The dynamic characteristics of deepwater riser usually present serried modes with lower frequencies, because structural flexibility is very large due to high aspect ratio (ratio of length to diameter of riser). Moreover, in practice flow velocity usually distributes non-uniformly along the riser length. A coupling model, for multi-mode VIV (vortex-induced vibration) of slender riser experiencing non-uniform flow, by means of finite element simulation combined with the hydrodynamic model taking account of the interaction between fluid and structure in time-domain, is proposed. VIV responses of slender risers respectively in uniform, stepped and shear flow are explored. Satisfied agreements with experiment results are observed. Additionally, based on the numerical simulations effects of reduced velocity and modal energy on modal weight are explored. We note that for case of multi-mode vibration the participating modes tend to distribute by groups.

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