The characteristics of the dynamic behavior of a free-hanging riser is analyzed under top excitation conditions by using a numerical method. A top excited riser that is free hanging presents strong nonlinear behavior characteristics. We verified that the top tension of a free-hanging riser under top-end forced excitation dominantly vibrates in the double with the top excitation frequency. The non-linear response of a top tension is disclosed from analysis for the local velocities at nodes along the riser length. The top tension of a free-hanging riser shows to respond in double with the top excitation frequency under no current. On the other hand, the top tension of a top-end forcibly excited riser has its double component as well as the excitation frequency component under a current. We proved that the axial vibration of a free-hanging riser dominates the riser tension under top-end forcibly excitation conditions.

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