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Analysis of Ice-Induced Damages to a Cargo Carrier and Implications wrt. Rule Requirements
Norwegian University of Science and Technology, Faculty of Engineering Science and Technology, Department of Marine Technology.
2014 (English)MasteroppgaveStudent thesis
Abstract [en]

In this thesis, an ice-induced damage to a DNV-GL registered cargo ship is investigated by looking into its damage survey report, and running nonlinear finite element analyses. The analyses are used for regeneration of the damage deformations and estimation the damage loading. The results are compared with design and capacity ice loads calculated from DNV-GL and IACS' rule requirements for the ice class of the ship studied, \cite{DNV_ICE}, \cite{IACS_PC}. The Finnish-Swedish Ice Class Rules (FSICR), which are adopted by DNV-GL, and the International Association of Classification Societies Unified Requirements for Polar Class (IACS UR PC), are derived and explained with focus on plating and framing requirements. From the rules design loads and capacity loads for the frames in the side bow of the case study ship, are calculated and applied to three different finite element models for analysis. The first model is a single frame with plate flange. The second is two neighbouring frames with two tripping brackets in between. The third model is the ship side damage area. In addition to the design loads from the rules, five proposed load cases are analyzed for the ship side model. The resulting model deformations are compared with deformation measurements from photos given in the surveyor report, in order to evaluate the applied load cases. A resemblance in the deformations indicates a load case that resembles the original damage load. The analyses of the frame models with design and capacity loads form the rules show that the frames have a considerable amount of capacity beyond the rule calculations. In one of the analyses a frame capacity of $15MPa$ is obtained, while the design capacity is $5MPa$. For the ship side model, only one of the five proposed load cases proves to be successful. Measurements of the deformation of the model are done, and they coincide with the photos where the deformations are large, but give a poor match elsewhere. A pressure of $6.9MPa$ over an area of $5.8m^2$ is needed to reproduce the largest of the deformations seen in the photos. The ship side analysis shows that a force about ten times the FSICR design load, or twice the IACS PC design load, is needed to produce the deformations seen in the photos. The large difference in the ratio for the FSICR and the IACS PC force originate from the difference in the size of the load application area. The rules appear to present very conservative design loads, as the finite element analyses reveal a considerable amount of load carrying capacity beyond the design load level. This is because the rules are derived to be conservative, hence, they are not suited for calculation of the actual capacity of a structure. For the ship side model, an ice class 3-5 notations higher than the notation it is classified for is needed to withstand the damage loading, depending on how the numbers are evaluated. This implies that the ship in question has been sailing in waters with ice conditions it was not designed for. Due to a lot of uncertainty related to the photo measurements, and the many assumptions made for the analyses' input, an uncertainty is related to the output of the analyses, and the conclusions based on these. This thesis is conducted in cooperation with DNV-GL, Tankers and Dry Cargo Section, Høvik, Norway. They supplied survey reports, ship drawings, and supervision along the way. The vessel documents are applied anonymously within the production of this report. In order to realize the true potential of ice damage investigation, more precise documentation of the scale of the actual damages must be recorded.

Place, publisher, year, edition, pages
Institutt for marin teknikk , 2014. , 142 p.
URN: urn:nbn:no:ntnu:diva-25089Local ID: ntnudaim:10737OAI: diva2:730491
Available from: 2014-06-27 Created: 2014-06-27 Last updated: 2014-06-27Bibliographically approved

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