Merry Christmas and a Happy New Year from the Department for Geodynamics and Sedimentology
After a scientifically very successful year, the executive of the Department for Geodynamics and Sedimentology wishes all our members, students and collaborators a peaceful and joyous holiday season and a prosperous New Year.
Santa and his reindeers experience the effects of an icebreaker.
Click image to start movie (animated gif; 3.5 MB).
About our Season’s Greeting Movie:
Distinct Element Method model of an icebreaker crushing ice and Santa. Both the ice and Santa are represented by bonded particles. The bow of the ice breaker is modelled as a rigid wall segment that is moving at a constant velocity. Buoyancy forces are added to particles that straddle or are below the water line. Drag forces are not implemented, since the drag coefficient would have to be computed for each fragment (the dynamics of the ice floes underneath the water is hence not accurately captured). Particles comprising the ice have a density of 900 kg/m3; the contact modulus of ice particles is 2.5 GPa and the breaking strength of inter-particle bonds is 2 MPa, values which are in the range reported for sea ice. In this two-dimensional simulation, the weight of Santa would push the ice underneath the water line, hence particles comprising Santa have a very low density above the water line. Bonds in-between particles comprising Santa have a lower stiffness than bonds within the ice, so that a larger strain can be accommodated elastically (otherwise Santa and his reindeers would be totally crumbled, which may be too cruel).
The ice is 0.5 m thick and coloured for layer parallel particle stress, with shades of red and blue indicating tensile and compressive stress, respectively. Icebreakers take advantage of the low bending strength of ice, hence their bows are typically shallowly sloping (in the simulation a dip angle of 40 degrees is used). Fractures are hence driven by bending induced stresses; the fracture spacing will depend on Young’s modulus, tensile strength and ice thickness. Although the present model was run just for fun, the DEM is actually used by engineers for estimating ice loads on ships and structures and is a powerful technique for optimising design.