英文原文
1 Introduction
The screw compressor is one of the most common types of machine used to compress gases. Its construction is simple in that it essentially comprises only a pair of meshing rotors, with helical grooves machined in them, contained in a casing, which fits closely round them. The rotors and casing are separated by very small clearances. The rotors are driven by an external motor and mesh like gears in such a manner that, as they rotate, the space formed between them and the casing is reduced progressively. Thus, any gas trapped in this case is compressed. The geometry of such machines is complex and the flow of the gas being compressed within them occurs in three stages. Firstly, gas enters between the lobes, through an inlet port at one end of the casing during the start of rotation. As rotation continues, the space between the rotors no longer lines up with the inlet port and the gas is trapped and thus compressed. Finally, after further rotation, the opposite ends of the rotors pass a second port at the other end of the casing, through which the gas is discharged. The whole process is repeated between successive pairs of lobes to create a continuous but pulsating flow of gas from low to high pressure.
These machines are mainly used for the supply of compressed air in the building industry, the food, process and pharmaceutical industries and, where required, in the metallurgical industry and for pneumatic transport.
They are also used extensively for compression of refrigerants in refrigeration and air conditioning systems and of hydrocarbon gases in the chemical industry. Their relatively rapid acceptance over the past thirty years is due to their relatively high rotational speeds compared to other types of positive displacement machine, which makes them compact, their ability to maintain high efficiencies over a wide range of operating pressures and flow rates and their long service life and high reliability. Consequently, they constitute a substantial percentage of all positive displacement compressors now sold and currently in operation.
The main reasons for this success are the development of novel rotor profiles, which have drastically reduced internal leakage, and advanced machine tools, which can manufacture the most complex shapes to tolerances of the order of 3 micrometers at an acceptable cost. Rotor profile enhancement is still the most promising means of further improving screw compressors and rational procedures are now being developed both to replace earlier empirically derived shapes and also to vary the proportions of the selected profile to obtain the best result for the application for which the compressor is required. Despite their wide usage, due to the complexity of their internal geometry and the non-steady nature of the processes within them, up till recently, only approximate analytical methods have been available to predict their performance. Thus, although it is known that their elements are distorted both by the heavy loads imposed by pressure induced forces and through temperature changes within them, no methods were available to predict the magnitude of these distortions accurately, nor how they affect the overall performance of the machine. In addition, improved modelling of flow patterns within the machine can lead to better porting design. Also, more accurate determination of bearing loads and how they fluctuate enable better choices of bearings to be made. Finally, if rotor and casing distortion, as a result of temperature and pressure changes within the compressor, can be estimated reliably, machining procedures can be devised to minimise their adverse effects.
Screw machines operate on a variety of working fluids, which may be gases, dry vapour or multi-phase mixtures with phase changes taking place within the machine. They may involve oil flooding, or other fluids injected during the compression or expansion process, or be without any form of internal lubrication. Their geometry may vary depending on the number of lobes in each rotor, the basic rotor profile and the relative proportions of each rotor lobe segment. It follows that there is no universal configuration which would be the best for all applications. Hence, detailed thermodynamic analysis of the compression process and evaluation of the influence of the various design parameters on performance is more important to obtain the best results from these machines than from other types which could be used for the same application. A set of well defined criteria governed by an optimisation procedure is therefore a prerequisite for achieving the best design for each application. Such guidelines are also essential for the further improvement of existing screw machine designs and broadening their range of uses. Fleming et al., 1998 gives a good contemporary review of screw compressor modelling, design and application.
A mathematical model of the thermodynamic and fluid flow processes within positive displacement machines, which is valid for both the screw compressor and expander modes of operation, is presented in this Monograph. It includes the use of the equations of conservation of mass, momentum and energy applied to an instantaneous control volume of trapped fluid within the machine with allowance for fluid leakage, oil or other fluid injection, heat transfer and the assumption of real fluid properties. By simultaneous solution of these equations, pressure-volume diagrams may be derived of the entire admission, discharge and compression or expansion process within the machine. A screw machine is defined by the rotor profile which is here generated by use of a general gearing algorithm and the port shape and size. This algorithm demonstrates the meshing condition which, when solved explicitly,enables a variety of rotor primary arcs to be defined either analytically or by discrete point curves. Its use greatly simplifies the design since only primary arcs need to be specified and these can be located on either the main or gate rotor or even on any other rotor including a rack, which is a rotor of infinite radius. The most efficient profiles have been obtained from a combined rotor-rack generation procedure.
The rotor profile generation processor, thermofluid solver and optimizer,together with pre-processing facilities for the input data and graphical post processing and CAD interface, have been incorporated into a design tool in the form of a general computer code which provides a suitable tool for analysis and optimization of the lobe profiles and other geometrical and physical parameters. The Monograph outlines the adopted rationale and method of modelling, compares the shapes of the new and conventional profiles and illustrates potential improvements achieved with the new design when applied to dry and oil-flooded air compressors as well as to refrigeration screw compressors.
The first part of the Monograph gives a review of recent developments in screw compressors.
The second part presents the method of mathematical definition of the general case of screw machine rotors and describes the details of lobe shape specification. It focuses on a new lobe profile of a slender shape with thinner lobes in the main rotor, which yields a larger cross-sectional area and shorter sealing lines resulting in higher delivery rates for the same tip speed.
The third part describes a model of the thermodynamics of the compression-expansion processes, discusses some modelling issues and compares the shapes of new and conventional profiles. It illustrates the potential
improvements achievable with the new design applied to dry and oil-flooded air compressors as well as to refrigeration screw compressors. The selection of the best gate rotor tip radius is given as an example of how mathematical modelling may be used to optimise the design and the machine’s operating conditions.
The fourth part describes the design of a high efficiency screw compressor with new rotor profiles. A well proven mathematical model of the compression process within positive displacement machines was used to determine the optimum rotor size and speed, the volume ratio and the oil injection position and jet diameter. In addition, modern design concepts such as an open suction port and early exposure of the discharge port were included, together with improved bearing and seal specification, to maximise the compressor efficiency. The prototypes were tested and compared with the best compressors currently on the market. The measured specific power input appeared to be lower than any published values for other equivalent compressors currently manufactured. Both the predicted advantages of the new rotor profile and the superiority of the design procedure were thereby confirmed.
1.1 Basic Concepts
Thermodynamic machines for the compression and expansion of gases and vapours are the key components of the vast majority of power generation and refrigeration systems and essential for the production of compressed air and gases needed by industry. Such machines can be broadly classified by their mode of operation as either turbomachines or those of the positive displacement type.
Turbomachines effect pressure changes mainly by dynamic effects, related to the change of momentum imparted to the fluids passing through them. These are associated with the steady flow of fluids at high velocities and hence these machines are compact and best suited for relatively large mass flow rates. Thus compressors and turbines of this type are mainly used in the power generation industry, where, as a result of huge investment in research and development programmes, they are designed and built to attain thermodynamic efficiencies of more than 90% in large scale power production plant. However, the production rate of machines of this type is relatively small and worldwide, is only of the order of some tens of thousands of units per annum.
Positive displacement machines effect pressure changes by admitting a fixed mass of fluid into a working chamber where it is confined and then compressed or expanded and, from which it is finally discharged. Such machines must operate more or less intermittently. Such intermittent operation is relatively slow and hence these machines are comparatively large. They are therefore better suited for smaller mass flow rates and power inputs and outputs. A number of types of machine operate on this principle such as reciprocating, vane, scroll and rotary piston machines.
