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Research at CWRU’s new structural laboratory could aid Lake Erie wind farm effort  

Credit:  John Funk, The Plain Dealer, www.cleveland.com 30 August 2010 ~~

CLEVELAND, Ohio – Case Western Reserve University has opened an unusual new laboratory, one that employs brute force – with electronic precision – to test the limits of materials.

And what is going on at the Vanderhoof Infrastructure Research and Education Facility and Schuette Structural Laboratory could help the effort to build wind farms in Lake Erie that can stand up to the lake’s destructive storms and icing without costing a fortune to build.

For several months, civil engineering professors Arthur Hucklebridge Jr. and Dario Gasparini have been carefully trying to destroy a hardened 9,000-pound concrete slab.

To do this scientifically, they have been using a computer-controlled hydraulic apparatus connected to the slab. The equipment pushes or pulls with a force of up to 150,000 pounds three times per second on the monolith, which, except for its color, could well have been taken right off the set of the Stanley Kubrick movie, “2001, A Space Odyssey.”

But this is no movie. The monster piece of high-strength concrete and steel rebar is an exact replica of a slice of what many land-based European wind turbines stand on.

In other words, it’s a foundation piece. And the foundation under a wind turbine is just as important as the foundation under a skyscraper.

Hucklebridge and Gasparini are foundation experts. They have “instrumented” the Inner Belt Bridge several times since the late 1990s to help the Ohio Department of Transportation keep track of the bridge’s tricky alignment problems.

And now General Electric has asked them to look into why wind turbine foundations sometimes fail despite their brawny composition.

GE, the nation’s largest wind turbine manufacturer, has an agreement with the Lake Erie Energy Development Corp. to supply 225-ton turbines for LEEDCo’s pilot project.

The plan is to build a five-turbine wind farm about seven miles out in the lake by the end of 2012, and then expand it over the next 15 years with hundreds of turbines, creating a new Northeast Ohio industry in the process.

But it all starts with a foundation. And a failing foundation at the bottom of the lake would be a much bigger problem than one in a cornfield.

Using GE specs, the two professors and students built the monolith in the spring in the brand new $4 million laboratory that occupies the space that once held three coal-burning steam boilers that heated the CWRU campus.

For the last couple of months, the two professors have had the monolith anchored to the lab floor for the 150,000-pound, three-times-per-second pulsing.

The plan is to do this about 4 million times, simulating the beating a turbine foundation would take in about 20 years of service. The score so far? A little over 3 million pulses.

But there’s more. Hucklebridge and Gasparini are trying to find out what’s happening inside the heavily reinforced slab as it takes this punishment. They are measuring the internal stresses the pulsing is causing.

They can do that because when they made the slab they buried and wired up about 40 pressure sensors inside the thick concrete.

The sensors have been diligently measuring internal pressures five to 20 times per second.

All of the digital data – the equivalent of about 30 full-length DVD movies – has been stored and will be analyzed to see where and when the internal deterioration began.

“This is a way to get history in a hurry,” Hucklebridge said. “That’s what we are trying to do here.”

In other words, when the testing is completed, the slab will have had the laboratory equivalent of about 20 years in the field taking a beating from an actual wind turbine.

While a turbine pivots to move its rotating blade into the wind, the foundation experiences this back and forth turning movement as an up and down movement, Hucklebridge said. And that movement can loosen the steel buried in the concrete to which the turbine’s tower is bolted.

GE is interested in the outcome to improve the life span of land-based wind farms that use the company’s turbines.

And if the lake turbine project ends up using massive reinforced concrete foundations on the lake bottom, what Hucklebridge and Gasparini are learning will be very important, said David Zeng, colleague and chairman of the civil engineering department.

Zeng is a geo-technical engineer who specializes in foundations and soil mechanics. He has been working with the National Aeronautics and Space Administration using synthetic moon soil to develop rovers and foundations for a moon base, if the space agency ever gets the go ahead to do that.

He is preparing to help out with the lake project as well.

Zeng is looking forward to receiving lake bottom soil samples and especially wants to analyze core samples taken from the bedrock under the lake. He said the turbines may have to be anchored to that bedrock.

Because Lake Erie freezes, there is another set of engineering problems that may be just as critical as foundation engineering.

The problem is that lake ice can exert tremendous pressure on a turbine’s tower. Zeng is developing an experiment to come up with a strategy to deal with that.

He said he will seek state and federal grants this fall in cooperation with LEEDCo.

Zeng plans to build a giant laboratory experiment in which a scaled-down turbine tower, known as a “monopile” in the industry, will be frozen in a simulated lake (actually a large tank of water).

Since the ice won’t move, the experiment will use computer-controlled hydraulic apparatus to move the pole against the ice, simultaneously measuring the pressure it will take to crack the ice.

In the lake, either the ice or the tower structure will crack, depending on which is stronger or whether the ice can be deflected up or around that structure.

As stone quarry operators once knew, when water becomes ice, it can exert incredible pressure. Quarry operators simply drilled a line of holes, filled them with water and let nature do the work, cracking massive chunks of stone.

Water expands in volume by about 10 percent when it freezes into ice, Zeng said. That’s the 10 percent that can rupture a water line.

Lake ice will have its way with a structure in the lake unless that structure is strong and the ice can be deflected, cracking the ice and dissipating the pressure.

While the wind industry has little experience putting turbines in fresh water, which freezes, engineers have plenty of experience putting bridge foundations in rivers – rivers that freeze while strong under-ice currents also keep pushing on a foundation.

“It’s not an issue of whether or not we can do it,” he said. “It’s a cost issue. The No. 1 issue [of a lake-based turbine] is to reduce cost to make it competitive.”

Zeng also is proposing to put a platform in the lake on a monopile sunk into the bedrock. The platform would house instruments that would take data from sensors in the lake to measure not only ice pressures, but also ice floes.

“My best guess is that ice stress is the most critical force we will have to deal with,” Zeng said.

Another CWRU professor, David Matthiesen, placed a camera on Cleveland’s 3-mile water intake crib about a year ago and has recorded images of ice movement, Zeng said. Matthiesen is also studying wind intensity, velocity, direction and turbulence.

Professor Iwan Alexander has been studying the most efficient layout for a wind farm. Wind turbulence created by the blade of one turbine can interfere with the wind – and efficiency – of turbines behind it. Others are looking into new, lighter materials for turbine blades. All of the professors are part of the new Great Lakes Energy Institute, which is refocusing CWRU’s engineering expertise on energy problems in a global economy.

“We feel this is the most suitable place to do the research,” Zeng said. “We have the faculty, the facility and the research strength.

“At the end of the day, we need to have thoroughly investigated the geo-technical and geological conditions of the site. Then we would have a better understanding of what type of foundation most suits the project.”

Source:  John Funk, The Plain Dealer, www.cleveland.com 30 August 2010

This article is the work of the source indicated. Any opinions expressed in it are not necessarily those of National Wind Watch.

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