UBC Theses and Dissertations
Application of simulation technique in the study of sawmill productivity Aune, Jan Erik
A computer simulation program which models the operation of a British Columbia coast dimension sawmill has been developed in FORTRAN IV. The model represents the initial log breakdown by a double cut, multi-pass band headrig, cant breakdown by a bulledger and the further processing on two resaws, pony edger and the double end trimsaw. Simulation of the headrig and bulledger operation is event oriented, whereas the piece flow through the other processing units is updated with 1-minute intervals. Flowcharts describe the routines briefly. The principal types of data input are sawlog population characteristics, machine characteristics, buffer storage capacities, and product output constraints. Information about the model operation is collected during the simulation runs, and the printed output includes productivity in Mbfm per 8-hour shift, the time each saw was operating, idle, busy or blocked, the time the bulledger queue contained a given number of cants and histograms showing the queue length distribution in 10-piece classes for subsequent saws. Validation of the model plays an important part in system simulation. The approach has been to attempt a verification of the piece flow arriving at trimmer, #l and #2 resaw, ponyedger and greenchain. Although the productivity figures obtained from simulation correspond to those experienced by the mill, the piece flow could not be verified. Irregular log shape, not reflected in the sawlog population characteristics and leading to more manufacturing of slabs in the real system, is considered to be the principal factor contributing to this. Preferably, further modelling should lead to the development of one general assembly-system, which regards sawmills as a collection of interconnected components, with increased input and output flexibility.
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