In general, positive displacement machines have a wide range of application, particularly in the fields of refrigeration and compressed air production and their total world production rate is in excess of 200 million units per annum. Paradoxically, but possibly because these machines are produced by comparatively small companies with limited resources, relatively little is spent on research and development programmes on them and there are very few academic institutions in the world which are actively promoting their improvement.
One of the most successful positive displacement machines currently in use is the screw or twin screw compressor. Its principle of operation, as indicated in Fig. 1.1, is based on volumetric changes in three dimensions rather than two. As shown, it consists, essentially, of a pair of meshing helical lobed rotors, contained in a casing.
The spaces formed between the lobes on each rotor form a series of working chambers in which gas or vapour is contained. Beginning at the top and in front of the rotors, shown in the light shaded portion of Fig. 1.1a, there is a starting point for each chamber where the trapped volume is initially zero. As rotation proceeds in the direction of the arrows, the volume of that chamber then increases as the line of contact between the rotor with convex lobes, known as the main rotor, and the adjacent lobe of the gate rotor
Fig. 1.1. Screw Compressor Rotors
advances along the axis of the rotors towards the rear. On completion of one revolution i.e. 360?by the main rotor, the volume of the chamber is then a maximum and extends in helical form along virtually the entire length of the rotor. Further rotation then leads to reengagement of the main lobe with the succeeding gate lobe by a line of contact starting at the bottom and front of the rotors and advancing to the rear, as shown in the dark shaded portions in Fig. 1.1b. Thus, the trapped volume starts to decrease. On completion of a further 360?of rotation by the main rotor, the trapped volume returns to zero.
The dark shaded portions in Fig. 1.1 show the enclosed region where therotors are surrounded by the casing, which fits closely round them, while the light shaded areas show the regions of the rotors, which are exposed to external pressure. Thus the large light shaded area in Fig. 1.1a corresponds to the low pressure port while the small light shaded region between shaft ends B and D in Fig. 1.1b corresponds to the high pressure port.
Exposure of the space between the rotor lobes to the suction port, as their front ends pass across it, allows the gas to fill the passages formed between them and the casing until the trapped volume is a maximum. Further rotation then leads to cut off of the chamber from the port and progressive reduction in the trapped volume. This leads to axial and bending forces on the rotors and also to contact forces between the rotor lobes. The compression process continues until the required pressure is reached when the rear ends of the passages are exposed to the discharge port through which the gas flows out at approximately constant pressure. It can be appreciated from examination of Fig. 1.1, is that if the direction of rotation of the rotors is reversed, then gas will flow into the machine through the high pressure port and out through the low pressure port and it will act as an expander. The machine will also work as an expander when rotating in the same direction as a compressor provided that the suction and discharge ports are positioned on the opposite sides of the casing to those shown since this is
effectively the same as reversing the direction of rotation relative to the ports. When operating as a compressor, mechanical power must be supplied to shaft A to rotate the machine. When acting as an expander, it will rotate automatically and power generated within it will be supplied externally through shaft A.
The meshing action of the lobes, as they rotate, is the same as that of helical gears but, in addition, their shape must be such that at any contact position, a sealing line is formed between the rotors and between the rotors and the casing in order to prevent internal leakage between successive trapped passages. A further requirement is that the passages between the lobes should be as large as possible, in order to maximise the fluid displacement per revolution. Also, the contact forces between the rotors should be low in order to minimise internal friction losses.
A typical screw rotor profile is shown in Fig. 1.2, where a configuration of 5–6 lobes on the main and gate rotors is presented. The meshing rotors are shown with their sealing lines, for the axial plane on the left and for the cross-sectional plane in the centre. Also, the clearance distribution between the two rotor racks in the transverse plane, scaled 50 times (6) is given above.
Fig. 1.2. Screw rotor profile: (1) main, (2) gate, (3) rotor external and (4) pitch circles, (5) sealing line, (6) clearance distribution and (7) rotor flow area between the rotors and housing
Oil injected Oil Free
Fig. 1.3. Oil Injected and Oil Free Compressors
Screw machines have a number of advantages over other positive displacement types. Firstly, unlike reciprocating machines, the moving parts all rotate and hence can run at much higher speeds. Secondly, unlike vane machines, the contact forces within them are low, which makes them very reliable. Thirdly, and far less well appreciated, unlike the reciprocating, scroll and vane machines, all the sealing lines of contact which define the boundaries of each cell chamber, decrease in length as the size of the working chamber decreases and the pressure within it rises. This minimises the escape of gas from the chamber due to leakage during the compression or expansion process.
1.2 Types of Screw Compressors
Screw compressors may be broadly classified into two types. These are shown in Fig. 1.3 where machines with the same size rotors are compared:
1.2.1 The Oil Injected Machine
This relies on relatively large masses of oil injected with the compressed gas in order to lubricate the rotor motion, seal the gaps and reduce the temperature rise during compression. It requires no internal seals, is simple in mechanical design, cheap to manufacture and highly efficient. Consequently it is widely used as a compressor in both the compressed air and refrigeration industries.
1.2.2 The Oil Free Machine
Here, there is no mixing of the working fluid with oil and contact between the rotors is prevented by timing gears which mesh outside the working chamber and are lubricated externally. In addition, to prevent lubricant entering the working chamber, internal seals are required on each shaft between the working chamber and the bearings. In the case of process gas compressors, double mechanical seals are used. Even with elaborate and costly systems such as these, successful internal sealing is still regarded as a problem by established process gas compressor manufacturers. It follows that such machines are considerably more expensive to manufacture than those that are oil injected.
Both types require an external heat exchanger to cool the lubricating oil before it is readmitted to the compressor. The oil free machine requires an oil tank, filters and a pump to return the oil to the bearings and timing gear.
The oil injected machine requires a separator to remove the oil from the high pressure discharged gas but relies on the pressure difference between suction and discharge to return the separated oil to the compressor. These
additional components increase the total cost of both types of machine but the add on cost is greater for the oil free compressor.
1.3 Screw Machine Design
Serious efforts to develop screw machines began in the nineteen thirties, when turbomachines were relatively inefficient. At that time, Alf Lysholm, a talented Swedish engineer, required a high speed compressor, which could be coupled directly to a turbine to form a compact prime mover, in which the motion of all moving parts was purely rotational. The screw compressor appeared to him to be the most promising device for this purpose and all modern developments in these machines stem from his pioneering work. Typical screw compressor designs are presented in Figs. 1.4 and 1.5. From then until the mid nineteen sixties, the main drawback to their widespread use was the inability to manufacture rotors accurately at an acceptable cost. Two developments then accelerated their adoption. The first was the development of milling machines for thread cutting. Their use for rotor manufacture enabled these components to be made far more accurately at an acceptable cost. The second occurred in nineteen seventy three, when SRM, in Sweden, introduced the “A” profile, which reduced the internal leakage path area, known as the blow hole, by 90%. Screw compressors could then be built with efficiencies approximately equal to those of reciprocating machines and, in their oil flooded form, could operate efficiently with stage pressure ratios of up to 8:1. This was unattainable with reciprocating machines. The use of screw compressors, especially of the oil flooded type, then proliferated.
Fig. 1.4. Screw compressor mechanical parts
Fig. 1.5. Cross section of a screw compressor with gear box
To perform effectively, screw compressor rotors must meet the meshing requirements of gears while maintaining a seal along their length to minimise leakage at any position on the band of rotor contact. It follows that the compressor efficiency depends on both the rotor profile and the clearances between the rotors and between the rotors and the compressor housing.
