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UBC Theses and Dissertations

Real-time fuzzy logic control of combined sewer flows Tamaki, Robert Dean


The use of fuzzy logic for the real-time control of flows in a combined sewer system is examined in this thesis. Using a simple computer model, two different combined sewer overflow control scenarios were developed to test the effectiveness of a fuzzy rule base for controlling wet weather flows using off-line storage. The control objective of the first scenario was to capture the more highly contaminated first flush flows from a two sub-catchment drainage basin. A fuzzy controller was developed using heuristic methods that was found to be relatively effective in achieving the desired objective. The control objective of the second scenario was to capture the peak flow issuing from a single catchment. In this case, two different control strategies were employed. The first involved the construction of a fuzzy algorithm from a database of historical flow control data. That data was obtained manuallly by determining an optimal control response for each storm event using multiple repetitions of each simulation. The results of using this method, however, were found to be highly inadequate, due mostly to flawed methodology. The poor results prompted the development of the second method in which a crisp controller output was modified on-line by a fuzzy adjustment algorithm in response to real-time measurements of the state variables. This method yielded improved results over the first method but some inadequacies were still apparent. These inadequacies could be attributed primarily to the complexity of the control problem and the difficulty involved in representing those complexities heuristically so that they could be converted to a fuzzy algorithm. Specifically, the dimensionality of the control problem was found to be too large to be able to produce an effective fuzzy controller.

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