Dynamic analysis of lattice type offshore structures

In this day and age, it is an urgent necessity to gain both renewable and exhaustable resources into consumption due to increasing energy need in the world. Construction of energy facilities increasingly move from land to seas because of Increase in the land costs of renewable energy resources and decrease in the reserve of exhaustable resources in land. To satisfy this need, steel piles, concrete pile types and steel lattice types of structures are frequently used in seas. Because of common usage area and importance while satisfying the environmental-social needs, offshore system types of structures will be analysed under the effects of wave forces. In this study, three storey lattice truss which is supported by four legged horizontal members formed of cylindiric ones and vertical diagonals is used. In the first method, the structure and its environment is modelled by using Fluid-structure interactive (FSI) finite elements method (FEM) is used as the second method of the study. Structure and its environment are modelled in the finite elements analysis. ABAQUS finite elements program is used in the solutions. While the structure is modelled in ABAQUS/Explicit solver, marine environment is modelled in ABAQUS/CFD one. First natural frequency of the structure, related mode shape, displacements and stress distributions are obtained by interaction of both solvers. Single degree of freedom system is used as the second method of the study. The equation of motion of the system will be solved by 4th degree of Runge-Kutta Method. Natural frequency and displacements of the structure will be obtained by this method. Linear Wave Theory will be used while modelling the environment around the structure. Morison Equation including drift and inertia forces will be used to calculate the forces effecting the structure from single regular wave. The study is concluded by determining the compatibility of the results of two different analyses.