Screw compressor rotors are usually manufactured on pecialized machines by the use of formed milling or grinding tools. Machining accuracy achievable today is high and tolerances in rotor manufacture are of the order of 5 μm around the rotor lobes. Holmes, 1999 reported that even higher accuracy was achieved on the new Holroyd vitrifying thread-grinding machine, thus keeping the manufacturing tolerances within 3 μm even in large batch production. This means that, as far as rotor production alone is concerned, clearances betweenthe rotors can
be as small as 12 μm.
中文译文
1 引言
螺杆式压缩机是一种最常见的用来压缩气体的机器。它的结构简单，因为它基本上只包括一对互相啮合的螺旋形转子，它们包含在一个壳体中，紧密地配合在周围，转子和机壳之间有非常小的空隙。转子由外部的发动机和齿轮驱动，当转子旋转时，转子间的空隙以及转子与机壳之间的空间逐渐缩小。因此，在这种情况下，里面的气体就被压缩了。这种机器的几何构造是复杂的，流动的气体被压缩分三个阶段。首先，通过启动时转子的旋转，气体通过机壳一端的进气口进入齿间。其次，随着旋转的继续，转子之间的空间不再与进气口联合，因此，里面的气体就被压缩。最后，进一步旋转之后，转子的另一端经过位于机壳另一端的第二个端口，通过这个端口气体被排出。整个过程在齿的持续啮合中重复着，形成了一个从低压到高压持续而脉动的气流。
这些机器主要用于建筑业、食品业、加工业、制药业以及在冶金工业和气动输送中需要的地方。它们也广泛地应用于制冷和空调系统中所用的制冷剂的压缩以及化学工业中烃气的压缩。在过去30年，它们之所以相对快速地被接受是由于相比其他类型的容积式机器，它们拥有相对高的转速，这使得他们更加紧凑，它们能够在大范围的运作压力下保持高效率、高流速并且使用寿命长，依赖性强。因此，螺杆式压缩机在当前出售和使用的容积式压缩机中占有很大比例。
螺杆式压缩机成功的主要原因归功于新型转子，它已大大减少了内部漏泄，以及先进的机床，它能以一个可接受的成本制造出最复杂的形状到3微米的公差。转子齿形的改善仍是最有前景的手段来更好地改进螺杆式压缩机。合理的程序正被研发，不仅用来代替早期经验得出的形状，而且能多样化地协调已选的轮廓，获得最佳的应用程序的压缩机必需的。尽管螺杆式压缩机大范围使用，但是由于它们内部构造的复杂性以及工序本身的不稳定性，直到现在，只有近似的分析方法能来预测它们的表现。因此，虽然众所周知，它们的单体被重物所施加的压力以及被自身的温度变化所扭曲，目前没法能精确预测这些扭曲的程度，也不能预测它们如何影响机器的总性能。另外，机器内部优化的流型模式有助更好的排气口设计。而且，更精确的测定轴承负载和它们波动的方式有助于更好的选择轴承。最后，由于压缩机自身温度和压力变化而导致转子和机壳扭曲，如果这个扭曲能被确实地预估，那么就能设计加工程序最大化地降低不利影响。
在螺杆机操作下的各种工作气体，其可以是与机器内的相位变化发生的气体，干蒸汽或多相混合物。他们可能会涉及驱油或其他液体注入过程中的压缩或膨胀过程中，没有任何形式的内部润滑。它们的几何形状可以依据每个转子上的齿，基本的转子轮廓和每个转齿片段上的相对部分来进行变化。因此没有通用的配置，适合各种应用程序的。因此，压缩过程详细的热力学分析和对各种性能设计参数的评估更能从这些机器上获得最好的结果，而非从能达到相同的用途的其他类型的机器上。所以，在优化程序主导下设计一套详细的标准是每个应用程序实现最好设计的前提。这样的指导方针，为进一步改善现有的螺杆机设计并扩大其广泛的用途也很重要。弗莱明等人在1998年对螺杆式压缩机的建模、设计和应用提供了一个很好的现代化评论。
热力学和流体流动过程的数学模型在这个专著中被提出，它在容积式机的螺杆压缩机和膨胀机的操作模式是有效的。专著中包括质量守恒定律公式的使用，包括运用于机器中的截面液即时控制卷的动力和能量，而这机器拨备液体渗漏、石油或其他流体注入、传热和实际流体参数。通过求解这些方程组，能获得机器中流体整体的吸收、释放、压缩或膨胀过程的压力容积图。
螺杆机的容量由转子轮廓而定，而转子轮廓根据普遍传动装置的使用以及气门的形状和大小。这个运算法则当解释明确时，能论证啮合条件，即能使多种转子的主要弧线通过分析或者离散点曲线得出。它的使用大大简化了设计，因为只有主要弧线需要被额定，而且这些能被设于主转子或闸转子或者其他任何包括齿条的拥有无限大半径的转子上。最有效的转子轮廓图已从一个联合转子架生成过程中得出。
转子轮廓形成处理器，热流体的解算器和优化器，连同预处理设施为输入数据和图形后处理和CAD 接口，已被纳入一个设计工具，它以通过计算机编码的形式为分析和齿形优化以及其他几何和物理参数提供一个适当的工具。这个专著对比新的和传统的轮廓，概述了采用的基本原理和建模方法，并阐明了当应用于有油或者无油的空气压缩机和制冷螺杆式压缩机时，新的设计有潜在的改进方面。
专著的第一部分综述了螺旋式压缩机当前的发展。
第二部分介绍了用数学的方法定义在一般情况下螺杆机转子的方法，还细节的描述了齿形的规范。它强调在主转子上拥有更薄的新型的薄型齿，这样的齿能形成一个更大的截面面积和更短的密封线以致同等的转速能产生更高的给料速度。
第三部分描述了压缩膨胀过程的热力学模型，讨论了一些建模的问题，对比新的和传统的剖面形状。它阐明了随着新的设计应用于无油和有油式空气压缩机和制冷螺杆压缩机时所能达到的潜在的改进。最好的闸转子齿顶圆半径的选择被作为一个例子来描述，说明数学模型可以用来优化设计和机器的操作条件。
第四部分描述了设计一个高效螺杆压缩机与新转子配置。一个得到确凿证实的容积式机器上压缩过程的数学模型能够决定转子的最佳尺寸和速度、体积比率、油的注入位置和喷射口直径。另外，像一个开放的进气孔、早期曝露在外的排气口，还有改良的轴承和密封件的规格等现代设计观念都包含在内，以最大限度地提高压缩机的效率。这个原型被测试过并与当前市场上最好的压缩机作了对比。实测功率输入似乎比当前生产的其他任何等效压缩机的公布值要低。预测的新转子外形的优势和设计程序的优越性因而得以证实。
1.1基本概念
用于气体和蒸汽压缩和膨胀的热力学机器是大多数发电和制冷系统的关键组分，而对工业上需压缩空气和气体来说也是必不可少的。这种机器可以根据它们的运行方式来广泛地分类，分成涡轮机或者容积式机型。
涡轮机主要通过动态效果引起气压变化，而这与传递给液体的动量的变化有关。这些与高速下液体的稳流有关，因此，这些机器结构紧凑，最适于相对大的流量。因此，这种类型的压缩机和涡轮机主要是用于发电行业。由于研究和开发项目上巨大的投资，它们经过设计和改造，能够在大规模的电力生产工厂获得90%以上的热力学效率。但是，在全世界范围内这种类型机器的生产率相对较低，而且每年的订单只有数万个单位。
容积式机器通过使定量的液体进入工作腔，在那压缩或膨胀再释放，从而引起气压变化。这样的机器必须或多或少间歇性地工作。这种间歇的运转相对缓慢，因而这些机器相对较大。因此，它们更加适合小规模的流量和功率输入与输出。许多种机器采用这种工作原理，例如往复式，叶片，滚动和旋转式活塞机器。
一般来说,容积式机器有广泛的应用,尤其在制冷、压缩空气领域，他们总世界产量超过2亿辆每年。出乎意料的是，不过这可能是由于这些机器是由相对较小的公司生产的，资源有限所以研发项目上的投入比较少，很少有世界学术机构,积极促进他们的进步。
(a)从正面和顶部看(b)从底部和后面看
图1.1 螺杆式压缩机转子
目前使用的最成功的容积式机器是螺杆式压缩机和双螺杆式压缩机。它的工作原理（图 1.1）是以三维空间而非二维空间中的容积变更为基础。如图所示，它基本包括位于机壳内的一对螺旋齿转子。每个转子齿间的空间形成了一系列的包含气体和蒸汽的工作腔。从转子前面的顶部开始，正如图1.1中浅色的阴影部分所示，有一个每个室的出发点，圈闭容积起初是零。随着转子朝着箭头方向运转，那个室的容积增加，也就是主转和闸转邻近齿之间的接触线也伴随着转轴向后部移动。主转子完成一次旋转，即360度，该室的体积达到最大值，而且以螺旋形式朝着整个长度延伸。继续旋转，旋转到主转的接合处，此时，随后的接触线上的闸齿从转前底部开始旋转并朝着后部移动，正如图1.1b深阴影部分显示的那样。因此，圈闭容积开始减少。主转完成一周360度的旋转后，圈闭容积返回到零。
图1.1中的深色阴影部分显示了转子被机壳包围，机壳紧紧围绕转子的封闭区域，而光的阴影区域显示了转子暴露在外部压力下的区域。因此，图1.1a中大光影区域对应于低压端口，而图1.1b中轴端B和D中的小的浅色阴影部分对应于高压端口。
转齿与暴露在外面的进气孔之间的间距能够使气体穿过它们之间形成的过道和机壳，直到圈闭容积达到最大值。压缩过程继续进行直到达到所需的压力导致后端露出排气口，该气体在大致恒定的压力下流出。
