Defining an Eulerian mesh motion boundary condition

Eulerian mesh motion allows an Eulerian mesh—which is usually rigid and undeformable—to expand, contract, and translate during an analysis. As part of the mesh motion definition you identify an object to follow, which can be either a Lagrangian surface or an Eulerian material instance; the Eulerian mesh resizes and moves during the analysis so that it always surrounds this object.

Context:

Eulerian mesh motion is calculated based on a rectangular bounding box that is constructed by Abaqus. The bounding box cannot be visualized in Abaqus/CAE, but it typically corresponds relatively closely to the Eulerian mesh. The creation and behavior of the bounding box is described in Eulerian Mesh Motion. You can set restraints and restrictions on the contraction, expansion, and translation of this bounding box as part of the mesh motion boundary condition definition. These restrictions may prevent the Eulerian mesh from completely encompassing the specified object to follow at all times during the analysis.

Eulerian mesh motion boundary conditions can be applied only to parts with an Eulerian section assignment, and they cannot be applied in the initial step of an analysis.

  1. Display the Eulerian mesh motion boundary condition editor using one of the following methods:

  2. Specify the Object to Follow:

    • To follow a Lagrangian surface, choose Surface region and click to select a surface:

      • Select a surface in the viewport. You can use the angle method to select a group of faces from geometry or a group of element faces from a mesh. For more information, see Using the angle and feature edge method to select multiple objects. When you have finished selecting, click mouse button 2.

      • To select from a list of existing surfaces, do the following:

        1. Click Surfaces on the right side of the prompt area.

          Abaqus/CAE displays the Region Selection dialog box containing a list of available surfaces.

        2. Select the surface of interest, and click Continue.

          Note:

          The default selection method is based on the selection method you most recently employed. To revert to the other method, click Select in Viewport or Surfaces on the right side of the prompt area.

    • To follow an Eulerian material, choose Eulerian material instance and select an instance.

  3. By default, the global coordinate system is used to construct the mesh bounding box. To change the coordinate system in which the mesh bounding box is constructed, click for the CSYS option and do one of the following:

    • Select an existing datum coordinate system in the viewport.

    • Select an existing datum coordinate system by name.

      1. From the prompt area, click Datum CSYS List to display a list of datum coordinate systems.

      2. Select a name from the list, and click OK.

    • Click Use Global CSYS from the prompt area to revert to the global coordinate system.

    Alternatively, click to define a new datum coordinate system.

    This coordinate system editing option is available only in the step in which the boundary condition is created.

  4. On the Controls tabbed page, specify general constraints and limitations on the motion of the mesh bounding box:
    1. To prevent the mesh from contracting during the analysis, toggle off Allow mesh contraction. This option is toggled on by default.
    2. Specify an Aspect ratio limit for the maximum change allowed in the length to width ratio in any of the three bounding box directions. The value must be greater than or equal to one.
    3. Specify the Mesh velocity factor. This factor defines the maximum velocity of the Eulerian mesh as a fraction of the velocity of the object being followed. The value must be greater than or equal to zero.
    4. If the object being followed is an Eulerian material, specify a Volume fraction threshold. Elements whose Eulerian material volume fraction are less than this threshold are considered empty for the purposes of mesh motion, and the mesh does not expand or move to account for the material in these elements. The value must be greater than zero and less than or equal to one.
    5. Specify the Buffer size, which preserves some distance between the object being tracked and the Eulerian mesh boundary:

      • Select Specify, and enter a value to define a buffer equal to the given value times the maximum Eulerian element size. The value must be greater than or equal to zero.

      • Select Initial to define a buffer equal to the initial distance between the object and the mesh boundary.

  5. On each of the Axis tabbed pages, specify limits on the motion of the bounding box in each of its three directions:
    1. Choose whether the original Center position is Free or Fixed along the selected axis.
    2. Choose whether the original Positive plane position is Free or Fixed. The positive plane is the face of the bounding box whose normal is aligned with the positive direction of the selected axis.
    3. Choose whether the original Negative plane position is Free or Fixed. The negative plane is the face of the bounding box whose normal is aligned with the negative direction of the selected axis.
    4. Specify the Expansion ratio along the selected axis:

      • Choose Unlimited to allow infinite scaling of the bounding box if necessary.

      • Choose Specify maximum, and enter a value to define a maximum scaling ratio. The value must be greater than or equal to one.

    5. Specify the minimum Contraction ratio along the selected axis. The value must be greater than or equal to zero and less than or equal to one.