 ## General Mechanical

• Colin Zhang
Subscriber

I have one bar with two ends. A one-step steady-thermal analysis was performed first to get the temperature field of the bar in which the temperature changes from one end of the bar to another end of the bar.  Next the temperature field was imported into the static structural analysis which has multiple steps of loading and unloading. For example, it has 4 steps. The first step is to apply the transverse pressure and temperature field obtained above to simulate the loading and heating process. The second step is to unload the transverse pressure and cool the bar to room temperature. The third step is the same as the first step while the fourth step is the same as the second step. How can I load and unload the tempearture field in Workbench Mechanical? Deactivating the temperature field in the 2nd step and 4th step directly in the Graph?

• Ashish Khemka
Ansys Employee
• Colin Zhang
Subscriber

Hello Ashish,

In fact, my Static Analysis has 7 steps. The 1st step is bolt-pretension. The 2nd, 4th and 6th steps are pressure loading and heating while the 3rd, 5th and 7th steps are unloading and cooling. See Figure 1 for pressure loading and unloading. The way of how I imported the temperature is shown in Figure 2 while your way is shown in Figure 3.  The Data View, Graph, and Tabular Data show the big difference. The "Auto Time Stepping" is ON. The Initial Substeps, Minimum Substeps and Maximum Substeps are 10, 5, and 100, respectively. So the Time(s) in Tabular Data is shown as 1.0001, etc.   • Colin Zhang
Subscriber
Hello Ashish,

My model involves material plasticity and contact pairs. It failed at the 4th step.

#The 2nd step involves many warnings like below.  Any actions needed?
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*** WARNING ***                         CP =    1035.703   TIME= 12:46:21
The current Level of Difficulty on the PCGOPT command may be inefficient for this model due to coupling equation(s) and/or constraint equation(s) present.  If this solution appears to be inefficient, you may find that switching to a Level of Difficulty equal to 1 [PCGOPT,1] more efficient for this model.
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#The 3rd step involve warnings, notes, and errors like below.  Any actions needed ?
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*** WARNING ***                         CP =   38533.234   TIME= 23:15:25
The current Level of Difficulty on the PCGOPT command may be inefficient for this model due to coupling equation(s) and/or constraint equation(s) present.  If this solution appears to be inefficient, you may find that switching to a Level of Difficulty equal to 1 [PCGOPT,1] more efficient for this model.

FORCE CONVERGENCE VALUE  =  0.5708E+05  CRITERION=   2632.
MOMENT CONVERGENCE VALUE =   28.08      CRITERION=  0.5102E-04

