带刚性连梁的双肢剪力墙结构的弹塑性分析

本文利用连续化分析方法对带刚性连梁的双肢剪力墙结构进行弹塑性全过程分析，考虑了连梁屈服后的硬化和下降段，计算结果与试验结果符合较好。     

一种基于应变插值大变形梁单元的刚-柔耦合动力学分析

柔性多体系统动力学中的“动力刚化”现象起因于变形间的耦合。一次近似模型成功地解决了小变形情况下的刚柔耦合建模问题,但在大变形情况下则需要考虑更多的耦合效应。本文选取表征梁弯曲应变的曲率和轴向应变作为单元参数进行离散;在大变形大转动基础上得到了单元两端节点运动学参数的递推关系,构造出了能够自动计及“动力刚化项”且适用于大变形刚柔耦合动力学分析的平面梁单元。最后采用本文所提应变插值单元求解了包含大变形和刚柔耦合动力学柔性梁的数值算例,验证了文中算法的正确性和有效性。     

旋转柔性梁的动力学建模及分析

基于一次近似理论，采用弧坐标分量和Cartesian坐标分量共同描述柔性梁的变形场，并采用Green应变张量描述应变能，用Hamilton原理建立系统动力学方程。揭示产生动力刚化现象的力学本质。采用有限元方法进行离散，基于数值实验系统地研究旋转柔性梁的动力刚化现象。计算表明，旋转柔性梁的横向固有频率随旋转角速度和中心刚体半径的增大而增大．从而只存在一阶临界转速，且当中心刚体半径超过临界半径时．不存在临界转速。     

Characterization of uncertainty (probabilistic models) in verification of unreinforced masonry shear wall / Charakterisierung der Unschärfe (probabilistische Modelle) beim Nachweis von Wandscheiben aus unbewehrtem Mauerwerk

The model uncertainty has significant role in determination of safety factor. Eurocode has been considered partial factor covering uncertainties in the resistance model. Moreover, the model uncertainty has important role in full probabilistic verification. A stochastic analysis may yield to realistic results, only if the uncertainties have been involved in the calculation, properly. The uncertainty in predicted load‐carrying model may be identified by comparing the observed (experimental records) load‐carrying behaviour with the predicted value. Some general recommendations for considering uncertainty in probabilistic verifications are available in literature. In this study, the deviation of predicted values according to DIN EN 1996‐1‐1/NA model of masonry shear wall from test results has been derived. The best‐fitted distribution with associated statistical parameters (type of distribution, mean and coefficient of variation) has been proposed for uncertainty model. The uncertainty models have been compared with recommendations in the literature.     

The effect of traditional reinforcement – prestressed reinforcement ratio on the behaviour of concrete beams

Firstly, the effect of traditional reinforcement – prestressed reinforcement ratio on the behaviour of concrete beams up to failure was experimentally investigated. The beams were 10 m long and 0.5 m high, with different ratios of traditional and prestressed reinforcement. The total quantity of reinforcement in each beam was selected to provide their equal ultimate bending bearing capacity. Deflections, stresses in concrete, traditional and prestressed reinforcement, as well as concrete cracks, were monitored until the beams failure. Using the previously developed numerical model of authors of this paper for static analysis of spatial frame structures, which can simulate main nonlinear effects of their behaviour, then numerical analysis of tested beams was performed. Good agreement was obtained between the experimental and the numerical results, which confirms the possibility of practical application of the adopted numerical model. Main conclusions and recommendations for practical applications according to results of performed tests are given at the end.     

柔性机械臂非线性动力学模型及控制的研究

针对轴向不伸长的Ｅｕｌｅｒ－Ｂｅｒｎｏｕｌｉ梁，采用假设模态法，根据能量一致性原理，利用变形约束方程和小变形假设条件，对带有末端荷载的柔性机械臂，推导出考虑动力刚化（ＤｙｎｍａｉｃＳｔｉｆ－ｅｎｉｎｇ）影响的柔性机械臂有限维一致线性化动力学方程。为实现柔性机械臂关节转角运动轨迹的精确跟踪，采用基于输入输出部分线性化的控制方法设计非线性控制器，对该非线性动力学模型进行解耦并产生理想关节转角运动轨迹的控制输入。采用线性系统最优状态反馈控制规律设计弹性模态稳态器抑制弹性体的振动。数值仿真验证了该控制策略的有效性。     

柔性机械臂的动力学模型及滑模变结构控制

本文针对轴向不伸长的Euler-Bernouli梁模型,采用假设模态法,对带有末端荷载的柔性机械臂,推导出考虑动力刚化影响的柔性机械臂有限维一致线性化动力模型.通过极点配置技术设计滑模超曲面参数,采用滑模变结构控制方法,实现关节转角的运动轨迹控制.采用LQR方法设计弹性模态稳态器,抑制由于刚体运动而激发的弹性振动.文中最后针对一单杆柔性机械臂进行了计算机仿真,验证了本文所提出的控制策略的有效性.     

