Adaptive Mesh General Workflow

The adaptive Mesh model enables a simpler setup of the initial mesh where detailed flow characteristics are captured with the adapted mesh during the simulation proceeds. The initial mesh only need to have enough cells to capture the basic flow characteristics.

In addition, the surface mesh of the initial mesh must represent the CAD geometry sufficiently well since no surface reconstruction is supported by Adaptive Mesh Refinement (AMR). The AMR adaption is always based on the tessellated surface in the initial mesh.

Once you start AMR, do not apply any region or boundary commands such as those for removing invalid cells, combining regions, or combining boundaries since these commands change the cell connectivity saved by the AMR solver.

注 AMR works for all the 3D volume mesh types, but not for 2D meshes or 2D axisymmetric analyses.
  1. Prepare the initial mesh according to the following guidelines:
    • Create a volume mesh that is fine enough to capture the basic flow characteristics.
    • Avoid creating an unnecessarily fine mesh as AMR cannot coarsen the initial mesh.
    • AMR cannot coarsen or refine the mesh of shell regions for fluid film. Therefore, if your simulation contains fluid film, create a mesh that is appropriate to capture the film flow characteristics throughout the entire simulation.
  2. If you are applying user-defined mesh adaption, prepare the field function or table that tells the AMR solver when and where to refine, keep, or coarsen the mesh. Refer to the following items for guidance:
    • To trigger mesh refinement during the solution initialization stage, select the [user-defined mesh adaption] node and activate Refine in Solution Initialization.

      Do not activate this option unless you are sure that the initial solution reflects the basic flow pattern. Refining the initial mesh with an inadequate initial solution is counterproductive when applying AMR. You are advised to deactivate this option whenever you use grid sequencing for the coupled solver.

    • To capture discontinuities such as shocks, you are advised to use gradient of discontinuous solution multiplied with the adaption cell size which represents the change in a cell. For example, mag(grad(${MachNumber}))*(${AdaptionCellSize})
    • To reduce the discretization error associated with smoothly varying functions, such as for applications in aerodynamics, use the Laplacian of representative solution variables. For example, abs(div(grad(${TotalPressure})))*pow(${AdaptionCellSize},2)
    • Select the [user-defined mesh adaption] node and set the value for Max Refinement Level.

      Choose the refinement level based on the initial mesh. If the initial mesh is relatively fine, use a low Max Refinement Level to avoid high cell count.

  3. To activate the Adaptive Mesh model:
    1. For an existing physics continuum, within the Optional Models category of the physics model selection dialog, add the Adaptive Mesh model.
    2. Select the Adaptive Mesh node and set the properties. Refer to Adaptive Mesh Model Properties for details.
      注To update the settings for Prism Cell Refinement or Initial Mesh, you must uninitialize the Adaptive Mesh solver through clearing Adaption. If you want to start from the initial mesh, check also Reset Mesh, otherwise the Adaptive Mesh solver considers the current refined mesh as a new input mesh. See also: 清除求解.
To complete the setup for AMR, you must add one or more adaptive mesh criteria. You can combine user-defined criteria with model-based criteria if necessary.
  1. To specify a user-defined mesh refinement:
    1. Right-click the [physics continuum] > Adaptive Mesh Criteria node and select New > User-Defined Mesh Adaption.
    2. Select the [user-defined mesh adaption] node and set the properties. Refer to User-Defined Mesh Adaption Settings for details.
    3. Select the [user-defined mesh adaption] > Adaption Request node and set the properties. Refer to User-Defined Mesh Adaption Settings for details.
To improve accuracy and efficiency for AMR supported models, use the built-in model-driven adaptive criteria instead of creating your own user-defined criteria. The built-in criteria are tuned to provide optimal adaption for these cases.
  1. For model-driven adaption criteria, refer to the model-specific workflows:
After specifying the mesh refinement criteria, you set up the adaptive mesh solver:
  1. Select the Solvers > Adaptive Mesh node and set the properties. Refer to 自适应网格求解器参考 for details.
    • To modify the update frequency of mesh adaption, select the Trigger node and set the Trigger Mode with the corresponding values. You can trigger adaption based on number of iterations, time-step frequency (including delta time), or through update events that you specify.

      The flow solution should proceed on a larger scale before you trigger AMR again to adapt the mesh.

If you have a flow solution on the initial mesh, you can preview the AMR behavior and then make adjustment through the following solver right-click action:
  1. Right-click the Solvers > Adaptive Mesh node and select Refine/Coarsen Mesh Once.
  2. To revert mesh refinement and restart from the initial mesh, you can choose from:
    • Select Solution > Clear Solution in the toolbar and activate both Adaption and Reset Mesh in the Clear Solution dialog.
    • Right-click the Solvers > Adaptive Mesh node and select Clear Adaption.
If you wish to apply AMR in some regions but not others, then you can disable the mesh adaption region-wise:
  1. Select the Region > [region] > Physics Condition > Adaption Option node and deactivate Enable Adaption.

For complete example workflows applying AMR, refer to the following tutorials: