A Numerical Investigation on the Influence of the Circular Ring on the Aerodynamic Noise Generated by a Cooling Fan

The influence of the width of the circular ring of a car cooling fan on the aerodynamic noise is investigated numerically through the determination of the overall sound pressure level(OASPL).The results demonstrate that when the circular rings cover near 2/3 of the width of the blade tips of the rotor in the axis direction,the rotor has the lowest OASPL and the related total pressure efficiency and flow mass rate are better than the corresponding values obtained for a reference rotor without a circular ring.With increasing the width of the circular ring in the axis direction,the tip vortex around the trailing edge of the blade tip becomes smaller and finally disappears.Meanwhile,a separated flow field arises gradually and then grows in size around the middle of the junction of the blade tips with the ring.When the circular rings cover nearly 2/3 s of the width of the blade tips of the fan in the axis direction,the extension of the separated flow around the blade’s tip attains a minimum.

GENERAL SOLUTION OF THE OVERALL BENDING OF FLEXIBLE CIRCULAR RING SHELLS WITH MODERATELY SLENDER RATIO AND APPLICATIONS TO THE BELLOWS (Ⅰ)-GOVERNING EQUATION AND GENERAL SOLUTION

The overall bending of circular ring shells subjected to bending moments and lateral forces is discussed. The derivation of the equations was based upon the theory of flexible shells generalized by E.L. Axelrad and the assumption of the moderately slender ratio less than 1/3 (i.e., ratio between curvature radius of the meridian and distance from the meridional curvature center to the axis of revolution). The present general solution is an analytical one convergent in the whole domain of the shell and with the necessary integral constants for the boundary value problems. It can be used to calculate the stresses and displacements of the related bellows. The whole work is arranged into four parts: (Ⅰ) Governing equation and general solution; (Ⅱ) Calculation for Omega_shaped bellows; (Ⅲ) Calculation for C_shaped bellows; (Ⅳ) Calculation for U_shaped bellows. This paper is the first part.

GENERAL SOLUTION OF THE OVERALL BENDING OF FLEXIBLE CIRCULAR RING SHELLS WITH MODERATELY SLENDER RATIO AND APPLICATIONS TO THE BELLOWS (Ⅳ)-CALCULATION FOR U-SHAPED BELLOWS

This is one of the applications of Part (Ⅰ),in which the angular stiffness, and the corresponding stress distributions of U_shaped bellows were discussed. The bellows was divided into protruding sections, concave sections and ring plates for the calculation that the general solution (Ⅰ) with its reduced form to ring plates were used respectively, but the continuity of the surface stresses and the meridian rotations at each joint of the sections were entirely satisfied. The present results were compared with those of the slender ring shell solution proposed earlier by the authors, the standards of the Expansion Joint Manufacturers Association (EJMA), the experiment and the finite element method. It is shown that the governing equation and the general solution (Ⅰ) are very effective.

GENERAL SOLUTION OF THE OVERALL BENDING OF FLEXIBLE CIRCULAR RING SHELLS WITH MODERATELY SLENDER RATIO AND APPLICATIONS TO THE BELLOWS (Ⅲ)-CALCULATION FOR C-SHAPED BELLOWS

This is one of the applications of Part (Ⅰ), in which the angular stiffness, the lateral stiffness and the corresponding stress distributions of C_shaped bellows were calculated. The bellows was divided into protruding sections and concave sections for the use of the general solution (Ⅰ), but the continuity of the stress resultants and the deformations at each joint of the sections were entirely satisfied. The present results were compared with those of the other theories and experiments, and are also tested by the numerically integral method. It is shown that the governing equation and the general solution (Ⅰ) are very effective.

MAGNETOHYDRODYNAMIC PIPE FLOW IN DUCTS WITH PARTIAL CIRCULAR RING CROSS SECTION AND ANNULAR CROSS SECTION

In this paper we use the Green function method to solve the problem of steady one dimensional flow of an incompressible viscous, electrically conducting fluid through a pipe with partial circular ring cross sec- tion and one with annular cross section, in the presence of an applied transverse uniform magnetic field, We ob- tain analytic solutions and carry out some numerical calculations of the velocity distribution and induced magnet- ic field.

