Failure Mode And Characteristic Of Tensile Armor Layer In Unbonded Flexible Risers Under Axial Compression Load

Unbonded flexible risers,as the key equipment in offshore engineering,may experience large axial compressive loads during installation and operation.The compressive loads may lead to radial failure or lateral failure for tensile armor layers and then the axial strength would decrease significantly.The structural failure may have an important impact on structural safety and marine environment.In this thesis,the failure mode and characteristic of unbonded flexible risers under axial compressive loads is studied.The main contents include:A three-dimensional numerical model of a 6 inches unbonded flexible riser is established by using parametric modeling technique in this thesis.The nonlinear finite element explicit dynamic analysis code is used to obtain the ultimate axial strength of flexible riser.The non-linear effects such as material nonlinearity,large geometrical deformation,contact and friction between layers are taken into account.In the case of failure of unbonded flexible risers under axial compressive loads,quantitative analysis of design parameters is carried out.Three design parameters--the number of helix bands in tensile armor layer,laying angle of tensile armor layer and thickness of outer polymer layer are variables to study the impacts on characteristics of the failure modes and axial compressive strength for unbonded flexible risers.The influence of different friction coefficient on failure mode and axial strength of unbonded flexible riser is studied.The change of ultimate compressive strength of unbonded flexible riser under different outer pressure is analyzed,as well as the characteristics of deformation of helix bands in tensile armor layer.The results and conclusions of this study may provide references for structural optimization design and safety assessment of unbonded flexible risers.