DC governor system outlined
DC governor is artificially or automatically change the direct current generator rotational speed to meet the For mechanical requirements. From the mechanical properties point of view, is that by changing the parameters or electric motors plus The voltage electric motors and other methods to change the mechanical properties, thus changing electric motors and mechanical properties Mechanical properties of the claimed identity work for the stability of operation of electric motors changed. There will be a link to the governor, usually through the middle enlarged link, calibration links, feedback links and other links to achieve protection. The rotational speed electric motors not given rotational speed automatic calibration and error system as a part of the governor control system. This governor system of rotational speed electric motors and power supply voltage fluctuations to be load fluctuations, the impact of external disturbances. Electric motors to the rotational speed automatic calibration and given rotational speed deviations from load voltage and power fluctuations, the impact of external disturbances to the rotational speed electric motors always consistent with the rotational speed of the governor to be known as loop system control system. This is due to a feedback loop control system link. Electrical transmission control systems usually by electric motors and control devices and information devices three parts. It can comply with the requirements of orders, the timely control of electric motors starting, braking, direction of the operation, location, speed and acceleration, work machinery and production processes to meet the requirements. With electrical, sensors, control devices, the flow of technology and change control theory, electrical transmission control systems have been greatly developed. Currently, the single aircraft used electrical capacity from a
few hundred kilowatts to tens of thousands of kilowatts, and change the flow of equipment from the rotary kiln electrical flow change Jingzhaguan stationary power units to change flow devices, and power off devices from static frequency conversion devices; Control module from the simulation of sensors, conditioners, will be integral to the development of devices to microprocessors chips at the core pay, DC generic digital volume control module; system control mode switching from manual operation of multi-parameter control to servo control; from simple mechanics to electrical transmission system expansion for location, speed, acceleration control of the important branches of the movement control. In short, modern electrical transmission control system has been developed into a new electrical transmission automation system.
DC governor advantage
Direct current generator is a good, braking performance, appropriate in a broader context, smooth mechanics, rolling mill, mine hoist, excavator, marine rigs, metal cutting machine tools, paper planes, such as the need for high-performance high-lift electricity fees Controllable areas received widespread application. In recent years, exchanges governor system developed rapidly, but direct current fees system in theory and practice are relatively mature, and from the feedback loop control perspective, it is the exchange control system based fees, so direct current governor system in the production and living and play a vital role. DC governor system, in particular the double-loop DC governor system is the most widely used industrial production process electrical transmission devices one. Widely used in steel rolling machines, metallurgy, printing, metal cutting machine tools, and many other areas of automatic control system. It is usually used three-phase full control of the bridge commutation circuits for power electric motors to control the
rotational speed of electric motors, the traditional control systems using analog components, such as transistors, various linear circuit operation, although to some extent to meet production requirements, but because of aging components and easy to use, are vulnerable in the outside interference effects, and complex circuits, overall poor control results by device performance, temperature and other factors, thereby causing the operation of the system characteristics also change accordingly, the operating system reliability and accuracy can not be guaranteed, even in accidents.
Double-loop system integral DC governor
Rotational speed, the current two-loop systems theory governor figure 2-1. By the plan shows that the system has two feedback circuit, a 2 loop circuit (so called double-loop). One is the current regulator Lt and current testing - the current part of a feedback link, and another by the speed regulator St rotational speed detection-a feedback link speed link. As part of the Central buildings currents, the currents that threatened to Central (boys Deputy Central), said speed link to cry (that the main part). In the circuit, a string St and Lt level connectivity from St to "drive" Lt, and then from "Lt" to the "control" trigger circuit. Chart speed regulator and current regulator are proportional plus integral (PI) regulator, the import and export of a limited Deputy currents are located. Rotational speed link called current rapid change in response to rotational speed, and currents are required to maintain current Central unchanged. This performance will be detrimental to current changes in response to rotational speed, the better to calm character soften Momentum. But as part of a dedicated rotational speed, current role only a part of a rotational speed of internal disturbances. Central, not the leading role. As a part of the rotational speed link enlarged multiple large enough, the last still relying on the scoring St. Eliminate rotational speed deviations.
Double-loop mechanical governor system features As for St Pi regulator, the system was not very bad, repeatable error small, the general said, mostly To meet production requirements. Its mechanical properties similar to a horizontal line, as shown in figure 2-2a. When electric motors serious overload, and when I>I, the current regulator would export fairing V oltage significantly reduced, which limits the current continued to grow, on the other hand will rotational speed rapidly in a very steep the droop characteristics figure 2-2b.
DC mechanics of the digital system
With microelectronic technology, microprocessors and computer software development for the control of the governor through a variety of functions in almost all microprocessors, the use of software to achieve. From the past to control the simulation modelling - controlled digital mixed development, the final realization of the entire digital. In digital systems, with the exception of the governor of conventional functions, but also a failure warning, dia gnosis and shows, and other functions, and digital systems usually have strong communication capabilities, through matching appropriate communications interface templates can easily achieve the main station (as mentioned level Plc or computer system) and from stations (single handed, DC transmission control devices), the number of digital communications, multi-aircraft formation automated classification system. For easy debugging, digital systems software, the general design of a regulator parameters optimized automation, optimization through a process to achieve an excellent and the automatic identification system dynamics parameters, and the achievement of identity, such as direct current generator magnetization curve automatic test
helps to shorten the debugging time and improve control performance. Some foreign companies have a range of electrical adjustment system with simulation corresponds to the all-digital, DC mechanics device products for the selection and development of new governor almost entirely digital system. And simulation systems similar, all-digital system developed for the compact style and mechanics of modular two broad categories. However, all-digital simulation of a governor or governor system incomparable advantages of the system, more advanced technology, easy to operate. Governor system and the digital system simulation governor compared technical performance following advantages : 1) high-precision attitude toward long-term maintenance. 2) good dynamic performance, dynamic parameters for the adjustment, given the rich software to achieve various adaptive and composite control. 3) governor a wide 4) Small voltage fluctuations 5) parameters of the software, no drift impact 6) the number of components used less difficult lapse 7) a high degree of value to quantify, and repeat rate good condition 8) coupled noise amplifier and a small class, small electromagnetic interference 9) the operation of flexible debugging convenient and easy to design and modify the design 10) the high degree of common standards and, in addition to the CPU module, only several additional modules Achievable, including parameters, multiple loop control techniques 11) scope of application can be achieved easily achieved with various gear shift control and communications systems Plc 12) conventional Jingzhaguan DC mechanics available software system to replace a large number of hardware, thus simplifying system architecture and reducing the electronic components Xuhan, access to undesirable substances such as lead and some failures, and maintenance convenience
DC governor system and the current development
Nearly 30 years ago, for the following reasons, and promoted the rapid development of power control systems exposed, one is to control the development of theory, a best control, the smart control self control, intelligence control. Corresponding control system is also exposed the practice gradually taking shape. The second is the development of electronic devices, control systems composition fees brought significant changes. Changes in the past used rotary flow units (electric motors to exchange direct current generator) for the smooth direct current generator mechanics, and the DC motors used to exciter also enlarged the magnetic power, magnetron control; By the 1960s, there have been Jingzhaguan the fairing, not only economically, and improved reliability, and also showed a great deal of technical superiority. Integrated operations, and many other electronic amplifier modules have been promoted control structure changes. Third, the 1980s computer technology and communications technology development, and created a new dynamic control system consists age eight Chanpianji -32 spaces and the application of control systems have appeared, making it simpler structure, function stronger, higher reliability. With the development of computer technology, both production and living among people of digital information increasing dependence. If the computer is the brain, the network is nervous, then the electrical drivetrain system is the skeleton and muscles. Between them is the perfect combination of modern industrial development. For DC governor system closely integrated with information systems, but also to improve its own performance DC governor system, the need for direct current governor of the entire digital control system. Shanpianji in DC has been widely governor system applications. For example, by Intel Corporation in 1983 to develop production MCS-96 series is currently one of the series of performance higher Shanpianji
apply to high-speed, high-precision industrial control. Its high-grade type : 8 x 196KB, 8 x 196KC, 8 x 196MC, in a part of the exchange governor system applications more. The continuous development of direct current machine control theory, control strategy and control algorithms also increasingly complex. Expand Cullman recovery, etc., state observation devices, adaptive control, artificial neural networks, etc. are applied to a variety of direct current machine or direct torque control, vector control. Therefore, the DSP chip in the high-performance digital communication systems governor found themselves in the display arena. MCS320F240 companies such as TI DSP chip, with its higher performance as a system-wide digital DC mechanics preferred. TI recently introduced MCS320F240X series products companies will lower prices to Danpianji level. In direct current governor of the entire digital process, the various bus also plays a very important role. STD bus, industrial PC bus, the bus and the can bus, in exchange automation applications governor system has played an important role. Although DC mechanics developed very quickly, but the whole digital DC reversible system will in the next governor will get a large number of application equipment.
