OptiStruct ignores the settings of NLPARM

cfuser

Dear all,

I have convergence problems with a model I am analysing with OptiStruct. I have set EPSU and EPSP to 0.01 both in NLPARM (see screen shot input). But the solver seems to ignore those tolerances and keeps reducing the incerement size until it errors out (see screen shot output) as my minimum increment size DTMIN is set to 0.0001 in NLADAPT (see screen shot input). Can somebody give me an advice on what I could do to solve this issue?

 

Cheers!

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Rahul Rajan_21763

Can you first try with PARAM LGDISP 1 

If it error out then,try with PARAM EXPERTNL with & without CNTSTB .

 

Note:It is not generally recommended to change the default values. Varying the tolerances or excluding criteria may help achieve a solution, but will affect the result accuracy.

cfuser

Thank you, Rahul, for the quick reply. I'll try your suggestion regarding PARAM EXPERTNL/CNTSTB, as PARAM LGDISP is already set to 1.

cfuser

Hi  Rahul, I've tried using PARAM EXPERTNL in all available options: AUTO, CNTSTB, YES, NO. Each analysis with these different settings was aborted due to nonconvergence - interestingly, always at the same increment and load step values. Have you got any clue as to what could cause this pattern?

 

Further regarding your reply, I usually try to solve nonlinear problems with the default settings given in the cards, but in this case analysis with default settings results in nonconvergence.

 

Simon Križnik

@cfuser

 

try to diagnose the problem with PARAM>NLMON>DISP 

For more details refer to OS-E: 0125 Diagnose Non-converged Solution using NLMON

https://insider.altairhyperworks.com/wp-content/uploads/2018/12/TT-1333-OptiStruct-On-the-fly-output-of-Displacement-Results-for-Nonlinear-Analysis.pdf

cfuser

Thank you for your tip, Hyperman. I'll have a look into the link and also the example OS-E 0125.