Orcina news

We have now released the non-linear seabed soil model in OrcaFlex 9.2e. The model has been developed by Professor Mark Randolph (Centre for Offshore Foundation Systems, University of Western Australia), a recognised expert in this field, and we have been working with Mark to implement the model in OrcaFlex.

The model is for modelling the seabed resistance for catenary pipeline contact. It takes as input the line diameter and the seabed soil geotechnical properties (undrained shear strength at the mudline, shear strength gradient with depth, soil saturated density). It then calculates the seabed reaction force on each line element as a function of the penetration, allowing for non-linear penetration resistance, hysteretic effects due to uplift and repenetration, and non-linear suction forces.

Some of the model characteristics are illustrated in the following diagram. For comparison, the standard OrcaFlex linear seabed model would give just a straight line seabed reaction curve in the diagram.

This article proposes some possible changes that we are considering, to the way OrcaFlex treats the water inside a hollow spar buoy, i.e. where a spar buoy object in an OrcaFlex model has a non-zero ID specified for one or more of its cylinders. We would welcome feedback from OrcaFlex users (and potential users) on whether the change that we are considering would be a useful.

The existing OrcaFlex treatment of hollow spar buoys is aimed at modelling hollow axi-symmetric structures that flood and drain very freely in the axial direction. But it is less suitable for hollow objects that do not flood and drain so easily, and these proposals aim to address this.

Continue reading “Possible changes to modelling of hollow spar buoys”

Orcina have recently carried out a validation of the way OrcaFlex handles buoyancy forces and pipe internal contents pressure effects, and the resulting effective tension and wall tension that OrcaFlex reports. We have validated these OrcaFlex results against results presented in Nigel Barltrop’s well-respected book “Dynamics of Floating Structures: a guide for design and analysis. Volume 2”. The OrcaFlex results matched the Barltrop results very well, confirming that OrcaFlex models buoyancy and internal pressure effects correctly.

Continue reading “Effective Tension Validation”