General Information

  • Solver Fortran File: MMG2D_MetricAniso.F90
  • Solver Name: ElmerIce_MeshAdapt2D(MMG2D_MetricAniso)
  • Required Output Variable(s):
    • (1) Metric (dofs = 3)
    • (2) hessian (dofs = 3)
  • Required Input Variable(s):
    • (1) Nodal gradient (dofs = 2)
  • Optional Output Variable(s): None
  • Optional Input Variable(s): None

General Description

This solver is used for the mesh adaptation (Mesh Adaptation) to compute the anisotropic metric M.

The metric M , used to define the element size, derives from a geometric error estimate based on an upper bound for the interpolation error of a continuous field to piecewise linear elements (Frey and Alauzet, 2005).

For a variable v, M depends on the eigenvalues lambda_i and eigenvector matrix R of the hessian matrix of v, H (i.e. small elements are required where the curvature is the highest):

M=R.Lambda.R^{-1} with Lambda=(matrix{2}{2}{lambda_1 0  0 lambda_2}) and \lambda_i=min ( max ( {{c|\lambda_i|}/{epsilon_v}},{{1}/{l^2_{max}}} ), {{1}/{l^2_min}} ),    (1)

where

  • c is a geometric constant equal to 2/9 in 2D
  • l_min (resp. l_max) is a prescribed minimal (resp. maximal) edge size
  • epsilon_v is the prescribed maximum error

First this solver compute the hessian matrix H; As computing second derivatives in linear elements in not straightforward this is done by solving the diffusive equation H_ij+ K ∇(H_ij) = 1/2 (dq_i/dx_j+dq_j/dx_i), where K=k A is a diffusivity proportionnal to the local element size (A) and g_i={{\partial v}/{\partial x_i}} are the nodal gradients of the variable v (This can be computed using using the Compute2DNodalGradient Solver).

Finally, the metric M is then computed from Eq. (1)

SIF contents

Solver 5
   Equation = "Metric2"
   Variable = -nooutput dumy

   Procedure = "ElmerIce_MeshAdapt2D" "MMG2D_MetricAniso"

   Metric Variable Name = String "M2"

   Hessian Variable Name = String "ddx2"
   Gradient Name = String "Gradient2"
   Diffusivity = Real 0.5 !! the diffusivity k; the total diffusivity is kA

   Linear System Solver = Direct
   Linear System Direct Method = umfpack

  Exported Variable 1 = -dofs 3 "M2"
  Exported Variable 2 = -dofs 3 "ddx2"
End


Body Force 1
!! Parameters in Eq. 1
  M2 Hmin = Real 1.0e-3
  M2 Hmax = Real 1.0
  M2 err =  Real 0.0033
End

Example

Examples for anisotropic mesh adaptation can be found under [ELMER_TRUNK]/elmerice/Tests/MMG2D_Aniso1 and [ELMER_TRUNK]/elmerice/Tests/MMG2D_Aniso2, where the mesh size is adapted using 1 or 2 variables (i.e. combining metric informations), respectively.

solvers/mmg2d_metricaniso.txt · Last modified: 2017/07/18 17:07 by fgillet
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