2022年热能与动力工程专业英语-翻译 .docx

精选学习资料 - - - - - - - - - 1.3 The Characteristics of Fluids 流体的特点subside ：下沉、沉淀、减退、衰减；constituent ：组成的；continuum ：连续体；tangential ：切向的；vessel：容器；hypothetically ：假设地、假想地；restrain ：限制、约束；tar ：焦油、柏油；sphere ：球、球体；equilibrium ：平稳,均衡；pitch ：树脂；microvolume ：微元体积；interface ：相互关系、分界面；imperceptibly ：发觉不到的, 微小的；rarest ：最稀奇的,虽宝贵的molecule ：微小颗粒、分子；restore ：复原；A fluid is a substance which may flow; that is, its constituent particles may continuously change their positions relative to one another. Moreover, it offers no lasting resistance to the displacement, however great, of one layer over another. This means that, if the fluid is at rest, no shear force that is a force tangential to the surface on which it acts can exist in it. A solid, on the other hand, can resist a shear force while at rest; the shear force may cause some displacement of one layer over another, but the material does not continue to move indefinitely. In a fluid, however, shear forces are possible only while relative movement between layers is actually taking place. A fluid is further distinguished from a solid in that a given amount of it owes its shape at any particular time to that of a vessel containing it, or to forces which in some way restrain its movement. 流体是可以流淌的物质,也就是说,组成流体的质点可以连续的转变它们的相对位置；而且,不管层与层之间的相对位移有多大都不会产生长久的抗击力；这意味着流体在静止状态下是不会存在剪切力的 剪切力是与其作用外表相切的力；另一方面, 固体在静止时却可以抗击剪切力,其中的剪切力也可以使层与层之间发生相对位移,但是固体材料却不肯定会有连续的运动；然而在流体中,只有当层与层之间有相对运动产生时才会有剪切力存在；流体和固体的进一步区分仍在于在特定的时刻,确定数量的流体其外形取决于承载它的容器,或者取决于一些限制其运动的力；The distinction between solids and fluids is usually clear, but there are some substances not easily classified. Some fluids, for example, do not flow easily: thick tar or pitch may at times appear to behave like a solid. A block of such a substance may be placed on the ground, but, although its flow would take place very slowly, yet over a period of time-perhaps several days-it would spread over the ground by the action of gravity, that is, its constituent particles would change their relative positions. On the other hand, certain solids may be made to flow when a sufficiently large force is applied; these are known as plastic solids. 固体和流体之间的区分通常是很明显的,但是也有些物质难于归类；比方说有些流体并不易流淌,如重油和树脂有时候会表 现得像固体一样,像这样的一块物质假如放在地面上,虽然它的流淌发生的特别缓慢,要经过很长的一段时间也 许要好几天,但是在重力的作用下它仍旧会在地面上扩散开来,也就是说,它的组成质点会转变它们之间的相对位置；另一方面,某些固体当足够大的力作用时也会“ 流淌” ,这就是我们所知的“ 塑性固体” ；Even so, the essential difference between solids and fluids remains. Any fluid, no matter how thick is, begins to flow, even if imperceptibly, under the action of the slightest net shear force. Moreover, a fluid continues to flow as long as such a force is applied. A solid, however, no matter how plastic it is, does not flow unless the net shear force on it exceeds a certain value. For forces less than this value the layers of the solid move over one another only by a certain amount. The more the layers are displaced from their original relative positions, however, the greater are the forces resisting the displacement. Thus, if a steady force is applied, a state will be reached in which the force resisting the movement of one layer over another balance the force applied and so no further movement of this kind can occur. If the applied force is then removed, the resisting forced will tend to restore the solid body to its original shape. 