Apply mass scaling for quasi-static simulations 1

[apal21]

Hello,

I want to do quasi-static simulations using Abaqus (Explicit). I read online that mass scaling is the best way of minimising kinetic energy and inertia in the system. The Abaqus manual mentions applying it in the 'Steps' section, but I don't quite see how to do it.

Can't I just set a constant mass scaling factor at the beginning of the simulation, and let it be? Why do I need to do it separately for different steps? Also, can't I just increase the mass directly in the Materials? Does that do something different?

 

[FEA way]

Mass scaling can significantly decrease the analysis time by increasing atable time increment. However, with too high mass scaling the results can become incorrect due to larger influence of inertia effects.

Mass scaling is defined in step settings (there’s a separate tab for it). Several options are available. It can be fixed (applied once at the beginning of the step) or variable (applied throughout the step).

Check Abaqus documentation chapter "Mass scaling" for details.

 

[apal21]

I was reading up the manual. It keeps mentioning the minimum 'stable time increment'. What exactly does that mean?

 

[FEA way]

Explicit time integration method is conditionally stable. It requires sufficiently small time steps. Abaqus calculates stable time increment for each element and uses the smallest value in the analysis. Based on Courant condition, stable time increment depends on element size and material properties (density, elasticity). For 1D problem stable time increment Δt is given by:

Δt = L_e/c_d

c_d = sqrt(E/ρ)

where:
L_e - characteristic element length, c_d - dilatational wave speed, E - Young's modulus, ρ - density