Performance Analysis of Plant Shells/PVC Composites under Corrosion and Aging Conditions

To make full use of plant shellfibers(rice husk,walnut shell,chestnut shell),three kinds of wood-plastic com-posites of plant shellfibers and polyvinyl chloride(PVC)were prepared.X-ray diffraction analysis was carried out on three kinds of plant shellfibers to test their crystallinity.The aging process of the composites was conducted under 2 different conditions.One was artificial seawater immersion and xenon lamp irradiation,and the other one was deionized water spray and xenon lamp irradiation.The mechanical properties(tensile strength,flexural strength,impact strength),changes in color,water absorption,Fourier transform infrared spectroscopy(FTIR),and microstructures of the composites before and after the two aging experiments were analyzed.The results showed that the chestnut shell had the highest crystallinity,which was 42%.The chestnut shell/PVC composites had the strongest interface bonding,the least internal defects,and the best general mechanical properties among the three composites.Its tensile strength,bending strength and impact strength were 23.81 MPa,34.12 MPa,and 4.32 KJ·m^(-2),respectively.Comparing the two aging conditions,artificial seawater immersion and xenon lamp irradiation destroyed the quality of the combination of plant shellfibers and PVC,making the internal defects of the composites increase.This made the water absorption ability and changes in the color of the composites more obvious and led to a great decrease in the mechanical properties.The general mechanical properties of the chestnut shell/PVC composites were the best,but their water absorption ability changed more obviously.

ON THE STABILITY ANALYSIS OF PLATES AND SHELLS USING A QUADRILATERAL,16-DEGREES OF FREEDOM PLAT SHELL ELEMENT DKQ16

The linear buckling problems of plates and shells were analysed using a recently developped quadrilateral,16-degrees of freedom flat shell element (called DKQ16).The geometrical stiffness matrix was established.Comparison of the numerical results for several typical problems shows that the DKQ16 element has a very good precision for the linear buckling problems of plates and shells.

Medium performance effect on the high output energy from a xenon lamp-pumped pyrromethene-567 solid-state dye laser

In order to obtain a high output energy from a xenon lamp-pumped solid-state dye laser, homogeneities of laser mediums and flatnesses of medium faces with different processing treatments are discussed in the paper. The mediums without aging treatment, which are prepared by using a prepolymer process and have diamond-machined end faces to produce the required optical finish, give a highest laser output of 281.9 mJ with 0.215% slope efficiency at 2.0x 10^-4 mol/L. The best medium lifetime is 21 shots to 50% of original output equating 74.6 k J/liter.

Shell Roof of Tall Buildings in Earthquake Zones

This paper studies and analyzes tall buildings with shell and flat roof responses designed for gravity and earthquake loads in different zones having different soil profiles. These tall buildings having two different heights and different configurations are simulated with different load combinations. The responses of the simulated structural models with flat and shell roofs are studied and analyzed. These responses draw recommendations and guidelines for preliminary design of structurally efficient and reliable tall buildings with shell roof in earthquake zones. Five different earthquake zone factors (Z1 - Z5) along with the five different soil profiles (S1 - S5) are selected in this study. The non-linear dynamic response of buildings was obtained using three simulated models of buildings;square/rectangular, circular, and tube-shaped building. Total of 12 building models, four under each category, are analyzed using the finite element software (STAAD pro) subjected to the gravity as well as earthquake loading defined by UBC and IBC codes. Each building model is analyzed with two different story heights;which are 120 meters for 30 stories and 72 meters for 18 stories respectively. Horizontal and vertical displacement comparison is made among the flat roof and shell roof building for 32 and 18 stories building satisfying the ACI code of design requirement and drift index of 1/500 (0.002). The results showed that the drift index value for all the studied buildings is close to 0.002. All the maximum horizontal and vertical deflections occur under the earthquake zone-5 (0.40 gravitational acceleration) with soil profile-5 (Soft soil). The shell roof slab with less thickness than the flat roof slab did satisfy the horizontal and vertical deflection limits, therefore, it is more economical than the flat roof slab.