这可以从图1.1的验证图中加以理解，如果转子的旋转方向颠倒，气体会通过高压端流进机器，通过低压端流出，就像膨胀器一样运转。倘若进气口和排气口置于机壳的对边，机器以相同方向旋转时，也会向膨胀器一样运转，因为这实际上与颠倒旋转方向无异。当像压缩机一样运作时，必须向轴A提供机械动力以使机器旋转。当像膨胀器一样工作时，它会自动旋转，自身生成的动力会通过轴A外部供给。
当波瓣动作时，它们的啮合动作就像斜齿轮的啮合动作一样，但是此外，它们的形状必须是：在任何接触位置，转子间以及转子与机壳间会形成封口以防止持续圈闭通道发生内部泄露。另一个要求是，波瓣的过道应尽可能大，这样能使每转的流体位移达到最大化。另外，转子间的接触力应该要低，以使内部摩擦损失达到最小值。典型的螺旋转子剖面图如图1.2所示，其中提出的结构在主转子和闸转子上第5-6个波瓣的位置。齿合转子和它们的密封线都在图上得以显示，在左侧的轴向平面和在中心的横截面的平面。此外，横截面上两个转子架上的间隙分布缩放了50倍（6）也显示在图上。
图1.2 螺旋转子剖面图：（1）主转子；（2）闸转子；（3）转子外部；（4）节距圆；（5）密封线；（6）间隙分布；（7）转子和外壳间的转子流通面积
喷油式无油式
图1.3 喷油式和无油式压缩机
螺杆式压缩机与其他容积式机器相比有许多优点。首先，与其他的往复运动的机械不同，螺杆式压缩机的运动部件都旋转，因此，它可以在高速中运转。第二，与叶片机不同，它们内部的接触力比较低，因此非常可靠。第三，不大被重视的是，不像往复式、涡旋机和叶片机，所有用来限定接触每个单体腔中的密封线，它的长度会随着工作室规格的减小而减小，而它里面的压力会上升。这最大限度地减小因过程中的压缩或者膨胀过程从腔室的气体的逸出。
1.2螺杆式压缩机的类型
螺杆式压缩机广义上可以分成两大类。如图1.3，与带有相同尺寸转子的机器对比：
1.2.1喷油式螺杆压缩机
这种压缩机依赖于相对大量的油注入来压缩气体，以便润滑转动装置，密封间隙并减少在压缩过程中的温度上升。它不需要密封件，机械设计简单，造价便宜，非常高效。因此，不管是用来压缩气体还是用在制冷工业它都作为压缩机被广泛使用。
1.2.2无油式压缩机
在这里没有混合的工作流体和·油，定时齿轮阻止了转子间的接触，工作腔外的外部被外部润滑。另外，为了防止润滑油进入工作腔，工作腔和轴承间的每个轴都需要密封。至于工艺气体压缩机，需要用双端面机械密封。即使拥有像这些精密昂贵的系统，成功的内部密封仍被目前的生产气体压缩机的制造商认为是一个问题。因此，这种机器比那些喷油式制造起来更加的昂贵。
两种类型的压缩机在油再次进入压缩机之前，都需要外换热器来冷却润滑油。无油机需要一个油缸，过滤器以及一个泵来使油回到轴承和定时齿轮。
喷油螺杆压缩机需要一个分离器来去除高压排除的气体中的油，但这需要吸入口与排气口有压力差以使得被分离的油返回压缩机。这些额外组件增加了这两种机器的总成本，但是对于无油机来说成本更大。
1.3螺杆机械设计
19世纪30年代，很多企业致力于发展螺杆机，这时涡轮机组相对来说效率不高。那时候瑞典杰出的工程师Alf Lysholm想要一个高速压缩机，这样的压缩机能直接连接涡轮机形成一个紧凑的原动机，原动机内所有的移动部件都是纯粹的转动。对他而言，螺杆式压缩机是实现这一目标最有希望的设备，而且这些机器所有的近代的发展都源于他开创性的工作。典型的螺杆式压缩机设计图如图1.4和图1.5所示。从那时开始直到19世纪60年代，阻碍螺杆式压缩机大范围使用的是，无法以可接受成本准确地生产转子。之后两个发展加速了螺杆式压缩机的应用。首先是螺纹切割铣床的发展。对于转子的制造，他们的使用能使这些组件以可接受的成本更加精确地制造。第二个发明是在1973年，SRM在瑞典引进了A剖面图，减小了90%的内部泄露路径区域，也就是所谓的气孔。螺杆式压缩机能以与那些往复机械大致相同的效率得以生产。在喷油方面，螺杆式压缩机也能以高于8:1的压力比有效运转。这是往复机械达不到的。螺杆式压缩机，尤其是喷油型压缩机的应用快速增加。
图1.4螺杆式压缩机的机械零件
图1.5齿轮箱中的螺杆式压缩机的横截面
为了有效运行，螺杆式压缩机的转子必须满足齿轮的啮合要求，即他们的长度上要保持密封以使在转子接触带的任何地方渗漏能最小化。因而压缩机的效率依赖于转子之间以及转子与压缩机外壳之间转子的结构和转子间的间隙。
特殊的机器使用成型的铣削或磨具生产螺杆式压缩机转子。当今可达到的加工精确度很高，转子生产中允许转齿周围5毫米的误差。霍姆斯在1999年报导说新型Holroyd玻璃化螺纹磨床可以达到更高的精确度，因此在大批生产的情况下能使生产误差保持在3微米范围内。这意味着，只要仅转子生产而言，转子
之间的间隙可以被缩小到12微米。
红外数据通信技术外文翻译文献(文档含中英文对照即英文原文和中文翻译) Infrared Remote Control System Abstract Red outside data correspondence the technique be currently within the scope of world drive extensive usage of a kind of wireless conjunction technique, drive numerous hardware and software platform support. Red outside the transceiver product have cost low, small scaled turn, the baud rate be quick, point to point SSL, be free from electromagnetism thousand Raos
etc. characteristics, can realization information at dissimilarity of the product fast, convenience, safely exchange and transmission, at short distance wireless deliver aspect to own very obvious of advantage. Along with red outside the data deliver a technique more and more mature, the cost descend, red outside the transceiver necessarily will get at the short distance communication realm more extensive of application. The purpose that design this system is transmit customer’s operation information with infrared rays for transmit media, then demodulate original signal with receive circuit. It use coding chip to modulate signal and use decoding chip to demodulate signal. The coding chip is PT2262 and decoding chip is PT2272. Both chips are made in Taiwan. Main work principle is that we provide to input the information for the PT2262 with coding keyboard. The input information was coded by PT2262 and loading to high frequent load wave whose frequent is 38 kHz, then modulate infrared transmit dioxide and radiate space outside when it attian enough power. The receive circuit receive the signal and demodulate original information. The original signal was decoded by PT2272, so as to drive some circuit to accomplish customer’s operation demand. Keywords: Infrared dray；Code；Decoding；LM386；Red outside transceiver 1 Introduction 1.1 research the background and significance Infrared Data Communication Technology is the world wide use of a wireless connection technology, by the many hardware and software platforms supported. Is a data through electrical pulses and infrared optical pulse switch between the wireless data transceiver technology.