即便如此,固体和 流体之间依旧有本质的差异；任何流体,无论多“ 稠” 或者粘性多大,在最微小的剪切力作用下都会流淌,即便这种流淌是极其微小的；而且,只要这种力连续作用,流体就会连续流淌；然而对于固体,不管它的可塑性有多强,只 有当作用其上的净剪切力超过肯定数值后才会流淌,而小于该值的力所引起的固体层之间的相对移动是有限的；层偏离原始位置的程度越大,抗击这种变形的力也就越大；因此,当一恒定力作用时,就会到达这样一个状态：即会产生一个抗击这种层间相对运动的力以平稳所施加的外力,所以不会产生进一步的运动；假如将所施加的外力移除,抗击力将会使固体复原到它的原始外形；In a fluid, however, the forces opposing the movement of one layer over another exist only while the movement is taking place, and so static equilibrium between applied force and resistance to shear never occurs. Deformation of the fluid takes place continuously so long as a shear force is applied. But if this applied force is removed the shearing movement subsides and, as there are then no forces tending to return the particles of fluid to their original relative positions, the fluid keeps its new shape. 然而,在流体中,只有当层间相对运动发生时才会存在这种阻挡运动的力；所以不会存在这种外力和抗击力之间的静态平稳；只要有剪切力作用,流名师归纳总结 - - - - - - -第 1 页,共 13 页精选学习资料 - - - - - - - - - 体便会产生连续变形；但是假如将外力移除,剪切运动便会减退,而且由于这时没有使流体质点回到它们初始位置的力,所以流体将保持它的“ 新” 外形；Fluids may be sub-divided into liquids and gases. A fixed amount of a liquid has a definite volume which varies only slightly with temperature and pressure. If the capacity of the containing vessel is greater than this definite volume, the liquid occupies only part of the container, and it forms an interface separating if from its own vapour, the atmosphere or any other gas present. 流体可以划分为液体和气体；肯定数量的液体其所占据的体积也是肯定的,它随温度和压力的变化很小；假如容器的体积大于这个肯定的体积,那么液体占据的只是 容器的一部分,而且会形成一个分界面将液体与该液体的蒸汽、空气或其它存在的气体分开；On the other hand, a fixed amount of a gas, by itself in a container, will always expand until its volume equals that of the container. Only then can it be in equilibrium. In the analysis of the behaviour of fluids the most important difference between liquids and gases is that, whereas under ordinary conditions liquids are so difficult to compress that they may for most purposes be regarded as incompressible, gases may be compressed much more readily. Where conditions are such that an amount of gas undergoes a negligible change of volume, its behaviour is similar to that of a liquid and it may then be regarded as incompressible. If, however, the change in volume is not negligible, the compressibility of the gas must be taken into account in examining its behaviour.而另一方面,容器内肯定数量的气体就通常都要膨胀到和容器相等的体积；这样它才会到达平稳状态；在分析流体特性时,液体和气体之间最重要的差异在于：鉴于在通常 的条件下液体是难以压缩的,因此常常将液体认为是不行压缩流体,而气体就简洁压缩的多；当肯定量的气体其体积变化可以被忽视的情形下,气体的表现和液体类似,因此也可以认为是不行压缩的；然而,假如体积的变化不行忽视,那么在分析其行为特点时就必需考虑气体的压缩性；In considering the action of forces on fluids, one can either account for the behavior of each and every molecule of fluid in a given field of flow or simplify the problem by considering the average effects of the molecules in a given volume. In most problems in fluid dynamics the latter approach is possible, which means that the fluid can be regarded as a continuum-that is, a hypothetically continuous substance. 在考虑作用于流体上的力时,可以用给定流淌区域内的流体上每个分子的行为来说明,也可以只考虑给 定体积内分子的平均效应而使问题得以简化；在流体动力学的很多问题中后一种方法是可行的,这意味着将流体看作是连续介质即一种假想的连续介质；The justification for treating a fluid as a continuum depends on the physical dimensions of the body immersed in the fluid and on the number of molecules in a given volume. Let us say that we are studying the flow of air past a sphere with a diameter of 1 cm. A continuum is said to prevail if the number of molecules in a volu me much smaller than the sphere s is sufficiently great so that the average effects pressure, density, and so on within the volume either are constant or change smoothly with time. 是否可以将流体看作是连续介质取决于浸入流体的物体的尺寸和给定体积内的分子数目；比方我们现在讨论空气流过一个直径为 1 厘米的球体的问题；假如在比球的体积小得多的体积内流体分子数目足够多以至于该体积的平均效应压力、密度等等为常数或者随时间缓慢变化,就认为该流体是连续介质；The number of molecules in a cubic meter of air at room temperature and sea-level pressure is about 1025. Thus the number of molecules in a volume of 10-19 m3 about the size of a dust particle, which is very much smaller than the sphere would be 106 . This number of molecules is so large that the average effects within the microvolume are indeed virtually constant. On the other hand, if the 1 cm sphere were at an altitude of 305 km, there would be only one chance in 108 of finding a molecule in the microvolume, and the concept of an average condition would be meaningless. In this case, the continuum assumption would not be valid for fluid flow except in the rarest conditions, such as those encountered in outer space. 