Computational Methods in Engineering

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Contaminant transport analysis was performed for four selected solid waste landfill designs using the computer code POLLUTE. The diffusion coefficients were determined for the natural soils (aquitard) and compacted soils from the Urumia landfill site, using the diffusion tests. These coefficients along with the geometrical, physical, and chemical parameters of the natural soil and engineered layers, as well as the dominant boundary conditions were used in the analysis of the four selected designs for the landfill. These designs were evaluated for the contamination of the underlying aquifer in a specified period, using the drinking water standard for chloride ion. The comparisons showed that the fourth design which includes the engineered elements of a blanket type leachate collection layer and a compacted clayey liner underneath the landfill base, has more certainty in controlling the contaminant transport from the landfill base to the underlying aquifer. This type of landfill could be introduced as an optimum and semi-engineered design to be used for solid waste landfills in Iran.

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Weighted Simulation-based Design Method (WSDM) is recently developed as an efficient method for Reliability-
Based Design Optimization (RBDO). Despite simplicity, this method degrades effectiveness to obtain accurate optimum design for
high dimension RBDO. Besides, its application range is restricted to RBDOs including only random design variables. In the
present study, local search strategy is employed to enhance the accuracy of conventional WSDOM, and to reduce the computational cost. Besides, a shifting strategy is proposed to increase the application range of WSDM for handling general RBDO problems. The efficiency of the proposed methods is investigated by solving some structural reliability problems.
Comparisonof the obtained results with exact solutions confirms accuracy and superiority of the proposed method for
solving various engineering problems.