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水利水电工程专业英语——水电站与水轮机篇 1. Energy and Power of Water Flow 1. 水流的能量和功率
As may be recalled from mechanics of fluids, the energy and power of a quantity of water in steady flow from A to B can be determined using Bernoulli’s theorem for specific energy. From the principle of conservation of energy it follows that the energy eA at A equals the energy eB at B plus the energy eAB released as the water flows from A to B. Assuming that the weight of the water is 1N, Bernoulli’s equation, which in effect expresses the law of conservation of energy, may then be written as
????+????+
????
2????????
2??
=
????+????????
+
2????????
2??
+?????? （1）
回顾流体力学，可以使用伯努利定理的比能来确定从A 到 B的一定量的稳定水流的能量和功率。根据能量守恒定律，A点的能量eA等于B点的能量eB加上水流从A到B的能量损失eAB。假设水体的质量是1N，那么实际上表述能量守恒的伯努利方程可以写作：
????+
????????
+
2????????
2??
=
????+????????
+
2????????
2??
+?????? （1）
Where ???? and ???? are respectively the elevations above a datum plane O-O of the centers of gravity of the stream cross sections at A and B(m), ????and ???? are respectively the pressures at the centers of gravity of the cross sections at A and B(Pa), ?? is the water density (kgm-3), ???? and ???? are respectively the average velocities of water at A and B(ms-1), g is the free fall accelerations (ms-2), and ???? and ???? are numerical coefficients accounting for a non-uniform velocity distribution over the cross sections (they are always larger than unity and generally range between 1.03 and 1.1).
其中????和????分别表示A和B处水流断面重心在基准面O-O以上的高程（m），????和 ????分别是A和B处水流断面重心的压力（Pa），??是水的密度（kgm-3），???? 和 ????分别是A和B处水的平均速度（ms-1），g是自由落体加速度，且????和????是考虑断面非均匀分布速度的数字系数（它们通常比单位的大，且通常范围为1.03-1.1）。
The first terms, z, on either side of Eq.(1), known as the elevation heads or potential heads, define the specific potential energy of water due to the elevation with respect to the selected datum. The second terms, ????, called the pressure heads, define the specific potential energy of water due to the respective pressure. The total specific potential energy may, therefore, be written as e=z+. It is the same for any point of a cross section, since an increase in z always
??????
??
produces a matching decrease in ????. Accordingly, the potential energy at a cross section may be evaluated in terms of the elevations of the points lying on the free surface of that cross section, assuming that ???? and e=h (where h is the elevation of the points on the free surface above the datum plane). Finally, the third terms, 2??, referred to as the velocity heads, define the specific 2????
??
??
kinetic energy of the quantity of water at the respective sections. Obviously, all the terms of Eq.(1) are measured in meters.
第一项Z在方程（1）两边都有，被称为位置水头或势头，确定了由于所选择的基准面得到高程的单位势能。第二项，被称为压力水头，确定了由于各自的压力产生的单位势能。
??????
因此，全部单位势能可以写作e=z+????。这对于一个断面任意点都是相同的，因为z的增加总是产生一个在相匹配的????的降低。相应地，某断面处势能可以以位于断面自由表面点的高程的形式提升，假设且e=h（其中h是基准面上方自由表面上点的高度）。最后，第三项，??指的????
2??
??
??2
??
??
是速度水头，确定了各断面处该质量水体的单位动能。很明显，方程（1）中所有的项都以米为单位。
Re-writing Eq.(1) for the free surface (with ????=0) yields
????+
2????????
2??
=????+
2????????
2??
+?????? （2）
Then, the lost head (or friction head) is given by
??????=?????????+
In reality, the difference
2????????
2????????
2??
?
2????????
2??
（3）
2??
?
2????????
2??
is negligibly small. So,
??????=?????????=HAB （4）
Here, HAB is the difference in elevation between the beginning and end of the portion AB (customarily referred to as the cross-head). If it is sea level (the elevation being Δ0) that is chosen as the datum plane, then hA=ΔA, hB=ΔB, and eAB=ΔA-ΔB=HAB.
对于自由表面（????=0）改写方程（1），得到
????+
那么，水头损失（或摩擦水头）即为
??????=?????????+
事实上，
2
????????
2????????
2????????
2??
=????+
2????????
2??
+?????? （2）
2??
?
2????????
2??
（3）
2??
?
2????????
2??
的差别可以忽略不计。所以，
??????=?????????=HAB （4）
此处，HAB是AB段开始和结束处的高程差（习惯上称之为水头差）。如果被选作参考平面的是海平面（高程为Δ0），那么hA=ΔA, hB=ΔB，且 eAB=ΔA-ΔB=HAB。
When the total energy of flow is desired, the respective terms in the above equations should be multiplied by the weight of the flowing fluid which depends on the discharge Q(m3s-1), meaning that over a time interval t the section A will let in, and the section B will let out, a quantity of water equal to Qt. Obviously, the weight of that volume of water is equal to Qt ??g, so the total energy (in joules) released as the water flows from A to B will be
EAB=HABQt ??g （5）
Power NAB, or the energy released per second, will be given by
NAB=
????????
