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Polar and Arctic Engineering

Estimation of Local Ice Pressure Using Up-Crossing Rate

[+] Author and Article Information
Chuanke Li

 Memorial University of Newfoundland, St. John’s, NL, A1B 3X5, Canadachuanke@engr.mun.ca

Ian J. Jordaan

 C-CORE, St. John’s, NL, A1B 3X5, Canadaian.jordaan@c-core.ca

Rocky S. Taylor

 Memorial University of Newfoundland, St. John’s, NL, A1B 3X5, Canadarstaylor@mun.ca

J. Offshore Mech. Arct. Eng 132(3), 031501 (Mar 17, 2010) (6 pages) doi:10.1115/1.4000403 History: Received January 20, 2009; Revised June 29, 2009; Published March 17, 2010; Online March 17, 2010

Ice load estimation is required in the design of ships and offshore structures for arctic and subarctic conditions. This paper focuses on the estimation of local ice pressures. The “event-maximum” method for local ice pressure analysis is a probabilistic method based on the maximum pressure of a given event; other local peaks in the data are not included. To study how this may affect local ice pressure estimates, a new probabilistic method based on the up-crossing rate was developed. Field data from 1982 Polar Sea arctic trials in the Beaufort Sea are processed as a time series. Up-crossing rates at different local pressure levels are obtained for local areas of interest. A relationship between up-crossing rate and local pressure-area results is established. Results from the analysis of full-scale data using the event-maximum method are presented for the selected data set; a more comprehensive set of results for the analysis of available ship-ice interaction data is presented in a companion paper. For a sample case, local ice pressure estimates obtained using the up-crossing rate method are compared with results obtained using the event-maximum method. The local pressure-area relationship is found to be similar for both the up-crossing rate method and the event-maximum method. For design curves based on the data set considered, estimates using the event-maximum method were more conservative than those obtained using the up-crossing rate method. The up-crossing rate approach is promising; analysis of additional data sets is recommended to allow broader comparison of the methods.

FIGURES IN THIS ARTICLE
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Copyright © 2010 by American Society of Mechanical Engineers
Topics: Pressure , Ice , Events
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References

Figures

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Figure 1

Polar Sea instrumentation during its 1982 Voyage (7)

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Figure 2

Illustration of local pressure methodology (5)

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Figure 3

Illustration of missing aspects in the event-maximum method resulting from (a) omission of peaks on panels other than the one having the overall event-maximum, and (b) omission of time-varying peaks on individual panels other than the event-maximum

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Figure 4

Illustrations of (a) the event-maximum process and (b) the intermittent continuous process

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Figure 5

Illustrative example of how up-crossing rate is determined from Polar Sea data for a given pressure threshold

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Figure 6

Up-crossing rate versus pressure with best-fit lines for different areas using logarithmic scale for up-crossing rate

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Figure 7

Plot of α versus area and line of best-fit based on analysis using up-crossing rate method for (a) linear scales and (b) logarithmic scales

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Figure 8

Plot of x0 versus area based on analysis using the up-crossing rate method

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Figure 9

Comparisons of event-maximum and up-crossing rate methods for (a) α versus area and (b) x0 versus area

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Figure 10

Comparisons of cdf curves for different areas based on both the event-maximum and up-crossing rate methods

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Figure 11

Comparison of pressures estimated using the two analysis methods corresponding to different exceedence levels (x0 is based on data in Fig. 9 for the event-maximum method and x0=−1 is for the up-crossing rate method (6))

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Figure 13

Comparison of pressures estimated using the two analysis methods corresponding to different exceedence levels (x0=0 for the event-maximum method)

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Figure 14

Difference between pressures estimated using the two analysis methods corresponding to different exceedence levels (x0=0 for the event-maximum method (4) and x0=−1 for the up-crossing rate method (6))

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Figure 12

Difference between pressures estimated using the two analysis methods corresponding to different exceedence levels

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