文献综述 《中国设计的力量》把当今市场上的白酒酒包装编辑成册，研究酒包装设计对人们的消费观念的影响。书中所列举的包装充分表现出了历史文化和高尚生活元素的结合。随着当今酒市场竞争的激烈，酒包装设计本身所呈现出的价值也越来越得到人们的认可，不仅带给人们实用和审美的艺术价值，还创造了不可估量的经济价值。酒并不是生活必需品，但在社会生活中，酒却具有其它物品所无法替代的功能。酒是随着人类文明不断的发展和创新的。酒包装设计也是在不断更新、变化、发展的。 《设计大师的对话》这不是一本普通的访谈录，而是凝聚着当代日本设计大师们发自肺腑心声的箴言集。本书汇编出了一组包罗万象的时代创意阵容，并且进行访谈的二十五个人物绝对不可缺一。用文字和图片去记录日本设计源头所发生的一切。凭着作者那股近乎门外汉般的好奇精神和不懈的努力，最终成就了他对智慧的生产现场的执著探访。从表面上看，除了要传递那些成为我们新的共同关注点，即设计专业的整体和真实以外，似乎并没有什么特别之处。但是本书却汇编出了一组包罗万象的时代创意阵容，并且到了书中的二十五个人物绝对不可缺一，若有一人被排斥在外便难以成书的微妙地步。 《包装设计基础与创意》这本书介绍了在艺术设计领域中，包装设计以其与人们生活的密切而占有重要的位置。今天的消费在一定程度上，已经成为一种文化消费的趋势。随着文化消费圈层的不断扩大，文化消费已经渗透到我们社会生活的各个层面。人们对商品的购买已经不再是单单的实用，而是越来越注重外观的美感。特别是产品的包装，更是文化和艺术的载体。这需要我们对包装的设计，进行深入地研究与发掘。在继承的前提下充分融合时代需求，不断地发展与创新，满足人们的文化追求。从包装发展的历史中涉取宝贵的经验与教训，这样才能在继承优秀的外在形式和内在的精神基础上不断提高和创新，才能超越和创造历史，把包装设计艺术不断的创新和发展下去。 《设计中的设计》这本书中，原研哉认真阐述了“设计领域的再配置”这一问题。显然，他对设计的思考已经远远超出了技术层面，而是围绕信息传达这一设计的本质功能，以充满自省的精神在深化和反思自己的设计意识。在原研哉看来，设计不是一种技能，而是捕捉事物本质的感觉能力和洞察能力。所以，设计师要时刻保持对社会的敏感度。他正是以这一想法为中心展开论述。原研哉以“无中生有”的理念为圭臬，凸现了“无”的力量。同时，作为一名非常具有社会责任感的设计师，他也把引导消费欲望作为自己的任务之一，并对其进行了深入的思考。 《绝对包装》此书体现了包装设计创新的精华理念。以大量成功经典作品为案例，对其创意的关键所在进行深入分析。食品、非酒精类饮料、酒精类饮料、CD、化妆品、生活用品、礼品盒等包装精品光彩夺目、美伦美奂；作者的点评文字，敏锐精当，每每切入作品独特奥妙之处。 《标牌与标签设计》在这本书中作者，列举了大量的实例。详细地介绍了国外标牌与标签设计的发展情况。在国外设计分工越来越细，一个小的标牌，不过方寸。却显示出大
本科毕业论文（翻译） 英文标题 学生姓名学号 教学院系石油与天然气工程学院 专业年级油气储运工程2011级 指导教师职称 单位 辅导教师职称 单位 完成日期2015年06月
利用天然气管道压差能量液化天然气流程 摘要 长输管道天然气的输送压力通常较高（高达10兆帕），在城市门站通常需要一套节流装置完成减压过程，这个过程通常由节流装置实现，而且在此过程中会浪费非常巨大的压力能。在该文章中通过HYSYS软件来设计和模拟回收利用该巨大能量来完成一股天然气的膨胀液化过程。将单位能量消耗和液化率作为目标函数并作为优化设计选择的关键变量。同样对天然气管道在不同运输用作压力下的工作情况进行计算和讨论，同时对不同设备压力能损失进行评估，并对具体细节进行分析。结果显示，这一液化率显然低于普通液化过程的液化率，该天然气膨胀液化过程适用于进行天然气液化是由于他的单位能耗低，过程简单及灵活。 1.介绍 长距离输送管线通常在较高的工作压力下运行（高达10兆帕），高压天然气通常在城市门站内通过一个不可逆的节流过程从而降压到达较低的压力为了适应不同的需求，在这个过程中有用的压力能就这样被浪费了，因而，利用合适的能源利用方法回收这部分大量的压力能是十分有价值的。 天然气管道压力能多用于发电，轻质烃的分离以及天然气的液化。现在已经有很多关于一些小型的LNG站场天然气液化的研究报告，天然气技术研究所开发了一个小型的利用混合制冷机制冷循环的天然气液化系统，起液化能力在4-40m3 /d，kirllow等人研究了利用涡流液化技术和膨胀液化技术的小型天然气液化调峰厂。Len等人描述了几个基于压力能回收利用的天然气液化流程。Lentransgaz公司开发了充分利用压力能而没有外来能源输入来液化天然气的天然气液化的新设备。 Mokarizadeh等人应用了基因遗传学的相关算法对于天然气调峰厂的液化天然气的压力能使用进行优化以及损失的评估，Cao等人使用Hysys软件分析了应用于小型天然气液化流程的使用混合制冷剂循环以及N2，CH4膨胀循环的撬装包。Remeljej等人比较了四种液化流程包括单级混合制冷循环，两级膨胀氮循环，两开环膨胀流程，以及类似的能量分析得到单级的混合制冷剂循环有最低的能量损失。 表1 符号命名 符号名称符号名称 a 吸入参量，Pa(m3/mol) t 温度K A 无量纲吸入参量v 摩尔体积m3/mol b 摩尔体积m3/mol W 能量kW
Inventory management Inventory Control On the so-called "inventory control", many people will interpret it as a "storage management", which is actually a big distortion. The traditional narrow view, mainly for warehouse inventory control of materials for inventory, data processing, storage, distribution, etc., through the implementation of anti-corrosion, temperature and humidity control means, to make the custody of the physical inventory to maintain optimum purposes. This is just a form of inventory control, or can be defined as the physical inventory control. How, then, from a broad perspective to understand inventory control? Inventory control should be related to the company's financial and operational objectives, in particular operating cash flow by optimizing the entire demand and supply chain management processes (DSCM), a reasonable set of ERP control strategy, and supported by appropriate information processing tools, tools to achieved in ensuring the timely delivery of the premise, as far as possible to reduce inventory levels, reducing inventory and obsolescence, the risk of devaluation. In this sense, the physical inventory control to achieve financial goals is just a means to control the entire inventory or just a necessary part; from the perspective of organizational functions, physical inventory control, warehouse management is mainly the responsibility of The broad inventory control is the demand and supply