20.1. Controls - Mass Scaling

Mass scaling is an artificial (numerical) mechanism for increasing the CFL (Courant-Friedrichs-Levy) timestep of individual elements that govern the maximum allowed timestep of explicit transient dynamic solutions in Autodyn. Increasing the timestep has the obvious benefit of reducing the number of cycles required to run a simulation to a given point in time. Educated use of this option can therefore result in significant improvements in efficiency.

The primary use of mass scaling is to increase the CFL timestep of a small number of very small (or stiff) elements in the model, which otherwise would have controlled the timestep for all elements. Using this option, Autodyn will automatically add artificial mass to individual elements to ensure that their CFL timestep is at least equal to a value defined by you. Mass scaling should only be used if the increased inertia of the scaled elements does not significantly affect the results of the simulation.

Mass scaling can also be used to increase the CFL timestep of elements that become highly distorted during the simulation. Extreme care should be taken to ensure that results obtained remain physical.

Mass scaling is activated under Controls, Timestep and the input parameters are defined as follows:

Automatic Mass Scaling

Activate automatic mass scaling.

Frequency (cycles)

Cycle frequency that Autodyn will adjust the element mass scaling. Recommended default is only at start-up (cycle 0). Post cycle 0 adjustment will only take place for solid elements (excluding ANP and NBS tetrahedra).

Min. CFL timestep

Mass scaling is applied to all elements with a CFL timestep less than the specified value.

Max. element scaling

Maximum mass scaling factor that can be applied to an element. Default is 100 (equating to 100 times original mass). If this limit is exceeded, no more mass is added to this element.

Max. part scaling

Maximum added mass that is allowed for an Autodyn Part, as a fraction of the original Part mass. Default is 0.05 (equating to 5% of the original mass. If this value is exceeded, the simulation will terminate with an error message.

Two new element variables have been introduced with the development. These variables are automatically activated when mass scaling is selected:

A typical procedure to invoke mass scaling would be as follows

Important notes and limitations:

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