Browsing by Subject "PLATFORM"

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    Evaluation of Offshore Wind Turbine Tower Dynamics with Numerical Analysis
    (HINDAWI LTD) Dagli, BY; Tuskan, Y; Gökkus, Ü
    A dynamic behaviour of a cylindirical wind tower with variable cross section is investigated under environmental and earthquake forces. The ground acceleration term is represented by a simple cosine function to investigate both normal and parallel components of the earthquake motions located near ground surface. The function of earthquake force is simplified to apply Rayleigh's energy method. Wind forces acting on above the water level and wave forces acting on below this level are utilized in computations considering earthquake effect for entire structure. The wind force is divided into two groups: the force acting on the tower and the forces acting on the rotor nacelle assembly (RNA). The drag and the inertial wave forces are calculated with water particle velocities and accelerations due to linear wave theory. The resulting hydrodynamic wave force on the tower in an unsteady viscous flow is determined using the Morison equation. The displacement function of the physical system in which dynamic analysis is performed by Rayleigh's energy method is obtained by the single degree of freedom (SDOF) model. The equation of motion is solved by the fourth-order Runge-Kutta method. The two-way FSI (fluid-structure interaction) technique was used to determine the accuracy of the numerical analysis. The results of computational fluid dynamics and structural mechanics are coupled in FSI analysis by using ANSYS software. Time-varying lateral displacements and the first natural frequency values which are obtained from Rayleigh's energy method and FSI technique are compared. The results are presented by graphs. It is observed from these graphs that the Rayleigh model can be an alternative way at the prelimanary stage of the structural analysis with acceptable accuracy.
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    Analysis of offshore wind turbine tower under environmental loads
    (TAYLOR & FRANCIS LTD) Gücüyen, E
    Researchers have started to use numerical methods in the fluid-structure interactive solutions with the advancing of computing technology. There are few studies investigating bidirectional fluid structure interaction (FSI) analysis due to requirements of high computer capacity. This insufficiency is attempted to be corrected in this study. Offshore wind turbine tower is selected to employ the method under environmental loads. To detect accuracy of the numerical analysis, the tower is modelled as a single-degree-of-freedom (SDOF) system. The equation of motion of the system is numerically integrated by using a fourth-order Runge-Kutta method. Time-varying lateral displacement of the tower and first natural frequency values are obtained from analysis. Afterwards, the structure and the environment are modelled in ABAQUS finite elements program. Bidirectional FSI technique is applied to the structure due to the interaction between ABAQUS/CFD-ABAQUS/Explicit. The accuracy of SDOF and bidirectional FSI analyses results is determined in the end.