The destruction unleashed upon New Orleans and the Gulf Coast during 2005’s Hurricane Katrina was horrific. Levees constructed to prevent flooding were no match for the storm. Entire sections of the I-10 Twin Span Bridge over Lake Pontchartrain broke away.
To prevent a repeat of these structure failures, the New Orleans District of the U.S. Army Corps of Engineers turned to researchers at Texas A&M University’s Reta and Bill Haynes ’46 Coastal Engineering Laboratory, one of the few facilities in the world housing a shallow-water 3-D wave basin. After studying levees and bridge segments under varying wave conditions, the Corps of Engineers left the lab with a greater understanding of what went wrong and how to fix it.
The Place To Be For Ocean Engineering
Only a few universities boast ocean engineering programs, and Texas A&M’s Zachry Department of Civil Engineering offers the country’s largest. The program and its facilities attract students and clients from across the globe. Last year, roughly 165 undergraduates and 80 graduate students studied ocean engineering at Texas A&M in such diverse areas as dredging, hurricane impacts, beaches, coastal erosion, shore protection, anchor moorings, computational fluid dynamics, wave energy and offshore platform design.
Key to the Texas A&M program’s stellar reputation is a collection of centers and laboratories that focus on virtually every aspect of ocean engineering. The Haynes lab is among them, housing both the wave basin and the nation’s only two-dimensional tow-dredge tank.
The Wave Basin
Robert E. Randall, Bauer Professor and director of the Ocean Engineering Program, is director of the Haynes lab and the Center for Dredging Studies, which the university and the Texas Engineering Experiment Station jointly support. He says both the wave basin and the tow-dredge tank attract government agencies, researchers and companies in the offshore industry and other fields involving rivers, harbors, coastal erosion and protection, and dredging.
In essence, the wave basin tests the ability of jetties, breakwaters, levees, vertical walls and bridges to perform as they should. It also studies the motion of ships and offshore vessels.
For the New Orleans Corps of Engineers study, researchers compared the pros and cons of a vertical wall to the sloping grade of a levee in terms of waves topping them. Other studies challenge the stability of structures not only with regular waves but also with irregular waves coming from different directions and at different intervals and heights.
“This is a unique tank in that we can have both waves and currents, and we can control the water depth,” Randall says.
An instrument carriage spans the wave basin, and a three-ton overhead crane services both it and the tow-dredge tank. Valves, pumps and weir gates are electronically controlled from a data-acquisition room. Operator control is manual or automatic using computers, and an observation well facilitates underwater viewing for both the basin and the tank. Both tanks may be viewed over the Internet by using two Web-based cameras. A motion-tracking system determines how much a structure rolls or moves up and down, resulting in a computerized picture and graph.
Of course, this wave pool typically tests 1/15–1/25-scale models rather than actual full-sized structures. Water depths are adjusted to accommodate the model size, with a maximum depth of four feet. Waves can reach a height of two feet.
“You design it, put it in model condition, and see if it acts as designed,” Randall says. “In many cases, we find that they need to make modifications.”
A Small Price To Pay
The Haynes lab is a self-supporting facility, and clients pay $1,600 per day for its use. But that amount is small compared with the fortune that could be lost with a faulty structure design.
“You must be able to test out your concepts for systems that are either very expensive to build or are protecting something that is very expensive,” Randall says. “If you spend millions of dollars creating a structure, you want to be certain that it works.”
To illustrate his point, Randall uses the example of breakwaters, offshore barriers resting on the seafloor to protect harbors and other coastal areas from large waves.
“Breakwaters are protecting important infrastructures and vessels in port from something like hurricanes,” he says. “If their armor stones are not heavy enough, the waves will dislodge them and destroy the breakwater’s ability to protect the infrastructure and vessels it was designed to protect.”
The Tow-Dredge Tank
When clients need to test anchors and similar seafloor structures, the Haynes lab’s tow-dredge tank can’t be beat. The 150-foot-long dredge tank lets clients test their structures either on a solid floor or through sand and mud contained in the subfloor sediment pit. Federal agencies and offshore oil and gas companies use the tow-dredge tank to test anchors. Dredging companies and government groups use it for simulated oil-spill studies and to test actual dredging equipment.
The computer-controlled carriage resting on rails atop the tow-dredge tank can move at a speed of four knots and allows motion in three directions. Towed models can be attached to a vertical ladder, where load cells determine forces on the ladder. Other equipment measures density, speed, suction, discharge pressure, cutter-shaft torque and flow through the dredge pump. The lab’s axial flow pumps can produce a maximum water flow of 35,000 gallons per minute.
Last year, the federal Minerals Management Service (now the Bureau of Ocean Energy Management, Regulation and Enforcement) came to the Haynes lab with the problem of drilling rigs that came unanchored during hurricanes. With the aid of the dredge tank, and research conducted jointly with the University of Texas at Austin, the service successfully determined anchor performance.
Shell turned to the Haynes lab’s dredge tank to study the fastening of vortex suppression devices on drilling risers. Delmar Systems used it to test the effectiveness of its anchor models. Others research how erosion affects structure stability, such as bridge abutments. Some dredging companies have replicated debris and sand conditions to settle lawsuits. One study looked at how ship-channel dredging affects turtles.
Along with conducting research for clients and offering courses and graduate thesis projects for ocean engineering students, the Center for Dredging Studies offers professional training for those already in the field. With their three cutter-suction dredge simulators, center faculty members and industry collaborators teach the fundamentals of dredging, along with an annual Dredging Engineering Short Course.
“It’s a unique situation that we have here at Texas A&M,” Randall says. “We have a degree-granting program, plus facilities that no one else has in the United States.”