Trans RINA, Vol 157, Part A3, Intl J Maritime Eng, Jul-Sep 2015
Figure 3: Absolute of relative deviation between CFD and experiments for light and heavy displacement and median total uncertainty of DTMB 5415 model [24].
3.2
HYDRODYNAMIC PROPERTIES OF SLENDER HULLS
3.2 (a) Total Resistance Coefficient
Figure 4 shows the total resistance coefficient (CT) of the full-scale ship based on numerical simulations and a consistent variation for changing Froude number and displacement can be observed. The resistance coefficient reduces with increasing slenderness and the hollow and humps in the resistance curve become less pronounced. The resistance coefficient of the hulls of L = 150 – 190 m remain almost unchanged for Fr = 0.40 – 0.49. However the hulls under consideration differ in displacement and wetted surface
area and no conclusions towards
appropriate performance on the most appropriate hull form can be drawn.
Figure 5: Drag non-dimensionalised by buoyancy force and divided by Froude number squared presented with respect to Froude number
R' = ρ gFr T
RT 2
This graph shows that the non-dimensional resistance decreases for increasing Froude number and reaches a minimum at Fr = 0.37 and increases at a varying gradient thereafter, whereas the 110 m and the 130 m hull show higher gradients. This is also the situation for the light and heavy displacements, but for Fr < 0.37 the 190 m hull shows a higher normalised resistance at the light displacement and the 110 m and 130 m hull at the higher displacement case.
The gradient of the resistance curve between Fr = 0.25 – 0.37 increases
with increasing displacement. The
minimum value at Fr = 0.37 is lowest for the light displacement followed by the medium and heavy displacement, vary from 0.12 – 0.15 across all hulls and displacements.
For the light displacement case the hulls of 110 – 150 m from Fr = 0.25 – 0.37 are grouped together, but are branching for higher speeds whereas the longer hulls have more beneficial
resistance behaviour. For the
medium displacement a grouping of the curves for L = 130 – 190 m was seen and for the heavy displacement a grouping of L = 150 – 190 m can be observed. Hulls outside that group had a higher normalised resistance.
3.2 (c) Shear Force
Figure 4: Total resistance coefficient for medium speed hull forms at medium displacement with respect to Froude number.
3.2 (b) Non-dimensional drag Figure 5 shows the drag non-dimensionalised
by
volumetric displacement, density, gravity and Froude number squared for the medium displacement case with respect to Froude number:
©2015: The Royal Institution of Naval Architects
Figure 6 shows the shear force coefficient for each displacement compared to the ship-model correlation lines of ITTC and Grigson and the values predicted in this study are well between the boundaries of the two lines. Furthermore a dependency on the Froude number can be observed for all cases under consideration. The shear force coefficient increased
displacement mode and decreased for the
for the light heavy
displacement case compared to the medium case, but still remained between the two empirical lines.
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