Outlook
From the traditional system, although in recent years the rapid exchange of electrical mechanics technology development in many areas is direct current machine mechanics technology expansion in DC mechanics research and manufacturing process, the design and assembly of hardware accounted for a large proportion. Manufacture and the manufacture of electrical devices require a large number of mechanics and skilled workers, a certain quality of personnel requirements. Foreign related industries relatively high labour costs in the last decade, manufacturing DC governor may transfer to developing countries. In the case of China, this is also an opportunity, if we seize this
opportunity, take advantage of their favorable market conditions, it is possible to form a direct current governor system in our manufacturing center for China's industry to a new level. It must be developed in high-tech areas will not easily give up, they paid great attention to the core technology and software protection and security and, to that end, we must increase research and development in the field of intensity. Switch to
Introduction to DC Machines
DC machines are characterized by their vcrsatility．By means of various combinanons of shunt，serie5,and separately excited field windings they can be designed to display a wide variety of volt—ampcre or speedtorque characlersics for both dynamic and stcady—state operation．Because of the ease with which they can be contro11ed，systems of DC machines are often used in applications requiring a wide range of motor speeds or precise contro of motor output.
The essential features of a DC machine are shown schematically．The stator has salient poles and is excited by one of more field coils．The air-gap flux distribution created by the field winding is symmetrical about the centerline ofthe field Poles．This axis called the field axis of direct axis．As we know,the AC voltage generated in each rotating armtue coiI is converled to DC in the external armature terminals by means of a rotating commutator and stationonary brushes to which the armature leads are connected．The commutingor—brush combination forms a mechanical rectifier ，resulting in a DC armature voltage as wellas an armature m．m．f.wave which is fixed in space．The brushes are located so that commutation occurs when the coil sides are in the neutral zone,midway between the field poles．The axis of the armature m．m．L wave then is 90 electrical degrees from the axis of the field poles，i．e，in the quadrature
axis ．In lhe schematic representation the brushes are shown in quadrature axis because this is the position of the coils to which they are connected ．The armature m ．m ．f ．wave then is along the brush axis as shown ．(The geomctricaI position of the brushes in an actual machine is approximately 90 electical degrees from their position in the schematic diagram because of the shape of the end conncdions to the commutator ．)
The magnetic torque and the speed voltage appearing at the brushes are independent of the spatial waveform of the flux distributions; for convcenience we shall continue to assume a sinusoidal flux —density wave in the air gap ．The torque can then be found from the magnetic field viewpoint.
The torque can be expressed in terms 0f the interaction of the direct —axis air —gap flux per pole d ? and the space —fundamental
component 1a F of the armature m ．m ．f ．wave ．With the brushes in the
quadrature axis the angle between these fields is 90 elcctrical de8rees ， and its sine equals unity ．For a P pole machine ：
2
1()22d a P
T F π
?= in which the minus sign gas been dropped because the positve difection of the torque can irection of the torque can bedetermined from Physical reasoning ．The space fundamental 1a F of thc sawtooth arma —ture
m ．m ．fwave 28
πtimes its peak ．Substitution in above equation then gives
2a
d a a d a P C T i K i m ??π=-
where a i =currcnt in external armature circuit ；
Ca ＝total number of conductors in armature winding;
m ＝number of parallel paths through winding ；
and 2a a P C K m π= is a constant fixed by the design of the winding.
The rectified voltage generated in the armatufe has already been disscussed before for an elementary single —coil armature. The effect of distributing the winding in several slots is shown in figure ，in which each of the recufied sine waves is the voltage generrated in one of the coils ，commutaion taking place at the moment when the coil sides are in the neutral zone ．The generated voltage as observed from the brushes shown by the rippling line labeled in figure ．With a dozen or so commutator segments per pole ，The ripple becomes very small and the average generated voltage observed from the brushes equals the sum of the average values of the rectified coil voltages ．The rectified voltage ea between brushes ，known also as the speed voltage,is
2a a d m a d m
P C e W K W m ??π== where Ka is the design constant ．The rechfied voltage of a distributed winding has the same average value as that or a concentrated coil ．The differcnce is that the ripple is greatly reduced.
From the abovc equations ，with a11 variable expressed in SI units ：
a a m e i Tw =
This equation simply says that the instantaneous electrlc power associated wKh the speed voltage equals the instantaneous mechanical power associated with the magnetic torque ，the direction of power flow being determlned by whether the machine is acting as a motor or generator.
The direct —axis air —gap flux is produced by the combined m ．m ．f ． f f N i ∑of thc field windings ，thc flux —m ．m ．f ． charactcristic
being the magnetization curve for the panlcular iron geonletry of the machine ．In the magnetization curve,it is assumed that the armature
m ．m ．f ．wave is perpendicular to the field axis ．It will be necessary to reexamine this assumption later in this chapter ，where the effccts of saturation are investigated more thoroughly . Because the armature e ．m ．f ． is proportional to flux times speed ，it is usually more convenicnt to express the magnetization curve in terms of the armature e ．m ．f ． 0a e at constant speed 0m ω.The voltage a e for a given flux at any other speed wn
is proportional to the speed i ．e ．
00m a a m e e ωω= Figure shows the magnetZation curve with only one field winding
exeited ．This curve can easily be obtained by test methods ，no knowledge of any design details being required ．
Over a fairly wide rage of exeitation the reluctance of the iron is negligible compared with that of the air gap ．In this region the flux is 1inearly propodional to the tota lm ．m ．f of the field windings ，the constant of proportionality being the derect-axis air-gap permeance.
