Dr Hema Wadhwa

A real-time understanding of the structural integrity of flexible risers is critical to avoiding
failures as well as unnecessary and costly replacements. Accurate and efficient computation of
tensile armor wire stress time-histories is the key to enabling the implementation of a flexible
riser digital twin. Accuracy requires capturing the nonlinear kinematics of the flexible’s helically
contra-wound tensile armor layers and their interaction with the other metallic and… Show more

A real-time understanding of the structural integrity of flexible risers is critical to avoiding
failures as well as unnecessary and costly replacements. Accurate and efficient computation of
tensile armor wire stress time-histories is the key to enabling the implementation of a flexible
riser digital twin. Accuracy requires capturing the nonlinear kinematics of the flexible’s helically
contra-wound tensile armor layers and their interaction with the other metallic and thermoplastic layers in a dynamic simulation. While it is generally accepted that high-fidelity 3D finite
element models best capture the complex kinematics required to produce accurate stresses, the
main issue is that simulation time remains prohibitive, for example, a single bending cycle on
modern day multi-core computers typically requires 24-48 hours. Therefore, any successful
implementation of a flexible riser digital twin requires an accelerated solver capable of realtime computation of 1000s of bending cycle inputs into the high-fidelity finite element model.
This paper demonstrates a flexible riser digital twin applications centered around the
accelerated solver FLEXAS. Show less

An accidentally dropped drill riser/blowout preventer (BOP) system can pose extreme and costly hazard to subsea facilities. High-fidelity multi-body nonlinear dynamic simulations are required to accurately predict the propagating axial compression waves along the riser due to BOP’s seabed impact, the evolution of the collapse of the riser, riser impact energies, the riser seabed layout, and the resulting impact zone to better manage risks.
The nonlinear simulations must involve detailed… Show more

An accidentally dropped drill riser/blowout preventer (BOP) system can pose extreme and costly hazard to subsea facilities. High-fidelity multi-body nonlinear dynamic simulations are required to accurately predict the propagating axial compression waves along the riser due to BOP’s seabed impact, the evolution of the collapse of the riser, riser impact energies, the riser seabed layout, and the resulting impact zone to better manage risks.
The nonlinear simulations must involve detailed finite element models (FEMs) to accurately capture the stiffness and mass distribution along the riser span, the asymmetrical bending stiffness/mass contribution and axial slip from the auxiliary lines, nonlinear behavior at the flex joint, and the flange/flange joint connections. These effects are critically important in the modeling the propagation of the compression waves that speed through the riser from the point of BOP impact and initiate the drill riser buckling and post-buckling dynamics/collapse.
To incorporate detailed FEM and at the same time maintain computational efficiency and accuracy, nonlinear dynamic substructuring (NDS) is utilized. NDS extends the frame work of dynamic substructuring to nonlinear problems enabling highly efficient multibody nonlinear system level simulations while maintaining the accuracy of individual FEM components. The multi-body NDS solver utilized for efficient computation of this large-order multi-physics problem enables the coupling of four physical models: (i) nonlinear dynamics, (ii) hydrodynamics, (iii) flexible body dynamics, and (iv) multi-body dynamics.
The simulations demonstrate that for this drill riser configuration, the top unbuoyed sections play a key role in the collapse process of the drill riser. The seabed impact zone and impact energies to assess potential impact with seabed infrastructure are discussed. Show less