Research On Coupling Vibration Characteristics And Response Of Composite Marine Riser Subjected To Gas-Liquid Mixed Transportation

The offshore oil and gas resources are abundant,and the riser system is an indispensable key engineering equipment for offshore oil and gas development.The mixed gas-liquid multiphase transportation can easily induce fatigue failure of the steel riser.The composite materials have many excellent properties such as high strength,light weight,corrosion resistance,fatigue resistance,and good designability,and they have great application potential in deep-water structural engineering.Due to the anisotropy of the composite material,the vibration of the riser is coupled,and the combined effect of multiple factors such as the gas-liquid multiphase mixed transport characteristics,the viscoelastic contact characteristics between the pipes,different layup methods,top tension,and ocean outflow,is even more dramatic.In view of the complexity of the dynamic behavior of the marine composite flexible riser structure,the research on the coupled vibration characteristics and response of the marine gas-liquid multiphase mixed transportation composite riser has both huge social and economic benefits and important academic theoretical value.This paper systematically studies the cross-flow and in-line flow coupling vibration characteristics and response behaviors of marine gas-liquid multiphase composite flexible risers,and analyzes the effects of gas-liquid mixed transport characteristics,internal flow velocity,fiber layup angle,axial tension and other parameters on composite bonded risers and non-bonded risers.The combined effects of various parameters on the cross-flow parameter instability,cross-flow and down-flow coupled vortex-induced vibration characteristics and frequency-locking laws of composite material-bonded risers are discussed.The main content and research results of the paper are as follows:Comprehensive considering the effects of gas-liquid multi-phase mixed transportation characteristics,ocean outflow fluid force,gas-liquid internal flow velocity,composite layering method,axial tension and riser weight and other factors,the Hamiltonian principle is used to establish the coupled vibration control equations of the gas-liquid mixed transportation composite material bonded riser.In addition,the marine composite non-bonded flexible riser is simplified into a pipe-in-pipe system,and the viscoelastic contact characteristics between the pipes are considered to establish the coupled vibration control equation of the marine gas-liquid mixed non-bonded riser.Finally,the above two models were degraded and verified through existing models.The influence of gas-liquid multiphase mixed transportation characteristics,composite layering method and axial tension on the coupling vibration characteristics and stability of marine risers is studied by the Green function method,and the influences of factors such as gas volume fraction,fiber layup angle,axial tension,liquid flow rate,slenderness ratio,boundary spring stiffness coefficient,spring stiffness coefficient between tubes,and damping coefficient between tubes on the coupled vibration characteristics of the system are analyzed.The result shows that the dimensionless frequency of the bending vibration of the composite-bonded riser decreases monotonously with the increase of the slenderness ratio,liquid phase velocity and the fiber layup angle,and increases with the increase of the gas volume fraction and the axial tension.The dimensionless critical flow velocity of the liquid phase and the gas phase internal flow decrease with the increase of the fiber layup angle,and that increase with the increase of the axial tension.For composite non-bonded risers,the dimensionless frequency of bending vibration increases with the increase of the equivalent stiffness between the tubes,and decreases with the increase of the fiber lay angle,liquid flow velocity and gas volume fraction.In addition,when the internal flow velocity reaches the critical value,the non-bonded riser system will be unstable and bifurcated,resulting in modal coupling.The existence of the elastic layer between the pipes makes the non-bonded riser structure modal exchange.The parametric vibration of the gas-liquid multiphase mixed transportation composite material bonded riser under the excitation of the pulsating time-varying internal flow velocity is discussed by the multi-scale method.The amplitude-frequency response curves and the influence of unstable regions of the gas volume fraction,fiber layup angle,axial tension,liquid phase pulsating internal flow velocity amplitude,and liquid phase internal flow average velocity on the system under the conditions of low-frequency parameter resonance and high-frequency parameter resonance are analyzed.The researches show that the unstable regions of composite-bonded riser system low-frequency parameter resonance,high-frequency parameter resonance,differential combined parameter resonance,and sum-type combined parameter resonance move to the high frequency region with the increase of axial tension,and move to the low frequency region with the increase of the fiber layup angle.For the nonlinear parametric vibration of the composite-bonded riser,there are two bifurcation points in the low-frequency parametric resonance and high-frequency parametric resonance,and the stable non-trivial solution of the low-frequency parametric resonance system is greater than that of the high-frequency parametric resonance system.The fiber layup angle increases the stable and unstable non-trivial solution amplitudes of the main parameter resonance of the system.Using the van der Pol nonlinear vibration equation to describe the fluid vortex shedding characteristics of the riser,and comprehensively considering the internal flow,the external flow,gas-liquid multiphase mixed transportation characteristics and composite layup methods,the coupling vortex-induced vibration characteristics of composite material bonding riser subjected to the gas-liquid multiphase mixed transportation are studied.The effects of ocean current velocity,gas volume fraction,fiber layer angle,axial tension,and internal liquid flow velocity on the nonlinear vortex-induced vibration characteristics of the composite riser system are analyzed.The results show that under different ocean current velocities,the mid-span displacement trajectory of the composite-bonded riser all showed "8" shape.The amplitude of vortex-induced vibration and the number of excited modes increased with the increase of ocean current velocity.Under the external ocean current velocity,the maximum displacement amplitude in the transverse direction is higher than the maximum displacement amplitude in the in-line flow direction.The offset in the downstream direction and the maximum vibration displacement in the cross-flow direction decrease with the increase of the gas volume fraction,and the vibration mode orders in the cross-flow and downstream directions of the riser decrease with the increase of the gas volume fraction.The vibration response mode gradually decreases with the increase of the fiber layup angle,and the offset in the downstream direction decreases with the increase of the fiber layup angle.In addition,with the change of the reduction speed of the external ocean current,the transverse amplitude of the vortex-induced vibration in the downstream and transverse directions of the composite-bonded riser will self-lock,resulting in a sudden change in the amplitude.The frequency-locking area increases with the increase of the internal flow velocity,and decreases with the increase of the fiber layer angle,and the cross-flow frequency-locking area is lagging behind the downstream frequency-locking area.Finally,the research content,research methods and research results of this article are summarized,and the future work is prospected.