HABQ ??g （6）
如果需要水流的全部能量，上述方程各项应该乘以取决于流量（m3s-1）的流体重量，意为在一个t的时间间隔内断面A处将流入、且断面B处将流出质量等于Qt的水量。很明显，该水体的重量等于Qt ??g，所以水流自A到B处释放的所有能量（单位为焦耳）将为
EAB=HABQt ??g （5）
功率NAB，或者每秒释放的能量，将表示为
NAB=
????????
HABQ ??g （6）
Since the total energy is in joules, the dimension of power is the watt (W). However, the watt is too small a unit. So, in power engineering, use is most commonly made of its multiples, such as the kilowatt(1kW=1000W) and the megawatt (1MW=1000kW=106W).
由于总量能的单位是焦耳，所以功率的单位就是瓦特（W）。然而，瓦特这个单位太小了。所以，在电力工程中，通常用它的倍数，比如千瓦（1千瓦=1000瓦）和兆瓦（1兆瓦=1000千瓦=106瓦）。
Considering that g=9.81m2s-1 and ??=1000kgm-3 (for pure fresh water), the power in kilowatts may be written as
NAB=9.81QHAB （7）
In power engineering, the common unit of measure for energy is the kilowatt-hour (1kWh=3600J). If the time interval T in question is expressed in hours, then the energy ?????? in kilowatt-hours will be given by
EAB=9.81QHABT （8）
Giving per year (T=8760h)
????????
??????=85936QHAB （9）
考虑g=9.81m2s-1 且??=1000kgm-3（对于纯鲜水），单位为千瓦的功率可以写作
NAB=9.81QHAB （7）
在电力工程中，度量能量的通常单位是千瓦·时。如果上述的时间间隔T是以小时表述的，那么以千瓦时为单位的能量??????就可以写作
EAB=9.81QHABT （8）
给定每年（T=8760小时）
????????
??????=85936QHAB （9）
Eqs. (7) and (9) are used to determine the potential of a watercourse in terms of its power or annual energy found on the basis of the average discharge through several years of record. The theoretical hydroelectric potential of a watershed, a region, or a country is evaluated by dividing the area in question into suitable sections and adding together the power and annual energy found for each section. Naturally, it seldom happens that all of the water bodies in a region can be used for power generation. The common practice is to locate the water courses (or their portions) that can be used by the industry and to determine what may be called their technical hydroelectric potential. Part of the technical potential whose development is economically advisable at a given time is termed the economic hydro potential. Of course, the last-mentioned quantity depends on the demand and overall economic situation and is, therefore, subject to certain variations.
基于若干年平均流量记录，方程（7）和（9）用于确定水系的功率或年发电量的潜力。一个流域、区域或国家的理论水电潜力是通过将上述区域分成合适的部分并将每个部分得出的功率和年发电量相加而评估的。通常来讲，很少存在某区域内的所有水体都可以用作发电的情况。通常做法是定位能够用作工业用途的水系，并确定其所谓的水电技术可开发潜力。
在给定时间经济可行的开发的技术潜力部分被称为经济水电潜力。当然，最后提到的数量决定于需求和整体经济情况，因此受到某些变量的影响。
2. Intake Structures 2. 取水建筑物
An intake structure is an arrangement by which water is satisfactorily diverted for the required use. Thus as shown is Figure 1, the intake is an arrangement which allows for water to be taken from its source and then discharged into the conveyance system from which it is led to the desired use. The desired use of water may be for domestic water supply, flood or irrigation discharge out of a dam through outlet outsluices, or for the purposes of generating electricity. 取水建筑物是通过其就可以将需要使用的水满足要求地调动的建筑物。正如图1中所示，进口就是允许从水源取水的建筑物，且随后排放到引向期望用途的输水系统内。水的期望用途可能是用作生活供水、大坝通过出水口的洪水或灌溉放水，或者是用于发电的目的。
Figure 1 Diagrammatic sketch of function of intake
图1 取水建筑物功能示意图
Irrespective of the desired use an intake structure should fulfill the following requirements: (1) assured water supply; (2) suitable quality of water; (3) control over supply of water.
The requirements of assured water supply would fix the location of the intake in (1) plan so that water is always available; (2) elevation so that the invert level of the intake is at such a location that the minimum water level is always above this invert level.
不管期望用途如何，一个取水建筑物都应该满足一下要求： （1）确保供水； （2）合适的水质； （3）控制供水。
确保供水的需求将会将取水定位于（1）总能够获得水的平面；（2）确保最低水位总是高出引水高程的高度。
The quality of water required would depend upon the use which the water is desired to be put to. In hydroelectric development general requirement for the quality of water will be that it should be free from debris, trash, ice and silt. In case of an irrigation scheme it may be desirable that the water is free from undesirable salts and other industrial effluents which harm the crop.
所要求的水质将取决于其期望的用途。在水力发电工程中通常对水质的要求时它应该