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Crews searching for Malaysian Airlines Flight 370 are facing major challenges from all sides as they try to locate the wreckage in the Indian Ocean off the coast of Australia.  In addition to the remoteness and depth of the water in the search area, the dynamics of the Indian Ocean itself are complicating the investigation even further, two University of North Carolina at Chapel Hill professors said.

It’s a unique difficulty grounded in the physics of fluids.  Richard McLaughlin, chair of the Department of Mathematics, and Roberto Camassa, Kenan Professor of Mathematics, both work in the College of Arts and Sciences. They said the varying density of the water in the ocean can interrupt the SONAR signals being used to find Flight 370 – or hide the wreckage from those signals altogether.

“If layers of different densities of water are present, SONAR signals can be severely deflected, making entire regions of the water column invisible, particularly for glancing sound ray propagation angles,” McLaughlin said.

To explain the concept, the professors, who have been studying the fluid dynamics of layered water columns for more than 15 years, created a demonstration in Carolina’s Joint Fluids Lab.  In the video, a ball, representing an object to be detected by sonar sound waves, disappears from view as it falls through a column of water layered by dissolving salt in it.  This is analogous to an object becoming virtually undetectable in SONAR signals from just a few feet away.

“Layered water columns naturally occur in the environment,” Camassa said.  “The fluid density varies with depth because of changes in temperature and salinity, such as from solar heating from the top, as well as evaporation, ice melting and rivers acting as agents varying water density.”

McLaughlin and Camassa said the varying ocean water density in the Indian Ocean also limited the ability of search crews to detect the audible ‘pings’ from the plane’s black boxes.  The difficulty of that search gave them the idea to re-do an experiment from their research to illustrate the cloaking of an object by layered fluids.

“A common thing we see in our experiments is the strong optical distortion caused by variations in the fluid density,” McLaughlin said.

“Hearing about the search for MH 370 using acoustic ping detection stirred us to re-perform the experiment to provide a visual illustration of the possibility of complete cloaking in a layered fluid.”

This isn’t the first time McLaughlin and Camassa have connected their research in fluid dynamics to a major news story.  In 2010, the professors made a video to demonstrate how plumes from the BP Deepwater Horizon oil spill were dispersed in the Gulf of Mexico.  After they produced the video, their work was featured in several news stories, including a live appearance on CNN.

“It is important to both our research and educational missions to try to make a broad impact,” Camassa said.  “We’re always excited to have an opportunity to discuss our work and how it can help the general public in understanding complex issues.”

By Rob Holliday, New Services.

May 1, 2014.