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Collaborating Authors
CARD
Abstract The study of ice loads and associated mechanics is highly important in supporting oil and gas exploration and development in ice-prone offshore regions. While knowledge gaps regarding full details of the dynamic ice structure interaction process remain, substantial research is being carried out over a range of scales to improve understanding of excitation mechanisms for structures subjected to compressive ice loading. The present paper is focused on the first of a new series of medium-scale laboratory tests that have been carried out as a part of a larger program of research aimed at improving understanding of compressive ice failure phenomena and links between the formation of high-pressure zones and the occurrence of ice-induced structural vibrations under controlled conditions. The tests presented in this paper focus on the indentation of ice using a single spherical indenter mounted on a compliant beam system. Nine tests were performed to investigate the effect of ice temperature and indenter size on ice failure processes associated with high-pressure zone formation and evolution during dynamic ice crushing tests. Ice failure events were observed from regular and high-speed video synchronized with LVDTs and load cell data. Observations of ice load dynamics and structural response are discussed, along with corresponding observations of failure processes in the ice. In general it was observed that ice at warm temperatures was more prone to ductile type failure with lower, less dynamic pressures. By contrast, results from tests conducted at colder temperatures were characterized by a combination of spalling and crushing failure, which corresponded more with large-amplitude, sawtooth load cycles, which often resulted in load drop to zero as the rebounding structure cleared the failed ice from around the indenter. In terms of scale effects, it was observed for the same indentation rate and temperature, smaller indenters produced higher amplitude, higher frequency sawtooth loading than was observed for larger diameter indenters.
- Europe (1.00)
- Asia (0.68)
- North America > United States (0.68)
- North America > Canada > Newfoundland and Labrador > Newfoundland > St. John's (0.46)
Abstract In ISO19906 (2010) (Arctic Offshore Structures) specific algorithms are provided for level ice loads on sloping structures; they are based on the separate work of Ralston and Croasdale. These methods were developed decades ago and comparisons with full scale data, especially from Confederation Bridge, suggest that certain idealizations can be improved; more importantly that they may be over-predicting the measured loads. For these reasons it was decided to critically review the existing Croasdale et al algorithm (as specified in ISO) and update it based on learnings from Confederation Bridge, other experience and new ideas. During the study, over 50 ice interaction events at Confederation Bridge were chosen as geometrically similar to thick ice acting on an Arctic structure. The interaction process and relevant parameters (such as ride-up height) were documented in detail and the measured loads compared with predictions for each event. The model, as currently specified in ISO, generally over-predicted by a factor of about 1.6. The model was improved in the course of the work; especially the physics of breaking and ride-up. The new model is capable of matching the Bridge measurements without bias. This paper presents the final methodology and equations which resulted from the study which was conducted over several years and resulted in an extensive report and documentation. The equations are closed form and can be applied relatively simply. Examples of using the method are provided. A more comprehensive description of the complete study is given in KRCA (2014) and Croasdale et al. (2016a).
Empirical Prediction of Sea Ice Surface Temperature from Surface Meteorological Parameters in Pistolet Bay Northern Newfoundland
Turnbull, Ian D. (Centre for Arctic Resource Development, C-CORE) | Taylor, Rocky S. (Memorial University of Newfoundland) | Bailey-Dudley, Eleanor (CARD) | Pritchett, Robert (CARD) | Crocker, Greg (Ballicater Consulting, Ltd.)
Abstract Thermodynamic models of sea ice are important tools for the prediction of the patterns of the seasonal evolution of regional ice concentration, thickness, as well as the flexural and compressive strength of the ice. These models aid in offshore operational planning, decision-making, and structural design in the sectors of marine transport and hydrocarbon development in ice-prone environments. The initialization of vertical ice temperature profiles and the definition of boundary conditions for temperature at the ice surface and base have a significant impact on the evolution of internal ice temperatures in these models and the associated melt, growth, and strength response of the ice. While the ice basal temperature in thermodynamic models is relatively straightforward to define as the freezing temperature of seawater, the ice surface temperature is less certain and is traditionally estimated using a surface energy flux balance. During February 27-29, 2016, six Temperature Acquisition Cables (TACs) and two data loggers were installed on the snow-free land-fast sea ice in Pistolet Bay, northern Newfoundland in Atlantic Canada. The TACs and data loggers recorded vertical ice temperature profiles and surface air temperatures at five-minute intervals. Two co-located tripod-mounted anemometers recorded oneminute surface wind speeds. Dew point temperatures and cloud areal fraction were obtained from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim Reanalysis, and downwelling longwave radiation was inferred from the surface air temperature measurements and cloud cover data. Incoming shortwave radiation was also calculated. In this paper, an alternative robust and more computationally efficient method is presented for solving the ice surface temperature as a linear function of the aforementioned surface meteorological parameters. Subsequently, the linear model is used to establish ice surface temperature boundary conditions in order to demonstrate its use in modeling the evolution of the vertical ice temperature profile as recorded by one of the TACs.
