Ice crushing pressure on non-planar surface

Kim, Hyunwook (2014) Ice crushing pressure on non-planar surface. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The objective of this study is to investigate ice-structure interaction and develop a numerical model to predict the changes of ice loads and pressure during ice-structure interaction on non-planar surfaces. It is important to understand the sequential ice pressure and load development during ice-structure interaction. This is particularly true for non-planar surfaces as most ships and many offshore structures are composed of near-flat panels that may be dented as part of in-service loading leading to panels that are concave. An important question is whether these concave surfaces act as load-increasers for subsequent ice interaction. Most laboratory and field trial tests have been performed based on the assumption that the structural shape is flat. Therefore, little information is available for cases where the structure is concave due to plastic deformation, or specific areas with intentional structural concave shapes. In support of this objective, a series of laboratory-scale ice crushing tests were performed. Force, time and displacement data were measured. It was observed that ice crushing on concave shape indenters induced higher ice loads and pressure magnitudes compared to flat indenters. As part of the experimental program, techniques to use pressure measurement film were adopted to obtain ice-structure contact location, actual contact area, and changes of magnitude of pressure within the contact region. Following the experimental program a numerical model of ice crushing for concave surfaces was developed. In order to achieve valid numerical simulation results, a crushable foam model was modified by adding failure criteria. This followed the effect of indenter shape, level of confinement, test speed and cone angle to be evaluated in the numerical model and compared with the experimental results. The numerical model is shown to be valid for the flat indenter cases and the wedge and conical-shaped indenter cases. The findings from this study show that the shape of the indenting surfaces does influence ice forces and pressure and that generally, concave indentation surfaces lead to increases in pressure and force arising from ice crushing. These effects can be qualified globally and locally using the pressure measurement film, and the effects can be modeled numerically. This work demonstrates that the assumption of ice loads associated with flat or convex shapes may lead to under design for concave shapes or may lead to structural overload in cases where structures previously that have been indented.

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