- September 26, 2016, 4:00 p.m.
- Professor James H. Duncan , Ph.D
- University of Maryland, Mechanical Engineering Dept.
- 117A Surge Building
- Faculty Host: Dr. Christine Ikeda
Solitary gravity-capillary waves generated by a surface pressure source moving at speeds near the linear gravity-capillary wave minimum phase speed (Cmin ≈ 23 cm/s) are investigated experimentally. The temporally evolving 3-D water surface shape behind the pressure source is measured using a combination of cinematic refraction-based and laser-induced fluorescence techniques. At towing speeds just below Cmin, an unsteady pattern is formed in which localized depressions periodically appear in pairs and move away from the source along the arms of a downstream V-shaped pattern. This behavior is analogous to the periodic shedding of solitary waves upstream of a source moving at the maximum wave speed in shallow water. The gravity-capillary depressions are rapidly damped by viscosity, but their speed-amplitude characteristics closely match those found in inviscid calculations of freely propagating gravity-capillary lumps. The shedding frequency of the lumps increases with both increasing source speed and strength. Significant evidence of the interaction of neighboring shed lumps is found and experiments with two side-by-side pressure sources are used to observe and measure oblique lump impacts.
Jim Duncan is a Professor of Mechanical Engineering at the University of Maryland at College Park. He received a Bachelor of Science in Mechanical Engineering from Brown University and a Doctor of Philosophy in Geophysical Fluid Dynamics from The Johns Hopkins University. He worked as a research scientist at Hydronautics, Inc. and Flow Research Company until he joined the faculty of the Department of Mechanical Engineering at the University of Maryland in 1987. Jim's research has included studies of fundamental aspects of breaking waves, cavitation bubbles, fluid-structure interactions and computer vision. Jim has received a number of teaching and research awards at the University of Maryland including the Poole and Kent Senior Faculty Teaching Award, the Distinguished Scholar Teacher Award and the Wilson H. Elkins Professorship. Jim is Fellow of the American Physical Society (APS) and has served in a number of roles on the Executive Committee of the Division of Fluid Dynamics of APS, including Division Chairman in 2015. He has served as Associate Editor of the Journal of Fluid Mechanics from 2010 to present.