Reliability is an important feature in the mechanical and electrical systems, which is discussed in the communications industries, internet networks, telecommunication systems, power generation systems, manufacturing facilities and etc. Finding the optimal level of reliability based on system constraints, is called a "reliability optimization problem". The variety of system structures and resource constraints for improving the reliability has led to design and analyze several optimization models. One of the methods to improve system reliability is using the redundant components in the system. it has proven that Redundancy Allocation Problem (RAP) is a kind of NP-hard problems and the computation grows exponentially by increasing problem size and constraints. Hence, finding the appropriate solution is important for these problems In this thesis, the redundancy allocation problem is studied for improving the reliability of series - parallel systems based on the multiple component choices, and ant colony algorithm has been applied for the purpose of solving. The present study investigates reliability optimization and system requirements in terms of both electrical and mechanical systems and suggests a new solution based on ant colony algorithm. In mechanical systems, maximizing system reliability, minimizing system cost, minimizing system weight and simultaneously optimization of the reliability, cost and weight of the system was studied based on the multiple component choices subject to the weight and cost and minimum reliability constraints. This mechanical system has been studied by different authors and the suggested algorithm has indicated better performance in comparison with the previous approaches. In order to illustrate the application of the redundancy allocation problem and performance of the proposed ant colony algorithm, an electrical system was also evaluated. Considered system is an electronic board which is used in medical equipments and now it is produced by the Isfahan Optics-Sa Iran Company. In this equipment, in addition to cost and weight constraints, it is necessary that the volume constraint (dimensions of system) be also considered. Adding the volume constraint (system dimensions) has not been studied in the multiple component choices so far, and it is also discussed in this thesis. In electrical system, maximizing system reliability and minimizing system cost was studied based on the multiple component choices subject to the cost, weight, volume and minimum
