Analysis on Stability of Span Submarine Pipeline Nonlinerity Vibration

Focuses on the free span of submarine pipelines.According to the free span of submarine pipeline’s characteristic,it had simplified the free span of submarine pipeline as a beam simply supported at both ends,and the vortex lift mechanism as tune load at the same time.Taking account to the nonlinear factor,the dynamic equation was set up.Using the harmonic balance method to solve the equation,at last the two scrip catastrophe model of the free span of submarine under the excited vortex inducing vibration with the current effect was obtained.Through which the unsteady criterion of free span of submarine pipeline is obtained.It had been found that the length of the free span of submarine pipeline lies in the main position by analyzing the unsteady criterion.And then supposing other conditions without changing,the analysis on the relationship between the factors which will effect the span submarine pipeline’s stability and the criterion span length is given.It can be found from the analysis that the critical span length decrease with the outer fluid flow velocity,internal fluid flow velocity and internal flow pressures’ increasing.Contrasted to the factors have been analyzed above,the factors such as the water’s density,the fluid damping and so on can be ignored with the increasing of elastic modulus,the external diameter of pipe and critical length in the span section.