1887

oa Civil Engineer in South Africa - Velocity distribution in open channels : analysis by the finite element method

 

Abstract

The finite element method is used to determine the velocity distribution in open channels of arbitrary cross-section, with turbulent flow conditions. Secondary flows which occur in turbulent conditions are neglected in this analysis as they do not affect the accuracy of the results significantly.


The turbulent flow condition has been modelled as a general equation of motion. This equation is solved numerically by the finite element method at a discrete number of co-ordinate positions. The eddy viscosity is used to account for the effect of turbulence on the mean flow. To overcome the rapid variation of the velocity close to the wall, which would require very small elements, the boundary of the finite element model has been situated at a prescribed distance therefrom.
The velocity distribution has been determined for different channel cross-sections using triangular finite elements. The results of this analysis compare well with those obtained from field measurements.

Die eindige elementmetode word gebruik om die vloeidistribusie in oop kanale van 'n willekeurige dwarssnit met turbulente vloeitoestande te bepaal. Sekondêre vloei wat in turbulente toestande voorkom, word in hierdie ontleding veronagsaam aangesien dit nie die akkuraatheid van die resultate aansienlik beïnvloed nie.


Die turbulente vloeitoestand is as 'n algemene vergelyking van beweging ontwikkel. Hierdie vergelyking word deur die eindige elementmetode by 'n bepaalde aantal koördinaatpunte numeries opgelos. Die invloed van turbulensie op die gemiddelde vloei word bepaal deur werwelviskositeit in ag te neem. Ten einde die skielike snelheidsverandering naby die wal wat baie klein elemente sou vereis te oorkom, is die grens van die eindige elementmodel op 'n voorgeskrewe afstand van die wal geplaas.
Die vloeidistribusie is vir verskillende kanaaldwarssnitte deur middel van driehoekige eindige elemente bepaal. Die resultate van hierdie ontleding vergelyk goed met dit wat van veldwaarnemings verkry is.

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/content/civeng1/22/11/EJC24790
1980-11-01
2016-12-03
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