Rocky S. Taylor

Estimation of Local Ice Pressure Using Up-Crossing Rate

Ice load estimation is required in the design of ships and offshore structures for arctic and subarctic conditions. This paper focuses on the estimation of local ice pressures. The “event-maximum” method for local ice pressure analysis is a probabilistic method based on the maximum pressure of a given event; other local peaks in the data are not included. To study how this may affect local ice pressure estimates, a new probabilistic method based on the up-crossing rate was developed. Field data from 1982 Polar Sea arctic trials in the Beaufort Sea are processed as a time series. Up-crossing rates at different local pressure levels are obtained for local areas of interest. A relationship between up-crossing rate and local pressure-area results is established. Results from the analysis of full-scale data using the event-maximum method are presented for the selected data set; a more comprehensive set of results for the analysis of available ship-ice interaction data is presented in a companion paper. For a sample case, local ice pressure estimates obtained using the up-crossing rate method are compared with results obtained using the event-maximum method. The local pressure-area relationship is found to be similar for both the up-crossing rate method and the event-maximum method. For design curves based on the data set considered, estimates using the event-maximum method were more conservative than those obtained using the up-crossing rate method. The up-crossing rate approach is promising; analysis of additional data sets is recommended to allow broader comparison of the methods.

Probabilistic Analysis of Local Ice Loads on a Lifeboat Measured in Full-Scale Field Trials

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Spherical Indentation Tests on Confined Ice Specimens at Small Scales

A recent series of small-scale ice indentation tests was conducted as a continuation of previous series, to cover additional strain rates and indentor sizes, and to test the effect of scaling. Tests using indentors 10, 20, 40 and 70 mm in diameter attached to a very stiff structure were carried out at indentation rates over three orders of magnitude, while scaling indentation rate with indentor diameter. Slow rates resulted in creep-like response and deep and wide damage zones. As indentation rate was increased, sawtooth loading and random failure activity were observed, together with a thin layer of microstructurally modified ice beneath the indentor.This latest test series also included indentation tests with a flexible beam apparatus, with the aim of generating locked-in vibrations. It was determined from previous tests that indenting at much faster rates was necessary to produce lock-in with such an apparatus. For this series, two new beam apparatus of differing stiffness and variable natural frequency were fabricated; the beams were designed in a manner that enabled control and testing of the outcome of varying these factors independently. Tests were conducted with either one or two indentors attached. The typical sawtooth behaviour occurred at lower indentation rates, progressing at higher rates into lock-in activity, which occurred over a range of speeds for both beams. The frequency of lock-in vibrations was found to be lower than the structure’s natural frequency, and to increase with indentation speed over the lock-in range. The ice load on the indentor during lock-in activity appears more ‘cusp’ shaped, rather than the assumed sawtooth.Copyright

Observations on the Time-Dependent Fracture of Ice

The results of a recent ice indentation series, along with a 4-point beam bending series, are analysed in the present paper with regard to time-dependent fracture. The beam bending series used a a 4-point apparatus to test the effects of velocity on fracture toughness, and to study time delayed fracture at loading rates below the fracture strength of ice. The indentor series used different indentors (diameters ranging from 10 mm to 70 mm), and applied various velocities used to test the time-dependent fracturing of ice. For experiments with a low ratio of velocity to indentor showed damaged-enhanced creep behaviour, ending in large, global failure during some tests. For the highest velocity tests, the ice showed increasingly brittle failure. The loading curve in these tests displayed many smaller spalling events, or ice extrusion events, with cyclic ramp-up of loads between each event.Copyright

Analysis of Iceberg, Pack Ice, and Ocean Current Dynamics Offshore Newfoundland and Labrador From Satellite-Tracked Buoys During the 2014 Ice Season

Shipping operations along the coasts of Newfoundland and Labrador associated with Grand Banks oil and gas production, as well as mining operations in Labrador, may be exposed to potentially hazardous ice conditions. Possible future development of oil and gas reserves offshore Labrador will also be exposed to risk associated with iceberg and pack ice conditions. Improved understanding of the characteristics of ice dynamics and metocean forcing mechanisms behind them will lead to more efficient operational planning and safer operations. Accordingly, CARD has initiated a long-term project to collect and analyze data on the pack ice and iceberg dynamics in these regions. This paper presents an analysis of the drift of pack ice features and two icebergs tagged with satellite-tracked buoys during April-August and July-August 2014, and characterizes their drift in the context of the winds and currents driving their dynamics.Copyright

The Gradient and the Hessian of the Distance between Point and Triangle in 3D

Computation of the distance between point and triangle in 3D is a common task in numerical analysis. The input values of the algorithm are coordinates of three points of the triangle and one point from which the distance is determined. An existing algorithm is extended to compute the gradient and the Hessian of that distance with respect to coordinates of involved points. Derivation of exact expressions for gradient and Hessian is presented, and numerical accuracy is evaluated for various cases. The algorithm has O(1) time and space complexity. The included open-source code may be used in applications where derivatives of point-triangle distance are required.

