Problem description

When the Time step determination for a Dynamic phase is set to automatic, the number of steps used for the time discretization will be automatically determined by the calculation kernel based on the critical time step. This critical time step is determined by the element properties (stiffness of the materials used in an element and this element’s size) and the dynamic input signal (Displacement multiplier or Load multiplier).

However, the automatic number of dynamic substeps is not always determined correctly in PLAXIS 2D AE.00 and PLAXIS 2D AE.01:

• when one of the used soil material types used in the phase is Linear Elastic or Mohr-Coulomb, the number of dynamic substeps for the time discretization will be set to 1 based on the element properties. With insufficient additional steps (Max steps) the results could be incorrect.
• when the default iterative setting for the numerical control parameters is deactivated, the automatic number of substeps is determined based on the element properties only: the input signal is not included in this. This could mean that the chosen time step will miss peak values in the signal as described in this related article Time steps used in a dynamic calculation. Especially in combination with the point above, this will lead to incorrect results.
• the Retrieve option from the side panel (when the Max. steps field or Number of substeps field is activated, it will be shown) includes the input signal, but it does not correctly determine the critical time step based on the element properties (stiffness and size).

Solution

This issue is now solved in PLAXIS 2D AE.02