Seismic design method of clamped-free thin cylindrical shells immersed in fluid

We carried out excitation experiments on clamped-free thin cylindrical shel ls immersed in fluid that represented thermal baffles of a fast breeder rea ctor. At a certain excitation level, occurred external pressure buckling. W e also observed that parametric vibration, which involved high-order circum ferential vibration modes, occurred at a certain combination of excitation frequency and excitation level. Concerning seismic design of the thermal ba ffles, we, therefore, take not only the buckling but also the effect of the parametric vibration into consideration. We adopt buckling eigenvalue anal yses to estimate buckling pressure and propose a formula to prevent the buc kling. Further, we discuss important factors such as buckling strength redu ction caused by initial shape imperfections and interaction between horizon tal and vertical seismic response. Concerning the parametric vibration, a s ignificant deformation of cylinders should be prevented. A practical method applying the dynamic stability theory is proposed to obtain the condition, under which the parametric vibration takes place. (C) 2001 Elsevier Scienc e B.V. All rights reserved.