网眼罗拉紧密纺集聚区三维流场数值模拟与分析

本文采用Fluent软件对网眼罗拉紧密纺系统集聚区流场进行数值仿真模拟,可以形象、直观地对流场内气流分布做出分析和评价,定量解析集聚区域内流场的静压特性及速度分布规律。研究结果表明：静压值由圆孔壁面向圆孔中心部分逐渐增大,并且吸风槽口中心线处的圆孔静压值要大于其他位置圆孔静压值;两个圆孔之间的气流流动并不孤立;低位置的气流流动受圆孔影响较大,各轴向速度分量随着圆孔的间隔出现呈现波动性,高位置的气流流动更加平稳,各轴向速度分量没有间隔性突变。     

热声激励下金属薄壁结构的随机疲劳寿命估算

金属薄壁结构在热声载荷作用下会发生复杂的大挠度非线性响应,结构内部快速变化的复杂应力严重降低了结构的疲劳寿命。在结构热声激振非线性响应分析基础上,采用雨流循环计数法对应力响应时间历程进行疲劳循环计数,通过Morrow TFS,SWT平均应力模型将疲劳循环进行零均值等效处理,结合Miner线性损伤累积理论,计算结构的热声疲劳寿命。以2024-T3型铝合金薄板为研究对象,计算得到了屈曲前后四种温度条件有限带宽高斯白噪声载荷作用下的非线性动态响应,并估算了疲劳寿命。分析结果表明,屈曲前结构的疲劳寿命随着温度升高下降,屈曲后结构持续跳变时的疲劳寿命持续下降直至最低,结构进入间歇跳变区域后疲劳寿命上升,结构热声疲劳寿命与非线性响应特征具有特定的对应关系。     

轴压下纵向开槽方形管的耗能能力

运用非线性有限元程序LS-DYNA对轴压下纵向开槽方形管的耗能能力进行研究。通过冲压作用开槽,在随后的碰撞试验中考虑了冲压作用中产生的有效塑性应变和厚度变化的分布。从模拟结果中可知:当在边墙中开槽时,一般钢管的耗能率将升高82·7%,钢管最大受力减少22·3%。对部分参数的影响进行了分析,包括钢管厚度、开槽长度和开槽数量,并且描述了开槽钢管变形模式的特征。研究发现:开槽可以有效提高薄壁结构的防撞性。     

Tensegrity Structures with Buckling Members Explain Nonlinear Stiffening and Reversible Softening of Actin Networks

In this paper, a three-member tensegrity structure is used as a conceptual model for the dendritic actin network in living cells. The pre and postbuckling behavior of the tensegrity is analyzed basing on the energy method. Analytical simulations are carried out on the tensegrity by using the experimentally obtained scales and mechanic properties of actin-filaments for the structural members of the tensegrity. The model exhibits a stress stiffening regime followed by a stress softening regime in the load-stiffness relationship, which qualitatively tallies with the experimentally observed response of actin networks. Due to the simplicity of the model, there is only a single compressed member and the structure buckles abruptly, which results a softening regime much steeper than that observed in the actin network. To take the member length variety into account, we propose a conceptual large-scale tensegrity system with various member lengths, and its behavior is approximately estimated by the mean response of a large number of three-member tensegrity cells with their member length varying in the range of filament lengths. The obtained mean response exhibits a much better fitness to the response of actin networks than those exhibited by the single tensegrity model. The findings reported in this paper indicate that the dendritic actin network may work as a complex tensegrity system, when it is subjected to a stress.     

Analysis of weld-induced residual stresses and distortions in thin-walled cylinders

Circumferential weld specifically in thin-walled structures is a common joint type in the fabrication of structural members in aerospace, aeronautical and pressure vessel industries. This type of weld joint suffers various types of weld-induced residual stress fields (hoop and axial) and deformation patterns (axial shrinkage, radial shrinkage). These imperfections have negative effects on fabrication accuracies and result in low strength welded structures that can lead to premature failures. To precisely capture the distortions and residual stresses, computational methodology based on three-dimensional finite element model for the simulation of gas tungsten arc welding in thin-walled cylinders is presented. Butt-weld geometry with single “V” for a 300 mm outer diameter cylinder of 3 mm thick is used. The complex phenomenon of arc welding is numerically solved by sequentially coupled transient, non-linear thermo-mechanical analysis. The accuracy of both the thermal and structural models is validated through experiments for temperature distribution, residual stresses and distortion. The simulated result shows close correlation with the experimental measurements. This paper was recommended for publication in revised form by Associate Editor Dae-Eun Kim Naeem Ullah Dar received the B.Sc. and M.S. degrees in mechanical engineering from the Univer-sity of Engineering & Technology, Taxila, in 1989 and 2004 respectively. Presently, he is PhD scholar in mechanical engineering at UET, Taxila. His publications are over 25 in different Int. journals and conferences. His research includes manufacturing process (GTAW welding process, HSM process, abrasive waterjet process, incremental forming etc), welding simulations, optimization, and expert system. He spent more than 16 years in different mechanical manufacturing fields. He also received MBA degree in project management and six sigma black belt from SQII in 2005. Ejaz M. Qureshi is currently a graduate student working for his PhD in computational weld mechanics at National University of Sciences and Technology (Pakistan). After receiving his B.S. degree in Mechanical Engineering in 1997, he worked for five years in an industrial manufacturing setup producing hi-tech welded structures. Qureshi has published numerous technical papers in professional refereed journals and conferences of international repute. He has also been an active referee for several conferences and journals. His current research interests include: manufacturing processes simulation, structural integrity of welded structures and computational plasticity of cylinders/pressure vessels. M.M.I. Hammouda received the B.Sc. and M.Sc. degrees in mechanical engineering from Al Azhar University, Cairo, Egypt in 1970 and 1975 respectively. He received his PhD degree in mechanical engineering from Cambridge University, England in 1978. His has more than 35 publications in different International journals and conferences. The research includes mechanical behavior of engineering materials, linear elastic and elastic-plastic fracture mechanics, manufacturing process modeling and simulations. Presently being a foreign faculty professor in mechanical engineering department of UET, Taxila, Pakistan, he spent more than 25 years in academic and teaching. He is a member of the Editorial Board of the International Journal of Fatigue and Fracture of Engineering Materials and Structures. [www.blackwell-science.com].     

