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Polar and Arctic Engineering

Local Design Pressures for Structures in Ice: Analysis of Full-Scale Data

[+] Author and Article Information
Rocky S. Taylor, Ian J. Jordaan

Memorial University of Newfoundland, St. John’s, NL, Canada C-CORE; Memorial University of Newfoundland, St. John’s, NL, Canada

Chuanke Li

Memorial University of Newfoundland, St. John’s, NL, Canada

Denise Sudom

J. Offshore Mech. Arct. Eng 132(3), 031502 (Jun 17, 2010) (7 pages) doi:10.1115/1.4000504 History: Received January 20, 2009; Revised June 26, 2009; Published June 17, 2010; Online June 17, 2010

Abstract

The design of structures for ice conditions requires knowledge of local ice pressures to allow for appropriate levels of structural strengthening. Full-scale field data are keys to enhancing our understanding and modeling of ice behavior. Data collected during icebreaker ramming events represent an important source of information for use in design load estimation, and the evaluation of design methodologies. This paper examines several ship-ice interaction data sets using the ‘event-maximum’ method of local pressure analysis developed by Jordaan and (1993, “Probabilistic Analysis of Local Ice Pressures,” ASME J. Offshore Mech. Arct. Eng., 115, pp. 83–89). In this method, the local pressure is obtained from a normalized curve, which contains two parameters $α$ and $x0$. The parameter $α$ is a function of the area, well represented by the curve $α=CaD$, where $a$ is the local area of interest, and $C$ and $D$ are constants. The parameter $x0$ is assumed a constant for a given design scenario. An alternative approach, the up-crossing rate method, is presented in a companion paper (2009, “Estimation of Local Ice Pressure Using Up-Crossing Rate,” Proceedings of the OMAE 2009, Honolulu, HI). Local pressure analysis results for data from the USCGS Polar Sea, CCGS Terry Fox, CCGS Louis St. Laurent, and Swedish Icebreaker Oden are presented. A discussion of panel exposure, event duration, and the effects of these factors on $x0$ is given. New design curves are included. For all data considered, the calculated values of $α$ fall below the design curve. For the design, it is recommended that $α$ is calculated using a $C$ value based on the impact data collected under ice conditions similar to those for the design scenario; $D$ may be treated as a constant having a value of −0.7. A design value of $x0$ may be determined based on the analysis of appropriate data sets. The treatment of exposure is described for data analysis and design. The effects of exposure must be removed during data analysis to provide a design curve based on single panel exposure. For the design, estimates from the design curves must be adjusted to properly reflect the design exposure.

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Figures

Figure 3

Treatment of exposure: data analysis versus design

Figure 4

Local pressure design curve (α versus area) developed by Jordaan (1)

Figure 5

Plot of α versus area for ship-ice interaction data analyzed in this study

Figure 6

Plot of x0 data showing results both with and without adjustment for exposure effects

Figure 7

Plot of x0 versus area (including exposure effects) for ship-ice interaction data analyzed in this study

Figure 1

Illustrations of (a) ice interacting with vertical-walled structure, and (b) the global interaction and local design areas

Figure 2

Illustration of the local pressure methodology for sample event (7)

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