Review of Free Vibration Response of Spar-Supported Wind Turbine with Tuned Mass Damper

Abstract

AbstractMany developed and developing countries are investing a huge amount of resources to tap the potential of offshore wind energy. It has advantages over onshore wind farms in many aspects as it neither uses landmass nor creates noise problem to the human habitat. Continuous wind availability and better wind quality are some other advantages of offshore wind farms. With the advancement of offshore technology, deep draft floating platforms like spar have been developed recently. These deepwater floating-type platforms experience extreme marine environmental forces such as wind and waves. Floating offshore structures that are form-dominant types resist the dynamic wind and wave loads by means of displacement responses. Platform tower fore-aft, platform surge, and platform pitch movements/vibrations are the dominant responses among them. The dynamic tower fore-aft displacement reduces the power generation efficiency of the turbines and causes fatigue failure at the tower base. Hence, these movements need to be controlled to increase the performance of the wind turbines. Tuned mass damper is one of the commonly adopted damper systems to mitigate such unintended dynamic movements. Several studies with tuned mass damper on offshore structures reported that it can reduce the unintended dynamic structural responses positively. The present study intends to review the free vibration responses (to review the basic dynamic characteristics of the structure) of the spar platform with and without tuned mass damper (placed at the tower nacelle). The OC3 Hywind spar platform (benchmark) developed by National Renewable Energy Laboratory (NREL) is taken as the study structure. The benchmark study wind turbine structure incorporated OpenFAST software work frame is used for the evaluation. For the vibration response control, tuned mass damper properties (mass, stiffness, and damping) are evaluated corresponding to different mass ratios (tuned mass to tower mass). Initially, free vibration analyses are carried out in OpenFAST to find the natural frequencies in the respective degrees of freedom. Similarly, for free vibration control analysis, fore-aft initial displacement conditions are set, and corresponding free vibration tests are carried out with and without tuned mass dampers and the resulting responses are evaluated.KeywordsFloating offshore wind turbinesFore-aft displacementTuned mass damper