下载文档原格式
英语课后重点短语LESSON 1(P15)1)the fundamental concept 基本概念2)cross section 横截面3)the internal stresses produced in the bar 棒内应力4)continuous distribution of bydrostatic pressure 净水压力的连续分布5)the tensile load 拉伸载荷6) a uniform distribution over the cross section 横截面上的均匀分布7)arbitrary cross-sectional shape 任意横截面形状8)tensile stress 拉应力9)compressive stresses 压应力10)a normal stress 正应力11)through the centroid of the cross sectional area 通过质心的横截面积12)the uniform stress condition 均应力状态13)the stress distribution at the end of the bar14)high localized stresses 局部高应力15)an axially loaded bar 轴向加载杆16)a tensile strain 拉伸应变17)an elongation or stretching of the material 延长或拉伸的材料18)a compressive strain 压应变19)the ratio of two lengths20)purely statical and geometrical considerations 从纯静态和几何关系考虑LESSON 2(P25)1)the main manifestations of capacity 功能的主要表现形式2)the maximum unit load(stress) 最大单位载荷3)stress-strain diagram 应力-应变图4)the simple tensile test 简单拉伸试验5)the percentage elongation at rupture 断裂延伸率6)the end of tensile specimens 拉伸试样的末端7)permanent deformation 永久变形8)the resulting load-displacement curve 所产生的载荷-位移曲线9) a substsntial yielding of the material 大量高产的物质10)yield point 屈服点11)the trainsition from elastic to plastic behavior12)material property table 材料性能表13)plastic defomation 塑性变形14)a specified standard length of the specimen 指定的标准试样的长度15)at the moment of rupture 在破裂时16)short cylindrical specimens 短圆柱试样17)ductile materials 任性材料18)high stress concentration 高应力集中19)ultimate tensile strength 极限抗拉强度20)strain hardening zone 应变硬化区LESSON 3(P37)1)circular cross section 圆截面2)the position of mountings 安装位置3)nominal size 标准尺寸4)length of shaft subjected to twist 轴的受扭长度5)minimize stress concentration 尽量减小应力集中6)from the standpoint of stress 从应力角度7)equations for a shaft in pure torsion 轴纯扭转的方程式8)diameter of solid shaft 实心轴的直径9)outside diameter of hollow shaft 空心轴的外径10)the amount of twist in a shaft 轴的扭转量11)torsional deflection 扭转变形12)shear modulus of elasticity 剪切弹性模量13)be closer to the vertical load 接近于垂直载荷14)the endurance limit 疲劳极限15)the allowable shearing stress 许用剪切应力16)equation for equivalent moments 方程的等效力矩17)the design stress values for flexure 设计弯曲应力值18)the angle of twist 扭转角19)antifricton bearings 滚动轴承20)the amount of twist in a shaft 轴的扭转量LESSOM 4(P51)1)herringbone gears 人字齿轮2)spiral gears 螺旋齿轮3)worn gears 蜗轮4)bevel gears 圆锥齿轮5)hypoid gears 准双曲面齿轮6)sizes of spur-gear teeth 齿轮轮齿的尺寸7)the automotive rear axle drives 汽车后桥驱动8)rack-and-pinion drives 齿条和小齿轮驱动器9)diametral pitch 径节10)pitch circle 节圆11)the tangency point 切点12)pressure angles 压力角13)an involute curve 渐开线14)the radial distant 径向距离15)at right angles 成直角16)the average number of teeth in contact17)the reciprocal of the diametral pitch 对等径节18)to change inches to millimeters 把英寸换算成毫米19)a line perpendicular to the centerlines 垂直中心线的直线20)center distance between two meshed gears 两个齿轮的中心距LESSION 5(P62)1)plate cams 盘形凸轮2)cylindrical cams 圆柱凸轮3)the cam assembles in automatic record players 汽车发动机上的凸轮组件4)cam profiles 凸轮轮廓5)make a full-scale template 制造一个实体样板6)in the course of several revolutions of the cam 在凸轮中转几圈7) a tangential plate cam 切向盘形凸轮8) a translation cam 移动凸轮9)the groove in the periphery of the cam 凸轮表面的槽10)a guided vertical reciprocated follower 做垂直运动的往复件11)a constant-diameter cam 等径凸轮12)automatic washing machines13)a face cam 面凸轮14)the edge of a pivoted follow 摆动从动件的边缘15)a reciprocating knife-edged follower 作往复运动的刀口式从动件16)miniature snap-action electrical switchies 小的速动开关17)a pivoted flat-faced follower 安装在摆臂上的滚子从动件18)air pilot values19)the abrupt change in cam profile 在凸轮轮廓上的突变20)a Scotch yoke mechanism 苏格兰的克机构LESSION 6(P73)1)developing and demanding industry 一个处在发展中社会需要的产业2)propeller shaft 传动轴3)suspension components4) a sliding splined type of joint 滑动花键连接5)two rear axle shafts 两个后半轴6)to mesh with a larger bevel gear 与更大的锥齿轮啮合7)the universal joint 万向节8) a steering wheel 转向轮9)unevenness of road surfaces 路面的不平度10)the transverse line of the axle shafts 后横半轴11)to cause excessive tyre wear 造成轮胎的过度磨损12)the exactly similar diameter 直径非常接近13)quarter-elliptic leaf springs 四分之一随圆形钢板板式弹簧14)the transmission of shock 冲击15)road surface variation 路面变化16)the final-drive gears 最终传动齿轮副17)the precise alignment of shaft 精确同轴18)a rotating drum 转动筒鼓19)a hand lever 手刹杆20)be locked in the one position 被固定某一位置LESSION 8(P99)1)bulk deformation of metals 金属的变形2)forging，rolling or extruding 锻造滚压挤压3)plastic deformation 塑性变形4)impact blows 冲击5)the recrystallization point of the mental6)hot working and cold working 热加工和冷加工7)better surface finish8)hammer forging 锤锻9)striking the hot metal 锻打热金属10)a slow squeezing action 缓慢加压11)open dies and closed dies 开模和闭模12)bevel gears with traight or helical teeth 用直齿或螺旋加工锥齿轮13)impression dies 型腔模14)each of several die cavities 每一个模膛15)mass production16)a homogeneous circumferential grain fiow 均匀的周向纤维流17)the three-dimensional description 三维描述18)computer simulation 计算机仿真19)hydraulic presses 液压压力20)be rough- and finished-machined 粗加工和精加工LESSION 9(P110)1)carrying high-amperage current 携带高安培电流2)the electrode and the work-piece 电机和工件3)the weld pool 焊接熔池4) a column of ionized gas called plasma 一个列的电离气体称为等离子体5)the oxides and nitrides 氧化物和氮化物6)the positive ions 阳离子7)deleterious substances 有害物质8)the newly solidified mental 刚凝固的金属9)in overhead welding 仰焊10)current density 电流密度11)deposition rate 沉积速率12)an unbalanced magnetic field 不平横磁场13)arc blow 电弧偏吹14)the electrode coating 电极涂层15)in overhead position 在仰焊的位置16)the cooling rate of the deposited metal 沉积金属的冷却速度17)a more homogeneous microstructure 更均匀的微观结构18)a smooth flow of molten metal 顺畅熔融19)cellulosic-coated electrodes 纤维质涂层的焊条20)perpendicular to the current path 与电路垂直LESSION 10(P123)1)plain carbon steel 碳素钢2)carbon content 碳含量3)low carbon steel 低碳钢4)medium carbon steel 中碳钢5)high carbon steel 高碳钢6)be cold worked 冷加工7)be heat treated 热处理8)contain 20 point of carbon 含20%的碳9)in the hot-rolled condition 在热轧条件下10)heat-treat-hardened plain carbon steel 热处理硬化普通碳钢11)free-machining steels 易切削钢12)hot short 热脆性13)cold shortness 冷脆性14)the isothermal transformation curves 等温移动曲线15)grain refinement 细化晶粒16)stainless steel 不锈钢17)AISI steels 美国钢铁协会钢18)Iron-carbon equilibrium diagram 铁碳平衡表19)Tool and die steel 工具钢和模具钢20)High corrosion chemical resistance 高耐腐蚀和耐化学性能LESSION 11(P134)1)allotropic materials 同素异晶材料2)plain low carbon steel 普通低碳钢3)hypoeutectiod steel 亚共析钢4)normalized steel 正火钢5)hypereutectoid steel 过共析钢6)eutectoid composistion 共析钢7)grain houndaries 晶界8)ferrite matrix 铁氧体矩阵9)about 60℃about the Ac1 temperature 大约Ac1温度以上60摄氏度10)the nose of the I-T curve I-T曲线鼻共处11)cooling rate 冷却速率12)quenching shock 淬火介质13)thermal stress 热应力14)thermal shock 热冲击15)a tempered steel 回火钢16)temper brittlement 回火脆性17)in the tempering or drawing proceduce 在回火阶段18)hardened steel 硬化钢19)full annealing 充分退火20)to dissolve all the cementite 溶解渗碳体LESSION 15(P177)1)turning，facing and boring 车削，车端面和镗孔2)split nut 对开螺母3) a single setup of the workplace 工件在一次性定位安装4)headstock assembly 主轴箱组件5)tailstock assembly 尾座组件6)carriage assembly 溜板箱组件7)lead screw and feed rod 丝杠和光杆8)two sets of parallel，longitudinal ways 两组平行的导轨9)to assure accuracy of alignment 为了保证装配的精确度10)a set of transmission gears 一套传动齿轮11)the maximum size of bar stock 棒料的最大尺寸12)gear box 齿轮箱13)a V-belt or silent-chain drive V型带和无声传动装置14)carbide and ceramic tools 硬质合金和金属陶瓷刀15)the inner ways of the end 床身的内侧导轨16)tailstock quill 尾座套筒17)a graduated scale 通常情况18)in the direction normal to the axis of rotation of the work 在垂直工件旋转轴线方向19)manual movement of the carriage 托盘的手工移动20)per revolution of the spindle 主轴旋转一周LESSION 16 (P188)1) a multiple-tooth cutter 多齿铣刀2)progressive formation 逐渐成形3)in a direction perpendicular to the axis of the cutter 在垂直刀具轴线的方向4)the metal removal rate 金属切除率5)produce good surface finish 产生好的表面光洁度6)in job-shop and tool and die work7)teeth located un the periphery of the cutter body8)slab milling 板铣9)face milling 端面铣削10)up milling 逆铣11)down milling 顺铣12)the direction of feed of the workpiece 工件的进给方向13)the clamping device 夹具14)the smoothness of the generated surface 铣削表面的平整度15)the sharpness of the cutter edges 切削刃的锋利程度16)at the end of the tooth engagement17) p rofile cutters 仿形铣刀18) c arbide- and ceramic- tipped cutters 硬质合金及陶瓷-硬质合金刀具19)negative-rake-angle cutters 负倾角刀20)arbor cutters and shank cutters 乔木刀和柄刀。
