Abstract
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) 
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Keywords
 dynamics
 ice
 interactions
 stochastic processes
 mathematical models
 elastic properties
 flexibility
 offshore structures
 crushing
 Greens function
 cold weather construction
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On dynamics of icestructure interaction : Dissertation. / KajasteRudnitski, Juri.
Espoo : VTT Technical Research Centre of Finland, 1995. 144 p.Research output: Thesis › Dissertation › Monograph
TY  THES
T1  On dynamics of icestructure interaction
T2  Dissertation
AU  KajasteRudnitski, Juri
N1  Project code: RTET95203
PY  1995
Y1  1995
N2  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.
AB  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.
KW  dynamics
KW  ice
KW  interactions
KW  stochastic processes
KW  mathematical models
KW  elastic properties
KW  flexibility
KW  offshore structures
KW  crushing
KW  Greens function
KW  cold weather construction
M3  Dissertation
SN  9513847950
T3  VTT Publications
PB  VTT Technical Research Centre of Finland
CY  Espoo
ER 