| Submarine pipelines have been used more widely with the rapid development of offshore engineering. The vortex induced vibration (VIV) of the free spanning pipelines causing fatigue determines the life of submarine pipelines, and it is the main problem in the reliability analysis design and assessment. The free span pipeline has, however, important non-linearity that should be taken into consideration because of the interaction with the seabed. The benefit from use non-linear model is to describe stresses more accurately, and to supply more useful information for future research to VIV for free span pipelines.In the present paper, a non-linear finite element model is established to develop the VIV of free span pipelines considering pipe-seabed-interaction modeled by springs with different P-8 curves. Combining the VIV ANA model with a flexible beam model, a numerical model is developed for VIV of free spanning pipelines. The response of the pipeline span is calculated in frequency domain with line boundary condition, and the same added mass, damping and load distribution are found by VIV ANA. Then the non-linear model is calculated in time domain. The necessity of considering pipe-soil interaction is discussed, and the velocity conditions in VIV with simply supported boundary or pipe-soil interaction were studied. The stress distribution and dynamic response with non-linear spring is also analyzed, and the effect of soil non- linearity, trench geometry on the VIV is investigated.
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