Trans RINA, Vol 161, Part A4, Intl J Maritime Eng, Oct-Dec 2019
Venant stiffness. Thereafter Lijima et al. (2004) developed a practical method for torsional strength assessment, including a wave load estimation method and a proposal of design loads by a dominant regular wave condition. Chirica et al. (2009) proposed both numerical and experimental methodology to analyze the ship hull torsion and found that the thin wall beam theory proposed for torsion analysis of the ship hull may be considered as a good tool for a very quick torsion calculation. Senjanovic et al. (2012) presented the direct response assessment of a 11,400 TEU container vessel by a beam model subjected to rule based load distributions i.e. pure torque and horizontal shear force induced torque and suggested that torsional response in waves is considered to be one of the most important in structural design of ultra large container vessels. Pelvazza et al. (2012) studied the theory of torsion of thin walled beams with influence of shear for open sections and suggested that the beams with single symmetrical section, such as U section or closed open sections, as container ship sections, loaded to torsion by couples in the cross section planes are also subjected to bending. For modern container ship structures, the shear influence on displacements is small but for container ships with single side structures, this influence could be significant. Carvalho (2015) analyzed the structural behavior of open deck ship hull structures subjected to bending, shearing and torsion by using analytic and finite element solutions and proposed that the simplified thin walled girder application, within the predefined boundary conditions, provides an almost perfect envelope for the axial warping stresses verified in the FE analysis.
3.
INVESTIGATED VESSEL WITHIN THE STUDY
The evaluation of structural strength of a river-sea container vessel has been carried out complying with the BV rules for the Classification of Inland Navigation Vessels [8]. Main features of the vessel are given in Table 1.
Table 1: Main particulars of the vessel Length overall
Length between perp. Breadth mld
Depth Draught
Range of navigation Loading sequence Propulsion
134.05m 131.55m
14.5m 5.7m
3.6m (Estuary) IN (1.7)
2R (2 Runs) Self-propelled
The vessel has longitudinal framing system on deck, inner side shell, side shell, inner bottom and bottom shell. The hatch coaming plate, main deck plate and shear strake plate has constructed with high tensile steel-
A-450
grade AH36 (Reh= 355 MPa). Whereas, the other hull structure is made of mild steel grade A (Reh=235 MPa). There are four cargo holds separated transversely by bulkheads. There are three ordinary frames arranged between two consecutive web frames (Figure 1).
Figure 1: Midship section of the investigated vessel 4.
PARTIAL SHIP STRUCTURAL ANALYSIS
The partial ship structural analysis, respectively cargo hold analysis, is used for the strength assessment of hull girder structural members, primary supporting members and bulkheads.
4.1 STRUCTURAL MODEL
The finite element model is extended up to four cargo holds. The ship is modelled by so called “coarse mesh” model, where the principal finite element type employed is the quadrilateral orthotropic shell element defined by four nodes, each with six degrees of freedom. The element mesh has to follow the local stiffener system as far as practicable; hence this mesh system is characterized by following parameters: • one shell element between every stiffener, • at least 3 elements over the depth of girders, floors, web frames and stringers
• all stiffeners are to be represented by eccentric beams
“Net” thickness approach has been used in the analysis, which means that the analysis is performed on thicknesses reduced due to corrosion. Corrosion deduction thickness is taken according to BV rules. In this way, it is ensured that the cargo ship will have satisfactory structural strength not only in “as-built” condition, but also at the end of her design life.
©2019: The Royal Institution of Naval Architects
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