The outstanding advantages of DC machines arise from the wide variety of operating characteriulcs which can be obtained by selection of the method of excitation of the field windings ．The field windings may be separately excited from an external DC source,or they may be self-excited;i ．e ．，the machine may supply its own excitation ．The method of execitation profoundly influences not only the steady-state characteristics,but also the dynamic behavior of the machine in control systems ．
The connection diagram of a separately excited genefator is given ．The required field currcent is a very small fraction of the rated armature current.
A small amount of power in the field circuit may contol a relatively large amount of Power in the armature circuit; i ．e.，the generator is a power amplifier. Separately excited generators are often used in feed back control
systems when control of the armature voltage over a wide range is required ． The field windings of self —excited generators may be supplied in three different ways ．The field may be connected in series with the armature,resulting in a series gencrator ．The field may be connected in shunt with the armature,resulting in a shunt gencrator ，or the field may be in two sections ，one of which is connected in series and the othcr in shunt with the armature,resulting in a compound generator. With self-excited generators residual magnetism must be present in the machine iron to get the self —excitation process started ．
In the typical steady-state volt-ampere characteristics ，constant —speed prime movers being as sumed.The relation between the steady-state generated e. m ．f ．Ea and the terminal voltage Vt is t a a a V E I R =-
where Ia is the armature cufrent output and Ra is the armature cifcuit resistance ．In a gen —erator ，Ea is larger than Vt; and the electromagnetic torque This a countcnorque opposing rotation ．and hence the voltage vary widely with load ．As a consequlnce ，series generators are not often used ．The voltage of shunt generators drops of somewhat with load ．Compound generators are normally connected so that the m ．m ．f ．of the series winding aids that of the
shunt winding ．The advantage is that through the action of the series winding the flux perpole can increase with load ，resulting in a voltage output which is nearIy usually,contains many turns of relatively small wire.the series winding,wound on the outside ，consists of a few turns of comparatively heavy conductor because it must carry the full armture cufrent of the machine ．The voltage of both shunt gnd compound generators can be controlled over reasonable Limits by means of rheostats in the shunt field ．＼；
Any of the methods of excitation used for generators can also be used for motors ．In the typical steady －state speed —torque characteristies ，it is assumed that the motor terminals are supplied from a constant —voltage source ．In a motor the relation between the e. m ．f. Ea generated in the armature and the terminal voltage Vt is
t a a a V E I R =+；
where Ia is now the armature current inPut.the generated e ．m ．f ．Ea is now smaller than the terminal voltage Vt ，the afmature current is in the opposite direction to that in a generator and the electromagnetic torque is in the direction to sustain of the armature ．
In shunt and separately excited motors the field flux is nearly constant ．Conscequently ，incrsead torque must be accompanied by a very nearly proportionincrease in armature current and hence by a small decrease in couter e ．m ．f ． to allow this increased current through the smallarmature re5istance ．5incl counter e ．m ．f ． is determined by flux and speed ，the speed must drop slightly. Like the squirrel —cage induction motor ，the shunt motor is substantially a constant —speed motor having about 5 Percent drop in speed from no load to full load ．Starting torque and maximum torque are limtted by the armature current that can be commutated successfully.
An outstanding advantage of the shunt motor is ease of speed contol ．With a rheostat in the shunt —field circuit ,the field current and flux per pole can be varied at will ，and varlation of flux causes the inverse variation of speed to maintain counter e ．m ．f ．approximately equal to the impressed terminal voltage ．A maximum speed range of about 4 to 5 can be obtained by this method ，the limitation being commutating condtions ．By variation of the impressed armature voltage ，very wide speed ranges can be obtained ．
