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The Washington Research Foundation Fellowship

Melyssa Nagamine, Civil and Environmental Engineering - 2009-10 - WRF/Space Grant

Melyssa Nagamine photo I am currently a junior studying civil and environmental engineering. I was first introduced to fluid mechanics last fall in an introductory fluid mechanics course taught by my current research mentor, professor Alex Horner-Devine. I developed a strong interest in the subject, and by the end of the quarter I managed to convince professor Horner-Devine to take me on as an undergraduate researcher. I have greatly enjoyed the challenge presented by working on independent research - as a highly motivated student, it has been extremely rewarding tackling open-ended problems where you are responsible for the development of a question and the interpretation of the results.

I am involved with the Environmental Fluid Mechanics research group here at UW, where I have been fortunate to find great support and motivation through the other graduate and post-doctorate students. My work to this point has consisted of laboratory experiments simulating coastal river plumes in the Harris Hydraulics Laboratory.

I am honored to have been chosen as a recipient for the Washington Research Foundation Fellowships and I am extremely grateful for the opportunity to continue with the research I have been involved in.

Mentor: Alex Horner-Devine, Civil Engineering

Project Title: A Pilot Experiment to Generate Age Fields in Coastal River Plumes

Abstract: In environmental engineering, it is essential to understand the manner in which water transports nutrients, contaminants, and other particles that affect the health of aquatic systems. The chemical and biological processes related to these substances are dependent on the residence time of the particular constituent and often proceed exponentially, making them sensitive to small variations in the age of a fluid parcel in the system. In practice, residence time is difficult to measure and is often estimated by a quantity known as hydraulic residence time, which represents a case of ideal behavior. However, in environmental flows, vortices and other singularities often cause large deviations from the ideal case, causing this to be an inaccurate representation of actual residence time. In the present experiment the spatial distribution of age is studied for the specific case of a coastal river plume. In order to measure two-dimensional fields of age, a new technique that uses linear mixing of two different color dyes to create a timescale has been developed. This timescale is applied to images of the flow to map age. The age fields will be compared to analytically determined average age distributions for idealized plume models in order to compare the structure of the experimental plume to theoretical examples. This experiment will provide data about age fields in coastal river plumes, which is relevant in the consideration of sediment loading into the oceans. It will also provide a basis for understanding how coherent structures in the flow are affecting age distributions. Results suggest that older fluid is trapped in the center of the plume while new, younger fluid circulates around the bulge perimeter. Overtime, however, instabilities that develop in the plume are thought to increase the amount of mixing within the bulge.