Notes

Activates the arc-length method and sets the minimum and maximum multipliers for controlling the arc-length radius based on the initial arc-length radius.

The initial arc-length radius, t₀, is proportional (in absolute value) to the initial load factor. The initial load factor is given by:

Initial Load Factor = TIME / NSBSTP

where TIME is the time specified by the TIME command for the arc-length load step, and NSBSTP is the number of substeps specified by the NSUBST command.

The factors MAXARC and MINARC are used to define the range for the arc-length radius to expand and shrink during the substep solution:

In each substep, the arc-length radius is kept constant throughout the equilibrium iterations. After each converged substep, the arc-length radius for the next substep is modified depending on the convergence behavior. If the substep converges and the program heuristic predicts an easy convergence, the arc-length radius is enlarged. If the enlarged value is greater than t_MAX, the arc-length radius is reset to t_MAX. If the substep does not converge, bisection will take place until the arc-length radius is reduced to t_MIN. If further nonconvergence is encountered, the solution terminates.

The arc-length method predicts the next time increment (that is, load factor increment). Therefore, the AUTOTS and PRED commands are ignored when the arc-length method is used.

The STABILIZE and LNSRCH commands are also ignored.

The arc-length method cannot be used in a multiframe restart.

For difficult problems, one suggestion is to increase the initial number of substeps (NSUBST), and to prevent the arc-length radius from increasing too rapidly (MAXARC = 1).

ARCLEN cannot be used for any load step that has no applied load or displacement.

The arc-length method does not support tabular loads. In order to use the arc-length method, you must replace tabular loads by other load types and then run the analysis again.

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