chain management, and the whole company's responsibility. Why until now many people's understanding of inventory control, limited physical inventory control? The following two reasons can not be ignored: First, our enterprises do not attach importance to inventory control. Especially those who benefit relatively good business, as long as there is money on the few people to consider the problem of inventory turnover. Inventory control is simply interpreted as warehouse management, unless the time to spend money, it may have been to see the inventory problem, and see the results are often very simple procurement to buy more, or did not do warehouse departments . Second, ERP misleading. Invoicing software is simple audacity to call it ERP, companies on their so-called ERP can reduce the number of inventory, inventory control, seems to rely on their small software can get. Even as SAP, BAAN ERP world, the field of
用于多跳认知无线电网络的分布式网络编码控制信道 Alfred Asterjadhi等著 1 前言 大多数电磁频谱由政府机构长期指定给公司或机构专门用于区域或国家地区。由于这种资源的静态分配，许可频谱的许多部分在许多时间和/或位置未使用或未被充分利用。另一方面，几种最近的无线技术在诸如IEEE802.11，蓝牙，Zigbee之类的非许可频段中运行，并且在一定程度上对WiMAX进行操作;这些技术已经看到这样的成功和扩散，他们正在访问的频谱- 主要是2.4 GHz ISM频段- 已经过度拥挤。为了为这些现有技术提供更多的频谱资源，并且允许替代和创新技术的潜在开发，最近已经提出允许被许可的设备（称为次要用户）访问那些许可的频谱资源，主要用户未被使用或零星地使用。这种方法通常被称为动态频谱接入（DSA），无线电设备发现和机会性利用未使用或未充分利用的频谱带的能力通常称为认知无线电（CR）技术。 DSA和CR最近都引起了无线通信和网络界的极大关注。通常设想两种主要应用。第一个是认知无线接入（CW A），根据该认知接入点，认知接入点负责识别未使用的许可频谱，并使用它来提供对次用户的接入。第二个应用是我们在这个技术中研究的应用，它是认知自组织网络（CAN），也就是使用 用于二级用户本身之间通信的无许可频谱，用于诸如点对点内容分发，环境监控，安全性等目的，灾难恢复情景通信，军事通信等等。 设计CAN系统比CW A有更多困难，主要有两个原因。第一是识别未使用的频谱。在CW A中，接入点的作用是连接到互联网，因此可以使用简单的策略来推断频谱可用性，例如查询频谱调节器在其地理位置的频谱可用性或直接与主用户协商频谱可用性或一些中间频谱经纪人另一方面，在CAN中，与频谱调节器或主要用户的缺乏直接通信需要二级用户能够使用检测技术自己识别未使用的频谱。第二个困难是辅助用户协调媒体访问目的。在CW A中存在接入点和通常所有二级用户直接与之通信（即，网络是单跳）的事实使得直接使用集中式媒体接入控制（MAC）解决方案，如时分多址（TDMA）或正交频分多址（OFDMA）。相反，预计CAN将跨越多跳，缺少集中控制器;而对于传统的单通道多跳自组织网络而言，这个问题的几个解决方案是已知的，因为假设我们处理允许设备访问的具有成
(文档含英文原文和中文翻译) 中英文翻译 平面设计 任何时期平面设计可以参照一些艺术和专业学科侧重于视觉传达和介绍。采用多种方式相结合，创造和符号，图像和语句创建一个代表性的想法和信息。平面设计师可以使用印刷，视觉艺术和排版技术产生的最终结果。平面设计常常提到的进程，其中沟通是创造和产品设计。 共同使用的平面设计包括杂志，广告，产品包装和网页设计。例如，可能包括产品包装的标志或其他艺术作品，举办文字和纯粹的设计元素，如形状和颜色统一件。组成的一个最重要的特点，尤其是平面设计在使用前现有材料或不同的元素。 平面设计涵盖了人类历史上诸多领域，在此漫长的历史和在相对最近爆炸视觉传达中的第20和21世纪，人们有时是模糊的区别和重叠的广告艺术，平面设计和美术。毕竟，他们有着许多相同的内容，理论，原则，做法和语言，有时同样的客人或客户。广告艺术的最终目标是出售的商品和服务。在平面
设计，“其实质是使以信息，形成以思想，言论和感觉的经验”。 在唐朝（ 618-906 ）之间的第4和第7世纪的木块被切断打印纺织品和后重现佛典。阿藏印在868是已知最早的印刷书籍。 在19世纪后期欧洲，尤其是在英国，平面设计开始以独立的运动从美术中分离出来。蒙德里安称为父亲的图形设计。他是一个很好的艺术家，但是他在现代广告中利用现代电网系统在广告、印刷和网络布局网格。 于1849年，在大不列颠亨利科尔成为的主要力量之一在设计教育界，该国政府通告设计在杂志设计和制造的重要性。他组织了大型的展览作为庆祝现代工业技术和维多利亚式的设计。 从1892年至1896年威廉?莫里斯凯尔姆斯科特出版社出版的书籍的一些最重要的平面设计产品和工艺美术运动，并提出了一个非常赚钱的商机就是出版伟大文本论的图书并以高价出售给富人。莫里斯证明了市场的存在使平面设计在他们自己拥有的权利，并帮助开拓者从生产和美术分离设计。这历史相对论是，然而，重要的，因为它为第一次重大的反应对于十九世纪的陈旧的平面设计。莫里斯的工作，以及与其他私营新闻运动，直接影响新艺术风格和间接负责20世纪初非专业性平面设计的事态发展。 谁创造了最初的“平面设计”似乎存在争议。这被归因于英国的设计师和大学教授Richard Guyatt，但另一消息来源于20世纪初美国图书设计师William Addison Dwiggins。 伦敦地铁的标志设计是爱德华约翰斯顿于1916年设计的一个经典的现代而且使用了系统字体设计。 在20世纪20年代，苏联的建构主义应用于“智能生产”在不同领域的生产。个性化的运动艺术在俄罗斯大革命是没有价值的，从而走向以创造物体的功利为目的。他们设计的建筑、剧院集、海报、面料、服装、家具、徽标、菜单等。 Jan Tschichold 在他的1928年书中编纂了新的现代印刷原则，他后来否认他在这本书的法西斯主义哲学主张，但它仍然是非常有影响力。 Tschichold ，包豪斯印刷专家如赫伯特拜耳和拉斯洛莫霍伊一纳吉，和El Lissitzky 是平面设计之父都被我们今天所知。 他们首创的生产技术和文体设备，主要用于整个二十世纪。随后的几年看到平面设计在现代风格获得广泛的接受和应用。第二次世界大战结束后，美国经济的建立更需要平面设计，主要是广告和包装等。移居国外的德国包豪斯设计学院于1937年到芝加哥带来了“大规模生产”极简到美国;引发野火的“现代”建筑和设计。值得注意的名称世纪中叶现代设计包括阿德里安Frutiger ，设计师和Frutiger字体大学;保兰德，从20世纪30年代后期，直到他去世于1996年，采取的原则和适用包豪斯他们受欢迎的广告和标志设计，帮助创造一个独特的办法，美国的欧洲简约而成为一个主要的先驱。平面设计称为企业形象;约瑟夫米勒，罗克曼，设计的海报严重尚未获取1950年代和1960年代时代典型。 从道路标志到技术图表，从备忘录到参考手册，增强了平面设计的知识转让。可读性增强了文字的视觉效果。 设计还可以通过理念或有效的视觉传播帮助销售产品。将它应用到产品和公司识别系统的要素像标志、颜色和文字。连同这些被定义为品牌。品牌已日益成为重要的提供的服务范围，许多平面设计师，企业形象和条件往往是同时交替使用。
