Trans RINA, Vol 161, Part A4, Intl J Maritime Eng, Oct-Dec 2019
Table 5. Specifications of the computational grids to evaluate the grid
Grid quality grid 1 grid 2 grid 3 grid 4 grid 5
Figure 11. Towing tank of subsea R & D center of Isfahan University of Technology
According to Table 4, the towing tests of the model were carried out at drafts of 8 and 16.5 cm and at five different speeds. The values obtained for the drag force of the model were recorded digitally for each test. The process of unifying and eliminating incomplete information was performed for each test. The total resistance coefficient was calculated using the drag force of the model. By subtracting the frictional resistance coefficient and air resistance from the proposed method by ITTC, the wave resistance coefficient of the model, which was equal to the wave resistance coefficient of the ship, was calculated. By adding coefficients of frictional resistance and air resistance as well as correction values resulted from the difference between the roughness of the surface of the prototype and that of the vessel to the wave propagation coefficient of the ship, the total resistance coefficient of SALINA and the resulting drag force of the ship at desired speeds were obtained.
Table
4.Model tests in the towing tank Number of whole tests
Number of repetitions
10 2
Number of tests
5
Model speed (m/s) 0.65
0.70 0.75 0.80 0.85 0.65
10 2 5
0.70 0.75 0.80 0.85
3. 3.1 RESULTS
EXAMINATION OF THE INDEPENDENCE OF RESULTS OBTAINED FROM THE SOLUTION GRID
In order to verify the independence of the simulation results obtained from the computational grid, five grids with the specifications presented in Table 5 were considered.
©2019: The Royal Institution of Naval Architects
As indicated in Figure. 15, by changing the grid from 1 to 2 and from 2 to 3, the drag force revealed changes of 16.8% and about 8%, respectively. Changing the grid from 3 to 4 and 4 to 5, the drag force of the ship presented the changes of 2.5% and 0.6%, respectively. Due to the high grid volume in the 5th mode and the 2.5% change of grid 3 compared to the very multi-mode grid 4, grid 3 was used as the optimal grid in the analyses.
Model draft (cm)
8 16.5
0 4 8
Total elements 1698528 3026562 4657860 6982774 9586322
+
60 60 60 60 60
To examine the independence of the numerical results obtained from the computational grid, the drag force of the tanker was extracted in the most critical simulation mode, that is to say draft of 0.165 meters and speed of 1.55knot (equivalent to 0.7974m/s), for each of the modes presented in Table 5. The results are presented in Figures 12 and 13.
10 11
6 7 8 9
0 1 2 3 4 5 6 7 8 9 10 11 Grid elements( milions)
Figure 12. Drag force variations of the ship and the solution grid quality
16.7822468 8
12 16
7.99659719 3
2.54922279 8
0.61791967
Grid 1 to grid 2 Grid 2 to grid 3 Grid 3 to grid 4 Grid 4 to grid 5
Figure 13. Drag force variation percentage of the ship in response to variations of grid type
A-463
Drag force variation (%)
Drag force ( Newtons)
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154 |
Page 155 |
Page 156 |
Page 157 |
Page 158 |
Page 159 |
Page 160 |
Page 161 |
Page 162 |
Page 163 |
Page 164 |
Page 165 |
Page 166
