Size Effect in Damping Caused by Water Submersion

An important effect of water submersion on dynamic response of a structure is the increase in effective damping. The dynamic response of submerged structures is of interest to the nuclear power industry for reasons of operational safety during seismic and other dynamic excitations. In this paper, the added damping contribution that results from the viscosity of water and the dependence of the contribution on structural size are examined. Other factors considered are the applicable range of viscous damping with respect to displacement amplitude and, as far as damping is concerned, how far must neighboring members be from each other to respond as if in open water. An expression is derived for relating the damping value to structural size. Estimated added-damping values for representative fuel elements, fuel bundles, and main steam-pressure-relief-valve lines that are based on our derived expression for added damping are given.