Safety of Industrial Development and Transportation Routes in the Arctic (SITRA) – Collaboration Project for Research and Education of Future High North Experts

Industrial development in the Arctic enhances the potential risk of accidents occurring under severe conditions. Detailed knowledge of the physical environment and understanding of risk reduction methods are necessary for technical experts and young specialists planning to work in companies dealing with the Arctic. The Arctic is a place of close contact between many countries, where harsh and fragile environment demands the most advanced technology for sustainable development and international collaboration to ensure safety of industrial activity. The SITRA (Safety of Industrial Development and Transportation Routes in the Arctic, 2015–2018) project focuses on organizing an international research and educational network of High North experts for joint investigation and teaching of Arctic engineering courses. SITRA is funded by the Norwegian Centre for International cooperation in Education (SIU). The project is a part of the High North Program. It continues the more than 20-year-long Norwegian-Russian collaboration in the field of Ice Engineering and expands it overseas by means of students and staff/professors exchange and joint field work. Canadian and US universities have also joined the team. The SITRA project multiplies the understanding and awareness of the Arctic problems through education and outreach.

An Accident Model for Arctic Shipping

This paper examines historical Arctic marine accidents from 1995–2004. It was seen during this time period that sinking and grounding of (fishing) vessels was the most common type of Arctic marine accident. A comprehensive accident model is presented to describe Arctic shipping accidents and their causation factors. The accident model is based on epidemiological concepts which explain how non-sequential factors result in an unwanted outcome, analogous to disease spreading through a human body. The causation factors are non-sequential and non-linearly dependent. The applicability of the model is demonstrated through examination of two past accidents: the Kolskaya and the Kulluk. Detailed description of how the accident model could be used for predictive accident modelling and risk analysis of Arctic shipping scenarios is also presented.Copyright

Surface Temperature Fluctuations in Ice Indentation Tests

Ice-structure interactions produce numerous, short-lived high pressure zones which transfer the majority of the load to the structure. Ice indentation tests have been used to observe the fluctuations in surface temperature at these zones. Previous investigations have shown that temperature fluctuates inversely to the applied load during cyclic loading. These fluctuations are believed to be due to rapid melting and refreezing cycles in the high pressure zones.A recent series of small-scale indentation tests investigated surface temperature fluctuations for indentor speeds at three orders of magnitude (0.21 mm/s to 21 mm/s). Freshwater granular ice specimens were grown in cylindrical steel moulds using seed ice and distilled water. A 70 mm diameter indentor with a radius of curvature of 89.6 mm was indented into the ice to depths between 10 and 15 mm. Seven thermocouples were installed in the indentor and made flush with its surface. These were used to measure the surface temperature of the ice during indentation. All tests took place at −10 degrees.Notable changes in temperature response were observed with changing speed. A steady increase in temperature was observed during low speed tests. Medium speeds lead to fluctuations in temperature due to the presence of spalling and cyclic loading that is consistent with the results of others. Some evidence of the inverse relationship between load and temperature can be observed in the highest speed tests, but the thermocouples sampling frequency was too low to accurately respond to high frequency loading and could not provide clear results.Copyright

Damage and Fracture during Contact between a Spherical Indenter and Ice: Experimental Results and Finite Element Simulations

Effective modeling of ice material behavior requires treatment of both damage and fracture. In this paper, a discussion of local ice damage and fracture processes observed during laboratory-scale indentation experiments conducted on unconfined polycrystalline ice using a spherical indenter is provided. Particular emphasis is placed on the interplay between fracture and extrusion processes corresponding to the failure of ice under a single zone of high contact pressure. Simulations have been conducted using a continuum damage mechanics user-material routine in conjunction with element removal techniques to simulate pressure-softening and discrete fracture processes, respectively. Simulation results provide good agreement with test data and provide important insights into interplay between damage and fracture mechanisms associated with compressive ice failure. Finite element modeling was found to work well for modeling pressure softening effects and for replicating the effects of discrete fracture events. For interactions involving multiple failure events, further work is needed to develop models that account for random aspects of fracture associated with flaw structure, contact geometry and the geometry of individual spalls.