Section 2 FE modelling

2.1.2 The most onerous (weakest) structural arrangement within a hull area may be used for the structural model provided arrangements within the area are similar.

2.2.1 The structural model is to represent the hull, hull stiffening (main/intermediate frames and primary structural members), deck stiffening and all brackets in the grillage under consideration, as shown in Ch 2, 2.2 Extent of structural modelling 2.2.1. The modelled grillage section is to extend longitudinally such that the boundary conditions on the longitudinal bounds do not influence the deformation near the ice load patch. The fine mesh area is to be extended to one AFT.FWD web frame of two transverse bulkheads as the grey area in Ch 2, 2.2 Extent of structural modelling 2.2.1.

Figure 2.2.2 Extent of structural modelling and evaluated region

2.2.2 It is recommended that the fine mesh model is to extend vertically to the deck above the upper ice waterline and the deck located below the lower ice waterline at least. Transversely, the fine mesh model extends from the side shell to the centre line or inner bulkhead if any. Longitudinally, the fine mesh model is to extend one or two more web frames from the AFT transverse bulkhead and the FWD transverse bulkhead to include the load cases in Ch 3 Design Loads. The full depth of the ship and two-tank length is to be modelled as shown in Ch 2, 2.2 Extent of structural modelling 2.2.1. Unless there is asymmetry of the ship about the ship’s centreline, then only one side of the ship needs to be represented with appropriate boundary conditions imposed at the centreline as shown in Ch 2, 2.3 Element type and mesh size 2.3.1.

2.2.3 Unless there is asymmetry of the ship about the ship’s centreline, then only one side of the ship needs to be represented with appropriate boundary conditions imposed at the centreline. However, it is recommended that both sides of the ship be modelled, as this will simplify the loading and analysis of asymmetrical loading conditions.

2.2.4 All areas for modelling are to be proposed by the designer and validated with LR.

2.2.5 The gross thickness which is obtained by deducting any thickness for voluntary addition from the as-built thickness is to be used for structural modelling.

2.3.1 Where FE models are used for non-linear analysis, the extent of the fine mesh model is expected to consider the size of the ice load patch and the distribution of supporting structures.

2.3.2 Element type: plate, stiffener web and flange should all be modelled using shell elements. The analysis may be carried out using 4-node shell elements.

2.3.3 Element size: the mesh should be fine enough to reflect the local deformations and stresses developed during buckling and collapse, as shown in Ch 2, 2.3 Element type and mesh size 2.3.3. Element size should be a minimum of eight (8) elements between stiffeners and the mesh size should be between t x t and 10t x 10t or 50 mm, whichever is smaller, where t is the plate thickness.

Figure 2.2.3 Fine mesh FE model in ice belt region