*** NOTE ***                            CP =   38790.953   TIME= 23:19:43
The preconditioned conjugate gradient solver failed to converge, and therefore no solution was obtained. The equation solver is now being automatically switched to the sparse solver (EQSLV,SPARSE) to allow this analysis to continue.
DISP CONVERGENCE VALUE   =  0.4709      CRITERION=  0.1124
EQUIL ITER   1 COMPLETED.  NEW TRIANG MATRIX.  MAX DOF INC= -0.4709
DISP CONVERGENCE VALUE   =  0.1518      CRITERION=  0.1147
LINE SEARCH PARAMETER =  0.3224     SCALED MAX DOF INC = -0.1518
FORCE CONVERGENCE VALUE  =  0.3857E+05  CRITERION=   171.9
MOMENT CONVERGENCE VALUE =   23.37      CRITERION=   248.1     <<< CONVERGED
EQUIL ITER   2 COMPLETED.  NEW TRIANG MATRIX.  MAX DOF INC=  0.7681E-01
DISP CONVERGENCE VALUE   =  0.7563E-01  CRITERION=  0.1171     <<< CONVERGED
LINE SEARCH PARAMETER =  0.9847     SCALED MAX DOF INC =  0.7563E-01
FORCE CONVERGENCE VALUE  =   1965.      CRITERION=   175.3
MOMENT CONVERGENCE VALUE =   2.255      CRITERION=   253.0     <<< CONVERGED
EQUIL ITER   3 COMPLETED.  NEW TRIANG MATRIX.  MAX DOF INC=  0.9337E-02
DISP CONVERGENCE VALUE   =  0.9337E-02  CRITERION=  0.1194     <<< CONVERGED
LINE SEARCH PARAMETER =   1.000     SCALED MAX DOF INC =  0.9337E-02
FORCE CONVERGENCE VALUE  =   401.8      CRITERION=   179.3
MOMENT CONVERGENCE VALUE =  0.5137E-01  CRITERION=   258.7     <<< CONVERGED
EQUIL ITER   4 COMPLETED.  NEW TRIANG MATRIX.  MAX DOF INC=  0.6605E-02
DISP CONVERGENCE VALUE   =  0.6605E-02  CRITERION=  0.1219     <<< CONVERGED
LINE SEARCH PARAMETER =   1.000     SCALED MAX DOF INC =  0.6605E-02
FORCE CONVERGENCE VALUE  =   198.5      CRITERION=   183.0
MOMENT CONVERGENCE VALUE =  0.5709E-01  CRITERION=   264.1     <<< CONVERGED
EQUIL ITER   5 COMPLETED.  NEW TRIANG MATRIX.  MAX DOF INC= -0.6990E-02
DISP CONVERGENCE VALUE   =  0.6990E-02  CRITERION=  0.1244     <<< CONVERGED
LINE SEARCH PARAMETER =   1.000     SCALED MAX DOF INC = -0.6990E-02
FORCE CONVERGENCE VALUE  =   210.0      CRITERION=   187.0
MOMENT CONVERGENCE VALUE =  0.3405E-01  CRITERION=   270.0     <<< CONVERGED
EQUIL ITER   6 COMPLETED.  NEW TRIANG MATRIX.  MAX DOF INC= -0.7422E-02
DISP CONVERGENCE VALUE   =  0.7422E-02  CRITERION=  0.1269     <<< CONVERGED
LINE SEARCH PARAMETER =   1.000     SCALED MAX DOF INC = -0.7422E-02
FORCE CONVERGENCE VALUE  =   142.2      CRITERION=   191.0     <<< CONVERGED
MOMENT CONVERGENCE VALUE =  0.1315E-01  CRITERION=   275.6     <<< CONVERGED
>>> SOLUTION CONVERGED AFTER EQUILIBRIUM ITERATION   6
*** LOAD STEP     3   SUBSTEP     4  COMPLETED.    CUM ITER =    109
*** TIME =   2.40000         TIME INC =  0.100000
*** MAX PLASTIC STRAIN STEP = 0.1679E-02   CRITERION = 0.1500
*** AUTO TIME STEP:  NEXT TIME INC = 0.15000      INCREASED (FACTOR = 1.5000)

*** NOTE ***                            CP =   43066.172   TIME= 00:30:59
The equation solver is automatically reverting from the sparse solver back to the preconditioned conjugate gradient solver.
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*** ERROR ***                           CP =   46802.359   TIME= 01:33:17
Element 73021 (type = 2, SOLID187) (and maybe other elements) has become highly distorted.  Excessive distortion of elements is usually a symptom indicating the need for corrective action elsewhere.  Try incrementing the load more slowly (increase the number of substeps or decrease the time step size).  You may need to improve your mesh to obtain elements with better aspect ratios.  Also consider the behavior of materials, contact pairs, and/or constraint equations.  Please rule out other root causes of this failure before attempting rezoning or nonlinear adaptive solutions.  If this message appears in the first iteration of first substep, be sure to perform element shape checking.
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*** NOTE ***                            CP =  201257.641   TIME= 20:30:35
The incremental plastic strain 62.2106268% computed in this iteration is larger than the criterion of 15% leading to bisection.  You may try incrementing the load more slowly by increasing the number of substeps or use the CUTCONTROL command to re-specify this criterion.
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#The solution stopped at load step 4, substep 16 with error as shown below. How can I correct the errors?

