In this paper, the versatility of discrete element analysis (DEM) in modeling ice-related problems is discussed and further demonstrated using the results from the DEM works conducted by the National Research Council's Institute for Ocean Technology (NRC-IOT) using a commercial code DECICE. These works include a wide range of ice-structure and iceship interaction problems of current interest, i.e., ice loads on conical structures, jamming of floes at bridge piers, modeling of the mechanical behavior of ice rubble, pack ice stability and associated forces on offshore structures, rubble loads exerted on an inclined retaining wall, ridge keel resistance during seabed scouring, dynamic response of a moored conical drill-ship in ice, and ship maneuvering performance in ice. Representative simulations for each case are presented including load, motion and/or interaction process, whichever is appropriate. The simulations from DECICE were compared with experimental data and found satisfactory in terms of accuracy and real-time simulation capability. The accuracy is important for design and engineering of marine structures and ships, whereas, the real-time simulation capability allows it to be used in marine simulators for personnel training and marine operation assessment. The performance of DECICE is also addressed and improve via the implementation of a new contact detection sequence and parallel considerations.

The stationkeeping performance prediction of a Dynamic Positioning (DP) vessel greatly depends on the accurate modelling of the ice forces, which in turn depends on managed ice field characteristics (ice concentration, floe thickness, floe size, ice drift speed and direction and inclusion of brash ice and small ice pieces) and the DP system characteristics (DP gain set-ups, control algorithms etc.). Physical model testing is a key tool in understanding and validating the fundamental relationships between the ice environmental parameters and the dynamics of a DP vessel. The National Research Council's Ocean Coastal and River Engineering Research Centre (NRC-OCRE) has conducted two comprehensive series of experiments with one 1/40 scaled and one 1/19 scaled DP vessels, in various realistic managed ice conditions in the ice tank facility in early 2015 and in early 2018, respectively. The primary objective of the model testing programs was to generate a database on managed ice-DP vessel interactions, which was the core to NRC-OCRE's ice force model development and validation activities. This paper describes the model test planning, preparation of managed ice field, the procedure of the model tests and the methodologies of data analysis for the two model testing programs. In both programs, the physical and mechanical characteristics of the ice field were modelled by controlling ice concentration, ice thickness, floe size, ice strength and the ice drift speed and direction. The ice concentration ranged from a light condition (7/10th) to a very heavy condition (9/10th+) with multiple ice floe sizes ranging between 12.5m to 100m. Multiple ice thicknesses ranging between 0.4m to 2m were used for multiple ice drift speeds (0.2 knots, 0.5 knots, and 1.2 knots) with various moderate to extreme ice encroachment angles. Ice forces were not measured directly but estimated based on the thrusters’ response. In addition, model's 6-DOF motions and accelerations were recorded. Multiple high definition cameras were used to capture the global and local ice-structure interactions both placed in above water and underwater locations. For the 2018 testing program, a new ceiling based video system was introduced that captured the images of the ice basin at multiple overlapping locations, which were processed offline to obtain time sequence full image of the ice basin. Model testing results for a few representative cases are presented in this article. The DP system used in the testing demonstrated capabilities of the vessel in maintaining station for majority of test cases. The measurements as well as the videos showed complex and highly stochastic ice-ship-boundary wall interactions, particularly for high oblique cases. The data and video captured provided sufficient information for developing novel ice force models for real time applications.

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This paper describes a high-fidelity numerical model that simulates vessel stationkeeping operations in ice-rich waters. The discrete event simulation engine incorporates several novel features, including new ice floe failure models for bow and midships locations; an ice floe creation strategy that facilitates rafting of ice floes; and a vessel thruster model that takes into account physical limitations such as thruster angle slew rates and propeller ramp rates. It accommodates a wide range of ice field specifications and runs in real-time on a standard desktop personal computer (Intel® Core™ i7 Processor or equivalent). The model has been validated using physical measurements of a generic drillship model in several broken ice conditions; it predicted thruster forces and motions that were comparable to those observed during dynamic positioning operations.

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