毕业设计外文资料翻译 附件1：外文资料翻译译文 一维多级轴流压缩机性能的解析优化 摘要 对多级压缩机的优化设计模型，本文假设固定的流道形状以入口和出口的动叶绝对角度，静叶的绝对角度和静叶及每一级的入口和出口的相对气体密度作为设计变量，得到压缩机基元级的基本方程和多级压缩机的解析关系。用数值实例来说明多级压缩机的各种参数对最优性能的影响。 关键词 轴流压缩机 效率 分析关系 优化 1 引言 轴流式压缩机的设计是工艺技术的一部分，如果缺乏准确的预测将影响设计过程。至今还没有公认的方法可使新的设计参数达到一个足够精确的值，通过应用一些已经取得新进展的数值优化技术，以完成单级和多级轴流式压缩机的设计。计算流体动力学（CFD ）和许多更准确的方法特别是发展计算的CFD 技术，已经应用到许多轴流式压缩机的平面和三维优化设计。它仍然是使用一维流体力学理论用数值实例来计算压缩机的最佳设计。Boiko 通过以下假设提出了详细的数学模型用以优化设计单级和多级轴流涡轮：（1）固定的轴向均匀速度分布（2）固定流动路径的形状分布，并获得了理想的优化结果。陈林根等人也采用了类似的想法，通过假设一个固定的轴向速度分布的优化设计提出了设计单级轴流式压缩机一种数学模型。在本文中为优化设计多级轴流压缩机的模型，提出了假设一个固定的流道形状，以入口和出口的动叶绝对角度，静叶的绝对角度和静叶及每一级的入口和出口的相对气体密度作为设计变量，分析压缩机的每个阶段之间的关系，用数值实例来说明多级压缩机的各种参数对最优性能的影响。 2 基元级的基本方程 考虑图1所示由n 级组成的轴流压缩机, 其某一压缩过程焓熵图和中间级的速度三角形见图2和图3，相应的中间级的具体焓熵图如图4，按一维理论作级的性能计算。按一般情况列出轴流压缩机中气体流动的能量方程和连续方程,工作流体和叶轮的速度。在不同级的轴向流速不为常数，即考虑i j u u ≠,i j c c ≠ (i j ≠) 时的能量和流量方程。在
英语专业毕业论文翻译 类论文 Document number：NOCG-YUNOO-BUYTT-UU986-1986UT
毕业论文（设计）Title:The Application of the Iconicity to the Translation of Chinese Poetry 题目:象似性在中国诗歌翻译中的应用 学生姓名孔令霞 学号 BC09150201 指导教师祁晓菲助教 年级 2009级英语本科（翻译方向）二班 专业英语 系别外国语言文学系
黑龙江外国语学院本科生毕业论文（设计）任务书 摘要
索绪尔提出的语言符号任意性，近些年不断受到质疑，来自语言象似性的研究是最大的挑战。语言象似性理论是针对语言任意性理论提出来的，并在不断发展。象似性是当今认知语言学研究中的一个重要课题，是指语言符号的能指与所指之间的自然联系。本文以中国诗歌英译为例，探讨象似性在中国诗歌翻译中的应用，从以下几个部分阐述：（1）象似性的发展；（2）象似性的定义及分类；（3）中国诗歌翻译的标准；（4）象似性在中国诗歌翻译中的应用，主要从以下几个方面论述：声音象似、顺序象似、数量象似、对称象似方面。通过以上几个方面的探究，探讨了中国诗歌翻译中象似性原则的重大作用，在诗歌翻译过程中有助于得到“形神皆似”和“意美、音美、形美”的理想翻译效果。 关键词：象似性；诗歌；翻译
Abstract The arbitrariness theory of language signs proposed by Saussure is severely challenged by the study of language iconicity in recent years. The theory of iconicity is put forward in contrast to that of arbitrariness and has been developing gradually. Iconicity, which is an important subject in the research of cognitive linguistics, refers to a natural resemblance or analogy between the form of a sign and the object or concept. This thesis mainly discusses the application of the iconicity to the translation of Chinese poetry. The paper is better described from the following parts: (1) The development of the iconicity; (2) The definition and classification of the iconicity; (3) The standards of the translation to Chinese poetry; (4) The application of the iconicity to the translation of Chinese poetry, mainly discussed from the following aspects: sound iconicity, order iconicity, quantity iconicity, and symmetrical iconicity. Through in-depth discussion of the above aspects, this paper could come to the conclusion that the iconicity is very important in the translation of poetry. It is conductive to reach the ideal effect of “the similarity of form and spirit” and “the three beauties”. Key words: the iconicity; poetry; translation
5G无线通信网络中英文对照外文翻译文献(文档含英文原文和中文翻译)
翻译： 5G无线通信网络的蜂窝结构和关键技术 摘要 第四代无线通信系统已经或者即将在许多国家部署。然而，随着无线移动设备和服务的激增，仍然有一些挑战尤其是4G所不能容纳的，例如像频谱危机和高能量消耗。无线系统设计师们面临着满足新型无线应用对高数据速率和机动性要求的持续性增长的需求，因此他们已经开始研究被期望于2020年后就能部署的第五代无线系统。在这篇文章里面，我们提出一个有内门和外门情景之分的潜在的蜂窝结构，并且讨论了多种可行性关于5G无线通信系统的技术，比如大量的MIMO技术，节能通信，认知的广播网络和可见光通信。面临潜在技术的未知挑战也被讨论了。 介绍 信息通信技术（ICT）创新合理的使用对世界经济的提高变得越来越重要。无线通信网络在全球ICT战略中也许是最挑剔的元素，并且支撑着很多其他的行业，它是世界上成长最快最有活力的行业之一。欧洲移动天文台（EMO）报道2010年移动通信业总计税收1740亿欧元,从而超过了航空航天业和制药业。无线技术的发展大大提高了人们在商业运作和社交功能方面通信和生活的能力无线移动通信的显著成就表现在技术创新的快速步伐。从1991年二代移动通信系统(2G)的初次登场到2001年三代系统（3G）的首次起飞，无线移动网络已经实现了从一个纯粹的技术系统到一个能承载大量多媒体内容网络的转变。4G无线系统被设计出来用来满足IMT-A技术使用IP面向所有服务的需求。在4G系统中，先进的无线接口被用于正交频分复用技术（OFDM），多输入多输出系统（MIMO）和链路自适应技术。4G无线网络可支持数据速率可达1Gb/s的低流度，比如流动局域无线访问，还有速率高达100M/s的高流速，例如像移动访问。LTE系统和它的延伸系统LTE-A，作为实用的4G系统已经在全球于最近期或不久的将来部署。 然而，每年仍然有戏剧性增长数量的用户支持移动宽频带系统。越来越多的
《文献检索》课程教学设计 目录 绪论：文献（信息）检索的意义及基础 (2) 项目一科技文献检索方法和图书馆的科学利用 (8) 项目二常见化学化工科技论文的写作 (11) 项目三美国化学文摘的使用 (14) 项目四专利文献的查询 (17) 项目五标准文献的查询 (20) 项目六计算机信息检索的应用 (23) 项目七信息检索策略综合应用训练 (26)
徐州工业职业技术学院教学设计（讲稿）
