FEMCI Book - Modal Mass Participation Output From MSC.NASTRAN


		Modal Mass Participation (Effective Weights) From MSC.NASTRAN Jeff Bolognese Goddard Space Flight Center Two methods are given here for determining the modal mass participation using MSC.NASTRAN. 1. Using MEFFMASS case contol commnad (for MSC/NASTRAN 2001) 2. Using Modal Participation DMAP (for MSC/NASTRAN v. 70.5) Method 1. MSC/NASTRAN version 2001 has the capability to extract modal mass participation directly from nomal modes analysis. No DMAP is required and it can be used with the normal modes solution sequence (unlike the UAI command on which it is based). The following is a sample executive and case control deck for a normal modes run with modal mass extraction. The cards that are specific for the modal mass extraction are shown in bold. Sample Input ID XYZ,MODALWT SOL 103 TIME 10 APP DISP CEND TITLE=XYZ TEST VERIFIED MODEL (english - renumbered) (08/96) SUBTITLE=FIXED BASE DYNAMICS W/ASET SPC=1 echo=none SPCFORCE=ALL METHOD=100 MEFFMASS(ALL)=YES BEGIN BULK
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Sample Output


           M O D A L   E F F E C T I V E   M A S S   S U M M A R Y



                           TOTAL EFFECTIVE MASS FRACTION
                 REFERENCE POINT AT ORIGIN OF BASIC COORDINATE SYSTEM


     T1                T2                T3                R1              R2             R3
3.948519E-01      7.700374E-01      9.790530E-01      9.802241E-01    5.374004E-01    4.438883E-01

(This is the total percentage of mass represented in the number of modes extracted in the EIGR card)



                                 EFFECTIVE MASS MATRIX   
***                                                                                  ***
*   1.301470E-02 -1.445757E-05  6.120819E-04 -1.217158E-02  7.967635E-01  2.766647E-01 *
*  -1.445757E-05  2.536148E-02 -3.641499E-04  3.149053E-03 -8.146847E-04 -3.397166E-04 *
*   6.120819E-04 -3.641499E-04  3.227054E-02 -6.531930E-01  2.772698E-02  1.234497E-02 *
*  -1.217158E-02  3.149053E-03 -6.531930E-01  1.323802E+01 -5.505087E-01 -2.455033E-01 *
*   7.967635E-01 -8.146847E-04  2.772698E-02 -5.505087E-01  4.954358E+01  1.663506E+01 *
*   2.766647E-01 -3.397166E-04  1.234497E-02 -2.455033E-01  1.663506E+01  6.176721E+00 *
***                                                                                  ***

                                 A-SET RIGID BODY MASS MATRIX
***                                                                                  ***
*   3.296097E-02  9.154070E-21 -5.196499E-20  9.980221E-19  1.717233E+00  6.654800E-01 *
*   9.154070E-21  3.293540E-02 -6.146909E-22 -5.571844E-05  3.835558E-19  1.002346E-04 *
*  -5.196499E-20 -6.146909E-22  3.296097E-02 -6.654800E-01 -9.742095E-05 -9.906851E-19 *
*   9.980221E-19 -5.571844E-05 -6.654800E-01  1.350510E+01  1.926013E-03 -2.541951E-05 *
*   1.717233E+00  3.835558E-19 -9.742095E-05  1.926013E-03  9.219119E+01  3.458480E+01 *
*   6.654800E-01  1.002346E-04 -9.906851E-19 -2.541951E-05  3.458480E+01  1.391504E+01 *
***                                                                                  ***

                                          MODAL EFFECTIVE MASS FRACTION (Translations Only)

MODE   FREQUENCY                     T1                                  T2                                  T3
NO.                      FRACTION            SUM             FRACTION            SUM             FRACTION            SUM

1    3.443978E+01      1.087428E-07      1.087428E-07      2.878337E-01      2.878337E-01      4.671222E-04      4.671222E-04
2    9.164602E+01      1.037630E-07      2.125058E-07      3.013015E-03      2.908467E-01      1.752554E-01      1.757225E-01
3    9.314177E+01      1.176210E-06      1.388716E-06      8.141640E-06      2.908548E-01      8.531422E-05      1.758078E-01
4    9.319604E+01      6.164517E-09      1.394880E-06      4.916736E-07      2.908553E-01      6.009478E-05      1.758679E-01
5    1.190980E+02      5.566692E-04      5.580641E-04      7.114702E-05      2.909265E-01      3.210024E-07      1.758682E-01
6    1.246129E+02      4.152403E-05      5.995881E-04      1.206140E-01      4.115404E-01      2.999131E-06      1.758712E-01
7    1.332887E+02      1.709978E-07      5.997591E-04      1.782257E-01      5.897661E-01      3.270761E-04      1.761983E-01
8    1.387781E+02      1.097554E-07      5.998688E-04      9.015527E-02      6.799214E-01      1.928480E-04      1.763912E-01
9    1.720068E+02      5.168283E-06      6.050371E-04      3.729035E-07      6.799218E-01      8.354106E-07      1.763920E-01
     (etc...)


