Trans RINA, Vol 153, Part A4, Intl J Maritime Eng, Oct-Dec 2011 designed with mild steel and the ends of the double bottom girders that are designed with HTS 36 material.
Figure 2: Midship Sections of the Ref. 14 Panamax ship of DWT 62,000[14](a) and basic Panamax ship of DWT 75,000 (b)
The ABS SafeHull[5] “net” scantling approach was used in FE model of the vessel where the minimum nominal design corrosion values are as shown in Figure 1 of part 5C Chapter 3 Section 2 of ABS 2009 Rules.
That means that the net scantlings were calculated by subtracting the nominal design corrosion values (NDCV) from the “as designed” scantlings.
5. FINITE ELEMENT 3D - 3 CARGO HOLD MODEL
ABS SafeHull V-10 was used for this study. The FE models consist of 3-cargo-hold-length of
girder and local behavior of the main supporting structures.
“One Step” FE method with combined (fine and coarse) mesh is used so that the simultaneous strength evaluation of both the hull girder and local structural members is achieved in one FE run. This method renders the local 2- D and / or 3-D fine mesh analysis redundant.
If for
instance, separate 2-D models were to be developed, the assumed boundary conditions, the omitted loads, moments and stresses in the 3rd dimension, result
in
detriment to the accuracy of the calculation. In short, the customary intermediate step that was usually followed by the designers / builders in order to reduce the computation effort by well over 60%, has been omitted.
Each FE model was modified and run separately. The modification involved alteration of the double bottom structure so as to correspond to five different double bottom heights. Figure 4 below, shows the FE model for the double bottom height of 1610 mm that is IACS CSR
the midship
structures, and are used to determine the global response of the hull
The models developed reflect the whole cross-section (no symmetry boundary conditions about the center line used) of the vessel. No cutouts for longitudinal stiffeners and other small openings were modeled. Very fine mesh modeling that could induce also the hot spot stresses to critical areas (i.e. the end connections of the double bottom girders) were also included in the analysis.
Three basic prismatic models were used which reflect the structural behavior of the mid hold of each 3 hold model as shown in Figure 3.
The application of the “One Step” strategy is intended for the estimation of the overall scantlings of plates and stiffeners but also the structural details. The mesh sizes for the “One Step” FE models are generally close to one stiffener spacing (560 ~ 900 mm), except for areas found to be highly stressed. The latter areas were re-modeled after the initial run using finer mesh, whereby various locations of interest (highly stressed) including various openings and manholes can be assessed. Figure 8 below shows the resultant stresses around a manhole and pipe opening, and adjacent critical joints of the inner bottom to lower stool side plate versus the same girder without an opening.
©2011: The Royal Institution of Naval Architects
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