bb
steady MS
PD
moving ship
[_MmHD }
ZN
moving MS
Rn
c / Tr
3 Z steady ship
£
3
no)
As
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[_mHD
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208
209 Figure 2: Graphical illustration of reality to modelling conversion for CFD simulation setup. (a) an example of the real ship’s path
210 where wind disperses the plume, (b) modified, for transient results production from CFD.
The concentration values of interest refer only to the ones detected at the VMS when
passing the ship’s plume, indicated by the uniformly separated red dots in Figure 2b. A typical
concentration time-series that can be observed, is depicted in the green frame in Figure 2b, which
gives information on the relationship between concentration and time. The number of red dots
collected plays an important role since measurements and CFD modelling results must be at the
same temporal resolution to be comparable. Therefore, the number of red dots is calculated by
Equation 1, where L is the length of the line that corresponds to the red points, Ugcruar 18 the actual
ship’s speed and resms is the monitoring station’s temporal resolution (5 s).
oints “
ai Ugctual * TeSMs
This work uses CO and SO2as reference dispersion gases. The mean ambient temperature
and pressure during the examples simulated herein are equal to 286K (varying between 285.9K to
286.5K) and 993 mbar, respectively.
The results of CO2 and SO2 concentration time-series detected from MS and the VMS
should be compared. The measured data are corrected for background concentrations, which are
constant at 412 ppm and 0.7 ppb for CO2 and SO», respectively, since measurements were
conducted within the same hour, where no alterations were detected. Simulation results give the
contribution by the ship without the background concentration. The reference numerical value that
this comparison is referred to is called the “peaksum” which corresponds to the summation of al]
concentration values that correspond in the detected peak area of each individual ship.
Concentration values from measurements correspond to the Measurements Peaksum (MEP), while
results from CFD are referred to as the Modelling Peaksum (MOP).
231 2.3 Computational Domain
10
