Model Scale Test of Towing Operations in Managed Sea Ice
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Towing operation in open water is a well-established marine operation. However, as offshore explorations move further north, more and more Arctic Offshore Platforms are to be designed and constructed. In the meantime, marine operations face a new challenge, i.e., the presence of sea ice. There is a driving need from both the industry and academics to understand the interwoven relationship among ice conditions, ice load, structural responses and towing methods.Sustainable Arctic Marine and Coastal Technology (SAMCoT), a NTNU based research centre, has been developing and improving a numerical simulator dedicated to extract ice load during ice-structure interactions. Currently, the simulator is composed of three important modules. These are: Multibody dynamic module; Sea ice fracture module; Hydrodynamic module.Although it is the most matured one, multibody dynamic (MBD) module still requires an idealised test program to verify this module. This is the starting point of this master thesis.Scale test in the wave tank of marine civil group of NTNU is performed with main motivation to verify and calibrate the MBD module. The aims of the models scale test include: Verification and calibration of analytical derivations Verification and calibration of multi-rigid body dynamic based numerical simulation; Study the kinematics and motion stability of the towed structure; Study the potential jamming events in different ice conditions.The results show that for ice concentration up to 60% the increase in the mean towing force in not significant (compared to the mean towing force in open water). In 80% ice concentration (i.c.) the interaction mechanism changes significantly. Although the tests in 80% i.c. were severely influenced by non-realistic boundary effects, it can be concluded that the in 80% i.c. higher ice resistance is expected.The mean trim of the floating structure remains unchanged when ice is introduced (compared to the open water tests), but the amplitude of pitch oscillatory motion does increase with higher ice concentrations. The same is valid for roll motion.The resulting increase in towing force shows good agreement with the analytical estimation of ice resistance in broken ice. Calibration of the analytical estimation formulation was necessary.Verification and calibration of multi-rigid body dynamic based numerical simulation was not done in this thesis, but the results give a good starting point for further research.