Thesis (MEng)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: Support tower structures of Wind Energy Conversion Systems (WECS) are major cost
items and by means of integrated design and optimization, the Life-Cycle Cost (LCC) can
be reduced substantially. In this thesis, Horizontal Axis Wind Turbine (HAWTs) tower
structures are investigated by means of a technique or tool that can bene t in decision
making related situations to reduce the LCC of such WECS support towers from inception
to disposal.
Often, during the conceptual design phase a certain level of uncertainty or fuzziness exists
and plays a role. The central focus in this project is on lattice type towers; however an
account on tapered, tubular monopole towers is given as well. The problem is identi ed to
be of a multi-objective nature, where a variety of criteria or objectives that are identi ed
play a role in the possible reduction of the total LCC of the structure. The study also
entails the delineation and discussion of the factors and components that a ect the LCC
of a steel structure. The decision maker has control over only a few of these factors and
components as identi ed, and these can be formulated by means of an objective to be minimized (or maximized in several other cases). Some of the objectives are incommensurable
and others are commensurable with each other. In other words, several of these
objectives either `compete' or don't `compete' against each other, respectively. The investigation
resulted in the development of a multi-objective LCC optimization using the
λ-formulation (or min-max formulation) as the objective aggregating approach for the
four objectives identi ed (varied during analysis for sensitivity checks). The objectives
are user-de ned in terms of membership functions that grade the degree of membership
from total acceptance to total rejection by means of boundary values. This formulation is
Non-Pareto based and the decision maker obtains the best trade-o or best compromise
solution. The detailed discussion around these objectives is included in the literature
study. The objectives in the multi-objective study are weight, cost, perimeter and nodal
deflections, and a weighting of the objectives is possible but this is excluded from this
study.
A Genetic Algorithm (GA), coded in MATLAB, is implemented as the optimization tool
or technique. The algorithm uses a quadratic penalty function approach and a natively
written Finite Element Analysis (FEA) tool is used for the response model in the tness
evaluation process, where the performance for stability, capacity and overall deflections
of an individual in the population is quanti ed. A GA has the advantage that it operates
on an entire population of individuals using basic principles such as genetics, crossover,
mutation, selection and survival of the ttest from biology and Darwinian principles.
GAs are very robust and e ective global search methods that can be applied to most
elds of study. GAs have previously been e ectively applied in structural, single objective
optimization (structural weight) problems. The GA is adopted and modi ed and veri ed
with results on academic problems obtained from literature. Satisfactory performance
was observed, although room for improvement is identi ed. A case study on a full scale model is performed, using circular hollow sections and equal leg angle sections. These are commonly used steel profi les for lattice type towers. The results
obtained are as expected. The structural mass was used as a measure to compare the
results. A heavier structure is obtained using the equal leg angle sections compared to the
CHS structure with a di fference of up to 20% in weight. The best compromise solutions
are feasible and near optimal, given the conditions of the equally weighted objectives in
this study. The membership function defi nition and boundary value determination still
remains a key issue when using fuzzy logic to incorporate the preference information of
the decision maker. / AFRIKAANSE OPSOMMING: Toringstrukture van windturbines is belangrike kostekomponente van `n windkragopwekking
stelsel. Deur middel van geï ntegreerde ontwerp en optimalisering kan die lewensikluskoste
aansienlik verminder word. In hierdie tesis word horisontale-as windturbinetoringstrukture
ondersoek. Deur middel van `n tegniek of hulpmiddel wat kan baat vind by
besluitneming situasies, word die lewensiklus-koste van sodanige windturbine ondersteuning
torings vanaf voorgebruik-fase tot lewenseinde-fase verminder.
