Nonlinear analysis of fixed steel jackets with considering interaction of Water, structure and soil

Recently progresses of offshore engineering have provided the possibility of optimum design and construction of jackets even in deep waters and complicated sea conditions. The optimum design leads the ductility of jackets to be increased, which causes the displacement and fluctuations often under extreme conditions to be important. For this reason in the analysis and design of these structures, effects of structure and soil on its treatmant versus waves and current should be considered. On the other hand by moving structure and soil the force induced by current and wave is also changed, so in flaxible jackets the concept of interaction of staucture, soil, wave and current is indicated. The method of analysis of these structures is also another important task. Ordinary analyses of jackets due to wave and current are linear but it has been shown that it is so for from exact solution. However nonlinear analysis must be considered. In this research, evaluationg the nonlinear treatment of fixed steel jackets agains waves and current with considering interaction of water and satructure and comparing it with linear treatment in both cases of with and out soil interaction is the final purpose. In this research three typical jackets named A,B and C are modeled and for three load condition with waves with return periods od 50, 150 years, the results of linear analyses ANSYS software is used and all analyses are performed dynamically in time domain. Deck's displacement and the force of members are selected as jackets responses the results show that with out considering effects of geometric nonlinesrly and soil interaction, considerable errors are encountered and with neglecting the effects the design should be nonconservative or some times noneconomic.