说明:“ ”表示重点，“ ”表示短语或固定搭配，通读表示本文可能考翻译，泛读表示本文可能考阅读，本复习指导仅供参与，建议有条件的同学将所有课文都泛读一遍。
8.America's Luckiest Stamp Find (美国最幸运的邮票的发现)1.The first United States airmail stamp has had an interesting story.关于美国的第一枚航空邮票有一个有趣的故事。
2.One hundred of the stamps sold to the public became known as "inverts",for the plane was printed upside down.因为蓝色的飞机被印颠倒了，仅仅有一百枚这种“倒转”邮票卖给公众。
3.The collector's heart stood still as he saw that the sheet which had been offered him had inverted centers.当这个集邮者看到邮票时他的心跳刹那间停顿了，给他的这版邮票有一个倒转的中心。
4.Yet no matter how much this valuable stamp is bought and sold,no owner can match the thrill that W.T.Robey had on that day in 1918 when he made America's luckiest stamp find! 不论这种价值极高的邮票卖多少钱、买多少钱，没有一个所有者的兴奋可与罗比在1918年发现最幸运的美国邮票那天的兴奋相比！10.The First Jet（参考译文：第一架喷气机）1.If that shell had hit us half a second sooner,it might have hit the pilot.如果那颗炮弹早半秒击中我们，它可能击中机长。
GRE阅读材料练习：摩天大楼向更高处伸展A new lightweight lift cable will let buildings soar ever upward.WHEN Elisha Otis stood on a platform at the 1854 World Fair in New York and ordered an axeman to cut the rope used to hoist him aloft, he changed cityscapes for ever.To the amazement of the crowd his new safety lift dropped only a few inches before being held by an automatic braking system.This gave people the confidence to use what Americans insist on calling elevators.That confidence allowed buildings to rise higher and higher.一种新型的轻型升降梯将会让建筑连续向更高处进展.当艾利沙·奥的斯在1854年纽约世界博览会上站在一个高楼的阳台下，命令一个持斧的人砍断那个把他带到高空的绳索时，他彻底转变了人们对城市景观的印象。
为了吸引人群的眼光，在新的自动制动系统起动前，他只让他的新安全电梯降落了几英寸。
这让人们在使用电梯时-美国人坚持这个称呼有了足够的信念，也正是缘于这种信念，后来的建筑造得越来越高。
They could soon go higher still, as a result of anotherbreakthrough inlift technology.This week Kone, a Finnish liftmaker, announced that after a decade of development at its laboratory in Lohja, which sits above a 333-metre-deep mineshaft which the firm uses as a test bed, it has devised a system that should be able to raise an elevator a kilometre or more.This is twice as far as the things can go at present.Since the effectiveness of lifts is one of the main constraints on the height of buildings, Kone”s technology—which replaces the steel cables from which lift cars are currently suspended with ones made of carbon fibres—could result in buildings truly worthy of the name “skyscraper”.当另一种升降技术取得突破后，很快，高楼大厦将会连续往更高处进展。
桥1 桥梁是人类征服空间的伟大象征。
当看到太平洋上深红色的金门大桥映照在日落的黄昏中时，或者看到加拉比高架拱桥从深谷中腾空而起时，人们一定感到神奇，并充满对建设者艺术创造力的崇拜。
这些桥梁是人类在追求一个更美好更自由的世界的过程中排除一切障碍的决心的永久印证。
它们的设计和施工技术令人们如梦如幻。
但是梦想和决心并不够。
各种自然界的力量和重力必须靠数学模型精确计算，只有运用正确的建筑材料和方式才能克服这些力量。
这需要结合艺术家的灵感和工匠的技术。
2 关于材料和结构性能的科学技术已经得到巨大发展，计算技术现在也可以很快的应付复杂的理论计算。
在过去的十年，工程师使桥梁设计和施工方法发生了革命性的变化。
这些进步应用于小跨、中跨和大跨桥梁。
3 对于永久使用的大桥来说，钢材和混凝土是最常使用的材料,很多不同类型的桥都是这些材料通过单独或者组合使用的方式建成的木材可能用于水上临时性构造物，水位线以下的结构构件或者次要道路上的小跨径桥梁。
几座实验性的小跨径铝桥已经在美国建成。
4 桥的主要部分分为“基础”和“上层结构”。
这种区分方法只是为了方便，因为在很多桥中并没有很明显的区分线来把这两个部分区分开。
5 “基础”的元素有桥台和桥墩桥台和桥墩通常放在单独建造的基础上，比如混凝土的扩展基础或者排架这些构造都是“基础”的一部分。
桥梁下部结构有时也由一组排架组成，这些排架露出水面，在上面有承台，由承台支撑桥的上部结构。
这种排架一般采用相同的结构形式，作为又长又低的水上桥跨的一部分。
6 近几年，短中长跨距的桥之间的分界线多少有些模糊了。
目前，许多设计者认为跨距在20到100英尺是短跨距桥，他们建立了很多标准模型以便经济的处理不同跨度的桥梁。
根据投入以及材料的选择，现代桥梁施工中的中跨距的可达400英尺。
而长跨距可达4000英尺以上。
不过净跨距1000英尺的桥是非常罕见的。
7 桥还可以分为上承式和下承式两种，上承类型的桥，桥面在支撑物以上，也就是说上部结构的支撑物在车道以下。
英译汉There is an increase in damand for all kinds of consumer goods in every part of our coun-trry. 译为：我国各地对各种消费品的需求量正大大增加。
We also realized the growing need and necessity to industrialize certain sectoymned to pur-sue it .译为我们也认识到越来越需要使某些经济部门工业化。
They are deeply convinced of the ourrectness of this pocicy and firmly determined to pur-sue it. 译为：我们深信这一政策是正确的，并有坚定的决心继续奉行这一政策。
Weseek a deep-rooted understanding through the multiplication of our economic, cultur-al,scientific , technical and human ties.译为：我们要通过加强我们之间的经济、文化、科学、技术和人员等方面的交流来加深彼此的了解。
Rockets heve found applications for zhe exploration of the universe译为：火箭已经用来探索宇宙。
If we were ignorant of the structure of the atom ,it would be impossible for us to study nuclear physics 译为：如果我们不知道原子的结构，我们我们就不可能研究核子物理学。
Electronic control techniques can be designed to take full advantage of quick response in-herent in a gas turbine proulsion system译为：电子控制技术可以充分地利用燃气轮机推进系统固有的反应快的优点。
Centrifugal Compressor Surge and Speed Control Jan Tommy Gravdahl,Member,IEEE,and Olav Egeland,Member,IEEEAbstract—Previous work on stabilization of compressor surge is extended to include control of the angular velocity of the compressor.First a low-order centrifugal compressor model is presented where the states are massflow,pressure rise,and rotational speed of the spool.Energy transfer considerations are used to develop a compressor characteristic.In order to stabilize equilibria to the left of the surge line,a close coupled valve is used in series with the compressor.Controllers for the valve pressure drop and spool speed are derived.Semiglobal exponential stability is proved using a Lyapunov argument.Index Terms—Compressors,Lyapunov methods,modeling, surge control.I.I NTRODUCTIONC OMPRESSOR surge is an axisymmetric oscillation ofthe massflow and pressure rise.Modeling and control of these oscillations is of considerable interest since surge limits the useful range of massflows where the compressor operates rge amplitude surge can also damage the compressor. Low-order models for surge in compression systems have been proposed by many authors,and a classical reference is[7].However,the compression system model of[17]has been widely used for surge control design.It was derived for axial compression systems,but[19]showed that it is also applicable to centrifugal compressors.The model has two states,normalized massflow and normalized pressure,and the compressor is treated as an actuator disc,with a third-order polynomialflow/pressure rise characteristic.Over the last decade many papers covering the area of surge control have been published.A review can be found in[16].Of many possible actuation schemes,closed coupled valve(CCV) control is considered one of the most promising[6],[18],[21], [25],[27].Experimental results of CCV control is reported in [6]and[21].Surge in a compression system can be explained by the throttle line crossing the compressor characteristic in an area of positive compressor characteristic slope.A close coupled valve is placed immediately downstream of the compressor(hence close coupled),and active control of the valve pressure drop is utilized to make the slope of the equivalent compressor(compressor in series with the valve) negative and thereby stabilizing the system.This approach was used in[21],[25],and[27]for surge control of the model of[17].Linear stability analysis was used in designing control laws resulting in local stability results.In [26]pressure disturbances were included in the analysis,andManuscript received November25,1997;revised July28,1998.Recom-mended by Associate Editor,M.Jankovic.The authors are with the Department of Engineering Cybernetics,Norwe-gian University of Science and Technology,N-7034Trondheim,Norway. Publisher Item Identifier S1063-6536(99)06452-0.a nonlinear CCV control law was designed for the model of[17]using the method of Lyapunov.By applying backstepping, [13]developed nonlinear surge controllers for the same model, but included disturbances both in massflow and pressure. Global stability results were presented.In[14]certain passivity properties of the model were utilized in designing a CCV control law.One drawback of CCV control is that the valve introducesa pressure drop in the compression system as discussed in[26].When using the valve as a steady-state device,such as in[6],this loss may become unacceptably large.However, as pointed out in[25]and[26],a time varying valve will introduce considerably less pressure drop than a valve with constant pressure drop.Since compressors are variable speed machines,it is of interest to investigate the influence of speed transients on the surge dynamics.Models describing this interaction were developed in[8]and[12]for axial compressors,and in[10] and[15](a preliminary version of