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Mechanical Properties of Concrete Tower of Wind Turbines and Isolation Research of the Bottom of Tow

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Tutor: FanYouHua
School: Harbin Institute of Technology
Course: Mechanics
Keywords: ultra high concrete tower,cavity periodic structure,low frequencyband-gap,isolat
CLC: TU352.12
Type: Master's thesis
Year:  2012
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Right now, the height of the MW class wind turbines is close to or more thanone hundred meters. When the tower reaches such ultra height, the cost of theconcrete tower is less than that of steel tower. So the ultra high concrete tower willbe more and more built in the large scale wind farm. However, when the height ofthe large fan reaches one hundred meters, the load bearing of the concrete tower ismuch larger than that of ordinary high tower. Then, whether the ultra high concretetower is safe or not in such work environment? Unfortunately, there is littlemechanical analysis of the ultra high concrete tower. In addition, there were moreand more tower collapse accidents in recent years, and the reason partly due to therole of the earthquake. How to isolate becomes particularly important for the ultrahigh concrete tower. For the two questions talked above, our work can be dividedinto two parts. The first part is that the static and mode analysis have been done forthe ultra high concrete tower by using the software-ABAQUS. The second part isperiodic structures have been introduced into the design of the tower base-at thebottom of the tower, and the isolation effect of the tower base has been analyzed.The details of the research contents show as follow:(1) Three95m ultra high concrete tower models, including plain concrete tower,reinforced concrete tower and pre-stressed concrete tower, have been constructed bythe software-ABAQUS. Under the simplified wind load, the static analysis showsthat: the maximum stress of the pre-stressed concrete tower increase about14%thanthat of the other two tower model, and the maximum displacement of thepre-stressed concrete tower reduces about30%than that of the plain concrete tower.Then when there is a door in the tower, stress concentration appears around theopenings and the maximum stress of the first tower section increases more than50%.(2) Mode analysis has been done for the three ultra high concrete towers,whether there is resonance or not is the focus of the attention. The result shows thatall of the natural frequencies of the three tower model are far away from thevibration frequency when the wind turbines work. The existing of the openings inthe concrete tower changes the natural frequencies of the tower, but makes a little effect on the mode of the whole tower. The range of the fundamental frequency ofthe concrete tower is about0.9-1.2Hz.(3) The traditional locally resonant periodic structure, which is twodimensional ternary, has been improved by setting cavity into the rubber layer.There is a low frequency band-gap in the new cavity periodic structure, which isabout0.63-2.5Hz, and the fundamental frequency of the concrete tower falls intothe first band gap of the new cavity periodic structure. The relationships betweenthe first band-gap and the parameters of the cavity periodic structure are listedbelow. One is that the greater of the filling ration of the scatters, the lower of theinitial frequency of the first band-gap, when the aspect ratio of the rubber blockbecomes more and more large. The other is compared to the effect on the startingfrequency of the band-gap; the length of the core of the scatter causes a greaterimpact on the termination frequency of the first band-gap. There are three methodsto get a wider band-gap, reduce the aspect ratio of the rubber block, and increase thefilling ratio or the size of the core of the scatter.(4) Frequency response analysis has been done for a limited number cycle¡¯scavity periodic structure of bottom of the tower. Displacement frequency responsefunction and the vibration characteristic of the tower base show that there is greatvibration consumption in the first band-gap of the cavity periodic structure.
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