Week - 8 Mass Scaling
Aim: Using the mass scaling to reduce the simulation runtime and increase the stability of the solution subject to 8% mass caling.
Objectives:
To understand the effect of mass scaling on the simulation by varying DT2MS and TSSFAC
Limiting the percentage of added mass to 8% and optimizing the DT2MS
Comparing implicit and explicit schemes for same problem.
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Step 1: Loading given files
Step 2: Varying DT2MS and TSSFAC in *CONTROL_TIMESTEP
--> DT2MS and TSSFAC are varied in *CONTROL_TIMESTEP card as shown below
Case 1: Running given file in explicit scheme without changing the parameters
Firstly, the given explicit scheme file was run. We can observe from the following figure that there is no mass added and clock time is 21 hrs 19 mins (1279 minutes).
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Trial 1: TSSFAC=0.9 and DT2MS 7e-5
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Trial 2: TSSFAC=0.9 and DT2MS=0.8e-5
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Trial 3: TSSFAC=0.9 and DT2MS=0.9e-5
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Trial 4: TSSFAC=0.9 and DT2MS=1e-4
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TSSFAC Variation
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Trial 5: DT2MS=1e-4, TSSFAC=0.5
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Trial 6: DT2MS=1e-4, TSSFAC=0.7
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Trial 6: DT2MS=1e-4, TSSFAC=0.9
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Results:
DT2MS variation: We can observe that the varying the DT2MS significantly varies simulation runtime. Hence it is crucial to find optimum DT2MS for a simulation to reduce the simulation time, which reduces the cost.
Mass scaling is an significant tuning parameter. In this study increasing the DT2MS reduces the runtime of the simulation.
% Added Mass
When the mass scaling parameter is used, at DT2MS=1e-4, we observe 6.43% mass is added which is within the stated limit. Hence we can keep 1e-4 at the cost of simulation time.
TSSFAC Variation:In this study time step scaling factor is varied keeping DT2MS=1e-4 as constant. We can observe that the TSSFAC does not affect added mass, but an increase in TSSFAC results in reduced simulation time.
Implicit Simulation:
Implicit cards are defined for implicit simulation as shwon in following figures
Implicit clock time = 1 minute 39 seconds
Explicit clock time = 21 hours
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Conclusions and lessons learnt
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Conclusions:
Mass scaling reduces the simulation runtime and thus the simulation costs
TSSFAC doesn't change or affect the DT2MS
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Lessons learnt:
How to use mass scaling using DT2MS
How to use TSSFAC and its effect on DT2MS