Tag Archives: Waves

Tsunami Surfing and the Giant Snot

Sam Harry’s research is filled with bizarre scientific instruments and massive contraptions in an effort to bring large natural events into the laboratory setting. 

Sam Harry, second year PhD candidate in Civil Engineering

“There’s only a couple like it in the world, so it’s pretty unique”. Unique may be an understatement when describing what may be the largest centrifuge in North America. A centrifuge is a machine with a rapidly rotating container that can spin at unfathomable speeds and in doing so applies centrifugal force (sort of like gravitational force) to whatever is inside. This massive scientific instrument– with a diameter of roughly 18 feet– was centerpiece to Sam’s Master’s work studying how tsunamis affect boulder transport, and the project drew him in to continue studying the impact of tsunamis on rivers for his PhD. 

But before we jump ahead, let’s talk about what a giant centrifuge has to do with tsunamis. Scientists studying tsunamis are faced with the challenge of scale; laboratory simulations of tsunamis in traditional water-wave-tank facilities are often difficult and inaccurate because of the sheer size and power of real tsunamis. By conducting experiments within the centrifuge, Sam and his research group were able to control body force within the centrifuge environment and thus reduce the mismatch in fluid flow conditions between the simulated experiment and real-life tsunamis. 

When tsunamis occur they cause significant damage to coastal infrastructure and the surrounding natural environment. Tsunamis hit the coast with a force that can move large boulders– so large, in fact, that they aren’t moved any other way. Researchers can actually date back to when a boulder moved by analysing the surrounding sediments, and thus, can back calculate how long ago that particular tsunami hit. However, studying the movement of massive boulders, like tsunamis, is not easily carried out in the lab. So, Sam used a wave maker within, of course, the massive centrifuge to study the movement of boulders when they are hit with some big waves. 

Sam’s work space. The Green dye added to the water within the glass tank is what gives this tank it’s name: The Giant Snot

As Sam was completing his Master’s an opportunity opened up for him to continue the work that he loves through a PhD program in civil engineering with OSU’s wave lab. Now Sam conducts his research using the “glass tank”, which, as the name alludes to, is a glass tank roughly the size of a commercial kitty pool that is used to contain the water and artificial waves the lab generates for their research. There are actually three glass tanks of varying sizes. The largest tank, which is larger than a football field, is used for more “practical applications”. Sam gives us the example of a recent study in which researchers built artificial sand dunes inside of the tank, let vegetation establish, and then hit the dunes with waves to study how tsunamis impact that environment. (Legend has it that the largest tank was actually surfed in by one of the researchers!)

Sam’s smaller glass tank, though, is really meant for making precision measurements to better study waves. He uses lasers to measure flow velocity and depth of water to build mathematically difficult, complex models. Essentially, his models are intended to be the benchmarks for numerical simulations. Sam, now into his second year of his PhD, will be using these models in his research to study the interaction between tsunamis and rivers, with the goal of understanding the movement and impact of tsunamis as they propagate upstream.

To learn more about tsunamis, boulders, rivers, and all of the interesting methods Sam’s lab uses to study waves, tune into KBVR 88.7 FM on Sunday, November 3rd at 7pm or live stream the show at http://www.orangemedianetwork.com/kbvr_fm/. If you can’t join us live, download the episode from the “Inspiration Dissemination” podcast on iTunes!

Ocean basins are like trumpets– no, really.

We’re all familiar with waves when we go to the coast and see them wash onto the beach. But since ocean waters are usually stratified by density, with warmer fresher waters on top of colder, saltier ones, waves can occur between water layers of different densities at depths up to hundreds of meters. These are called internal waves. They often have frequencies that are synched with the tides and can be pretty big–up to 200 meters in amplitude! Because of their immense size, these waves help transfer heat and nutrients from deep waters, meaning they have an impact on ocean current circulation and the growth of phytoplankton.

The line of foam on the surface of the ocean indicates the presence of an internal wave.

We still don’t understand a lot about how these waves work. Jenny Thomas is a PhD student working with Jim Lerczak in Physical Oceanography in CEOAS (OSU’s College of Earth, Ocean, and Atmospheric Sciences). Jenny studies the behavior of internal waves whose frequencies correspond with the tides (called internal tides) in ocean basins. This requires a bit of mathematical theory about how waves work, and some modeling of the dimensions of the basin and how it could affect the height of tides onshore.

Picture a bathtub with water in it. Say you push it back and forth at a certain rate until all the water sloshes up on one side while the water is low on the other side. In physics terms, you have pushed the water in the bathtub at one of its resonant frequencies to make all of it behave as a single wave. This is called being in a normal mode of motion. Jenny’s work on the normal modes of ocean basins suggests that the length-to-width ratio and the bathymetry of an ocean basin influence the structure of internal tides along the coast. Basically, if the tidal forcing and the shape of the basin coincide just right, they can excite a normal mode. The internal wave can then act like water in a bathtub sloshing up the side, pushing up on the lower-density water above it.

It turns out that water isn’t the only thing that can have normal modes. The air column in a wind instrument is another example. Jenny grew up a child of two musicians and earned a degree in trumpet performance from the University of Iowa, and she occasionally uses her trumpet to demonstrate the concept of normal modes. She can change pitches by buzzing her lips at different resonant frequencies of the trumpet–the pitch is not just controlled by the valves.

Jenny uses her trumpet to explain normal modes.

Near the end of her undergraduate degree at the University of Iowa, Jenny discovered that she had a condition called fibrous dysplasia that could potentially cause her mouth to become paralyzed. Deciding a career as a musician would be too risky, and realizing her aptitude for math and physics, she went back to school and earned a second undergraduate degree in physical oceanography at Old Dominion University. After a summer internship at Woods Hole Oceanographic Institution conducting fieldwork for the US Geological Survey, she decided to pursue a graduate degree at OSU to further examine the behavior of internal waves.

Tune in to 88.7 KBVR Corvallis to hear more about Jenny’s research and background (with a trumpet demo!) or stream the show live right here.

You can also download Jenny’s iTunes Podcast Episode!

Jenny helps prepare an instrument that will be lowered into the water to determine the density of ocean layers.

Jenny isn’t fishing. The instrument she is deploying is called a CTD for Conductivity, Temperature, and Depth–the three things it measures when in the water.