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The paper presents results of a combined experimental and analytical study on the dynamic responses of a deepwater tripod tower platform to regular and random waves. The purpose of the study was to understand and to predict the near resonant responses of a large diameter deepwater structure. The experimental effort involved the fabrication of a large hydroelastic model at a scale of 1:50 and the testing of it in a 200x12x7m deepwater wave tank. The fundamental natural frequencies were identified by modal testing of the structure in water. They were found to be in close agreement with the finite element model results. The structural responses were predicted using a finite element model. Relative velocity formulation was used in Morison's approach to wave solved in the time domain. Realistic hydrodynamic coefficients, obtained from the model experiments, were used in the analysis. A separate force measuring experiment was conducted using a prominent portion of the cylinder. Good agreement between the experimental and the predicted results was obtained., 10th International Conference on Offshore Mechanics and Arctic Engineering, 23-28 June 1991, Stavanger, Norway.

Using indentation experiments on freshwater ice as a starting point, numerical models for ice damage, clearing and flexure have been developed together with a mechanical model of ice-induced vibration. Indentation speeds were such as to cover a range of ice behaviour, from essentially pure crushing to situations where both flexural failure and crushing took place. Modelling of the damage process was used to estimate the thickness and equivalent viscosity of the crushed layer under various circumstances, and also to demonstrate the change in pressure distributions at different stages in the loading cycle. Crushing is complicated by the presence of spalling as well as distributed damage. Analysis of these effects and associated local high pressure zones is important for determining when crushing failure occurs. With regard to flexural failure, important issues that are dealt with are the influence of local crushing, the effect of speed and the hydrodynamic effect on the distance at which circumferential cracks are formed. The distance to primary flexural cracks was predicted successfully using analytical plate bending solutions and an equivalent beam model was calibrated. Hydrodynamic effects did not account for observed secondary cracks at shorter distances. A simple mechanical model was developed to integrate the above behaviour with regard to crushing and flexure. The model includes the structural and far field ice responses, and was successful in simulating peak forces and the frequency of dynamic loading cycles in a variety of ice and loading conditions., 11th International Conference on Port and Ocean Engineering Under Arctic Conditions, September 24-28, 1991, St. John's, Nfld.

A fundamental approach has been taken to address problems related to the resistance to ship transit in level ice and the forces exerted by moving ice on fixed structures. Using indentation experiments on freshwater ice as a starting point, numerical models for ice damage, clearing and flexure have been developed together with a mechanical model of ice-induced vibrations.

Near-resonant responses of a deepwater platform to wave excitation are controlled by inducing additional hydrodynamic damping in the system. The study used a device designed to induce flow-separation around a vertical column at low Kc numbers. The results of two experimental investigations are presented in this paper. In the first experiment, in-line forces on a 0.3m diameter vertical cylinder were measured without and with the attachment of the flow-separation device. At low Kc numbers the drag coefficients increased by five times due to the attached device to the cylinder, whereas the inertial coefficients were found to be insensitive to the device. The second experiment investigated the wave induced responses of a 8.6m high hydroelastic model of a deepwater tripod tower platform in a 200x12x7m wave tank. A significant reduction in responses at and close to resonance, due to the induced drag damping, observed in the experimental measurements shows that the device is very effective for damping applications. The experimental findings are also supported by analytical results., 23rd Offshore Technology Conference, 6-9 May 1999, Houston, TX.

Analysis of the ship-ice interaction problem using finite element method is presented in this report to determine the failure loads and the total stress and deformation states developed in the ice-field during the interaction process. The ice sheet is discretized using 20-noded three-dimensional finite elements and the failure in ice is described by Tsai-Wu criterion.

Analysis of the ship-ice interaction problem using finite element method helps us to determine the failure loads and the total stress and deformation states developed in the icefield during the interaction process. The mechanism of the interaction process which was mathematically formulated as a contact process with experimentally determined contact coefficients has been numerically solved and the induced loads computed., 2nd International Conference on Technology for Polar Areas, June 15-17, 1988, Trondheim, Norway

A parametric study using finite element method is carried out to investigate the ship/ice interaction for ice thickness up to 80cm and ship velocity up to 4 m/sec. In the dynamic analysis the mechanism of load transfer during the ship/ice impact is treated as a contact process taking account of the area of contact. The ice failure is specified by the Tsai-Wu criterion. The effects of frame angle and impact velocity of the ship, and thickness of the ice sheet on the failure loads are critically investigated., Offshore and Arctic Operations Symposium, Houston, Tex., 1995

This paper presents results of a series of experiments conducted on 0.3m diameter fixed cylinder in a wave tank. The total forces exerted on the vertical cylinder for random waves have been measured directly using a sophisticated experimental arrangement. Representative spectra were selected and used to simulate random wave conditions. The numerical simulation procedure is discussed. The problems encountered due to the reflection of waves were solved by choosing a proper cut-off-frequency and the number of components for the target spectrum. The random wave force spectra were predicted using least square method, cross-spectral method and equivalent KsubC number method. The equivalent KsubC number method uses the hydrodynamic coefficients obtained from a regular wave test for the corresponding KsubC number. Good correlations between the predicted wave force spectra and the measured wave force spectra were obtained. It is also shown that the equivalent KsubC number method is accurate enough to predict the random wave forces on large structures at very low KsubC numbers. [Author Abstract], 9th International Conference on Offshore Mechanics and Arctic Engineering, February 18-23, 1990, Houston, Texas, united States

Presented in the report is a three dimensional finite element analysis of the ship-ice interaction problem using an elasto-plastic model. After investigating two types of three dimensional solid elements, the 20-noded isoparametric solid element is chosen to model the discretized sea ice cover. The failure load is obtained as the load that acts normal to the ship hull plating when the ship fractures the ice in a "ramming" mode, using incremental iterative analysis. The ice strength data utilized in the analysis is obtained from published data of laboratory tests on sea-ice, and the ship is considered as a "rigid-body" indenting ice.