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PII: S238309801400005-3

Using of Method of Moments for Solve a Class of Optimal Control Problem

Original Research, C5

Dehghan R.

Sci. J. Mech. Ind. Eng., 3(3): 33-38, 2014

ABSTRACT: In this paper, we solve a class of optimal control problem where the objective function given by the ratio of two integrals. We propose an alternative method for computing effectively the solution of fixed-terminal-time, fractional optimal control problems when they are given in non-linear forms. This method works well when the nonlinearities in the control variable can be expressed as polynomials. The essential of this proposal is the transformation of a non-linear, non-convex optimal control problem into an equivalent optimal control problem with linear and convex structure. The method is based on global optimization of polynomials by the method of moments. With this method we can determine either the existence or lacking of minimizers. In addition, we can calculate generalized solutions when the original problem lacks of minimizers. We also present the numerical schemes to solve some examples.
Key Words: Optimal control, Fractional programming, Convex optimization, Method of Moments

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PII: S238309801400006-3

An Integrated Casual Loop and Cumulative Sum Control Chart for Reliability Assessment in a Maintenance System

Original Research, C6

Rashidzadeh E, Golmohammadi A.M, Golmohammadi A.H.

Sci. J. Mech. Ind. Eng., 3(3): 39-46, 2014

ABSTRACT: Measuring the reliability of a maintenance system is a crucial issue, in which the system reliability could be one of the essential performance indicators to evaluate whether the system is capable or not. The objective of this study is to develop a novel approach for reliability assessment in a maintenance system. Due to the dynamic nature of this system, the concept of system dynamics is employed to determine and analyze its most critical elements, structural characteristics, relationships and feedbacks with respect to reliability. Therefore, series of casual loop diagrams assisting in better understanding of casual influences of maintenance system are developed. The casual loop diagrams plotted here provide a tool for management to hypothesize the dynamic influencing effectiveness of maintenance management, particularly the impact on reliability indices. Then, cumulative sum control chart (CUSUM) being analyzed as a visual objective to determine performance accuracy is considered. In addition, the ability of the CUSUM schemes to detect important types of changes in the optimal reliability indices are analyzed. As a result, these discussions would help system administrators to have better perception and use quantified indices to configure the reliability index in maintenance systems.
Key words: Maintenance, Reliability, Casual loop, Cumulative sum control chart (CUSUM)