A series solution for spatially coupled deflection analysis of thin-walled Timoshenko curved beam with and without elastic foundation

The exact solutions for the spatially coupled deflection and the normal stress at an arbitrary location of a crosssection of the thin-walled Timoshenko curved beam with symmetric and non-symmetric cross-sections with and without two types of elastic foundations are newly presented using series solutions for the displacement parameters. The equilibrium equations and the force-deformation relations are derived from the elastic strain energy including the effects of shear deformation and the axial-flexural-torsional coupling, and the strain energy considering the foundation effects. The explicit expressions for displacement parameters are derived by applying the power series expansions of displacement components to the simultaneous ordinary differential equations. Next, the element stiffness matrix is determined by using the force-deformation relationships. The normal stress at any arbitrary location of the cross-section for a curved beam is evaluated from the stiffness matrix. To verify the validity and the accuracy of this study, the displacements and the normal stresses of curved beams are presented and compared with the analytical solutions, the finite element results using the isoparametric curved beam elements based on the Lagrangian interpolation polynomial, and the detailed three-dimensional analysis results using the shell elements of SAP2000. This paper was recommended for publication in revised form by Associate Editor Maenghyo Cho Nam-Il Kim received his B.S. degree in Civil and Environmental Engineering from Sungkyunkwan University, Korea, in 1996. He then received his M.S. and Ph.D. degrees from Sungkyunkwan University in 1998 and 2004, respectively. Dr. Kim is currently a research professor at Civil and Environmental Engineering at Myongji University in Korea. Dr. Kim’s research interests include stability and vibration of steel and composite structures. Dong Ku Shin received his B.S. and M.S. degrees in Civil Engineering from Seoul National University, Korea, in 1983 and 1985, respectively. He then received his Ph.D. degree from Virginia Tech. at Blacksburg, VA, USA, in 1990. Dr. Shin is currently a professor of Civil and Environmental Engineering Department at Myongji University in Korea. Prof. Shin’s research interests include LRFD design of steel bridges and stability of composite structures.     

基于神经网络的铣削复杂薄壁件受力变形分析和建模研究

铣削过程的复杂性使加工变形问题很难得到精确的解析解。为研究铣削过程中复杂薄壁件受力变形模型,将人工神经网络引入到摆线轮加工变形模型研究过程中,以有限元仿真结果为依据,通过改进的BP神经网络算法,建立了高速铣削轴承钢摆线轮铣削力与变形之间的非线性映射模型。结果显示所建立的网络模型具有较高的精度和良好的泛化能力,为进一步实现变形控制提供科学依据。     

工业废渣混凝土多孔砖的试制

工业废渣混凝土多孔砖是指以粉煤灰、炉渣及其他废渣、水泥、各种轻集料、外加剂、水等为主要成分拌合制成的,其中,粉煤灰和各种废渣掺量不低于70%。具有节约材料资源、降低成本、方便运输的使用优点,为此介绍了该类产品的原材料技术配制与处理要求、工艺流程与生产操作控制等。     

2008-2009CUVA女排队员非技术指标比较分析

以参加2008-2009年度中国大学生排球联赛南北赛区普通组女排队员为对象,运用文献资料调研、数理统计等方法,对其年龄、身高、网上高度等非技术指标进行分类比较分析．结果表明：南北赛区队员的平均年龄、身高、网上高度呈现显著性差异,总体上北区队员的非技术指标高于南区,其中北1集团的优势更为明显．     

On sixfold coupled vibrations of thin-walled composite box beams

This paper presents a general analytical model for free vibration of thin-walled composite beams with arbitrary laminate stacking sequences and studies the effects of shear deformation over the natural frequencies. This model is based on the first-order shear-deformable beam theory and accounts for all the structural coupling coming from the material anisotropy. The seven governing differential equations for coupled flexural–torsional–shearing vibration are derived from the Hamilton’s principle. The resulting coupling is referred to as sixfold coupled vibration. Numerical results are obtained to investigate the effects of fiber angle, span-to-height ratio, modulus ratio, and boundary conditions on the natural frequencies as well as corresponding mode shapes of thin-walled composite box beams.