Numerical and Experimental Investigation of an Elliptical Paraboloid Shell Model

For practical engineering purpose, a new flat shell element baptized （ACM_Q4SBE1） is presented in this paper. The formulated element can be used for the analysis of thin shell structures; no matter how the geometrical shape might be. Tests on standard problems have been examined. Since, the analysis of thin shell structures has generally been purely carried out on a theoretical basis; it is of importance to present some experimental results of an elliptical paraboloid under uniformly distributed load pressure. The results obtained from both numerical and experimental work are presented.

Numerical Simulation of Continuous Tension Leveling Process of Thin Strip Steel and Its Application

Cold-rolled thin strip steel of high flatness quality undergoes multistage deformation during tension leveling. Thus, the parameters of set-up and manipulating are more difficult. With the aid of FE code MSC. MARC, the tension leveling process of thin strip steel was numerically simulated. Concentrating on the influence of the roll intermeshes in 2# anti-cambering on the distribution and magnitude of residual stresses in leveled strip steel, several experiments were clone with the tension leveler based on the results from the simulation. It was found from the simulation that the magnitude of longitudinal residual stresses in the cross-section of the leveled strip steel regularly presents obvious interdependence with the roll intermeshes in 2# anti-cambering. In addition, there is a steady zone as the longitudinal residual stresses of the surface layers in leveled strip steel vary with the roll intermeshes of 2# anticambering, which is of importance in the manipulation of tension levelers. It was also found that the distribution of strains and stresses across the width of strip steel is uneven during leveling or after removing the tension loaded upon the strip, from which it was found that 3D simulation could not be replaced by 2D analysis because 2D analysis in this case cannot represent the physical behavior of strip steel deformation during tension leveling.

Static Analysis of Eolic Blade through Finite Element Method and OOP C＋＋

This work deals with a description of an elastic analysis of eolic blade （preprocessing, processing and post-processing stages）. The eolic blade geometry is approximated by flat finite elements in which the membrane effects are evaluated using the FF （free formulation） finite element and the flexure effects are calculated using DKT （discrete shear triangle） finite element. The pre-processing stage is implemented using OpenGL library, to provide the graphical construction for geometry, mesh orientation, and other requirements of the finite element model. For the processing stage is built a specific dll （dynamic link library） library implemented in C＋＋ language for the FF and DKT elements analysis. The post-processing stage has been built using specific dialogs to present all results in the graphic interface, where the static displacements of the eolic blade model are shown.

Parametric Tool for Static and Dynamic Analysis of Wind Turbine Tower Using Finite Element Method

This work deals with a description of a parametric tool for elastic analysis of wind turbine tower, incorporating all analysis steps （preprocessing, processing and post-processing）. The tower geometry is approximated by fiat elements in which the membrane effects are evaluated using the FF （free formulation） finite element and the flexure effects are calculated using DKT （discrete shear triangle） finite element. The user-friendly system is implemented using OpenGL library to provide the graphical construction for geometry, mesh orientation, and other requirements of the finite element model. For the processing stage is built a specific dll library implemented in C＋＋ language for the analysis using the FF and DKT finite elements. The post-processing stage is build using specific dialogs box to present all results. The displacement results are visualized in the graphic interface to show the static and dynamic deformations of the tower. Some examples are presented to show all the tasks of the parametric tool.

