Numerous historical accounts describe the formation of "whirpools" inside ports and harbors during tsunami events, causing port operation disruptions. Videos from the Japan 2011 tsunami revealed complex nearshore flow patterns, resulting from the interaction of tsunami-induced currents with the man-made coastline, and the generation of large eddies (or turbulent coherent structures) in numerous ports and harbors near the earthquake epicenter. In one video taken in the port of Oarai, a gigantic eddy that occupies a big part of the port basin can be seen spinning for tens of minutes, trapping ships inside the rotational flow, until it was washed out by the next incoming wave.
To better understand how these tsunami-induced turbulent coherent structures (TCS) are generated and how they evolve with time, we set-up an experiment in a well-controlled environment using realistic scaling. A physical configuration was created in the image of a port entrance at a scale of ~1:27, and a small-amplitude, long-period wave creates a transient flow through an asymmetric harbor channel. Separated region forms, which coupled with the transient flow, lead to the formation of a stable monopolar TCS. The surface flow is examined through mono- and stereo-PTV techniques to extract surface velocity vectors. Surface velocity maps and vortex flow profiles are used to study the experimental TCS generation and evolution, and finally characterize the TCS flow structure. First-order analytical tools are used to describe the TCS growth rate and kinetic energy decay. This analysis provides the predictive tools to infer time-scales of TCS development in shallow water flows, to first order. The experimental set-up, analysis and results of this work are presented here.
Nikos Kalligeris is a Postdoctoral scholar in Civil Engineering at University of California, Los Angeles. He received a BEng in Civil Engineering from University of Brighton (UK), an MSc in Earthquake Engineering from Imperial College (UK), an MSc in Environmental Engineering from the Technical University of Crete (Greece), and a PhD in Civil Engineering from the University of Southern California. His primary research interests lie in nearshore hydrodynamics during extreme events, such as tsunamis and hurricanes. His analysis uses numerical modeling, well-controlled laboratory experiments and field observations. Dr Kalligeris has been a member of several reconnaissance field surveys for tsunamis around the world. Outside academia, he has worked as a part-time professional civil engineer in Greece and has worked on numerous occasions as a private consultant for international engineering firms in projects related to tsunami and storm hazard assessment for nuclear and LNG facilities.
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