"Separate structure" during model calculation in Robot Structural Analysis

Autodesk Support

Sep 30, 2024

Products and versions covered

Issue:

"Separate structure" warning is displayed in Robot Structural Analysis after starting calculations of a model. Sometimes it is followed by an instability error.

separate structure



 

 

Causes:

Possible causes:

  • A structure is built from separate parts. If one of parts is either incorrect or not supported, an instability warning is shown.
  • Separate structure parts are connected by claddings or panels, for which "No finite elements" option is activated, in panel calculation model. 
  • Imprecisely defined structure - members intended to be connected are defined with small distances.
  • Duplicated, supported nodes defined along common panel edges not merged while model generation.

Solution:

Possible solutions:

Identify the separate parts of the model and make sure they are intended to be detached from the rest of a structure.

For example, dilatation/expansion joint gaps in a model would trigger the "separate structure" warning.

Correct geometry as needed. If geometry is correct, check defined supports, releases, and so on, to determine the cause of the instability.

To detect the separate parts of a model:
  1. Stop calculations after the separate structure warning has been displayed.
  2. Open the node selection dialog.
  3. Switch to the Group tab.
  4. Select the automatically created SUB..$ group and press the double arrow icon to select nodes that belong to the separate part of the model.

Replace claddings or panels for which, in calculation model, No finite elements - option, is activated, with panels, where in calculation model, Finite element type - Shell is defined.

For panels with no finite elements are defined follow the steps:

    1. Open Geometry > Properties > Calculation model.
    2. Double-click calculation model used for panels.
    3. Activate Finite element type -Shell.
    4. Add.
    5. Calculate model.
    7. For claddings defined in model follow the steps:
    8. Open Geometry > Properties >Thickness.
    9. Assign panel thickness to claddings to change object type to panel (if necessary define new thickness required for panels).
    10. Open Geometry > Properties > Calculation model.
    11. Assign Shell calculation model to panels.
    12. Calculate model.

Increase model generation tolerance while model generation

Follow the steps:
    1. Open Analysis > Analysis types.
    2. Go to Structure model tab.
    3. Activate User-defined tolerance.
    4. Increase tolerance.
    5. Run Generation of computational model.
model generation tolerance
 

Correct imprecisely defined model.

Repeat model meshing to merge duplicated supported nodes.

Follow the steps
  1. Select structure panels.
  2. Mesh selected panels with Analysis >Meshing>Local mesh generation.
Note
To avoid model remeshing (for instance for complex shell models) follow the steps.
  1. Delete all supports
  2. Run Analysis >Generation of computational model
  3. Redefine supports for model with merged nodes
  4. Run analysis


 

See Also:

Find error Separate structure (Robot Structural Analysis forum)
 

Products:

Robot Structural Analysis Products;

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