More than one steady-state solution is shown to exist for the problem of steady-state heat transfer across the walls of a duplex tube when the initial prestress between the inner and outer tubes is sufficiently low. This determination was used in explaining the apparently erratic heat-transfer performance of prestressed duplex tubes in the steam generating system of the Experimental Breeder Reactor II. The importance of the results lies not only in showing that nonuniqueness of steady-state solution applies to more complex geometries than heretofore analyzed, but also in demonstrating that such multiple steady-state conditions appear in practical situations.

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SUMMARYA stochastic critical excitation is defined as that excitation with a given variance that maximizes the variance in the dynamic response of a system. A non-stationary filtered shot noise is used to develop a stochastic critical excitation model of an earthquake ground motion process, and the response statistics for a linear system are determined in both time and frequency domains. The sensitivity of response to several assumed earthquake pulse arrival rate functions is examined. Responses to recorded strong ground motion and to stochastic critical excitations with the same total energy are compared to assess the degree of conservatism in the procedure. An application of the procedure to seismic qualification of equipment is presented.