Graduate Thesis Or Dissertation
 

Seismic protection of flexible rotating machines using base isolators

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  • Base isolation is an alternative seismic design strategy in which the primary structures and their internal components are uncoupled from the potentially damaging horizontal components of an earthquake by base isolators which attenuate the transmission of horizontal acceleration into the system. Rotating machines are among the key internal components of many modern structures. In this study, flexible rotating machines protected against seismic excitations by two particular types of base isolation systems, Resilient-Friction Base Isolation (R-FBI) and Laminated Rubber Bearing (LRB), are investigated. A comparative study is carried out to compare aseismic responses of base isolation systems and their corresponding fixed-base ones in protecting a rotating machine rigidly attached to a floor level or independently isolated. Finite-element analysis techniques based on energy methods are proposed to investigate a general complex model of the rotating system which incorporates nonuniform properties as well as one or more rigid disks along the length of the flexible shaft and complicated bearing support systems. The equations of motion for the rotating machines using these methods are developed. An approximate linear analysis to gain insight into the behavior of a simple linear two-degree-of-freedom isolated structure is presented. This elementary analysis allows us to develop an analytical expression for the fundamental frequencies, and their corresponding mode shapes, amplification factors and design response spectra of base shear. It also demonstrates that the transmission of ground motion to the systems is effectively controlled through the isolation of the system at its base. The combined rotating machine-isolator; rotating machine-structure-isolator; and structure-isolator systems, and their corresponding fixed-base ones are investigated and compared. The governing equations of motion and the criteria of phase transition (R-FBI only) are presented. Parametric studies to examine the sample response and response spectra, as well as effects of variations in some system properties including friction coefficient, damping ratio, mass ratio, ground motion excitation intensity, shaft flexibility, bearing rigidity and rotating speed, on the response of these systems are performed. The peak accelerations and relative displacements of the base isolated systems and corresponding fix-base ones are analyzed and compared. Other response quantities of special interest such as sliding displacement, residual displacement, cumulative displacement and relative-to-ground displacement of the structure are also evaluated. Based on the numerical results, conclusions of the effectiveness of the R-FBI and LRB systems in protecting the rotating machines and the structures are made.
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