二耦合度9杆巴氏桁架位置分析的超混沌数学规划法

应用求解非线性方程组全部实数解的超混沌数学规划法完成了第30种二耦合9杆巴氏桁架的位置正解的求解.结合矢量法和复数法建立了该机构四回路的4个约束方程,利用正、余弦函数关系增设4变量,建立了4个补充方程,从而构造了该机构位置分析的8变量约束方程组.将超混沌序列和数学规划法相结合,应用二维离散超混沌系统产生迭代初始点,提出...     

圆锯片横向再生颤振模型及计算

通过分析圆锯片切割工件横向振动情况,得出横向再生切削力表达形式。基于Kirchhoff线弹性板理论建立圆锯片横向再生颤振方程式。利用伽辽金法对横向颤振方程进行变换,得出以各阶振型分量为变量的延迟微分方程组,并用状态变量形式表示延迟微分方程组。通过延迟微分方程组状态变量表达形式编写MATLAB函数来描述圆锯片切割系统横向再生颤振的动态模型,调用dde函数求解各阶振型分量随时间的变化关系,从而得出圆锯片横向再生颤振响应。     

非饱和土三维固结问题探讨

本文推导了非饱和土三维固结控制方程组，它由三个静力平衡方程、一个连续性方程和一个吸力状态方程组成，包含五个基本未知量（三个位移分量、一个孔隙水应力和一个孔隙气应力）。这是不同于前人思路的一种尝试，饱和度可用其它基本未知量表达，不作为独立变量而只作为方程中的可变参数出现。饱和土的Ｂｉｏｒ固结方程可作为该方程组的一个特例而存在。文中还就方程组求解、本构模型和参数测定等问题提出了一些设想。     

按γmin≥[γ]设计对心型曲柄摇杆机构的图表方法

为了简化设计对心型曲柄摇杆机构,通过对曲柄摇杆机构几何参数之间的关系分析,运用解析法建立综合方程,并以此推导出极位夹角条件下,传动角、摇杆摆角及单位杆长之间的计算公式.采用描点法绘制出满足最小传动角条件的设计曲线图.该图表可简捷、方便、直观地反映出各参数之间的关系,为设计对心型曲柄摇杆机构提供一种新的设计方法.     

3SPS—PRPS并联型机器人机构位置正解分析

本文提出由三支ＳＰＳ和一支ＰＲＰＳ运动链连接上下平台的并联型机器人机构的位置正解分析方法，以上平台顶点坐标为输出变量建立起几何约束方程组，通过消元推导出一元八次多项式的输入输出方程。     

按γmin≥［γ］设计对心型曲柄摇杆机构的图表方法

为了简化设计对心型曲柄摇杆机构,通过对曲柄摇杆机构几何参数之间的关系分析,运用解析法建立综合方程,并以此推导出极位夹角条件下,传动角、摇杆摆角及单位杆长之间的计算公式。采用描点法绘制出满足最小传动角条件的设计曲线图。该图表可简捷、方便、直观地反映出各参数之间的关系,为设计对心型曲柄摇杆机构提供一种新的设计方法。     

闭链刚柔五杆机构动力学建模与仿真研究

复杂机构动力学的快速建模与高效计算,是机构学领域关注的难题之一,对复杂机构高效运动预测和优化设计具有重要的理论与实用价值.应用多体系统离散时间传递矩阵法,定义了平面闭链刚柔五杆机构的状态矢量,推导了典型元件的传递方程和传递矩阵,实现了对平面闭链刚柔五杆机构动力学的快速建模与计算.分别应用本文方法和Lagrange方法实例计算了某闭链平面刚柔五杆机构动力学,计算结果对比验证了本文方法的有效性和高效性.本文方法无需建立系统总体动力学方程,涉及系统矩阵阶次与系统自由度无关,建模灵活,计算速度快,可推广应用于其他复杂机构动力学研究.     