Dikwels, tydens die konseptuele ontwerp-fase, speel `n sekere vlak van onsekerheid of
verwarring ook `n rol. Die sentrale fokus in hierdie projek is op staal vakwerk tipe torings
gelê. `n Vereenvoudigde ontleeding van buisvormige torings is ook benader. Die probleem
is van multikriteria aard, waar `n verskeidenheid van kriterie of doelwitte ge denti seer
was. Hulle speel `n rol in die moontlike vermindering van die totale lewensiklus-koste
van die struktuur. Die studie behels ook die bespreking en afbakening van die faktore en
komponente wat die lewensiklus-koste van 'n staal struktuur bepaal. Die besluitnemer het slegs beheer oor sekere van hierdie faktore en komponente, en hierdie word deur middel van
`n saamgevoegde doel-funksie gede neer wat dan geminimeer word. Sommige van die doelfunksies
kompeteer met mekaar en sommige kompeteer nie met mekaar nie. Die ondersoek
het gelei tot die ontwikkeling van `n multikriteria lewensiklus-koste optimalisering met
behulp van die λ-formulering (of min-max formulering). Hierdie is `n tegniek wat die
kriterie in vorm van `n verteenwoordigende doel-funksie saamvoeg. Daar is vier doelwitte
wat geï denti seer was. Die gebruiker de nieer spesiale, lineêre doel-funksies wat van
totale aanvaarding tot totale verwerping streek. Dit word deur middel van randwaardes
gedoen. Hierdie formulering is nie Pareto gebaseer nie, en die besluitnemer verkry die
`best trade-off ' of die beste kompromis oplossing. Die detailleerde bespreking rondom
hierdie doelwitte is in die literatuurstudie ingesluit. Die doelwitte wat in die multikriteria
studie gebruik word is gewig, koste, omtrek van die snitpro el en strukturêle defleksie. `n
Gewig kan aan elke kriterium toegeken word, maar dit word van hierdie studie uitgesluit.
`n Genetiese algoritme (GA), geï mplementeer in MATLAB, word as die optimalisering
instrument en tegniek gebruik. Die algoritme gebruik `n kwadratiese `straf-funksie' en
`n MATLAB Eindige Element Analise (EEA) word gebruik vir die gedragsmodel in die
`fi ksheid' evalueringsproses. Die prestasie vir stabiliteit, kapasiteit en algehele verlegging
van `n individu in die GA bevolking word daardeur gekwanti seer. `n GA het die voordeel,
dat dit met `n hele bevolking van individue werk. Dit is gebaseer op beginsels van genetika
en Darwin se beginsels. GAs is baie stabiel en ook e ektiewe globale soek metodes wat
van toepassing in verskillende studierigtings is. GAs is al e ektief toegepas in strukturêle
optimalisering (veral strukturêle gewig optimalisiering). Die GA in hierdie studie was
aangepas en die gedrag en prestasie is bevestig met resultate van akademiese probleme
uit die literatuur. Bevredigende prestasie is waargeneem, maar ruimte vir verbetering is
ook geï denti seer. `n Gevallestudie oor `n grootskaal model is uitgevoer, en die gebruik van ronde holpro ele
en gelykbenige hoekpro ele is uitgevoer. Dit is algemeen gebruikte staalpro ele vir vakwerk
tipe torings. Die resultate wat verkry is, is soos verwag. Die strukturêle massa is
gebruik as `n maatstaf om die resultate te vergelyk. `n Swaarder struktuur is die resultaat
wanneer gelykbenige hoekpro ele gebruik word in vergelyking met die ronde holpro el
struktuur. `n Verskil tot 20% in gewig is waargeneem. Die beste kompromis oplossing
is haalbaar en naby-optimaal, gegewe die omstandighede van die gelyk geweegde doelfunksies
in hierdie studie. Die doel-funksie de nisie, die voorkeur van die besluitnemer
en die bepaling van die randwaardes bly steeds `n belangrike kwessie by die gebruik van
hierdie benadering.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/85839 |
| Date | 12 1900 |
| Creators | Horsthemke, Hagen Wolfgang |
| Contributors | Van Der Klashorst, Etienne, 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 | xxiii, 208 p. : ill. |
| Rights | Stellenbosch University |
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