Problem description

In PLAXIS 2D AE some additional numerical tools were introduced to improve convergence in some situations. One of these tools is the “Line Search” option. This option helps to determine the optimal overrelaxation value during the calculation thus resulting in faster calculation for some situations. Typically this option works best for serviceability limit state calculations.

The Line Search option performs additional iterations (in addition to the “global” iterations) to determine the optimal over-relaxation. These additional iterations however cause an issue with the determination of the “inaccurate plastic points”. The determination of the inaccurate plastic points is related to the stresses and used strain from the last iteration. Now in case of the Line Search option the stresses and strains are used from the previous Line Search iteration, whereas the program should use the stress from the previous “global” iteration. As a result of this issue it may happen that all of a sudden the inaccurate plastic points become zero thereby incorrectly “loosening” the convergence criteria. In this case the converged model has technically not yet fulfilled the requirements and thus may present incorrect results.

Solution

This issue is now solved since PLAXIS 2D 2015.00, and PLAXIS 3D AE.00.

For older versions: we recommend users not to use the Line Search option in the above mentioned versions of PLAXIS (Applications).