Dear Itasca Support Team,
I am currently reviewing the dynamic timestep formulation in the FLAC manual, particularly Equations (3.13) and (3.14), and I would appreciate some clarification regarding their practical interpretation in FLAC2D.
I modeled a single rectangular zone in order to eliminate any influence from adjacent zones on the dynamic timestep. Using Equation (3.13) and (3.14), I estimated the critical timestep for a simple rectangular grid and obtained a value of Δt ≈ 0.0024 s. However, FLAC2D reports a higher dynamic timestep (≈ 0.0039 s), and I would like to understand the reason for this discrepancy.
From my understanding:
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Equation (3.13) provides a simplified estimate for regular rectangular zones.
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Equation (3.14) computes the timestep based on gridpoint quantities, where mass and stiffness contributions from all connected subzones (including adjacent zones) are summed, and the minimum over all gridpoints is selected.
My questions are:
Could you please clarify the reason for this discrepancy in td values?
When visualizing the “Zone Dynamic Timestep” in 2D models (even before activating model dynamic active or zone dynamic multi-step on), different timestep values are displayed for different zones. How does FLAC2D compute the “zone dynamic timestep” shown in the plot if timestep is obtained as the minimum over all gridpoints ?
Thanks for your support.