Trans RINA, Vol 161, Part A4, Intl J Maritime Eng, Oct-Dec 2019
INVESTIGATION OF HULL STRENGTH OF RIVER SEA CONTAINER VESSEL (DOI No: 10.3940/rina.ijme.2019.a4.558a)
S Rahman, University of Liege, Belgium SUMMARY
River sea vessels are ships for inland navigation and suitable for restricted navigation at sea in regions where, - significant wave height does not exceed 2m, according to Bureau Veritas Rules for the classification of inland vessels. In a container vessel structure, almost the entire deck space is occupied by hatches, leaving a narrow strip of deck plating outboard. This calls for a topside structure of heavy plating or a double hull to provide material in tension, stiffness against lateral and torsional loads, and resistance to buckling in compression when the vessel is in sagging condition. For sea going open deck vessels, torsional loading plays a predominant part to the hull girder strength and for inland navigation open deck vessels; the effect of torsion is rather negligible. Keeping this scenario in mind, the aim of this project is to investigate the hull strength of a river sea container vessel under combined bending and torsional loading to study the effect of torsion on river sea open deck vessel. To perform the strength analysis, firstly, a finite element model is created using Femap with NX Nastran software for the investigated vessel. Therefore, still water and wave loads are calculated using direct calculation. To find out the still water loads Argos software is used and for the wave induced loads potential flow software Hydrostar is used. Next, Finite element model is verified with classical beam theory and thin wall girder theory. Then the effect of various loading conditions on structural response is investigated. After, structural response of different hull configurations are scrutinized under combined bending and torsional loading. Finally, some recommendations are proposed for structural response of river sea container vessel subjected to combined bending and torsional loading.
1. INTRODUCTION
A river-sea vessel, is subjected to various load patterns with many magnitudes which cause deformation of its structure, as well as stresses. The first design step is to calculate exact loads acting on the structure concerned, in order to estimate the structural strength in a reasonable way and consequently to develop the design. Container vessels are characterized by exceptionally wide hatch coamings and are sometimes often called open deck vessels. The use of wide hatches has significant effects on torsional strength and rigidity of hull girder. Due to its particular construction, vessel hull structure can be considered as thin walled structures. Axial (warping) stresses as well as shear stresses are normally- assessed using the thin-walled theory with open cross sections subjected to torsion. The torsional strength and rigidity of open deck vessels depend mainly on the structural arrangements of both vessel ends. All vessels are subjected to torsional moments which tend to twist the hull girder along its length. In general, torsional stiffness is more than adequate to prevent undue distortion of the structure. Torsional loading induces additional stresses, usually called warping stresses, near hatch corners. Wave induced torsion loading results from motion of a vessel in oblique waves. When the vessel is sailing obliquely into the predominant waves the vertical wave bending moments are reduced but the horizontal bending moments and torsional moments are increased.
For sea going container vessels, torsional stress plays an important part to the hull strength. Torsion induced stresses and deformation is generally negligible on inland vessels solely operated on inland waterways. But when inland container vessels are operated in restricted
©2019: The Royal Institution of Naval Architects
maritime water stretches, the impact of torsion on vessel’s hull strength has not yet deeply been investigated. It is thus of importance to better understand the torsional strength as well as bending strength and hull girder deformation characteristics of river-sea vessels with large hatch openings. Keeping this scenario in mind, this paper attempts to investigate the hull strength of a river-sea container vessel.
2. LITERATURE REVIEW
Ship structure design and analysis has always been a very important and active field of scientific research, making those structures more reliable and cost effective. A lot of research and studies have been performed regarding the structural response under combined bending and torsional loading in both analytical and numerical (mainly FE) approaches. At first, Elbatouti et al. (1974) investigated the structural analysis of SS-7 containership under combined loading of vertical, lateral and torsional moments using finite element techniques. They analyzed the hull structure and found that local deformation due to non-prismatic nature of the structure and the deck openings can cause considerable increase of global stress level in the inner bulkhead plating. Next Vernon et al. (1987) compared the St. Venant and warping based thin walled beam theories and their application in the torsional analysis and suggested that warping based theory provides a better model of the behavior of prismatic thin walled sections because of the account of longitudinal deformation. The non-localized axial and secondary shear stresses associated with warping restraint can significantly add the overall stress distribution, particularly in open sections with low St.
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