Thesis (MScIng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: The primary aim of the research was to determine the optimum diversion location in a
curved channel to minimise the abstraction of sediment. The secondary aim was to
determine the optimum diversion angle for a diversion channel located on the outside
of a bend at the optimum diversion location.
The velocity distribution in the curved channel was investigated to try obtain a better
understanding of curvilinear flow. The scour patterns in the channel were monitored
in order to compare them with the measured velocity distributions.
Simulations were carried out with the DELFT 3D (hydrodynamics) and Mike21C
(sediment dynamics) modelling programmes and compared with the results obtained
from laboratory experiments and with existing empirical formulas.
The optimum diversion location was found to be located on the outside of the bend in
the downstream section of the bend. Three main scour zones were identified with the
third scour zone at the location of the maximum velocity. The location of the
maximum velocity was found to be relatively constant with varying Froude numbers,
but moving in the downstream direction with increasing radius of curvature-to-width
ratio. The velocity distributions in the horizontal and vertical planes are well defined
and correspond to descriptions in the literature.
It is evident that the diverted discharge ratio increases with an increase in the
diversion angle while it decreases with an increase in Froude number. Higher Froude
numbers in the curved channel lead to more favourable conditions for the diversion of
water. The diversion does not influence the secondary flow patterns (for the range of
Diversion Discharge Ratio’s tested) and that the maximum velocity zone stayed in the
same location as in the tests without a diversion.
The hydrodynamics of the laboratory experiments were well simulated with the
DELFT 3D hydrodynamic model, using three-dimensional and two-dimensional
formulations. Mike21C was used to simulate the sediment dynamics of some of thelaboratory experiments that gave relatively good agreement with experimental data.
A two-dimensional depth averaged model could therefore be used with reliability to
simulate field conditions in relatively shallow rivers, and is preferred to empirical
methods to predict maximum scour that were calibrated under very specific hydraulic
conditions. / AFRIKAANSE OPSOMMING: Die primêre doel van navorsing was om die optimum uitkeer-posisie in ‘n draai te
bepaal om sodoende sediment onttrekking te minimiseer. Die sekondêre doel was om
die optimum uitkeringshoek vir ‘n uitkeerkanaal te bepaal wat geleë is aan die
buitekant van ‘n draai by die voorgestelde optimum uitkeer-posisie.
Die snelheidsverspreiding in die draai was ook ondersoek om te probeer om
spiraalvloei beter te verstaan. Die uitskuurpatrone in die kanaal is ook gemonitor om
dit te kon vergelyk met die gemete snelheidsverspreiding.
Numeriese simulasies is gedoen met DELFT 3D (hidrodinamika) en Mike21C
(sediment dinamika) modelleringsprogrammatuur en is vergelyk met die resultate van
die laboratorium eksperimente asook met die van bestaande empiriese vergelykings.
Daar is gevind dat die optimum uitkeer-posisie aan die buitekant van ‘n draai aan die
stroomaf-kant van die draai geleë is. Drie hoof uitskurings-areas is gevind terwyl die
derde area ooreenstem met die posisie van maksimum snelheid. Die posisie waar die
maksimum snelheid voorkom is relatief konstant met ‘n verandering in Froude-getal,
maar beweeg in die stroomaf-rigting met ‘n styging in die radius-tot-wydte
verhouding. Die vertikale en horisontale snelheidsverspreiding is goed gedefinieer en
stem ooreen met soortgelyke beskrywings in die literatuur.
Die uitkeer-vloei verhouding styg met ‘n stygende uitkeerhoek terwyl dit daal met ‘n
styging in Froude-getal. Daar is ook gevind dat groter Froude-getalle meer gunstige
omstandighede skep vir die uitkeer van water. Die uitkeer-kanaal beïnvloed nie die
sekondêre vloei-patrone nie (vir die reeks van uitkeer vloei-verhoudings wat getoetsis) en die sone van maksimum snelheid bly in dieselfde omgewing vir hierdie toetse
as vir die toetse sonder ‘n uitkeer kanaal.
Die hidrodinamika van die laboratorium eksperimente is goed gesimuleer m.b.v die
DELFT 3D numeriese program, terwyl Mike21C gebruik is om die sedimentdinamika
te simuleer. Die resultate van die Mike21C simulasies vergelyk relatief goed met die
eksperimentele data en kan met ‘n redelike graad van vertroue aangewend word om
veldkondisies te simuleer in relatiewe vlak riviere. Dit word aanbeveel bo die
empiriese vergelykings om maksimum uitskuring te voorspel aangesien die empiriese
vergelykings gekalibreer is vir baie spesifieke hidroulise kondisies.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/16262 |
| Date | 12 1900 |
| Creators | Brink, C.J. |
| Contributors | Basson, G. R., University of Stellenbosch. Faculty of Engineering. Dept. of Civil Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xv, (various foliations) : ill. |
| Rights | University of Stellenbosch |
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