ARCLEN
ARCLEN, Key, MAXARC, MINARC
Activates the arc-length method.
KeyArc-length key:
OFF
—
Do not use the arc-length method (default).
ON
—
Use the arc-length method.
MAXARCMaximum multiplier of the reference arc-length radius (default = 25).
MINARCMinimum multiplier of the reference arc-length radius (default = 1/1000).
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:
tMAX = MAXARC * t0 |
tMIN = MINARC * t0 |
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 tMAX, the arc-length radius is reset to tMAX. If the substep does not converge, bisection will take place until the arc-length radius is reduced to tMIN. 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.
The arc-length method can only be used with the sparse solver (EQSLV,SPARSE). If any other solver is specified, the solver method is automatically changed to sparse, and a warning message is issued to notify you.