旋转的沙堡

通过叙述小行星研究的发展,介绍小行星结构特点和自转规律. 以双小行星的形成机制为例阐述碎石堆小行星的自转瓦解作用. 以小行星(29075)1950DA为例阐述碎石堆结构中的范德华力.     

转动的圆盘

对于应力沿厚度变化的转动圆盘, 仍考虑为平面应力问题进行了分析.     

Unsteady MHD Flow on a Rotating Cone in a Rotating Fluid

Unsteady flow over an infinite permeable rotating cone in a rotating fluid in the presence of an applied magnetic field has been investigated. The unsteadiness is induced by the time-dependent angular velocity of the body, as well as that of the fluid. The partial differential equations governing the flow have been solved numerically by using an implicit finite-difference scheme in combination with the quasi-linearization technique. For large values of the magnetic parameter, analytical solutions have also been obtained for the steady-state case. It is observed that the magnetic field, surface velocity, and suction and injection strongly affect the local skin friction coefficients in the tangential and azimuthal directions. The local skin friction coefficients increase when the angular velocity of the fluid or body increases with time, but these decrease with decreasing angular velocity. The skin friction coefficients in the tangential and azimuthal directions vanish when the angular velocities of fluid and the body are equal but this does not imply separation. When the angular velocity of the fluid is greater than that of the body, the velocity profiles reach their asymptotic values at the edge of the boundary layer in an oscillatory manner, but the magnetic field or suction reduces or suppresses these oscillations.     

Sedimentation of solid discs in viscous medium

Free sedimentation velocities of thin discs have been measured in castor oil and liquid paraffin at constant temperature. Wall and end corrections have been applied to the measured velocities and the corrected values have been compared with those calculated fromOverbeck andGans' equations. Sedimentation velocities have been measured in both edgewise and broadsideon positions. Good agreements have been obtained with the theory in both types of sedimentation. The broadsideon position has been found to be the preferred orientation and all particles deviating even slightly from the edgewise position take the preferred orientation quickly. Results of other investigators have been discussed in the light of the present findings.Based on a dissertation submitted by (1) in partial fulfilment of the requirements for M. Sc. degree of the Dacca University in 1961.     

Vortex shedding behind rings and discs

The wake structure of discs and bluff rings has been investigated experimentally in a wind tunnel. The rings have an inner diameter d_i, and an outer diameter d_o and are classified according to the parameter (d_o + d_i)/(d_o − d_i) = d/w. the ratio of mean diameter to ring width. As d/w → ∞ the flow approaches that around a two dimensional bluff body whereas as d/w tends to unity the body approaches a solid disc. A distinct change in the vortex shedding pattern is found around d/w = 5. Below this critical value velocity fluctuations in the wake have a weak periodic component which is 180° out of phase across a diameter of the body. Above d/w = 5. regular and coherent axisymmetric vortex ring shedding is observed with shedding occurring alternately from the inner and outer circumferences of the bluff body. Flow visualization and conditional averaging of hot-wire data are used to investigate the vortex structure.     

Editorial: Recent advances in mechanics of unconventional electronics

正Conventional electronics is planar,hard,and rigid due to the intrinsic brittle nature of inorganic semiconductor materials(e.g.,silicon and gallium arsenide).The modern electronic technology has typically been concerned with large or small but durable and long-lasting electronics.Recently developed materials and mechanics concepts yield unconventional electronics with unique     

Boundary Regularity of Rotating Vortex Patches

We show that the boundary of a rotating vortex patch (or V-state, in the terminology of Deem and Zabusky) is C ^∞, provided the patch is close to the bifurcation circle in the Lipschitz norm. The rotating patch is also convex if it is close to the bifurcation circle in the C ² norm. Our proof is based on Burbea’s approach to V-states.     

旋转压电纳米梁的振动分析

本文基于非局部弹性理论，对旋转压电纳米梁模型的振动进行了分析．首先由哈密顿原理导出旋转压电纳米梁的动力学控制方程及相应的边界条件；再通过微分求积法对控制方程和两类边界条件进行离散；最后通过数值计算分析振动特性．通过改变旋转角速度、轮毂半径、非局部参数以及外部电压分析它们对压电纳米梁振动频率的影响关系．数值结果表明这些参数对压电纳米梁固有频率有不可忽略的影响，本文进一步讨论了旋转角速度对结构模态的影响．     

旋转翼面尾迹的流态显示技术

本文介绍了一种可用于显示旋转弹翼面在非旋转和旋转过程中拖出的涡及其轨迹的流态显示技术。本方法在烟线技术的基础上,采用新的发烟装置,既提高了发烟的浓度,延长了发烟的时间,并不增加任何附加力矩而使发烟部件随旋转弹体一起转动,从而实现了在旋转过程中进行动态的流态显示。文中对于应用此方法得到的流态的真实性进行了分析讨论,分析表明用此方法显示的流态具有一定的真实性,可以提供定性的旋转翼面尾涡流动特性。     

Predicting the draught requirements of concave agricultural discs

The paper presents a rapid method for calculating the draught force generated by a concave disc tool when cutting a Mohr-Coulomb soil. The mean equivalent stress derived by distributing the draught force uniformly over the furrow cross-section is calculated using a set of non-dimensional factors in a two term additive equation. Tables of these factors are provided to cover the analysis of any disc of standard size and curvature operating over a practical range of cutting depths and disc and tilt angle settings. The furrow area can be estimated from published calculation tables (not reproduced here). From a knowledge of these parameters it is possible to calculate the draught force acting on the disc. A number of simplifying assumptions have been made to facilitate the development of an uncomplicated calculating procedure. Consequently the calculated values of draught must be considered as order of magnitude predictions.     