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>>> SOLUTION CONVERGED AFTER EQUILIBRIUM ITERATION   7
*** LOAD STEP     4   SUBSTEP    15  COMPLETED.    CUM ITER =    416
*** TIME =   3.41150         TIME INC =  0.100000E-01
*** MAX PLASTIC STRAIN STEP = 0.3756       CRITERION = 0.1500
*** AUTO STEP TIME:  NEXT TIME INC = 0.10000E-01  UNCHANGED

FORCE CONVERGENCE VALUE  =   2963.      CRITERION=   277.2
MOMENT CONVERGENCE VALUE =  0.4922      CRITERION=  0.5102E-04
DISP CONVERGENCE VALUE   =  0.5154E-01  CRITERION=  0.1124     <<< CONVERGED
EQUIL ITER   1 COMPLETED.  NEW TRIANG MATRIX.  MAX DOF INC= -0.5154E-01
DISP CONVERGENCE VALUE   =  0.2969E-01  CRITERION=  0.1147     <<< CONVERGED
LINE SEARCH PARAMETER =  0.5760     SCALED MAX DOF INC = -0.2969E-01
FORCE CONVERGENCE VALUE  =   1259.      CRITERION=   136.2
MOMENT CONVERGENCE VALUE =  0.2087      CRITERION=   196.5     <<< CONVERGED
EQUIL ITER   2 COMPLETED.  NEW TRIANG MATRIX.  MAX DOF INC=  0.2179
DISP CONVERGENCE VALUE   =  0.1155E-01  CRITERION=  0.1171     <<< CONVERGED
LINE SEARCH PARAMETER =  0.5303E-01 SCALED MAX DOF INC =  0.1155E-01
FORCE CONVERGENCE VALUE  =   1190.      CRITERION=   138.9
MOMENT CONVERGENCE VALUE =  0.1977      CRITERION=   200.5     <<< CONVERGED
EQUIL ITER   3 COMPLETED.  NEW TRIANG MATRIX.  MAX DOF INC=  0.1992
DISP CONVERGENCE VALUE   =  0.1992      CRITERION=  0.1194
LINE SEARCH PARAMETER =   1.000     SCALED MAX DOF INC =  0.1992
FORCE CONVERGENCE VALUE  =   7999.      CRITERION=   141.7
MOMENT CONVERGENCE VALUE =  0.8859E-02  CRITERION=   204.6     <<< CONVERGED
EQUIL ITER   4 COMPLETED.  NEW TRIANG MATRIX.  MAX DOF INC= -0.3821E-01
DISP CONVERGENCE VALUE   =  0.3821E-01  CRITERION=  0.1219     <<< CONVERGED
LINE SEARCH PARAMETER =   1.000     SCALED MAX DOF INC = -0.3821E-01
FORCE CONVERGENCE VALUE  =   4421.      CRITERION=   144.7
MOMENT CONVERGENCE VALUE =  0.9883E-02  CRITERION=   208.8     <<< CONVERGED
EQUIL ITER   5 COMPLETED.  NEW TRIANG MATRIX.  MAX DOF INC= -0.1681
DISP CONVERGENCE VALUE   =  0.6666E-01  CRITERION=  0.1244     <<< CONVERGED
LINE SEARCH PARAMETER =  0.3966     SCALED MAX DOF INC = -0.6666E-01
FORCE CONVERGENCE VALUE  =   3094.      CRITERION=   147.6
MOMENT CONVERGENCE VALUE =  0.6133E-02  CRITERION=   213.1     <<< CONVERGED
EQUIL ITER   6 COMPLETED.  NEW TRIANG MATRIX.  MAX DOF INC= -0.3314

*** ERROR ***                           CP =  248350.578   TIME= 09:35:44
Element 1293421 (type = 5, SOLID187) (and maybe other elements) has become highly distorted.  Excessive distortion of elements is usually a symptom indicating the need for corrective action elsewhere.  Try incrementing the load more slowly (increase the number of substeps or decrease the time step size).  You may need to improve your mesh to obtain elements with better aspect ratios.  Also consider the behavior of materials, contact pairs, and/or constraint equations.  Please rule out other root causes of this failure before attempting rezoning or nonlinear adaptive solutions.  If this message appears in the first iteration of first substep, be sure to perform element shape checking.

*** WARNING ***                         CP =  248350.781   TIME= 09:35:45
The unconverged solution (identified as time 4 substep 999999) is output for analysis debug purposes.  Results should not be used for any other purpose.
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Although the solution has many element distortions, they might not be the root cause. May increasing the Maximum substeps from 100 to 200 help solve the errors?

Thank you,
Colin

• Ashish Khemka
Ansys Employee

Hi Colin,

For the loads - it looks like the temperature is ramped for each active step. For element distortion please see if the following link is of help:

Dealing with Convergence Issues - Element Distortion Error - FEA Tips

Thanks and Regards,

Ashish Khemka 