this paper)for centrifugal compressors.As surge can occur during acceleration of the compressor speed,it is of major concern to develop controllers that simultaneously can control both surge and compressor speed.In this paper,a surge control law for variable speed cen-trifugal compressors is presented and analyzed.The speed is controlled with a PI-control law.Inspired by[9]and [29],we make a departure from the third order polynomial approximation of the compressor characteristic commonly used in the surge control literature.Fluid friction and incidence losses,as well as other losses,in the compressor stage are modeled,and a variable speed compressor characteristic is developed based on this.Both annular and vaned diffusers are studied.Semiglobal exponential stability results for the proposed controllers are given using Lyapunovs method,and the results are confirmed through simulations.II.M ODELThe centrifugal compressor consists essentially of a sta-tionary inlet casing,a rotating impeller which imparts a high velocity to the gas,and a number offixed diverging passages in which the gas is decelerated with a consequent rise in static pressure.The latter process is one of diffusion, and consequently,the part of the compressor containing the diverging passages is known as the diffuser,[2].Fig.1is a diagrammatic sketch of the impeller and diffuser of a centrifugal compressor.The function of the inlet casing is to deliver gas to the impeller eye.A volute(also known as a scroll or a collector)may befitted at the diffuser exit.Its1063–6536/99$10.00©1999IEEEFig.1.Diagrammatic sketch of a radially vaned centrifugal compressor.Shown here with a vaneddiffuser.pression system.function is simply to collect the diffuser exitflow,and to guide it as efficiently as possible to the compressor outlet,without impeding the effectiveness of the diffuser[29].We are considering a compression system consisting of a centrifugal compressor,close coupled valve,compressor duct, plenum volume,and a throttle.The throttle can be regarded as a simplified model of a turbine.The system is shown in Fig.2. The model to be used for controller design is in theform(1)whereis the inlet stagnation sonicvelocity,is the spool moment ofinertia,is thedrive torqueandof the compressor is included as astate in addition to massflow and pressure rise which are thestates in Greitzers surge model.The equationforIt will also be shown that anexpression for the compressor characteristic results from thisderivation.Incoming gas enters the impeller eye(the inducer)of thecompressor withvelocityand(2)where is the constant stagnation inlet density.The tangen-tialvelocityis thenumber of revolutions per second.The averagediameter(4)GRAHVDAHL AND EGELAND:CENTRIFUGAL COMPRESSOR SURGE AND SPEED CONTROL569Fig.4.Velocity triangle at impeller tip.whereIII.E NERGY T RANSFERA.Ideal Energy TransferFor turbomachines,applied torque equals the change in angular momentum of thefluidis the tangential component of the gasvelocityof the gas velocity leaving the impeller tipshouldequalThis effect is known as slip .The flow isdeflected away from the direction of rotation of the impeller,which it leaves at an angle smaller than the vane angle.The slip factor is definedas,where is the number of compressorblades.We are now able to compute the compressortorque(11)Noticethat,and ideally we would have the same energy transfer for allmass flows (if backswept impellerblades,,wereconsidered,).However,due to various losses,the energy transfer is not constant,and we now include this in the analysis.According to [29],[9],[23]and other authors,the two major losses,expressed as specific enthalpies,are the following.1)Incidence losses in impeller anddiffuser,and .2)Friction losses in impeller anddiffuser,.The incidence losses and fluid friction losses play an impor-tant role in determining the region of stable operation for the compressor.Other losses,such as back flow losses,clearance losses,and losses in the volute will be taken into account when computing the efficiency of the compressor.There also exist other losses such as inlet casing losses,mixing losses and leakage losses,but these will be ignored in the following.For a further treatment on this topic,some references are [1],[20],[32],and [3].B.Incidence LossesThe losses due to incidence onto the rotor and vaned diffuser play an important role in shaping the compressor characteristic.There exists several methods of modeling this loss,and a570IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY,VOL.7,NO.5,SEPTEMBER 1999comparative study is given in [31].The two most widely used approaches are the following.1)The so called “NASA shock loss theory”reported in [29]and [31],which is based upon the tangential component of kinetic energy being destroyed.2)A constant pressure incidence model reported by [31]where it is assumed that the flow just inside the blades has adapted to the blades via a constant pressure process.For centrifugal compressors,the differences between the mod-els are small [29].According to [31],the main difference lies in the prediction of the incidence angle at which zero loss occurs.For model (1)zero loss is predicted when the flow angle at the inlet equals the blade angle.This is not the case for model (2).Based on this,and the simplicity of (1),the NASA shock loss theory is used here.Depending on the mass flow being lower or higher than the design flow,positive or negative stall is said to occur.The use of model (1)leads to a loss varying with the square of the mass flow,symmetrical about the design flow.In [9]it is stated that the incidence loss in practice increase more rapidly with reduction of flow below design flow,than with increase of flow above the design flow.This would lead to a steeper compressor characteristic below the design point than above,but for simplicity this will not be treated further here.According to [28],such a characteristic is said to be right skew.1)Impeller:The velocity of the incoming gas relative to the inducer isdenotedand the directionof the gasstream,as shown in Fig.5.The angle of incidence is definedby,and the kinetic energyassociated with the tangentialcomponent(14)Furthermore,(16)Fig.5.Incidence angles atinducer.Fig.6.Incidence angles at diffuser.and the incidence loss (13)can bewritten,and the kinetic energy associated with thetangentialcomponent(19)For simplicity the choice1is made.The diffuserinletangleGRAHVDAHL AND EGELAND:CENTRIFUGAL COMPRESSOR SURGE AND SPEED CONTROL571 incidence loss in both impeller and diffuser for the same massflow(20)From Fig.6and(20)it followsthat(22)and consequently the diffuser incidence loss(19)can bewrittenis the meanchannel lengthand(25)where the frictionfactoris definedasandperimetercorrespondsto a circle witharea Although the passagesbetween the blades in the compressor are neither circular nor ofconstant area,[1]reports of good agreement between theoryand measurement using(26).Using Fig.5,it is seenthatweget(29)2According to[29]diffusion losses in the impeller are small compared toimpeller friction losses,but they may be included in the analysis by choosingC h to suit.Inserting(2)and(29)in(24)gives(30)As can be seen from(30),the friction losses are quadratic inmassflow and independent of wheelspeedthrougha pipe of hydraulicdiameter(31)In the vaned diffuser a pipe friction loss is calculated for eachdiffuser passage.D.EfficiencyThe isentropic efficiency of the compressor is defined as(see,e.g.,[3])(32)where,in thispaperwhereis the axial clearanceandoccurs because the compressor has toreprocess thefluid that has been reinjected into the impellerdue to pressure gradients existing in the impeller tip region.Due to the lack of accurate modeling of this loss,[29]suggesta loss of three points of efficiency astypical:572IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY,VOL.7,NO.5,SEPTEMBER 1999(a)(b)Fig.7.Efficiencies for compressor with(a)vaned and(b)annular diffuser.In Fig.7,theefficiencyis a second-degree polynomialinthatisensuresthatWe now have an expression for thepressureGRAHVDAHL AND