某型发电机可靠性试验系统研究

为了对某型发电机进行可靠性试验，根据试验需求，设计了带能量反馈的试验系统。该系统与发电机输出带纯电阻性负载方案相比，大大节约了试验的耗电量，并利用仿真软件PSCAD／EMTDC建立了试验系统的仿真模型，对系统在不同扰动下的动态特性进行了仿真研究。仿真结果与试验结果相吻合，说明所建试验系统模型的正确性，也得出了该试验系统具有良好的运行稳定性的结论。     

基于生物质燃料的水冷式温差发电机的实验研究

为解决无电区域和火灾、地震和雪灾等特殊条件下的供电问题,设计了一种可燃用木柴和木炭等生物质燃料的水冷式温差发电机,其特点在于引入了一种辐射型的集热器。温差发电机的总质量为23.3 kg,集成了直流稳压器,可稳定地对外输出电能。测试了温差发电机的启动特性、空载特性和功率负载特性,结果表明：该温差发电机的平均工作温差为68℃,最大空载电压达到116.3 V。当接入负载时,输出功率随外部负载电阻的增大而降低。当外部负载为1.6 Ω时,温差发电机可对外输出最大功率为22.4 W;继续降低负载电阻时,温差发电机将不能维持稳定地输出电能。     

基于全局非线性可分离的最小二乘法的飞机颤振模态参数辨识

本文考虑在输入-输出数据都带有噪声的前提下,将偏差补偿最小二乘算法（CLS）进行推广得到非线性可分离的最小二乘算法（NSLS）。采用适用于噪声环境的非线性可分离的最小二乘算法可准确地辨识飞机的颤振模态参数,该算法结合传递函数模型,将带噪声系统的辨识问题转化为非线性可分离的最小二乘问题。利用该算法,两噪声的方差值和传递函数中的模型参数可分离地估计出来。最后利用试飞试验数据辨识飞机的系统参数,验证了该方法的有效性。     

模块化能馈型直流模拟负载单元设计

针对能量回馈电网型(能馈型)直流负载多样化的负载测试需求,提出基于交错并联Boost的模拟负载单元模块化设计方案,设计电流均值跟踪和电流峰值保护两者兼备的信号调理电路,研究基于逐个周期电流峰值限制的负载模拟双环控制策略。通过建立单个模拟负载模块电流控制的小信号模型,得到模拟负载模块输入电流的传递函数,并基于小信号模型设计PI调节器,改善模拟负载模块的性能。仿真与实验结果表明:模拟负载模块在启动后12 ms即可进入稳定工作状态,并且能在0.21μs内完成过流保护动作,恒流模式下负载模拟相对误差绝对值为3.602%。与目前市场产品相比,该方案动态响应快,精度高,更加稳定安全。     

非量测数码相机成像性能测定方法研究

非量测相机广泛应用于摄影测量领域,因此必须对其成像性能进行测定。本文分析了影响调制传递函数的因素,设计了利用影像的灰度曲线测定非量测相机成像性能的方法,经过与调制传递函数曲线的对比实验,表明了该方法具有简单、便于操作、稳定可靠的特点。     

一种飞机电源车测试系统的设计

针对飞机电源车在飞行现场对电源性能进行测试的需求,设计了一种可移动式自动测试系统。重点介绍了该测试系统的设计方案,阐述了测试系统设计中的关键技术。该系统基于单片机开发技术,设计了多功能负载实现对飞机电阻特性的模拟,自动化程度高、重量轻、移动方便,具有很强的灵活性与可靠性,有着广泛的应用前景。     

基于软轴式随动控制的运煤车液压转向系统分析

为了完善矿用车辆行驶转向系的设计体系,对某型运煤车的全液压动力转向随动系统进行了研究.该系统反馈采用独特的软轴结构,把转向控制机构与空间连杆机构连接,实现了运煤车转向控制机构的机液随动控制.通过对该转向系统的稳定性与响应特性的分析,得到了控制系统开环和闭环传递函数,可知:提高速度放大系数Kv,对于减小速度误差和负载误差都是有利的,但同时会降低系统稳定性;减小流量-压力系数Kce,可以减小负载误差,但会使阻尼比减小.研究结果表明,该转向系统幅值裕量为12.5dB,相位裕量为86.2°,系统响应上升时间为0.03s,最大超调量为52%,系统相位裕量较大,阻尼比较小,但响应快速性较好,系统处于稳定状态.该转向系统的独特结构也为工程机械车辆转向系的设计提供了一定的借鉴.     

基于CATIA技术的飞机典型零件变型设计

为提高产品设计效率,研究了组件框架技术,借助CATIA二次开发平台,在参数化建模技术的基础上实现对飞机典型零件的变型设计,快速提取特征信息,实现智能化操作.利用面向对象的程序语言,开发出与CATIA系统集成的变型设计模块,能够提高飞机典型零件的设计效率.以飞机典型零件机加件中的拉杆为例,对变型设计方法的验证表明,利用CATIA二次开发技术以及CAA编程工具,能够对飞机典型零件参数化建模,实现变型设计.     

基于UG的平面尺寸链的计算机辅助飞机公差设计

随着CAD 技术的普及,飞机三维外型计算机辅助设计基本实现数字化,但目前飞机公差设计尚未实现计算机辅助设计。公差设计仍然需要大量手工计算,导致飞机公差设计与产品总体设计不协调,制约飞机数字化设计、制造技术的发展。探讨如何以现有CAD 三维造型系统为技术平台,开发计算机辅助飞机公差设计模块,实现平面尺寸链的飞机公差分析和分配的计算机辅助设计。给出在UG 平台上实现计算机辅助飞机公差设计模块的开发方案,并有利用该模块进行飞机装配件公差设计的运行实例。     

航空变焦镜头的小型化设计

航空相机的光学系统决定相机的外形尺寸,针对一个25倍航空变焦镜头的光学设计指标要求,进行小型化设计.为缩短筒长,采用负组补偿偏离物像交换变焦结构,缩短变倍补偿系统各组元焦距,增加前固定组和变倍组间距的设计方案,通过解初级像差方程求得初始结构,依据像差理论,利用ZEMAX自动设计软件进行像差校正平衡.设计结果表明,该系统可以实现20～500 mm的连续变焦,筒长只有198 mm,中心视场传递函数值大于0.4,0.7视场传递函数值大于0.2.     

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.     

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.     

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.……     

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...     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

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.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...