Some problems with Nastran

[snide]

I have some problems: when i generate surface as a boundary surface (by boundary curves) the bending moment diagram isn't same as when i generate surface by 4 corners.
Properties of generated surfaces:
1 Boundary surface (by 4 curves)
- width 100cm
- length 200cm
- thickness 20cm
- mass density 2500kg/m3
- E 3000000000000
- nu 0.3
- Type element plate
- Acceleration gravity 9.81 m/sec/sec
- constraint pinned (by short edges (width))

2 Surface (by 4 corners)
- width 100cm
- length 200cm
- thickness 20cm
- mass density 2500kg/m3
- E 3000000000000
- nu 0.3
- Type element plate
- Acceleration gravity 9.81 m/sec/sec
- constraint pinned (by short edges (width))

As you can see all properties of these generated surfaces are similar. Why the bending moment diagrams different.How can i achieve these bending moment diagrams similar.

 

[renelcm]

Hello snide

I'd like to help you but before starting some tests here, I would like to have more information about your problem.

You said that the bending moments aren't the same, right? Where are you checking it? In the border? In the middle? In the same elements in both surface construction? I have to agree with chandransss that I have never used bending moments in plate elements. Only in line ones (bar and beams).
Another question: since you are using 2 surfaces built differently, do they have the same mesh configuration? That’s might be another problem.

I’ll wait your reply.

Bye

renelcm

 

[Ishmael]

snide,

the plate bending moments MX MY are referred to the ELEMENT csys, not in the GLOBAL! Even if the elements in the two models look the same, their csys may be different, and consequently you would obtain different moments.
Each element has his own coordinate system, take a look of the manual to see how it's defined.
To check model it's better to evaluate displacements (in the SAME point!) and stress invariants, such as Von Mises, Max/Min Principal

Hope that helps