May 22, 1997
Contact Nick Houtman, 207-581-3777
Waves might be great for surfers and sports fans, but if you're trying to find a safe harbor to dock your boat, they can be a disaster. Vijay Panchang, associate professor of civil and environmental engineering at the University of Maine, and his students have developed a computer model now being used to predict wave heights in harbors around the world.
The model is considered the most advanced of its type, says Panchang. It provides architects and engineers with a crucial link between waves at sea and the forces which affect coastal structures such as marinas, sea walls and breakwaters. "If you build a pier for loading and unloading cargo, you need to avoid creating conditions which will lead to large waves. Operations are hampered if the ship rocks too strongly," says Panchang, "and the resulting down time is extremely expensive."
"The problem is resonance, the same principle which causes the tides in the Bay of Fundy to be so high. The size and shape of the Gulf of Maine just happen to resonate with the tides, and the result is some of the highest tides in the world. In the same way, waves can resonate with the shape of a harbor. Hard surfaces like concrete sea walls and breakwaters can also cause waves to reflect back into the harbor and make the problem worse." The model provides a framework into which engineers and planners enter information about water depth, the harbor's shape and waves offshore. Once all the data have been entered, the program calculates predicted wave heights over a series of time steps. A visual interface displays the data in a view from a point directly above the harbor.
In Maine, the model has been used to evaluate proposed aquaculture sites. Over the past 15 years, it has been expanded for use in India, Australia, Hawaii, California and the Caribbean. During that time, two students have received their masters degrees and one a Ph.D. through work on the model.
Currently, Karl Schlenker, a masters candidate in civil and environmental engineering from Belfast, and Liu Zhao, a Ph.D. candidate from China, are developing new model components. In particular, they will enable users to predict wave directions and velocities as well as height. These factors affect the harbor bottom and thus the movement of sediment, the foundations of structures and the location of military devices such as mines. An additional model is planned to help engineers predict the degree of heaving or swaying a ship may encounter.
The effort has been support by grants from public and private organizations. Current and past users include the U.S. Army Corps of Engineers, Scripps Institute of Oceanography, the U.S. Office of Naval Research, the Sea Grant College Program and the National Oceanic and Atmospheric Administration. Coastal Systems of Key Largo, Florida, has also adapted the model to a Caribbean development.
For the last several years, Panchang has maintained a strong ongoing relationship with the Army Corps of Engineers which is using the model for modifications to two harbors in Hawaii, Barber's Point and Kahului. He is also working on a project funded by the University of California Sea Grant Program to renovate a harbor in Oceanside. "Working on the West Coast poses some special problems. The water can get very deep a short distance off shore. As a result, the distance between wave crests can become quite long, and the model has to take in a larger area. If you don't match the model with the scale of the entering waves, the results you get would be meaningless."
As the model receives greater attention, it must be applied to increasingly complex circumstances, Panchang points out. Results from Panchang's modeling research and applications have been published in a variety of journals including the Proceedings of the Royal Society of London.
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