Load factor coefficients for post-processing

[benoit.neu-faber]

Hi,

I would like to run an analysis that have two load cases :

- Gravity

- External CFD load

The post-processing has to be made in different cases :

- 1.2G + 1.2 CFD load

- 1.1G + 1.5 CFD load

- ...

Is there a way to that ?

Thanks

[John_Holtz · Accepted solution]

Hi @benoit.neu-faber 

You need to setup the subcases for the loads before you run the analysis. In other words, you cannot create new combinations from the results after the analysis is completed. The general steps are as follows:

1. Create all of the subcases needed. In fact, you should create the first subcase with all of the loads that are needed for any subcase, and then duplicate the subcases as many times as needed. For example, apply gravity with a value of 9.81 m/s^2 (not 1.2 times gravity), apply the CFD load, etc. Then when you duplicate the subcase, all of the loads and constraints will be applied to the new subcases.
2. Rename the subcases so that you can identify them in the Nastran file, such as "1.2 G + 1.2 CFD" and "1.1 G + 1.5 CFD".
3. Instead of running the analysis, generate the Nastran file. (Right-click in the model tree and choose "Generate Nastran File".) This will show the Nastran File tab.
4. The subcases are listed near the top, and the label indicates which LOAD corresponds to which subcase. Locate the corresponding LOAD command further down in the file. Edit the multipliers (columns 4, 6, 8, ...) to scale the loads as needed. (See Figure 1.)
5. Click the first button on the toolbar to "Run Nastran File". Do not use the "Solve > Run" button on the ribbon because that will overwrite the manual changes you make.

 Figure 1: A portion of the Nastran file. Load 8 (for the second subcase) equals 1.1 times load 5 plus 1.5 times load 6 (whatever loads 5 and 6 are). The numbers added to the figure correspond to the following:

1. The LABELs in the SUBCASE section are the names that you entered for the subcases. (Step 2 above.)
2. The LOAD = n command corresponds to the LOAD ID commands further down in the file. LOAD 7 is for the first subcase (ID 3 in this example, but the ID number 3 is not important), LOAD 8 is for the second subcase, and so on.
3. The LOAD command in the BULK section gives an equation that multiplies individuals loads and adds them together to create the total load for the subcase. The value in column 3 scales the entire equation and defaults to 1.0. This number is normally not changed.
4. Item 4 (in columns 4, 6, ...) are the multipliers for each type of load. The default values will be 1.00. You need to change these to give the load magnitude that is required.
5. Item 5 (in columns 5, 7, ...) is the ID number for each individual load. You need to look further down in the file to find the actual load information (such as GRAV for the gravity load, PLOAD4 for a pressure load, FORCE for a force, etc.) to see what load corresponds to ID 3, 4, 5, and 6. (The second column of the GRAV, PLOAD4, FORCE, ... card is the ID number that corresponds to item 5.) Naturally, the multipliers (item 4) need to be the appropriate value for the appropriate load.

[benoit.neu-faber]

@John_Holtz 

Awesome answer !!!

Thanks

Benoit