Thesis (MScEng (Industrial Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: During the 2009 financial year the sawlog production from plantations in South Africa
amounted to 4.4 million m
3
and sawn timber of R4.2 billion was produced from these logs.
At the current average price for structural timber, a 1% increase in volume recovery at a
medium-sized South African sawmill with an annual log intake of 100 000m
3
will result in
additional profit of about R2.2 million annually.
The purpose of this project was to evaluate the potential of increasing in value recovery at
sawmills through optimization of the positioning of a log at the primary workstation by
considering the internal knot properties. Although not yet commercially available, a high
speed industrial log CT scanner is currently in development and will enable the evaluation of
the internal characteristics of a log before processing.
The external profiles and the internal knot properties of ten pine logs were measured and the
whole log shape was digitally reconstructed. By using the sawmill simulation program
Simsaw, explicit enumeration was performed to gather data. This data include the monetary
value that can be earned from sawing the log in a specific log position. For every log a total
of 808 020 sawing positions were evaluated.
In the sawmill production environment only a few seconds are available to make a decision
on the positioning of each log. Meta-heuristic optimization algorithms were developed in
order to come to a near optimal solution in a much shorter time than that required when
simulating all possible log positions. The algorithms used in this study include the Genetic
algorithm, Simulated Annealing, Population Based Incremental Learning and the CrossEntropy method. An Alternative algorithm was also developed to incorporate the trends
identified through analysis of the sawmill simulation results.
The effectiveness of these meta-heuristic algorithms were evaluated using the sawmill
simulation data created. Analysis of the simulation data showed that a maximum increase in
product value of 8.23% was possible when internal knot data was considered compared to
using conventional log positioning rules. When only external shape was considered a
maximum increase in product value of 5% was possible compared to using conventional log
positioning rules. The efficiency of the meta-heuristic algorithms differed depending on the
processing time available. As an example the Genetic algorithm increased the mean product
value by 6.43% after 200 iterations. Finally, a method to evaluate the investment decision to
purchase an internal scanning and log positioning system is illustrated. / AFRIKAANSE OPSOMMING: Gedurende die 2009 finansiële jaar is daar 4.4 miljoen m
3
rondehout op plantasies in Suid
Afrika geproduseer en saaghout ter waarde van R4.2 biljoen is hieruit vervaardig. Met die
huidige gemiddelde prys vir strukturele hout, kan ‘n 1% verhoging in volumeherwinning by ‘n
gemiddelde grootte saagmeul in Suid Afrika met ‘n jaarlikse rondehout inname van 100 000
m
3
‘n bykomende wins van R2.2 miljoen lewer.
Die doel van hierdie projek was om die potensiële verhoging in waardeherwinning by ‘n
saagmeul te evalueer, indien die posisionering van ‘n stomp by die primêre werkstasie
geoptimeer word deur interne kwas eienskappe in ag te neem. Kommersiële CTskandeerders word tans nog nie hiervoor aangewend nie, maar ontwikkelinge in tegnologie
sal dit moontlik binnekort prakties moontlik maak om die interne karakteristieke van ‘n stomp
te evalueer voor prosessering.
Die eksterne profiel en interne kwas eienskappe van tien Pinus rondehout stompe is gemeet
en die al tien stompe is digitaal geherkonstrueer. Met behulp van die
saagmeulsimulasieprogram, Simsaw, is 808 020 verskillende saagsimulasielopies uitgevoer.
Elk van hierdie simulasielopies het ‘n ander beginposisie gehad in terme van rotasie,
skeefheid en horisontale verskuiwing. Die finansiële waarde wat verdien kan word deur ‘n
stomp in ‘n sekere posisie te saag is telkens bepaal.
In die saagmeulomgewing is daar slegs ‘n paar sekondes beskikbaar om ‘n besluit te maak
oor hoe ‘n stomp geposisioneer moet word. Meta-heuristiese optimisering algoritmes is
ontwikkel om ‘n naby optimale oplossing te bepaal in ‘n baie korter tyd as wanneer alle
saagposisies geëvalueer word. Vyf verskillende meta-heuristiese algoritmes is teen mekaar
opgeweeg. Vier van hierdie algoritmes is bestaande heuristieke wat vir verskeie ander
optimeringsprobleme ingespan word. Die vyfde algoritme is spesifiek vir doeleindes van
hierdie projek ontwikkel om die neigings wat tydens die data-analise van die
saagmeulsimulasie geïdentifiseer is, te inkorporeer.
Die effektiwiteit van hierdie meta-heuristiese algoritmes is bepaal deur van die saagmeul
simulasiedata wat gegenereer is gebruik te maak. Analise van die simulasiedata toon dat ‘n
maksimum toename in produk waarde van 8% moontlik is wanneer interne kwaseienskappe
ook geïnkorporeer word tydens besluitneming teenoor die konvensionele
stompposisioneringreëls. Wanneer slegs die eksterne stompprofiel in ag geneem word, is ‘n
maksimum produkwaardeverhoging van tot 5% moontlik teenoor resultate wat verkry word
met konvensionele stompposisioneringsreëls.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/6715 |
| Date | 03 1900 |
| Creators | Van Zyl, Fritz |
| Contributors | Van Dyk, L., Wessels, C. B., University of Stellenbosch. Faculty of Engineering. Dept. of Industrial Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 116 p. : ill. |
| Rights | University of Stellenbosch |
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