As a professor in the Department of Civil and Environmental Engineering, my primary responsibilities are to teach and to conduct research in the fluid mechanics and hydraulic engineering areas. I also advise undergraduate and graduate students on matters related to course work selection and career options, supervise student research and capstone design projects, and participate in professional and outreach activities both within and outside the university.
I pursue a focused and sustained research program in breaking waves and bridge hydraulics. In the first area, my primary effort has been to quantify the kinematics (fluid velocities) and dynamics (fluid stresses) of large-scale turbulent flow structures produced by wave breaking on a plane beach. My students and I have conducted a large number of flow measurements in the Fluid Mechanics Laboratory, systematically analyzing the breaking-wave-generated flow fields under solitary, regular and irregular wave conditions. We used laser Doppler anemometer (LDA) and acoustic Doppler velocimeter (ADV) for single-point measurements, and particle image velocimetry (PIV) for two-dimensional (2-D) and three-dimensional (3-D) velocity field measurements in a plane. We have also experimented with volumetric three-component velocimetry (V3V) measurement in a 3-D flow volume under spilling and plunging regular waves. Two-phase (liquid and solid) flow measurement over an erodible bed using V3V has the potential to transform our understanding of sediment transport in the surf zone. The research may answer fundamental questions such as: how breaking waves suspend and transport sediment? How important is this mode of transport compared to other mechanisms such as bed-load transport.
My research in bridge hydraulics and scour deals with scour rate in cohesive soils and hydraulics of bridge waterways in compound channels. In 2010, we completed a research project to evaluate the Scour Rate In Cohesive Soils (SRICOS) method by comparing its predictions with measured scour at three bridge sites in South Dakota. The SRICOS method produced scour estimates that are much closer to the measured scour than the traditional HEC-18 method, because it takes into account the slower rate of scour in cohesive soils. The study also identified the following critical input parameters to the method. They are: (1) flow velocity; (2) critical shear stress; and (3) magnitude, duration and frequency of floods. In an on-going project, we use computer models to predict 2-D flow around highway structures in different morphological settings (e.g., crossing at sharp bend, severely contracted bridge opening) and compare the computed results with field measurements. Our goal is to find cost-effective ways to utilize 2-D flow models in bridge hydraulics and scour analysis.
- Experimental Study of Two-Phase Suspended Sediment Transport in Breaking Waves, National Science Foundation, September 2011 - August 2017