Meshing 2D to 1D interface FEMAP

[Burner2k]

Hi folks,
I am trying to determine if there is a way to copy or project an existing mesh seed (mesh seed in PATRAN is the basis for generating a mesh...kinda like telling software where on entity the elemental nodes while meshing, needs to be placed) on to a curve.

In Patran, for components like Skin-STR, the way I used to mesh is:

1. Mesh either the skin or Stringer first (usually Skin using 2D elements)

2. Project (copy) nodes from edge of Skin to an existing curve (STR)

3. Create a mesh seed from copied nodes on the curve

4. Create 1D elements from existing mesh seed

I like the above procedure because I can play around with meshing on the 2D surface to my satisfaction and still can get matching nodes on the curve. Merging coincident nodes (equivalence) is almost ensured by the above procedure.

Trying to replicate the same procedure in FEMAP. I tried projecting nodes on to a curve but it seems like no nodes are appearing on the curve entity. From FEMAP manual, I could gather that project in FEMAP is more like "moving" nodes rather than copying it like in Patran. Perhaps that is the reason why nodes aren't appearing on the curve? I also tried copying the mesh > nodes option, but the feature is more like copying nodes in space rather than copy on to an entity.

I am open to adopting a much more easier procedure if its possible in FEMAP.

Thanks & regards,
- B

 

[Burner2k]

Update: I found a way by going through the FEMAP Manual.

Mesh -> Mesh Control - > Custom Size on Curve -> Match Mesh

This gave me the desired result. I still would like to learn alternate ways (if exists) to accomplish the above in FEMAP.

 

[Burner2k]

Folks,
I am unsure if I should be doing type of a comparative study between two different FEM softwares, but anyways here it goes.

I did a stiffened panel with a racetrack (capsule shaped) cutout subjected to unidirectional axial forces. I created the geometry, FE model (meshing), defined element type, material property, elements property, constraints & loading in FEMAP.

Just for sake of comparison I exported a NASTRAN bdf file and had it imported in MSC PATRAN/NASTRAN. Ran the analysis in both packages. Intent was to get a better understanding of post-processing in FEMAP.

The total deformation values match in both packages. The peak Von Mises stress values is also matching in both magnitude & location within the model.

If I choose stress value in loading direction (in my case its Y), there is a markedly difference between Patran & FEMAP. In Patran, the peak stress & location is close to Von Mises output (< 10% difference). However when I choose Plate Top Y Normal Stress output in FEMAP, both the magnitude & location of peak stresses are changed. In FEMAP, the value is nearly 40% less than of Von Mises output. I feel like there is something I am missing in FEMAP. I tried changing the output orientation C/S to Global in Nodal, Plate Forces/Stress/Strain to Global & then to Y but I am not seeing any change in output values.

Also another curious observation. The 2D elements are defined as membrane but there is a difference in Normal stress output values between the plate top & bottom layers in FEMAP.

In PATRAN, the top & bottom (Z1 & Z2) values remain constant.

I have a feeling that I am not requesting the correct output contour in FEMAP. I would appreciate if more experienced folks in FEMAP would help elucidate post processing. I can provide any further info/pics as needed.

I can hit up the help desk but I am unsure if I can say that FEMAP is giving different values when compared to PATRAN

Thanks in advance,
- B

 

[rb1957]

is PATRAN showing the plate average (= membrane) and FEMAP the plate (= membrane+bending) ?

another day in paradise, or is paradise one day closer ?

 

[Burner2k]

The stress values across the thickness of the 2D element is uniform (membrane) in PATRAN, where as in FEMAP, the values are different. Come to think of it, you may be right RB1957. The stress values do not range from positive to negative (pure bending); both are positive but are of different magnitudes. So its probably membrane + bending.

Any suggestions RB1957, on why FEMAP is showing a different output value when compared to PATRAN?

 

[rb1957]

'cause maybe PATRAN is showing the plate CL (= membrane) results, 'cause maybe PATRAN thinks you've got a thin plate (without bending).

what is the .f06 file saying ? I mean PATRAN and Femap are only pre- and post-processors, and not FE codes. What are the underlying FEA results that they are trying to show ?

another day in paradise, or is paradise one day closer ?

