| Summary: | Thesis (M.Eng.)--Stellenbosch University, 2000. === ENGLISH ABSTRACT: This study entailed the investigation and evaluation of a new methodology for measuring high
discharges passing through bridges. Pressure differences generated around bridge piers have been
measured and related to the discharges. These pressure differences are mainly functions of
downstream flow conditions. The pressure differences have been converted into velocities by
applying Newton's second law expressed in terms of the laws of conservation of energy;
momentum; and of power.
The energy principle was re-evaluated following a preVIOUSstudy (Retief, 1999) on a limited
number of model pier combinations and flow conditions. Comparison of the energy approach with
newly developed theories in terms of the momentum and power laws respectively led to the
conclusion that the energy principle gave the best results. The question of applicability of the
theory to practical pier/stream width and length ratios as well as its validity under flow conditions
commonly found under flood conditions required that additional laboratory tests be done.
The energy-based discharge equation was calibrated in terms of newly selected measuring points,
different pier width and length ratios, as well as pier rotations for both super and sub-critical
downstream conditions. According to the new tests performed at the Hydraulics Laboratory of the
University of Stellenbosch on model piers, clear relationships were found between discharges and
pressure differences measured against the pier. Calibration curves for practical flow measurement
application were derived in terms of principle dimensionless parameters.
Application of the energy approach at the prototype level needs further investigation. === AFRIKAANSE OPSOMMING: Hierdie studie het behels die ondersoek en evaluering van 'n nuwe metode om hoë vloeie verby
brïïe te meet. Drukverskille wat rondom brug pylers opgewekword is gemeet en omgeskakel na
vloeie. Hierdie drukverskille is hoofsaaklik funksies van die stroomaf vloei toestande. Die
drukverskille is omgeskakel na vloeisnelhede deur die toepassing van Newton se tweede wet,
uitgedruk in terme van die behoud van energie, momentum so wel as drywing.
Die energie beginsel is weer geëvalueer sedert 'n vorige studie (Retief, 1999) gedoen is op 'n
beperkte aantal model pylerkombinasies en vloeitoestande. Hierdie energie-benadering is met nuwe
metodes vergelyk, naamlik die momentum en drywings wette. Die gevolgtrekking is gemaak dat die
energie metode die beste resultate gee. Die vraag oor die toepaslikheid van die teorie met praktiese
pyler/stroom wydte en lengte verhoudings so wel as die toepaslikheid hiervan onder die vloei
toestande wat algemeen onder vloedtoestande voorkom het addisionele laboratoriumtoetse vereis.
Die energie gebaseerde vloeivergelyking is gekalibreer in terme van nuut geselekteerde meetpunte,
verskillende pyler wydte en lengte verhoudings, asook pyler rotasies vir beide super en sub-kritiese
stroomaf toestande. Na aanleiding van die toetse gedoen in die Hidroulika Laboratorium van die
Universiteit van Stellenbosch op brugpylers, is duidelike verbande gekry tussen die vloeie en die
drukverskille soos gemeet teen die pyler. Kalibrasie-kurwes vir die toepassing van praktiese vloeimeting
is ontwikkel in terme van die toepassing van dimensielose parameters. Die toepassing van die energiebenadering op prototipe vlak verg verdere ondersoek.
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