4. OPTIMUM HULL FORM DESIGN SYSTEM
Discussion in the previous chapter indicated that Computational Fluid Dynamics could be a practical design tool to estimate the propulsive performance, maneuverability and sea-keeping performance. According to the establishment of IMO manoeuvrability standard, optimum hull form design procedure and tool should be considered to maximize propulsive performance within a restriction of manoeuvrability and sea-keeping performance. Former times, check of maneuverability was carried out mainly by the limitation of principal particulars such as Cb/(L/B) and determination of required rudder area by empirical chart base.
Although numerical simulation based on MMG model is already put into practical use, necessary parameters are normally determined using principal particulars only. To realize the compromised design for aft frame line shape, evaluation for both maneuverability and propulsive performance should be done at the same time during the early stage of hull form selection. To realize this design, CFD code seems to be an essential tool for the evaluation of both performances precisely. Fig.23 shows an outline of latest hull form design system base on a CFD code in which check of IMO Standard is included through numerical simulation based on MMG model.
Although MMG type simulation requires a number of parameters, only hydrodynamic derivatives are estimated by CFD code in this case. Fig.24 shows an example of this simulation for Z-maneuvering motion using both calculated hydrodynamic derivatives by CFD and measured one by captive model test, the results of which show a good agreement to each other. Finally, during the optimized process of aft body shape, attainable propulsive performance depends on the degree of restriction from maneuverability, in other words, IMO maneuverability standard, Since second overshoot angle for Z-maneuvers is a most severe criterion for full ship within a present standard, this value should be carefully considered based on the fact that effect of this restriction is very sensitive to the propulsive performance.
Hull form design system including the affirmation of IMO standard
Example of Z-maneuver simulation based on hull form design system
This paper described the state of the art for optimized hydrodynamic design considering maneuverability, propulsive performance and sea-keeping performance at the initial design stage. Concluding remarks are summarized as follows.
(1) Relationship between principal particulars and three performances are discussed based on the tank test data. Conflicting design aspects, which shipbuilders normal]y encounter at the initial design stage, are explained.
(2) CFD calculation and tank test results for hydrodynamic properties of three performances are compared, Results of comparison indicate that CFD code could be a practical tool at the initial design stage.
(3) Optimized hull form design system based on CFD including the affirmation of IMO maneuverability standard is proposed.
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Mr. T.Ishiguro belongs to the Hydrodynamics Engineering Dept, of IHI Marine United Inc. and mainly engaged in both hull form basic design works and development of soft ware for ship maneuvering simulator. Dr. T. Ohmori belongs to the Ship & Marine Technology Dept. of Ishikawajima-Harima Heavy Industries and engaged in a research activities for both propuisive performance and maneuverability based on the CFD and EFD techniques at ship model basin.