Week - 8 Mass Scaling

Objective: To study the effect of mass scaling on a simulation and to understand the use of parameter of CONTROL_TIMESTEP card in controlling the added mass percentage and run time on a simulation.

Procedure:

Open the key word file and open CONTROL_TIME STEP CARD for the given simulation file.

The unit system being used is kgms upon seeing the material property card. Also the simulation lasts 600 sec with constant louds making it a static simulation.

Explicit Method:

As we can see the CONTROL_TIME_STEP card has the following parameters.

Run the simulation to check the mass scaling and expected completion time.

this is too big so we will modify the values given in the dt 2ms section and see how it affects the simulation time while keeping the added mass below 8%

After running many iterations of dt 2ms and checking the output we get the following data:

highlighted in orange is the best value for dt 2m which gives the best value for mass scaling and estimated completion time. The simulation time can further be reduced by using a value of more than 1.

this is the graph for dt 2ms v/s completion time.

this is the graph for dt 2ms v/s added mass.

In this way we have found out the best way to perform this simulation in explicit manner

Implicit method: to perform the simulation with implicit method we can make the following changes in the model.

control cards:

control implicit auto to set the number of iteration being performed per load step and the maximum and minimum time step.

Control_Implicit_Dynamic:

This card is used so that it runs the simulation in a quicker manner treating it like a dynamic simulation instead od quasi-static.

Control_Implicit_General:

to ensure the simulation starts in implicit manner.

Control_Implicit_solution:

This is used to set the convergence parameter for non-linear solution.

Control_Time step:

This card is used to set the minimum time step below which mass-scaling occurs.

here a dt 2ms value of negative 0.1 is chosen.

contacts:

The contact definition is changed to automatic_surface_to_surface_mortar since this is better suited for implicit analysis.

Another simulation is also run using the standard contact.

On running the simulation, we see that the simulation complete rather quickly as compared to explicit analysis with no mass addition. 

time taken=00:42:16

Added mass=0kgs

Conclusion: Hence for quasi-static type simulation with long run time it is better to use implicit type analysis as we are mostly concerned with end result it solves quicker ensuring equilibrium and there is no added mass.