 

[Burner2k]

RB1957,

The F06 files from both PATRAN & FEMAP show same output values for Membrane Forces. Posting an excerpt of them for your reference

FEMAP:

F O R C E S   I N   Q U A D R I L A T E R A L   E L E M E N T S   ( Q U A D 4 )        OPTION = BILIN  
 
    ELEMENT                    - MEMBRANE  FORCES -                      - BENDING   MOMENTS -            - TRANSVERSE SHEAR FORCES -
      ID       GRID-ID     FX            FY            FXY           MX            MY            MXY           QX            QY
0      9126    CEN/4  4.969427E+00  2.211816E+01  2.415492E+00  0.0           0.0           0.0           0.0           0.0
                9445  7.219423E+00  2.133038E+01  2.415713E+00  0.0           0.0           0.0           0.0           0.0
                9446  7.240109E+00  2.290835E+01  2.415921E+00  0.0           0.0           0.0           0.0           0.0
                9465  2.701882E+00  2.290507E+01  2.415268E+00  0.0           0.0           0.0           0.0           0.0
                9464  2.722568E+00  2.133366E+01  2.415066E+00  0.0           0.0           0.0           0.0           0.0
0      9127    CEN/4  5.702855E+00  1.247377E+01  1.232673E+01  0.0           0.0           0.0           0.0           0.0
                9553  2.559906E+00  1.094562E+01  1.175867E+01  0.0           0.0           0.0           0.0           0.0
                8974  2.079403E+00  1.398508E+01  1.210138E+01  0.0           0.0           0.0           0.0           0.0
                8975  9.311507E+00  1.399615E+01  1.294848E+01  0.0           0.0           0.0           0.0           0.0
                9555  8.725924E+00  1.112359E+01  1.250302E+01  0.0           0.0           0.0           0.0           0.0
0      9129    CEN/4 -2.704498E+00  1.980803E+01 -4.739243E+00  0.0           0.0           0.0           0.0           0.0
                9555 -1.723292E+00  2.029302E+01 -4.619415E+00  0.0           0.0           0.0           0.0           0.0
                9546 -1.726783E+00  1.933485E+01 -4.702972E+00  0.0           0.0           0.0           0.0           0.0
                9547 -3.710917E+00  1.929057E+01 -4.863889E+00  0.0           0.0           0.0           0.0           0.0
                9552 -3.699244E+00  2.031214E+01 -4.774175E+00  0.0           0.0           0.0           0.0           0.0
0      9130    CEN/4  2.083475E+01 -2.072709E-01  1.507577E+00  0.0           0.0           0.0           0.0           0.0
                9545  1.994909E+01  2.171786E+00  1.586057E+00  0.0           0.0           0.0           0.0           0.0
                9546  2.018188E+01 -2.343240E+00  1.364149E+00  0.0           0.0           0.0           0.0           0.0
                9555  2.149886E+01 -2.551261E+00  1.419747E+00  0.0           0.0           0.0           0.0           0.0
                9556  2.175710E+01  2.387784E+00  1.688341E+00  0.0           0.0           0.0           0.0           0.0
0      9131    CEN/4  6.360424E+00  1.982272E+01 -6.907729E+00  0.0           0.0           0.0           0.0           0.0
                9545  5.590028E+00  1.819054E+01 -7.301867E+00  0.0           0.0           0.0           0.0           0.0
                9556  5.673775E+00  2.141685E+01 -6.762075E+00  0.0           0.0           0.0           0.0           0.0
                8976  7.037451E+00  2.094579E+01 -6.612098E+00  0.0           0.0           0.0           0.0           0.0
                9544  6.968540E+00  1.874184E+01 -6.982785E+00  0.0           0.0           0.0           0.0           0.0
0      9132    CEN/4  7.215018E+00  1.963966E+01  1.001093E+01  0.0           0.0           0.0           0.0           0.0
                9555  5.798089E+00  1.658200E+01  8.593695E+00  0.0           0.0           0.0           0.0           0.0
                8975  6.791518E+00  2.241441E+01  1.087189E+01  0.0           0.0           0.0           0.0           0.0
                8976  8.587219E+00  2.297595E+01  1.151408E+01  0.0           0.0           0.0           0.0           0.0
                9556  7.725587E+00  1.630217E+01  8.975658E+00  0.0           0.0           0.0           0.0           0.0
0      9133    CEN/4  1.594914E+00  4.259715E+00 -1.211115E+01  0.0           0.0           0.0           0.0           0.0
                9553  1.960776E+00  8.900267E+00 -1.207947E+01  0.0           0.0           0.0           0.0           0.0
                9554  2.122225E+00 -1.031516E+00 -1.214281E+01  0.0           0.0           0.0           0.0           0.0
                8973  1.032269E+00 -2.292093E+00 -1.215611E+01  0.0           0.0           0.0           0.0           0.0
                8974  1.194651E+00  1.016080E+01 -1.207496E+01  0.0           0.0           0.0           0.0           0.0
0      9134    CEN/4  2.459303E+01  4.635577E+00  4.828727E+00  0.0           0.0           0.0           0.0           0.0
                8976  2.846647E+01  5.707854E+00  4.966055E+00  0.0           0.0           0.0           0.0           0.0
                8956  2.907081E+01  3.517280E+00  4.932869E+00  0.0           0.0           0.0           0.0           0.0
                9543  2.010475E+01  3.502368E+00  4.672130E+00  0.0           0.0           0.0           0.0           0.0
                9544  2.071145E+01  5.708644E+00  4.740851E+00  0.0           0.0           0.0           0.0           0.0
0      9135    CEN/4 -5.618246E+00  5.495642E+00 -8.151872E+00  0.0           0.0           0.0           0.0           0.0
1    STATIC PANEL                                                         SEPTEMBER  15, 2015  NX NASTRAN  5/ 5/15   PAGE    70

