The strength of the primary vortex is weakened due to the fluid stream engulfed in to the upstream cavity, resulting in diffusion of the mainstream. Consequently, the circulation of the primary vortex is weakened. This paper was presented at the 7th JSME-KSME Thermal and Fluids Engineering Conference, Sapporo, Japan, October 2008. Seung Jin Song has received his undergraduate and graduate degrees from Duke University and MIT, respectively. He has taught in the Department of Aerospace Engineering at Inha University from 1995 to 1999. Since 1999, he has been teaching in the School of Aerospace Engineering at Seoul National University. His research interests include turbomachinery, propulsion, and fluid engineering.     

Effect of anisotropic yield functions on the accuracy of hole expansion simulations

The deformation behavior of 780 MPa grade dual-phase steel sheet subjected to hole expansion is investigated both experimentally and analytically to clarify the effect of the material model (anisotropic yield function) on the predictive accuracy of finite element analysis of hole expansion. Biaxial tensile tests of the material were conducted; contours of plastic work and the directions of plastic strain rates are precisely measured and are in good agreement with those predicted from the Yld2000-2d yield function with an exponent of 4 ( [Barlat et al., 2003] and [Yoon et al., 2004]). Finite element and experimental analyses on the hole expansion of the material were conducted. The Yld2000-2d yield function with an exponent of 4 provides closer agreement with the experimental results than other yield functions. Consequently, the anisotropic yield functions significantly affect the predictive accuracy of the deformation behavior of the steel sheet subjected to hole expansion, and the biaxial tensile test is effective for identification of the appropriate anisotropic yield function to be used for hole expansion simulation.     

聚丙烯DQ型球形催化剂的工业应用

将DQ型球形催化剂在间歇式液相本体法聚丙烯装置上的工业应用试验情况与其他高效催化剂进行对比。结果表明，DQ型球形催化剂操作性能好，生产效率高，对丙烯原料适应性强；其产品质量好，后加工性能优良。     

Error estimation in a stochastic finite element method in electrokinetics

Input data to a numerical model are not necessarily well known. Uncertainties may exist both in material properties and in the geometry of the device. They can be due, for instance, to ageing or imperfections in the manufacturing process. Input data can be modelled as random variables leading to a stochastic model. In electromagnetism, this leads to solution of a stochastic partial differential equation system. The solution can be approximated by a linear combination of basis functions rising from the tensorial product of the basis functions used to discretize the space (nodal shape function for example) and basis functions used to discretize the random dimension (a polynomial chaos expansion for example). Some methods (SSFEM, collocation) have been proposed in the literature to calculate such approximation. The issue is then how to compare the different approaches in an objective way. One solution is to use an appropriate a posteriori numerical error estimator. In this paper, we present an error estimator based on the constitutive relation error in electrokinetics, which allows the calculation of the distance between an average solution and the unknown exact solution. The method of calculation of the error is detailed in this paper from two solutions that satisfy the two equilibrium equations. In an example, we compare two different approximations (Legendre and Hermite polynomial chaos expansions) for the random dimension using the proposed error estimator. In addition, we show how to choose the appropriate order for the polynomial chaos expansion for the proposed error estimator. Copyright © 2009 John Wiley & Sons, Ltd.     

Bed expansion ratio of mono-sized and binary mixtures in fluidized,spouted, and spout-fluid beds

Studies on bed expansion ratio were carried out in fluidized, spouted, and spout-fluid beds. A single column has been used to compare the characteristics of fluidized, spouted, and spout-fluid beds. Experiments were carried out using air and glass beads under fluidized, spouted, and spout-fluid bed conditions separately to study the effect of gas velocity, bed mass, and particle size on bed expansion ratio. Glass beads of different sizes (0.75, 1.2, 1.7, and 3.075?mm) have been used as solid bed material. Bed expansion ratio was determined for mono-size particles and binary mixtures (different diameter ratios and composition). It was found that the bed expansion ratio decreases with increase in bed mass for only spouting condition and spout-fluidization conditions. The bed expansion ratio increases with increase in bed mass for only fluidization condition.     

Optimization to the tube-fin contact status of the tube expansion process

The tube-fin contact status is an important factor influencing both thermal resistance and service life of the tube-fin heat exchanger. Tube expansion process brings forming defects of gaps at the tube-fin interfaces. And elimination of this forming defect is proved to be difficult. This paper presents a novel method in improving the tube-fin contact status of heat exchanger. From simulation results, distribution of the contact pressure along the tube-fin interface can be obtained. Then, an optimization process integrated with FE simulation is established for the sectional profile of the fin collar. The fin collar is represented with spline curves. Results show that after the optimization, the gap at the tube-fin interfaces is basically eliminated and the tube-fin contact status is significantly improved. Furthermore, flanging process for the optimized sectional shape of the fin collar is discussed.     

Note on eddy formation for stokes flows in circular cavities

Abstract

In this note, a simple model of a circular cavity with two arcs rotated in opposite directions on the boundary is employed to demonstrate flow patterns of recirculation. A particular streamline “cutting” the domain into two separating eddies is formed as a circular arc. When the rotating angular speed of the arc is proportional to the length of the arc, the streamline degenerates to a straight line.