平屋顶VS薄壳屋顶——20世纪初钢筋混凝土结构发展的两条路径与现代主义建筑运动之反思

钢筋混凝土结构的出现、成熟及其应用是19世纪以来现代建筑发展的一条重要线索。20世纪以后,从钢筋混凝土结构发展出两种基本的屋顶形式——平屋顶和薄壳屋顶。当前建筑史著述常聚焦于前者,对薄壳屋顶的缘起、发展以及二者的关联关注不多。本文将钢筋混凝土结构的发展历程分为20世纪之前由法国推动、模仿新古典主义的初始期,和20世纪后尤其是德意志制造联盟成立后由德国建筑师领导的成熟期,后一时期的突出标志包括钢筋混凝土结构的设计和施工与工业化过程相结合、包豪斯学派登上历史舞台并成为现代主义运动的主要推动力量,以及钢筋混凝土薄壳体系的创立及完善。1920年代以降,随着平屋顶崛起为现代主义建筑的象征之一以及薄壳结构体系逐渐成熟,现代主义运动也发展壮大,形成世界性影响。本文梳理钢筋混凝土结构的这两条发展路径及其相互关联,并在此视角下反思现代主义的若干核心命题。

发夹式换热器U型扁弯壳结构静力学分析及结构优化设计

采用Ansys有限元分析软件针对发夹式循环冷却器的法兰U型扁弯壳结构进行静力学分析和强度校核。基于有限元模拟结果,依据标准JB 4732—1995进行强度校核的结果表明,在U型扁弯壳封头极值路径处,一次应力与二次应力之和为397 MPa,超出许用应力值351 MPa,强度校核不合格。设置3个轴向加强筋板和1个竖直方向加强筋板后,U型扁弯壳封头的最大应力由515 MPa下降至124 MPa。

浸润性对沟槽平板微热管传热性能的影响

对于沟槽平板微热管,浸润性是影响其传热性能的重要因素。为研究沟槽平板微热管管壳内壁浸润性对传热性能的影响,文中使用机械加工的方法在管壳内壁打磨出沟槽,以甲醇为工质,通过控制化学刻蚀时间,制备出全管壳接触角约为10°、29°、84°、87°的管壳内壁。将此结构引入沟槽平板微热管中,对其进行了传热性能实验和试样表面的表征。实验结果表明:当接触角为29°、输入功率为2.5 W时,沟槽平板微热管的传热性能最好,其传热热阻比接触角为84°的沟槽平板微热管减小了55.4%。还发现沟槽平板微热管全管内壁接触角过小,会导致绝热段工质流速减慢,从而影响传热性能。

改进有限条法在平壳条振动特性研究中的应用

针对平壳条结构的振动特性问题,通过分析有限单元法的特点和应用,将改进的傅里叶级数法与有限单元法结合实现了任意边界条件的模拟,解决了平壳条结构对其梁函数边界条件的依赖性,从而提出一种高效、准确的半解析半数值方法—改进有限条法。根据Hamilton能量变分原理,推导出有限条元的刚度矩阵和质量矩阵并进行了平壳条结构自振特性分析。通过上机编程完成数值计算,并与商业有限元软件计算得到的结果进行对比分析,验证了该方法的有效性和准确性。进一步分析了截断级数、边界弹簧刚度系数、尺寸参数对系统频率的影响规律。

新型折板式空腹拟扁网壳的动力性能研究

折板式空腹拟扁网壳是结合空腹夹层板和折板网壳的力学优势形成的一种新型结构。为了研究该结构在地震作用下的力学性能,论文基于有限元分析软件ANSYS,选出三组8度罕遇地震下的地震波,分别对其进行水平、竖向和三向地震作用下的研究。讨论跨中顶点处位移响应和各构件刚度改变对动内力系数的影响情况。结果表明:结构刚度很好;结构受水平地震作用影响较大,与动力特性分析中,结构一阶振型X向平动相对应;结构弯矩动内力系数大于轴力动内力系数;相同条件下的地震波对结构动内力系数影响不大;矢跨比增大会降低构件的动内力系数;构件刚度的改变对该类型构件的动内力系数影响较大,对其他类型构件影响较小。

Construction and Application of Multivariable Finite Element for Flat Shell Analysis

Based on B-spline wavelet on the interval （BSWI） and the multivariable generalized variational principle, the multivariable wavelet finite element for flat shell is constructed by combining the elastic plate element and the Mindlin plate element together. First, the elastic plate element formulation is derived from the generalized potential energy function. Due to its excellent numerical approximation property, BSWI is used as the interpolation function to separate the solving field variables. Second, the multivariable wavelet Mindlin plate element is deduced and constructed according to the multivariable generalized variational principle and BSWI. Third, by following the displacement compatibility requirement and the coordinate transformation method, the multivariable wavelet finite element for fiat shell is constructed. The novel advantage of the constructed element is that the solving precision and efficiency can be improved because the generalized displacement field variables and stress field variables are interpolated and solved independently. Finally, several numerical examples including bending and vibration analyses are given to verify the constructed element and method.

