Center of gravity

Rahul_P1

I like to ask, can I set a point for center of gravity during the Inspire's optimization?

Rahul_P1

gabor.dull

From what I understand you would like to set a point to be the proposed centre or gravity and the optimized shape should have the cog as proposed, this would add a very complex constraint to the optimization process, I am afraid I do not see such an option currently,
Could you please explain the purpose or why you would like to set a point for the cog?

Rahul_P1

Visualising and locating the cog is quite easy,

You can use the measure tool to see the cog, While the Measure Weight tool is active, you can display the model's center of gravity coordinates in the modeling window.

Use the Show CG check boxes to show and hide the model's center of gravity in the modeling window.

Rahul_P1

Quote from Rahul Ponginan on October 16, 2013, 06:25

gabor.dull

From what I understand you would like to set a point to be the proposed centre or gravity and the optimized shape should have the cog as proposed, this would add a very complex constraint to the optimization process, I am afraid I do not see such an option currently,

Could you please explain the purpose or why you would like to set a point for the cog?

I tried to work out a chassis frame of high-clearance tractor. It could be important that the COG is in a proposed point because of the rate of shaft loading.

For instance, to solve that the final COG doesn't depend on the filled of spray liquid's tank, therefore, the rate of shaft loading is constant so the condition of turning is constant during the field work ...

BTW, it is possible to solve the final problem on other way without fixing the COG during the topology optimization.

Rahul_P1

gabor.dull

In that case I suggest you get into OptiStruct the optimization solver that even inspire uses in the background.

It is very easy to take your design from inspire into HyperMesh and preprocess for Optistruct,

Export to optistruct from inspire

1. Click the Optimize icon. The Run Optimization window appears.
2. Click the Export button.
3. Choose a directory and a name for your file, then click Save. Inspire writes the FEM file to that location, using the currently active unit system for the model.

Import this deck from this location into HyperMesh, in the optistruct user profile,

1. Launch HyperMesh.
2. Choose OptiStruct in the User Profiles dialog and click OK.
User Profiles… can also be accessed from the Preferences drop-down menu on the toolbar.
3. From the File drop-down menu on the toolbar, select Import….
An Import tab is added to your tab menu.
4. Set the Import type: to Import FE Mode by clicking on the icon or choose import > solver deck.
5. For File type:, select OptiStruct.
6. Click on the Select Files button
7. Select the .fem file, created by inspire located in the directory specified before while exporting from inspire and click open.
8. Click Import.
The .fem OptiStruct input file is loaded into the current HyperMesh session.
9. Click Close to exit the Import tab menu.

Create a COG response

then go to analysis > optimization > responses and create a response with type as cog and choose the x or y or z coordinate of the cog you want to constrain, (you can create three constraints with one coordinate in each, if you need to completely set the cog)

1. Select the responses panel in the analysis page.
2. Click response = and enter any name for eg cog 1.
3. Click on the switch below response type and select cog from the pop-up menu.
4. Click on x, y or z radio button, leave at total if the cog is to be global or choose the property (which in turn describes the design space)
5. Click create.
A response, cog 1, is defined for the cog of the model.
6. Click return to go to the Optimization Setup panel.

Create a design constraint

Now go to dconstraints and create a design constraint with the upper bound and the lower bound values of the cog coordinate.

1. Enter the dconstraints panel from the optimization panel.
2. Click constraint= and enter any name say cog constrain 1.
3. Check the box to the left of upper bound =.
4. Click upper bound = and enter the upper limit of the cog coordinate, do the same for the lower bound of the coordinate using the lower bound option.
5. Click response = and select cog 1 created above from the response list.
6. Click create.
7. Click return to return to the optimization panel.

Run the analysis

1. From the Analysis page, select OptiStruct.
2. Click save as…, enter any name with extension .fem as the file name, and click Save.
3. Click the run options: switch and select optimization.
4. Click OptiStruct to run the optimization.
The following message appears in the window at the completion of the job:
OPTIMIZATION HAS CONVERGED.
FEASIBLE DESIGN (ALL CONSTRAINTS SATISFIED).
OptiStruct also reports error messages if any exist. The file .out can be opened in a text editor to find details regarding any errors. This file is written to the same directory as the .fem file specified in step 3 above.