EGELAND:CENTRIFUGAL COMPRESSOR SURGE AND SPEED CONTROL573Fig.8.Energy transfer for N=35000r/pressor with annular diffuser.Fig.9.Centrifugal compressor characteristic.The left plot is for a annular diffuser,and the right for a vaned diffuser.The inlet stagnation temperature,specific heat capacityand574IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY,VOL.7,NO.5,SEPTEMBER1999 In Figs.8and9the numerical values for the compressorparameters are taken from[10].The surge line is the line inthe compressor map that divides the map into an area of stablecompressor operation and unstable(surge)operation.The linepasses through the local maxima of the constant speed linesin the map,and is drawn with a solid line in Fig.9.When theflow reaches sonic velocity at some cross sectionof the compression system,theflow chokes.Assuming isen-tropicflow,[5]calculated the chokingflow for the componentsmost likely to choke in centrifugal compressors,the impellereye(the inducer)and at the entry of the diffuser.In this paperit is assumed that choking takes place in the impeller eye.The effect of choking can be seen in Fig.9,where a chokeline,also known as a stone wall[23],has been drawn.Inthis paper,the effect of choking is treated in a approximatemanner.Due to sonic effects,the pressure rise would fall offmore gradually when approaching the stone wall than shownin Fig.9.The chokingflow is givenasis the inlet stagnation densityandis the inlet stagnation sonic velocity.It isseen that the choking massflow is dependent on bladespeed(40)where(41)Using(3)it is seenthatwould make it possible to minimize the incidence lossesover a range of massflows.Thus variable inducer blades mightbe used as a means of surge stabilization.On the other hand,the maximum energy transfer andminimum incidence loss do not occur for the same massflow.This is due to the friction losses.The friction shifts the pointof maximum energy transfer,and consequently pressure rise,to the left of the point of minimum incidence loss.From thiswe conclude that the friction losses in fact have a stabilizingeffect,and introducing additionalfluid friction would movethe point of maximum energy transfer to the left.The effectof this is that the surge line will be shifted to the left,and thearea of stable compressor operation is expanded.This motivates us to introduce a valve in series withcompressor.The pressure drop over this valve will serve asthe control variable,and it will be used to introduce additionalfriction at low massflows in order to avoid surge.The CCVwill be regarded as a idealized actuator,a device which canproduce a desired pressure drop.VII.C ONTROLLER D ESIGN AND S TABILITY A NALYSISThe equivalent compressor characteristic for compressorand close coupled valve is definedasis the pressure drop across the CCVandV p=A1L c;where V p is the plenum volume and L c isthe length of the compressor and ing(43),a nonlinear differentialequation for B can befound.GRAHVDAHL AND EGELAND:CENTRIFUGAL COMPRESSOR SURGE AND SPEED CONTROL575 The equations of motion(45)are now transformed so that theorigin becomes the equilibrium under study.Notice that noassumptions are made about the numeric valuesof(49)where a hat denotes transformation to the new coordinates(48),and is the equilibrium.From(10)it is knownthat(52)and calculatedas(53)Bychoosing(54)the last equation in(49)follows from the last equation in(45).Theorem1:The surge controllawmakes the origin of(49)semiglobal exponentiallystable.Proof:Define(58)where(59)whereis positive definite and radially unbounded,providedthat(61)Calculating the time derivative of(59)along the solutions of(49)and accounting for(56)gives(62)The last term in(62)can be upper boundedas-term can be upper boundedas(65)where576IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY,VOL.7,NO.5,SEPTEMBER1999Fig.10.Transient response of centrifugal compression system with annular diffuser.Without surge control,the compressor goes into surge.This is plotted with a solid line.The dashed lines are the system response when the CCV surge controller is in use.Demandingand(69)wheresatisfies the sectorconditionNow,the CCV pressuredrop(74)is satisfied.SinceGRAHVDAHL AND EGELAND:CENTRIFUGAL COMPRESSOR SURGE AND SPEED CONTROL577Fig.11.(m(t);p(t)=p01)-trajectories plotted together with the compressor characteristic.N is the compressor speed in r/min. guarantees that(76),and thereby(74)is satisfied.Moreover,ifwegetandare upper bounded using Young’sinequality(84)(85)where(87)(88)(90)If(91)andandBy(90)the origin of(49)is exponentially stable.Due to assumption(73),the stability result holdswhenever,and thusthe origin is semiglobal exponential stable.Notice that theparameter578IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY,VOL.7,NO.5,SEPTEMBER1999Fig.12.Transient response of centrifugal compression system with vaned diffuser.Without surge control,the compressor goes into surge.This is plotted with a solid line.The dashed lines are the system response when the CCV surge controller is in use.VIII.S IMULATIONSThe two cases of annular and vaned diffuser are nowsimulated with and without surge control.A.Annular DiffuserIn Fig.10the response(solid lines)of the compressionsystem during surge is shown.The set point for compressorspeedwasandwhichgives an unstable equilibrium to the left of the surge line.Notice the oscillations inspeedhas been plotted versus the massflow together withthe compressor characteristic,the throttle line and the surgeline.As can be seen,the compressor undergoes deep surgeoscillations.Now,the surge controller(55)is usedwithIn this simulation thegain was setto to dominate the maximum positiveslope of the compressor characteristic.The resulting trajectoryof this simulation in also plotted in Fig.11.The equilibriumis located somewhat below the intersection of the throttle lineandtheandGRAHVDAHL AND EGELAND:CENTRIFUGAL COMPRESSOR SURGE AND SPEED CONTROL579By comparing the in-surge response of the two cases,it is seen that the frequency of the surge oscillations is lower for the vaned diffuser(3Hz),than for the annular diffuser(7Hz). This is in accordance with[18]and[33]where it is shown that the surge frequency depends on the slope of the compressor characteristic in such a way that a steeper slope leads to lower frequency,and a less steep slope leads to higher frequency.IX.C ONCLUSIONA surge control law and a PI speed control law for a centrifugal compression system have been developed.The modeling of the compressor characteristic was based on energy losses in the compressor stage.Incidence and friction losses in the impeller and the diffuser were considered in addition to other losses.A close coupled valve was chosen as an actuator for the surge ing Lyapunovs method,the systems equilibrium was shown to be semiglobal exponentially stable. Through simulations it was confirmed that the compressor can operate stable and reach desired speed in the previous unstable area to the right of the surge line in the compressor map. From a surge control point of view,the main difference between the annular and vaned diffusers are the steeper slope of the compressor characteristic.A consequence of this is that if a CCV is used to control surge,a greater pressure drop must be accepted over the valve in the case of a vaned diffuser than in the case of an annular diffuser.R EFERENCES[1]O.E.Balj´e,“A contribution to the problem of designing radial turbo-machines,”Trans.ASME,vol.74,pp.451–472,1952.[2]H.Cohen,G.F.C.Rogers,and H.I.H Saravanamuttoo,Gas TurbineTheory,4th ed.Essex,U.K.:Longman,1996.[3]N.A.Cumpsty,Compressor Aerodynamics.Essex,U.K.:Longman,1989.[4]I.J.Day,“Axial compressor performance during surge,”J.PropulsionPower,vol.10,no.3,pp.329–336,1994.[5]S.L.Dixon,Thermodynamics of Turbomachinery,3rd ed.Oxford,U.K.:Pergamon,1978.[6]J.L.Dussourd,G.W.Pfannebecker,and S.K.Singhania,“An experi-mental investigation of the control of surge in radial compressors using close coupled resistances,”J.Fluids Eng.,vol.99,pp.64–76,1977. [7]H.W.Emmons,C.E.Pearson,and H.P.Grant,“Compressor surge andstall propagation,”Trans.ASME,vol.77,pp.455–469,1955.