In the series motor，increase in load is accompanied by incrlase in the armature current and m．m．f．and the stator field flux(provided the iron is not completely saturated)．Because flux increases with load，speed must drop in order to maintain the balance belween impressed voltage and counter e. m．f．; more over，the increase in armature currcnt caused by increas torque is smaller than in the shunt motor bccause of the increased flux．The series motor is therefore a varying -peed motor with a markedly drooPing speed—load characteristic．For applications requiring heavy torque overloads，this characteritic is particu1arly advantageous because the corresponding power overloads are held to more reasonable values by the associated speed drops．V ery favoralle starting characteristics also resuIt from the increase in fIux with increased armature current．
In the compound motor the series field may be connected either cumulatively，so that its m．m．f．adds to that of the shunt field，or differentially so that it oppose6d．The differencial connection is very rarely used．A cumulatively compounded motor has speed一load characteristic intermediate between those of a shunt and a series motor，the drop of speed with load depending on the relative number of ampere—turns in the shunt and sefies fields．it does not have the disadvantage of very high light—load speed associated with a series motor,but it retains to a considerable degree the advantages of series excitation．
The application advantages of DC machines lie in the vafiety of performance characteristics offered by the possibilities 0f shunt,series，and compound excitaion . Some of these characteristics have been touched upon briefly in this article．Still greater possibilities exist if additional sets of brushes are added so that other voltages can be obtained from the commutotor．Thus the versatility of DC machine systems and their adaptability
to control，both manual and automatic，are their outsanding features．
直流调速系统概述
直流调速是指人为地或自动地改变直流电动机的转速，以满足工作机械的要求。从机械特性上看，就是通过改变电动机的参数或外加工电压等方法来改变电动机的机械特性，从而改变电动机机械特性和工作特性机械特性的交点，使电动机的稳定运转速度发生变化。调速通常通过给定环节，中间放大环节，校正环节，反馈环节和保护环节等来实现。电动机的转速不能自动校正与给定转速的偏差的调速系统称为开环控制系统。这种调速系统的电动机的转速要受到负载波动及电源电压波动等外界扰动的影响。电动机的转速能自动的校正与给定转速的偏差，不受负载及电网电压波动等外界扰动的影响，使电动机的转速始终与给定转速保持一致的调速系统称为闭环控制系统。这是由于闭环控制系统具有反馈环节。电气传动控制系统通常由电动机、控制装置和信息装置三部分组成。它能按照规定的指令，及时的控制电动机的启动、制动、运转方向、位置、速度和加速度等，以满足工作机械及生产过程的要求。随着电机、传感器、控制器件、变流技术和控制理论的发展，电气传动控制系统也得到了很大的发展。目前，所用电机的单机容量从几百瓦发展到数万千瓦，变流设备从旋转式电机变流机组发展到大功率晶闸管静止变流装置，中小功率自关断器件静止变频装置；控制单元从模拟量触发器、调节器、给定积分器发展到以微处理器芯片为核心的交、直流通用的数字量控制模块；系统的控制方式从手动操作的开关控制发展到闭环多参量控制；电气传动以从单纯的调速系统扩展为实现位置、速度、加速度控制的运动控制中的重要分支。总之，现代电气传动控制系统业已发展成为全新的电气传动自动化系统。
直流调速的优点
直流电动机具有良好的起、制动性能，宜于在广泛范围内平滑调速，在轧钢机、矿井卷扬机、挖掘机、海洋钻机、金属切削机床、造纸机、高
层电梯等需要高性能可控电力拖动的领域中得到了广泛的应用。近年来，交流调速系统发展很快，然而直流拖动系统无论在理论上和实践上都比较成熟，并且从反馈闭环控制的角度来看，它又是交流拖动控制系统的基础，所以直流调速系统在生产生活中有着举足轻重的作用。直流调速系统，特别是双闭环直流调速系统是工业生产过程中应用最广的电气传动装置之一。广泛地应用于轧钢机、冶金、印刷、金属切削机床等许多领域的自动控制系统中。它通常采用三相全控桥式整流电路对电动机进行供电，从而控制电动机的转速，传统的控制系统采用模拟元件，如晶体管、各种线性运算电路等，虽在一定程度上满足了生产要求，但是因为元件容易老化和在使用中易受外界干扰影响，并且线路复杂、通用性差，控制效果受到器件性能、温度等因素的影响，从而致使系统的运行特性也随之变化，故系统的运行可靠性及准确性得不到保证，甚至出现事故。
双闭环直流调速系统的组成
转速、电流双闭环调速系统原理如图2-1。由图可见，该系统有两个反馈回路，构成两个闭环回路，（故称双闭环）。其中一个是由电流调节器LT 和电流检测—反馈环节构成的电流环，另一个是由速度调节器ST 转速检测—反馈环节构成的速度环。由于速度环包围电流环，因此称电流环为内环，（又称副环），称速度环为外环（又有称主环）。在电路中，ST 和LT 实行串级联接，即由ST 去“驱动”LT，再由“LT”去“控制”触发电路。图中速度调节器和电流调节器均为比例加积分（ＰＩ）调节器，其输入和输出均设有限副电流。转速环要求电流迅速响应转速的变化而变化，而电流环则要求维持电流不变。这种性能会不利于电流对转速变化的响应，有使静特性变软的趋势。但由于转速环是外环，电流环的作用只相当转速环内部一种扰动而已，不起主导作用。只要转速环的开环放大倍数足够大，最后仍能靠ST 的积分作用。消除转速偏差。
双闭环调速系统的机械特性
由于ST 为PI 调节器，系统为无静差，稳态误差小，一般讲来，大多能满足生产上的要求。其机械特性近似为一水平线，如图2—2a 所示。当电动机发生严重过载，并当I＞I 时，电流调节器将使整流装置输出
电压明显降低，这一方面限制了电流继续增长，另一方面将使转速迅速下降，出现了很陡的下垂特性，见图2—2b 段。
直流调速系统的数字化
随着微电子技术、微处理机以及计算机软件的发展，使调速控制的各种功能几乎均可通过微处理机，借助软件来实现。即从过去的模拟控制向模拟-数字混合控制发展，最后实现全数字化。在数字化系统中，除具有常规的调速功能外，还具有故障报警、诊断及显示等功能，同时，数字系统通常具有较强的通信能力，通过选配适当的通信接口模板，可方便地实现主站（如上一级PLC 或计算机系统）和从站（单机交、直流传动控制装置）间的数字通信，组成分级多机的自动化系统。为易于调试，数字系统的软件，一般设计有调节器参数的自动化优化，通过启动优化程序，实现自动寻优和确定系统的动态参数，以及实现如直流电动机磁化特性曲线的自动测试等，有利于缩短调试时间和提高控制性能。国外一些电气公司都有成系列的与模拟调整系统相对应的全数字交、直流调速装置产品可供选用，新开发的调速系统几乎全是数字式的。与模拟系统类似，全数字调速系统已发展成为紧凑式和模块式两大类。但全数字调速系统还是有模拟调速系统无法比拟的优点，技术更先进，操作方便。数字调速系统与模拟调速系统相对比，技术性能有如下优点：
（1）态精度高且能长期保持。
（2）动态性能好，动态参数调整方便，借助于丰富的软件，易于实现各类自适应和复合控制。
（3）调速范围宽
（4）电压波动小
（5）参数实现软件化，无漂移影响
（6）所用元件数量少，不易失效
（7）设定值量化程度高，且状态重复率好
（8）放大器和级间耦合噪声很小，电磁干扰小
（9）调试即投产灵活方便，易于设计和修改设计
（10）标准及通用化程度高，除主CPU 模块外，仅数种附加模块可实现，包括工艺参数在内的多元闭环控制
（11）适用范围广，可实现各类变速控制及易于实现与PLC 系统通信（12）常规的晶闸管直流调速系统中大量硬件可用软件代替，从而简化系统结构，减少了电子元件虚焊、接触不良和漂移等引起的一些
故障，而且维修方便。
国内外直流调速系统发展现状
近30多年来，由于以下原因，推动了电力拖动控制系统的迅速发展，第一是控制理论的发展，出现了最优控制，智能控制，自适应控制，智能控制等。相应的拖动控制系统也在实践中逐步形成。其二是电子器件的发展，带来了拖动控制系统组成结构的重大变化。过去采用旋转变流机组（交流电动机带动直流电动机）来实现直流电动机的平滑调速，而直流发动机的励磁又采用交磁功率放大机，磁放大器进行控制；到了六十年代，出现了晶闸管整流装置，不仅在经济上和可靠性上有所提高，而且在技术上也显示了很大的优越性。别外集成运算放大器和众多的电子模块的出现，不断促进了控制结构的变化。其三是八十年代计算机技术和通信技术的发展，开创了拖动控制系统蓬勃发展的新年代，8位-32位单片机的相继出现并应用于控制系统，使其结构更加简单，功能更强，可靠性更高。随着计算机技术的发展，无论是生产还是生活当中，人民对数字化信息的依赖程度越来越高。如果说计算机是大脑，网络是神经，那么电机传动系统就是骨骼和肌肉。它们之间的完美结合才是现代产业发展方向。为了使直流调速系统与信息系统紧密结合，同时也为了提高直流调速系统自身的性能，必须使直流调速系统实现全数字化控制。单片机已经在直流调速系统中得到了广泛地应用。例如由Intel公司1983年开发生产的MCS - 96系列是目前性能较高的单片机系列之一，适用于高速、高精度的工业控制。其高档型：8×196KB、8×196KC、8×196MC等在通用开环交流调速系统中的应用较多。
