Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

The physics of ocean undertow

13.05.2014

Small forces make a big difference in beach erosion, according to new article in Physics of Fluids, which may lead to better solutions for sustainable beaches

People standing on a beach often feel the water tugging the sand away from under their feet. This is the undertow, the current that pulls water back into the ocean after a wave breaks on the beach.


This image shows a sliff-like erosion escarpment on a Florida beach.

Credit: CREDIT: U.S. Geological Survey/photo by Randolph Femmer

Large storms produce strong undertows that can strip beaches of sand. By predicting how undertows interact with shorelines, researchers can build sand dunes and engineer other soft solutions to create more robust and sustainable beaches.

"Formulation of the Undertow Using Linear Wave Theory," a new paper in the journal Physics of Fluids, clears up some of the controversy in undertow modeling, so planners can assess erosion threats faster and more accurately.

... more about:
»breaks »differences »physics »properties »storms »waves

The paper's authors are coastal engineer Greg Guannel of the Natural Capital Project, which seeks smarter ways to integrate natural resources into development, and Tuba Ozkan-Haller, an associate professor of coastal engineering at Oregon State University.

Researchers have studied undertow for more than 40 years, and have developed very accurate models of its behavior. The most sophisticated ones are based on Navier-Stokes equations, which describe fluid flow in exquisite detail.

Unfortunately, such precision comes at a price. The mathematics are complex and it takes powerful supercomputers to run them quickly.

"You can't use them to solve day-to-day erosion problems," Guannel said.

For real-world use, researchers need mathematical shortcuts, the engineering equivalent of rounding numbers so they are easier to work with. Researchers turn to linear wave theory, which simplifies things by using idealized forms. Beaches, for example, are wall. Waves are given perfect "S" shapes based on average properties. Instead of modeling everything, researchers make assumptions about some of the weaker forces acting on waves.

"We try to come up with a set of equations that describes flow properties in one step, rather than hundreds of steps, so we can solve problems faster," Guannel said.

Several research teams, each with its own approach, built simplified models based on linear theory. And each came up with a different solution.

This bothered Guannel, who said, "If you start with a single theory, no matter how you approach the problem, you should come up with only one solution, not many."

So Guannel and Ozkan-Haller retraced the work of each team. They found their differences were not due to approach, but to the way they handled weak forces generated by waves. They then developed more consistent ways to describe those forces. The strongest of them was the force exerted by water moving from the top of the wave to the bottom.

"A major advance in our paper was to describe that force correctly," Guannel said.

Another weak force is advection, which occurs as the undertow is sucked into the larger current created by the waves. "In the larger scheme of things, advection of the undertow is weak. But here, it can play an important role," Guannel explained.

"We found that all the differences between researchers were due to the erroneous formulation or the neglect of these weak terms. When we add them back in, everyone who did the math correctly comes up with the same solution," he said.

Instead of debating methodology, researchers can now focus on improving the accuracy of their models. If they can do this, Guannel said, they can build better models to help preserve the shoreline and enable beaches to recover faster after storms.

###

The article "Formulation of the Undertow Using Linear Wave Theory" is authored by G. Guannel and H.T. Özkan-Haller. It appears in the journal Physics of Fluids on May 13, 2014 (DOI: 10.1063/1.4872160). After that date, it can be accessed at: http://scitation.aip.org/content/aip/journal/pof2/26/5/10.1063/1.4872160

ABOUT THE JOURNAL

Physics of Fluids is devoted to the publication of original theoretical, computational, and experimental contributions to the dynamics of gases, liquids, and complex or multiphase fluids. See: http://pof.aip.org

Jason Socrates Bardi | Eurek Alert!

Further reports about: breaks differences physics properties storms waves

More articles from Physics and Astronomy:

nachricht What happens when we heat the atomic lattice of a magnet all of a sudden?
17.07.2018 | Forschungsverbund Berlin

nachricht Subaru Telescope helps pinpoint origin of ultra-high energy neutrino
16.07.2018 | National Institutes of Natural Sciences

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

Im Focus: Chemical reactions in the light of ultrashort X-ray pulses from free-electron lasers

Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.

Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

Microscopic trampoline may help create networks of quantum computers

17.07.2018 | Information Technology

In borophene, boundaries are no barrier

17.07.2018 | Materials Sciences

The role of Sodium for the Enhancement of Solar Cells

17.07.2018 | Power and Electrical Engineering

VideoLinks
Science & Research
Overview of more VideoLinks >>>