Abstract: Complex load conditions of offshore wind turbine cylindrical tower are analyzed. The dynamic response numerical analysis method of the offshore wind turbine cylindrical tower is investigated under combined unsteady aerodynamic loading and wave loading. The relationship between aerodynamic loading especially unsteady ones on the cylindrical tower and Reynolds is studied. On the basis of the linear wave theory, two-dimensional linear wave theory is extended into three-dimensional linear wave theory after the coordinate transformation. Accordingly, the plane system of wave forces (MORRISON formula) is extended into space system of wave forces. In order to adapt to the three-dimensional space analysis and calculation the analysis calculating model of wave loading is established and the corresponding analysis program of irregular linear wave forces is developed. By using the finite element analysis method and modeling the cylindrical tower with space beam element, the displacements, velocities, accelerations and stress responses of tower are resolved. As an example, the dynamic response of a 1.5 MW offshore wind turbine tower is analyzed and the results show that the work offers applied analysis method for the entire offshore wind turbine system aeroelastic analysis, wind turbine tower vibration analysis and fatigue life analysis, etc.

Key words: Linear wave theory, Offshore wind turbines, Unsteady aerodynamic loading, Wave loading