Numerical Simulation on Flow and Heat Transfer at Shell-Side of Flat-Tube Heat Exchangers

The fluid flow and heat transfer of the shell-side in one type of flat-tube heat exchangers（FHE） were studied through numerical simulation and experimental methods.In the numerical simulation,hot/cold air was set as working fluid,and the standard k-ε turbulence model supplemented by boundary conditions was used,and also the control volume method was used to the discrete control equations.Compared with the same type of circular-tube heat exchangers（CHE）,the numerical simulation results show that the pressure drop at the shell-side of FHE decreases by 12%-20%,and heat transfer coefficient increases by about 24%.The coefficient of integral performance Nu/ζ 0.29 has an increment of 22%-34%.Under the same conditions,the experimental results of temperature and the overall pressure drop show that the deviation percentage with those of numerical simulation are less than 8% and 25%,respectively.Both results verify that the heat transfer efficiency and flow resistance characteristics of FHEs are superior to that of CHEs.

国内外复合材料工艺设备发展述评之十三——布带缠绕

本文分析了复合材料布带缠绕生产所用设备的发展历程,指出其优缺点,并对今后发展提出建议。

钢拱桥边跨三角区扁平钢箱梁剪力滞影响研究

为了研究扁平钢箱梁的剪力滞效应对大跨径钢拱桥边跨三角区刚度的影响,分别建立了梁单元模型和梁壳混合单元模型,结果表明:该扁平钢箱梁的剪力滞后导致边跨三角区刚度减小,使得钢箱梁和拱肋的挠度比按全截面有效的梁单元计算的结果大。

新型无极LCD平板背光源

为了降低制作成本,提高生产效率,实现液晶显示器在大尺寸品种上的高画质化,文章介绍研制的一种新型等离子体激发发光平板背光源。该电光源无电极,在两片平板玻璃中间充入纯氙气(气压2.67×104Pa),玻璃的外表面上密封一层透明水膜作为导电介质,以1.1mm厚的玻璃板作为介质阻挡层,在高频交变电压的作用下,产生等离子体,激发荧光粉发光。发光亮度可达3000cd/m2,最佳激发频率10.2kHz,启动电压6kV,发光均匀度大于92%;并综合评价了驱动电压、激发频率和样品厚度等因素对背光源发光特性的影响。

无汞等离子体平板光源发光效率的研究

研究了无汞等离子体平板荧光光源的气压、气隙、气体组成、光源结构及荧光粉加工对光源发光效率的影响。通过优化,光源的发光效率显著提高。实验结果表明,在450Torr、纯氙气、气体间隙0.7mm、前板玻璃厚为2.8mm,在前板采用60%浓度荧光粉图案印刷获得约20 m厚荧光粉层时,尺寸130mm×90mm的等离子体平板光源的发光效率和亮度超过40lm.W 1、11000cd.m 2,光通量超过500lm。通过优化,获得了较高的亮度和较高的发光效率,讨论了各影响因素引起光源发光效率变化的原因。

平面介质阻挡Xe放电荧光灯型LCD背光源的新进展

近年来随着大屏幕液晶显示器的快速发展,对背光源性能的要求也越来越高,使得各种新型背光源不断被开发出来。平面介质阻挡Xe放电荧光灯因其具有优越的光电特性,可望被用于台式电脑液晶显示器和液晶电视中。本文对具有代表性的几种新型平面介质阻挡Xe放电荧光灯进行了介绍,分析了进一步提高放电灯性能需要解决的问题。