Drifting-ice structure interaction, a dynamical systems approach

Drifting-ice structure interaction, a dynamical systems approach

Van Dijk, T.S.J.

Mechanical, Maritime and Materials Engineering

Marine & Transport Technology

Ship and Offshore Structures

2015-07-03

Offshore structures are placed in regions where they can these structures can exhibit unfavourable dynamical behaviour when these ice floes fail in a crushing manner against the structures. Three modes of interaction have been observed: (1) intermittent crushing, (2) frequency locking, (3) continuous crushing. This master thesis has been conducted to develop a model which predicts these interaction modes, in terms of deflection of the structure and the ice forces that act on the structure. Ice structure interaction is a non-linear phenomenon. Non-linear systems can have coexisting solutions. These solutions are sought for. Their dependency on input parameters is made visible through a bifurcation diagram. The developed models are based on earlier work with friction based self-sustained oscillations, with additional modifications to describe the inhomogeneity of the ice, the unidirectionality of the ice force and the possible arise of a gap between the ice and the structure. Such a gap occurs when the structure moves faster than the ice rim. Results calculated with the models that have been developed are then compared with data from laboratory experiments. The sticktion friction model with the above described modifications shows good results for the intermittent crushing regime and continuous crushing regime. However, it fails to describe the response of the structure satisfactorily in the frequency locking regime. These differences between calculated results and experimental results are caused by the fact that the ice force cannot be characterized properly by only two parameters as is the case in the sticktion friction model. Using ice characteristics as a function of both the relative velocity between the structure and the ice, as well as the absolute acceleration of the structure, resolves this short-coming. It is expected that the velocity dependent and acceleration dependent ice forces are ice type specific. Therefor further tests are recommended in order to determine these dependencies.

http://resolver.tudelft.nl/uuid:0d0de28b-5396-4038-aeff-42fdf0b36021

Student theses

master thesis

(c) 2015 Van Dijk, T.S.J.