Arclength method does not gives converged solution in buckling analysis

- September 28, 2019 at 4:59 am
  
  venugopal4048
  Subscriber
  
  Hello all!
  
  I am doing nonlinear buckling analysis in an dome structure. Many of the expertises suggested Arclength method is best method for nonlinear buckling analysis. I used Arclength method for my analysis with material nonlinearity and geometric imperfection. Anyway I have get a converged solution for structure with high geometric imperfection(More than 10%). If I use very small amount of geometric imperfection (like 0.5,1and 2 percent), It does not converged to a solution. I have tried with maximum number of substeps, still not converging.
  
  Also raised many times this problem in this community but no one respond.
  
  I have attached my file of 0.1% geometric imperfection with this. Please give some suggestion to solve it.
  
  Thanking you
  
  Venugopal B
- November 12, 2019 at 1:58 am
  
  Sandeep Medikonda
  Ansys Employee
  
  First, have you tried the Nonlinear Stabilization route? Energy Method or the Damping Method? Does it overcome the instability?
  
  Some suggestions have been provided in the help. Please go through it.
  
  The arc-length method (ARCLEN and ARCTRM) is another way to solve unstable problems. This method is restricted to static analyses with proportional (ramped) loads only.
  
  When choosing the number of substeps (NSUBST), consider that more substeps result in a longer solution time but sometimes help the program to converge. Ideally, you want the minimum number of substeps required to produce an optimally efficient solution. You might have to make an educated guess of the desired number of substeps, and adjust and re-analyze as needed. The modification of the MAXARC argument of the ARCLEN command can also help the program to converge by preventing the reference arc-length radius from increasing too rapidly (MAXARC = 1).
  
  When the arc-length method is active, do not use line search (LNSRCH), the predictor (PRED), adaptive descent (NROPT,,,ON), automatic time stepping (AUTOTS, DELTIM), or time-integration effects (TIMINT). Likewise, do not try to base convergence on displacement (CNVTOL,U); instead, use the force criteria (CNVTOL,F).
  
  If an arc-length solution fails to converge within the prescribed maximum number of iterations (NEQIT), the program automatically bisects and continues the analysis. Bisection continues until a converged solution is obtained or until the minimum arc-length radius is used. (The minimum radius is defined by NSBSTP (NSUBST) and MINARC (ARCLEN).
- March 11, 2021 at 9:20 am
  
  venugopal4048
  Subscriber
  
  Thank you sir.n