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### Orifice and hydraulic coefficients

The orifice is a small opening in the wall or base of a vessel through which the fluid flows. A mouthpiece is an attachment in the form of a small tube or pipe fixed to the orifice. Its length is usually two or three times the diameter of orifice. It is used to increase the amount of discharge.

### Hydraulic coefficients

1. Coefficient of contraction :- It is defined as the ratio of area of jet at vena contracta (the points at which the streamlines first become parallel is called vena contracta) to the area of orifice.
2. Coefficient of velocity :- It is defined as the ratio of the actual velocity of the jet at vena contracta to the theoretical velocity.
3. Coefficient of discharge(Cd) :- It is defined as the ratio of the actual discharge through the orifice to the theoretical discharge. The coefficient of discharge is equal to the product of coefficient of contraction and coefficient of velocity.
4. Coefficient of resistance :- It is defined as the ratio of loss of head in the orifice to the  head of water available at the exit of orifice.
NOTE :- The coefficient of velocity is determined experimentally by using the following relation

### Important expressions used in Orifices and Mouthpieces\

#### g) Discharge through the internal mouthpiece is an internal mouthpiece NOTE:-
1. The re-entrant or Borda's mouthpiece is an internal mouthpiece.
2. If the jet of the liquid after contraction does not touch the sides of the mouthpiece, then the mouthpiece, is said to be running free. In this case, the length of mouthpiece is equal to diameter of the orifice.
3. If the jet of the liquid after contraction expands and fills up the whole mouthpiece, then the mouthpiece is said to be running full. In this case, the length of mouthpiece is more than three times the diameter of orifice

### Correction due to curvature and refraction AND combined correction in surveying

In geodetic surveying, error due to curvature and refraction is taken into action when the area is greater than 256 km²   Correction due to curvature (Cc)             Error due to curvature is taken into action because during leveling with theodolite    or Autolevel the horizontal line and level line do not coincide. Level line is curved line parallel to the earth surface and horizontal line is straight line.               this correction is given by Cc =0.07849 d² OR 0.0785d²                                                                 here, d is the linear distance (in km)   Correction due to refraction (Cr)             Error due to refraction is taken into action due to the changing of medium of light either from a denser medium to lightier medium or viceversa.                    it is 1/7 of correction due to curvature                                               1/7x(0.785 d²)                                                   it is equals to 0.112d²

### Prestressed concrete

The basic concept of prestresssing the concrete consists in introducing the artificially the compressive stresses in a structure before it is loaded. The tensile stresses in the prestressed concrete structure may be reduced to a great extent or even entirely eliniminated depending upon the magnitude of prestressing. In a prestressed concrete structure, the cost of supporting structure and foundation is reduced, dead load of structure is reduced and cracking of concrete is avoided. The high strength concrete and high tensile steel should be used in a prestressed concrete member. According to Indian standards, the cube strength of the concrete used should bot be less  than 35N/mm 2 . The ultimate strength of high tensile steel wires used in prestressing varies from 1500N/mm 2 for 8mm diameter bars to 2350N/mm 2 for 1.5 mm diameter bars. The various methods adopted in prestresssing are as follows: Pre-tensioning The method of providing desired amount of compressive stress in

### Estimation of maximum flood discharge

The following empirical formulae may be adopted to compute the maximum flood discharge: Dicken's formula Ryve's formula Inglis formula Nawab Jang Bahadur formula Fanning's formula Fuller's formula  1) Dicken's formula According to Dicken's formula, the flood discharge (Q) in cumecs is given by The value of C taken as 11.4 for Northern India, 13.9 to 19.5 to Central India and 22.5 to 25 for Western Ghats 2) Ryve's formula According to Ryve's formula, for Madras catchments, the flood discharge (Q) in cumecs is given by The value of C is taken as 6.75 for areas within 24 km from the coast, 8.45 for areas within 24 km to 161 km form the coast and 10.1 for limited areas near hills 3) Inglis formula According to Inglis formula, the flood discharge (Q) in cumecs is given by This formula is used for estimating flood discharge for the catchments of former Bombay presidency. 4) Nawab Jang Bahadur formula According to Nawab Ja