一、材质中英文对照表 1.摇粒绒：Polar Fleece 2.珊瑚绒：coral fleece / soft terry 3.羊羔绒：Berber fleece / polyester faux sherpa 4.短毛绒：short plush 5.长毛绒：long plush 6.毛绒：fur 7.天鹅绒：velvet 8.拖把绒：cord velour 9.PV绒：PV plush 10.毛巾布：terry 11.灯芯绒：corduroy 12.双色毛绒：two-tone faux fur 13.毛线针织：knitting 14.麂皮绒：microfiber/microsuede 15.格利特：glitter 16.亮片：sequin 17.佳积布：nylex 18.尼龙布：nylon 19.汗衫布：jersey 20.沙丁布：satin 21.网布：mesh 22.帆布：canvas 23.斜纹棉布: cotton twill 24.PU 25.镜面PU：patent PU 26.平纹PU：smooth PU 27.EV A 28.点塑底：fabric with dot / skid free dot/non skid dot 29.TPR 30.PVC注塑：PVC injected 二、鞋子装饰物（ornament） 1.松紧带：elastic gore 2.魔术贴：velcro 3.电绣：embroidery 4.蝴蝶结：bow 5.爱心：heart 6.鞋带：lace 7.鞋眼：eyelet 8.人造钻石：rhinestone 9.搭带：strap 10.拉环：loop 11.毛球：POM 12.织唛标：Woven label 13.烫印：heat seal 14.贴片：patch 15.拉链：zipper 三、颜色 1. 豹纹：leopard/ cheetah 2. 斑马纹：zebra 3. 虎纹：tiger 4. 米黄色：beige 5. 桃红色：fuschia 6. 淡紫色：lilac 7. 海军蓝：Navy 8. 咖啡色：Brown 9. 迷彩：camo 10. 湖水蓝：blue atoll/ turq / lake blue 11. 格子：plaid / gingham 12. 紫色：purple 13. 灰色：grey/gray 14. 条纹：strip 15. 银光粉：neon pink 16. 金属色：metallic 17. 栗色：chestnut AI Artwork 设计稿
附录 科技译文： Numerical Control Numerical Control(NC) is a method of controlling the movements of machineComponents by directly inserting coded instructions in the form of numerical data(numbers and data ) into the system.The system automatically interprets these data and converts to output signals. These signals ,in turn control various machine components ,such as turning spindles on and off ,changing tools,moving the work piece or the tools along specific paths,and turning cutting fluits on and off. In order to appreciate the importer of numerical control of machines ,let’s briefly review how a process such as machining has been carried out traditionally .After studying the working drawing of a part, the operator sets up the appropriate process parameters(such as cutting speed ,feed,depth of cut,cutting fluid ,and so on),determines the sequence of operations to be performed,clamps the work piece in a workholding device such as chuck or collet ,and proceeds to make the part .Depending on part shape and the dimensional accuracy specified ,this approach usually requires skilled
外文出处： 《Exploiting Software How to Break Code》By Greg Hoglund, Gary McGraw Publisher : Addison Wesley Pub Date : February 17, 2004 ISBN : 0-201-78695-8 译文标题： JDBC接口技术 译文： JDBC是一种可用于执行SQL语句的JavaAPI（ApplicationProgrammingInterface应用程序设计接口）。它由一些Java语言编写的类和界面组成。JDBC为数据库应用开发人员、数据库前台工具开发人员提供了一种标准的应用程序设计接口，使开发人员可以用纯Java语言编写完整的数据库应用程序。 一、ODBC到JDBC的发展历程 说到JDBC，很容易让人联想到另一个十分熟悉的字眼“ODBC”。它们之间有没有联系呢？如果有，那么它们之间又是怎样的关系呢？ ODBC是OpenDatabaseConnectivity的英文简写。它是一种用来在相关或不相关的数据库管理系统（DBMS）中存取数据的，用C语言实现的，标准应用程序数据接口。通过ODBCAPI，应用程序可以存取保存在多种不同数据库管理系统（DBMS）中的数据，而不论每个DBMS使用了何种数据存储格式和编程接口。 1．ODBC的结构模型 ODBC的结构包括四个主要部分：应用程序接口、驱动器管理器、数据库驱动器和数据源。应用程序接口：屏蔽不同的ODBC数据库驱动器之间函数调用的差别，为用户提供统一的SQL编程接口。 驱动器管理器：为应用程序装载数据库驱动器。 数据库驱动器：实现ODBC的函数调用，提供对特定数据源的SQL请求。如果需要，数据库驱动器将修改应用程序的请求，使得请求符合相关的DBMS所支持的文法。 数据源：由用户想要存取的数据以及与它相关的操作系统、DBMS和用于访问DBMS的网络平台组成。 虽然ODBC驱动器管理器的主要目的是加载数据库驱动器，以便ODBC函数调用，但是数据库驱动器本身也执行ODBC函数调用，并与数据库相互配合。因此当应用系统发出调用与数据源进行连接时，数据库驱动器能管理通信协议。当建立起与数据源的连接时，数据库驱动器便能处理应用系统向DBMS发出的请求，对分析或发自数据源的设计进行必要的翻译，并将结果返回给应用系统。 2．JDBC的诞生 自从Java语言于1995年5月正式公布以来，Java风靡全球。出现大量的用java语言编写的程序，其中也包括数据库应用程序。由于没有一个Java语言的API，编程人员不得不在Java程序中加入C语言的ODBC函数调用。这就使很多Java的优秀特性无法充分发挥，比如平台无关性、面向对象特性等。随着越来越多的编程人员对Java语言的日益喜爱，越来越多的公司在Java程序开发上投入的精力日益增加，对java语言接口的访问数据库的API 的要求越来越强烈。也由于ODBC的有其不足之处，比如它并不容易使用，没有面向对象的特性等等，SUN公司决定开发一Java语言为接口的数据库应用程序开发接口。在JDK1．x 版本中，JDBC只是一个可选部件，到了JDK1．1公布时，SQL类包（也就是JDBCAPI）
外文翻译 专业机械设计制造及其自动化学生姓名刘链柱 班级机制111 学号1110101102 指导教师葛友华
外文资料名称： Design and performance evaluation of vacuum cleaners using cyclone technology 外文资料出处：Korean J. Chem. Eng., 23(6), (用外文写) 925-930 (2006) 附件： 1.外文资料翻译译文 2.外文原文
应用旋风技术真空吸尘器的设计和性能介绍 吉尔泰金，洪城铱昌，宰瑾李， 刘链柱译 摘要：旋风型分离器技术用于真空吸尘器 - 轴向进流旋风和切向进气道流旋风有效地收集粉尘和降低压力降已被实验研究。优化设计等因素作为集尘效率，压降，并切成尺寸被粒度对应于分级收集的50％的效率进行了研究。颗粒切成大小降低入口面积，体直径，减小涡取景器直径的旋风。切向入口的双流量气旋具有良好的性能考虑的350毫米汞柱的低压降和为1.5μm的质量中位直径在1米3的流量的截止尺寸。一使用切向入口的双流量旋风吸尘器示出了势是一种有效的方法，用于收集在家庭中产生的粉尘。 摘要及关键词：吸尘器; 粉尘; 旋风分离器 引言 我们这个时代的很大一部分都花在了房子，工作场所，或其他建筑，因此，室内空间应该是既舒适情绪和卫生。但室内空气中含有超过室外空气因气密性的二次污染物，毒物，食品气味。这是通过使用产生在建筑中的新材料和设备。真空吸尘器为代表的家电去除有害物质从地板到地毯所用的商用真空吸尘器房子由纸过滤，预过滤器和排气过滤器通过洁净的空气排放到大气中。虽然真空吸尘器是方便在使用中，吸入压力下降说唱空转成比例地清洗的时间，以及纸过滤器也应定期更换，由于压力下降，气味和细菌通过纸过滤器内的残留粉尘。 图1示出了大气气溶胶的粒度分布通常是双峰形，在粗颗粒（>2.0微米）模式为主要的外部来源，如风吹尘，海盐喷雾，火山，从工厂直接排放和车辆废气排放，以及那些在细颗粒模式包括燃烧或光化学反应。表1显示模式，典型的大气航空的直径和质量浓度溶胶被许多研究者测量。精细模式在0.18?0.36 在5.7到25微米尺寸范围微米尺寸范围。质量浓度为2?205微克，可直接在大气气溶胶和 3.85至36.3μg/m3柴油气溶胶。
