Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The compliant tower is a slender jacket type structure which falls in the category of compliant platforms and is suited to deep water situations. Towers of this type resist the static loads through their stiffness while the first order wave loads are resisted primarily by inertia. Their typical first natural period is around 30 to 40 seconds and the second natural period is about 3 seconds so there would be little amplification of the response due to the first order wave forces. There is, however, dynamic amplification of the response due to the turbulent wind and nonlinear wave forces including the second order drift forces, and this response is significantly affected by the wave/motion induced drag damping.;This thesis investigates the importance of wind and wave loads on the model of a typical compliant tower. Numerical models both in frequency and time domains were developed to predict the response characteristics of the tower to the action of wave, wind and wind induced currents. The wave-structure interaction was incorporated using a modified form of the Morison equation.;In the first series of experiments, using a surface piercing cylinder supported from a heavy three point pendulum moving just above the water surface, the force and displacement time histories (free vibration) were recorded and the amplitude dependent damping forces were evaluated. Based on these experiments, the modified forms of the Morison's equation (relative velocity model and independent flow fields model) were used to derive the values of the force coefficients, C{dollar}\rm \sb{lcub}D{rcub},\ C\sb{lcub}M{rcub},{dollar} and hydrodynamic damping. The experiment covered the structural oscillation in still water, and a variety of both regular and random waves. This work is believed to be the first which obtains the values of the drag coefficient in the case of structural motion in the presence of waves, and compares the results for both forms of the Morison's equation. These results are later used as input to the dynamic analyses performed in the last stage of this work.;The importance of second order drift forces including the free surface effect and bounded long waves were examined through another series of laboratory experiments. The drift forces on a surface piercing cylinder were measured and the results compared to different theoretical models. It was concluded that, in a deep water situation, it is the free surface effect which is responsible for most of the observed drift forces and the contribution of the bounded long waves is not significant. (Abstract shortened by UMI).



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