For a wide range of engineers and scientists, the sound generated by a vibrating structure represents a critically important phenomenon. These sounds can be of significance for accomplishing rapid, low-cost inspection of critical infrastructure. For example, there are approximately 600,000 highway bridges in the United States. The timely inspection of these bridges requires a significant outlay of resources from federal, state, and local governments. A system capable of detecting significant structural flaws without requiring extensive physical contact with the structure would increase the frequency of inspections, thus improving the safety of the aging bridge infrastructure.

Acoustic Energy interacting with local topography around bridge.
Computational methods have been developed to detect and differentiate sound waves generated by vibrating structures such as bridges. These methods can be used to assess vibration modes of the structure and calculate the acoustic energy generated by these vibrations. COMSOL Multiphysics software enables a user to solve for the vibration modes of the structure and use the results as the driving force for the analysis of the propagation of the acoustic waves through the surrounding atmosphere. This is important because it enables integration of two different finite element modeling techniques that have presented a significant challenge for other computational software. This challenge stems from the use of beam elements to calculate natural modes of vibration in civil engineering structures. These elements are not appropriate, however, as the source in acoustic analyses due to their lack of surface area. To overcome this challenge, the inherent capability in COMSOL Multiphysics to drive the acoustic analysis based on the results of the modal analysis was used.

The figure shows the acoustic waves generated by a vibrating bridge reflecting off the local topology surrounding the bridge. The plane at the bottom represents the topology with colors that specify relative elevation. At the center of the topology is a riverbed that appears white; the bridge spans the riverbed at the center of the image. A cut plane in the figure shows the distribution of sound pressure level as it propagates away from the bridge. These results provide clear guidance for specifying the type and location of sensors necessary for assessing the structural condition of the bridge.

This research was sponsored by the US Army Engineer Research and Development Center under the Infrasound Assessment of Infrastructure program.

This work was performed by Dr. K.C. Koppenhoefer, Dr. J.S. Crompton, and Dr. S. Yushanov of AltaSim Technologies, LLC using COMSOL Multiphysics software. For more information, Click Here .

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This article first appeared in the September, 2009 issue of Software Tech Briefs Magazine.

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