AltairUser
Automotive
- Dec 19, 2012
- 2
I am working on a rough road analysis using sol 112. This is spotweld life analysis on a
full car. We use the load time history measured during the test.
I tried two options for the frequency range:
OPTION1:
frequency in 0.0-100 Hz range to get the RB modes
EIGRL 400.0 100.0 MASS
My top 7 frequencies are:
1.111156E-02
1.313891E-02
1.485175E-02
1.602749E-02
1.630331E-02
1.651331E-02
2.662587E+01
The top 6 appear to be RB modes but they do not meet the criteria suggested in the Nastran manual (A good acceptance criteria is to have the rigid body modes
frequency being less than 0.0001x(first flexible mode frequency).
Should I be including these frequencies in my fatigue calculation? If I include these, I see lot more damage.
OPTION2:
The other thing I tried was requesting frequency in 0.5-100 Hz range
EIGRL 400.5 100.0 MASS
The analysis runs fine but it gave me the following warning messages:
^^^ USER WARNING MESSAGE 9128 ( AUTOSPRT)
^^^ F1 ON THE EIGR OR EIGRL ENTRY IS GREATER THAN 0. AND THEREFORE AUTO-SUPORT CANNOT BE PERFORMED.
^^^
*** USER INFORMATION MESSAGE 4158 (DFMSA)
---- STATISTICS FOR SPARSE DECOMPOSITION OF DATA BLOCK KYY FOLLOW
NUMBER OF NEGATIVE TERMS ON FACTOR DIAGONAL = 0
MAXIMUM RATIO OF MATRIX DIAGONAL TO FACTOR DIAGONAL = 1.2E+11 AT ROW NUMBER 5890532
*** SYSTEM INFORMATION MESSAGE 4159 (DFMSA)
THE DECOMPOSITION OF KYY YIELDS A MAXIMUM MATRIX-TO-FACTOR-DIAGONAL RATIO OF 1.212805E+11
*** USER WARNING MESSAGE 4698 (DCMPD)
STATISTICS FOR DECOMPOSITION OF MATRIX KYY.
THE FOLLOWING DEGREES OF FREEDOM HAVE FACTOR DIAGONAL RATIOS GREATER THAN
1.600000E+08 OR HAVE NEGATIVE TERMS ON THE FACTOR DIAGONAL.
USER INFORMATION:
THIS MESSAGE MAY BE IGNORED IF NO GRID POINT IDS OR HIGH RATIO MESSAGES APPEAR IN THE TABLE ON THE NEXT PAGE.
1 DECEMBER 4, 2012 MD NASTRAN 5/ 8/08 PAGE 33
0
0
GRID POINT ID DEGREE OF FREEDOM MATRIX/FACTOR DIAGONAL RATIO MATRIX DIAGONAL
6756724 T1 8.16563E+10 3.48191E+08
6756724 T2 1.21281E+11 3.79991E+08
6756724 T3 1.12507E+10 3.87439E+07
Let me know if anyone has any suggestions for the above.
Thanks!
full car. We use the load time history measured during the test.
I tried two options for the frequency range:
OPTION1:
frequency in 0.0-100 Hz range to get the RB modes
EIGRL 400.0 100.0 MASS
My top 7 frequencies are:
1.111156E-02
1.313891E-02
1.485175E-02
1.602749E-02
1.630331E-02
1.651331E-02
2.662587E+01
The top 6 appear to be RB modes but they do not meet the criteria suggested in the Nastran manual (A good acceptance criteria is to have the rigid body modes
frequency being less than 0.0001x(first flexible mode frequency).
Should I be including these frequencies in my fatigue calculation? If I include these, I see lot more damage.
OPTION2:
The other thing I tried was requesting frequency in 0.5-100 Hz range
EIGRL 400.5 100.0 MASS
The analysis runs fine but it gave me the following warning messages:
^^^ USER WARNING MESSAGE 9128 ( AUTOSPRT)
^^^ F1 ON THE EIGR OR EIGRL ENTRY IS GREATER THAN 0. AND THEREFORE AUTO-SUPORT CANNOT BE PERFORMED.
^^^
*** USER INFORMATION MESSAGE 4158 (DFMSA)
---- STATISTICS FOR SPARSE DECOMPOSITION OF DATA BLOCK KYY FOLLOW
NUMBER OF NEGATIVE TERMS ON FACTOR DIAGONAL = 0
MAXIMUM RATIO OF MATRIX DIAGONAL TO FACTOR DIAGONAL = 1.2E+11 AT ROW NUMBER 5890532
*** SYSTEM INFORMATION MESSAGE 4159 (DFMSA)
THE DECOMPOSITION OF KYY YIELDS A MAXIMUM MATRIX-TO-FACTOR-DIAGONAL RATIO OF 1.212805E+11
*** USER WARNING MESSAGE 4698 (DCMPD)
STATISTICS FOR DECOMPOSITION OF MATRIX KYY.
THE FOLLOWING DEGREES OF FREEDOM HAVE FACTOR DIAGONAL RATIOS GREATER THAN
1.600000E+08 OR HAVE NEGATIVE TERMS ON THE FACTOR DIAGONAL.
USER INFORMATION:
THIS MESSAGE MAY BE IGNORED IF NO GRID POINT IDS OR HIGH RATIO MESSAGES APPEAR IN THE TABLE ON THE NEXT PAGE.
1 DECEMBER 4, 2012 MD NASTRAN 5/ 8/08 PAGE 33
0
0
GRID POINT ID DEGREE OF FREEDOM MATRIX/FACTOR DIAGONAL RATIO MATRIX DIAGONAL
6756724 T1 8.16563E+10 3.48191E+08
6756724 T2 1.21281E+11 3.79991E+08
6756724 T3 1.12507E+10 3.87439E+07
Let me know if anyone has any suggestions for the above.
Thanks!
