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You are here : eLibrary : IAHR World Congress Proceedings : 36th Congress - The Hague (2015) ALL CONTENT : Water engineering : Optimisation of lighting techniques for photometric measurement of sedimentladen
Optimisation of lighting techniques for photometric measurement of sedimentladen
Author : RICHARD I WILSON(1)
ABSTRACT
The use of photometry is becoming a more prevalent method for analysing the dynamics of sediment-laden flows in the
laboratory. This is due to advances in technology and its non-intrusive nature on flow propagation. When coupled with
established velocity and density measurement techniques, significant data can be obtained and analysed. For
photometric data to be accurately captured, a robust lighting configuration must be installed. It must ensure that current
boundaries have a strong contrast with the surrounding ambient environment. The following study compares three
different lighting configurations of a lock-exchange turbidity current interacting with a rectangular obstacle in a flume: (a)
side-view illumination using halogen lamps combined with overhead illumination using LED strips; (b) side-view
illumination using halogen lamps without any overhead illumination; (c) side-view and overhead illumination using
halogen lamps. Photometry is used to delineate the current boundary and produce high-resolution spatio-temporal
contour plots. Visual influence of a UVP and siphon instrument rack on the delineation process is also taken into
account. The contour plots provided detailed insights into the dynamic processes of the current interaction, such as
reduction in velocity of the approaching current head, vortices formed above and after the obstacle and the formation of
Kelvin-Helmholtz instabilities at the rear of the head upon collision with the obstacle. Investigation of the delineated tests
showed that the LED overhead lamp provided an even illumination distribution above the current, however its weak
illuminance caused unwanted noise to be present on the flume bed. The lighting configuration without overhead
illumination resulted in low contrast of the current boundary and isolated patches of delineation within the current body
due to shadows. The configuration using halogen lamps from the side and overhead provided strong contrast and
eliminated noise, however the overhead lamps provided poor light distribution due to their point-source nature, which
also resulted in isolated areas of delineation. The results showed using either LED or halogen overhead lamps is
promising for future tests, however it is recommended that additional LED strips are installed to improve contrast, or
additional halogen lamps are installed overhead to improve light distribution.
File Size : 3,365,405 bytes
File Type : Adobe Acrobat Document
Chapter : IAHR World Congress Proceedings
Category : 36th Congress - The Hague (2015) ALL CONTENT
Article : Water engineering
Date Published : 18/08/2015
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