常用单位的中英文对照翻译 单位 Unit. 单位制 system of units 米 meter (m) 毫米 millimeter (mm) 英尺 foot (ft) 英寸 inch (in) 弧度 radian (rad) 度degree (°) 摄氏 Celsius. (C) 华氏 Fahrenheit (F) 磅／平方英寸 pounds per square inch (psi) 百万帕斯卡 million pascal (MPa) 巴 bar 千克（公斤） kilogram (kg) 克 gram (g) 牛顿 newton (N) 吨 ton (t) 千磅 kilopound (kip) 平方米 square meter (m 2) 方毫米 square millimeter (mm2 ) 立方米 cubic meter (m3 ) 升 liter; litre (L) 转／分 revolutions per minute (rpm) 百万分之一 parts per million (ppm) 焦（耳） Joule (J) 千瓦 kilowatt (kW) 伏（特） volt (V) 安（培） ampere (A) 欧（姆）ohm (Ω) （小）时 hour (h) 分 minute (min) 秒 second (s)
管道组成件专业英语(中英文对照) 1 管道组成件 Piping component 1.1 管子 Pipe 管子(按照配管标准规格制造的) pipe 管子(不按配管标准规格制造的其他用管) tube 钢管 steel pipe 铸铁管 cast iron pipe 衬里管 lined pipe 复合管 clad pipe 碳钢管 carbon steel pipe 合金钢管 alloy steel pipe 不锈钢 stainless steel pipe 奥氏体不锈钢管 austenitic stainless steel pipe 铁合金钢管 ferritic alloy steel pipe 轧制钢管 wrought-steel pipe 锻铁管 wrought-iron pipe 无缝钢管 seamless (SMLS) steel pipe 焊接钢管 welded steel pipe 电阻焊钢管 electric-resistance welded steel pipe 电熔（弧）焊钢板卷管 electric-fusion (arc)-welded steel-plate pipe 螺旋焊接钢管 spiral welded steel pipe 镀锌钢管 galvanized steel pipe 热轧无缝钢管 hot-rolling seamless pipe 冷拔无缝钢管 cold-drawing seamless pipe 水煤气钢管 water-gas steel pipe 塑料管 plastic pipe 玻璃管 glass tube 橡胶管 rubber tube 直管 run pipe; straight pipe 1.2 管件 Fitting 弯头 elbow 异径弯头 reducing elbow 带支座弯头 base elbow k半径弯头 long radius elbow 短半径弯头 short radius elbow
中文姓氏的英文翻译对照表 中文姓氏的英文翻译对照表.txt我们用一只眼睛看见现实的灰墙，却用另一只眼睛勇敢飞翔，接近梦想。男人喜欢听话的女人，但男人若是喜欢一个女人，就会不知不觉听她的话。在互联网上混的都时兴起个英文名字，一是方便注册用户名，二是有个好英文名容易显得自己比较Cool。但是起英文名时，中文姓氏还是要保留的，并且姓氏一般都有专门的英文翻译，比如“刘德华”的英文名是Andy，刘姓对应的英文翻译是Lau，所以全称便是“Andy Lau”。当然了，我们一般人直接用汉语拼音作为姓氏的英文翻译也可以，但在比较正式的场合下，最好还是用相应的英文翻译。 姓氏的英文翻译跟汉语拼音是有一些细微差别的，这主要由中西方人发音的不同特点来决定的。比如，从声母上来看，D开头的姓，英文翻译对应的是T，G对应的是K，X对应的是HS，Z、J 一般对应的是C，韵母也会有一些细微差别。详细的，请参考如下中文姓氏的英文翻译对照表，正在起英文名的朋友可以看看。 A: 艾--Ai 安--Ann/An 敖--Ao B: 巴--Pa 白--Pai 包/鲍--Paul/Pao 班--Pan 贝--Pei 毕--Pih 卞--Bein 卜/薄--Po/Pu 步--Poo 百里--Pai-li C: 蔡/柴--Tsia/Choi/Tsai 曹/晁/巢--Chao/Chiao/Tsao 岑--Cheng 崔--Tsui 查--Cha
常--Chiong 车--Che 陈--Chen/Chan/Tan 成/程--Cheng 池--Chi 褚/楚--Chu 淳于--Chwen-yu D: 戴/代--Day/Tai 邓--Teng/Tang/Tung 狄--Ti 刁--Tiao 丁--Ting/T 董/东--Tung/Tong 窦--Tou 杜--To/Du/Too 段--Tuan 端木--Duan-mu 东郭--Tung-kuo 东方--Tung-fang E: F: 范/樊--Fan/Van 房/方--Fang 费--Fei 冯/凤/封--Fung/Fong 符/傅--Fu/Foo G: 盖--Kai 甘--Kan 高/郜--Gao/Kao 葛--Keh 耿--Keng 弓/宫/龚/恭--Kung 勾--Kou 古/谷/顾--Ku/Koo 桂--Kwei
附录 INTEGRATION OF MACHINERY （From ELECTRICAL AND MACHINERY INDUSTRY）ABSTRACT Machinery was the modern science and technology development inevitable result, this article has summarized the integration of machinery technology basic outline and the development background .Summarized the domestic and foreign integration of machinery technology present situation, has analyzed the integration of machinery technology trend of development. Key word：integration of machinery ，technology，present situation ，product t，echnique of manufacture ，trend of development 0. Introduction modern science and technology unceasing development, impelled different discipline intersecting enormously with the seepage, has caused the project domain technological revolution and the transformation .In mechanical engineering domain, because the microelectronic technology and the computer technology rapid development and forms to the mechanical industry seepage the integration of machinery, caused the mechanical industry the technical structure, the product organization, the function and the constitution, the production method and the management system has had the huge change, caused the industrial production to enter into “the integration of machinery” by “the machinery electrification” for the characteristic development phase. 1. Integration of machinery outline integration of machinery is refers in the organization new owner function, the power function, in the information processing function and the control function introduces the electronic technology, unifies the system the mechanism and the computerization design and the software which constitutes always to call. The integration of machinery development also has become one to have until now own system new discipline, not only develops along with the science and technology, but also entrusts with the new content .But its basic characteristic may summarize is: The integration of machinery is embarks from the system viewpoint, synthesis community technologies and so on utilization mechanical technology, microelectronic technology, automatic control technology,
