Two-dimensional Cartesian air-gap element (CAGE) for dynamic finite-element modeling of electrical machines with a flat air gap

This paper extends the air-gap element (AGE) to enable the modeling of flat air gaps. AGE is a macroelement originally proposed by Abdel-Razek et al.for modeling annular air gaps in electrical machines. The paper presents the theory of the new macroelement and explains its implementation within a time-stepped finite-element (FE) code. It validates the solution produced by the new macroelement by comparing it with that obtained by using an FE mesh with a discretized air gap. It then applies the model to determine the open-circuit electromotive force of an axial-flux permanent-magnet machine and compares the results with measurements.

Experimental Study on Convective Boiling Heat Transfer in Narrow-Gap Annulus Tubes

Since convective boiling or highly subcooled single-phase forced convection in micro-channels is an effective cooling mechanism with a wide range of applications, more experimental and theoretical studies are required to explain and verify the forced convection heat transfer phenomenon in narrow channels. In this experimental study, we model the convective boiling behavior of water with low latent heat substance Freon 113 (R-113), with the purpose of saving power consumption and visualizing experiments. Both heat transfer and pressure drop characteristics were measured in subcooled and saturated concentric narrow gap forced convection boiling. Data were obtained to qualitatively identify the effects of gap size, pressure, flow rate and wall superheat on boiling regimes and the transition between various regimes. Some significant differences from unconfined forced convection boiling were found,and also, the flow patterns in narrow vertical annulus tubes have been studied quantitatively.

拟压缩性方法在非定常球形Couette-Taylor流模拟中的应用

本文以拟压缩性法和物理时间/伪时间双重时间推进,数值求解非定常不可压缩流N=S方程。拟压缩性项是对伪时间的导数项,在每一物理时间层,进行对伪时间的推进使拟压缩性项趋于零,从而使连续方程得到满足。用Lower-Upper Symmetric Gaus-—Seidel(LU-SGS)恪式求解离散所得的方程。针对前人LU-SGS格式未计及隐式物理粘性,在计算中低Re数流动时容易发散或造成收敛率低的问题,利用简化的隐式粘性项改善了格式的稳定性,并用三阶迎风紧致差分逼近无粘通量,提高了伪时间推进的收敛率。模拟了间隙比σ=0.18的两同心旋转球之间轴对称Couette-Taylor流的0-、1-和2-涡三种流态和它们之间的转变过程。

过渡领域圆柱间Couette流动

<正> 圆柱间Couette流动问题是最简单的流动情况之一,当圆柱转速较大(M≈1)而间隙与半径之比[δ=(R_2-R_1)/R_1]不为小量时,却可用以检验求解过渡领域中非线性问题的各种方法。不久前,文献[1,2]在M≈1,δ=0.5条件下用电子束做了同心圆柱间氩气密度分布的测量,提供了一组比较流场结构的实验数据。在较早的稀薄气体Couette

Decomposing the Gender Wage Gap: The effect of firms, occupations and Job Stratification

This paper presents new evidence on the role of segregation into firms, occupations within a firm and stratification into professional categories within firm-occupations in explaining the gender wage gap. I use a generalized earnings model that allows observed and unobserved group characteristics to have different impact on wages of men and women within the same group. The database is a large sample of individual wage data from the 1995 Spanish Wage Structure Survey. Results indicate that firm segregation in our sample accounts for around one-fifth of the raw gender wage gap. Occupational segregation within firms accounts for about one-third of the raw wage gap, and stratification into different professional categories within firms and occupations explains another one-third of it. The remaining one-fifth of the overall gap arises from better outcomes of men relative to women within professional categories. It is also found that rewards to both observable and unobservable skills, particularly those related to education, are higher for males than for females within the same group. Finally, mean wages in occupations or job categories with a higher fraction of female co-workers are lower, but the negative impact of femaleness in higher for women.