GENERAL SOLUTION OF THE OVERALL BENDING OF FLEXIBLE CIRCULAR RING SHELLS WITH MODERATELY SLENDER RATIO AND APPLICATIONS TO THE BELLOWS (Ⅱ)- CALCULATION FOR OMEGA-SHAPED BELLOWS

is one of the applications of (Ⅰ), in which the angular stiffness, the lateral stiffness and the corresponding stress distributions of Omega_shaped bellows were calculated, and the present results were compared with those of the other theories and experiments. It is shown that the non_homogeneous solution of (Ⅰ) can solve the pure bending problem of the bellows by itself, and be more effective than by the theory of slender ring shells; but if a lateral slide of the bellows support exists the non_homogeneous solution will no longer entirely satisfy the boundary conditions of the problem, in this case the homogeneous solution of (Ⅰ) should be included, that is to say, the full solution of (Ⅰ) can meet all the requirements.

Orbital Angular Momentum Generation Using Circular Ring Resonators in Radio Frequency

Electromagnetic field generators based on circular ring resonators, whose perimeters are integer times of equivalent wavelength, are well known to have attractive potential for producing radio vortexes carrying orbital angular momentum （OAM）. We study the radiation characteristics of the generators based on radiation vector and antenna array theory. The behaviors of radiation patterns, field intensity and phase distribution are investigated in detail, and show classical features of OAM beams. The evolution of the generators performance versus the OAM state is also analyzed. The proposed generators can be realized by all kinds of microwave transmission lines, verified by two different prototypes. The discussions and conclusions drawn in this study are useful and meaningful for the radio OAM generator design.

AERODYNAMIC ANALYSIS OF CIRCULAR PLATE-SHAPED AND CIRCULAR RING-SHAPED SQUEEZE FILM BEARINGS

Aerodynamics of circular plate- and circular ring-shaped squeeze film hearings is analyzed in detail, yielding analytic expressions for the pressure distribution of these hearings. Several formulae for these hearings are modified using the developed method. The paper also gives numerical results oj pressure distribution and load-hearing capacities of these hearings.

COMPLEX EQUATIONS OF FLEXIBLE CIRCULAR RINGSHELLS OVERALL_BENDING IN A MERIDIAN PLANE AND GENERAL SOLUTION FOR THE SLENDER RING SHELLS

Complex equations of circular ring shells and slender ring shells overall-bending in a meridian plane are presented based on E. L. Axelrad's equations of flexible shells of revolution render asymmetrical lending. It turns out that the equations are analogous to Novozhilov's equations of symmetrical ring shells, where general sollutions have been given by W. Z. Chien. Therefore, by analogy with Chien's solution, a general solution for equations of the slender ring shells is put forward, which can be used to salve bellow's overall-bending problems.

Thermohydraulics of Turbulent Flow Through Heat Exchanger Tubes Fitted with Circular-rings and Twisted Tapes

circular-ring turbulators (CRT ) 和扭曲的磁带(TT ) 的影响打漩在一个圆试管的热转移改进，压力落下和热表演因素特征上的发电机被报导。circular-ring turbulators 个别地被采用并且和扭曲的磁带打漩在试管的激烈的节的发电机。三不同沥青比率(l/D = 1.0， 1.5，和 2.0 ) CRT 和三不同扭曲比率(y/W = 3， 4，和 5 ) TT 被介绍。实验在一个一致的墙热流动条件下面作为工作液体用空气被进行，为在 6000 和 20000 之间的雷纳兹数字。试验性的结果表明热转移率，磨擦因素和联合 CRT 和 TT 的热表演因素独自比 CRT 的那些更加高。为检验的范围，在与联合设备装备的试管，分别地，吝啬的 Nusselt 数字，磨擦因素和热性能的增加在在试管的那些上是 25.8% ， 82.8% 和 6.3% 与 CRT 独自一个。1.42 的最高热的表演因素被作出对有利的裁决与 l/D = 由 CRT 组成的联合设备 1.0 并且有 y/W = 的 TT 3。Nusselt 数字，磨擦因素和有联合设备的试管的热表演因素的关联也以雷纳兹数字， Prandtl 数字，扭曲比率和沥青比率被开发。

Large eddy simulation of a vortex ring impinging on a three-dimensional circular cylinder

