A Reliability-Based Method for Determining Design Ice Loads on Offshore Structures

Abstract

This paper describes a reliability-based methodology that has been developed at ExxonMobil Upstream Research Company (URC) for determining rational design ice loads on offshore structures. The URC methodology provides a systematic framework to account for Type I (aleatory) and Type II (epistemic) uncertainties in assessing global probabilistic ice hazards. Specifically, a logic-tree based approach is developed to model Type II uncertainties in the assessment of ice hazards. Although the method has general applicability, the present work considers a wide, vertical-sided, gravity-based structure (GBS) in a dynamic, annual ice environment. Both FORM/SORM methods and Monte Carlo simulation are used in the analyses. Results obtained from this reliability-based approach indicate that the modeling of Type II uncertainties plays a significant role in quantifying the ice hazards for determining the design ice load. Further, this effort may potentially reduce over-conservatism in typical deterministic ice load calculations. The probabilistic methodology developed in this study has broad applicability and can provide a rational framework for calculating design ice loads on other types of structures for arctic offshore development.

Sakhalin–1: Technology Development for Frontier Arctic Projects

“…The lack of definitive ice characteristics that existed at the time for offshore Sakhalin is representative of most new Arctic development areas. Data collected from these programs facilitated the calculation of probabilistic ice loads as documented in Wu et al [2]. In general, a minimum of three seasons of field observations is needed for extrapolation to rare return interval events.…”