Symmetric, Asymmetric vibration mode shapes and determination of bending frequencies on windmill blades using free vibration analysis

Abstract

Wind mill is one of the most leading alternatives in the present energy production, where the energy of wind is converted into the mechanical energy by means of vanes called sails or blades. Force that acts on the surface of the blade is due to flow of the wind, which in turn causes vibration. This vibration, when matches with the natural frequency will produce high stresses. The materials of the blades play a prominent role in this scenario. The Light weight galvanized steel or aluminium is currently used in the outer shell of the blade. World Energy Council (WEC) projected that; this may be replaced by thermoplastic foam. In this paper the effects of vibration on these materials were studied and natural frequencies were found out, there by finding the frequencies at which the plates in the blades should not be exposed and the frequencies at which bending should be considered. Using this conditions the minimum amount of damper or stiffness addition needed for resonance avoidance can be calculated for a plate there by calculating for a whole blade. This leads to the most optimised safest design for wind mill blade. 3D Modelling is done and is been analysed using FEA.