Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2002. / 198 leaves double sided printed, preliminary pages i-xx and numberd pages 1-1-12-6.Includes bibliography. List of tables, figures and appendices and acronyms. Scanned with a HP Scanjet 8250 Scanner to pdf format (OCR). / ENGLISH ABSTRACT: In this study the numerical short wave model SWAN is evaluated for application to a
selected coastal region in South Africa. The aim of this study was to evaluate the
degree of accuracy with which SWAN can simulate prototype nearshore wave spectra
and wave parameters (e.g. wave height, mean wave direction and mean wave period)
for an Algoa Bay field case. Algoa Bay represents a typical deep, sheltered
embayment on the South African south coast, which is exposed to high-energy swell.
Sensitivity analyses on various wave-related processes were also done, with the aim of
establishing the dominant physical processes and appropriate model setup for the
Algoa Bay field case. With the dominant wave-related processes and appropriate
model setup for the Algoa Bay field case established, selected final runs were
performed to determine the degree of accuracy with which SWAN can simulate
prototype conditions, by comparing its results with available field recordings.
This study comprises a review of the SWAN evaluation work conducted to date by
others, an overview of South African coastal conditions, and numerical model
simulations. The model simulations, which represent the main focus of this study, were
conducted for a selection of available offshore wave conditions (at 85 m water depth)
observed during the Algoa Bay field case and were compared to available nearshore
observations (at 17 m water depth). Environmental conditions of waves, wind and
currents were included in these simulations. The study focuses on model application
and sensitivity analysis, rather than model development, and includes evaluation of all
relevant processes, without focussing on any specific model aspect.
The results of this study show that SWAN simulations correlated well with observations
at the nearshore station in Algoa Bay, both in wave spectral shape and its associated
parameters. Dominant processes identified for the field case were depth-induced
refraction, bottom friction and directional spreading. This finding agrees with those of
previous evaluations of SWAN and previous modelling experience by others. It is
shown that high-energy swell is relatively more sensitive to the choices of model setup
than wind sea. Based on the simulation results of high-energy swell, it is concluded
that the calculation of depth-induced refraction in SWAN seem to contain a degree of
inaccuracy. It is also concluded that the findings of this study could be used as a
guideline to SWAN modelling studies along the South African south coast. / AFRIKAANSE OPSOMMING: In hierdie studie word die toepassingsmoontlikhede van die numeriese kortgolf model
SWAN vir 'n geselekteerde gedeelde van die Suid-Afrikaanse kuslyn beoordeel. Die
doel van hierdie studie is om die vlak van akkuraatheid waarmee SWAN prototipe
golfspektra en golfparameters (bv. golfhoogte, gemiddelde golfrigting en gemiddelde
golfperiode) in die vlakwater kan simuleer te beoordeel, vir 'n Algoabaai gevallestudie.
Algoabaai verteenwoordig 'n tipiese diep, beskermde baai aan die Suid-Afrikaanse
kuslyn, wat blootgestel is aan hoe-energie deining. Sensitiwiteitstoetse is ook
uitgevoer vir verskillende golfprosesse, met die doel om die dominante fisiese prosesse
en gepaste modelopstelling vir die Algoabaai gevallestudie te vind. Nadat die
dominante golfprosesse geidentifiseer is, en die toepaslike modelopstelling gevind is,
is finale simulasies uitgevoer vir geselekteerde gevalle om die mate van akkuraatheid
te bepaal waarmee SWAN prototipe kondisies kan simuleer, deur simulasie resultate
met beskikbare veldmetings te vergelyk.
Hierdie studie bestaan uit 'n samevatting van die evaluasiewerk verrig op SWAN deur
andere, 'n samevatting van golf-, wind- en stroomtoestande aan die Suid-Afrikaanse
kus en numeriese modelsimulasies. Die modelsimulasies, wat die hooffokus van
hierdie studie is, is uitgevoer vir 'n seleksie van beskikbare diepsee golftoestande (in
85 m waterdiepte) uit die Algoabaai gevallestudie en is vergelyk met beskikbare
vlakwater metings (in 17 m waterdiepte). Omgewingstoestande van golwe, wind en
seestrome is ingesluit in hierdie simulasies. Die studie fokus op modeltoepassing en
sensitiwiteits-analise, eerder as modelontwikkeling, en behels die beoordeeling van alle
toepaslike modelprosesse, sonder om te fokus op enige spesifieke model aspek.
Die resultate van hierdie studie toon aan dat die SWAN simulasies goed korrileer met
vlakwater meetings in Algoabaai, vir beide golfspektraalvorm en verwante
golfparameters. Bodemrefraksie, bodemwrywing en rigtingsspreiding is geidentifiseer
as dominante modelprosesse. Hierdie resultaat kom ooreen met bevindings van
vroeere beoordeling van SWAN en modelleer-ervaring deur andere. Dit word
aangetoon dat hoe-energie deining relatief meer sensitief is vir modelopstelling as
wind-see. Gebasseer op resultate van simulasie met hoe-energie deining, word die
gevolgtrekking gemaak dat die berekening van bodemrefraksie in SWAN 'n mate van
onakkuraatheid toon. Die gevolgtrekking word ook gemaak dat die resultate van
hierdie studie as riglyn gebruik kan word vir modelleerwerk met SWAN aan die Suid-Afrikaanse suidkus.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/3632 |
| Date | 03 1900 |
| Creators | Van der Westhuysen, A. J. |
| Contributors | Bosman, D. E., University of Stellenbosch. Faculty of Engineering. Dept. of Civil Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | University of Stellenbosch |
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