Dynamic Base Analysis for the NSGS Induced Draft Fans by Single Degree-of-freedom Models


The vibration response of a large industrial rotary fan is a complicated problem that involves the contribution of such items as the fan rotor, bearings, soil conditions, concrete and steel pedestals, and finally the supporting concrete foundation. Each of these components provide mass, stiffness, and sometimes damping values that determine the ultimate motion of the machine. The displacements that the machine experiences are directly related to the reliability and performance the fan will provide to the owner. Often, the equipment manufacturer is blamed for an unreliable piece of equipment because imbalance problems are frequently encountered. In turn, the fan manufacturer directs the blame towards the architect/ engineer for a faulty foundation design. Numerous approaches have been developed to more thoroughly analyze the motions of this type of dynamic imbalance problem, and some are extremely complex and do not lend themselves to practical usage for the design engineer. It is conceivable that multi-degree-of-freedom system modeling of a large fan could have well over one hundred degrees-of-freedom. This research effort has narrowed its area of study to single degree-of-freedom models in order that a simplified approach for solving actual design problems or troubleshooting existing installations can be realized. The investigation of the dynamic response for two identical 92" diameter induced draft fans at the Northside Generating Station, in Jacksonville, Florida included soil testing and physical monitoring to determine actual soil characteristics and fan motions. The history of dynamic imbalance of these machines is long and repetitive. Numerous attempts have been made to rectify these ongoing problems with only minor success. These solutions normally were generated by the fan manufacturer who took field measurements and then made recommendations based on the interpretation of the recorded data and personal experience. A more analytical approach is taken in this research effort to assess the actual recorded field data with that of the theoretical response and then compare the results. Recommendations based on this comparison were made as well as a determination of the root cause for the fan imbalance.


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Graduation Date





Carroll, William F.


Master of Science (M.S.)


College of Engineering


Civil and Environmental Engineering





Length of Campus-only Access


Access Status

Masters Thesis (Open Access)


Dissertations, Academic -- Engineering; Engineering -- Dissertations, Academic

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