[8]K.M.Eveker and t,“Model development for active surgecontrol rotating stall avoidance in aircraft gas turbine engines,”in Proc.1991Amer.Contr.Conf.,1991,pp.3166–3172.[9]T.B.Ferguson,The Centrifugal Compressor Stage.London,U.K.:Butterworths,1963.[10] D.A.Fink,N.A.Cumpsty,and E.M.Greitzer,“Surge dynamics ina free-spool centrifugal compressor system,”J.Turbomachinery,vol.114,pp.321–332,1992.[11] A.M.Foss,R.P.G.Heath,P.Heyworth,J.A.Cook,and J.McLean,“Thermodynamic simulation of a turbo-charged spark ignition engine for electric control development,”in Proc.7th IMechE Int.Conf.Automotive Electron.,London,U.K.,Oct.1989,Paper C391/044,pp.195–202. [12]J.T.Gravdahl and O.Egeland,“A Moore–Greitzer axial compressormodel with spool dynamics,”in Proc.36th IEEE Conf.Decision Contr., San Diego,CA,Dec.1997,pp.4714–4719.[13],“Compressor surge control using a close-coupled valve andbackstepping,”in Proc.1997Amer.Contr.Conf.,Albuquerque,NM, June1997.[14],“Passivity based compressor surge control using a close-coupledvalve,”in Proc.1997COSY Wkshp.Contr.Nonlinear Uncertain Syst.,A.Isidori and F.Allg¨o wer,Eds.,Zurich,Switzerland,Jan.1997,pp.139–143.[15],“Speed and surge control for a low-order centrifugal compressormodel,”in Proc.1997Int.Conf.Contr.Applicat.,Hartford,CT,Oct.1997,pp.344–349.[16],Compressor Surge and Rotating Stall:Modeling and Control,Advances in Industrial Control.London,U.K.:Springer-Verlag,1999.[17] E.M.Greitzer,“Surge and rotating stall in axialflow compressors,PartI:Theoretical compression system model,”J.Eng.Power,vol.98,pp.190–198,1976.[18],“The stability of pumping systems—The1980Freeman scholarlecture,”J.Fluids Eng.,vol.103,pp.193–242,1981.[19]K. E.Hansen,P.Jørgensen,and rsen,“Experimental andtheoretical study of surge in a small centrifugal compressor,”J.Fluids Eng.,vol.103,pp.391–394,1981.[20]J.P.Johnston and R. C.Dean,“Losses in vaneless diffusers ofcentrifugal compressors and pumps.Analysis,experiment and design,”J.Eng.Power,Jan.1966,pp.49–62.[21]W.M.Jungowski,M.H.Weiss,and G.R.Price,“Pressure oscillationsoccurring in a centrifugal compressor system with and without passive and active surge control,”J.Turbomachinery,vol.118,pp.29–40,1996.[22]J.A.Lorett and S.Gopalakrishnan,“Interaction between impeller andvolute of pumps at off-design conditions,”J.Fluids Eng.,vol.108,pp.12–18,Mar.1986.[23] A.E.Nisenfeld,Centrifugal Compressors:Principles of Operation andControl.Instrument Soc.Amer.,1982.[24]R.C.Pampreen,“Small turbomachinery compressor and fan aerody-namics,”J.Eng.Power,vol.95,pp.251–256,July1973.[25]J.E.Pinsley,G.R.Guenette,A.H.Epstein,and E.M.Greitzer,“Activestabilization of centrifugal compressor surge,”J.Turbomachinery,vol.113,pp.723–732,1991.[26]J.S.Simon and L.Valavani,“A Lyapunov based nonlinear controlscheme for stabilizing a basic compression system using a close-coupled control valve,”in Proc.1991Amer.Contr.Conf.,1991,pp.2398–2406.[27]J.S.Simon,L.Valavani,A.H.Epstein,and E.M.Greitzer,“Evaluationof approaches to active compressor surge stabilization,”J.Turboma-chinery,vol.115,pp.57–67,1993.[28]H.-H.Wang and M.Krsti´c,“Control of deep hysteresis compressorsunder limited actuator bandwidth,”in Proc.1997Int.Conf.Contr.Applicat.,Hartford,CT,Oct.1997,pp.657–662.[29]N.Watson and M.S.Janota,Turbocharging the Internal CombustionEngine.New York:MacMillan,1982.[30] F.M.White,Fluid Mechanics,2nd ed.New York:McGraw-Hill,1986.[31] A.Whitfield and F.J.Wallace,“Study of incidence loss models inradial and mixed-flow turbomachinery,”in Proc.Conf.Heat Fluid Flow in Steam and Gas Turbine Plant,Univ.Warwick,Coventry,U.K.,Apr.1973,pp.122–12.[32] A.Whitfield and F.J.Wallace,“Performance prediction for automotiveturbocharger compressors,”Proc.Inst.Mech.Eng.,vol.189,no.12,pp.59–67,1975.[33] F.Willems,“Modeling and control of compressorflow instabilities,”Eindhoven Univ.Technol.,The Netherlands,Tech.Rep.WFW96.151,1996.Jan Tommy Gravdahl(S’94–M’98)born in Nor-way in1969.He received the Siv.Ing.degree inelectrical engineering in1994and the Dr.Ing.degreein engineering cybernetics in1998,both from TheNorwegian University of Science and Technology(NTNU),Trondheim.His doctoral dissertation wastitled“Modeling and control of surge and rotatingstall in compressors.”He is currently a Postdoctoral Fellow at theDepartment of Engineering Cybernetics,NTNU.Hisresearch interests include nonlinear control with applications to mechanical systems,topics related to compressor modeling andcontrol.Olav Egeland(S’85–M’86)was born in Trondheim,Norway,in1959.He received the Siv.Ing.degreein1984and the Dr.Ing.degree in1987in electricalengineering from the Norwegian University of Sci-ence and Technology,Trondheim.He became Assistant Professor in1987and Pro-fessor in1989at the Department of EngineeringCybernetics,Norwegian University of Science andTechnology,where he is currently Head of Depart-ment.The academic year1988to1989he was aVisiting Scientist at the German Aerospace Research Establishment(DLR)in Oberpfaffenhofen.His research interests include the modeling and control of nonlinear mechanical systems with focus on industrial applications.Dr.Egeland is Associate Editor of IEEE T RANSACTIONS ON A UTOMATIC C ONTROL and received the Automatica Prize Paper Award in1996.。
The Best Cars for a Luxurious andOpulent InteriorWhen it comes to luxurious and opulent interiors in cars, there are several options that stand out in the automotive market. These cars not only offer top-notch performance and cutting-edge technology but also provide a lavish and comfortable interior that exudes elegance and sophistication. From high-end materials to advanced features, these vehicles are designed to provide an unmatched driving experience for those who appreciate the finer things in life. One of the top contenders for the best car with a luxurious and opulent interior is the Rolls-Royce Phantom. This iconic luxury car is renowned for its exquisite craftsmanship and attention to detail. The interior of the Phantom is a testament to the brand's commitment to luxury, with premium leather upholstery, handcrafted wood trim, and an array of customizable options to suit the owner's preferences. The cabin is designed to cocoon its occupants in absolute comfort, with features such as massaging seats, a premium sound system, and ambient lighting adding to the overall opulence of the interior. Another standout in the luxury car segment is the Bentley Mulsanne. The Mulsanne's interior is a showcase of British luxury at its finest, with hand-stitched leather, polished wood veneers, and metal accents adorning every surface. The attention to detail in the Mulsanne's cabin is second to none, with the option for bespoke customization to create a truly unique and personalized driving environment. The car also features advanced technology such as a high-resolution infotainment system, a premium audio system, and advanced climate control to ensure a first-class driving experience for both the driver and passengers. For those who prefer a more modern take on luxury, the Mercedes-Benz S-Class is a top choice. The S-Class sets the standard for luxury sedans, with a spacious and well-appointed interior that is packed with cutting-edge technology and premium materials. The cabin of the S-Class is designed to provide a serene and comfortable environment, with features such as heated and ventilated seats, a panoramic sunroof, and a state-of-the-art Burmester sound system. The car also offers advanced driver assistance features and a comprehensive infotainment system to cater to the needs of the most discerningdrivers. In the realm of SUVs, the Range Rover stands out as a top contender for the best luxurious and opulent interior. The Range Rover's cabin is a blend of refined luxury and rugged capability, with premium leather upholstery, real wood trim, and aluminum accents creating a sophisticated and upscale atmosphere. Thecar also offers a range of advanced features such as a dual-screen infotainment system, a premium Meridian sound system, and configurable ambient lighting tocreate a personalized driving experience. Despite