Model Tests for Non-Eccentricity Dynamic Instability Closely Related to Folsom Dam Tainter-Gate Failure

Abstract

This study addresses a type of dynamic instability of the Folsom Dam (radial) Tainter gates that is not related to the eccentric location of the trunnion pin about which the gate rotates. In these gates, the skinplate is concentric with the trunnion center (i.e., there is no eccentricity). This type of instability, hereafter called non-eccentricity dynamic instability, results from the coupling of the rigid body vibration of the whole gate about the trunnion pin with a streamwise bending vibration mode of the skinplate and is accompanied by a flow rate variation in the gate’s discharge. A two-dimensional 1/31-scale model of the Folsom Dam Tainter gates was constructed to verify the non-eccentricity dynamic instability mechanism. An intense instability was induced in the model, especially when the in-water natural frequency of the skinplate streamwise vibration was slightly smaller than the in-air frequency of the rigid body vibration of the whole gate about the trunnion pin. Further, a theoretical analysis of the non-eccentricity dynamic instability, in which the vibration-induced hydrodynamic forces are calculated by a potential theory developed by Rayleigh for dissipative wave radiation, was also conducted. The theoretical results are compared with the experimental results to verify the validity of the analytical model and its implicit assumptions.