Incorporating the effects of memory into sea ice friction models
In winter in the polar regions the sea freezes over, and this frozen cover then breaks up. Engineers and planetary scientists are then interested in how the broken cover moves around, driven by wind and ocean currents. As the ice floes slide against each other, energy is lost due to friction.
I worked on a series of experiments in the HSVA Ice Tank in Hamburg, investigating friction on a reasonably large scale (a few metres). I then ran equivalent experiments on a smaller scale (a few centimetres) in the laboratory at UCL. In both cases I was interested in memory effects in friction: that the current friction state depends not only on the current sliding situation, but also on the sliding history of the ice surfaces. One simple way to characterise such behaviour, used in rock mechanics, is a rate-and-state friction law. Such a law allows us to incorporate memory effects into friction models without a great increase in complexity.
More recently, I noticed that memory effects in our experiments all tend to decay over a similar time period: about ten seconds. This leads to a slightly different form of rate-and-state model, with critical slip (the decay of memory effects) encapsulated in a time constant rather than a displacement.
I went on to test the applicability of such a model to a range of sliding scenarios. The effects of varying the friction law can be tested using a discrete element model. I'm working on making these models more realistic. Please feel free to contact me if you would like to know more.
Publications:
Lishman, Sammonds and Feltham, A Rate and State Friction Law for Saline Ice. JGR, vol. 116, C05011, 13 pp., doi:10.1029/2010JC006334.
Lishman, Sammonds, Feltham, Wilchinsky The Rate- and State- Dependence of Sea Ice Friction. In Proc. POAC 2009.
Lishman, Sammonds, Feltham, Wilchinksky, Sea Ice Friction and Arctic Sea Ice Dynamics. In Proc. Hydralab III JUM, 2010.
Lishman, Sammonds and Feltham, Critical Slip and Time Dependence in Sea Ice Friction. Cold Regions Science and Technology, 90-91, pps 9-13, doi:10.1016/j.coldregions.2013.03.004
Lishman and Sammonds, Memory in Sea Ice Friction. In Proc. POAC 2013.