This paper explores new analysis techniques and mitigation concepts developed to extend the current state of the art acoustic induced vibrations (AIV) analyses. These new methods are intended to provide more accurate evaluations of this phenomenon in an attempt to solve AIV problems found in blowdown and piping systems. Current screening methods for AIV are based on pass/fail data with minimal or undesired options for reducing the likelihood of failure for AIV events. Computational fluid dynamics simulations and finite element analysis in combination with lab testing of novel mitigation options using accelerometers, dynamic pressure transducers, and strain gages were performed to better understand the phenomenon and develop possible solutions to reduce the impact of AIV on piping systems.
Results of the testing and analyses performed at the Southwest Research Institute (SwRI) indicate that there is a possible correlation with acoustic modes, structural modes, and elevated stresses during AIV events. Minor reductions in dynamic pressure fluctuations throughout piping during AIV events can be made by changes in valve geometry and piping configurations. Results of CFD modeling and analysis demonstrate that computational analysis can be used to evaluate mitigation strategies and suggest that the use of a dampener as a mitigation technique may be successful in reducing the amplitudes of dynamic pressure waves in piping systems caused by AIV events.
Acoustic Induced Vibration (AIV) is a phenomenon that has been known to cause high-frequency fatigue failures at piping discontinuities that present a stress concentration, such as branch connections or pipe supports. Broadband noise generated from upstream flow restrictions providing high pressure ratios, such as control valves or relief valves, may excite high-frequency acoustic modes and piping shell modes within the main line, generally in the range of 100 – 3,000+ Hz. The resulting alternating stresses can cause high cycle fatigue failures within minutes of operation 1,2.