Eduction and Analyses of Streaky Structure on Thermographic Images of Laboratory Wind Waves
Date Issued
2015
Date
2015
Author(s)
Ku, Meng-Chiao
Abstract
Thermal streaky structures can be observed on wind-wave surface. They are induced by the underlying coherent eddies in parallel with the wind. The temperature in these streaks is lower than that in the surrounding area when the heat flux is upward from the water to the air, and vice versa. Cold streaky structures, therefore, are observed on infrared thermographic images. In this study, an image recognition method is developed to automatically capture these streaky structure on thermographic images of laboratory wind waves. The method of empirical mode decomposition is first applied to filter out the short-length noises in the thermographic images. The local temperature minima in the spanwise direction are then identified. A streak passing a local temperature minimum is formed by connecting the neighboring downstream/upstream local temperature minima within a chosen radius. Spanwise spacings between the neighboring streaks can then be calculated and analyzed. It is found that the probability density distribution of the streak spacing is close to lognormal distribution, similar to the streaks observed next to a no-slip wall. The non-dimensional mean streak spacing based on friction length, however, increases with the friction wind speed. This is different from the flow next to a no-slip wall in which the non-dimensional mean streak spacing approximates 100 friction unit.
Subjects
wind wave
infrared images
empirical mode decomposition
characteristic streak
turbulent boundary layer
streak spacing
logarithmic-normal distribution
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-104-R02525006-1.pdf
Size
23.54 KB
Format
Adobe PDF
Checksum
(MD5):806369709ed166914d56e85ae905685b