PATRAN:

F O R C E S   I N   Q U A D R I L A T E R A L   E L E M E N T S   ( Q U A D 4 )        OPTION = BILIN  
 
    ELEMENT                    - MEMBRANE  FORCES -                      - BENDING   MOMENTS -            - TRANSVERSE SHEAR FORCES -
      ID       GRID-ID     FX            FY            FXY           MX            MY            MXY           QX            QY
0      9126    CEN/4  4.969468E+00  2.211822E+01  2.415660E+00  0.0           0.0           0.0           0.0           0.0
                9445  7.219532E+00  2.133040E+01  2.415917E+00  0.0           0.0           0.0           0.0           0.0
                9446  7.240197E+00  2.290844E+01  2.416158E+00  0.0           0.0           0.0           0.0           0.0
                9465  2.701885E+00  2.290515E+01  2.415401E+00  0.0           0.0           0.0           0.0           0.0
                9464  2.722550E+00  2.133369E+01  2.415167E+00  0.0           0.0           0.0           0.0           0.0
0      9127    CEN/4  5.702811E+00  1.247386E+01  1.232670E+01  0.0           0.0           0.0           0.0           0.0
                9553  2.559890E+00  1.094570E+01  1.175863E+01  0.0           0.0           0.0           0.0           0.0
                8974  2.079404E+00  1.398517E+01  1.210134E+01  0.0           0.0           0.0           0.0           0.0
                8975  9.311414E+00  1.399623E+01  1.294846E+01  0.0           0.0           0.0           0.0           0.0
                9555  8.725850E+00  1.112368E+01  1.250299E+01  0.0           0.0           0.0           0.0           0.0
0      9129    CEN/4 -2.704433E+00  1.980798E+01 -4.739363E+00  0.0           0.0           0.0           0.0           0.0
                9555 -1.723258E+00  2.029291E+01 -4.619531E+00  0.0           0.0           0.0           0.0           0.0
                9546 -1.726733E+00  1.933486E+01 -4.703081E+00  0.0           0.0           0.0           0.0           0.0
                9547 -3.710847E+00  1.929057E+01 -4.864016E+00  0.0           0.0           0.0           0.0           0.0
                9552 -3.699156E+00  2.031203E+01 -4.774304E+00  0.0           0.0           0.0           0.0           0.0
0      9130    CEN/4  2.083479E+01 -2.072883E-01  1.507317E+00  0.0           0.0           0.0           0.0           0.0
                9545  1.994909E+01  2.171752E+00  1.585827E+00  0.0           0.0           0.0           0.0           0.0
                9546  2.018188E+01 -2.343248E+00  1.363830E+00  0.0           0.0           0.0           0.0           0.0
                9555  2.149893E+01 -2.551370E+00  1.419448E+00  0.0           0.0           0.0           0.0           0.0
                9556  2.175719E+01  2.387858E+00  1.688159E+00  0.0           0.0           0.0           0.0           0.0
0      9131    CEN/4  6.360506E+00  1.982264E+01 -6.907715E+00  0.0           0.0           0.0           0.0           0.0
                9545  5.589988E+00  1.819045E+01 -7.301874E+00  0.0           0.0           0.0           0.0           0.0
                9556  5.673764E+00  2.141676E+01 -6.762078E+00  0.0           0.0           0.0           0.0           0.0
                8976  7.037619E+00  2.094573E+01 -6.612068E+00  0.0           0.0           0.0           0.0           0.0
                9544  6.968735E+00  1.874172E+01 -6.982759E+00  0.0           0.0           0.0           0.0           0.0
0      9132    CEN/4  7.215245E+00  1.963938E+01  1.001109E+01  0.0           0.0           0.0           0.0           0.0
                9555  5.798303E+00  1.658171E+01  8.593880E+00  0.0           0.0           0.0           0.0           0.0
                8975  6.791689E+00  2.241414E+01  1.087201E+01  0.0           0.0           0.0           0.0           0.0
                8976  8.587437E+00  2.297565E+01  1.151418E+01  0.0           0.0           0.0           0.0           0.0
                9556  7.725892E+00  1.630191E+01  8.975871E+00  0.0           0.0           0.0           0.0           0.0
0      9133    CEN/4  1.594726E+00  4.259722E+00 -1.211111E+01  0.0           0.0           0.0           0.0           0.0
                9553  1.960628E+00  8.900353E+00 -1.207945E+01  0.0           0.0           0.0           0.0           0.0
                9554  2.122061E+00 -1.031482E+00 -1.214274E+01  0.0           0.0           0.0           0.0           0.0
                8973  1.032052E+00 -2.292215E+00 -1.215602E+01  0.0           0.0           0.0           0.0           0.0
                8974  1.194416E+00  1.016105E+01 -1.207494E+01  0.0           0.0           0.0           0.0           0.0
0      9134    CEN/4  2.459288E+01  4.635702E+00  4.828874E+00  0.0           0.0           0.0           0.0           0.0
                8976  2.846632E+01  5.708115E+00  4.966161E+00  0.0           0.0           0.0           0.0           0.0
                8956  2.907058E+01  3.517264E+00  4.932976E+00  0.0           0.0           0.0           0.0           0.0
                9543  2.010469E+01  3.502381E+00  4.672329E+00  0.0           0.0           0.0           0.0           0.0
                9544  2.071131E+01  5.708886E+00  4.741031E+00  0.0           0.0           0.0           0.0           0.0
0      9135    CEN/4 -5.618423E+00  5.495655E+00 -8.151755E+00  0.0           0.0           0.0           0.0           0.0
1   STATIC PANEL                                                          SEPTEMBER  15, 2015  MSC Nastran 11/13/14   PAGE    73