On the solid state heat transport phenomena measurement

The paper deals with theoretical and experimental aspects of lumped capacitance model (LCM) application for the study of heat transport in different materials. Patented construction of the measuring chamber together with special software the fundamental features of which are presented here allows evaluating thermal conductivity k, specific heat capacity c_p and thermal diffusivity α. Obtained results are in relatively very good agreement with those obtained from independent measurement or table values.     

Innovatives Elektronenstrahlschweißen hochschmelzender Metalle

Innovative electron‐beam welding of high‐melting metals Since its establishment as nuclear research plant Juelich in the year 1956, the research centre Juelich (FZJ) is concerned with the material processing of special metals. Among those are, above all, the high‐melting refractory metals niobium, molybdenum and tungsten. Electron beam welding has always been considered to be an innovative special welding method; in the FZJ, electron beam welding has, moreover, always been adapted to the increasing demands made by research partners and involved manufacturing and design sectors. From the manual equipment technology right up to highly modern multi‐beam technique, the technically feasible for fundamental research has, this way, always been realised.     

Flexible multibody dynamics based on a non‐linear Euler–Bernoulli kinematics

This paper presents a new dynamic model of a multi‐beam system in the floating‐frame approach. The proposed solution can be used to model light flexible manipulators in fast dynamic conditions or large space structures undergoing moderate but finite deformations. The model is based on the non‐linear Euler–Bernoulli kinematics proposed in J. Mech. Mach. Theory 1999; 34 :205. From this ‘exact’ kinematics we develop two approximate models. The first one is a linear model with respect to the deformation parameters, the second is a quadratic one. These two models capture the dynamic stiffening, and are consistent in the sense that they contain all the terms up to their maximal order with respect to the energy conservation. These two models are tested by simulation and compared with the standard floating frame model based on linear elastic kinematics and with the finite element codes of Reference [23] (Module d'analyse de mécanismes flexibles MECANO: Manuel d'utilisation. LTAS report, University of Liege, Belgium, 1988). Copyright © 2002 John Wiley & Sons, Ltd.     

Effects of magneto-electric loadings and piezomagnetic/piezoelectric stiffening on multiferroic interface fracture

Interface fracture of a multiferroic composite is studied by the methods of integral transform and singular integral equation. Parametric studies on the stress intensity factor yield three conclusions. (a) The multiferroic composite is more likely to fracture in electric field than in magnetic field. (b) Under magnetostriction, piezomagnetic stiffening does not affect the interface crack, but the influence of piezoelectric stiffening is notable. Under electrostriction, inverse results are obtained. (c) In magnetic loading cases, the piezomagnetic layer should be softer and the piezoelectric strip stiffer; however, if electric loading is applied instead, opposite conclusion should be expected.     

Monolithisches Mauerwerk aus Leichtbetonsteinen erfüllt die Anforderungen der Energieeinsparverordnung 2009

Die Energieeinsparverordnung (EnEV) 2009 beinhaltet verschärfte Anforderungen an den Jahresprimärenergiebedarf und den Transmissionswärmeverlust von Gebäuden. Damit sinkt der durchschnittliche U‐Wert von Außenwänden auf 0,28 W/(m²K). Mauersteine aus haufwerksporigem Leichtbeton wurden in den letzten Jahren wärmetechnisch so verbessert, dass sich diese Anforderungen mit Mauerwerksdicken von 36,5 cm problemlos erfüllen lassen. Selbst die Kriterien für ein KfW‐Effizienzhaus 70 oder 55 lassen sich auf diese Weise mit monolithischem Mauerwerk ohne zusätzliche Dämmung noch einhalten. Monolithic masonry made of lightweight concrete blocks meets demands of energy saving regulations. The Decree for Saving Energy (Energieeinsparverordnung, EnEV — regulation for energy saving in buildings and building systems) 2009 consists stronger regulations for the yearly demand of energy and the loss of transmission heat of buildings. Therefore the average U‐Value for enclosure walls decreases to 0.28 W/(m²K). Blocks made of aggregate lightweight concrete have been improved by the industry concerning their thermal conductivity in the last years, so these demands can be fulfilled with masonry in 36,5 cm thickness. Even the criteria of a KfW Efficiency House 70 or 55 can be fulfilled in this way with monolithic masonry without an additional thermal insulation.     

