ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

according to (Eq. 2), nor averaged material properties at the AF-NP interface allowed
stabilizing the FV predictions when applied separately (Fig. 3b). The creation of a
material transition zone, refining more the annulus did not solve the problem either,
whereas refining more the nucleus area showed significant improvements, though some
oscillation remained.
a) b)
Fig. 3: FV oscillations predicted under extension along Path 1, a) in the different models
studied and b) in model 3 with and without material transition area.
The analysis of the Darcy’s law parameters revealed that oscillations came mostly from
variations of the pore pressure gradients along the path (Fig. 4).
Fig. 4: Relation between the oscillation at the FV with the gradient of pore pressure.
It is worth to highlight that the AF outer boundaries acted as material discontinuities as
well and had to be locally refined (Fig. 5a). An additional tangential refinement was
required so that model 3 results converged to model 4 results (Fig. 5b).
a) b) c)
Calculation time: 1h 30 Calculation time: 2h 30 Calculation time: 16h
Fig. 5: FV predictions and computational time for, a) model 3 with local radial
refinements at the AF-NP interface, b) model 3 optimized with an additional tangential
refinement and c) model 4.
By using the model locally refined that included the interpolated transition material
properties, instabilities disappeared after 30 minutes of load relaxation (Fig. 6a). The