Experimental investigation of oscillation of loads in ice high-pressure zones, part 2: Double indentor system — Coupling and synchronization of high-pressure zones

• Indentation tests were conducted on confined ice using two spherical-cap indentors.
• Indentation rate and configuration of the indentation system were varied among tests.
• In- and anti-phase synchronized failures occurred dependent on rate and configuration.
• Variations of lock-in and sawtooth response depended on rate and configuration.
• Synchronized regular failures may be seen as self-sustained oscillation with coupling.

The oscillation of loads in high-pressure zones (hpzs) formed in ice compressive failure is shown, under the right conditions, to constitute a regular self-sustained oscillation. This occurs in a system comprising the moving ice field, which supplies an internal source of energy, and a compliant structure with which the ice interacts. The supplied energy is dissipated within a layer of microstructurally modified ice by means of viscoelastic deformation enhanced by damage processes, as well as by spalling fracture. An important question arises with regard to vibrations found in large structures such as the Molikpaq. Given that high-pressure zones in field situations are on the order of 1 m in size, how do large structures respond and participate in ice-induced vibrations? The concept of ‘entrainment’ or synchronization of hpzs via elastic and inertial structural feedback is introduced. In this, failure of one high-pressure zone leads to failure of another through structurally-coupled feedback, whereby the first failure increases the load on another as a result of elastic rebound of the structure. This constitutes in-phase coupling and synchronization, but anti-phase coupling whereby failure of one high-pressure zone leads to a decrease in load on another, is also considered. These hypotheses were confirmed in an experimental programme, in which a series of tests with a compliant beam applying load to ice specimens through a pair of indentors was carried out. The test results confirm the hypotheses, with both in- and anti-phase synchronization being observed. Relevance to real structural systems is discussed in the context of the Molikpaq structure and the JZ-20-2-1 jacket platform.