There are many optimizing procedures using sensitivity analysis or genetic algorithms, and they are successfully applied to a wide varaiety of practical problems. In general, however, an optimizing procedure using sensitivity analysis frequently fails to find the global minimum of an objective function, depending on the initial values of parameters. The present paper is concerned with application of cellular automata [1] [2] [3] [4] [5] combined with the boundary element method to finding optimal shapes of the sound-insulating wall. In application of the cellular automata, the domain of interest is discretized into a number of uniform cells. Some quantity defining the cell state is assigned each cell, and then modified by a transition rule under the condition that a local rule for cells is satisfied. An optimal solution can thus be found in an iterative procedure. No sensitivity analysis is required in the cellular automata, and it is reported that the optimal solution or a 'satisfactory' solution can be rather easily obtained under a simple local rule and also a simple transition rule. The present paper aims at finding optimal or satisfactory shapes of the sound-insulating wall for auto-highways. A two-dimensional model of the auto-highway with wall, in which a sound-insulating wall stands perpendicularly to the infinite horizontal plane of the ground and a point source of noise is located at the central point on the road. Details of the cellular automata applied together with the boundary element method are discussed in authous' separate paper[6]. After the optimization procedure using BEM and cellular automata is briefly explained in this paper, it is applied to finding the optimal shapes of the sound insulating wall under several important situations. It will also be demonstrated that an optimal or satisfactory shape of the wall which can drastically reduce noise can be found if the cells change even in the diagonal directions.
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