Gravity Currents and Internal Bores

Date: 
Friday, March 3, 2017 - 2:30pm
Location: 
3110 Etcheverry Hall
Speaker: 
Professor Harry Yeh

School of Civil & Construction Engineering

Oregon State University, Corvallis, OR

About: 

E-201 Ocean Engineering Seminar Series, Spring 2017

 

2:00 - 2:30pm Beverages & Refreshments

2:30 - 4:00pm Seminar

 

A gravity current is a gravity-driven flow by the fluid-density difference from that of its surroundings. When a similar flow advances into a quiescent two-layer fluid of which the thinner layer has the same fluid density as the advancing current and distinct wave breaking is formed at the leading wave, the flow is called an internal bore. Salient features of gravity currents and internal bores are investigated in a horizontal flume with a lock-exchange device, i.e. by lifting a partition that initially separates fresh water from saline water. With the use of laser-induced fluorescein-dye illumination in the laboratory, qualitative flow characteristics and behaviors are examined.

 

Rotational motion (vorticity) is created within a fluid domain by two mechanisms: baroclinic torque and viscous-shear torque. We show that vortical motion in an internal bore is generated by baroclinic torque caused by the static-pressure gradient along the interface of two fluids; the viscous-shear torque plays an insignificant role in the creation of vorticity.

 

In the second set of the experiments, gravity currents and internal bores are first generated in a channel of finite breadth to establish its quasi-steady condition. Then, the established current is let off to spread from the end of the channel to open environment. The spreading flow pattern and mixing around the end of the channel is examined and interpreted based on the vortex dynamics. What we wish to present here is a clarification of features and mixing mechanisms associated with gravity-current and internal-bore phenomena, and the differences between the two flows.

 

Biography:

Harry Yeh is a Professor of Civil & Construction Engineering at Oregon State University.  He also holds the position of Adjunct Professor in College of Earth, Oceanic and Atmospheric Sciences.  Yeh received an AB in Economics from Keio Gijuku University (Japan), BS and MS degrees in Agricultural Engineering from Washington State University, and a PhD in Civil Engineering from University of California, Berkeley.  He worked for Bechtel Inc. in late 1970s, primarily analyzing engineering problems involved in electric power plants.  Yeh began his academic career in 1983 at the University of Washington, and joined the faculty of School of Civil and Construction Engineering at Oregon State University in 2003.  His primary research interest is in the field of hydrodynamics, focusing on controlled laboratory experiments. His current research interests are for seeking the basic mechanics of extreme wave amplification in shallow waters and tsunami-induced soil liquefaction. He participated in many reconnaissance field surveys for tsunamis – from the 1992 Nicaraguan event to most recent Japanese (Fukushima) Tsunami.

 

Hosted by: Prof. Reza Alam (reza.alam@berkeley.edu) & Prof. R. W. Yeung (rwyeung@berkeley.edu)