Sawmill Analysis Using Queuing Theory Combined with a Direct Search Optimizing Algorithm

An expanded and interactive version of a previously reported computer model is explained and its use demonstrated in analysis of an existing chipper-canter lumber-mill. The model, DSMIN, finds optimal solutions to mill design and operating problems from a number of alternatives. It is based upon queuing theory combined with a direct search optimizing algorithm. The results of the analysis of the chipper-canter mill indicated that the primary constraints to production were related to design and equipment selection in the portion of the mill immediately preceeding the headrig. Output from the model showed that management options include: (1) increase the length of a sawbolt buffer deck from 91 feet to 279 feet, (2) maintain the present buffer deck at 91 feet but provide temporary storage for debarked bolts, (3) add a second debarker in parallel with the existing one, or (4) replace the old debarker with a unit which has at least a 25 percent greater capacity. Use of the model revealed that should any of these options be adopted, capacity at other processing stations (such as the edger transfer deck or edger itself) would not be limiting. Direct output from the DSMIN model is illustrated in this paper. It shows how the model moves quickly to an optimal solution, thus avoiding the kind of trial and error procedures common to simulation. DSMIN, thus, provides solutions more quickly and less expensively than do simulation models. This article also indicates the general nature of the DSMIN model, which makes it readily applicable to a variety of situations.

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