Fig. 7 Whole scheme of the selection process

　

5.2. Multiple Attribute Decision Making Scheme for Machinery Selection (MADM)

Generally, all of the considerations in selecting marine machinery can be grouped into three categories, namely, considerations which are closely related to the mission requirements, the techno-economic aspects, and environmental aspects, as shown in Fig.7.

Reliability itself and reliability evaluation in particular mainly consists of two main attributes: qualitative and quantitative attributes¹¹. Reliability index assessment, criticality evaluation, cost subjected to the system / component reliability is associated with the quantitative attributes. On the other hand, any aftereffects of the components and system reliability that can be quantified are acknowledged as qualitative attributes.

　

Fig. 8 The Considerations of Marine Machinery Selection

　

Sen. P^11-14 has been promoting a consistent research on the engineering-economic decision-making particularly based on the Multiple Criteria. Based on the logical algorithm presented on his paper, a case study on the selection of the centrifugal pump has been completed. This is mainly aimed for model verification. Along with the case study, a set of databases, consisting of marine machinery on board and its related consideration, has also been formed. The database structure can be seen as shown in Fig.9. (Dotted line shows the structure and coding sequence of the components and systems) The problem in the selection of the centrifugal pump (CP1-CP4), as shown in Table 4, has been solved by using a window-based computer program which is written using Visual Basic-5.

　

Table 4. Attributes and their Designated Value

　

By regarding the problem as a Hybrid-MADM¹², the evaluation matrix of each alternative can be presented as in Table 5.

　

Table 5. Evaluation Matrix

　

By using the Entropy Method¹⁴ the ranking of the available components is

　

Table 6. Component Ranking

　

It is clearly seen that the centrifugal pump no 2 (CP 2) is the most preferred alternative since having the highest Entropy Index. Comparing the quantitative attributes only seems to be difficult, since each alternative has almost similar characteristic. However its entropy index became significantly different, since the input value (preference degree) of the qualitative attribute were substantially unlike. This is the common case in the real engineering problem, where the quantifiable characteristics are harshly assorted. The preciseness of the MADM then lay on the accuracy on how we determine the preference degree of the qualitative attributes.

　

5.3. Multiple Constraints Optimization Scheme for Marine Machinery Selection

　

Multiple constraint optimization schemes can also be used to solve the problem on the selection and design of marine machinery systems. It is obviously sensible since the selection in real engineering problems is a multi-considerations problem.

　

Fig. 9 Marine Machinery Database Structure

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