It’s a clear summer day in South Florida, but a storm rages inside the SUSTAIN Laboratory at the University of Miami’s (UM) Rosenstiel School of Marine and Atmospheric Science, where the world’s biggest hurricane simulation tank is in full swing. Category 5 strength wind and waves wallop a makeshift stilt house, pound at its foundation, as a suite of sensors collect data on the structure’s stability. Brian Haus, an ocean scientist and director of the facility, leans his whole body against the 3-inch thick acrylic as if he wants to be closer to the action. I’ve lived through a handful of hurricanes as a kid growing up in South Florida, but never one of this magnitude or from this point of view—never seen sawtooth waves consume a shoreline or heard the terrifying strength of 157-mph winds.
Warm water is like fuel for hurricanes, so as climate change intensifies and ocean temperatures rise, hurricanes will grow less frequent but more powerful.
SUSTAIN (short for Surge Structure Atmosphere Interaction Facility) is about as big as a shotgun house: 75 feet long, 20 feet wide, and 6.5 feet deep. At the flip of a switch, the UM researchers roil nearly 40,000 gallons of calm water into an ersatz force of nature, as an immense fan sucks air in through a wind tunnel, whirls it around some chambers, and hurls it into the box, where underwater paddles churn up choppy waves. Wind and water collide. Spray particles smack against the acrylic sides like millions of tiny bugs against a windshield. I can hardly hear Haus shout over the cacophony.
“All the fluctuation we see in the air is the result of interactions with the waves,” he yells, perhaps observing something I do not. By studying these interactions, Haus and his team hope to answer questions about how hurricanes gain strength and what sort of structures engineers can create to help dissipate storm surge, the tsunami-like event that causes the majority of hurricane-related deaths. “We can control conditions in ways that allow us to look at these specific problems.”
Meanwhile, about 20 miles west, researchers at Florida International University use a facility called the Wall of Wind (yup, they call it WOW) to summon hurricanes on demand. The facility’s array of 8-foot fans are designed to destroy. They obliterate objects placed in their wake, pushing structures to failure to improve the overall integrity of building designs.
And the research can’t come soon enough. Warm water is like fuel for hurricanes, so as climate change intensifies and ocean temperatures rise, scientists predict hurricanes will grow less frequent but more powerful. With their state-of-the-art simulators, researchers like Haus hope to gain critical insights that help improve forecasting models and fortify our coastal cities before the next big one hits.
Making a Hurricane
Hurricanes are fickle things, known to explode from a tropical storm to a Category-5 with little warning. Take Hurricane Wilma, which surprised forecasters in 2005 when it jumped from a Cat-2 to a Cat-5 in just a few hours while making landfall in Mexico.
“Hurricane rapid intensification is one of the big issues we’re chasing,” says Haus. SUSTAIN is tailor-made to probe this problem.
There are three key components to creating a hurricane in the $15 million SUSTAIN tank. The first is its fan, whose 1,460-horsepower engine uses so much energy that it relies on an emergency backup generator so as not to sap vital power from the various life sciences studies being conducted on campus. When Haus turns the machine on, it begins with a low hum and within minutes grows into the roar of a muffled jet engine.
The second key feature is its array of twelve underwater paddles, which can create a myriad of wave types, from calm and uniform to chaotic and complex. “If we just had wind blowing over the box of water, we wouldn’t be able to study the wide range of conditions on the real ocean,” Haus says. The paddles allow the researchers to “represent all the randomness of the ocean surface.”
Finally, the tank’s acrylic exterior is itself critical. Transparent on all sides, SUSTAIN allows researchers to observe the inner workings of a hurricane from all angles. Where Haus and I stand, we can observe a cross-section of the thrashing storm. From above, remote sensors can peer down and monitor the storm like satellites, perhaps helping improve measurements made by weather satellites. Researchers can even position lasers underneath the tank in an attempt to glean insight from beneath the waves. “I wanted it designed so that LeBron James could walk underneath,” Haus jokes.
Since it was built in 2015, SUSTAIN has been used to conduct a variety of tests too difficult and dangerous to pull off in the middle of an actual storm.
One of Haus’s main interests is on the air-sea interface, or where wind and water meet. High winds whip the air and ocean into a frothy concoction, the friction of which creates complex energy transfers that are all but impossible to measure in the midst of an actual storm. SUSTAIN puts researchers and their monitoring devices right in the thick of it. Haus and his team hope to use these interactions to build better models capable of predicting how hurricanes grow in intensity.
