pedram Pourkarim guilani; Mani Sharifi; parham azimi; maghsoud Amiri
Abstract
Due to the high sensitivity in applying of electronic and mechanical equipment, creating any conditions to increase the reliability of a system is always one of the important issues for system designers. Hence, making academic models much closer to the real word applications is very attractive. In the ...
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Due to the high sensitivity in applying of electronic and mechanical equipment, creating any conditions to increase the reliability of a system is always one of the important issues for system designers. Hence, making academic models much closer to the real word applications is very attractive. In the most studies in the reliability area, it is assumed that the failure rates of the system components are constant and have exponential distributions. This distribution and its attractive memory less property provide simple mathematical relationships in order to obtain the system reliability. But in real word problems, considering time-dependent failure rates is more realistic to model processes. It means that, the system components do not fail with a constant rate during the time horizon; but this failure rate changes over the time. One of the most useful statistical distributions in order to model the time-dependent failure rates is the Weibull distribution. This distribution is not a memory less one, so it was impossible to apply simple and explicit mathematical relationships as the same as exponential distributions for the reliability of a system. Therefore, researchers in this field have used simulation technique in these circumstances which is not an exact method to get near-optimum solutions. In this paper, for the first time, it is tried to obtain a mathematical equation to calculate the reliability function of a system with time-dependent components based on Weibull distribution. Also, in order to validate the proposed method, the results compared with exact solution that exists in literature.
Parham Azimi,; Mohammad Reza ghanbari,*
Volume 13, Issue 38 , October 2015, , Pages 133-161
Abstract
Considering the increasing demand for operational activities in ports, ports managers are facing the challenge of optimal usage of port facilities and equipment. (In the last two decades, maritime transportation systems have been experienced an increasing development. Now the rate of development in this ...
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Considering the increasing demand for operational activities in ports, ports managers are facing the challenge of optimal usage of port facilities and equipment. (In the last two decades, maritime transportation systems have been experienced an increasing development. Now the rate of development in this section has been reached 8 percent per year. Nowadays, the port managers are faced with the challenge of optimal use of equipment and facilities). One of these challenges is to reduce the waiting times of ships at the ports.so that in this study, placing the buffer area for loading and unloading cereals has been investigated using a simulation optimization model based on queuing theory at SHAHID RAJAEE port. Three important criteria of the port performance have been considered including the ship turn-around time, number of loaded ships and loading norm. The results indicate that optimization of cereal transportation between the buffer area and the port can increase the capacity of transportation and loading- unloading capacity up to (The results show that the proposed model can increase the capacity of loading and unloading of the system up to %15.5between the port and buffer area.)
