Study On The Characteristics Of Vortex-induced Vibrations Of The Submarine Suspended Pipeline Under General Boundary Conditions

The submarine pipeline is the lifeline of the transportation system of submarine oil and gas resource.Due to the uneven seabed and the scouring of the current,it will become suspended on the seabed.The vortex-induced vibration(VIV)of the suspended pipeline is easily caused by the outer flow,which can cause severe structural fatigue damage,and lead to serious environmental pollution and huge economic losses.In this paper,based on the Euler-Bernoulli beam theory,the structural vibration equations of single-span and multi-span pipeline are constructed according to the general boundary constraint conditions and the structural continuous conditions.The classical van der Pol equation of wake oscillator model is adopted here to describe the interaction of the outer flow and the pipeline structure.According to the experimental data,the parameters of the wake oscillator model are calibrated.Based on the orthogonality of the modes,the governing equations of the interaction of the outer flow and the pipeline structure are decoupled.After this,the Runge-Kutta method is used here to calculate the differential equations,and the time domain response of the VIV of suspended pipeline is obtained and the frequency domain response is obtained through the Fast Fourier Transform.The results of the present model are compared with the experimental results,the DNV specification and the VIVANA software.The validation results are satisfactory.Depended on the present theoretical model,the influence of the external flow velocity,the inner flow velocity,the inner flow pressure,the suspended length,the axial force,the boundary constraint conditions and the intermediate constraints on the VIV characteristics of the single-span and multi-span pipeline are analyzed.Some conclusions are drew below:(1).With the increase of the outer flow velocity,the VIV response of submarine suspended pipeline is dominated by the higher order modes,and the VIV response frequency is gradually increasing.(2).The influence of inner flow velocity on the VIV of submarine suspended pipeline is small.But the larger the pressure of the inner flow,the longer the length of the suspension,the smaller the axial force,the easier the occurrence of the VIV of submarine suspended pipeline,the higher order of the dominant mode,and the smaller the response frequency of VIV.(3).The more intense the end restraint conditions or the intermediate constraints are,the more difficult the occurrence probability of the VIV of submarine pipeline is,the more difficult the higher order modes are excited,and the higher the response frequency of VIV is.