New Design Approach for Computing Peak Dynamic Response of Turbo Generator Pedestals Using Modal Synthesis

Turbo generator pedestals are one of the critical structures in any power plant complex. Stringent vibration requirements particularly at the bearing locations have been stipulated for proper functioning of turbo generator installations. Normally the dynamic analysis is carried out using a deterministic approach with constant material properties. The effect of variability of modulus of elasticity of concrete, and operating speed of the turbo generator can lead to increased amplitudes of vibration. The designer always looks for conservative estimates of the expected responses and is interested in keeping them within allowable limits. This paper provides a methodology for computing peak dynamic response at bearing locations once the results of the dynamic analysis with a given input stiffness is available. The approach is essentially based on modal synthesis of responses, namely contribution of individual modes to amplitude of vibration at a particular location. The frequency range of interest is divided into three regions, namely, nonresonant region where undertuned conditions exist, nonresonant region where overtuned conditions exist, and the resonant region. Simple analytical formulation has been developed to compute the peak dynamic response and is illustrated with an example. The suggested method can be programmed for effective use through spread sheet and MS EXCEL software.