                                          MODAL EFFECTIVE MASS FRACTION (Rotations Only)
 
MODE   FREQUENCY                     R1                                  R2                                  R3
NO.                      FRACTION            SUM             FRACTION            SUM             FRACTION            SUM

1    3.443978E+01      5.643318E-04      5.643318E-04      1.352309E-07      1.352309E-07      1.171721E-07      1.171721E-07
2    9.164602E+01      1.997144E-01      2.002787E-01      3.633747E-07      4.986056E-07      2.032208E-07      3.203930E-07
3    9.314177E+01      9.733624E-05      2.003761E-01      1.086912E-06      1.585518E-06      1.360715E-06      1.681108E-06
4    9.319604E+01      6.838387E-05      2.004444E-01      2.265038E-09      1.587783E-06      1.896154E-09      1.683004E-06
5    1.190980E+02      2.877842E-07      2.004447E-01      5.968428E-04      5.984306E-04      1.837002E-02      1.837171E-02
6    1.246129E+02      8.937288E-06      2.004537E-01      3.818008E-05      6.366107E-04      6.438512E-05      1.843609E-02
7    1.332887E+02      4.437017E-04      2.008974E-01      7.682432E-07      6.373789E-04      7.551849E-07      1.843685E-02
8    1.387781E+02      2.582847E-04      2.011557E-01      5.440199E-09      6.373844E-04      3.157543E-08      1.843688E-02
9    1.720068E+02      6.662045E-07      2.011563E-01      5.183653E-06      6.425680E-04      5.199454E-06      1.844208E-02
     (etc...)

                                              MODAL PARTICIPATION FACTORS

MODE   FREQUENCY            T1                T2                T3                R1                R2                R3
NO.

1    3.443978E+01     -5.986876E-05     -9.736486E-02     -3.923876E-03      8.730038E-02     -3.530878E-03     -1.276892E-03
2    9.164602E+01      5.848186E-05     -9.961669E-03     -7.600386E-02      1.642304E+00      5.787913E-03      1.681614E-03
3    9.314177E+01     -1.968985E-04     -5.178302E-04     -1.676914E-03      3.625652E-02     -1.001018E-02     -4.351368E-03
4    9.319604E+01      1.425442E-05     -1.272535E-04     -1.407403E-03      3.038965E-02      4.569645E-04      1.624347E-04
5    1.190980E+02     -4.283498E-03      1.530770E-03     -1.028618E-04      1.971435E-03     -2.345712E-01     -5.055883E-01
6    1.246129E+02      1.169903E-03      6.302753E-02      3.144110E-04     -1.098631E-02      5.932847E-02      2.993194E-02
7    1.332887E+02     -7.507498E-05     -7.661549E-02     -3.283405E-03      7.740952E-02     -8.415774E-03     -3.241670E-03
8    1.387781E+02     -6.014686E-05      5.449128E-02      2.521202E-03     -5.906065E-02     -7.081938E-04     -6.628523E-04
9    1.720068E+02      4.127368E-04      1.108229E-04      1.659396E-04     -2.999526E-03      2.186063E-02      8.505915E-03
     (etc...)

                                                  MODAL EFFECTIVE MASS   

MODE   FREQUENCY            T1                T2                T3                R1                R2                R3
NO.

1    3.443978E+01      3.584268E-09      9.479916E-03      1.539680E-05      7.621356E-03      1.246710E-05      1.630454E-06
2    9.164602E+01      3.420128E-09      9.923486E-05      5.776588E-03      2.697162E+00      3.349994E-05      2.827825E-06
3    9.314177E+01      3.876902E-08      2.681481E-07      2.812040E-06      1.314536E-03      1.002037E-04      1.893440E-05
4    9.319604E+01      2.031885E-10      1.619346E-08      1.980782E-06      9.235310E-04      2.088166E-07      2.638505E-08
5    1.190980E+02      1.834836E-05      2.343255E-06      1.058055E-08      3.886554E-06      5.502365E-02      2.556195E-01
6    1.246129E+02      1.368672E-06      3.972469E-03      9.885427E-08      1.206990E-04      3.519867E-03      8.959212E-04
7    1.332887E+02      5.636253E-09      5.869933E-03      1.078075E-05      5.992234E-03      7.082525E-05      1.050842E-05
8    1.387781E+02      3.617645E-09      2.969299E-03      6.356459E-06      3.488161E-03      5.015384E-07      4.393732E-07
9    1.720068E+02      1.703516E-07      1.228172E-08      2.753594E-08      8.997157E-06      4.778871E-04      7.235059E-05
     (etc...)

The type of information presented by the MEFFMASS card can be modifed. Check the MSC user manual for information on the parameters available for this card.

Method 2.

If you don't have MSC.NASTRAN 2001, the modal mass participation can also be extracted using a DMAP. Simply place the DMAP in the executive control section of your NASTRAN data deck, generally right before the CEND card. Or you can use an INCLUDE statement that refers to a text file, e.g., MPF_v705.dmp with the DMAP in it, e.g., INCLUDE '\path\MPF_v705.dmp'. Comment lines can be removed from the DMAP to keep things short. The MSC NASTRAN modal participation DMAP and description can be found in the DMAP library page.

Jeff Bolognese

Modal Mass Participation (Effective Weights)From MSC.NASTRAN

Jeff Bolognese Goddard Space Flight Center

Method 1.

Method 2.

Modal Mass Participation (Effective Weights)
From MSC.NASTRAN

Jeff Bolognese
Goddard Space Flight Center