在室温、海平面压 力下,每平方米空气中的分子数大约为 1025 个,因此 10-19 m3 体积中的分子数为 106 个 10-19 m3 大约是一个 灰尘的体积, 这要远远小于上面所说的球体；如此多的分子数目使得在该微元体积内的平均效应实际上为常数；另 一方面, 假如 1 厘米的球体被置于海拔 305 千米处,那么在该微元体积内发觉一个分子的概率只有 108 分之一, 所 以平均状态的概念也就没有任何意义；在这种情形下,除了像在外层空间这种空气特别淡薄的情形之外,流体流淌 的连续性假设都是无效的；1.4 Scope Significance and Trend of Fluid Mechanics Fluid mechanics,as the name indicates,is that branch of applied mechanics which is concerned with the statics and dynamics of liquids and gases.Dynamics,the study of motion of matter,may be divided into two part-dynamics of rigid bodies and dynamics of non-rigid bodies. The latter is usually further divided into two general classifications-elasticitysolid elastic body and fluid mechanics. 流体力学,正如名字所指,是和液体,气体的静态和动态有关的应用力学的分支；动力学,物体运动的讨论,可以名师归纳总结 - - - - - - -第 2 页,共 13 页精选学习资料 - - - - - - - - - 分为两部分刚性物体动力学和无刚性物体动力学；后者通常进一步分为两大一般类别；弹性固定弹性物体和流淌力学；The subject of fluid mechanics can be subdivided into two broad categories: hydrodynamics and gas dynamics. Hydrodynamics deals primarily with the flow of fluids for which there is virtually no density change,such as liquid flow or the flow of gas at low speeds.Hydraulics,for example, the study of liquid flows in pipes or open channels, falls within this category. The study of fluid forces on bodies immersed in flowing liquids or in low-speed gas flows can also be classified as hydrodynamics. 流体力学学科可以再分为两大广泛的类别：水动力学和气体动力学；水动力学主要处理的是实际没有密度变化的流体流淌；例如液体和气体在低速情形下的流淌；水动力学,例如在管道和开放式通道中液体流淌的讨论,属于这一 类别；对浸入流淌液体和低速流淌其他的物体所受流体力的讨论也可以分类为水动力学；Gas dynamics,on the other hand, deals with fluids that undergo significant density changes.High-speed gas flowing through a nozzle or over a body ,the flow of chemically reacting gases, or the movement of a body through the low density air of the upper atmosphere falls within the general category of gas dynamics. 气体动力学,另一方面,处理经受有效密度变化的流体；高速气体流淌通过一个喷嘴或者拂过一个物体,发生化学反应气体的流淌,物体通过更高大气中低密度空气中的运动属于气体动力学的一般类别；An area of fluid mechanics not classified as either hydrodynamics or gas dynamics is aerodynamics, which deals with the flow of air past aircraft or rockets,whether it be low-speed incompressible flow or high-speed compressible flow. 流体力学中即不归类水动力学也不属于气体动力学的那一领域称为航空动力学,是否它是低速不行压缩流淌或者是高速可压缩流淌；它处理穿过飞机和火箭的空气流淌,There are, however,two major aspects of fluid mechanics which differ from solid-body mechanics.The first is the nature and properties of the fluid itself, which are very different from those of a solid. The second is that, instead of dealing with individual bodies or elements of known mass, we are frequently concerned with the behavior of a continuous stream of fluid, without beginning or end. 然而,流体力学不同于固体力学有两个主要方面；第一个是流体的本质和性能,他和那些固体有很大不同；其次个 是,我们常常关注流体的一个连续单位的行为,没有首节和末端而不是处理单独物体或是已知固体的组分；Knowledge and understanding of the basic principles and concepts of fluid mechanics are essential in the analysis and design of any system in which a fluid is the working medium. Many applications of fluid mechanics make it one of the most vital and fundamental of all engineering and applied scientific studies. The flow of fluids in pipe and channels makes fluid mechanics of importance to civil engineers. The study of fluid machinery such as pumps,fans, blowers, compressors,turbines, heat