Abstract A vortex ring impacting a three-dimensional circular cylinder is studied using large eddy simulation （LES） for a Reynolds number Re = 4 × 10^4 based on the initial translation speed and diameter of the vortex ring. We have investigated the evolution of vortical structures and identified three typical evolution phases. When the primary vortex closely approaches to the cylinder, a secondary vortex is generated and its segment parts move inward to the primary vortex ring. Then two large-scale loop-like vortices are formed to evolve in opposite directions. Thirdly, the two loop-like vortices collide with each other to form complicated small-scale vortical structures. Moreover, a series of hair-pin vortices are generated due to the stretching and deformation of the tertiary vortex. The trajectories of vortical structures and the relevant evolution speeds are analyzed. The total kinetic energy and enstrophy are investigated to reveal their properties relevant to the three evolution phases.

Analysis of Metamaterial Cloaks Using Circular Split Ring Resonator Structures

A novel microwave cloak using circular split ring resonator(SRR)based metamaterial structure has been proposed in this paper.The cloak which operates at a frequency of 10.6 GHz is composed of cylindrical dielectric sheets printed with circular split ring resonators of spatially varying and anisotropic material properties.The article also focuses on the phenomenon of resonant splitting in circular SRR microwave cloak.A detailed analysis of various linear metamaterial arrays and their response has also been elucidated.

Compact and broadband circularly polarized ring antenna with wide beam-width for multiple global navigation satellite systems

A compact and broadband circularly polarized （CP） annular ring antenna with wide beam-width is proposed for multiple global navigation satellite systems （GNSS） in the L1 band. The annular ring is excited by two modified L-probes with quadrature phase difference. It has a 36.3% 10-dB return loss bandwidth and a 13% 3-dB axial ratio bandwidth, because of the orthogonal L-probes with 90° phase difference. The measured peak gain of the antenna is 3.9 dBic. It can detect the satellites at lower elevation as its half power beam-width （HPBW） is 113° in both the x-z and y-z planes, achieving a cross-polarization level of larger than 25 dB. Noticeably, the antenna achieves 89% size reduction compared with the conventional half wavelength patch antennas. It can be used in hand-held navigation devices of multiple GNSS such as COMPASS, Galileo, GPS and GLONASS.

四塔支承超大直径圆环复杂结构设计

上海临港新片区新建一幢地标建筑,该建筑为四幢46.8 m高的塔楼支承一个直径150 m、高度8.6 m的超大直径圆环,结构复杂。结构主要特点是超大直径圆环内侧采用倒三角形空间桁架、楼面梁采用变截面悬挑钢梁,四幢塔楼采用钢框架-屈曲约束支撑-屈曲约束钢板墙结构体系,超大直径圆环和四幢支承塔楼之间采用一个对角铰接、另一个对角滑动支座加黏滞阻尼器的连接方式。由于建筑师的要求,超大直径圆环横截面为外侧开口的C形截面,如何克服圆环外侧开口带来的扭转作用是设计难点。主要进行了支承塔楼的结构设计和计算分析,超大直径圆环的结构选型和抗扭性能研究,圆环和支承塔楼连接设计,支承塔楼和圆环组成的整体结构计算分析,整体结构大震下弹塑性时程分析。设计和研究成果可为圆环结构、多个塔楼共同支承一个上部结构等类似工程设计提供借鉴。

不同钢纤维类型对高性能混凝土抗折性能影响模拟分析

本文以钢纤维混凝土抗折强度计算理论为基础,分析混凝土在分别添加平直形和圆环形钢纤维的情况下抗折强度的变化。运用有限元模拟分析软件ABAQUS进行数值模拟,不同掺量的平直形和圆环形钢纤维掺入混凝土梁,得到梁受压损伤云图和荷载位移曲线的变化,分析平直形和圆环形钢纤维对高性能混凝土抗折性能的影响,验证了有限元模拟的合理性。通过对有限元数值模拟结果的分析,相比较钢纤维体积掺量为0.5%,当钢纤维体积掺量为1.0%和1.5%时,平直形钢纤维混凝土的抗折强度分别增加了20.02%和26.62%,圆环形钢纤维混凝土的抗折强度分别增加了9.64%和46.98%。而对比两种形状的钢纤维掺入,体积含量为1.5%的圆环形钢纤维对混凝土的抗折强度,延性性能的增强效果更优。

