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How can extract the mass, stiffness and structural damping matrices from a .bdf file?

kenny.fernando.conto
Hi,
 
I need to extract the mass, stiffness and damping structural matrices from a .bdf files. Normally I just needed to add the following lines after BEGIN BULK in the .bdf file to get that:
 
"PARAM,EXTOUT,DMIGPCH"
"PARAM,COUPMASS,1"
 
Unfortunately when I'm trying to get that, Nastran is not able to create the .pch file where all information related to the matrices are stored.
 
So, How can I solve this problem? Is needed to add some addicional information inside to the .bdf file?
 
Thank you for your support
  • 0
    Hi- it would take more information to help you figure out why this isn't working.
    Is it possible to supply your input file? What version of Nastran are you running? What errors are you getting?
     
    I have attached a sample that works as expected... please try running it to see if that does what you want so we at least know if it 'can' work!
     
    Attached Files (1)
  • 0
    Hi,
    As I said before, in order to extract that information I only needed to write the following lines after BEGIN BULK in a .bdf:
    "PARAM,EXTOUT,DMIGPCH"
    "PARAM,COUPMASS,1"
     
    Unfortunately, when I tried to get that, the Nastran is not able to return me the PCH file where that information is stored.
     
    Actually I'm using the Apex model in order to generate the BDF files.
    The version of Nastran that I'm using is the 2019.0.
     
    I'm attaching the bdf file of my model.
     
    Thank you for your support.
  • 0
    When it is necessary to send us models, it is probably best to open a customer support case, rather than posting the model on this public forum.
     
    I ran your input file and see that there is a FATAL error- always check the f06 for errors. This FATAL is due to have MAT1 with an id of '1' twice in the input file. If you change one of them (and the corresponding PSHELL that uses it) to a new id, it should run.
     
    I changed:
     
    $ Material Record: Glass
    MAT1   1      6.6+10         .21    2500.                  .01
    $ Elements and Element Properties for Section: Mat1_01
    $ This PSHELL entry was generated from the following Apex objects
    $ Apex Behavior: Apex Default Behavior
    $ Apex Section: Mat1
    $ Apex Material: Glass
    PSHELL 463    1      1.-5   1              1
     
    to:
     
    $ Material Record: Glass
    MAT1   2      6.6+10         .21    2500.                  .01
    $ Elements and Element Properties for Section: Mat1_01
    $ This PSHELL entry was generated from the following Apex objects
    $ Apex Behavior: Apex Default Behavior
    $ Apex Section: Mat1
    $ Apex Material: Glass
    PSHELL 463    2      1.-5   2              2
     
     
  • 0
    Hi Graff,
     
    I think that is not the problem because I've modified my model in order to use just one material and, even like this, the Nastran cant be able to extract the matrices. I really would like to open a custumer suppor case in order to send you the Apex models and their bdf files.
     
    By the other hand, there is one way to extract the matrices from Nastran but this is not a practical way which is described below:
     
    1.- The only way in which the bdf file can be read by the NASTRAN is: Firstly: I have to copy the first forty lines from an old bdf file (this BDF file corresponts to old model made in APEX, i.e. Template.bdf) and copy all of then into the new BDF file (i.e. MyNewModel.bdf). Second, the following lines must be written after the "BEGIN BULK" and run it in NASTRAN:
    "PARAM,EXTOUT,DMIGPCH"
    "PARAM,COUPMASS,1"
     
    2.- If the matrices are getting using step 1, a PCH file is created. Unfortunately, in the matrices that I obtained, it must be content the information about all nodes, instead of that, the nodes which form part of two different FE-elements are deleted from the matrices in th PCH file.  I don't know if I need to do something else or write another line in the bdf file in order to get the matrices where all nodes are included.
     
    I really hope that issue can be solved shortly.
     
    I'm attaching both the Template.bdf and the new bdf files
     
    Thank you for your help.
     
    Fernando Conto
     
     
     
     
     
    Attached Files (1)
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