its off-road prowess, the Range Rover's interior is designed to provide a serene and comfortable environment forits occupants, making it a top choice for those who prioritize luxury in their SUV. In the electric vehicle segment, the Tesla Model S stands out for its luxuriousand opulent interior. The Model S offers a minimalist yet sophisticated cabin,with premium materials and advanced technology creating a futuristic and upscale driving environment. The car's large touchscreen infotainment system, premiumaudio system, and advanced autopilot features add to the overall luxury and convenience of the interior. The Model S also offers a spacious and comfortable seating arrangement, making it a top choice for those who want a luxurious driving experience with the added benefit of electric power. In conclusion, there are several options for cars with luxurious and opulent interiors, each offering a unique blend of craftsmanship, technology, and comfort. Whether it's the timeless elegance of a Rolls-Royce, the bespoke luxury of a Bentley, the modernsophistication of a Mercedes-Benz, the rugged opulence of a Range Rover, or the futuristic luxury of a Tesla, these cars are designed to cater to the most discerning of drivers. With their attention to detail, premium materials, and advanced features, these vehicles set the standard for luxury in the automotive world, providing a driving experience that is truly unparalleled.。
Part BDirections:In the following text, some sentences have been removed. For Questions 41-45, choose the most suitable one from the list A-G to fit into each of the numbered blanks. There are two extra choices, which do not fit in any of the blanks. Mark your answers on ANSWER SHEET1.（10 points）Think of those fleeting moments when you look out of an aeroplane window and realise that you are flying, higher than a bird. Now think of your laptop, thinner than a brown-paper envelope, or your cellphone in the palm of your hand. Take a moment or two to wonder at those marvels. You are the lucky inheritor of a dream come true.The second half of the 20th century saw a collection of geniuses, warriors, entrepreneurs and visionaries labour to create a fabulous machine that could function as a typewriter and printing press, studio and theatre, paintbrush and gallery, piano and radio, the mail as well as the mail carrier. (41)——————The networked computer is an amazing device, the first media machine that serves as the mode of production, means of distribution, site of reception, and place of praise and critique. The computer is the 21st century's culture machine.But for all the reasons there are to celebrate the computer, we must also tread with caution.(42)——————I call it a secret war for two reasons. First, most people do not realise that there are strong commercial agendas at work to keep them in passive consumption mode. Second, the majority of people who use networked computers to upload are not even aware of the significance of what they are doing.All animals download, but only a few upload. Beavers build dams and birds make nests. Yet for the most part, the animal kingdom moves through the world downloading. Humans are unique in their capacity to not only make tools but then turn around and use them to create superfluous material goods - paintings, sculpture and architecture - and superfluous experiences - music, literature, religion and philosophy. (43)————For all the possibilities of our new culture machines, most people are still stuck in download mode. Even after the advent of widespread social media, a pyramid of production remains, with a small number of people uploading material, a slightly larger group commenting on or modifying that content, and a huge percentage remaining content to just consume. (44)————Television is a one-way tap flowing into our homes. The hardest task that television asks of anyone is to turn the power off after he has turned it on.(45)————What counts as meaningful uploading? My definition revolves around the concept of "stickiness" - creations and experiences to which others adhere.[A] Of course, it is precisely these superfluous things that define human culture and ultimately what it is to be human. Downloading and consuming culture requires great skills, but failing to move beyond downloading is to strip oneself of a defining constituent of humanity.[B] Applications like , which allow users to combine pictures, words and other media in creative ways and then share them, have the potential to add stickiness by amusing, entertaining and enlightening others.[C] Not only did they develop such a device but by the turn of the millennium they had also managed to embed it in a worldwide system accessed by billions of people every day.[D] This is because the networked computer has sparked a secret war between downloading and uploading - between passive consumption and active creation - whose outcome will shape our collective future in ways we can only begin to imagine.[E] The challenge the computer mounts to television thus bears little similarity to one format being replaced by another in the manner of record players being replaced by CD players.[F] One reason for the persistence of this pyramid of production is that for the past half-century, much of the world's media culture has been defined by a single medium - television - and television is defined by downloading.[G]The networked computer offers the first chance in 50 years to reverse the flow, to encourage thoughtful downloading and, even more importantly, meaningful uploading.参考译文当你从飞机的窗口望出,想一想那飞逝即逝的瞬间,意识到你正在飞行，飞得比鸟还要高。
职称英语考试模拟题之阅读(3)
2015年职称英语考试模拟题之阅读
答案：31C建筑设计是否能使建筑具有抵御恐怖袭击的性能，是
一个月前世界贸易中心受到袭击之前人们从未想过的'一个问题。
这是第一段的主要内容。
所以，只有C是正确答案。
32DA不是正确选项，因为文章没有提及谁首先提出这个项目。
B
或C都不是文章所述的内容。
答案可以在第三段中找到。
33B有关本题的句子是第四段的第三句，“ThisbuildingismanymetersawayfromtheWorldTradeCenterandyet weseeacolumntherethatusedtobePartofthatbuilding."这里的thisbuildin9指的是thebuildingmanymetersawayfromtheWorldTradeCenter，而thatbuildin9指的是WorldTradeCenter。
34B选项A不是答案，因为文章说，
thefloorfram ingsysteminoneoftheadjacentbuildings…remainint act.C不是文章表达的内容。
D在文中提到，但不是asurprisingdiscovery.只有B是正确答案。
35D选项A的内容是正确的，根据是本段最后一句(“…developnewones”)。
选项B和C的内容也是正确的，根据是
本段最后两句(关键词是applicable和transfer)。
只有D是答案。
因为Reinhorn没有说：blastengineeringemergesasanewbranchofscience。
A Large Linear Interior Permanent MagnetMotor for Electromagnetic LauncherMehran Mirzaei,Seyed Ehsan Abdollahi,and Hamid LesaniAbstract—In this paper,a magnetic analysis of large linear motors with long primary and short interior permanent magnet (PM)secondary is presented.The calculations are carried out using afinite-element method,taking into account the secondary motion and saturation in iron parts.Reluctance force could be increased using interior PM secondary.The thrust force oscilla-tions are evaluated to obtain minimum force ripple.Furthermore, a magnet demagnetization analysis is presented to evaluate the magnet demagnetization risk under loading.Reduction in the magnet volume is considered for cheaper and simpler secondary structure.Index Terms—Finite-element method,interior permanent magnet secondary,large linear motor,thrust force.I.I NTRODUCTIOND IFFERENT types of linear motors are widely used forlinear motion applications,which include low-power ac-tuator to very high thrust force linear motors for Earth to space launching.Accelerating a mass to reach a desired speed at short time and distance can be achieved using high-thrust force density linear motors.For example,these motors are employed in car-accident simulator,aircraft and satellite launching from carriers,and other instances where high thrust is needed at a short time.The aircraft launch systems currently use steam technology for launching,which has been used operationally for over 50years.However,the old mechanical system can be replaced by an electromagnetic launch system with linear motor propul-sion[1],[2].Recently,linear induction,permanent magnet (PM),superconducting,and reluctance synchronous motors have been analyzed,and no full-scale electromagnetic launch-ers for aircraft