submodeling in ansys

2010 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary 2010 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary

Submodeling

2010 ANSYS, Inc. All rights reserved. 2 ANSYS, Inc. Proprietary

Introduction to Submodeling

Submodeling is a finite element technique that you can use to obtain more accurate results in a particular region of a model

Submodeling is based on St. Venant's principle.

The submodeling technique has been successfully used not just for stress analyses, but also for thermal, electromagnetic and CFD analyses.


Submodeling - Example

Global Model

Sub Model


Submodeling - Procedure

Five main steps:1. Create and analyze the initial model

2. Create the submodel

3. Perform cut boundary interpolation

4. Analyze the submodel

5. Verify that the distance between the cut boundaries and the stress

concentration is adequate



1. Create and analyze the initial (coarse) model Follows the same steps as in a normal static analysis.

The geometry need not include local details such as fillet radii.

The mesh must be fine enough for accurate displacement results since submodeling theory is based on displacements interpolated from the coarse

model to the submodel.



2. Create the submodel The submodel is an independent, more finely meshed model of a region of

interest within the initial model.

Typically, the submodel will include details such as a fillet radius that were omitted in the initial model.

Some rules for the submodel: It must be in the same location with respect to the global origin as the corresponding portion in

the initial model.

It must have the same loading conditions as the initial model: gravity, symmetry boundaries, temperatures, etc.

Apply all loads and boundary conditions that need to be duplicated from the initial model. Examples:

symmetry conditions

gravity

temperatures



3. Perform cut-boundary interpolationa) This is the key step in submodeling, where displacements from the initial

model are mapped to the cut boundaries of the submodel.

b) Steps involved: First select the nodes on the cut boundary of the submodel [CMSEL Command]

Write those nodes to a file [NSWRITE Command]

c) Restore the full set of nodes, save the database, and exit PREP7.



d) Activate results from the initial analysis [SET Command]

(Remember, we need the displacements from the initial analysis.)

e) Initiate cut-boundary interpolation [CBDOF Command]

f) Exit POST1, change to the submodel jobname, and resume the submodel

database [RESUME Command]

g) Apply cut-boundary displacements to the submodel [/INPUT Command]



4. Analyze the submodel Ensure that all loading conditions have been duplicated on the submodel.

Solve the Submodel

5. Verify the cut-boundary distance This is an important step since submodeling theory is based on the

assumption that the cut boundary is far away from the stress concentration

region.

You can do this by comparing stress or strain results at the cut boundary: Compare path plots at that location between the initial model and submodel.

Use the query option.

List the results.

Etc.


Submodeling - Tutorial

Submodeling is a finite element technique that you can use to obtain more accurate results in a particular region of a model.

Global_Model

Sub_Model



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1. Open a empty Workbench Project file.

2. Drag and Drop Geometry from the Component Systems3. File Save. Name the file as Model2



4. RMB on the Geometry (A2) and select Import Geometry and selec t the geometry file Model-2.agdb

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5. Drag & Drop Static Structural from the Analysis Systems on Geometry (A2). Rename the Static Structural to Global Model

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6. RMB on Model (A4) of Static Structural and select Edit to open ANSYS Mechanical

7. Select Units from the utility menu and change the unit system to Metric (mm,kg,N,s,mV,mA)

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8. Expand the Geometry from the model tree. The geometry is a Multi-Body Part. All the 3 bodies will be used for Global Model and only Sub_Model will be

used for Sub Modeling. Default Structural Steel is used for this analysis



9. RMB on Mesh and select InsertSizing to include a local body sizing10. Select all the parts and type Element Size = 1 mm. 11. RMB on Mesh and select Generate Mesh

91010



12. RMB on Static Structural and select InsertFrictionless Support. Select the 2 faces as shown in the image below for Frictionless Support

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Select Analysis Settings from the model tree and review the Step & Solver controls. It is a 1 Loadstep Linear Analysis

13. Under Analysis Data Management, change Save MAPDL db to Yes. This database file will be used in the sub-model

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14. RMB on Static Structural and select InsertForce. Select the face as shown in the image and select the same face for direction. The force is applied

normal to the selected force.

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15. RMB on Solution and select InsertTotal Deformation & Equivalent Stress. 16. RMB on Solution and select InsertCommands.17. RMB on Commands (APDL) from the model and select Import and select the file Global_Model.txt

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18. RMB on Solution and select Solve, to solve the model. Once the solution is done, you can post-process the Equivalent Stress as shown in the

figure below

After reviewing the results, close ANSYS Mechanical. FileClose Mechanical

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Once the solution is done, the APDL Command object will copy the result and database file from the solver directory of the global model to the root directory

of this model. These files will used for sub-model



19. RMB on Static Structural on the Workbench Project Page and select Duplicate.20. Link the Geometry (A2) to the Geometry (C2) of Static Structural and raname the project to Sub Model

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21. RMB on Model (C4) of Static Structural to open ANSYS Mechanical

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22. Expand the Geometry from Model tree and suppress 2 bodies named as Global_Model. We need only the sub_model as shown in the image below

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23. Select all the load/constraint and the Command object under solution and

delete them

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24. Select Body Sizing and change the element size to 0.1 mm25. RMB on Mesh and select Generate Mesh

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26. Select the 4 faces (of the cut boundary as shown in the image below) and

RMB and Create Named Selection and name the 4 faces as CUT_BOUNDARY. Click OK to close the dialob box

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27. RMB on Static Structural and select InsertCommands.28. RMB on Commands (APDL), select Import and browse for the file Sub_Model.txt

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29. RMB on Solution and select Solve.30. RMB on Commands (APDL), select Import and browse for the file Sub_Model.txt. Review the results

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submodeling in ansys

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