In models undergoing large localised deformations, the mesh may eventually become very distorted leading to rapid element quality degradation and compromising the numerical stability often resulting in premature termination of the simulation.  The location of regions that exhibit high strain rates may be continually changing during the evolution of a geological structure development.  Additional complexities not present in the original model may emerge; e.g. due to localisation of the deformation, altering the element density necessary for obtaining accurate solutions. Adaptive mesh refinement is used to overcome these problems by:

 

1Evaluating the distortion of the elements and triggering a remesh once elements become too distorted, or if the element size is too large to capture changes in local deformation patterns; e.g. the onset of a fault.

 

2Evaluating the target mesh using a combination of:

(a) User defined maximum and minimum allowable element sizes, applied to the complete mesh or parts of the mesh,

(b) Error indicators that identify the spatial distribution of target element size; e.g. based on the plastic strain rate.

 

3Performing the remesh and then mapping the solution data from the old mesh to the new mesh while addressing:

(a)  Consistency with the constitutive equations,

(b)  The requirement of equilibrium (which is fundamental for implicit FE simulation),

(c)  Compatibility of the history-dependent internal variables transfer with the displacement field on the new mesh,

(d)  Compatibility with evolving boundary conditions,

(e)  Minimisation of the numerical diffusion of transferred state fields.

 

 

Mesh in Initial Configuration

Mesh in After Extension and Deposition of a Syn-Kinematic Layer

Mesh Refinement on Faults and Coarse Mesh in Elastic Fault Blocks

 

Adaptivity is defined using:

 

1Adaptivity_control_data - which identifies that adaptive remeshing is to be used and defines the key control data.

 

2One or more Adaptivity_set_data  - which define additional data to control the error estimation and target element size either for the whole domain or specific regions of the domain.

 

 

Examples

 

Tutorial examples demonstrating usage of adaptivity data are:

 

Mech_003: Rift sandbox simulation using prescribed boundary data

 

Mech_004: Biaxial test on sand using adaptivity