圆环非线性恢复力的梁约束模型建模

圆环隔振器是一种以圆环结构为基础的非线性隔振器,圆环结构在压缩变形过程中会受到压力和环面拉伸的耦合作用,从而产生非线性恢复力,对圆环结构非线性恢复力的精确建模是研究隔振器性能的关键。将圆环结构等分为多段曲梁,利用梁约束模型对每段曲梁建立计及几何非线性的力-位移关系模型,结合曲梁间的力传递关系和几何约束关系,建立了圆环整体在压缩过程中的非线性恢复力模型,并计算了圆环变形过程中所有分段点处的正应力。通过电子伺服疲劳试验机对圆环结构在压缩过程中的恢复力进行了测量,验证了梁约束模型的建模精度。研究结果表明,利用梁约束模型可以表征圆环结构非线性恢复力特性,其建模精度与椭圆积分法相当,而模型表达式和求解过程都比椭圆积分法简洁。圆环在压缩量最大时正应力最大,此时最大正应力在圆环的上下端点。梁约束模型的建模精度随着分段数的增加而提高,当分段数大于12时,梁约束模型的恢复力计算误差小于2%。

Application of Non-homogeneous Solution for Equations of Slender Ring Shells to Overall-Bending Problem of Ω-Shaped Bellows

A linear complex equation for slender ring shells overall bending in a meridian plane is given based on E. L. Axelrad's theory of flexible shells. And the non homogeneous solution is obtained from W. Z. Chien's solution for axial symmetrical slender ring shells to investigate the overall bending problem of Ω shaped bellows subjected to pure bending moments. The values calculated in the present paper are very close to the existing experiment. Thus Chien's work on axial symmetrical problems for ring shells has been extended to overall bending problems.

弹性环梁支撑下圆形深基坑支护结构变形解析解

将环梁和支护结构分别视为弹性圆环和弹性圆柱薄壳,基于环梁和圆柱壳的变形协调,得到了具有任意数目弹性环梁支撑圆形深基坑支护结构变形的解析解.在验证解析解合理性和可靠性的基础上,针对某一实际圆形基坑工程,比较了在刚性和弹性环梁支撑下支护结构变形和内力的差异,并分析了支护结构底部边界条件、环梁弹性模量、尺寸和数量以及位置等参数对支护结构变形和内力分布的影响.研究结果表明:相对于刚性环梁支撑,弹性环梁支撑处内力变化较小,环梁弹性模量和尺寸的改变只对基坑挖掘面以上支护结构变形和内力影响显著,而对挖掘面以下的支护结构变形和内力几乎没有影响.该研究成果为圆形基坑支护结构设计提供了理论依据和指导.

周期变半径薄圆环模态实验研究

针对变半径法向等厚薄圆环的面内振动模态问题,依据振动测试理论,提出了定测量点、变激振点的实验方法,以简化实验操作流程。利用激光多普勒测振仪和LMS振动测试系统进行测振实验,得到了变半径圆环前八阶振动的固有频率和振型,并将结果与有限元仿真及现有文献相关结论对比,验证了实验方法的可行性。归纳了半径变化周期p和模态阶数n不同关系时结构固有频率的分裂规律,并总结了法向厚度h和半径变化幅度Δ对圆环固有频率的影响。

基于有限元分析的薄壁圆环零件加工工艺研究

目的针对薄壁圆环零件刚性差、强度弱、加工过程中易发生受力变形的难题,基于薄壁圆环零件加工成形工艺,优化零件的加工工艺和装夹方式。方法考虑到工艺对零件加工质量的影响,对零件的加工方法和装夹方式进行研究,提出一种新的加工工装,运用ANSYS软件对零件装夹受力情况和振动变形进行有限元模拟仿真分析。结果该工装不仅能够防止零件发生应力集中,还提升了零件加工精度和表面质量,工装设计为一夹一顶方式,只需调整顶尖压紧力便可确保圆环件在加工中不会发生变形,同时拆装方便,提高了生产效率。结论对于薄壁圆环件的数控加工,可通过科学设计零件加工工艺流程和装夹工装,解决零件受力变形问题,保证薄壁圆环零件的尺寸、形位公差和表面粗糙度符合要求,提高了生产加工效率,满足产品批量生产使用要求,为类似薄壁件的加工提供了参考。