The values are the same. So definitely output vector in FEMAP is indeed presenting (at least for me) an incorrect value.

 

[Burner2k]

OK.

So I checked the local 2D elemental co-ordinates in FEMAP and it looks like each element has its own co-ordinate system. How can I modify all the 2D plates to an uniform local C/S?

I have a feeling that I am getting erroneous values when I chose component output vector in FEMAP is due to the above.

Edit: I made sure the elemental material orientation aligns towards Global X-Axis. Then when I choose Plate Top Y Normal Stress and then in the Plate Force/Stress/Strain -> Material Direction, the output values are matching PATRAN (or F06) values.

Further, the membrane property seems to have preserved. Obtaining uniform stress values across the thickness of Plate.

I would love to hear any improvement if possible on the above procedure.

Thanks & regards

 

[Burner2k]

Folks,
Is there any way to make all the element coordinate systems align? When I open the FEMAP supplied examples, the element coordinate systems are all beautifully aligned with each. When I mesh, the elemental coordinate systems are all off sync.

I have gone through both FEMAP User Guide & Command guide and have found nothing referenced to accomplish the above.

Would appreciate if experienced users would suggest a way to do the above. I can do the above in PATRAN using Meshing -> Modify -> Element -> Shell Orientation.

 

[ThomasH]

Hi
I have a vague regarding this.

I you are using MSC/Nastran i thing you need to transform the results into the Material directions. Model-Output-Transform. I think it was something like that.
Today I work with NEI/Autodesk Nastran and there I get the results directly in the material directions so I can't test it.

But it might help you.

Thomas

 

[ThomasH]

And it should be vague memory .

 

[Burner2k]

ThomasH,
Thanks for the reply.

My question (latest one) was not so much as on how to change the output C/S to a specific one rather than how to modify or change the 2D (or 3D) elemental coordinate system once the mesh is created.

In the stiffened panel, the skin has quad mesh and if I display the elemental coordinate system of each element, the X & Y orientation are all over the place. Where as in FEMAP supplied examples, the X & Y axes of all elements are in the same directions.

I wanted to know if there is a way to modify the elemental coordinate system so that I can make all element's X & Y axes orientation same.

 

[ThomasH]

Burner2k

Have you tried Modify-Update Elements-Material Orientation? That is a method to control the orientation for 2D elements.

Regarding my previous comment. That method was to transform the results from MSC.Nastran to the elements local orientation. I remember tat there were some issues for moments in slabs.

Thomas