An Implementation of ISO 19906 Formulae for Global Sea Ice Loads within a Probabilistic Framework

Abstract

The ISO 19906 standard provides guidance for the calculation of characteristic ice loads on offshore structures in arctic and cold regions. Ice failure is a complex process and the development and improvement of ice load models can be challenging, in large part because of difficulties obtaining full-scale data and scaling issues when extrapolating small-scale test data. Many of the ice load models referenced in ISO 19906 were developed during arctic exploration in the 70's and 80's. Typically, simplified geometries are assumed for both the structure and ice features in order to obtain analytic solutions; other simplifications may be incorporated appropriate for the specific applications considered and information available. A significant proportion of referenced models provide the maximum load during an interaction, rather than the development of the load over time. This can be a limitation were penetration into a thick ridge is limited by available driving force and kinetic energy. Given the large variety of ice conditions to which a structure may be subjected and the apparent randomness in ice fracture and damage mechanisms, there can be considerable variation in loads. Ice strength may be set to a characteristic fixed value, the ISO model for global sea ice loads is based on a relationship that considers ice thickness and contact width and is based on upper envelop fits to failure data. When determining the appropriate characteristic load on a structure, consideration should be given to exposure (i.e., the number and durations of ice interactions). Loads based on characteristic values for parameters such as ice thickness and ice strength could be inaccurate for scenarios where the exposure is significantly different than that on which the characteristic values were based. The application of probabilistic methods can be used to account for differences in exposure. While ISO 19906 references such methods, guidelines on implementation is limited. This paper examines issues in implementing available formulae for ice loads on fixed structures within a probabilistic framework and shows how characteristic ice loads differ depending on the model and assumptions used. The Sea Ice Loads Software (SILS), a probabilistic framework developed by C-CORE for calculating characteristic ice loads using the methods referenced in ISO19906, is used for the analyses and comparisons.

Update on Probabilistic Assessment of Multi-year Sea Ice Loads on Vertical-faced Structures

“…In the previous version of SILS (Fuglem et al, 2014a), when a ridge interacted with the structure, it was assumed that the ridge extended over the full width of the floe-structure interaction and that the ridge did not break out of the floe (i.e. In the previous version of SILS (Fuglem et al, 2014a), when a ridge interacted with the structure, it was assumed that the ridge extended over the full width of the floe-structure interaction and that the ridge did not break out of the floe (i.e.…”

Implementation of ISO 19906 for probabilistic assessment of global sea ice loads on offshore structures encountering first-year sea ice

“…This paper addresses issues that may be encountered in determining design first-year ice loads for sloping structures; similar issues for multi-year ice were addressed in [2] for vertical structures and [3] for sloping structures.…”

“…The referenced models in ISO 19906 cover deterministic and probabilistic approaches to determine loads from both first and multi-year ice on vertically-faced and sloping structures. Consideration should be given to (1) limit stresses at the ice-structure interface, based on the dominating ice failure mechanisms; (2) limit forces associated with the available driving force that can act on the interacting ice floe due to wind, currents and surrounding ice; and (3) the kinetic energy of the impacting ice feature. Models describing each of these three limit types are to be included in the ice load calculations.…”

Accelerating Numerical Ice Engineering Tools Using GPGPU

“…This development in GPU computation has enabled the simulating of massive event set in timely and practical way. C-CORE is engaged in understanding the iceberg and sea ice design loads needs of the energy sector and has several applications related to icebergs and sea ice including the sea ice loads software (SILS) (Thijssen et al, 2014), iceberg load software (ILS) (Fuglem et al, 2014) and models for sea ice forecasting (Howell et al, 2015). SILS is used to determine design loads for fixed offshore structures encountering sea ice.…”