Week - 8 Mass Scaling
Objective - To perform Mass scaling and understand the change in computational time by varying values of DT2MS and TSSFAC.
Mass Scaling - Mass scaling refers to a technique whereby non-physical mass is added to a structure in order to achieve a larger explicit time step.
Difference between using a positive or negative numbers for DT2MS -
Negative - Mass is added to only those elements whose timestep would be otherwise less than TSSF*abs(DT2MS).
Positive - Mass is added or taken away from elements so that the time step of every element is the same equal to DT2MS.
By using Explicit Solver - 5 different values of DT2MS and 2 different values of TSSFAC were used for this analysis.
DT2MS values were used based on trial and error until a value for %age mass added became 8% whereas default value of 0.9 was used for TSSFAC and later 0.8 for other trials.
Below Histogram shows variation in computational time with change in DT2MS values. Blue coloured bars shows TSSFAC value = 0.9 whereas Red coloured bars shows TSSFAC value = 0.8
From the graph it is clear with TSSFAC value = 0.9 the model would take less time compared to TSSFAC value =0.8 as it is basically a scale factor which helps maintain stability of the model.
| Trials | DT2MS | TSSFAC | Estimated Time | Mass %age Increase |
|
Original Model with TSSFAC = 0.9 |
-3.50E-05 | 0.9 | 21H 40M | 0.00% |
| Original Model with TSSFAC = 0.8 | -3.50E-05 | 0.8 | 26H 42M | 0.00% |
| Trial 1 | -1.00E-04 | 0.9 | 7H 54M | 6.42% |
| Trial 2 | -1.00E-04 | 0.8 | 13H 15M | 6.42% |
| Trial 3 | -1.03E-04 | 0.9 | 7H 43M | 7.76% |
| Trial 4 | -1.03E-04 | 0.8 | 20H 08M | 7.76% |
| Trial 5 | -1.03E-04 | 0.9 | 7H 42M | 7.91% |
| Trial 6 | -1.03E-04 | 0.8 | 11H 36M | 7.91% |
| Trial 7 | -1.03E-04 | 0.9 | 7H 41M | 8.00% |
| Trial 8 | -1.03E-04 | 0.8 | 11H 35M | 8.00% |
By Using Implicit Solver - Time taken 2M 38S
Analysis Setup -
Control Implicit General card used to turn on Implicit Solver with Initial Time step as 10.
Control Implicit Solution card used to switch to Non-linear solver considering Non-linearities involved in the model.
Conclusion -
Computational time taken by Inplicit Solver is far less than compared to Explicit Solver.
Whereas for Explicit Solver with correct value of DT2MS and TSSFAC solution time was decreased to 1/3rd of the original time required to solve the model.