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API for Model Kinetic Energy

Hi,

I'm working on a transient dynamics model and need to calculate the total Kinteic energy of the model for each time step / result.

 

Currently using FEMAP with NXNASTRAN version 11.3.2

 

Does anybody have a suitable API?

 

Many thanks

Jeff

5 REPLIES

Re: API for Model Kinetic Energy

Are you getting the element kinetic energies in Femap and just need an api to sum them up? Or do you need help getting the element kinetic energy actually calculated by Nastran so it is available? Nastran only outputs this result for modal transient solution and you must use param,ddrmm,-1 also.

 

If you have the the EKE Case control request added to the deck, then you could also use the "print" option( if the problem is not too big) and in addition to the individual elements values, the f06 will have the totals for each step.

 

Regards,

 

Joe

Re: API for Model Kinetic Energy

Hi Joe,
I don’t believe NASTRAN or FEMAP report kinetic energy, if anybody knows any different please shout.

So the KE will need to be determined by calculating the following for each element from the NASTRAN results:

CoG
Mass
Resultant rotation velocity
Resultant translational velocity
KE =1/2MV^2 +1/2 I W^2

Re: API for Model Kinetic Energy

Nastran does calculate kinetic energy for some cases. See the QRG for the 2 case control commands:

EKE which requests element kinetic energy

GPKE which requests grid point kinetic energy

There are some limitations described in the QRG. Like for modal transient, you need to set param,ddrmm,-1

Some of these options are supported in Femap in the Analysis Set Manager, however, you can also add the case control commands manually via "Start Text" and Femap does support reading of the results. As I pointed out, the f06 actually contains the summation of the element kinetic energy if you request printed output, but you could use API in Femap to sum the element values . The data table should make it easy to do and organize.

The case control section would like something like this:

CEND
TITLE = Direct Transient
ECHO = NONE
DISPLACEMENT(SORT1,PLOT) = ALL
ACCELERATION(SORT1,PLOT) = ALL
SPCFORCE(SORT1,PLOT) = ALL
SPC = 1
DLOAD = 1
METHOD = 1
TSTEP = 1
EKE(print)=all
BEGIN BULK
$ ***************************************************************************
$ Written by : Femap with NX Nastran
$ Version : 11.3.2
$ Translator : NX Nastran
$ From Model : C:\apps\FEMAPv1132\Examples\Dynamics\Direct Transient\directdone.modfem
$ Date : Mon Apr 03 10:53:49 2017
$ ***************************************************************************
$
PARAM,PRGPST,YES
PARAM,POST,-1
PARAM,OGEOM,NO
PARAM,AUTOSPC,YES
PARAM,GRDPNT,0
CORD2C 1 0 0. 0. 0. 0. 0. 1.+FEMAPC1
+FEMAPC1 1. 0. 1.
CORD2S 2 0 0. 0. 0. 0. 0. 1.+FEMAPC2
+FEMAPC2 1. 0. 1.
PARAM,G,.2
PARAM,W3,565.4867
PARAM,DDRMM,-1

 

 

Here is a sample of the F06 information:

 

2017-04-04 08_07_23-TextPad - C__apps_FEMAPv1132_Examples_Dynamics_Direct Transient_directdone-001.f.png

 

 

 

 

 

Regards,

 

Joe

Re: API for Model Kinetic Energy

Joe,
Many thanks that I will try those params out.

Regards
Jeff

Re: API for Model Kinetic Energy

Ke is not reported for NL Transient analysis according to QRG.

 

So does anybody have an API? Or something that would get me going so to speak - I've never written an API before.

 

Regards

 

Jeff