颗粒调谐质量阻尼器在竖直细长杆顶端的减振试验研究EI北大核心CSCD

针对航空测试设备涉及的一种竖直细长杆支撑结构的顶端振动问题,进行了基于颗粒调谐质量阻尼器的减振试验研究。该竖直细长杆为空心钢圆管结构,长细比43∶1;使用工况为两根一组,顶部共同带载,根部固定于回转装置,跟随回转装置做回转运动,回转半径2.5 m,回转速度0.1°/s;回转时细长杆顶端易产生振动,影响测试运动精度和支撑安全性;为解决该问题,设计了三种质量比的颗粒调谐质量阻尼器,应用至刚度较弱、振动较明显的空载单根细长杆顶端进行减振试验,验证阻尼器在该类型结构中的有效性。试验结果显示,单杆最大减振幅度可达31%。进一步针对实际应用工况下的带载双杆设计阻尼器并进行减振试验。结果显示,双杆最大减振幅度可达43%,减振效果良好。     

直齿锥齿轮的公法线长度测量法

目前直齿锥齿轮的弦齿厚测量是在齿背锥面上以齿顶锥面作为基准,容易带来附加的误差。捷克有人曾提出计算这种齿轮公法线长度的超越方程组。方程组的推导是基于 Tredgold 近似方法,其联解运算相当繁复。本文首先用球面啮合的观点简述球面渐开线的几何基础,并写出直齿锥齿轮公切两面角的准确表达式。然后根据公切两面角来推导公法线长度的计算公式。在保证相对误差小于10~(-6)的条件下,用级数逼近法得出的实用公式十分简明,计算方便。文中还讨论一些测量的具体问题。     

钢构件弯扭屈曲总势能方程的合理性分析

为研究钢构件弯扭屈曲总势能方程的合理性,该文通过分析推导总势能方程的两个方法——应力法和应变法的基本过程,揭示了应变表达式和位移模式是影响总势能方程推导结果的两个关键因素,建立了这两个关键因素合理性的判定准则,并验证了准则的正确性。依据该文建立的准则,对两种典型位移模式和三种典型总势能方程进行了判定。结果表明:符拉索夫位移模式较Trahair位移模式更为合理,吕烈武等学者的总势能方程较 Bleich的总势能方程和Trahair的总势能方程更为合理。最后,建议了推导钢梁临界弯矩Mcr设计公式应采用的总势能方程。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

We associate a variety of innovations with the term ＂Industry 4.0＂. The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...     

Roman iron and steel: A review

ABSTRACT

The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them.     

The Research of Anti-Wear Properties of Organomolybdenum Compounds in the Engine Oils

A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Synthesis of Alumina-Zirconia Nanocomposites by Solgel Process

Al₂O₃-ZrO₂ nanocomposites were developed starting with the solgel process. Composite alumina-zirconia nanopowders were synthesized from metallorganic precursors (Aluminium secondary butoxide and zirconium Iso propoxide) using the solgel process. The parameters affecting the synthesis—solvent, concentration of precursor, R/H ratio (i.e., dilution of water in solvent)—were varied as also the temperature and pH. BET and TEM were used to measure nanosize. Diffuse reflectance spectroscopy and also qualitative optical absorption led to identical particle size estimate. The variation of process parameters was used to study the effect and interdependence of process parameters. Artificial Neural Networks was used to rigorously analyze the process. Although this led to confirmation of interdependence of parameters, the presence of a single overwhelming solvent variable was also established. Then the optimal process was used to synthesize more nanopowder. To produce bulk nanocomposite the nanopowders were sintered by varying the temperature and time period. The sintered lithoids were probed with a vickers hardness tester to measure elastic modulus, hardness, and fracture toughness. The results showed high elastic modulus, modest hardness, and very high fracture toughness.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Friction Stir Processing Strategies for Uniform Distribution of Reinforcement in a Surface Composite

Friction stir processing (FSP) is an important technique for preparing surface composites. Fabricating defect-free surface composites with uniform particle distribution by FSP is a challenging task. In this study, silicon carbide particles reinforced AA5083 alloy surface composites was fabricated using different FSP strategies including variation in process parameters, dual-tool processing and tool offset overlapping. Material flow of the processed material with reinforcement particles demonstrated that the distribution of particles was influenced by the stirring action of the probe as well as the extrusion of the plasticized material due to the movement of the tool. Process parameters, particularly rotational speed, showed a dominant influence on the distribution of silicon carbide particles.