Experiences with Flow-Induced VibrationS

Difficulties encountered in U. S. Bureau of Reclamation structures because of flow-induced vibrations show that similar problems can occur elsewhere and that measures can be taken to avoid or control them. Vibrations interfered with operation and caused structural damage in several radial gates in canals because of control shifting front the flexible bottom seals to the backing plates and back again. It was eliminated by redesigning the seals to produce a positive spring point. In Parker Dam Powerplant, turbine runner blade vibration was induced by vortex trails in the flow behind the blades. Tapering the trailing edge of the blades changed the frequency of vortex shedding and eliminated resonance. At Grand Coulee Pumping Plant vibration in steel discharge lines was reduced by modifying the pumps to lower the magnitude of periodic impulses, and by stiffening the pipeline to avoid resonance. Low frequency vibration or surging in the Coachella Pipeline Distribution System was reduced by changing the natural periods of sections to avoid resonance, reducing the number of sections, and providing a snubbing action. Fluttering in overfalling nappes was eliminated by splitting the jets so full aeration occurred under the nappes.