Hydraulics, with working tables; by Bellasis Edward Skelton 1855-

Author:Bellasis, Edward Skelton, 1855- [from old catalog]
Language: eng
Format: epub
Tags: Hydraulics
Publisher: London, Rivingtons
Published: 1903-03-25T05:00:00+00:00

Pig. 103.

Pig. 104.

Digitized by

Google

4. Irregular SectiosB.—The cross-section of a stream may be called 'irregular' when the border contains undulations or saliences of such a character as to divide the section into well-marked divisions (Fig. 105). .^ In this case the water in each division has a velocity of its own, and in order to calculate the discharge of the whole stream by the use of the formula V^Cs]^^ it is necessary to consider each division separately, finding its hydraulic radius from its area and border. The length AB is not included in the border of either division, since if there is any friction along it, it accelerates the motion in one division and retards it in the other. If ^i ^2 s^re the sectional areas, and R^ ^% the hydraulic^radii,

The discharge of the whole channel, calculated from the equation Q=CA jJBS, equals Qi+Q^ only when -Ri=^8, otherwise it is less. The more B^ and B^ differ, the more Q differs from Qi+Qt, and for given values of ^1 and B^ the difference is greatest when A^ssA^, If either Ai or A^ is relatively very small, the difference between Q and Qi+Q^ will be small. It may happen that Bi and Bt differ greatly with low supplies, and not much with high supplies. If without altering either the length of the border or the sectional area of the stream the border be changed to CDEF^ the section is no longer irregular, and the equation F= C JBS is the proper one to use. There are thus two cross-sections with equal values of B and different mean velocities, that is, different values of C. Even in a regular section the same principle holds good. The discharge is the sum of the discharges of a number of parts, and may be affected by a change in the form of the border alone. (See also art. 13.)

An instance of an irregular section occurs when a stream overflows its banks (Fig. 106). As the overflow occurs the border of the whole stream may increase far more

. -, , _ Fio. 106.

rapidly than the sectional area, and Q, if calculated as a whole, would diminish with rise of the water-level. The velocity and discharge of the main

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.