[GeoMechanicsApplication] Investigate the UPw elements and identify a more suitable structure

[rfaasse]

Geometrically nonlinear behaviour

There are six element classes that consider geometrically nonlinear behaviour by adopting the Updated Lagrange (UL) Formulation:

1. UPwUpdatedLagrangianElement
2. UPwUpdatedLagrangianAxisymmetricElement
3. UPwUpdatedLagrangianFICElement
4. UPwUpdatedLagrangianAxisymmetricFICElement
5. UpdatedLagrangianUPwDiffOrderElement
6. UpdatedLagrangianUPwDiffOrderAxisymmetricElement

Due to how the element classes are related through inheritance, certain parts of the code have been duplicated with only minor modifications. These duplications and differences are detailed below.

UPwUpdatedLagrangianElement

This class derives from class UPwSmallStrainElement and it overrides the following relevant member functions:

• CalculateAll: differences with respect to the base class implementation include:
  • The base class implementation calls CalculatePermeabilityUpdateFactor (implemented by the base class itself), whereas the derived class doesn’t call this member at all. This might be a discrepancy that needs to be fixed. We need to investigate that first.
  • When the stiffness matrix is calculated, the UL element (i.e. this class) also considers a “geometric stiffness” contribution (by calling member CalculateAndAddGeometricStiffnessMatrix of class UPwSmallStrainElement), whereas the base class doesn’t.
• CalculateOnIntegrationPoints(const Variable<double>&, …): provides a dedicated implementation when the given variable equals REFERENCE_DEFORMATION_GRADIENT_DETERMINANT. Possibly, this code is used for postprocessing purposes only.
• CalculateOnIntegrationPoints(const Variable<Matrix>&, …): provides dedicated implementations when the given variable equals either REFERENCE_DEFORMATION_GRADIENT or GREEN_LAGRANGE_STRAIN_TENSOR. Again, possibly this code is used for postprocessing purposes only.

UPwUpdatedLagrangianAxisymmetricElement

This class derives from UPwUpdatedLagrangianElement (see the previous section). It appears this class only overrides member functions that need different behaviour to account for the axisymmetric stress state. In other words, when it comes to geometrically nonlinear behaviour, it exhibits the exact same behaviour as its base class (and no code was duplicated to achieve that).

UPwUpdatedLagrangianFICElement

This class derives from class UPwSmallStrainFICElement and it is not related to class UPwUpdatedLagrangianElement. It overrides the following relevant member functions:

• CalculateAll: like for class UPwUpdatedLagrangianElement, when the stiffness matrix is calculated, the UL element (i.e. this class) also considers a “geometric stiffness” contribution (by calling member CalculateAndAddGeometricStiffnessMatrix of class UPwSmallStrainElement), whereas the base class doesn’t.
• CalculateOnIntegrationPoints(const Variable<double>&, …): the implementation appeared to be identical to the one of class UPwUpdatedLagrangianElement.
• CalculateOnIntegrationPoints(const Variable<Matrix>&, …): the implementation appeared to be identical to the one of class UPwUpdatedLagrangianElement.

UPwUpdatedLagrangianAxisymmetricFICElement

This class derives from class UPwUpdatedLagrangianFICElement (see the previous section). As for class UPwUpdatedLagrangianAxisymmetricElement, this class appears to only override member functions that need different behaviour to account for the axisymmetric stress state. In other words, when it comes to geometrically nonlinear behaviour, it exhibits the exact same behaviour as its base class (and no code was duplicated to achieve that).

UpdatedLagrangianUPwDiffOrderElement

This class derives from class SmallStrainUPwDiffOrderElement and it overrides the following relevant member functions:

• CalculateAll: differences with respect to the base class implementation include:
  • The base class implementation calls CalculatePermeabilityUpdateFactor (implemented by the base class itself), whereas the derived class doesn’t call this member at all. This might be a discrepancy that needs to be fixed. We need to investigate that first.
  • When the stiffness matrix is calculated, the UL element (i.e. this class) also considers a “geometric stiffness” contribution when requested (by calling member CalculateAndAddGeometricStiffnessMatrix), whereas the base class doesn’t.
• CalculateOnIntegrationPoints(const Variable<double>&, …): the implementation appeared to be identical to the one of class UPwUpdatedLagrangianElement.
• CalculateOnIntegrationPoints(const Variable<Matrix>&, …):
  • The resizing of the output vector is based on the size of constitutive law vector (why??) rather than the number of integration points. [Or are these numbers somehow related and do they have identical values??]
  • The code related to the case where the given variable equals REFERENCE_DEFORMATION_GRADIENT appears to be nearly identical to the one of class UPwUpdatedLagrangianElement, the difference being that the model dimension is not a template parameter, but taken from the element’s geometry.
  • Variable GREEN_LAGRANGE_STRAIN_TENSOR is simply not considered here.
• CalculateOnIntegrationPoints(const Variable<Vector>&, …): provides a dedicated implementation when the given variable equals GREEN_LAGRANGE_STRAIN_VECTOR.

UpdatedLagrangianUPwDiffOrderAxisymmetricElement

This class derives from class UpdatedLagrangianUPwDiffOrderElement (see the previous section). As for class UPwUpdatedLagrangianAxisymmetricElement, this class appears to only override member functions that need different behaviour to account for the axisymmetric stress state. In other words, when it comes to geometrically nonlinear behaviour, it exhibits the exact same behaviour as its base class (and no code was duplicated to achieve that).

[rfaasse]

As discussed, this ticket has resulted in 4 issues for further steps:

1. 12061

2. 12067

3. 12068

4. 12069

Since the high-level plan is clear, we close this issue.