The flow induced pipe vibration during its sagging process

Abstract

The flow induced pipe vibration problems have been studied experimentally. The emphasis of the present paper is placed on the pipe vibration during its sagging process. The bed scour below a pipeline is promoted notably by the pipe vibration. Provided the scour hole below the pipeline is large enough, gravity and the flexibility of the pipeline allow it to sag into the scour hole. Flow velocity is an important factor, but the eroded bed has some restrictive action on the pipe vibration. The gap ratio e₀/D between the pipe bottom and the initial plane bed is another important factor. With respect to the pipe vibration the pipe state can be classified as the pre-vibration stage, the lock-in stage and the lock-out stage. For different pipe states the amplitude response tendencies of the pipe are quite different during its sagging process. When the pipe is in the lock-in stage and very close to the bottom of the scour hole, the pipe may vibrate with such an amplitude that it may be damaged due to its impact on the scour hole.