Global ice loads at different locations on a ship during rams into ice are a function of ship motions and added mass in addition to the failure mode and strength of the ice. In the literature, various analytical added mass models have been used for ship-ice interactions, which could lead to significant differences in the prediction of global ice loads on ships. In this work, an improved added mass model has been developed based on numerical results and existing analytical models. Added mass coefficients of three ice-going ships, CCGS Amundsen, CCGS Louis S. St-Laurent and MVArctic, were estimated using four analytical added mass models. It was found that the differences in added mass coefficients predicted by these models are significant and enhancements can be made. A body-exact numerical simulation tool based on the potential-flow theory, MAPS0, has been used to compute the added mass coefficients of the three vessels in the frequency domain and the results were used for the development of the improved added mass model. The improvement in the load predictions has been demonstrated by applying the new added mass model to the three vessels.
Icebergs can pose risks to platforms in arctic and subarctic regions. These risks require careful consideration during design, and as well during operations. Platforms must be designed to withstand potential impacts from icebergs, or to disconnect and move offsite to avoid impacts. ISO 19906 allows use of ice management to mitigate iceberg and sea-ice actions. In the case of icebergs, management may include detection, monitoring, towing, disconnection and evacuation. Threat assessment is also a critical input to the iceberg management decision-making process. For example, given one or more detected icebergs and available information on the iceberg and environment characteristics, what is the probability of exceeding platform design ice actions? Based on the threat assessment, better decisions can be made regarding which iceberg to manage, whether more information should be acquired, and whether shut-down or evacuation is needed. This paper describes a new tool developed to estimate the distribution of iceberg impact actions from an encroaching iceberg given concurrent metocean conditions, conditional on impact. The tool can be used in a number of ways depending on the information available to the user. It can be used to assess the threat from a single iceberg or can be used to compare actions from multiple icebergs in the region, or for the same iceberg but with changing weather conditions. The iceberg load assessment tool is demonstrated for several example cases on the Grand Banks, showing the benefit of improved iceberg characterization obtained through rapid iceberg profiling.
The Iceberg Loads Software (ILS) was developed initially to determine design iceberg loads for the Hebron Gravity Base Structure (GBS). The ILS framework has since been adapted for assessing iceberg loads on other structures such as the West White Rose Platform, subsea protection structures, pipelines laid on the seabed and floating production structures (spars and FPSOs). When the ILS was developed, the available iceberg geometry dataset (collected in the 1980s) was relatively limited, which required certain assumptions (i.e., flat wall interaction) and parametrizations (i.e., length distribution, length/draft/mass relationships, eccentricity, etc.) in the formulation of the interaction model. Renewed iceberg profile collection began in 2012, with ongoing improvements in the data collection methodology such that, of the 200 iceberg profiles collected from 2012 onwards, 134 were collected in 2019. The profile data were collected using LiDAR for the iceberg sail and multibeam sonar for the keel. The ILS has been updated using the recent three dimensional (3D) profiles, and a comparison of original versus updated iceberg load distributions for a generic structure show a decrease in loads. Updated ILS loads are compared with another iceberg load analysis tool that directly incorporates iceberg profile data rather than relying on some of the assumptions and parametrizations used in the original ILS formulation. This comparison shows some differences, particularly for extreme loads, which are the subject of on-going investigation.
The move to reduce greenhouse gas emissions in the offshore hydrocarbons production industry has resulted in a growing interest in the possibility of using offshore wind to reduce on-platform power generation. While some offshore areas are progressing towards or planning for the use of offshore wind to electrify hydrocarbon producing platforms, they do not have the challenges associated with Newfoundland & Labrador's offshore environment.This region is prone to incursions by icebergs and pack ice, which would present a risk to offshore wind turbines. Analysis approachesto assess these risks, along with preliminary results, are presented herefor floating offshore wind turbines (FOWT). An area of interest (AOI), covering 45°N to 51°N and 45°W to 51°W, was defined covering all development licenses on the Grand Banks, Flemish Pass and Orphan Basin. Iceberg and pack ice contact rates and loads were calculated using data from the Nalcor NESS Metocean database, Canadian Ice Service (CIS) ice charts and satellite imagery. Ice loads corresponding to 50-year return periods levels were assessed, with and without ice management, giving a basis for determining whether ice management and/or disconnection capabilities are required. The frequency and severity of atmospheric icing of turbines was also modelled using available data and models.
When planning oil and gas exploration and production operations off the east coast of Canada, the potential for iceberg impacts must be considered. Environmental conditions in this region can be very harsh, and iceberg trajectories are notably unpredictable. When an iceberg has the potential to impact a Floating Production, Storage, and Offloading (FPSO) platform, ice management through towing will be attempted; and if this fails, the production system will be shut down, line flushed, the mooring and riser systems disconnected, and the platform moved off site. If trajectory forecasting were highly accurate, only icebergs passing very close to the platform would require ice management and possible shutdown of the platform. Given natural variations in wind, currents, and waves, and challenges measuring and forecasting these parameters, there is considerable forecast uncertainty. This results in added expenses for extra ice management and unnecessary shutdowns. Improvements in trajectory forecasting accuracy, characterization of forecast uncertainty, and methods to account for these uncertainties in operations would all be beneficial. This paper outlines an approach for simulating large numbers of iceberg trajectories in varied and realistic environmental conditions from hindcast met-ocean data in conjunction with a forecasting uncertainty model derived from forecast validation studies. A model, named BergCast, was developed so that proposed strategies for improving ice management operations can be evaluated, and the value of reducing forecasting uncertainty quantified.
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