A conical beam finite element formulation for wind turbine tower modal analysis

Modern wind turbines are of slender and elasticconstruction, above all the rotor blades and the tower.Therefore, they are structures which are extremely proneto vibration. So, it’s necessary to carry out modal analysison these components. In this paper, tower dynamicbehavior is modeled using Lagrange equations withlinearly tapered conical cross section beam elementbased on Timoshenko beam model. Then the proposeddynamic model is used to perform modal analysis on abenchmark 5 MW wind turbine tower. To verify theproposed model, the numerical modal analysis onaforementioned tower is conducted in finite elementsoftware. Comparison of the results show greatagreements in eigenvalues and eigenvectors betweenboth methods and maximum calculated error in all modesand configurations is about 5 percent. Moreover, to studythe accuracy of shell elements for modal analysis of windturbine tower, two tower models are simulated. Thecalculations show that shell model provides acceptableresults compared to solid model. At the end the effects ofrotor and nacelle mass and inertia on modal behavior oftower is investigated. It’s observed that neglecting the topmass and rotor inertia in modal analysis affects the towervibrational behavior significantly.

A conical beam finite element formulation for wind turbine tower modal analysis Keywords:

dynamical behavior , natural vibration , tapered beam element , wind turbine , Lagrange equation.