have been built based on the references cited [3]–[7].The advantage of linear induction motors is low-mass secondary using aluminum secondary;however,the power factor is poor because of large magnetic airgap.Nevertheless, using permanent magnet or superconductors in the secondary improves the power factor of motor but results in high mass and complicated secondary.Interior permanent magnet secondary is a solution for large-dimension electrical machines to simplify the manufacturing process.Manuscript received May3,2010;revised January1,2011;accepted March1,2011.Date of publication May12,2011;date of current version June10,2011.M.Mirzaei is with the Electrical Engineering Department,Amirkabir University of Technology,Tehran15914,Iran(e-mail:mehranamirzaei@ ).S.E.Abdollahi and H.Lesani are with the Electrical Engineering Depart-ment,University of Tehran,Tehran11365-4563,Iran.Color versions of one or more of thefigures in this paper are available online at .Digital Object Identifier10.1109/TPS.2011.2140401Fig.1.Electromagnetic launch system with(left)blade configuration and(right)speed–distance characteristics.In this paper,electromagnetic calculations of large linearinterior PM motors for electromagnetic launcher are presented.The secondary structures are changed with the same primary toobtain the optimum output.The analysis is carried out for loadand no-load conditions at sinusoidal and block-shape currentsources[3],[8]–[10].II.S TRUCTURE AND M ODELINGFig.1shows the general view of linear motors used in elec-tromagnetic launcher for aircraft.Blade-type(two primariesand one secondary)shape is used for secondary to achieveminimum secondary ing long primary signifies thatpower sources and switches are distributed in the total lengthof the launching path,which complicates the control system.The total path is divided into many small sections to simplifythe supply system,which get energized and de-energized oneafter the other to launch the aircraft[3].Here,the launcher should accelerate the aircraft to100m/s in100-m(l a)distance and decelerate the secondary to0m/s afterthe aircraft takes off in10m(l d)(Fig.1).The maximum weightof the moving part(aircraft and secondary)is25000kg,and thesecondary weight is2500kg.The accelerating and deceleratingtimes are2and0.2s,respectively[6].The maximum active secondary weight in the design processis considered to be80%(2000kg)of the maximum allowableweight of2500kg,indicating that the rest of the20%is for themechanical support of the secondary.Thefirst model with blade-shape configuration(Pattersonmodel)is shown in Fig.2.The linear motor is a three-phaseand20-pole machine with150-mm pole pitch.The magnet di-mensions are as follows:100mm width(two-thirds pole pitch),100-mm thickness,and1000-mm length in the transverse direc-tion.The magnets are placed inside iron laminations with2-mmiron bridge.Two current sources are considered to evaluate the thrustforce oscillations for brushless dc and synchronous configura-tions,respectively(Fig.3)[9].The leading of current relativeto back-EMF voltage with an optimum phase angle(β)makes 0093-3813/$26.00©2011IEEEFig.2.Two-dimensional model of thefirst design of linear interior permanent magnet motor and no-load magnetic-fluxdistribution.Fig.3.Applied current model for(left)sinusoidal and(right)block shapes, and related back-EMF voltage.bigger thrust force,owing to reluctance torque,and smaller terminal voltage to obtain higher power factor.The Fourier analysis of block-shape current with120◦con-duction is as follows[8]:i=2√3π·I·(cos(ωt)−1/5cos(5ωt)+1/7cos(7ωt)−1/11cos(11ωt)+1/13cos(13ωt)+···)ω=2πf(1) where I and f are the dc current and main frequency of the source,respectively.The dc current and frequency for a 20-pole linear motor in the Patterson model are18kA and 333.33Hz,respectively.It is assumed that each slot carries 18kA.Thefirst term in(1)is used in sinusoidal current source simulations,which is equal to14kA(rms).This indicates that the sinusoidal current model has less ohmic losses when compared with the block-shape current model.Selection of the magnet type for electromagnetic launcher is important in the design process to obtain maximum thrust force and avoid magnet demagnetization at high temperatures. Fig.4shows the magnetic characteristics of the magnet,where the intrinsic coercive force is greater than1600kA/m at100◦C (working magnet temperature)and the remnant magnetic-flux density at20◦C is1.15T.It has been shown that the magnet can operate easily up to150◦C at fault conditions.III.A NALYSISA.First DesignThe magnetic calculations for thrust force and voltage for thefirst design at sinusoidal and block-shape sources with120◦conduction are shown in Figs.5–8.The required thrust force is 1.25MN[6].A value of1.3MN is considered as the required thrust force to compensate for the unpredictable effects,such as end effects in practice.The simulation of no-loadcogging Fig.4.B−H curves of the considered permanent magnet for simulation at differenttemperatures.Fig. 5.(Left)Cogging and(right)load thrust force with sinusoidal current—β=0electrical degrees—firstmodel.Fig.6.(Left)No-load and(right)underload voltages with sinusoidal current at100m/s—β=0electrical degrees—firstmodel.Fig.7.Load thrust force and load voltage with sinusoidal source at 100m/s—β=−20electrical degrees—first model.thrust force shows that the peak-to-peak no-load cogging force is5%of the average load thrust force with sinusoidal source. The average force is1.094MN at thefirst design,which is smaller than1.3MN.The transverse length of the linear motor should be increased from1000to1190mm to compensate for the smaller simulated thrust force.The no-load voltage is observed to increase considerably from2560to4122V at load with a leading angleβ=0 electrical degrees.Leading the applied current to back-EMF voltage is a well-known method to reduce the terminal voltage of the proposed linear motor to improve the power factor and reduce the required converter output voltage.In interior PMFig.8.Load thrust force with(left)β=0electrical degrees and(right)β=−20electrical degrees with block-shape source at100m/s—firstmodel.Fig.9.Magneticfield intensity distribution in the magnet with sinusoidal source at100◦C to evaluate the demagnetization of the magnets(owing to the symmetry;only half of the two-pole model is shown)-first modellinear motor,applyingβbetween current and voltage increases the thrust force,owing to reluctance thrust force.Fig.7shows the terminal voltage and thrust force with β=−20electrical degrees.The thrust force did not change considerably,but the terminal voltage decreased by13.75%to 3555.5V,which increased the power factor from0.64to0.74 with nonzeroβ.The results for block-shape current with differentβangles are shown in Fig.8,which illustrates approximately the same thrust force.It can be observed that the thrust force oscillations are two times higher when compared with those obtained from the sinusoidal current source.The secondary skewing is a method to reduce the thrust force oscillations,but the average value of the thrust force is reduced.The demagnetization calcu-lation results are shown in Figs.9and10with different current sources.It can be observed that the maximum demagnetization value is lower than1600kA/m at100◦C,which,according to Fig.4,shows the safety of the magnet.The average thrust force in all the results shows that the required thrust force has not been provided.Increasing the reluctance force may be a method to increase the thrust force.The volume between the magnets of two adjacent poles isfilled with iron(Fig.11)to provide low reluctance path forflux to produce more force(reluctance).The simulated results with sinusoidal current source are shown in Figs.12and13for differentβangles.The thrust force increased for nonzeroβwhen compared with thefirst model,but the average thrust force of1.17MN was still smaller than1.3MN. However,by using higher current or bigger transverse machine, one can increase the thrust force.Higher current signifies bigger converter,and bigger width implies more