# Linear Dynamics not converging to Linear Static solution (or Nonlinear Static/Dynamic)

Question asked by Loren Galarza on Nov 3, 2015

SW Community,

My situation:

• I am running a study between 4 different SW Sims: Linear Static, Linear Dynamic, Nonlinear Static, and Nonlinear Dynamic.
• The goal: to validate that all 4 approaches will give similar steady-state solutions (over time).
• My part: a simple cylindrical boss, measuring 5" tall x 1" diameter, made from 7075-T6 (using the SW Materials Library).
• The sim: A 10,000 psi step-load that is suddenly applied to the top of the part (Y-axis). The load starts at 0 PSI, then builds to 10,000 PSI, and then remains at 10,000 PSI for the duration of the simulation (in this case, 0.015 seconds). The cylindrical part is fixed at the base.
• My problem: The Linear Dynamic sim is not converging to the same solutions as the other 3 studies (the stress plot is displaying odd results, but the displacement plots are virtually identical).
• The mesh size on all 4 sims is identical, and the loading profile for the dynamic sims is identical (static sim has a 10,000 PSI load).
• I've run the Linear Dynamic sim with a high number of frequencies (1000) to get the highest mass participation possible, but the stresses do not converge.
• I'm using a pressure instead of a force b/c the stress is straight-forward to estimate (10,000 PSI pressure should result in roughly a 10,000 PSI stress at the pressure surface).
• All 4 sims "should" show the same long-term values, but the Linear Dynamic seems to be the odd man out.
• Some logic: Imagine that a 200 lb person jumps on a weight scale. Initially, the scale will read greater than 200 lbs (due to the dynamic nature of the impact), but eventually, the scale will return to 200 lbs (over time), due to dampening and what-not. Now imagine that the same 200 lb person slowly steps onto the scale (and negates any dynamic loading). The scale will still read 200 lbs. In both cases, the scale reads 200 lbs (eventually).

Has anyone had any experience with this sort of thing? Is there any way to get the Linear Dynamic solution to converge to the other 3 sims?. I've attached my model for anyone interested.

Pictures (model, stress compare, and displacement compare) Thanks in advance for any help,

Loren