使用高级分析法的钢框架创新设计 1．导言 在美国，钢结构设计方法包括允许应力设计法(ASD)，塑性设计法(PD)和荷载阻力系数设计法(LRFD)。在允许应力设计中，应力计算基于一阶弹性分析，而几何非线性影响则隐含在细部设计方程中。在塑性设计中，结构分析中使用的是一阶塑性铰分析。塑性设计使整个结构体系的弹性力重新分配。尽管几何非线性和逐步高产效应并不在塑性设计之中，但它们近似细部设计方程。在荷载和阻力系数设计中，含放大系数的一阶弹性分析或单纯的二阶弹性分析被用于几何非线性分析，而梁柱的极限强度隐藏在互动设计方程。所有三个设计方法需要独立进行检查，包括系数K计算。在下面，对荷载抗力系数设计法的特点进行了简要介绍。 结构系统内的内力及稳定性和它的构件是相关的，但目前美国钢结构协会（AISC）的荷载抗力系数规范把这种分开来处理的。在目前的实际应用中，结构体系和它构件的相互影响反映在有效长度这一因素上。这一点在社会科学研究技术备忘录第五录摘录中有描述。 尽管结构最大内力和构件最大内力是相互依存的（但不一定共存），应当承认，严格考虑这种相互依存关系，很多结构是不实际的。与此同时，众所周知当遇到复杂框架设计中试图在柱设计时自动弥补整个结构的不稳定（例如通过调整柱的有效长度）是很困难的。因此，社会科学研究委员会建议在实际设计中，这两方面应单独考虑单独构件的稳定性和结构的基础及结构整体稳定性。图28.1就是这种方法的间接分析和设计方法。
在目前的美国钢结构协会荷载抗力系数规范中，分析结构体系的方法是一阶弹性分析或二阶弹性分析。在使用一阶弹性分析时，考虑到二阶效果，一阶力矩都是由B1,B2系数放大。在规范中，所有细部都是从结构体系中独立出来，他们通过细部内力曲线和规范给出的那些隐含二阶效应，非弹性，残余应力和挠度的相互作用设计的。理论解答和实验性数据的拟合曲线得到了柱曲线和梁曲线，同时Kanchanalai发现的所谓“精确”塑性区解决方案的拟合曲线确定了梁柱相互作用方程。 为了证明单个细部内力对整个结构体系的影响，使用了有效长度系数，如图28.2所示。有效长度方法为框架结构提供了一个良好的设计。然而，有效长度方法的
1. The Dragon Boat Festival, also called the Duanwu Festival, is celebrated on the fifth day of the fifth month according to the Chinese calendar. For thousands of years, the festival has been marked by eating Tzung Tzu and racing dragon boats. The most important activities of this festival are the dragon boat races. Competing teams drive their colorful dragon boats forward to the rhythm（节奏,韵律） of beating drums. These exciting races were inspired by the villager's attempts to rescue Chu Yuan from the Mi Lo River. This tradition has remained unbroken for centuries. A very popular dish during the Dragon Boat festival is tzung tzu. This tasty dish consists of rice dumplings with meat, peanut, egg yolk（蛋黄）, or other fillings wrapped in bamboo leaves. The tradition of tzung tzu is meant to remind us of the village fishermen scattering rice across the water of the Mi Low River in order to appease the river dragons so that they would not devour Chu Yuan. 一，端午节 龙舟节也叫做端午节，它位于每年农历的五月初五，经过几千年的时间，划龙舟和吃粽子已经成为这个节日的标志。 端午节最重要的活动是龙舟竞赛，比赛的队伍在热烈的鼓声中划著他
1.Sales Agreement The agreement, (is) made in Beijing this eighth day of August 1993 by ABC Trading Co., Ltd., a Chinese Corporation having its registered office at Beijing, the People’ Repubic of China (hereinafter called “Seller”) and International Trading Co., Ltd., a New York Corporation having its registered office at New York, N.Y., U.S.A. (hereinafter called “Buyer”). 2.WITNESSETH WHEREAS, Seller is engaged in dealing of (product) and desires to sell (product)to Buyer, and WHEREAS, Buyer desires to purchase(product) from Sellers, Now, THEREFORE, it is agreed as follows: 3.Export Contract th This Contract is entered into this 5 day of August 1993 between ABC and Trading Co., Ltd. (hereinafter called “Seller”) who agrees to sell, and XYZ Trading Co., Ltd. (hereinafter called “Buyer”) who agrees to buy the following goods on the following terms and condition. 4.Non-Governmental Trading Agreement No. ＿＿ This Agreement was made on the＿day of＿ 19＿, BETWEEN ＿(hereinafter referred to as the Seller) as the one Side and ＿ (hereinafter referred to as the Buyer) as the one other Side. WHEREAS, the
本科毕业论文(设计) 外文翻译 学院：机电工程学院 专业：机械工程及自动化 姓名：高峰 指导教师：李延胜 2011年05 月10日 教育部办公厅 Failure Analysis，Dimensional Determination And
Analysis，Applications Of Cams INTRODUCTION It is absolutely essential that a design engineer know how and why parts fail so that reliable machines that require minimum maintenance can be designed．Sometimes a failure can be serious，such as when a tire blows out on an automobile traveling at high speed．On the other hand，a failure may be no more than a nuisance．An example is the loosening of the radiator hose in an automobile cooling system．The consequence of this latter failure is usually the loss of some radiator coolant，a condition that is readily detected and corrected．The type of load a part absorbs is just as significant as the magnitude．Generally speaking，dynamic loads with direction reversals cause greater difficulty than static loads，and therefore，fatigue strength must be considered．Another concern is whether the material is ductile or brittle．For example，brittle materials are considered to be unacceptable where fatigue is involved． Many people mistakingly interpret the word failure to mean the actual breakage of a part．However，a design engineer must consider a broader understanding of what appreciable deformation occurs．A ductile material，however will deform a large amount prior to rupture．Excessive deformation，without fracture，may cause a machine to fail because the deformed part interferes with a moving second part．