First-year ridge loads on moored offshore structures

This paper describes the background, test methodology, experiment program and analytical methods used for a project to predict the peak mooring system loads that occur when a floating offshore structure encounters a first year ice ridge. The project included the construction of simplified physical models of a Spar at 1/30 scale and a Floating Production Unit (FPU) at 1/40 scale. The Spar was a representative structure with a downward breaking cone and a vertical neck designed for operation in ice. A partial spar, consisting of the cone only was also evaluated. The Floating Production Unit (FPU) was a simplified barge. This model was tested with a rigid connection to the towing carriage and also on a representative mooring system that allowed for some compliance. The model FPU was also fitted with two load measuring panels designed to measure local ice loads on the hull. The methods of producing the model ridges and measuring their physical properties are described. Each model was tested in a range of ridge geometries from temperate to Arctic regions. The experiments were carried out in the ice tank of the National Research Council of Canada's Institute for Ocean Technology. This paper describes the first phase of experiments on the spar model completed in December 2009 and the first phase of experiments on the FPU completed in June 2010. The paper also presents the description of a parallel numerical approach to the problem, which looks at the methods needed to model the ridge-structure interaction using finite element methods. The results of the simulations and experiments are discussed in general terms. Copyright 2011, Offshore Technology Conference.Peer reviewed: YesNRC publication: Ye