Acoustically Induced Vibration


Department Publications

Brochures

Technical Publications


Contact Information

Timothy Allison, Ph.D.
Manager
Rotating Machinery Dynamics
(210) 522-3561
tallison@swri.org

High-frequency acoustic mode

High-frequency acoustic modes are excited within the pipe from broadband noise sources.

High-frequency shell modes

High-frequency shell modes in the pipe are excited by the internal acoustics, resulting in high stresses at branches or supports.

Acoustically induced vibration analysis

AIV analysis often involves attenuation and addition of multiple noise sources for multiple operating scenarios.

Stiffening rings

Stiffening rings may be a promising solution for AIV risk reduction at existing facilities and may be evaluated via finite element analysis.

Acoustically induced vibration testing

AIV testing performed at SwRI’s blowdown facility to investigate fatigue life and to quantify effectiveness of AIV solutions.

At high mass flow rates and pressure drops, flow across a restriction (e.g. a control valve, pressure safety valve or orifice plate) will result in extremely high levels of broadband noise. The consequential acoustically induced vibration (AIV) in the downstream piping can cause fatigue failures through the pipe wall at branch connections and/or welded supports. Due to the high frequencies involved, these fatigue failures can occur within only a few minutes of operation.

Cause of AIV

The broadband noise source excites high-frequency acoustic and structural modes within the pipe, resulting in shell-type vibration around the pipe wall. Asymmetric welds on the pipe wall (e.g. branches, welded supports, or partial wraparound reinforcement) amplify the local stresses, resulting in fatigue failures.

Analysis Methods

AIV risk is most often evaluated by comparing with historical failure/non-failure data from the literature. These data have been incorporated into multiple company design codes and guidelines. These methods typically involve predicting the sound power from multiple sources, attenuating sound power downstream of each source, and combining multiple sources as appropriate for multiple operational scenarios. Local sound power level at each branch is evaluated along with the main line & branch diameter, wall thickness, and fitting type in order to determine the risk of AIV failures at each location.

Finite element analysis is not recommended as a method for calculating fatigue life due to the high uncertainty in critical analysis parameters such as noise level, acoustic amplification, structural damping, mean loads, etc. SwRI utilizes finite element analysis to determine a relative stress reduction for various detailed design changes (e.g. stiffening rings) that can then be used in conjunction with historical methods. The use of finite element analysis is particularly useful for situations where it is not possible to increase pipe wall thickness and alternative design recommendations must be evaluated.

Solutions

Southwest Research Institute (SwRI) can perform several types of AIV analyses for various applications. A basic analysis will provide risk of failure for all downstream branches/supports, and recommendations for low-noise valve trim, main line wall thickness, full-wraparound reinforcement, branch fitting type, and branch diameter to reduce the risk of failure to acceptable levels. For existing facilities, alternative design changes (e.g. stiffening rings) may be evaluated with finite element analysis. SwRI also provides testing services to evaluate AIV risk for specific piping configurations and to quantify performance of other potential solutions such as damping wraps, AIV dampers, or acoustic inserts.

Contact us for more information about acoustically induced vibration analysis and testing capabilities at SwRI or how you can contract with SwRI.

Benefiting government, industry and the public through innovative science and technology
Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 10 technical divisions.
02/08/16