Jim Day
Ansys Employee

For LS-DYNA implicit simulations that don’t converge, please apply the guidelines as specified as follows:

(Last updated June 10, 2019)

When running implicit, use a double precision executable.  

Because the implicit solver continues to evolve and improve,
the latest production release as listed in 
http://ftp.lstc.com/anonymous/outgoing/support/FAQ/ReleaseNotes/releasedates is recommended.
Starting at R11, a new implicit memory scheme is implemented which makes life easiler for the analyst.
To get the very latest improvements, try the latest Development version, i.e., "version dev".
To download version dev, send an email to support@lstc.com and provide the banner from one of your 
messag or mes0000 files.  

Appendix P in the latest DRAFT of the User's manual includes a checklist of implicit modeling guidelines,
which are primarily aimed at nonlinear implicit problems.

For theoretical information on implicit, refer to the following sections in the latest DRAFT of
the Theory Manual:
  29.21  Mortar Contact
  37     Implicit

The DRAFT Manuals are available at www.lstc.com/download/manuals .

The zip file at 
includes a comprehensive implicit guidelines document 
LS-dyna_implicit_guideline.pdf, as well as examples that are described in a readme.txt file.

More examples featuring implicit analysis are available at 

Below is a very abbreviated list of implicit guidelines.  Please also refer to the checklist in 
Appendix P of the LS-DYNA User's Manual for other important guidelines.

-  For mildly nonlinear problems, use NSOLVR = 12 with LSMTD=4 (*CONTROL_IMPLICIT_SOLUTION).
   These are the default settings.

-  For highly nonlinear problems, setting ILIMIT = 1 to invoke the Full Newton method may 
   be beneficial.  
   Bumping LSMTD from 4 to 5 may offer some benefit, but rarely. 

   More on ILIMIT:  
   Start out using the default, and then  switch to full Newton if iteration is erratic with norms behaving erratically. 
   Conversely, if full Newton is slow, with residual norms going down very slowly, use ILIMIT>1.

-  Set ABSTOL=1.0E-20 in *CONTROL_IMPLICIT_SOLUTION to prevent premature convergence.


-  For non-tied contacts, use MORTAR type contacts. 

-  For tied contact, follow Remark 4, "Tied Contact Types and the Implicit Solver" in the *CONTACT section
   of the latest DRAFT of the User's Manual (www.lstc.com/download/manuals).
   Briefly, without providing the details mentioned in the Manual, the subset of tied contacts suggested are:

-  Set VDC=0 in *CONTACT cards.

-  Set OSU=1, INN=4, and IACC=1 in *CONTROL_ACCURACY.

-  Element formulations:
     -  Use ELFORM = -16 for shells (that's negative 16), and apply hourglass type #8
     -  Use solid ELFORM -2 for solid hexahedral elements, especially when the solid elements have bad aspect ratios.
     -  Use ELFORM=2 instead of ELFORM=13 for beams.
     -  For a convenient way to change element formulation for implicit, see the variables 

-  If there are *RIGIDWALLs, set RWPNAL to -1.0 (that's a negative one).

-  Invoke the non-symmetric solver by setting LCPACK=3 in *CONTROL_IMPLICIT_SOLVER if
   convergence is a problem and ... 
     -  damping is included in an eigenvalue analysis (in this case, use SMP only), or
     -  MORTAR contact with friction is included, or
     -  beam formulation 2 is used.
     -  See the User's Manual (*CONTROL_IMPLICIT_SOLVER) for other less common conditions 
          that have a non-symmetric contribution.
     -  Note that LCPACK=3 will double the time taken by the linear equation solver and the 
        presence of the aforementioned conditions doesn't necessarily require that it be used,
        that is, it's very model-dependent.

-  http://ftp.lstc.com/anonymous/outgoing/support/FAQ_docs/implstat_v2.0_in_lspp.pdf
   describes how to generate implicit statistics plots from d3hsp using LS-PrePost executables 
   (version 4.3 or later, dated 23-Apr-2016 or later; http://ftp.lstc.com/anonymous/outgoing/lsprepost ).

-  If a fatal error message that mentions the solver is encountered,
   set LPRINT=3 in *CONTROL_IMPLICIT_SOLVER and then look for added information in the mes* file(s)
   that provides further details concerning the source of the problem. 

-  If an implicit analysis is sharing computing resources with other LS-DYNA runs and/or 
   with other applications, and a memory-related  error occurs, try reducing RDCMEM in 
   *CONTROL_IMPLICIT_SOLVER from the default of 0.85 to 0.50.  This advice applies starting 
   with version R11.

-  Before running an implicit static analysis, it's good practice to run an eigenvalue analysis 
   to determine if the model has any rigid body modes.  If such modes exist they need to be
   constrained out or else *CONTROL_IMPLICIT_DYNAMICS activated (to run a dynamic analysis 
   rather than a static analysis). 

Information on implicit is also provided at http://www.dynasupport.com/howtos/implicit, 
but if any of that information is in conflict with information above, the information above
takes precedence.