TENTATIVE DESIGN GUIDE FOR CALCULATING THE VIBRATION RESPONSE OF FLEXIBLE CYLINDRICAL ELEMENTS IN AXIAL FLOW.

Many reactor and plant equipment components, such as fuel pins, control rods, and heat exchanger tubes, are long, slender, beam-like members which are exposed to nominally axial coolant flow. The flowing coolant represents a source of energy which can induce vibratory motion of these components. This design guide presents a relationship for calculating the root-mean-square (rms) displacement of a flexible rod or tube in axial flow. The relationship is based on the results of a parameter study and is valid for components that can be approximated as beams with either simply-supported or fixed-fixed ends. It is given in terms of beam natural frequency, damping factor, and intensity of the mean-square spectral density of the pressure field in the low-frequency range; all three are functions of mean axial flow velocity. Empirical expressions are developed for damping factor and intensity of the mean-square pressure spectrum. With these, an empirical equation for rms displacement is written which is in terms of known quantities and, therefore, provides a tool which can be used by designers. Since the equation is based on experiments involving a smooth rod in flow with minimal entrance effects, the predicted displacements should be interpreted and used with care. They are not conservative and, at best, will represent the minimum response to be expected. (auth