Fig. 10 Basic Format of the Optimization Process
Input consists entirely of independent variables, which will be used along the optimization process. Those variables can be classified into several directories to make the fault identification easier. Moreover, the use of directories will make the optimization process easier since it designs an optimization process and the relationship between each directory will be clearer.
All basic calculations for the optimization process are located in the "equation folder". The results of each equation will continuously be adapted since the optimization process in the "constraints" and "output" will always affect the variable employed on the equation.
Constraints, which are requirements to be fulfilled, become the engine of this optimization process. Any consideration, which will directly affect the objective, can be set as a constraint. A minimum and maximum value is set to give the working area of the optimization process. The optimum values are located in the center of the form and will change as the constraints are changed. Determination of the minimum and maximum value absolutely depends on the characteristic of the constraints. Some consideration can be logically adopted from the "rule of thumb" value such as the range of length-beam ratio of a tanker or power allowance factor of the main engine.
Output has a characteristic, which nearly the same as the constraints except that the output is set from independent value (optimization result) which is different with the equation that is adopted in the constraint. Multiple output can be obtained from the optimization process. The maximum and minimum values are also set to direct the optimization process. All optimization methods have the same pattern in which they are formed to find either a maximum or minimum solution from a single or multiple objectives. In the engineering-economic decision making process, it is common to use economic criterion as the measure of merits. For instance, it is better to select an alternative from main engine which provides the best rate of return or the lowest required freight rate for a certain type of ship, capacity, voyage pattern, etc.
6. Conclusions
This paper is an information of a long-term scheme in the research agenda of which the authors are interested in. Some significant points can be drawn. Those points are:
・ It is realized 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. Reliability and its economic end result is only one of the considerations to be taken into the analysis.
・ As shown in the case of centrifugal pump selection, the preciseness of result of the MADM apparently depends on the accuracy in how we assign the preference degree of the qualitative attributes.
・ For design purposes, the concept on the use of multi constraint optimization process might generate reliable solutions.
The subsequent step of this research scheme is constructing the computer-based selection and design method and software for marine machinery selection. This is mainly based on the concept of multiple constraint optimization method. Real data from related sources will be used to verify the result.
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