A dynamic behaviour of a cylindirical wind tower with variable cross section is investigated under environmental and earthquake\nforces. The ground acceleration term is represented by a simple cosine function to investigate both normal and parallel\ncomponents of the earthquake motions located near ground surface. The function of earthquake force is simplified to apply\nRayleighââ?¬â?¢s energy method. Wind forces acting on above the water level and wave forces acting on below this level are utilized in\ncomputations considering earthquake effect for entire structure. The wind force is divided into two groups: the force acting on the\ntower and the forces acting on the rotor nacelle assembly (RNA). The drag and the inertial wave forces are calculated with water\nparticle velocities and accelerations due to linear wave theory. The resulting hydrodynamic wave force on the tower in an unsteady\nviscous flow is determined using the Morison equation. The displacement function of the physical system in which dynamic analysis\nis performed by Rayleighââ?¬â?¢s energy method is obtained by the single degree of freedom (SDOF) model. The equation of motion is\nsolved by the fourth-order Rungeââ?¬â??Kutta method. The two-way FSI (fluid-structure interaction) technique was used to determine the\naccuracy of the numerical analysis. The results of computational fluid dynamics and structural mechanics are coupled in FSI analysis\nby using ANSYS software. Time-varying lateral displacements and the first natural frequency values which are obtained from\nRayleighââ?¬â?¢s energy method and FSI technique are compared. The results are presented by graphs. It is observed from these graphs that\nthe Rayleigh model can be an alternative way at the prelimanary stage of the structural analysis with acceptable accuracy.
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