教学内容与设计 绪论：文献（信息）检索的意义及基础 自我介绍 提问一：你会检索吗？ 如果会，那么会用检索以下毕业专题的相关资料吗？ ?杜仲叶中绿原酸的提取分离 ?有机废水处理工艺设计 ?蚕丝蛋白制备工艺研究 ?铁矿石含铁量测定方法新工艺 ?基因工程干扰素生产工艺研究 提问的目的：突出检索技术直接是为毕业专题服务，这是一门技术。提问二：信息检索课是什么？ 学生如是说： 文献检索课程是井底之蛙的升降机，是雄鹰的翅膀，是横跨天堑的桥梁。 针对某一课题，通过电子检索查阅有关资料，才知道知识的浩瀚，才知道世界的宽广，才知道“山外青山，楼外楼”。 它是我在大学期间所学的最重要，最有用的课程之一，有了它，我们将会受益终生。教会我们一种方法，一种主动 了解外界，提高自己，放眼世界的方法。 检索不仅是我们学习的制胜法宝，更是一条贯穿我们生活的红线。正因为有了这门课的学习，现在大脑的检索意识 就比较强烈，越搜越快！前几天，问同学借自行车，他告 诉我车子大致地点，是永久牌，有车栏，略有一点蓝。到 了现场，脑海中一下就有了先找有栏的，再找蓝颜色的， 最后确定是不是永久的，很快就找到了。 我爱检索，就像爱自己的生命一样。 最后我想说，我们是幸运的！我们学到了一门真正有用的课，它对我的影响和帮助将是伴随我一身的。 提问三：借鉴与创新的关系？ 科学研究是“站在前人肩膀上”的事业，而创新又是科学研究的灵魂，即要求“前无古人”。 时间分配 2min 引导学生回答 8min 10min 通过往届学生对信息检索课的评价能够激起学生学习这门课的兴趣，也可以突出这门课对个人的作用。 10min 通过提问让学生
包装设计外文翻译文献(文档含中英文对照即英文原文和中文翻译)
包装对食品发展的影响 消费者对某个产品的第一印象来说包装是至关重要的，包括沟通的可取性，可接受性，健康饮食形象等。食品能够提供广泛的产品和包装组合，传达自己加工的形象感知给消费者，例如新鲜包装/准备，冷藏，冷冻，超高温无菌，消毒（灭菌），烘干产品。 食物的最重要的质量属性之一，是它的味道，其影响人类的感官知觉，即味觉和嗅觉。味道可以很大程度作退化的处理和/或扩展存储。其他质量属性，也可能受到影响，包括颜色，质地和营养成分。食品质量不仅取决于原材料，添加剂，加工和包装的方法，而且其预期的货架寿命（保质期）过程中遇到的运输和储存条件的质量。越来越多的竞争当中，食品生产商，零售商和供应商；和质量审核供应商有着显著的提高食品质量以及急剧增加包装食品的选择。这些改进也得益于严格的冷藏链中的温度控制和越来越挑剔的消费者。 保质期的一个定义是：在规定的贮存温度条件下产品保持其质量和安全性的时间。在保质期内，产品的生产企业对该产品质量符合有关标准或明示担保的质量条件负责，销售者可以放心销售这些产品，消费者可以安全使用。 保质期不是识别食物等产品是否变质的唯一标准，可能由于存放方式，环境等变化物质的过早变质。所以食物等尽量在保质期未到期就及时食用。包装产品的质量和保质期的主题是在第3章中详细讨论。
包装为消费者提供有关产品的重要信息，在许多情况下，使用的包装和/或产品，包括事实信息如重量，体积，配料，制造商的细节，营养价值，烹饪和开放的指示，除了法律准则的最小尺寸的文字和数字，有定义的各类产品。消费者寻求更详细的产品信息，同时，许多标签已经成为多语种。标签的可读性会是视觉发现的一个问题，这很可能成为一个对越来越多的老年人口越来越重要的问题。 食物的选择和包装创新的一个主要驱动力是为了方便消费者的需求。这里有许多方便的现代包装所提供的属性，这些措施包括易于接入和开放，处置和处理，产品的知名度，再密封性能，微波加热性，延长保质期等。在英国和其他发达经济体显示出生率下降和快速增长的一个相对富裕的老人人口趋势，伴随着更加苛刻的年轻消费者，他们将要求和期望改进包装的功能，如方便包开启（百货配送研究所，IGD）。 对零售商而言存在有一个高的成本，供应和服务的货架体系。没有储备足够的产品品种或及时补充库存，特别是副食品，如鲜牛奶，可能导致客户不满和流失到竞争对手的商店，这正需要保证产品供应。现代化的配送和包装系统，允许消费者在购买食品时，他们希望在他们想任何时间地点都能享用。近几年消费者的选择已在急剧扩大。例如在英国，20世纪60年代和90年代之间在一般超市的产品线的数量从2000年左右上升到超过18000人（INCPEN）。 自20世纪70年代以来，食品卫生和安全问题已成为日益重要的关注和选择食物的驱动力。媒体所关注的一系列问题，如使用化学添
英文原文 Screw Compressor The Symmetric profile has a huge blow-hole area which excludes it from any compressor applicat -ion where a high or even moderate pressure ratio is involved. However, the symmetric profile per -forms surprisingly well in low pressure compressor applications.More details about the circular p -rofile can be found in Margolis, 1978. 2.4.8 SRM “A” Profile The SRM “A” profile is shown in Fig. 2.11. It retains all the favourable features of the symmetric profile like its simplicity while avoiding its main disadvantage,namely, the large blow-hole area. The main goal of reducing the blow hole area was achieved by allowing the tip points of the main and gate rotors to generate their counterparts, trochoids on the gate and main rotor respectively. T -he “A” profile consists mainly of circles on the gate rotor and one line which passes through the gate rotor axis.The set of primary curves consists of: D2C2, which is a circle on the gate rotor with the centre on the gate pitch circle, and C2B2, which is a circle on the gate rotor, the centre of whi ch lies outside the pitch circle region.This was a new feature which imposed some problems in the generation of its main rotor counterpart, because the mathematics used for profile generation at tha -t time was insufficient for general gearing. This eccentricity ensured that the pressure angles on th -e rotor pitches differ from zero, resulting in its ease of manufacture. Segment BA is a circle on th -e gate rotor with its centre on the pitch circle. The flat lobe sides on the main and gate rotors were generated as epi/hypocycloids by points G on the gate and H on the main rotor respectively. GF2 is a radial line at the gate rotor. This brought the same benefits to manufacturing as the previously mentioned circle eccentricity on Fig. 2.11 SRM “A” Profile
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