“We can actually measure the rate at which the heat is being transferred.”
“By throwing a whole bunch of detailed computers models [at the problem], you can try to figure out where hurricanes are going,” Haus says. “But we still have this problem of how fast they can grow. These kind of transfers at the surface could be a big part of that.”
Civil engineers also stand to benefit from research conducted in the tank. An on-going study is investigating how hybrid reefs and breakwaters might be able to dissipate energy and protect coastal properties from rising sea levels and stronger storms. Two perforated structures sit in the middle of the tank during my visit. “The idea is that you could incorporate living shorelines, such as mangroves, inside of these structures, instead of just having a solid straight wall as a shoreline,” Haus explains. Preliminary results suggest there’s about a 30 percent reduction of wave energy when the wave passes over the coral.
Miami is among the most American cities most at risk of climate change, as the ocean creeps insidiously higher up its shores. Haus hopes to use SUSTAIN to better understand how warming waters could impact hurricanes by studying gas and heat transfer at the ocean’s surface. “People talk about warmer oceans contributing to stronger hurricanes because you need warm water to power hurricanes,” he says. “We can actually measure the rate at which the heat is being transferred.”
SUSTAIN’s predecessor has already been used to improved hurricane tropical storm and hurricane forecasting models. Sitting next to the massive new tank is its svelte younger sibling, a long and narrow wave tank that Haus and his team still use for smaller scale experiments. A fraction of the size of the current tank, the first-generation machine could only reach around Cat-3 wind speeds but research still revealed how frictional drag between wind and water acts differently than expected at higher wind speeds. “For intensity forecasting, this drag coefficient relationship that we developed based on studies in this lab is now used in all hurricane forecasting,” Haus said. The discovery has been used to make better hurricane models and narrow the “cone of uncertainty” that predicts a hurricane’s path.
Welcome to the Wall of Wind
The anthropomorphizing of hurricanes doesn’t end when meteorologists give them names. Storms have personalities too. Close to the ground, hurricane winds dance and swirl in peculiar patterns. As the wind climbs higher, its speed increases as well.
Researchers at FIU employ the National Hazards Engineering Research Infrastructure Wall of Wind Experimental Facility (or WOW for short) to recreate the unique characteristics of hurricane winds and study how these winds collide with buildings, from single-family houses to high-rises. Their goal is to decrease the impact storms have on the built environment, in turn saving lives and money.
WOW consists of 12 fans stacked in two curved rows. The curve helps funnel wind towards the center for increased speed. The fans suck ambient air into a contraction zone, where the tighter space causes it to speed up precipitously. The wind then immediately rushes into a big box called a flow management zone, where spires and mechanical tiles create a layer of friction that slows the wind down and adds a bit of turbulence to near the ground. In this way, WOW replicates not just to speed of a Cat-5 winds but also their frenetic dynamics.
“Hurricane wind isn’t nice, straight, laminar, and smooth,” says Erik Salna, who heads education at outreach at FIU’s International Hurricane Research Center. “In real life, windspeed increases with height and at the ground surface there are objects like buildings and trees, which cause friction.”
It’s not unusual to find a makeshift roof blown hundreds of feet into the open field behind the wind chamber.
From a control room next to the facility, researchers can control WOW, cranking winds speeds up to 160 mph, and adjust models placed on a rotating platform behind the fans. They use sensors and high-definition cameras to monitor the condition of the models, gaining insight into how and why structures fail.
Built in 2012, two decades after Hurricane Andrew devastated entire communities in South Florida, the $9 million facility was funded by the National Science Foundation to help prevent wind hazards from becoming disasters. WOW is helping improve construction designs in the United States and abroad. When the architectural Boeri Studio wanted to build its verdant Bosco Verticale (Vertical Forest) in Milan, the designers first tested a model of the structures at WOW to make sure trees wouldn’t fly off like green projectiles in high winds.
When running at full capacity, WOW doesn’t pull punches. It’s designed to test buildings to failure, which means it’s not unusual to find a makeshift roof blown hundreds of feet into the open field behind the wind chamber.
And for good reason—hurricanes don’t pull punches either. In the past 15 years alone, the Atlantic has borne ten Cat-5 hurricanes, which have caused thousands of deaths and hundreds of billions of dollars in damages. As climate change threatens to send more powerful hurricanes our way, unlocking the secrets of these deadly storms has never been more pressing.
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