BUCOPT

BUCOPT, Method, NMODE, SHIFT, LDMULTE, RangeKey
Specifies buckling analysis options.

Valid Products: Pro | Premium | Enterprise | PrepPost | Solver | AS add-on

Method

Mode extraction method to be used for the buckling analysis:

LANB

 — 

Block Lanczos

SUBSP

 — 

Subspace iteration

See Eigenvalue and Eigenvector Extraction in the Mechanical APDL Theory Reference for more information on these two methods.

NMODE

Number of buckling modes (that is, eigenvalues or load multipliers) to extract (defaults to 1).

SHIFT

By default, this value acts as the initial shift point about which the buckling modes are calculated (defaults to 0.0).

When RangeKey = RANGE, this value acts as the lower bound of the load multiplier range of interest (LDMULTE is the upper bound).

LDMULTE

Boundary for the load multiplier range of interest (defaults to ).

When RangeKey = CENTER, the LDMULTE value determines the lower and upper bounds of the load multiplier range of interest (-LDMULTE, +LDMULTE).

When RangeKey = RANGE, the LDMULTE value is the upper bound for the load multiplier range of interest (SHIFT is the lower bound).

RangeKey

Key used to control the behavior of the eigenvalue extraction method (defaults to CENTER):

CENTER

 — 

Use the CENTER option control (default); the program computes NMODE buckling modes centered around SHIFT in the range of (-LDMULTE, +LDMULTE).

RANGE

 — 

Use the RANGE option control; the program computes NMODE buckling modes in the range of (SHIFT, LDMULTE).

Notes

Specifies buckling analysis (ANTYPE,BUCKLE) options. Additional options used only for the Block Lanczos (LANB) eigensolver are specified by the LANBOPTION command. For more difficult buckling problems, you can specify an alternative version of the Block Lanczos eigensolver (LANBOPTION,,,ALT1).

Eigenvalues from a buckling analysis can be negative and/or positive. The program sorts the eigenvalues from the most negative to the most positive values. The minimum buckling load factor may correspond to the smallest eigenvalue in absolute value, or to an eigenvalue within the range, depending on your application (that is, linear perturbation buckling analysis or purely linear buckling analysis).

It is recommended that you request an additional few buckling modes beyond what is needed in order to enhance the accuracy of the final solution. It is also recommended that you input a non zero SHIFT value and a reasonable LDMULTE value (that is, a smaller LDMULTE that is closer to the last buckling mode of interest) when numerical problems are encountered.

When using the RANGE option, defining a range that spans zero is not recommended. If you are seeking both negative and positive eigenvalues, it is recommended that you use the CENTER option.

This command is also valid in PREP7. If used in SOLUTION, this command is valid only within the first load step.

Menu Paths

Main Menu>Preprocessor>Loads>Analysis Type>Analysis Options
Main Menu>Solution>Analysis Type>Analysis Options