System work the way a Tsunami

To engineer better buildings, researchers at Oregon State University's Wave Research Laboratory bust walls with waves generated by this artificial tsunami machine.

The wavemaker at OSU’s lab can generate both regular and random waves.

More than half of the U.S. population lives within 50 miles of the coast, where it is vulnerable to hurricanes, tsunamis and other severe weather. Researchers at Oregon State University’s O.H. Hinsdale Wave Research Laboratory believe that engineering solutions could prevent the loss of life and property along America’s seaboards—and they’re using a giant wavemaker to prove it. A hydraulically driven piston at one end of a 342-foot-long tank filled with 300,000 gallons of water is used to replicate waves generated by nature. The waves roll down the length of the tank and crash into nearly life-size walls and levees. “You can’t scale down a telephone pole hitting an object and expect it to behave as it would in real life,” says Dan Cox, who directs the lab. Ultimately, the data could be used to design new types of buildings, levees and other structures. “A research lab like this is trying to create an accurate wave that replicates what you’d see in nature,” says John Bushey of MTS Systems, which designed the wavemaker. “Those waves are a lot more complicated than what you see in a typical amusement park wave pool.”

Anatomy of an Artificial Tsunami

Scientists generate waves in a 342-foot-long, 15-foot-deep flume filled with 300,000 gallons of fresh water. The bottom of the tank is flat, then slopes up and ends in a plateau. The profile, varied by experiment, simulates the effect of a beach, making waves break when they hit shallower depths. The machine allows scientists to study regular waves, which consist of a series of troughs and crests, and tsunamis, which are generated as solitary waves; here’s how a tsunami is created.

A steel waveboard extends forward at 13 feet per second, generating a 4.5-foot-tall, bell-curve-shaped wave that moves down the flat-bottomed flume—meant to replicate the deep ocean—at 15 feet per second. When the mini-tsunami encounters a ramp on the flume floor, the wave leans forward and grows to a height of 5 feet. In water depth roughly equal to its height—at a plateau in the tank that acts like a sandbar—the wave breaks, generating a wall of water sometimes known as a hydraulic bore. The bore hits test structures with 8000 pounds of force and can generate a 20-foot-high splash. The wave’s journey down the flume lasts 10 seconds.

A. Servo Computers: Scientists control the wave machine with a servo computer, which they use to adjust the amplitude and frequency of the waveboard’s movement. This allows them to generate not just sine waves, but the nonlinear waves seen in nature. The computer is connected to two servo valves on the wave machine, which regulate how much hydraulic fluid flows into or out of the pistons that move the waveboard. For regular waves, the board is placed at its center of travel and moved back and forth. For a tsunami, the board is fully retracted, then fully extended. It peaks at a velocity of 4 meters per second and stops at 4 meters of stroke, creating a bell-curve-shaped solitary wave.

B. Hydraulics: Once researchers have indicated to the computer what type of waves they want, the machine’s two servo valves kick into action. To generate random waves, one servo valve regulates flow into and out of two piston-type cylinders—one that extends and one that retracts—which move the waveboard back and forth; a third cylinder acts as a counterbalance to the pressure on the board from the water in the flume. Researchers use both valves—with a total capacity of 750 gallons per minute—to create the energy needed to generate a tsunami.

C. Waveboard: OSU’s previous waveboard was hinged at the bottom, and pistons moved the top back and forth to replicate waves created by wind in the middle of the ocean. To move the massive amount of water required to simulate a 5-foot-high tsunami, researchers installed the current waveboard— a single piece of welded and bolted steel, 15 feet high and 12 feet wide.