exchangers,jet and rocket engines, and the like, makes fluid mechanics of importance to mechanical engineers.Lubrication is an area of considerable importance in fluid mechanics.The flow of air over objects,aerodynamics ,is of fundamental interest to aeronautical and space engineers in the design of aircraft,missiles and rockets.In meteorology,hydrology and oceanography the study of fluids is basic since the atmosphere and the ocean are fluids. And today in modern engineering many new disciplines combine fluid mechanics with classical disciplines. For example,fluid mechanics and electromagnetic theory are studied together as magnetogas-dynamics. In new types of energy conversion devices and in the study of stellar and ionospheric phenomena, magnetogasdynamics is vital. 流体力学最基本的原理和概念的学问和懂得在以流体作为工作介质的任何系统的分析和设计中是特别重要的；很多流体力学的应用是它成为全部工程和运用科学讨论中最重要的基础的一环；流体在管子和隧道中的流淌使流体力学对土木工程师很重要；流体机械的讨论,例如泵,风扇,鼓风机,压缩机,涡轮机,热交换器,喷气飞机和火箭引擎等等,使流体力学对机械工程师很重要；润滑在流体力学中是相当重要的一个领域；拂过物体的空气流淌,航空动力学是空气动力学和空间工程师在飞机,导弹,火箭的设计中的基本爱好；在气象学,水文学,海洋学中,流体的讨论是基本由于大气和海洋是流体；在当今现代工程中,很多新学科是结合了流体力学和传统学科；例如,流体力学和电磁理论放在一起讨论称为磁性气体动力学；在能量转换装置的新类型和在星球的讨论以及电离现象中,磁性气体动力学很重要；名师归纳总结 - - - - - - -第 3 页,共 13 页精选学习资料 - - - - - - - - - On the contrary ,the collapse of the Tacoma Narrows Bridge in U,S.A. is evidence of the possible consequences of neglecting the basic principles of fluid mechanics .On a memorable day in November 1940.,Nature decided to teach us all a lesson.The wind could not even be considered strong on that day,but it happened to disturb the great Tacoma Narrows suspension bridge cyclically with a frequency close to the bridges natural frequency of vibration.The entire bridge started to dance. Traffic was stopped;and an astonished public watched the bridge itself to pieces. 相反地, 美国塔科马海峡吊桥的垮塌是无视流体动力学基本原理的可能结果的证明；在 1940 年 9 月,难忘的一天,大自然打算教我们一堂课,在那天风据说不是很强,但是它刚好以一个接近桥自然振动频率的频率周期性的打扰宏 伟的塔科马吊桥；整座桥开头摇动,交通停止,一个震动的公民看着桥身分裂成碎片；We see that a good familiarity with fluid mechanics is essential to the modern engineer and scientist,and it is probably obvious that fluid mechanics and its applications is a broad subject with far-flung fields of specialization.What we should do is to master the basic concepts and principles of fluid mechanics.Once these fundamentals are mastered more advanced books and research literature may be studied to increase ones understanding of more specialized aspects of fluid mechanics. 我们看到,很好的熟识流体力学对现代工程师和科学家至关重要；并且很明显,流体力学和他的应用是具有专业户 的长远领域的广泛学科；我们应当做的是把握最基本的流体力学的概念和原理；一旦这些基础的东西被把握,更多 先进的书籍和讨论文献可以被讨论用来增加流体力学更多专业化方面的懂得The significance of fluid mechanics becomes apparent when we consider the vital role it plays in our everyday lives.When we turn on our kitchen faucets,we activate flow in a complex hydraulic network of pipes,valves, and pumps.When we flick on a light switch ,we are drawing energy either from a hydroelectric source that operates by the flow of water through turbines or from a thermal power source derived from the flow of steam past turbine blades. 流体力学的意义变得很明显,当我们摸索它在我们日常生活中起到的重要作用；当我们打开我们厨房的插口,我们 推动在一个复杂水力管网,阀和泵中的流淌；当我们弹开一个灯的开关时,我们正在引导自由通过涡轮机的水流淌 操作的水力源或者来自起源于流过涡轮叶片蒸汽流淌的热力源；When we drive our cars, pneumatic tires provide suspension, hydraulic shock absorbers reduce road shocks,gasoline is pumped through tubes and later atomized,and air resistance creates a drag on the auto as a whole;and when we stop, we are confident in the operation of the hydraulic brakes,Very complex fluid processes are also involved in the manufacture of the paper on which this book is printed, And our very lives depend on a very important fluid mechanic process-the flow of blood through our veins and arteries.