Page 485 - Practical Design Ships and Floating Structures
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performance of a ship in advance to derive desirable arrangement of funnel and accommodation. The
estimation can be made in various ways e.g., model test, CFD and preferably simple empirical formula
or statistical methods that can be obtained through full-scale ship observations, model tests or CFD
analyses. To obtain useful formula or tables that can be used in the estimation of the smoke exhaust
performance, numerous cases must be analyzed. Using CFD in this kind of analysis has merits in cost
over model tests. Moreover, when CFD is used, simulation results can be observed more closely than
in model tests both qualitatively and quantitatively.
The objective of this study was to observe the influences of the funnel and accommodation
arrangement on the smoke behavior through a CFD-based parametric study. Also, if possible, a simple
measure to expect the smoke exhaust performance was to be obtained. For these purposes, three
parameters were chosen and calculations were executed for the models obtained through the variations
of the parameters. Each calculation result was analyzed with several appropriate methods prepared
beforehand.
2 CALCULATION MODEL
The ship adopted as a model of the analysis is an oil canier having the shape presented in Figure 1.
The result of the analyses using this model could be referred to in the design of the ships of similar
shape.
Figure 1 : Model of the Calculation
In the analysis of the flow around a ship funnel using CFD, calculation model must be carefully chosen.
It requires much effort to describe the like hull and other appendages such as radar mast or on-deck
pipe system due to their complicated shapes or small sizes. Besides, if they are included in the analysis,
calculation time will increase according to the increased mesh size to describe the complex geometry.
On the other hand, among those there can exist one or more elements that have little influence on the
flow around the funnel. For the efficiencies in the modeling and calculation procedure, it is better to
exclude the elements having minor effect on the flow field from the model.
Thus prior to the main calculation, effects of hull, radar mast and on-deck pipe system on the flow
around the funnel was investigated through several calculations. As a result of those calculations, the
hull had a significant effect on the flow around the funnel, while the effect of the radar mast and on-
deck pipe system was so small. Consequently, the radar mast and on-deck pipe system might be
excluded from the model, but the hull must be included.
The effect of bow shape was considered by changing the bow part of the hull into a vertical prism of
which the section has the same shape as the deck plane. The intention of this analysis is to make the
hull modeling procedure efficient, i.e., if the difference between the result of the bow-modified model
and that of the original model is not great, the modified bow shape is adopted in the modeling. The
result of this analysis is that the difference between the two cases is not significant.