1- Open GiD file called staticgear.gid. This file is localized in the Examples folder in the GiD installation directory.
To get this file, use the Internet Retrieve option of GiD and download Nastran Examples.
Internet Retrieve option is available under:
Data ->Problem Type -> Internet Retrieve
For more information see GiD manuals.
Comment:
If you want to create the gear's CAD model manually without downloading it, see the Post-process Tutorial of GiD, which can be obtained from the GiD web page in Support section.
With the target to obtain a good mesh some changes in meshing preferences of GiD have to be made.
1- Open Preferences window:
Utilities -> Preferences
2- Select meshing tab and set window entries to the following values:
Surface mesher: Rsurf
Mesh until end: Activated
Automatic correct sizes: Activated
Unstructured size transition: 0.6
Smoothing: High Angle
No mesh frozen layers: Activated
Allow automatic structured: Disable
These settings will prevent the creation of tetrahedron elements with seek angle bigger than 80 degrees. Please note, that gear's CAD model is designed like unique volume to allow the creation of a correct finite element model.
1- Define and assign the properties for the surface.
Data -> Properties -> Property
Select from the top combo boxes the property Tetrahedron.
Click on the following icon to create a new
property:
Enter name for the new property gear.
Fill all statements like in the picture:
Make sure, that a one of the default materials is defined in Composition Material.
Click on the following icon to save the new
property:
Now click on the Assign button, and select the unique volume of the geometry.
To see if the property is well assigned click on Draw button, select This property option.
The NASTRAN Interface program window should look like this:
1- Assign prescribed displacements and rotation.
Data-> Boundary Conditions -> Constraints
Click on the following icon to set the condition over surfaces:
The model has the two lids of octagonal axis pinned, which means that all degrees of freedom have to be prescribed.
To do this it is necessary to check all statements.
2- Select the two lids of octagonal cylinder (axis of the gear).
Assign Normal distributed pressure over one tooth of the gear.
Data -> Loads -> Static Loads
Click on the following icon to set the condition over surfaces:
From the top combo box static load select Normal-Surface-Load.
Set the value of the load to 2e4 (positive sign means that
load is oriented inward to the surface) and select the three interior surfaces of one tooth of the gear, as stated in the following image:
Design Executive Control Section.
Data -> Problem Data -> Executive Control
Select the NASTRAN Type you want to use for the analysis.
Check STATICS and leave all the other statements uncheck.
Leave the rest of statements with the default values.
Click on the Accept Data button.
2 - Design Case Control Section.
Data -> Problem Data -> Case Control
2.1. - Input data
In this example we don't consider the acceleration due to the gravity. Leave all statements with default values.
2.2. - Output data
Set Title to “Gear_example”
Select which format file you want to use:
- Small: Every file of a Bulk Data statement will use the 8- characters definition.
- Large: Every file of a Bulk Data statement will use the 16- characters definition.
Check Displacements, constraints forces, elements forces and elements stresses, uncheck the rest of output requests.
In Output Design section leave the default values.
Note: If you want to post process the results of MI/NASTRAN analysis with NASTRAN Interface, you have to set the output device to PUNCH.
Click on the Accept Data button.
1-Create a mesh.
Meshing -> Generate
Now you are asked about the size of elements to be generated, set the value to 18.
Click on the OK button
The following mesh information window appears when the mesh is created:
Num. of Tetrahedra elements = 45100
Num. of nodes = 13728
Option 1:
Calculate -> Calculate
Option 2:
File -> Import/Export -> Write Calculation File
Select a folder and a file name to write the file. It is very important to write the correct extension of the NASTRAN input file (i.e. *.nas, *.dat, *.nid …).
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