TS-124
Reliability - Based Marine Machinery Selection:
A Case Study In Main Engine Cooling Systems
Kenji ISHIDA*), Ketut Buda ARTANA**), Takeshi HASHIMOTO***)
Abstract
The objective this paper is to evaluate and describe methods based on reliability in selecting and evaluating the main engine cooling system of ships. The work sequence is commenced by setting up the model of the main engine cooling system, which is the object of the case study. A Monte Carlo simulation based random number generator is then used to produce the maintenance schedule by adopting several distribution types. Evaluation of the influence of component reliability to the total system reliability performance is then assessed by means of component's criticality evaluation. The significance of the cost components is also assessed to find the optimum maintenance schedule. The general scheme of qualitative and quantitative optimization methods is discussed at the end of the paper. This work obviously indicates that marine machinery selection is a multi consideration problem, hence the use of multi consideration (attribute/constraint/objective) method will provide us a more realistic picture of the real problem in the field of engineering.
Key Words: Reliability, Main Engine Cooling System, Distribution, Criticality, Maintenance, MCDM
1. Introduction
With the development of the marine machinery systems on board, in terms of complexity and number of components, it clearly bears an influence on the increase of the capital cost and the complexity of the design option. The decision on selected machinery must guarantee that the machinery will operate with a low level of failure, safely and efficiently, with a high level of availability and at the end, will deliver an optimum rate of return on the capital being employed. Precision in selecting marine machinery for ships, therefore, would be one of the most critical points in achieving reliable ship operation.
The problems in selecting marine machinery appear due to the complexity of the consideration that must be taken into account. In selecting a main engine, for instance, the consideration that is based only on the power required by the ship is not enough to be taken as the only parameter, since several extra variables remain to be taken into account. Those considerations comprise1]: reliability, maintainability, space and arrangement requirement, weight requirement, type of fuel required, fuel consumption, fractional power and transient performance, interrelation with auxiliaries, operating personnel, rating limitation, costs, spare part availability, on-shore service capability etc.
Thorp2) has already utilized a comprehensive method for economic assessment in selecting marine machinery for a Panamax-size bulk carrier of 70.000 TDWT. Integration of each component has also been analyzed in determining the selected machinery. This could be the important point in extending the consideration of the marine machinery selection process.
Life Cycle Cost (LCC) and its constituents, which are important economic considerations in the selection and operation of marine machinery, has year after year became the object of analysis. Rasmussen3), Jambulingan4) took Reliability Centered Maintenance (RCM) as a basic concept in the structuring maintenance decision support model for gas field equipment and maritime equipment respectively.
Reliability, which is the main focus of this paper, has already been widely used as a tool either for theoretical analysis or applied engineering problem solving. References [5] to [9] are some of the examples.
This particular paper has comprehensively brought two general aspects of reliability, qualitative and quantitative attributes together into the analysis and will be the starting point of a long-term research, which will take all substantial considerations into account. Consideration on the system reliability will be the logical model of the next development of the whole research scope.
2. The Reliability of Main Engine Cooling System
Reliability terminology can be perceived as the probability of a system or component performing its intended function within defined tolerance for the assigned service time5).
In assessing system or component reliability, numerous available methods can be adopted and the utilization depends on the characteristic of the problem. Generic Part Count Reliability (GCPR), and Markov chain/process, are two examples of several available methods. None of the methods can be assigned as the best method. Again, it does fully depend on the type of the problem. In the case of the analysis of the simple series system, GPCR would be the most effective method. When the maintenance point of view is taken into account, however, the GPCR would not be able to handle the process, and the Markov process will be more appropriate.
Hashimoto6), 7) in conjunction with other authors, has taken the main engine cooling system as a case study in statistical review of the component reliability. Some reliability indexes of the component of the main engine cooling system have been obtained by evaluating the failure trend of some ships from 1965 to 1980. This value is certainly obtained during the components are in the useful life period.
