393 of stack exit due to the dilution of the plume since DR ranges between 10°:1 and 10*:1. The blue- 
394 coloured line of the DR indicates fluctuations close to the vessel due to the turbulence effects of 
395 the structure. The fact that dilution is mainly affected by the wind speed (Bai et al., 2020), denotes 
396 that DR contour lines for Ships 2, 3, 4 and 5 cases would present a similar behaviour as for Ship 
397 1. This is explained by the fact that the average wind speed does not differ that much to affect the 
398 dispersion of the cases studied (Table 4). However, in several cases where downwash phenomena 
399 are affecting the plume dispersion, along with the influence from the relative angle between the 
400 ship and wind vectors, the contour lines at the x-y plane might be accumulated in one side of the 
401 plane (+y or -y). Downwash phenomena occurred due to the turbulence that is separated on the 
402 vessel’s surfaces, such as the deck, the forward, the stern, the accommodation, etc.(Dobrucali & 
403 Ergin, 2019; Syms, 2004). Downwash phenomena are also associated with the plume rise which 
404 is affected by the vessel’s bulk, the exhaust gas flow and the funnel height (Badeke et al., 2021: 
405 Lietal., 2022). 
Dilution Ratio (-} 
A 
= y=0m ] 
' 10°:1 | 105:1 aut. 
m 300 400 500 600 
Da 
Rear View 
ud | 10 
n 1000 1100 
1200 
ann 
00 
100 
D 
“4 
„| 
0 
ww 
z=9m | 
40 4 
= 1 1 + * 
| VMS line | Bottom View 
ı Tr 
} 1000 1100 1200 
+ + 
zz 
X Axisime 
“a 
FE m 1000 1100 1b 
an 
200 
In0 
A 
400 
200 
106 
407 
108 
409 
410 
411 
412 
413 
Figure 6: Contour lines of dilution ratio of the plume for the measurement conditions of Ship 1, as an example: (a) Slice cut of the 
subdomain along the x-z plane at y = Om, (b) Slice cut of the subdomain along the x-y plane at z = 9m 
3.2 Analysis on the modelling concentration time-series 
The production of the concentration time-series constitutes the basic result of the modelling 
work in the current study. "The data from concentration time-series are appropriate for the 
estimation of the MOP. The concentration factor (CF) is the reference numerical value that was 
used for the production of concentration time-series, it is the inverse of DR and is identical for 
18