Thermal conductivity issues of EB‐PVD thermal barrier coatings

The thermal conductivity of electron‐beam physical vapor deposited (EB‐PVD) thermal barrier coatings (TBCs) was investigated by the Laser Flash technique. Sample type and methodology of data analyses as well as atmosphere during the measurement have some influence on the data. A large variation of the thermal conductivity was found by changes in TBC microstructure. Exposure at high temperature caused sintering of the porous microstructure that finally increased thermal conductivity up to 30 %. EB‐PVD TBCs show a distinct thickness dependence of the thermal conductivity due to the anisotropic microstructure in thickness direction. Thin TBCs had a 20 % lower thermal conductivity than thick coatings. New compositions of the ceramic top layer offer the largest potential to lower thermal conductivity. Values down to 0.8W/(mK) have been already demonstrated with virgin coatings of pyrochlore compositions.     

四分之一波长间距阵抗拖船干扰研究

为改善拖曳线列阵声呐的尾向探测能力,降低拖船噪声对半波长间距阵尾向探测性能的制约,本文关注四分之一波长间距阵对连续波信号和带限噪声的响应。研究表明,四分之一波长间距阵具有非对称的端向指向性,与半波长间距阵相比有约20 d B的空间抑制能力,能有效抑制拖船辐射噪声干扰。本文还提出用零陷权组合传感器构成四分之一波长间距阵,理论上其抗拖船噪声干扰的效果比四分之一波长间距阵更好。     

Cost‐effectiveness of nearly zero energy detached houses

While new buildings or appropriately carried out refurbishment can already show considerable potential for the reduction of greenhouse gas emissions with the available technology and definite measures, a certain ”last mile“ problem would arise if the requirements were made increasingly stringent toward zero‐energy building: the more saved in the overall balance, the more laborious are the measures that have to be introduced. Using the example of a typical detached house, this article eva luates variants for the building envelope and building supply systems from the viewpoints of energy‐saving and economy, and derives the possible consequences for future requirements and the arrangement of the framework conditions.     

Bauweise mit Zukunft: Durch und durch mineralisch —Wärmedämmendes Mauerwerk mit mineralischem Putz

Hat Mauerwerk eine Zukunft? Oder dienen Wände bald nur noch als Trägermaterial für Dämmschichten? Dabei ist gerade wärmedämmendes Mauerwerk aus gutem Grund im Wohnungsbau nach wie vor die Nummer Eins — und wird es nach Einschätzung der Fachleute auch bleiben. Dieser Beitrag schildert aktuelle Entwicklungen und beleuchtet Hintergründe. Construction with a future — theral insulating brick with mineral plaster. Does brickwork has a future? Couldn’t it be that walls will soon only serve as backing material for insulation layer? However, there are good reasons that heat insulating brickwork is still the number one in domestic constructions — according to experts this will remain so. The following article will characterize current developments und backgrounds.     

Elektronenstrahl‐Randschichtbehandlung für die Herstellung verschleißbeständiger Auftragschichten auf nichtrostenden Stählen

Stainless steel components exposed to mechanical stresses are subjected not only to corrosion, but to abrasive wear. There are several possibilities for enhancing the wear resistance of stainless steels; however, such processes are very often associated with a reduction in corrosion resistance. This paper presents an electron beam surface treatment technology to significantly improve the wear resistance of austenitic steels (e.g. X6CrNiMoTi17‐12‐2) and duplex steels (e.g. X2CrNiMoN22‐5‐3), without a negative influence on the corrosion behavior. Fe‐ and Co‐additive wires were deposited thermally by electron beam cladding. The cladding layers produced were free of defects such as cracks and pores, and were well metallurgical bonded to the base materials. Microstructural analysis, hardness measurements, wear tests and corrosion tests were carried out. The wear rate k was reduced by a factor of 100 compared to the base materials for electron beam cladding with Fe‐based wire and by a factor of 10 with Co‐based wire. Corrosion resistance was preserved for the Fe‐based cladding layers and slightly increased (by a factor of 3) for the Co‐based cladding layers.     

Effect of phosphoric acid on the performance of low antimony grid of Pb‐acid cell under constant current charging and discharging

Effect of phosphoric acid on the performance of Pb‐1.7%Sb grid of lead‐acid cell is studied in 5 M H₂SO₄ by cyclic galvanostatic polarization and impedance spectroscopy. An increase in capacitance to a maximum is recorded during the initial stages of the electro‐reduction of PbO₂ into Pb(II) compounds and attributed to concurrent compositional and dimensional changes. These changes include removal of O₂ bubbles, insertion of large amounts of H₂SO₄ and H₂O. Efficiency of PbO₂ formation decreases, while its rate of self‐discharge increases with increasing the charging current and in the presence of H₃PO₄. The charge capacity increases with increasing the discharging current due to the decrease in the self‐discharge. The charge capacity is lower in the presence of H₃PO₄. On increasing the cycle number, the corrodibility of the grid increases, because more layers of the surface Pb are involved in the self‐discharge. H₃PO₄ significantly retards the effect of cycle number.