Fluid-structure interaction during hydraulic transients in pressurized pipes: experimental and numerical analyses

Pressurized pipes may be endangered by failure due to excessive hydraulic transients, the so-called waterhammer. These pressure waves are strongly affected by fluid-structure interaction (FSI), unsteady skin friction, dry friction or pipe-wall viscoelasticity. With his research project Dr. David Ferras made a significant contribution towards the improvement of onedimensional (1D) waterhammermodelling in the time-domain by means of the well-known method of characteristics. He identified, described and quantified the principal mechanic hydraulic relationships during hydraulic transients in pressurized pipe flows in view of better design criteria and, consequently, reducing risk of failure. Dr. Ferras has given a new perspective regarding the theoretical background of FSI 1D modelling by means of a novel classification based on pipe degrees-of-freedom and suggesting an original standpoint for tackling FSI problems. Dr. Ferras produced new extensive series of experimental data acquired from several pipe rigs, with different pipematerials and geometries which constitute relevant benchmark data for validating numerical models. The coil ‘breathing’ effect was highlighted by the candidate as the cause of a systematic reduction of the waterhammer wave amplitude, which has never been described in literature before. He developed a new model considering fluid-structure interaction mechanisms, unsteady skin friction and dry friction. He has demonstrated the importance of unsteady skin friction when the pipe is fully anchored and the role of dry friction when the pipe is free to move. In a second approach, Dr. Ferras added internal conditions to the numerical model allowing the description of the pipe anchoring and thrust blocks taking into account their resistance to movement due to the inertia and the dry friction. A novel model was proposed which was proven to be reliable, efficient and accurate in the description of hydraulic transients in straight pipelines for different anchoring conditions.

Schleiss, Anton
Lausanne, EPFL-LCH

 Record created 2017-03-20, last modified 2019-03-17

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