weight for the secondary.The considered length for voltage calculations is3000mm(20poles).The net weight of20-pole secondary was1550kg for thefirst model,which is lower than2000kg;however,in the modified first model,the net weight was2310kg.Fig.10.Magneticfield intensity distribution in the magnet with block-shape current source with120◦conduction at100◦C to evaluate the demagnetization of the magnets(owing to the symmetry;only half of the two-pole model is shown)—firstmodel.Fig.11.Two-dimensional load magnetic-flux distribution with complete iron bridge between two poles—modifiedfirst model(owing to the symmetry;only half of the two-pole model isshown).Fig.12.Load thrust force and load voltage with sinusoidal source at 100m/s—β=0electrical degrees—modified secondmodel.Fig.13.Load thrust force and load voltage with sinusoidal source at 100m/s—β=−45electrical degrees—modified second model.B.Second DesignThe width and thickness of the magnet are changed from100 and100mm in Patterson model to125and80mm,respectively, in the second design,with the same magnet volume as in the first model.Fig.14shows the magnetic-flux distribution in the second design,where the stator or primary isfixed.It can be observed that the cogging no-load thrust force increases approximately from60000N to more than80000N in the second model.TheFig.14.Two-dimensional load magnetic-flux distribution—second model (owing to the symmetry;only half of the two-pole model isshown).Fig.15.(Left)Cogging and(right)load thrust force with sinusoidal current—β=0electrical degrees—secondmodel.Fig.16.(Left)No-load and(right)underload voltages with sinusoidal current at100m/s—β=0electrical degrees—secondmodel.Fig.17.Load thrust force and load voltage with sinusoidal source at 100m/s—β=−20electrical degrees—second model.load force atβ=0electrical degrees is the same as thefirst model,but the thrust force atβ=−20electrical degrees in-creases slightly to1.15MN in the second design.Furthermore, it can be noted that the no-load and load terminal voltages for the whole length of the secondary(3000mm)are higher than thefirst model(see Figs.15–17).The power factor obtained was0.72in the second design. The thrust forces with120◦-conduction block-shape current with differentβangles are shown in Fig.18.It can be noted that the average values of the forces are slightly lower than the sinusoidal ones.Furthermore,the thrust force oscillationsare Fig.18.Load thrust force with(left)β=0electrical degrees and(right)β=−20electrical degrees with block-shape source at100m/s—secondmodel.Fig.19.Two-dimensional load magnetic-flux distribution—final model (owing to the symmetry;only half of the two-pole model isshown).Fig.20.(Left)No-load and(right)underload voltages with sinusoidal current at100m/s—β=0electrical degrees—finalmodel.Fig.21.(Left)Cogging and(right)load thrust force with sinusoidal current—β=0electrical degrees—final model.half of those obtained with thefirst design,which may be an important key in the electromagnetic aircraft launcher.C.Final DesignOptimization is applied in thefinal design(Fig.19)to obtain the desired thrust force with the current source and reduced magnet volume.The width and thickness of the magnet in each pole were125and60mm,respectively.The transverse length of the linear motor was increased to1175mm(17.5%longer) to obtain the required thrust force value.Fig.22.Load thrust force and load voltage with sinusoidal source at 100m/s—β=−35electrical degrees—finalmodel.Fig.23.Load thrust force with(left)β=0electrical degrees and(right)β=−35electrical degrees with block-shape source at100m/s—finalmodel.Fig.24.Magneticfield intensity distribution in the magnet with block-shape current source at100◦C to evaluate the demagnetization of the magnets—final model(owing to the symmetry;only half of the two-pole model is shown).It can be noted that the load voltage(Fig.20)atβ=0 electrical degrees is about100%higher when compared with the no-load voltage,demonstrating poor power factor and inadequacy of load thrust force(Fig.21)(1.15MN).The iron bridge between the magnets is observed to cause more reluctance force.Furthermore,by changing theβvalue from 0to−35electrical degrees,the average thrust force(Fig.22) with sinusoidal current is observed to increase to1.313MN, indicating higher reluctance thrust force in thefinal design and better power factor.The average value for the thrust force is also found to be higher in block-shape current source with nonzeroβthan the zero one and close to the required thrust force(Fig.23).The demagnetization calculation demonstrates the safety of the magnet under load at working temperature (Fig.24).Furthermore,magnetic saturation of the primary and the secondary iron is observed to be the main limitation factor to increase the thrust force for these types of motors,owing to very high primary current(Fig.25).In all the models,thrust force oscillations with6th harmonic order are considerable when compared with the average force.The interaction of the5th and 7th harmonics of the primary and secondaryfields produced force oscillations.The use of short-pitched or fractional-slot windings decreases the force oscillations,as well as the average thrustforce.Fig.25.Magnetic-flux density distribution in the magnet with block-shape current source at100◦C—final model(owing to the symmetry;only half of the two-pole model is shown).IV.C ONCLUSIONIn this paper,three types of interior permanent magnet sec-ondary for one primary have been analyzed and presented.The dynamic magnetic calculations were carried out by taking into account the secondary motion and iron saturation,to evaluate the force oscillations.The two types of current sources with sinusoidal and block shapes with120◦conduction were ana-lyzed,and the results have been presented.Furthermore,the application of a leading phase angle between the current and voltage produced a considerable reluctance thrust force in the final model with12%less magnet,when compared with the first model.Demagnetization calculations showed that thefinal model is safe under load using the aforementioned permanent magnet.R EFERENCES[1]M.R.Doyle,D.J.Samuel,T.Conway,and R.R.Klimowski,“Electro-magnetic aircraft launch system-EMALS,”IEEE.Trans.Magn.,vol.31, no.1,pp.528–533,Jan.1995.[2]R.R.Bushway,“Electromagnetic aircraft launch system developmentconsiderations,”IEEE Trans.Magn.,vol.37,no.1,pp.52–54,Jan.2001.[3]D.Patterson,A.Monti,C.W.Brice,A.Dougal,R.O.Pettus,S.Dhulipala,D.C.Kovuri,and T.Bertoncelli,“Design and simulation of a perma-nent magnet electromagnetic aircraft launcher,”IEEE Trans.Ind.Appl., vol.41,no.2,pp.566–575,Mar./Apr.2005.[4]G.Stumberger,D.Zarko,M.T.Aydemir,and T.A.Lipo,“Designand comparison of linear synchronous motor and linear induction motor for electromagnetic aircraft launch system,”in Proc.IEEE IEMDC, pp.494–500.[5]G.Stumberger,D.Zarko,M.T.Aydemir,and T.A.Lipo,“Design of lin-ear bulk superconductor magnet synchronous motor for electromagnetic aircraft launch systems,”IEEE Trans.Appl.Supercond.,vol.14,no.1, pp.54–62,Mar.2004.[6]J.R.Quesada and J. F.Charpentier,“Finite difference study ofunconventional structures of permanent magnet linear machines for elec-tromagnetic aircraft launch system,”IEEE Trans.Magn.,vol.41,no.1, pp.478–483,Jan.2005.[7]M.Mirzaei and S.E.Abdollahi,“Design optimization of reluctancesynchronous linear machines for electromagnetic aircraft launch system,”IEEE Trans.Magn.,vol.45,no.1,pp.389–395,Jan.2009.[8]L.Parsa and L.Hao,“Interior permanent magnet motors with reducedtorque pulsation,”IEEE Trans.Ind.Electron.,vol.55,no.2,pp.602–609, Feb.2008.[9]Y.F.Shi,Z.Q.Zhu,and D.Howe,“Torque-speed characteristics ofinterior-magnet machines in brushless AC and DC modes,with particular reference to theirflux-weakening performance,”in Proc.IEEE Power Electron.Motion Control Conf.,2006,vol.3,pp.1–5.[10]S.M.Sue,K.L.Wu,J.S.Syu,and K.C.Lee,“A phase advancedcommutation scheme for IPM-BLDC motor drives,”in Proc.4th IEEE Conf.Ind.Electron.Appl.,2009,pp.2010–2013.Author photographs and biographies not available at the time of publication.。
