KBC
KBC, KEY
Specifies stepped or ramped loading within a load step.
MP ME ST PR PRN <> <> <> EM EH <> PP <> EME MFS
KEY

Ramping key:

0 — 

Loads are linearly interpolated (ramped) for each substep from the values of the previous load step to the values of this load step.

1 — 

Loads are step changed (stepped) at the first substep of this load step to the values of this load step (i.e., the same values are used for all substeps). Useful for rate-dependent behavior (e.g., creep, viscoplasticity, etc.) or transient load steps only.

Command Default

When SOLCONTROL is ON, ANSYS performs ramped loading if ANTYPE,STATIC, or if ANTYPE,TRANS and TIMINT,OFF. It performs stepped loading if ANTYPE,TRANS and TIMINT,ON. (In a transient analysis, TIMINT,ON is the default.)

When SOLCONTROL is OFF, ramped loading for all types of transient or nonlinear analysis.

Notes

Specifies whether loads applied to intermediate substeps within the load step are to be stepped or ramped. Used only if DTIME on the DELTIM command is less than the time span or, conversely, if NSBSTP on the NSUBST command is greater than one. Flags (FSI, MXWF, MVDI, etc.) are always stepped.

Changing the ramping KEY (i.e., switching between ramped and stepped boundary conditions) between load steps is not recommended.

For ramped loading (KBC,0), when a load is applied for the first time, it is interpolated from zero to the value of the current load step, and not from the initial condition or value of the degree of freedom from the previous load step. Spatially varying tabular loads or boundary conditions do not support direct ramping or stepping options and, instead, apply their full values according to the supplied tabular functions regardless of the KBC setting.

For a static or harmonic cyclic symmetry analysis, any load that varies by sector (CYCOPT,LDSECT) is tabular and is applied as a step change, regardless of the KBC setting; however, any non-tabular loads in the same analysis are ramped or stepped according to the KBC setting.

Irrespective of the KBC setting, loads are usually step-removed. See Stepping or Ramping Loads in the Basic Analysis Guide for more information.

It is sometimes difficult to obtain successful convergence with stepped loading in a nonlinear transient problem. If divergence is encountered, determine if stepped loading was used by default, then determine if it is appropriate for the analysis.

If you run an analysis using optimized nonlinear solution defaults (SOLCONTROL,ON) but do not issue the KBC command, the program chooses whether or not to use stepped or ramped loads. The program-chosen option will be recorded on the load step files as KBC,-1.

This command is also valid in PREP7.

Menu Paths

Main Menu>Preprocessor>Loads>Analysis Type>Sol'n Controls>Transient
Main Menu>Preprocessor>Loads>Load Step Opts>Time/Frequenc>Freq and Substeps
Main Menu>Preprocessor>Loads>Load Step Opts>Time/Frequenc>HOWP and Substeps
Main Menu>Preprocessor>Loads>Load Step Opts>Time/Frequenc>Time - Time Step
Main Menu>Preprocessor>Loads>Load Step Opts>Time/Frequenc>Time and Substeps
Main Menu>Solution>Analysis Type>Sol'n Controls>Transient
Main Menu>Solution>Load Step Opts>Time/Frequenc>Freq and Substeps
Main Menu>Solution>Load Step Opts>Time/Frequenc>HOWP and Substeps
Main Menu>Solution>Load Step Opts>Time/Frequenc>Time - Time Step
Main Menu>Solution>Load Step Opts>Time/Frequenc>Time and Substeps

Release 14.0 - © 2011 SAS IP, Inc. All rights reserved.