Abstract: The vibration characteristics of offshore cylindrical tanks are studied in this paper. This is a typical topic of liquid-shell interaction system. In this paper, a general analytical method is presented by which the axial modal functions of liquid and shell are represented as the same complete orthogonal series for uncoupling the mode of liquid and shell. Simultaneously, the mode functions are expanded into a uniform convergence series and a linear polynomial, so that the problem.of convergence and differentiation of mode series is solved. Therefore, the rather exact natural frequency and its corresponding mode of off shore cylindrical tank with different liquid depths, with arbitrary boundary conditions and with intermediate constraints can be obtained.

Key words: vibration characteristics, natural frequency, radiation damping, added mass