Thesis (MSc (Forest and Wood Science))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The percentage yield of sawn timber recovered from logs has a large influence on the profitability of a
sawmill. The positioning of the log as it is fed into the primary breakdown saw is one of the factors that
impacts on the volume recovery percentage. The log’s position can be adjusted by changes in rotation,
offset and skewness and depending on the ranges and increments used for these variables, the number
of possible combinations can become substantial. In a sawmill the time available to assess possible log
positions is limited and different strategies can be followed to arrive at an optimal or close‐to‐optimal
positioning solution without an exhaustive evaluation of solutions. Meta‐heuristics are sometimes used
to arrive at solutions for combinatorial optimisation problems in a limited time. The effectiveness of this
approach on the optimisation of timber volume recovery based on log form is evaluated in this study
using sawmill simulation data of sixty SA pine logs.
A new meta‐heuristic, for convenience named the Tentacle algorithm, was developed specifically for the
problem of log positioning optimisation. The results obtained with the Tentacle algorithm was compared
with results from three existing meta‐heuristics i.e. the Simulated Annealing algorithm, the Population
Based Incremental Learning algorithm and the Particle Swarm Optimisation algorithm, in terms of its
efficiency and effectiveness in finding good log positioning solutions in a limited time. A fifth method,
that of exhaustively searching smaller, high quality areas around the centered and “horns‐up” and
“horns‐down” positions in the search space was compared to that of using the meta‐heuristic
algorithms. In terms of volume recovery, the Tentacle algorithm performed, on average, the best of the
four algorithms evaluated. However, exhaustive searches in the smaller, high quality areas in the search
space, outperformed the algorithms. / AFRIKAANSE OPSOMMING: Die herwinningspersentasie van gesaagde planke uit saagblokke het ‘n groot invloed op die
winsgewendheid van ‘n saagmeul. Die posisionering van die blok in die primêre saag is een van die
faktore wat die herwinningspersentasie beïnvloed. Die blok se posisie kan verstel word deur
veranderinge in rotasie, oplyning en skeefheid. Afhangend van die veld ‐en inkrementgrootte kan die
hoeveelheid moontlike kombinasies beduidend wees. In ‘n tipiese saagmeul is die beskikbare tyd om
moontlike posisies te evalueer beperk en verskeie strategieë kan gevolg word om optimale of nabyoptimale
kombinasies te bereik sonder om alle moontlike kombinasies te evalueer. Meta‐heuristieke
word soms gebruik om in ‘n beperkte tyd oplossings te vind vir kombinatoriese optimeringsprobleme.
Die doeltreffendheid van hierdie metode by die optimering van herwinningspersentasie gebaseer op
blokvorm is in hierdie studie ondersoek. Dit is met behulp van saagmeulsimulasiedata soos van sestig SA
dennehoutblokke verkry, uitgevoer.
‘n Nuwe meta‐heuristiek, genaamd die Tentakelalgoritme, is tydens hierdie studie spesifiek vir die
probleem van blokposisie‐optimering ontwikkel. Die resultate verkry met die Tentakelalgoritme is
vergelyk met drie bestaande meta‐heuristieke, nl. die “Simulated Annealing”‐algoritme, die “Population
Based Incremental Learning”‐algoritme en die “Particle Swarm Optimisation”‐algoritme in terme van
doeltreffendheid om goeie blokposisies in ‘n beperkte tyd te vind. ‘n Vyfde metode, die gebruik van ‘n
volledige ondersoek van verkleinde versamelings, rondom hoë‐kwaliteit areas in die soekarea, is
vergelyk met die gebruik van die meta‐heuristieke. Hierdie hoë‐kwaliteit areas word gevind rondom die
gesentreerde “horns‐up” en “horns‐down” posisies. Die Tentakelalgoritme het gemiddelde die beste
herwinningsresultate van die vier meta‐heuristieke wat ondersoek was gelewer. Die volledige ondersoek
van verkleinde versamelings in die hoë kwaliteit areas het egter die meta‐heuristieke oortref.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/5209 |
| Date | 12 1900 |
| Creators | Du Plessis, Johan de Villiers |
| Contributors | Wessels, Brand, University of Stellenbosch. Faculty of Agrisciences. Dept. of Forest and Wood Sciences |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Format | 115 p. : ill. |
| Rights | University of Stellenbosch |
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