Experimental and Numerical Analysis of a New Simplified Model for theDeepwater Unbonded Flexible Risers

A new simplified model is proposed for the analysis of deepwater unbonded flexible risers，in which the influence factors of flexible risers’tensile，torsion and rigidity are discussed. The unbonded flexible riser is suitable for rough deep-sea conditions due to its structural features，i.e. small rigidity，light in mass，strong corrosion resistance and anti-fatigue performance. However，the numerical simulation analysis of the unbonded flexible riser are confronted with a number of challenges resulted from its strong nonlinear characteristics in the friction and contact between different layers of the unbonded flexible riser. Thus， it is difficult to guarantee both accuracy and efficiency when evaluating an unbonded flexible riser model. Aiming at this problem，a new simplified model is proposed by employing a simplified beam and shell element model and considering the axial elastic modulus of the carcass and pressure armour. In order to validate the proposed model，the experimental data are compared with the numerical solution，and the results show that the simplified model does not only reduce the computation cost，but also agrees well with the actual constitutive relation of the flexible riser.