Week - 8 Mass Scaling
CASE (i)
WITHOUT MASS SCALING
PROCEDURE:-
- Model file is imported.
- Unit system defined is in Kg, m, Sec.
- CONTROL >The Control_Timstep card > delete to run model using mass scaling.
- The Termination Time Is Given as 600 sec.
- Save and run the model
Time is noted to be 173372 sec Which is 48hrs 9mins, long time to complete the simulation.
Case-2:
WITH MASS SCALING-
- Mass scaling of approximate -3.5e-5 is added in the time step.
- TSSFAC which is Known as scale Factor is Used as a factor of safety. The DT2MS value is Multiplied with TSSFAC and that value is the Minimum Value that the Solver will take as the Safety value.
- LS RUN is made to run
- The Time taken to complete is reduced by 10 Hrs compared with previous run without time step
- There is no mass added in the system.
The DT2MS value Can be Increased Till the Percentage of mass reaches 8% After that adding mass will cause a Change in Inertia in the Model
- Increasing DT2MS Value
- Changing the DT2MS to -6.000E-05 and Running the model, we get
- The Time taken to complete is reduced by 5 Hrs further, when compared with previous run.
- There is no mass added in the system, so DT2MS value can be increased
- Increasing DT2MS Value
- Changing the DT2MS to -9.000E-05 and Running the model, we get
- The Time taken to complete is reduced by 14 Hrs further, when compared with previous run.
- There is 2.74% mass added in the system, so DT2MS value can be increased
- Increasing DT2MS Value
- Changing the DT2MS to -1.2000E-04 and Running the model, we get
- The Time taken to complete is reduced by 8 Hrs further, when compared with previous run.
- There is 4.11% mass added in the system, so DT2MS value can be increased
- Increasing DT2MS Value
- Changing the DT2MS to -1.3000E-04 and Running the model, we get
- The Time taken to complete is reduced by 8 Hrs further, when compared with previous run.
- There is 6.36% mass added in the system, so DT2MS value can be increased
- Increasing DT2MS Value
- Changing the DT2MS to -1.368E-04 and Running the model, we get
- The Time taken to complete is increased by 5 Hrs further, when compared with previous run.
- There is 8.00% mass added in the system, so DT2MS value can be increased
Mass scaling can be modified by TSSFAC values.Decreasing TSSFAC will scale down our time step to a lower value. Reducing the TSSFAC will increase our runtime.
| DT2MS | PERCENTAGE OF MASS | RUN TIME(Hours) | RUN TIME(sec) |
| -3.50E-05 | 0 | 37.5 | 136221 |
| -6.50E-05 | 0 | 32.2 | 116407 |
| -9.00E-05 | 2.74 | 18.2 | 65993 |
| 1.20E-04 | 4.11 | 10 | 39393 |
| 1.30E-04 | 6.36 | 14.2 | 51281 |
| 1.37E-04 | 8 | 19.1 | 69112 |
From the chart, we can see that when the mass is added, the simulaton time is decreased. For the 0.9 scale factor, 1.20E-04 is the optimum value of mass scaling for the steady Simulation.
As the percentage of mass added is 4.11%
MASS SCALING FOR IMPLICIT FUNCTION
Implicit must be switched on, to solve the problem as implicit function
CONTROL_IMPLICIT_AUTO
- Input value for Automatic time step control flag = IAUTO = 1 (automatic time step control)
CONTROL_IMPLICIT_GENERAL
CONTROL_IMPLICIT_GENERAL card is used to activate implicit analysis
The input value for IMFLAG=Implicit/Explicit switching flag = 1 (implicit analysis)
DT0=Initial time step size for implicit analysis = 1.
CONTROL_IMPLICIT_SOLUTION
CONTROL_IMPLICIT_SOLUTION card is used to specify whether a linear or nonlinear solution is desired. The default values are set as it is in the card.
CONTROL_IMPLICIT_SOLVER
CONTROL_IMPLICIT_SOLVER card is used for implicit calculation.
CONTROL_TERMINATION
The Termination Time Is Given as 600 sec.
STEP-1:-
DT2MS -3.500E-05 is Given with TSSFAC 0.9
The Keyword is Saved and Simulated using LS Dyna Manager
Step-2:-
DT2MS -1.350E-04 is Given With TSSFAC=0.9
The Keyword is Saved and Simulated using LS Dyna Manager
The runtime required to complete the simulation for DT2MS = -3.5E-5 is 2 mins 06 sec and for DT2MS = -1.35E-4 is 2 mins 10 sec.
The Mass added and percentage is not observed, and hence it is negligible in implicit analysis. DT2MS & TSSFAC doesnt affect implicit results
| DT2MS | RUN TIME(Minutes) | RUN TIME(sec) |
| -3.50E-05 | 2.06 | 126 |
| -1.35E-04 | 2.1 | 131 |
CONCLUSION:-
- By Trail & Error method is performed on the model.
- By considering the chart, adding mass can decrease the computation time. For the 0.9 scale factor, 1.20E-04 is the optimum value of mass scaling for the steady Simulation. The percentage of mass added is 4.11%
- Comparing the mass scaling both on explicit and implicit we see that .On explicit it decreases the computation time, whereas in implicit, DT2MS and TSSFAC do not affect the runtime.