Abstract
Icestructure interaction is a complicated dynamic
process of the failure of moving ice against an
offshore structure often resulting in violent vibrations,
thus endangering the normal exploitation operation.
Beside the nonlinear ice crushing in the contact zone,
the entire ice field behaviour as a part of the
icestructure system should be studied. In the process of
icestructure interaction, elastic waves propagate
outwards from the contact area into the depth of a large
moving ice sheet. These waves carry away a certain amount
of energy. If the ice sheet is not infinite, the waves,
reflected from the boundary, return and interfere on
their way back towards the source with still outgoing
waves. The ice sheet boundary conditions (finite or not)
should be taken into account in any icestructure
interaction model. Actually the ice sheet presented as an
elastic halfplane is subjected to the unit impulse force
acting on its boundary edge. The method of potentials is
used to find a Green function for a halfplane in the
time domain. The convolution theorem enables one to
extend this solution to the arbitrary force. The dynamic
properties of the ice sheet are also studied in the
frequency domain. The effect of the large (infinite) ice
sheet may be described by its complex dynamic stiffness
matrix and the notion of radiation damping is introduced.
The stochastic approach to the problem is proposed next
as an alternative to the direct material and interaction
modelling. The structural response to spatially random
excitation of ice crushing is studied. The notion of
characteristic spatial dimensions of excitation is
formulated and its effect on the structural response is
examined as well.
The quantitative relation between dominating ice crushing
frequency, the ice sheet velocity and thickness, and the
structural stiffness is found. This relation enables
spectra of ice load to be established for various
structures and ice environment on the basis of the
available experimental or computed data. Having such a
spectrum as an input excitation, the structural response
can be easily found using the linear spectral analysis
and the mode superposition methods, thus avoiding ice
nonlinearities. Assuming an exponential correlation in
space of the ice crushing forces, the spectral analysis
can be applied to large structures.
Original language  English 

Qualification  Doctor Degree 
Awarding Institution 

Supervisors/Advisors 

Award date  19 Jan 1996 
Place of Publication  Espoo 
Publisher  
Print ISBNs  9513847950 
Publication status  Published  1995 
MoE publication type  G4 Doctoral dissertation (monograph) 
Keywords
 dynamics
 ice
 interactions
 stochastic processes
 mathematical models
 elastic properties
 flexibility
 offshore structures
 crushing
 Greens function
 cold weather construction
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KajasteRudnitski, J. (1995). On dynamics of icestructure interaction: Dissertation. VTT Technical Research Centre of Finland.