In order to analyze the longitudinal vibration of a pipe-string for mining mineral resources at deep-sea bottoms, the fluid forces acting on the buffer and pump-module attached to the pipe-string must be evaluated in advance. In this study, first, a new method was developed for determining the drag and added-mass coefficients of a buffer vibrating axially, and then both coefficients for various shapes of buffers were determined. The results obtained on the spherical buffer-models proved to be in fairly good agreement with those by Sarpkaya and showed the validity of the new method. Furthermore, the results of other buffer-models indicated that there was a good correlation between those coefficients and Keulegan-Carpenter number, KC, and that as KC increases, the drag coefficient decreases exponentially and the added-mass coefficient increases or decreases linearly according to the shapes of the buffer models.

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