Week - 8 Mass Scaling
Aim : to perform mass scaling to reduce run time of model simulation using trail and error method .
Theory:
Time step size for mass scaled solutions
DT2MS >0
Every element must have the time step, in case of element have high mass it will reduce stable time step and which have less time step it will increase respectively to get balance mass.
Positive values are for quasi-static analyses or time history analyses where the inertial effects are insignificant.
DT2MS<0
In this case whatever element have higher time step will not get touched , only the element where the stable time step is low they has to brought to the level of DT2MS , mass is added so that the element get that stable time step
In this case we will add mass which is less than 8% of model mass
TSSFAC × |DT2MS| is the minimum time step size
Permitted and mass scaling is done if and only if it is necessary to meet the Courant time step size criterion.
This option can be used in transient analyses if the mass increases remain insignificant. See also the variable MS1ST below and the *CONTROL_TERMINATION variable ENDMAS.
Time Step Scale Factor TSSFAC. During the solution we loop through the elements and determine a new time step size by taking the minimum value over all elements:
Δtn+1 = TSSFAC × min {Δt1, Δt2,, . . . , ΔtN}… where N is the number of elements.
open .k file in LS prepost
Case 1: Run .k file without mass scalling i.e without control_timestep card
Here we get total click time is 34 hrs 24 mins and dt is 0.000044
here mass added is 0 and mass scaling= 0%
Case 2 : run the simulation with mass scaling : tssfac : 0.9 and dt2ms : -3.5000E-5
Total clock time : 37 hrs 30 mins
Added mass : 0
mass scaling= 0%
DT : 0.000044
Case 3: like 2nd case we will run simulation with increase the DT2MS time
TSSFAC : 0.9 & DT2MS -5.500e-05
Total clock time : 29 hrs 5 mins
Added mass :2855.2
mass scaling= 0.00010034 %
DT : 0.0000495
Case 4 :
TSSFAC: 0.9 & DT2MS: -7.500e-05
Case 5 :
TSSFAC: 0.9 & DT2MS: -9.500e-05
...
Case 8 : dt2ms: -1.2500E-4
Case_9
DT2MS : -0.000155
Case 10 :
DT2MS : -1.7500E-4
Case 11 :
DT2MS : -2.000E-04
Case 12
DT2MS : -2.25E-04
Case 13
DT2MS: -2.5000E-4
Case 14 :
DT2MS : -2.7500E-4
Case 15 :
DT2MS: -3.0000E-4
Case 16 :
DT2MS: -3.2500E-4
Case_17
DT2MS: -3.1000E-4
Case 18 :
DT2MS: -3.1400E-4
Here we get more that 8 % mass added to the model which is not accepted so wi will reduce some amount time step to get acurate value for dt2ms with 8 % mass scaling
Case 19
-3.1350e-04
Result
| Case | tssfac | dt2ms | total clock time | total clock time | added mass | percentage increase | dt | Steps |
| In Minute | ||||||||
| Case_1 | - | - | 34 hrs 24 mins | 2064 | - | - | 4.40E-05 | 1.36E+07 |
| Case_2 | 0.9 | -3.500E-05 | 37 hrs 30 mins | 2250 | 0.00E+00 | 0.0000E+00 | 4.40E-05 | 1.36E+07 |
| Case_3 | 0.9 | -5.500E-05 | 29 hrs 5 mins | 1745 | 2.86E+03 | 1.0034E-04 | 4.95E-05 | 1.21E+07 |
| Case_4 | 0.9 | -7.500E-05 | 24 hrs 15 mins | 1455 | 1.06E+05 | 3.7280E-03 | 6.75E-05 | 8.89E+06 |
| Case_5 | 0.9 | -9.500E-05 | 21 hrs 58 mins | 1318 | 1.23E+06 | 4.3136E-02 | 8.55E-05 | 7.02E+06 |
