| Summary: | 碩士 === 國立臺灣大學 === 機械工程學研究所 === 107 === The perturbation caused by external influences on the surface of liquids has been receiving constant attention from scientists and engineering. In this study, we will measure the contour of an impinging drop on a solid surface. Generally, the main methods for measuring three-dimensional shape of an object are divided into contact and non-contact measurement. The fluid is deformed by external force. Therefore, in order to measure the contour of the fluid, a non-contact measurement system must be used to measure without disturbing the fluid.
In this study, an optical measurement system was built and used with Fourier Transform Profilometry (FTP) to measure the deformation of an impinging droplet on a solid surface. We use the projector to project fringe patterns onto the droplets, and record the image by using high speed camera at different timing. After the operation of Fourier transform, the wrapped phase of each pixel can be obtained. By utilizing phase unwrapping, the original phase is also obtained. The original phase differences can be converted into height by optical geometry, and the surface of the droplet can be further determined. In addition, we built a simulation system to find the best reconstruction parameters by adjusting different parameters, such as the fringe frequency, the bandwidth or the reflectivity. Finally, We discuss the pros and cons of the reconstruction results by using FTP.
By the simulation, we found that the reconstruction result is better as the fringe frequency increases. When the fringe frequency is so high that our device cannot distinguish the fringe, which will increase the reconstruction error. The reconstruction result is the best when the reflectivity of object and reference plane is equal. We learned from experiment that the reconstruction result is worse with the increase of the object slope, and the reconstruction result is better when the object height is increases.
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