Week - 8 Mass Scaling

Aim- To understand and evaluate the mass scaling procedure to perform the explicit analysis and use trial and error method to optimize TSSFAC and DT2MS and reduce the run time and also maintain the stability

Objective- To achieve the hard limit on mass scaling of 8% and stability should be completely intact.

Procedure- The attached model was used to perform the trial and error method playing with the TSSFAC AND DT2MS.

The Control Timestep card was used in order to utilize the mass scaling procedure. DT2MS<0 was used thus adding fictitious mass, time step scaling factor TSSFAC was used with the range (0.9-0.6), TSSFAC reduces dt2ms a bit , it does not affect added mass. Increasing dt2ms increases added mass. After each trial, it was made sure that added mass % was <10%, as our objective was to achieve the hard limit on mass scaling of 8% and also ensure that the stability intact.

In our case, TSSFAC was maintained at the default value of 0.9 and DT2MS was varied, looking for the reduced run time.

Trial 1: DT2MS of -4.5e-5 was considered, which gave us a run time of 16 hrs 51 minutes with 0 added mass.

Trial 2: DT2MS of -7e-5 was considered, which gave us a run time of 10 hrs 49 minutes which took % increase mass of 0.142%

Trial 3: DT2MS of -9e-5 was considered, which gave us a run time of 7 hrs 51minutes which took % increase mass of 2.744%

Trial 4: DT2MS of -9.5e-5was considered, which gave us a run time of 7 hrs 37 minutes which took % increase mass of 4.313%

Trial 5: DT2MS of -9.75e-5was considered, which gave us a run time of 7 hrs 4 minutes which took % increase mass of 5.284%

Trial 6: DT2MS of -9.93e-5 was considered, which gave us a run time of 6 hrs 57 minutes which took % increase mass of 6.088%

Trial 7: DT2MS of -1.025e-4was considered, which gave us a run time of 6 hrs 53 minutes which took % increase mass of 7.766%

Trial 8: DT2MS of -1.029e-4was considered, which gave us a run time of 7 hrs 2 minutes which took % increase mass of 8.004%

The hard limit on mass scaling of 8% was achieved with DT2MS of -1.029e-4 which gave us a run time of 7 hrs 2 minutes which took % increase mass of 8.004%.

Similarly, the same model was ran using implicit solver with necessary changes and implicit and explicit runtime was compared.

All the CONTROL_IMPLICIT_AUTO, CONTROL IMPLICIT GENERAL, CONTROL IMPLICIT SOLUTION was used with default values required in order to rum an implicit solution.

It was seen as expected that the run time for implicit was 12 mins 15 seconds, this is obvious as time step is larger than explicit and thus mass scaling is not needed in this case.

Histogram plot of (a) DT2MS VS Run time and (b) DT2MS VS Mass % increase has been shown below.

(a) DT2MS VS Run time

(b) DT2MS VS Mass % increase

It was found that as expected with the increase of DT2MS, the run time decreased and also the mass % increased.