| Case_6 | 0.9 | -1.050E-04 | 18 hrs 45 mins | 1125 | 3.06E+06 | 1.0748E-01 | 9.45E-05 | 6.35E+06 |
| Case_8 | 0.9 | -1.250E-04 | 17 hrs 47 mins | 1067 | 1.48E+07 | 5.2168E-01 | 1.13E-04 | 5.31E+06 |
| Case_9 | 0.9 | -1.550E-04 | 12 hrs 29 mins | 749 | 3.65E+07 | 1.2811E+00 | 1.40E-04 | 4.29E+06 |
| Case_10 | 0.9 | -1.750E-04 | 10 hrs 29 mins | 629 | 5.34E+07 | 1.8779E+00 | 1.58E-04 | 3.80E+06 |
| Case_11 | 0.9 | -2.000E-04 | 8 hrs 40 mins | 520 | 7.76E+07 | 2.7256E+00 | 1.80E-04 | 3.33E+06 |
| Case_12 | 0.9 | -2.250E-04 | 7 hrs 6 mins | 426 | 1.05E+08 | 3.6863E+00 | 2.02E-04 | 2.97E+06 |
| Case_13 | 0.9 | -2.500E-04 | 6 hrs 32 mins | 392 | 1.35E+08 | 4.7600E+00 | 2.25E-04 | 2.67E+06 |
| Case_14 | 0.9 | -2.750E-04 | 5 hrs 56 mins | 336 | 1.69E+08 | 5.9468E+00 | 2.47E-04 | 2.43E+06 |
| Case_15 | 0.9 | -3.000E-04 | 5 hrs 30 mins | 330 | 2.06E+08 | 7.2466E+00 | 2.70E-04 | 2.22E+06 |
| Case_17 | 0.9 | -3.100E-04 | 5 hrs 32 mins | 332 | 2.22E+08 | 7.7981E+00 | 2.79E-04 | 2.15E+06 |
| Case_19 | 0.9 | -3.135E-04 | 6 hrs 1 mins | 361 | 2.28E+08 | 7.9954E+00 | 2.82E-04 | 2.13E+06 |
| Case_18 | 0.9 | -3.140E-04 | 5 hrs 9 mins | 309 | 2.28E+08 | 8.0238E+00 | 2.83E-04 | 2.12E+06 |
now we will compare run time by changing TSSFAC
is 1st case we will use default setting which is TSSFAC =0.9 and DT2MS = -3.135E-04
Case 20
Case 21 : TSSFAC =0.6 and DT2ms 3.135E-04
Result :
| Case | tssfac | dt2ms | total clock time | total clock time | added mass | percentage increase | dt | Steps |
| In Minute | ||||||||
| Case_19 | 0.9 | -3.135E-04 | 6 hrs 1 mins | 361 | 2.28E+08 | 7.9954E+00 | 2.82E-04 | 2.13E+06 |
| Case_20 | 0.8 | -3.135E-04 | 5 hrs 52 mins | 352 | 2.28E+08 | 8.00E+00 | 2.51E-04 | 2.39E+06 |
| Case_21 | 0.7 | -3.135E-04 | 6 hrs 17 mins | 377 | 2.28E+08 | 8.00E+00 | 2.19E-04 | 2.74E+06 |
| Case_22 | 0.6 | -3.135E-04 | 8 hrs 18 mins | 498 | 2.28E+08 | 8.00E+00 | 1.88E-04 | 3.19E+06 |
COnclusion : The tssfac = 0.9(default) gives lowest run time for the simulation at -3.135E-4 dt2ms value.
Case 3: run the same model using implicit solver with necessary changes and compare implicit and explicit runtime.
Now we will activate the implicit solver by indusducing implit _auto and implicit_general card
Model and part >> keyword manager >> all >> control >> implicit_auto
IAUTO: 1
ITEOPT : 100
ITEWIN : 5
model and part >> keyword manager >> all >> control >> implicit_general
IMFLAG: 1
DT0:=Initial time step size for implicit analysis : 1
ELAPSED TIME : 363 second
The Implicit_auto keyword heps to automatically control the timestep in implicit analysis thus controlling the simulation time optimizing the run time
conclusion :
The mass scaling is carried out in explicit method and observed that for a simple simulation like this the total run time can be significantly reduced from aproximately 37 hrs 30 mins to 5 hrs 32 mins.
The tssfac value is changed and compared with default value
he Explicit and implicit run time for the same simulation is executed. It is found that implicit can automatically change timestep using implicit auto keyword and drastically reduce the simulation run time.
EXPLICIT RUN TIME : 5 hrs 32 mins
IMPLICIT RUN TIME : 362 Second ,(6 min 2 second )