Dynamic Model Analysis Of A Fluid-Conveying Riser For FDPSO-TLD Under Multi-Parameter Excitation

Floating Production,Drilling,Storage and Offloading units represent a new technologywith a promising future in the offshore oil industry.An important role is played by risers,which are installed between the subsea well head and the Tension Leg Deck(TLD)located in the middle of the moon-pool in the hull.TLD is one of the dry tree concepts developed by the SBM offshore company in recent decades.TLD is based on using the gravity of weights,instead of buoyancy,as in existing dry tree concepts,as a means to pretension risers.During exploitation oil and gas operations,TLD applied axial tensions and changing tension in the production risers which are used as a parametric excitation at the top of riser.When the risers are located in deeper waters,the riser will suffer considerable wave-induced vibration(WIV)and vortex-induced vibration(VIV),which can last for almost the whole design life in harsher environments.Besides this,the fluid flowing inside the riser may have an undesirable influence on the lateral deflection response of the riser,with random wave forces in the time domain.To investigate this effect,a riser is modeled as a Bernoulli–Euler beam.By linearizing the wave drag force,the riser's lateral deflection is obtained through a partial differential equation.Applying the Galerkin method,the equation is reduced to an ordinary differential equation that can be solved using the pseudo-excitation method in the time domain.This paper aims to develop a time domain method to study the parametric dynamics under wave excitation and stability of fluid-conveying risers.The equations of motion of fluid-conveying risers under wave excitation are first established.The random response of a riser is then determined by a suitable method.The stability,the variable axial tension of riser,the velocity of fluid,and the coupling of these factors on the vibration mode,and the maximal displacement and stress of the simply supported riser are studied.The results show the calculations for effects of internal flow are more exact and stable,and the calculations for effects of without internal are unreasonable.The result of my paper could decrease the burden of TLD platform and the cost of deep oil and gas development.