Session: 07-04-01 Vessels in Ice and model test

Paper Number: 107769

107769 - Multi-Particle Modelling of Compressive Ice Failure During Indentation by Rock Particles 

The indentation of rock particles into ice is an important aspect of understanding subsea interactions involving ice features. If rock particles are present at the interface between ice and an engineered structure, the question arises: Will localization of contact by the rocks cause the ice to fail more easily, resulting in reduced ice pressures, or will rocks transmit high ice pressures through smaller contact areas between the rock and structure resulting in more intense contact stresses on the surface of the structure?

This paper investigates the indentation of rock particles into an ice specimen, where observations have been made both for tests completed on single unconstrained rock particles and layers of multiple uniformly spaced rock particles. During the multi-particle ice indentation tests, observations were made on 170g samples of rocks ranging in size from 3/4”-3/8” for tests completed at an indentation rate of 0.5 mm/s for indentation depths of 5 mm and 7 mm. For the single particle tests, experiments were conducted for three indentation rates: 10 mm/s, 0.5 mm/s, and 0.01 mm/s for three unique spacing distances (as a multiple of mean rock diameter) between the rock particle and previous damage zones. These setpoint spacings were taken as 2D (26 mm), 5D (65 mm), and 7D (96 mm), where the diameter ‘D’ was based on a mean rock diameter of 13 mm.

Maximum observed forces and pressures exerted onto the ice by the rock particles have been analyzed to assess their dependence on the noted test parameters. From analysis of results from the single-particle tests, it is evident that forces resulting from the indentation of individual rock particles may be assumed to be independent of neighboring rock particle indentations for spacing distances of 2D or greater. Using this assumption of independence between individual particle indentations, a MATLAB model of multi-particle rock indentation has been developed. The purpose of this model is to simulate multi-particle interactions for various scenarios using empirical data from the single-particle tests. This model uses randomly sampled rock dimensions and corresponding empirical force data from single-particle tests and combines them in an aggregate model assuming each rock in the multi-particle test interacts independently with the ice. In this model, combined loads can be simulated for different numbers and sizes of independent, randomly sampled single particles for interactions of specified overall indentation depth, while accounting for local differences in indentation depth associated with differences in individual particle sizes.

 

To enable simulation results to be compared with multi-particle test results, simulations were conducted using the same average number of rocks, n, as were present during corresponding experiments (n = 55). Rock size distributions used in these simulations were derived from statistical image analysis of rock particles from the noted experiments. A comparison of simulated ice failure loads for the multi-particle model with test results for the multi-particle experiments shows very good agreement, supporting the assumption of independence between individual particles. Moreover, plots obtained for independent runs of the simulation exhibit similar characteristics to the multi-point tests, wherein fluctuation in aggregate loads may be linked back to individual ice failure events at the scale of individual rock particles. The aggregation of local ice loads measured at the individual particle level to model loads over the entire contact zone presents a promising direction for modeling interactions over larger areas of interest in assessing design implications, although additional research is needed. Since this model indicates that each single-particle test is reasonably representative of individual ice failure events during a multi-particle test, additional single-particle tests are recommended to better understand the effects of particle shape, size, and other factors. The results described in this paper will inform future research on the nature of subsea interactions of icebergs with the ocean floor, and how this may affect potential risks related to subsea installations.

Presenting Author: Thomas Fitzpatrick Memorial University of Newfoundland

Presenting Author Biography: Master’s in Mechanical Engineering Student | Ice Mechanics, Compressive and Shear Failure of Ice, Ice-Particle Embedment Effects.

Authors:

Thomas Fitzpatrick Memorial University of Newfoundland
Rocky S. Taylor Memorial University of Newfoudland
Jan Thijssen CCORE