径向磁化的多环嵌套永磁轴承轴向磁力解析模型

为了解决径向磁化双环永磁轴承轴向磁力偏小的问题,设计了径向磁化多环嵌套永磁轴承新结构。基于磁路及虚功原理法,结合径向磁化多环嵌套永磁轴承结构特点及线性叠加原理,建立了径向磁化多环嵌套永磁轴承轴向磁力解析模型。模型表明:径向磁化多环嵌套永磁轴承轴向磁力与磁环剩磁平方成正比,磁力随磁环间隙的增大而减小,随磁环数的增大而增大;在正常轴向工作范围内,轴向磁力随轴承轴向偏移的增大而增大。模型计算结果与有限元计算结果基本吻合。对比计算说明:径向磁化多环嵌套永磁轴承轴向磁力远大于由原多嵌套磁环所构成的若干双环永磁轴承轴向磁力之和。     

Exact and numerical solutions of a micropolar fluid in a vertical annulus

In this article, we have analyzed the effects of heat transfer on a peristaltic flow of a micropolar fluid in a vertical annulus. The governing equations of two‐dimensional micropolar fluid are simplified by using the assumptions of long wavelength and neglecting the wave number. A close form solutions are obtained for velocity field υ_x and microrotation component υ_θ. Further, the numerical solutions of the simplified equation of υ_θ are computed and the results are compared with the exact solution. The influence of pertinent parameters are analyzed through graphs. Trapping phenomena is also discussed for different parameters. © 2009 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2010     

Nevanlinna theory of meromorphic functions on annuli

In this survey paper, we discuss the recent development of Nevanlinna theory of meromorphic functions on annuli, which extends results in Nevanlinna theory in the complex plane or in a disk. In particular, we show that the approach taken on annuli is a unified treatment of functions meromorphic in the complex plane, a disk and an annulus. It allows one to obtain many results in the complex plane and in a disk as corollaries of our results in annuli.     

非牛顿流体在偏心环空中轴向层流的摄动解

本文应用摄动方法研究了非牛顿流体在偏心环形空间中轴向层流的流动规律.文中以相对偏心度ε作为摄动参数,得到了其流场、极值速度、压力梯度等流动参数的一阶解.     

Application of differential quadrature method to simulate natural convection in a concentric annulus

In this paper, the Fourier expansion‐based differential quadrature (FDQ) and the polynomial‐based differential quadrature (PDQ) methods are applied to simulate the natural convection in a concentric annulus with a horizontal axis. The comparison and grid independence of PDQ and FDQ results are studied in detail. It was found that both PDQ and FDQ can obtain accurate numerical solutions using just a few grid points and requiring very small computational resources. It was demonstrated in the paper that the FDQ method can be applied to a periodic problem or a non‐periodic problem. When FDQ is applied to a non‐periodic problem (half of annulus), it can achieve the same order of accuracy as the PDQ method. And when FDQ is applied to the periodic problem (whole annulus), it is very efficient for low Rayleigh numbers. However, its efficiency is greatly reduced for the high Rayleigh numbers. The benchmark solution for Ra=10², 10³, 3×10³, 6×10³, 10⁴, 5×10⁴ are also presented in the paper. Copyright © 1999 John Wiley & Sons, Ltd.     

Thermoelastic analysis of functionally graded annulus with arbitrary gradient

A thermoelastic problem of a circular annulus made of functionally graded materials with an arbitrary gradient is investigated. Different from previous works, our analysis neither requires a special form of the gradient of material properties nor demands partitioning the entire structure into a multilayered homogeneous structure. Instead, we propose a new method for solving the thermoelastic problem of a functionally graded circular annulus by transforming it to a Fredholm integral equation. The distribution of thermal stresses and radial displacement can be obtained by solving the resulting equation. Illustrative examples are given to show the effects of varying gradients on the thermal stresses and radial displacement for given temperature changes at the inner and outer surfaces. The results indicate that the thermal stresses can be relaxed for specified gradients, which is beneficial to design an inhomogeneous annulus to maintain structural integrity.     

Entanglement entropy of an annulus in holographic thermalization

The thermalization process of the holographic entanglement entropy(HEE)of an annular domain is investigated in the Vaidya-AdS geometry.We determine numerically the Hubeny-Rangamani-Takayanagi(HRT)surface,which may be a hemi-torus or two disks,depending on the ratio of the inner radius to the outer radius of the annulus.More importantly,for some fixed ratio of the two radii,the annulus undergoes a phase transition,or a double phase transition,during thermalization from a hemi-torus to a two-disk configuration,or vice versa.The occurrence of various phase transitions is determined by the ratio of the two radii of the annulus.The rate of entanglement growth is also investigated during the thermal quench.The local maximal rate of entanglement growth occurs in the region with a double phase transition.Finally,if the quench process is sufficiently slow,which may be controlled by the thickness of the null shell,the region with a double phase transition vanishes.     

疏水表面减阻环带实验研究

针对疏水功能材料在流动减阻方面的应用, 选取典型不同粗糙度、不同疏水性的功能涂层表面, 通过新型环带实验研究了其阻力特性, 并获得了相应的扭矩和减阻率曲线. 实验采用测量圆盘带动环带旋转时的扭矩的方法间接计算环带表面所受的摩阻, 突破了传统微管道实验在尺度上的限制, 避免了水洞实验中影响因素过多的弊端, 对疏水材料的宏观应用有着重要意义. 实验证实了在宏观尺度下疏水涂层在低雷诺数时的减阻作用; 但在高雷诺数时, 减阻作用减弱, 甚至部分涂层有增阻作用, 而压差阻力的迅速增大是造成增阻的主要原因. 通过对比分析认为: 低雷诺数时, 疏水特性对于减阻效果影响更大; 而高雷诺数时, 粗糙度起更大作用, 甚至可能起到增阻的反效果. 关键词： 疏水表面 环带实验 粗糙度 减阻