- North America > Canada > Quebec > Arctic Platform (0.98)
- North America > Canada > Nunavut > Arctic Platform (0.98)
Abstract This paper is focused on new field data collected for drift behaviour of first-year sea ice, a multi-year ice floe and two icebergs offshore Newfoundland and Labrador. Offshore operations in ice environments require detailed knowledge of ice conditions. Moreover, reliable forecasts of ice drift behaviour for first-year sea ice and extreme ice features such as thick multi-year (MY) ice and icebergs are essential in supporting ice management activities and in supporting effective operational decision-making. Central to the development of improved drift forecasting models is the collection of new field data that can be used to improve understanding of the physical environment and to validate and improve predictive tools. Three ice drift beacons have recently been deployed offshore Newfoundland and Labrador. In the present paper, a description of the beacons used, deployment activities, as well as results from these beacons are reported, along with initial analysis of these data. These new data provide interesting and sometimes unexpected drift behaviour. Results from these beacons are analyzed in light of ocean current and wind data and conclusions regarding the correlations between these environmental conditions and observed drift behaviour are discussed for each case.
Abstract The Development of Ice Ridge Keel Strengths is a four-year collaborative venture between the C—CORE Centre for Arctic Resource Development (CARD) and the National Research Council – Ocean, Coastal & River Engineering (NRC-OCRE). The main focus of the project is to investigate the failure mechanisms associated with gouging ice ridge keels and the conditions under which these keels will continue to gouge without failure. This is important for the design of subsea structures in shallow waters, where ice keels have been observed to scour the sea floor, posing a threat to pipelines and subsea infrastructure. A series of near full-scale keel-gouge tests were carried out to investigate the strength characteristics of a first-year ice keel and its subsequent failure as it was pushed into an artificial seabed. The ice keels were constructed using freshwater ice blocks with a nominal thickness of 10 cm, produced in a cold storage facility prior to the start of the test program. The ice keels were constructed with the aid of a keel former that produced idealized keel geometries of 1.7 m depth, 4 m length and 3.5 m width. Once constructed, the keels were lowered into the water and left overnight to consolidate with air temperatures held at −20°C. The keel samples were tested using a custom-built frame that was designed and used in the Pipeline Ice Risk Assessment and Mitigation (PIRAM) Joint Industry Project. The frame applied a vertical surcharge load to the top of the keel whilst a soil tray was displaced horizontally, causing the bottom of the ice keel to interact with an artificial seabed. A total of ten keel tests were conducted in this test program. The parameters varied were the initial temperature of the ice (−3° and −18°C), the initial surcharge pressure (5–60 kPa), the soil tray velocity (1–20 mm s) and the consolidation time (19–48 hrs). An overview of the test program and preliminary results are discussed.
- North America > Canada (0.47)
- North America > United States > Texas (0.28)
Abstract A simple, rectangular sub-surface caisson was evaluated using physical andnumerical modeling to develop a method for protecting subsea installationsagainst scouring keels of icebergs on the Grand Banks. This protection strategywas developed to assess the feasibility of the structure as an alternative tocostly excavations used to protect subsea equipment on the Grand Backs. Thescenario considered was an ice keel (i.e., iceberg) scouring over a buriedcaisson, avoiding direct contact but with minimal clearance. A centrifugetesting program, consisting of five tests, formed the basis for calibration ofa finite element model. The first four centrifuge tests were carried out withwater as the pore fluid in order to simulate drained conditions during thekeel-soil-structure interaction. In the field, fully drained conditions may notexist; hence the fifth centrifuge test was conducted using a viscous pore fluidto simulate the partially drained conditions. The numerical analyses wereconducted using the commercially available finite element software packageABAQUS. This study demonstrated that the Coupled Eulerian Langrangian (CEL)technique is capable of modeling slow keel-soil-structure interaction events insand. The numerical model performed satisfactorily in simulating the centrifugetests. The results indicated that such a system can potentially provide theprotection needed for subsea installations in ice infested waters. Althoughthis work was based on the conditions encountered on the Grand Banks, theconcept would be applicable to other regions. Future work should involveevaluating various ice keel-soil-structure interaction scenarios and attackangles, development of Inspection, Repair and Maintenance (IRM) strategies aswell as a detailed assessment of construction and installation issues.