Therefore，a part fails(even if it has not physically broken)whenever it no longer fulfills its required function．Sometimes failure may be due to abnormal friction or vibration between two mating parts．Failure also may be due to a phenomenon called creep，which is the plastic flow of a material under load at elevated temperatures．In addition，the actual shape of a part may be responsible for failure．For example，stress concentrations due to sudden changes in contour must be taken into account．Evaluation of stress considerations is especially important when there are dynamic loads with direction reversals and the material is not very ductile． In general，the design engineer must consider all possible modes of failure，which include the following． ——Stress ——Deformation ——Wear ——Corrosion ——Vibration ——Environmental damage ——Loosening of fastening devices
毕业设计（论文） 外文翻译 题目西安市水源工程中的 水电站设计 专业水利水电工程 班级 学生 指导教师 2016年
研究钢弧形闸门的动态稳定性 牛志国 河海大学水利水电工程学院，中国南京，邮编210098 nzg_197901@https://www.doczj.com/doc/c78819348.html,，niuzhiguo@https://www.doczj.com/doc/c78819348.html, 李同春 河海大学水利水电工程学院，中国南京，邮编210098 ltchhu@https://www.doczj.com/doc/c78819348.html, 摘要 由于钢弧形闸门的结构特征和弹力，调查对参数共振的弧形闸门的臂一直是研究领域的热点话题弧形弧形闸门的动力稳定性。在这个论文中，简化空间框架作为分析模型，根据弹性体薄壁结构的扰动方程和梁单元模型和薄壁结构的梁单元模型，动态不稳定区域的弧形闸门可以通过有限元的方法，应用有限元的方法计算动态不稳定性的主要区域的弧形弧形闸门工作。此外，结合物理和数值模型，对识别新方法的参数共振钢弧形闸门提出了调查，本文不仅是重要的改进弧形闸门的参数振动的计算方法，但也为进一步研究弧形弧形闸门结构的动态稳定性打下了坚实的基础。 简介 低举升力，没有门槽，好流型，和操作方便等优点，使钢弧形闸门已经广泛应用于水工建筑物。弧形闸门的结构特点是液压完全作用于弧形闸门，通过门叶和主大梁，所以弧形闸门臂是主要的组件确保弧形闸门安全操作。如果周期性轴向载荷作用于手臂，手臂的不稳定是在一定条件下可能发生。调查指出:在弧形闸门的20次事故中，除了极特殊的破坏情况下，弧形闸门的破坏的原因是弧形闸门臂的不稳定;此外，明显的动态作用下发生破坏。例如:张山闸，位于中国的江苏省，包括36个弧形闸门。当一个弧形闸门打开放水时，门被破坏了，而其他弧形闸门则关闭，受到静态静水压力仍然是一样的，很明显，一个动态的加载是造成的弧形闸门破坏一个主要因素。因此弧形闸门臂的动态不稳定是造成弧形闸门(特别是低水头的弧形闸门)破坏的主要原是毫无疑问。
美国学校提供的学位有很多种，依所学领域的不同，而有不同的学位。以下列出的是美国高等教育中较常见的学位: Ph.D.（Doctor of Philosophy）: 博士学位。而有些领域的博士课程会有不同的学位名称，如D.A.(Doctor of Arts)、Ed.D.(Doctor of Education) M.B.A.（Master of Business Administration）: 商学管理硕士。 M.A.（Master of Arts）硕士；B.A.（Bachelor of Arts）学士: 两者皆属于人文、艺术或社会科学的领域，如文学、教育、艺术、音乐。 M.S.（Master of Science）硕士；B.S.（Bachelor of Science）学士: 两者皆属于理工、科学的领域，如数学、物理、信息等。 Associate Degree（副学士学位）: 读完两年制小区大学或职业技术学校所得到的学位。 Dual Degree（双学位）: 是由两个不同学院分别授与，因此得到的是两个学位。 Joint Degree：为两个不同学院联合给予一个学位，如法律经济硕士。 major 主修 minor 辅修 大家要搜索自己的专业, 请按 ctrl + F 打开搜索窗口, 然后输入关键字查询 学士 Bachelor of Arts B.A. 文学士 Bachelor of Arts in Education B.A.Ed., B.A.E. 教育学文学士 Bachelor of Arts in Computer Science B.A.CS 计算机文学士 Bachelor of Arts in Music B.A.Mus,B.Mus 音乐艺术学士 Bachelor of Arts in Social Work B.A.S.W 社会工作学文学士 Bachelor of Engineering B.Eng., B.E 工学士 Bachelor of Engineering in Social Science B.Eng.Soc 社会工程学士 Bachelor of Engineering in Management B.Eng.Mgt 管理工程学士 Bachelor of Environmental Science/Studies B.E.Sc., B.E.S 环境科学学士 Bachelor of Science B.S 理学士 Bachelor of Science in Business B.S.B., B.S.Bus 商学理学士 Bachelor of Science in Business Administration B.S.B.A 工商管理学理学士 Bachelor of Science in Education B.S.Ed., B.S.E 教育学理学士 Bachelor of Science in Engineering B.S.Eng., B.S.E 工程学理学士 Bachelor of Science in Forestry B.S.cF 森林理学士 Bachelor of Science in Medicine B.S.Med 医学理学士 Bachelor of Science in Medical Technology B.S.M.T., B.S.Med.Tech 医技学理学士 Bachelor of Science in Nursing B.S.N., B.S.Nurs 护理学理学士 Bachelor of Science in Nutrition B.SN 营养学理学士 Bachelor of Science in Social Work B.S.S.W 社会工作学理学士 Bachelor of Science in Technology B.S.T 科技学理学士 Bachelor of Computer Science B.CS 计算机理学士 Bachelor of Computer Special Science B.CSS 计算机特殊理学士 Bachelor of Architecture B. Arch. 建筑学士 Bachelor of Administration B.Admin. 管理学士
胡壮麟语言学术语英汉对照翻译表 1. 语言的普遍特征： 任意性arbitrariness 双层结构duality 既由声音和意义结构 多产性productivity 移位性displacement:我们能用语言可以表达许多不在场的东西 文化传播性cultural transmission 2。语言的功能： 传达信息功能informative 人济功能：interpersonal 行事功能：Performative 表情功能：Emotive 寒暄功能：Phatic 娱乐功能recreatinal 元语言功能metalingual 3. 语言学linguistics：包括六个分支 语音学Phonetics 音位学phonology 形态学Morphology 句法学syntax 语义学semantics 语用学pragmatics 4. 现代结构主义语言学创始人：Ferdinand de saussure 提出语言学中最重要的概念对之一：语言与言语language and parole ，语言之语言系统的整体，言语则只待某个个体在实际语言使用环境中说出的具体话语 5. 语法创始人：Noam Chomsky 提出概念语言能力与语言运用competence and performance 1. Which of the following statements can be used to describe displacement. one of the unique properties of language: a. we can easily teach our children to learn a certain language b. we can use both 'shu' and 'tree' to describe the same thing. c. we can u se language to refer to something not present d. we can produce sentences that have never been heard befor e. 2.What is the most important function of language? a. interpersonal b. phatic c. informative d.metallingual 3.The function of the sentence "A nice day, isn't it ?"is __ a informative b. phatic c. directive d. performative