Mechanical APDL Basic Analysis Guide - Ansys

Figure 2.2 Transient Load History Curve
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2.2. Load Steps, Substeps, and Equilibrium Iterations
Substeps are points within a load step at which solutions are calculated. You use them for different reasons:
• In a nonlinear static or steady-state analysis, use substeps to apply the loads gradually so that an accurate
solution can be obtained.
• In a linear or nonlinear transient analysis, use substeps to satisfy transient time integration rules (which
usually dictate a minimum integration time step for an accurate solution).
• In a harmonic response analysis, use substeps to obtain solutions at several frequencies within the
harmonic frequency range.
Equilibrium iterations are additional solutions calculated at a given substep for convergence purposes. They
are iterative corrections used only in nonlinear analyses (static or transient), where convergence plays an
important role.
Consider, for example, a 2-D, nonlinear static magnetic analysis. To obtain an accurate solution, two load
steps are commonly used. (Figure 2.3 (p. 24) illustrates this.)
• The first load step applies the loads gradually over five to 10 substeps, each with just one equilibrium
iteration.
• The second load step obtains a final, converged solution with just one substep that uses 15 to 25
equilibrium iterations.
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