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            Calculation domain was set as shown in Figure 4. For an efficient mesh generation, calculation domain
            was divided into a cylindrical inner part surrounding the ship and a cubic outer. These two domains
            were filled with tetrahedral meshes. Total number of the meshes is about 500,000.






                                                              332x58~63




                                       Figure 4: Calculation Domain

            3.2.2  Calculation setting

            The ship is advancing with its speed in a wind.  And nitrogen dioxide is included in the exhaust gas
            with the concentration of 1200 ppm. Although many other noxious gases are included in real exhausts,
            they need not be included in the analysis because their concentrations are generally too low to cause
            on-board pollution.
            Principal features of the analysis are summarized in TABLE 2. Multiple species model was adopted in
            order  to  simulate the  dispersion of  nitrogen dioxide and  energy equation was  included  into the
            governing equation set because of the high temperature at the exits of the exhausts.

                                              TABLE 1
                                    PRINCIPAL FEATURES OF THE ANALYSIS

                 Coordinate system ' Right-handed Cartesian coordinate system, vertically upward z-axis
                 Problem type   3D steady state, energy equation included
                 Solver         Segregated explicit
                 Turbulence model  RNG k-E model with standard wall function
                 Discretization   Standard for Dressure. fist order uDwind for all the other variables


            3.3 Evaluation of the Smoke Exhaust Performance
            Some measures are required to judge the smoke exhaust performance from simulation results. Those
            can  be  prepared considering the problems caused  by  exhaust gas from the  funnel exhausts. For  a
            common merchant ship, the problems caused by exhaust gas can be divided into two categories. The
            first is the dispersion of the noxious gases, and the second is the possibility of pollution caused by ash
            included in the exhaust. In this study, following items are introduced for the purpose of the evaluation
            of the smoke exhaust performance:
            3.3. I  Dispersion of the noxious gas

            As  mentioned  before,  nitrogen  dioxide  was  adopted  as a  typical  noxious  gas.  It  starts  with
            concentration of 1200 ppm and disperses rapidly. If its concentration at the deckhouse, engine room
            intake or other principal points is higher than  a  certain value,  there exists a possibility of  health
            problem of the crews. Two methods were adopted to inspect the dispersion of nitrogen dioxide. The
            first is to observe the shape of the iso-surface of NO2 concentration. The region covered with the iso-
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