特殊工况下抽水蓄能电站系统参数过渡过程分析

在抽水蓄能电站水力过渡过程数值模拟中,由于水泵-水轮机全特性曲线所具有的特殊性,使得尾水管进口最小压力在机组相继甩负荷工况下会大幅度降低,且时常会成为控制值。以一维刚性水锤及弹性水锤的特征线方法(MOC)为理论基础,结合某"一洞两机"布置形式的抽水蓄能电站工程实例,对该电站相继甩负荷工况下引水隧洞洞径及尾水岔管相对位置对过渡过程的影响进行了数值模拟。结果表明:在设置尾水调压室的情况下,拟通过改变引水隧洞洞径来调节尾水进口最小压力的措施是不经济的,引水隧洞的面积只需使其中的水流能够保持经济流速即可;在满足工程布置的前提下,应尽量减小尾水支管的长度,以保证输水发电系统的安全运行。     

异形孔零件的线切割编程与加工

通过对典型零件的加工工艺分析，介绍了用北京迪蒙卡特线切割机床加工锥度、上下异形类零件的程序编制规则和方法，该方法相比TurboCAD软件自动编程操作简单快捷，编程者更易掌握。     

High performance VLSI CORDIC algorithms,architecture and chip design

Abstract

CORDIC is a rotation based computation kernel algorithm which has been found to be very attractive for problems which require intensive, frequent evaluations of elementary functions. This paper addresses the implementation issues in the design of a VLSI CORDIC processor for digital signal processing and numerical linear algebra computations. The first part of this paper will discuss various design considerations for practical CORDIC algorithms. In particular, we have established criteria for the selection of nearly optimal shift sequences which are crucial to the performance of the CORDIC computation. The various design considerations of a CORDIC processor are discussed. Finally, the architecture of a prototype CORDIC processor data path chip is described.     

基于CAE的汽车档位手球结构优化及模具设计

利用Moldflow对某汽车档位手球塑料件结构进行分析,以此为参考,对塑料件结构作一定的改进,并对改进后的塑料件进行模具设计,介绍了模具结构分析及相关设计要点,并通过实际试模得到了合格塑料件。     

Stereoscopy and Scanning Electron Microscopy of Brazil Nut (Bertholletia excelsa H.B.K.) Shell,Brown Skin,and Edible Part: Part One—Healthy Nut

In this article, tissue layers and cells characteristics of the Brazil nut (Bertholletia excelsa H.B.K.) shell (tegument), brown skin (testae), and edible part (cotyledons) were identified by stereoscopy (SM) and scanning electron microscopies (SEM). (a) The shell (a lignin rich, protective wall) varies in thickness throughout the nut structure and comprises different tissue types (total 3)/texture (hard/mid‐hard/soft), layers (2 to 5), colors (light to dark brown and white to cream), cell shape (amorphous/flattened on both surfaces; polygonal and cylindrical with thick, porous primary and secondary wall in cross‐section), and vascular distribution (helically and polyedrical thickened vessels at soft tissue and locule/channel structures). These variations are observed either in the shell faces, face corners, nut tips, or locule in testae. (b) The brown skin (shell nut part linked to both the shell and edible part) is made of flattened irregular‐shaped parenchymal cells distributed in several layers with more flexible fibrous, thinner wall tissue than shell. It has both rough and smooth shiny texture on the upper and lower surfaces, respectively. However, the nut (c) edible part, that is the nut storage tissue, shows several different tissue/cell layers starting from epidermis (double/triple cells sequence of round and palisade shapes) layer–the endosperm tissue. The parenchymal tissues show cells of irregular shape with small and larger sizes distributed in regular and randomly layers, respectively, separated by a short meristem tissue layer. The cortex cells increase in size as they approach the cotyledons junction. The Brazil nut part's tissue layers and cells were identified by the SM and SEM microscopy methods applied, which provides knowledge for further understanding of nut alterations that may occur either in the forest or during the factory processing.     

基于Solid Edge的机械标准件库的研究

介绍了Solid Edge二次开发的原理和方法,分析和比较了两种不同设计方法的优缺点,并以六角头螺栓为例详细说明了应用数据库及Solid Edge变量设计标准件库的基本方法和框架。通过直接调取库中的零件,能够大幅提高设计效率,减少设计工作量,进而缩短产品的开发周期。     

超大型桥式起重机安装技术研究

某钢厂改造工程中钢水接收跨新增加一台200/63/20mA7铸造超大型冶金桥式起重机。由于场地狭小,精度要求高、安装难度大。针对该项目的施工难点和特殊工艺,打破常规,运用3D3S软件进行三维空间模拟实际吊装来确定吊装参数,创新地采用地面组装、分件抬吊、整体就位的安装技术,解决了超大型冶金桥式起重机安装技术难题,取得了良好的经济效益和社会效益。     

深圳市海水入侵形成原因分析

在分析海水入侵形成机理的基础上,从特殊地质环境及相关自然因素和人类工程经济活动两大方面分析了深圳市海水侵入的原因,启示我们在大力发展经济建设时,应统筹考虑对人类生存的自然环境的保护,不能以牺牲生态环境来换取经济效益。     

核电厂电气设备陶瓷部件受风生飞射物的冲击破坏

为研究沿海台风中的风生飞射物对核电厂电气设备的冲击破坏，以核电厂户外高压电气设备的陶瓷绝缘材料为研究对象，基于LS-DYNA和HyperMesh，分析陶瓷部件在小球和钢管打击下的破坏情况。结果表明：在受到钢管垂直打击时，陶瓷部件很容易发生破坏；在受到小球冲击时，陶瓷部件局部表面发生破坏。进一步计算得到小球对陶瓷部件的临界破坏冲击速度，可为后续设计和研究提供参考。     

Soil-to-Plant Transfer Factors of Stable Elements and Naturally Occurring Radionuclides (1) Upland Field Crops Collected in Japan

In long-term dose assessment models for radioactive waste disposal, an important exposure pathway to humans is via ingestion of contaminated foods. In order to obtain soil-to-plant transfer factors (TFs) of radionuclides under equilibrium conditions, naturally existing elements were measured as analogues of radionuclides. Crops grown in upland fields and associated soil samples were collected from 62 sampling sites throughout Japan. The total concentrations of 52 elements in the crops and 54 elements in the soil samples were measured. The TFs of 40 elements (Li, Na, Mg, Al, Si, P, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Y, Mo, Cd, Sn, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Pb, Th and U) were calculated on a dry weight basis.

Among all the TF data, K showed the highest TF with a geometric mean (GM) of 2.1, followed by P. The GMs of TFs for rare earth elements, Th and U were on the order of 10^?4. Most of the TF-GMs for green vegetables were higher than GMs of all crops for the elements. The obtained TFs of some elements for green vegetables and potatoes were compared with those in the technical report series-364 (TRS-364) compiled by IAEA in 1994. The TF-GMs were usually lower than the best estimates (expected values) listed in TRS-364; however, the GMs of TF for La and TF for Th observed for potatoes were slightly higher than the expected values.