Quiet Please: Mitigating Underwater Noise
- Monday, Jul 30, 2012
Preston Wilson, associate professor in the Department of Mechanical Engineering, and Kevin Lee, postdoctoral researcher, test the bubble curtain system.
University of Texas at Austin researchers have developed a bubble curtain system that reduces the impact of underwater noise from offshore drilling, underwater construction and other activities.
Mitigating subsurface noise can be important for marine life in many environments.
The bubble curtain has drawn interest from drillers, construction companies and government agencies, and its inventors are in the process of licensing the intellectual property through the university's Office of Technology Commercialization and forming a company to make and sell the system.
The research is being conducted at the university's Applied Research Laboratories (ARL), and it's funded by a $1.5 million grant from Shell Oil Company. ARL, the oldest of the university's research units, conducts research on sonar and other technologies.
The ARL researchers on the project are Preston Wilson, an associate professor in the Department of Mechanical Engineering; Mark Wochner, a research associate; and Kevin Lee, a postdoctoral researcher. A team, which included a business student and a law student, presented the system to the Texas Venture Labs Venture Expo in May.
Ship noise, like all noise, can be characterized by its frequency content (related to musical pitch) measured in Hertz (Hz), and its loudness, measured in decibels, or dB. Both aspects of underwater sound can affect sea creatures.
Noise created by ships is low frequency, ranging from 20 to 200 hertz.
"That's right around a frequency that will affect certain aquatic life," Wochner said. "It can affect changes to migratory patterns. It can affect the way they communicate and their predation patterns."
Making the curtain
The bubble curtain system is undergoing testing by UT
Austin researchers at the Applied Research Laboratories.
Officials from Shell approached the researchers three years ago about developing a bubble curtain based on previous research at Texas A&M University. At first, they wanted a curtain of freely rising bubbles pumped from an aerator around the noise source — much like a fish tank.
The previous research had shown that bigger bubbles are most effective in mitigating the low frequencies that ship noise creates. But big bubbles break up too quickly to do much mitigating. There's also the problem of the noise and energy used to generate the bubbles.
But that line of research proved to be a dead end.
So they moved on to encapsulated bubbles, which are contained in a material. The challenge was to find a durable material with the right resonance to mitigate noise and vibration.
They tried children's balloons, red kick balls, ring-shaped balloons, boat bumpers and more.
None of them had the properties they needed. Actually, kids' balloons came close, but they weren't rugged enough to withstand the rigors of Arctic waters.
And then, they found a material that worked and that material is … well, they're not saying right now because of commercialization possibilities.
What they do say is that it's a common product that meets the specs of what they're looking for.
So the system they've developed, Wilson says, "is using completely off-the-shelf components. They've been around and they're very well tested, they're inexpensive and we can get a hold of them very easily."
The curtain at work
The bubble curtain encircles the noise source — a mobile drilling ship, pile driving system or air-gun array — so that when the noise hits the bubbles, the noise is dissipated to levels that are less likely to harm marine creatures or interfere with their communications.
They've tested it in the massive test tank at ARL's site on Burnet Road in Austin and at the ARL station on Lake Travis. And it has passed each test.
Shell is particularly interested because of the technology's possible implication as offshore Arctic energy resources are developed.
The researchers say that a bubble curtain could improve offshore drilling by reducing the effect on marine life and potential interruptions in operations.
So far, Wilson, Wochner and Lee have developed the bubble curtain with Shell's backing. But at some point, they said, Shell will seek to form a consortium of companies interested in using the technology to support development. Because it addresses an environmental issue, it should be made available to the industry as a whole.
The researchers say the system is more efficient than currently deployed technologies. It can be customized for different uses and can grow to meet larger needs, including the mitigation of sound in sensitive marine areas during underwater construction for bridges, ferry ports, docks, piers and wind turbines used to produce energy.
Developing a product
Much of ARL's work has been to develop sonar technologies or model underwater sound. So the bubble curtain is a bit different.
"This was the perfect place to do it, but really nothing like it had been done (at ARL) before," Wilson said. "We had all the infrastructure to do it."
To commercialize the bubble curtain, they joined with a business student, who developed a business plan, and law student, who helped with legal aspects of managing the company. The team presented the system to the Texas Venture Labs Venture Expo in May.