Application of Upcrossing Rate Methodology to Local Design of Icebreaking Vessels
- Freeman Ralph (CARD, C-CORE) | Ian Jordaan (Ian Jordaan and Associates) | Mike Manual (CARD, C-CORE)
- Document ID
- Offshore Technology Conference
- Arctic Technology Conference, 24-26 October, St. John's, Newfoundland and Labrador, Canada
- Publication Date
- Document Type
- Conference Paper
- 2016. Offshore Technology Conference
- 6.1 HSSE & Social Responsibility Management, 5.7.4 Probabilistic Methods, 6.1 HSSE & Social Responsibility Management, 5 Reservoir Desciption & Dynamics, 5.7 Reserves Evaluation
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Design of icebreaking vessels or ice-capable vessels must include consideration of extreme local ice pressures and exposure. Application of probabilistic methods used for data analysis, and then directly applied in design, with consideration of exposure is most useful. The Maximum Event (ME) Method is formulated for cases where ramming of ice is the dominant event. The peak pressures on a hull panel through the ram duration for each ram event is modelled. Data for each panel area are ranked and an exponential distribution fit to the tail of the ranked data. For design, we are then concerned with the maximum of n events expected in a specified period of time (e.g., a year). The random occurrence of ice along a route will also translate in to an annual number of expected impacts depending on ice and vessel dimensions. Vessel Ice classes would correspond to an annual number of impact events. This approach was used during the Arctic Shipping Pollution Prevention Regulation (ASPPR) revisions to validate maximum forces for different class vessels (e.g., a CAC4 vessel would be designed for 10-15 rams per year). For continuous-type interactions (e.g., a large floe crushing around a stationary vessel, or continuous icebreaking) an alternative approach is to use the Up-crossing Rate (UCR) Method. The number of local pressure upcrossings above a specific threshold on a particular panel area within a specified time (e.g., one year of operation) is determined. Exceedance curves for the UCR for increasing pressures on incremental panel areas are determined including an exponential fit to the tail of the distribution. For design, one only needs duration of interactions with the specified ice conditions through the year. The methodology was exercised to estimate local pressure parameters for transit segments during the ODEN 1991 trials. The greater the number of impact events and the longer the event duration, the greater the local pressures on panel areas. These high pressure zones occur and disappear, randomly shifting in location and intensity as fracture and spalling processes reshape the interaction area. For future development of the ISO design code, it is recommended that two modeling approaches be considered, the traditional ME method for short duration events and the UCR method for continuous interactions. The UCR method provides a simple means to design icebreaking vessels for extreme local pressures during continuous interactions. The method is also attractive for design of a stationkeeping vessel operating in broken ice where modeling individual floe interactions is not practical.
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Carter, J.E., C. Daley, M. Fuglem, I.J. Jordaan, A. Keinonen, C. Revill, T. Butler, K. Muggeridge, B. Zou, 1996. Maximum Bow Force for Arctic Shipping Pollution Prevention Regulations Phase II. Report for Transport Canada Ship Safety, Northern Region by Memorial University of Newfoundland Ocean Engineering Research Center. Report TP12652.
Piercey, G., Ralph, F., Barrett, J., Macneill, A., Jordaan, I.J., Younan, A., Fenz, D. (2016). " Design of a Shipboard Local Load Measurement System to Collect Managed Ice Load Data." In Proc. of the Arctic Technology Conference (ATC). St. John's, Newfoundland and Labrador, Canada, October 24-26, 2016. OTC-27455."
Ralph, F., (2016). Design of Ships and Offshore Structures: A Probabilistic Approach for Iceberg and Multi-Year ice Impact Loads for Decision-making with Uncertainty. A Thesis submitted to School of Graduate Studies in partial fulfillment of the requirements for the degree of Doctor of Philosophy. Faculty of Engineering and applied Science, Memorial University, St. John's, NL.