[MBDyn-users] How to change the aerodynamic output ?

Rix, Patrick Patrick.Rix at repower.de
Mon Mar 22 11:09:57 CET 2010

Hello MBDyn-team,

I'd like to know how to change the aerodynamic output from the default setting "Coefficients at Gauss points" to "Node" giving nodal aerodyn. forces & couples.

The input-manual states in chapter 8.1.1 about the aerodynamic elements:
"...Three different formats are available; the format can be selected only at compile time, so it must be the same for all the elements. Note: eventually the format will freeze; if all the output formats are be maintained, they will be made selectable at run-time, on a per-element basis."

Unfortunately it is not mentioned if it is already run-time selectable AND/OR  how or where to set the switch in the code at compile-time. Browsing the source code in  /mbdyn/aero/  I found in aeroelem.cc and aeroelem.h various definitions of binary constants (like: AEROD_OUT_STD,  AEROD_OUT_PGAUSS,  AEROD_OUT_NODE ) and keyword-checks for the parser.

What is unclear to me:
It looks like MBDyn is already capable of switching the aero-output at run-time but I found no way to make the parser accept my output statements: It always complies about invalid output modes after the line "jacobian, yes" .
The only thing that worked after the jacobian statement was "output, yes" or "output, no".

Reading the code in aeroelement.cc I can see in function ReadAerodynamicBeam(...) that after having read the aerodata and an optional "jacobian,yes" a function ReadOptionalAerodynamicCustomOutput(...) is called which honours the (optional) key combination "custom"+"output" invoking ReadAerodynamicCustomOutput(...) which looks for one of the keywords ["position"|"orientation"|"velocity"|"velocity"|"angular"+"velocity"|"configuration"|"force"|"moment"|"forces"|"all"].
The next line in ReadArodynamicBeam() is
   flag fOut = pDM->fReadOutput(HP, Elem::AERODYNAMIC);
calling function DataManager::fReadOutput(...) reading an optional "output" followed by ["yes"|"no"|"default"].
Then in ReadArodynamicBeam() subsepuently checks for one of the keywords ["std"|"gauss"|"node"] which for my understanding should be the desired switch for changing the aero output.

So resuming the above the definition of an aerobeam element could have the last 3 optional lines as follows:

    [ jacobian , { yes | no | <bool> } , ]
    [ custom output , { position | orientation | velocity | angular velocity | configuration | force | moment | forces | all } ]
    [ output , {yes | no | default }  [ , { std | gauss | node  } ] ]

Is this code  interpretation correct ?

Would this change of aero-output affect both destination files, i.e. the ascii output in *.aer and the binary *.nc file (assumed that MBDyn(>= 1.3.13) was compiled with NetCDF support and "output: netcdf;" was given in the model) ?

Any help on that would be very appreciated.

Kind regards,

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