Defining Fluid Cavities

You can define a fluid cavity to model a hydraulic or pneumatic fluid-filled structure and to simulate its mechanical response. You can define the fluid cavity for two-dimensional and three-dimensional models, as well as for axisymmetric models.

After you define a fluid cavity, you can specify its internal cavity pressure using a cavity pressure restraint in your simulation scenario app.

Note: This feature is not related to the computational fluid dynamics (CFD) capabilities of the Fluid Model Creation or Fluid Scenario Creation apps.

This task shows you how to:

See Also
About Fluid Cavities

Define a Fluid Cavity in Any Type of Simulation Step

  1. From the Abstractions section of the action bar, click Fluid Cavity .
  2. Optional: Enter a descriptive Name.
  3. Select a Cavity surface as the support.

    The cavity surface is composed of the model faces that enclose the cavity. You can select the faces of the cavity, a named geometry publication, or a named group of mesh objects.

  4. Select a Point, which is a reference node (not connected to any elements in the model) used to identify the cavity.

    For symmetric models, select a point on the model or on a node-based group that contains a single node. The point or node must lie on the axis (or axes) of symmetry or on the plane of symmetry for a half-symmetric model.

    For axisymmetric models, if you do not select a point, the simulation computes a default point at a location central to the cavity surfaces.

  5. Click Search to apply a material to the fluid inside the cavity.
    The Material Palette dialog box opens.
  6. Select Specify ambient pressure to specify a pressure on the structure that accounts for external ambient pressure, and enter a value in the field.
  7. Select Specify added volume to specify the additional volume in the fluid cavity as it expands, and enter a value in the field.
  8. If you are specifying fluid cavity behavior in an explicit dynamics step, proceed to Define Fluid Cavity Behaviors That Are Specific to Explicit Dynamics Steps.
  9. Click OK.
    For nonaxisymmetric models, a glyph appears in the model to represent the fluid cavity feature. Axisymmetric models do not display a glyph.

Define Fluid Cavity Behaviors That Are Specific to Explicit Dynamics Steps

  1. Select Set minimum volume=initial volume to specify that the fluid cavity volume will never be smaller than the volume at the start of the analysis.
  2. Select Specify minimum volume to specify a minimum volume for the fluid cavity that is not the initial volume, and enter a value in the field.

    Note: Specifying a minimum volume can help you avoid simulation problems that occur when the fluid cavity volume is very small.

  3. Select Specify switch time to specify the time when the app switches from the lumped kinetic molecular procedure to the uniform pressure method, and enter a value in the field.
  4. If you are using an ideal gas model, select Specify adiabatic behavior to specify the adiabatic behavior for the gas.
  5. If you specified adiabatic behavior for the gas, select Specify ambient temperature to define the ambient temperature for analyses where heat energy flow is defined for a pneumatic fluid.
  6. Click OK.
    For nonaxisymmetric models, a glyph appears in the model to represent the fluid cavity feature. Axisymmetric models do not display a glyph.