| When the rectangular elastic fluid-shell coupled systems is excited on the shell with a certain frequency, different kinds of large magnitude and low frequency gravity waves will appear. This experiment is aim to get the 3-D shape and the time histories. As the object is water wave, the magnitude is large and water splash, it asks more of the measure technique and data processing.In this paper, the general achievements and the future of development of the measurement for three-dimensional shapes is discussed in detail. Through the expatiation of the main methods of the 3-D measurement, the FTP method is chosen according to the character of the experiment object and the need of dynamic measurment. According to the crossed optical axis theory we designed the experiment system. The space between the raster is adjustable. The raster is projected by a LCD projector and the images are taken by a high speed camera.After got the images, different image processing methods are analyzed and appropriate methods are chosen. In Fourier transform Profilometry, there are frequency leakage, frequency aliasing and frequency railing, methods of elimination are produced after causation analyzed. Pretreatment of the images are taken in the spatial domain, the noises are eliminated and the quality of the images is enhanced. After Fourier transformation, frequency filter, ifft, unwrapping etc. the height information and the 3-D shape of the waves is got. Through the processing of several pictures of the same period the time histories of the waves are gained.In this paper, we measured the gravity waves of several fluid-shell coupled systems such as rectangular shell, rotundity shell and the long-xi shell system. Wave information and time histories of different gravity waves are gained. The work of this paper is a new trial of the measurement of the free surface wave in the fluid-shell coupled systems, and the experimental data are significant references for the further theoretical study. |
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