Centre of gravity

[ananthaces]

is there a way nastran can caluclate the centre of gravity for the whole model because i want to apply my loads at this point and i have planar model.Thanks.

 

[GBor]

In NENastran's modeler, it is "Tools: Mass Properties: Mesh Properties". "Select All" at the element dialog box and hit "OK". Double click on the screen at the bottom to enlarge it to the size of the interface window.

If you are using a different flavor of Nastran pre-processor, this is probably useless.

Garland E. Borowski, PE

 

[ananthaces]

Thanks Gbor, I have another question. how do i cut a hole in NE/Nastran in a planar model.Thanks

 

[GBor]

Not sure I fully understand the question, but, basically, you delete elements. I tend to draw the geometry for the hole that I need and delete all the elements or lines that I see within the geometry. FEMAP will delete the nodes when you do the check on the geometry. The problem with this is that you occasionally create 5 (or more)-sided elements that won't decode, so you may have to add a line back to reduce the elements to 3 or 4 sided.

Depending on how simple the planar geometry is, you may want to delete the entire mesh, draw the hole in the plane and remesh.

Garland E. Borowski, PE

 

[ananthaces]

what i meant was ,if i have a plate with a hole how do i model that hole on the plate.the plate is 2-dimensional.so in the modeling even before meshing how do i create this hole on the plate.Thanks

 

[ThomasH]

Provided you have som "advanced" geometry engine active you should be able to either add/remove material using the solid commands or slice your surface and remove the redundant parts. The most convinent method depends on what exactly you want to do and your geometry.

Regards

Thomas

 

[ananthaces]

the advanced geometry engine is active and if i switch it off it is not letting me get into the solid section at all.So, how do i just cut a hole on a 2d-plate.I have tried lot of things but it isnt working.Like i used solid feature but since my geometry is 2d in nature its not allowing me to remove hole. Any ideas?

 

[ThomasH]

I tried by first creating a surface. Then another surface within the boundarys of the first one. (I don't think that you have to be within the boundarys but mine was). Then I used the solid-remove command with the first surface as primary.
I think you can also (if needed) extrude the second surface to a 3d solid to make sure that it goes entirely trough the first one.

I tried it and it worked just fine for my. I worked with the parasolid engine if that makes any difference. I think that parasolid is the "native" engine within femap.

Good Luck

Thomas

 

[GBor]

ananthaces,

Again, I think I'm missing something. It sounds like you have a planar plate lying in 2 dimensions (the x-y plane, perhaps), but that it was modeled as a solid, so your elements are bricks, not quads. If you are, in fact, attempting to create plate elements, then the plate would be a rectangle and the hole would be an interior circle (somewhat like ThomasH described). If you automesh this geometry, 2-D elements will be formed from the rectangle to the circle, but not inside the circle. You then define the thickness in your "property" that is tied to those elements. If you would prefer to turn them into bricks, you can copy the 2-D mesh remembering that you need at least 3 bricks through the thickness to get reasonable results.

Not sure if this rambling answered your question, but hopefully it helps.

Garland

Garland E. Borowski, PE

 

[ananthaces]

GBor, thanks for your reply. I actually found a way to create a circular cut out on a 2 dimensional model.
Geometry>curve from surface> project and delete>surface are the commands used for this purpose. Thanks.