Adaptivity System

Refinement Patterns

MOOSE employs "self-similar", isotropic refinement patterns, as shown in the figure. When an element is marked for refinement, it is split into elements of the same type. For example, when using Quad4 elements, four "child" elements are created when the element is refined. Coarsening happens in reverse, children are deleted and the "parent" element is reactivated. The original mesh starts at refinement level 0. Each time an element is split, the children are assigned a refinement level one higher than their parents.

Self-similar refinement pattern utilized by MOOSE for adaptivity for 1D linear, 2D quadrilateral, and 3D hexahedron elements.

P-Refinement

P-refinement can be selected by setting adaptivity_type = p in the Adaptivity block (whether using the older Executioner/Adaptivity syntax which uses libMesh error estimators or the newer top-level Adaptivity block (referenced by this page) using the Indicators and Markers introduced towards the beginning of this page). P-refinement level mismatches are not supported for continuous, non-hierarchic finite element families. Additionally, p-refinement of NEDELEC_ONE and RAVIART_THOMAS elements is not supported. Consequently, by default we disable p-refinement of the following bases: LAGRANGE, NEDELEC_ONE, RAVIART_THOMAS, LAGRANGE_VEC, CLOUGH, BERNSTEIN, and RATIONAL_BERNSTEIN. Users can control what families are disabled for p-refinement by setting the disable_p_refinement_for_families parameter.

HP-Refinement

MOOSE includes experimental HP refinement capability. HP refinement can be selected by setting adaptivity_type = hp in the Adaptivity block. HP-refinement works by performing a coarsening test on elements just flagged for h-refinement (using libMesh error indicators or the Indicator/Marker systems). The coarsening test coarsens in both h and p and notes whichever changes the solution more. If p shows a larger solution change (after doing some weighting based on how many degrees of freedom are added) and the solution is sufficiently smooth as determined by decay rates of Legendre coefficients, then we switch the element refinement choice from h to p. As noted in the documentation for the HPCoarsenTest class, more development is likely required to produce optimal hp meshes.

Cycles and Intervals

MOOSE normally performs one adaptivity step per solve. However, developers have the ability to increase or decrease the amount of adaptivity performed through the "cycles" and "interval" parameters.

The "cycles" parameter can be set to perform multiple adaptivity cycles for a single solve. This is useful for cases where one would like to resolve a sharp feature in a single step, such as in the case of an introduced nucleus.

[./Adaptivity<<<{"href": "index.html"}>>>]
  refine_fraction = 0.3
  max_h_level<<<{"description": "Maximum number of times a single element can be refined. If 0 then infinite."}>>> = 7
  cycles_per_step<<<{"description": "The number of adaptive steps to use when on each timestep during a Transient simulation."}>>> = 2
[../]

The "interval" parameter can be set to decrease the amount of adaptivity is performed so that it is performed on every _nth_ step. This can sometimes help to speed up your simulation as adaptivity can be somewhat expensive to perform.

[./Adaptivity<<<{"href": "index.html"}>>>]
  interval<<<{"description": "The number of time steps betweeen each adaptivity phase"}>>> = 2
  refine_fraction = 0.2
  coarsen_fraction = 0.3
  max_h_level<<<{"description": "Maximum number of times a single element can be refined. If 0 then infinite."}>>> = 4
[../]

Input Parameters

Available Subsystems

• Moose App
• Indicators
• Markers