Natural Frequency of Mono-pile Wind Turbine Considering Interaction between Pile and Elastic Foundation
In this paper,we analyze the mono-pile wind turbine,comprising blade bodies,a hub, a cabin,a conical shell tower,a transition piece,and a mono-pile foundation.Our study obj ective was to determine the natural frequency of the mono-pile wind turbine above the mudline.We as-sumed the conical shell tower,transition piece,and mono-pile foundation to be a vertical steel tube (VST)with a uniform cross section and with the same elastic modulus.We used the lumped-mass method to simplify the mono-pile wind turbine above the mudline as two concen-trated masses.One concentrated mass at the VST top is the summation of the mass of the blade bodies,hub,cabin and one-fourth the mass of the VST above the mudline.The other concentrat-ed mass at the middle of the VST is one-half the mass of the VST above the mudline.Taking the mono-pile foundation below the mudline as a semi-infinite long pile,we used Zhang's method to obtain the horizontal stiffness and rotational stiffness of the pile top.In this way,we can deter-mine the deflection of the VST under horizontal load at any point of the wind turbine above the mudline.The flexibility coefficient of the unit horizontal load at any position of the VST can be determined accordingly.Then,using both the flexibility and lumped-mass methods,we can de-termine the natural frequency of the mono-pile wind turbine above the mudline.Lastly,with an example,we retrieved the natural frequency value of the mono-pile wind turbine above the mud-line.We then compared the analysis result with the mono-pile wind turbine natural frequency ob-tained without considering the interaction between the pile and elastic groundwork,and found lit-tle difference between them.The new theory we propose in this paper is more accurate theoreti-cally and should be validated experimentally.
mono-pile wind turbinenatural frequencyinteraction between pile and elastic foun-dationflexibility methodlumped-mass method
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