SPATIAL AND TEMPORAL VARIATIONS OF LOCAL ICE PRESSURES
Dmitri G. Matskevitch and Ian J. Jordaan, Memorial University of Newfoundland, St. John's, Newfoundland, A1B 3X5, Canada
ABSTRACT
Ice-structure interaction is a complicated dynamic process attendant on the micro- and macroscale fracture of ice sheets, and the damage and physical changes in the ice structure. All these phenomena contribute to very fast time variations of both global a n d local ice loads. The most important events, from the ice load standpoint, take place in a relatively narrow layer of highly damaged ice near the contact face with the structure referred to as a contact zone. On the other hand, so-called 'far ice field' (i.e. that part of ice field which does not make direct contact with a structure and is not affected by damage) may contribute noticeably to the interaction process, as well.
Measurements of extremely high local pressures have been reported during both ice indentation tests and icebreaker rams. The peak value of the local pressures can be up to one order of magnitude higher than the uniaxial compressive strength of granular ice. Such a high concentrated load can cause macrofracture of the ice sheet in the form of spalling. This area of high local pressure, which is usually called a "hot spot" or "critical zone", along with accompanying spall events are considered in the present paper using data from mediumscale field indentation tests carried out on the Hobson's Choice Ice Island in 1990
SELF-EXCITED OSCILLATIONS IN SEA ICE AND EVALUATION OF THE ICE FORCES
Victor N. Smirnov, Arctic and Antarctic Research Institute, St. Petersburg, Russia
ABSTRACT
The processes of the dynamical interactions of the ice are described. Especial attention is given to the self-excited oscillating processes when the ice goes through periodical deformations similar to these which appear in the structures in the sea ice. The range of the self-excited oscillations periods is from 0,1 s to 20 s. The jump-like processes transform themselves into the quasiharmonical ones up to sound frequency range. For comparison purposes the spectra of the frictional self-excited oscillations in the glaciers are presented. An iceberg interacting with the drifting ice also forms self-excited oscillating system with period of up to 10 s.
An example of numerical evaluation of the forces of interaction between a drifting ice island and the sea ice is given.
