Structural resistance of polar ships and FPSO´s to ice loading
Due to the substantial increase in oil and gas activities in Polar areas the demand for ice strengthen vessel has increased greatly. This increase in demand has highlighted the importance of designing ice strengthened ship structures that are more producible and maintain adequate safety and integrity. In order to encounter these new challenges, the international association of classification societies (IACS) has developed unified regulations for the designing of ice strengthened ship. In addition to these requirements, most of the classification societies have their regulation for design of polar ships.
Stiffened plates are the basic structural building blocks of ships. So, the study mainly explores the plastic response of stiffened plate subject to lateral ice loads. The Non Linear Finite Element Method (NLFEM) is extensively used to study the plastic behavior of stiffened plates. The Abaqus non linear finite element program is used in this study.
The aims of the study are to investigate the validity of the limit state equation employed in the IACS new Unified Requirements for Polar Ships , investigate the membrane effect at large deformation, determine the ALS design load, and assess limit loads when fracture in plating likely to take place. The study also focuses on the warping effect of unsymmetrical sections and the effect of end brackets on the lateral load carrying capacity of the stiffener. The effect of mid-span tripping bracket on the load deflection behavior of L and T stiffeners is also studied. In particular, the study focuses on the behavior of inclined T and L stiffener.
As ships move forward by crushing ice, sides of ships bow come across with ice initially. To design ice strengthen vessel, its very important to understand the behavior of ships side structure subjected to ice loads. So, this study extensively focuses on the non-linear finite element analysis of ships side structure subjected to ice loads. Normally, ship design rules are based on the behavior of single frame subjected to loads. Its reasonable to consider frames singly under the uniform loading but in case of ice loading which is non uniform, the behavior of the structure obtained from single frame based design does not accurately represent the true behavior of the structure. The load-deflection characteristic of frames in isolation, frames as part of a ½+1+½ frames and frames as part of a grillage subjected to unsymmetrical loading is studied. As, stiffeners in the side structure of ships bow are not normally perpendicular with shell plate, the lateral capacity of frames as part of a ½+1+½ frames and as part of a grillage is obtained for inclined stiffener.
The analyses in this study cover the full range of stiffener behavior from elastic, through yield, through the formation of initial mechanisms, through large deformations. The parameters considered for the analyses are:
frame profile: Angle, Tee
load length: patch (transverse), uniform (longitudinal)
end brackets: with, without
Angle of inclination of stiffener web with the plate flange
Tripping bracket at mid span
Place, publisher, year, edition, pages
Institutt for marin teknikk , 2012. , 148 p.
ntnudaim:8059, MSN1 Marine Technology, Marine Structures
IdentifiersURN: urn:nbn:no:ntnu:diva-18633Local ID: ntnudaim:8059OAI: oai:DiVA.org:ntnu-18633DiVA: diva2:566144
Amdahl, Jørgen, Professor