Hi Sina S. Is your model a 3D structure?

Dear Sina S.,

In case you are dealing with 3D structure, there is method which is call "Submodeling" or "Substructure" where you can cut a portion of a structure and perform a very detailed investigation on it. The followings are the step by step process for performing this method.

1. Defining the substructure geometry. You can use slice, cut, boolean or other commands in DesignModeler (Spaceclaim) for defining the substructure geometry (See Capture1).

2. Apply bonded contact at the contact surface between the substructure and rest of the structure.

3. Perform structural analysis.

4. Transfer the "Solution" Data to "Setup" of second module (See Capture2). This schematic enables refining the mesh on the substructure geometry in the second module, however, if you would like to use same size mesh then you simply transfer "Model" data to "Model" of second module (See Capture3).

5. Open the second module and suppress the main geometry. Adjust (refine) the mesh the way you like.

6. You see that one item is already added to BCs which is "Submodeling". Right click on it and insert a "Cut boundary Constraint" and select the cut surface as scope "Geometry" (See Capture4). This process is going to import displacements calculated in the first module to second module, therefore, you do not need any other BCs.

7. Now you can run the analysis and calculate the results on the substructure geometry (See Capture5).

This method is very useful where you are dealing with a very big structure that you only need to focus on a portion of that structure, e.g. investigating an existing crack somewhere on a big pressure vessel!!!

Hope this answer helps!!

Hi Sina S.

If you want to evaluate the effect of different loadings on the structure, you may try substructuring. In submodeling, you can only evaluate the effect of one single set of loads that act on the structure. If the load acting on the sub model is changed, the results would not be physically valid. But if you use substructuring, the set of loads acting on the substructured part can be changed arbitrarily as long as the rest of the model is elastic and the loading on the rest of the model is not changed. Hope this helps.

Dear all Hamidreza Ahmadi Moghaddam Claudio Pedrazzi

Thanks for your interesting suggestions... I am wondered how to use the sub-modeling technique for harmonic analysis where the displacement condition of the cut section is variable with frequency...

Claudio Pedrazzi

The displacement condition of all nodes is variable with respect to natural frequency. So that for sub modeling, the displacement condition of the cut section nodes should change with respect to frequency. It means frequency dependent boundary condition!

I do agree with your statement that this is an old modeling approach for the period that computation cost was a big deal. However, I believe simplification not only reduces the computation cost but helpful in vibration control from both simulation and experiment points of view.

Claudio Pedrazzi

The displacement condition of all nodes is variable with respect to natural frequency. So that for sub modeling, the displacement condition of the cut section nodes should change with respect to frequency. It means frequency dependent boundary condition!

I do agree with your statement that this is an old modeling approach for the period that computation cost was a big deal. However, I believe simplification not only reduces the computation cost but helpful in vibration control from both simulation and experiment points of view.

Hi @Sina S.

I think substructuring might help although some approximation would be introduced due to approximation of the mass matrix of the superelement.