Recommended Checklist

These aspects are:

• Time step value evolution and comparison with the targeted time step:
  • The time step should follow the targeted time step without time step drop (occasionally)
  • If the time step is at any time smaller than the targeted one, the target time step should be reduced
• Entity controlling the time step at cycle (SOLID, SHELL, SPRING, BEAM, NODE, INTER, and so on.)
• Energy Error evolution (should decrease slowly negatively - not increase)
• Output the number of AMS iterations per cycle via /DT/AMS/Iflag - I_flag =2 may help monitoring convergence quality at no extra CPU cost.

  Maximum allowed iterations before the divergence stops is 1000. 75 to 100 iteration per cycle is a sign of a poor convergence 50 still may provide some speedup

  30 iterations or less is considered a good convergence.

Starting from the constant nodal time step value (/DT/NODA/CST traditional in production) as a "reference" and applying a progressively increased target AMS time step (/DT/AMS) has shown four stages involving both numerical stability and result quality:

1. Too close to the traditional constant nodal time step value, the AMS numerical stability is excellent and results almost identical to the "reference". Of course, speedups are poor due to AMS iteration cost. In theory, a targeted x3 factor will return an "effective speedup" of x1 which is of no benefit.
2. Slightly above the previous case AMS numerical stability remains satisfactory mostly showing references to element related minimum time steps (possible references to interfaces). Results are still close to the "reference", AMS iteration cost becomes amortized and speedups start to rise. As an estimate targeted factors from x3 to x10, most likely return effective speedups ranging from x1.5 to x3, possibly more.
3. Above that, numerical stability may look satisfactory with possibly, higher numbers of iterations per cycle and more references to interface related minimum time steps. Results may either still look acceptable or significantly different compared to the "reference". Speedups continue to grow, unless penalty-based interfaces dictate the minimum time step causing iteration number increase and possible time step drops, what affects the speedup. However, targeted factors from x10 to x20 possibly x30 may return effective speedups ranging respectively from 4 to 6, possibly 9 (more was found in stamping simulation) that should NOT be considered a success as long as AMS results are not checked and compared to above defined "reference" results.
4. Above previous cases, computations either diverge then stop with an explicit AMS message or will stop due to Energy Error limit (no added mass) or the time step dramatically drops and the run needs to be interactively stopped.

Example:

/DT/AMS/1
$\text{Δ}{T}_{sca}$$\text{Δ}{T}_{\min }$
Tol_AMS
/DT/NODA/CST
$\text{Δ}{T}_{sca}$$\text{Δ}{T}_{\min }$

Nodes that are slave of both: a tied interface TYPE2 and a contact interface (TYPE7 or TYPE11) will have their contact stiffness removed a Starter message in the 0.out file is then issued:

** WARNING SLAVE NODE OF AN INTERFACE TYPE2 & AMS 
   INTERFACE TYPE[7 or 11], ID=xxxxxx: 
   SLAVE NODE ID=yyyyyyy IS ALSO SLAVE NODE OF AN INTERFACE TYPE2
THE NODE CONTACT STIFFNESS WILL BE DE-ACTIVATED CASE OF /DT/AMS

$\alpha =0$ and $\beta =0.05\text{Δ}{t}_{AMS}$ is AMS target time step.