Thesis (PhD)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: All of the Ports along the South African coastline are subject to bound infragravity
wave action to a greater or lesser degree, for example, at the Ports of Saldanha Bay on
the west coast and Ngqura on the south-east coast. Saldanha Bay harbour principally
services loose- and liquid-bulk carriers and the Ngqura harbour mainly services
container ships. The long wave actions when severe cause moorings to be broken,
ships to leave the quay and loading to stop.
This research has confirmed that the sea surface is a multifractal structure
characterised by many singularities ranging from highly irregular or rough features to
smooth or calm features. Any wave train is comprised of the full range of these
features to various degrees and in varying percentages of occupancy.
Notwithstanding this problem, relatively little is known about them in the South
African context due to the fact that they cannot be visually detected and specialised,
sophisticated equipment is required to physically measure them. The country is
currently planning the development of a new port and the expansion of others for
larger ships. Under these circumstances this research is seen to be appropriate from
the point of view of obtaining a new method for the characterisation of these
hazardous wave conditions.
The objective of the research was achieved. This was to identify a set of fractal
dimensions that describe the surface geometry of a hazardous bound infragravity
wave sea state.
In order to achieve the objective, a set of fractal dimensions was firstly determined
from video imagery of an open water wave field, by analysing a set of single point
time series data derived from the imagery. This has been done in order to be able to
visually compare the derived set of fractal dimensions with video imagery of the sea surface that they represent. It also has the advantage of proving that fractal methods of
analysis are applicable for the study of sea surface single point time series data. Secondly, periods when long wave action occurs at both Saldanha Bay and Ngqura
harbours were identified by the presence of their actions in the harbours.
Thirdly, single point time series data recorded by the Council for Scientific and
Industrial Research (CSIR) were obtained during the identified periods as well as two
days before these times and fractal sets of dimensions for the periods were
determined. This was achieved by means of the following methods of analysis:
● The rescaled range (R/S) method,
● The Multifractal Detrended Fluctuation Analysis (MDFA) method,
● The Power Spectral Density (PSD) method in both the Fourier and the wavelet
domains, and
● The Wavelet Transform method.
Fourthly, the fractal data sets from each harbour were compared to confirm that the
sets of dimensions for the hazardous sea state are clearly different from those of the
non-hazardous sea state and can be used to describe the condition.
Finally, the fractal sets of dimensions for hazardous sea states at both harbours were
compared to identify any variances between them.
During the research it was found that a hazardous sea state could be profiled for
identification purposes and for complementing the currently determined significant
wave height and peak period details by means of fractal indices.
These indices were identified by comparison with a similar set of indices for nonhazardous sea states at the same location, as part of a ‘calibration’ process and clearly
identified shifts in the Holder exponents of the sea states enabled the unambiguous
identification of the hazardous condition.
Having completed the research and analysis work, the author has identified other
areas of coastal engineering, besides the identification of hazardous bound infragravity wave sea states, where a study of multifractal geometry could be applied
advantageously. / AFRIKAANSE OPSOMMING: Alle hawens langs Suid Afrika se kuslyn is tot ‘n meerdere of mindere mate
onderworpe aan gebonde infragravitasie golf aksie. Hierdie probleem is egter veral
straf by die hawens van Saldanhabaai aan die weskus en Ngqura, aan die suidooskus.
Saldanhabaai voorsien dienste hoofsaaklik aan massa draers van los stowwe en
vloeistof, terwyl Ngqura hoofsaaklik houerskepe bedien. Die lang golf aksies
veroorsaak dat ankertoue breek en die skepe die kaai verlaat, sodat laai van die skepe
tot stilstand kom.
In die loop van hierdie navorsing is gevind dat die seevlak ‘n multifraktale struktuur
is, met singulariteitseienskappe wat wissel van hoogs onreëlmatig of rowwe
eienskappe tot gladde, reëlmatige eienskappe. Enige golfreeks behels die volle
omvang van hierdie eienskappe in verskillende grade en wisselende teenwoordigheids
persentasies.
Die navorsing is gefokus op die geometrie van gebonde infragravitasie golfaksie
seetoestande, wat oral langs die Suid Afrikaanse kuslyn voorkom, en in twee hawens
‘n beduidende bedreiging vir vasgemaakte skepe is. Ondanks die probleem, is min
bekend oor hierdie toestande in Suid Afrikaanse konteks, omdat hulle nie visueel
bespeur kan word nie en spesiale gesofistikeerde gereedskap nodig is om hulle fisies
te kan meet. Daar word tans beplan om ‘n nuwe hawe te ontwikkel, wat hierdie
navorsing veral gepas maak, met die doel om ‘n meer volledige beskrywing van
hierdie bedreigende golftoestande te weeg te bring. Die doel van die navorsing is om ‘n stel fraktale dimensies te identifiseer wat die
oppervlakgeometrie van ‘n bedreigende gebonde infragravitasie golf-seetoestand
omskryf. Hierdie dimensies kan dan gebruik word om ‘n indentifiserende profiel van
die seetoestand te teken om die inligting tans beskikbaar oor beduidende golfhoogte
en piektye, aan te vul.
Om hierdie doel te bereik is ‘n stel fraktale dimensies eerstens bepaal deur middel van
videobeelding van ‘n oopwater golfveld. ‘n Stel enkelpunt tydserie data, afgelei van
die beelding, word dan ge-analiseer. Dit het visuele vergelyking tussen die afgeleide
stel fraktale dimensies en die videobeelding van die seevlak wat dit verteenwoordig
het, moontlik gemaak. ‘n Verdere voordeel is dat dit bewys het dat fraktale
analisemetodes toepaslik is vir die bestudering van seevlak enkelpunt tydreeks data.
Tweedens is die tye wanneer lang golfaksie teenwoordig was in die hawens by
Saldanha en Ngqura, vasgestel deur die uitwerking daarvan in die hawens.
Derdens is enkelpunt tydreeks data wat deur die WNNR aangeteken is vir die
vasgestelde tydperke, sowel as twee dae voor elke tydperk, verkry en is fraktale
dimensiestelle vir elke tydperk vasgestel.
Vierdens is die fraktale datastelle van albei die hawens vergelyk om te bevestig dat
die stelle dimensies vir bedreigende seetoestande duidelik verskil van die vir niebedreigende
toestande, en dus geskik is om die seetoestand te beskryf.
Ten slotte is die fraktale dimensiestelle vir bedreigende seetoestande in die twee
hawens vergelyk om enige verskille tussen hulle te bepaal.
Na voltooiing van die navorsing en analise is ander gebiede van kusingenieurswese
behalwe die bepaling van bedreigende gebonde infragravitasie golf seetoestande,
identifiseer waar multifraktale geometrie ook tot voordeel aangewend kan word.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/96920 |
| Date | 03 1900 |
| Creators | MacHutchon, Keith Robert |
| Contributors | Basson, G. R., Toms, Geoff, Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 212 pages : illustrations, maps |
| Rights | Stellenbosch University |
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