Wind tunnels have been invaluable tools for assessing the susceptibility of building materials to wind damage and providing insurers with data to better predict losses and promulgate property rates. But wind tunnels have an inherent limitation when it comes to modeling a hurricane's effects: They can't test full-scale buildings.
"Wind tunnels rely on models that shape the geometry of buildings, but they cannot test all individual [building] elements because not all of those elements can be brought down to size," says Dr. Arindam Gan Chowdhury, assistant professor in the civil and environmental engineering department at Florida International University (FIU) in Miami. It's also difficult to conduct destructive testing in a wind tunnel for fear of damaging the tunnel itself.
Therefore, FIU's International Hurricane Research Center (IHRC) devised a plan to use an array of seven-foot industrial fans to simulate hurricane conditions in an external testing environment. Phase one of the plan, a two-fan prototype funded by the Florida Department of Community Affairs, was completed in early 2005 and successfully used to test full-scale roof models under wind and wind-driven water conditions.
Based on what it learned in phase one, FIU began work on a larger fan array in phase two of the project. RenaissanceRe signed on as main corporate sponsor of the project, now dubbed the RenaissanceRe Wall of Wind, and AIR Worldwide Corporation agreed to sponsor fan turntable installation and programming software. The new six-fan array is being constructed on a public parcel of land adjacent to Homestead Air Force Base and is scheduled for completion by late summer.
The six fans, each powered by a racecar engine with 502 horsepower, will be able to replicate hurricane conditions with up to 140-mile-per-hour winds. The engines operate by means of remote-controlled servos and computer-based algorithms the IHRC developed within the National Instruments LabVIEW software.
"Individual engines can be controlled separately," Chowdhury says. "We can run the top at one speed, the bottom at other speeds; we can vary engine speeds quickly to get wind gusts." The IHRC uses hurricane wind data from the Florida Coastal Monitoring Program to match produced wind speeds to actual storm data. High-speed cameras will monitor the effect of wind and wind-driven rain on individual building materials and full structures.
"This will be a reliable way of testing full-scale buildings in a realistic wind and rain environment. We'll get a lot more statistical credibility and a repeatable, controllable environment, which is important for vulnerability modeling," says Craig Tillman, president of Weather Predict Consulting, an affiliate of RenaissanceRe Holdings Ltd., in describing why RenaissanceRe decided to fund the Wall of Wind project.
Phase-one testing already has produced insight that could not be gained through scale testing. "When we did full-scale testing on roofing, we saw there are hot spots on roofs where the damage initiation begins, which can be underestimated by current codes," Chowdhury explains.
Phase three of the project will be the development of an 18-fan array and, ultimately, a "community" of buildings to test new building materials and revised construction methods in a natural environment and for additional environmental forces, such as storm surge and debris impact. Expected to take five to 10 years to complete, this final phase will require FIU to partner with universities in other coastal states for resources and also will require getting additional support and funding from private and government sectors.
"At the end, we should have significant research data to build a hurricane-resilient community in every respect: wind, rain, storm surge, debris impact, and business continuity," Chowdhury notes.
Tillman expects the Wall of Wind to produce data RenaissanceRe and other insurers can use to manage risk. "We obviously have experiments we want to do that will help us predict losses with more precision and help insurers better manage catastrophes," he says.
And just as full-scale testing of automobile crashes has changed automobile safety, more important are the public benefits of the Wall of Wind project. "We hope it will help by identifying hurricane-resistant designs, materials, and construction techniques. Being able to give your typical homeowner visual evidence of what works and what doesn't will help motivate better risk management behavior," Tillman concludes. "It's a step toward reducing losses; that's the bigger picture."
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