Oliver Fringer, Associate Professor, Department of Civil and Environmental Engineering, Stanford University
Abstract: I will present results of high-resolution, numerical simulations of fine sediment erosion in turbulent wave-current boundary layers. The focus will be on parameters typically found in estuarine environments where wind waves are the dominant mechanism for fine sediment resuspension while mean currents by the tides and winds are responsible for mixing the sediment into the water column and making it available for horizontal transport. Parameterizations of sediment erosion in coastal models typically assume a turbulent wave boundary layer and a hydraulically rough sediment bed, which leads to more sediment erosion when waves are superimposed over tidal currents. However, in estuarine environments the waves can be laminar and the bed can be hydraulically smooth. Therefore, I will show that a laminar wave superimposed over a turbulent current can act to reduce the turbulence and bottom stress over part of the wave cycle, thereby reducing the bottom drag and sediment erosion. Owing to settling, I will also show that the near-bed suspended sediment concentration can be high enough to stratify the flow and reduce the vertical turbulent mixing, thus acting to further reduce the bottom drag and erosion.
About the Speaker: Oliver Fringer is professor in the Department of Civil and Environmental Engineering at Stanford University, where he has been since 2003. He received his BSE from Princeton University in Aerospace Engineering and then received an MS in Aeronautics and Astronautics, followed by a PhD in Civil and Environmental Engineering, both from Stanford University. His research focuses on the application of numerical models and parallel computing to the study of laboratory- and field-scale environmental flows to understand the physics of salt and sediment transport in lakes and estuaries, internal waves and mixing, and turbulence in rivers. Dr. Fringer received the ONR Young Investigator award in 2008 and was awarded the Presidential Early Career Award for Scientists and Engineers in 2009.