Settling of discs inside a vertical fluid-filled tube

The broadside settling of discs along the centerline of a fluid-filled tube is studied. The Stokes equation is solved by a method of eigenfunction expansions and collocation. Depending on the geometry, the flow field shows different arrangements of recirculating eddies. Due to mutual shielding, the discs settle faster when they are closer together.     

分子模拟在非常规油气开发中的应用

非常规油气资源储量丰富,具有广阔的开发前景.我国低渗/特低渗油藏以陆相沉积为主,储层特征差异性大,孔喉细小,孔隙度低,可动原油气大量储集于亚微米孔隙中,开采难度大,采收率低.岩油界面微观力学作用和限域传质力学机理是其中的关键科学问题.近年来,分子模拟技术在非常规油气开采的研究领域已经成为一种重要的研究手段.本文介绍了分...     

A theory for swaging of discs and lugs

A practical theory for swaging bored holes within plates and cylinders is proposed which can take into account work-hardening in the presence of small plastic strains based upon equivalent stress-strain data. With the appropriate choice of yield function, this theory applies to the swaging of both thin and thick plates under respective plane stress and plane strain conditions. The theory can be adapted further to the autofrettage of open and closed-ended, thick-walled cylinders where similar plane deformations conditions apply. Here swaging refers to the practice in which an oversized plug or sphere is forced into the bore thereby expanding it permanently to leave a residual circumferential compression in the bore material upon removal of the expanding tool. A similar effect results from applying an initial over-pressure to a long thick-walled cylinder in an autofrettage process. Both treatments are employed to enhance the fatigue resistance when the service loading upon the disc or cylinder amounts to a cyclic, circumferential tension within its bore. Strain gauges bonded to the entry face of the plate are used to monitor the circumferential and radial strain distributions both during and after the swaging process. Experimental results presented for swaging of thin and thin annular discs in aluminium alloy show that the measured residual strain distributions concord with the theory for large discs with a 10/1 diameter ratio. The agreement is less satisfactory with the loss in axial symmetry for parallel-sided lugs with a width to hole diameter ratio of 4/1.     

Bifurcation from Discrete Rotating Waves

Discrete rotating waves are periodic solutions that have discrete spatiotemporal symmetries in addition to their purely spatial symmetries. We present a systematic approach to the study of local bifurcation from discrete rotating waves. The approach centers around the analysis of diffeomorphisms that are equivariant with respect to distinct group actions in the domain and the range. Our results are valid for dynamical systems with finite symmetry group, and more generally, for bifurcations from isolated discrete rotating waves in dynamical systems with compact symmetry group.     

Rotating viscosimeters for process control

Summary Compared to the viscosity measurement under laboratory conditions there are additional demands on the measuring instrument when viscosity-dependent processes are to be monitored, controlled or regulated. Rotational-type viscosimeters with a coaxial cylinder system lend themselves for solving this problem. The various problems of viscosity measurement in production processes make high demands on the universal applicability of the viscosimeters. An instrument-technical solution on the basis of standardized basic modular units is of advantage. An instrument system process viscosimeters for viscosity measurements in receptacles and pipe lines is described.

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Zusammenfassung Gegenüber der Viskositätsmessung unter Laboratoriumsbedingungen ergeben sich zusätzliche Forderungen an das Meßgerät, wenn viskositätsabhängige Produktionsprozesse überwacht, gesteuert oder geregelt werden müssen. Rotationsviskosimeter mit koaxialem Zylindersystem sind zur Lösung dieser Aufgabe geeignet. Die unterschiedlichen Viskositätsmeßprobleme in Produktionsprozessen stellen hohe Anforderungen an die universelle Einsetzbarkeit der Viskosimeter. Vorteilhaft ist eine gerätetechnische Lösung auf der Basis von typisierten Grundbausteinen. Ein Gerätesystem Prozeßviskosimeter für Viskositätsmessungen in Behältern und Rohrleitungen wird beschrieben.

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With 3 figures     

Air-cooled gas-turbine discs: a review of recent research

The flow between corotating compressor or turbine discs and the flow between a turbine disc and an adjacent stationary casing can be respectively modelled by a rotating cavity and by a rotor-stator system. This paper reviews some of the recent experimental and theoretical work on flow and heat transfer in these two classes of rotating-disc systems. Comparisons between the theoretical and measured distributions of velocity, pressure, and Nusselt numbers are made for the rotating cavity with a superimposed radial flow of cooling air. For the rotor-stator system, some recent work on the fluid dynamics is outlined, and particular mention is made of the so-called “ingress problem” and of the use of pre-swirl air to improve the blade-cooling effectiveness.     

Rotating electroosmotic flow of an Eyring fluid

A perturbation analysis is presented in this paper for the electroosmotic(EO) flow of an Eyring fluid through a wide rectangular microchannel that rotates about an axis perpendicular to its own. Mildly shear-thinning rheology is assumed such that at the leading order the problem reduces to that of Newtonian EO flow in a rotating channel, while the shear thinning effect shows up in a higher-order problem.Using the relaxation time as the small ordering parameter,analytical solutions are deduced for the leading-as well as first-order problems in terms of the dimensionless Debye and rotation parameters. The velocity profiles of the Ekman–electric double layer(EDL) layer, which is the boundary layer that arises when the Ekman layer and the EDL are comparably thin, are also deduced for an Eyring fluid. It is shown that the present perturbation model can yield results that are close to the exact solutions even when the ordering parameter is as large as order unity. By this order of the relaxation time parameter, the enhancing effect on the rotating EO flow due to shear-thinning Eyring rheology can be significant.