Ryuji Takaki*, Akijiro Katsu* and Yoji Arai**
*Physics Department, Tokyo University of Agriculture and Technology
**Physics Department, University of Electro-communication
Abstract. Images of a vibrating liquid drop on a high-speed 16 mm movie film were processed in oder to obtain contours of instantaneous drop shapes in plane view. The film had been taken by Adachi (Ref. ) for a drop of liquid nitrogen, which was laid on a horizontal floor with the room temperature and aquired a flattened shape owing to the gravity and the surface tention. The drop began vibrating by a certain kind of self-induction and the mode of vibration (characterized by the number of vertices n) changed suddenly as the drop became smaller through evaporation. The purpose of this paper is to investigate the mechanism of this mode change by the use of image processing technique. The images were taken into the digital data through a video camera, and defects of images due to incomplete lighting were eliminated by correcting the digital data. A function defining the drop contour in the plane view was obtained from each image. Fourier components of spatial variation of this contour function was calculated. From timewise variation of these Fourier components, variation of vibrational modes of the drop at several instants was obtained. The results showed existence of a peculier transition among the modes, and agreed with qualitative observation by the naked eye. Moreover, it was revealed that in the transition from the mode with pentagon shape (n=5) to the mode with triangular shape (n=3) the third mode with n=2 appeared and that there was a certain kind of nonlinear interaction among the three modes. n=5,3 and 2.