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Nodes not connected to any active elements may "float," or pick up stray degree-of-freedom (DOF) responses. You may want to constrain inactive DOFs (D, CP, etc.) in some cases to reduce the number of equations to be solved and to avoid ill-conditioning. Constraining inactive DOFs can become more important for cases in which you want to reactivate elements with a specific shape (or temperature, etc.). If so, remove the artificial constraints when you reactivate elements, and remove nodal loads from inactive DOFs (that is, at nodes not connected to any active elements). Similarly, you must specifically add nodal loads (if any) to reactivated DOFs.

13.4.2.1.1. Sample Input for First Load Step

Part of your input listing could look like this for your first load step:

! First load step

 

TIME,...

! Sets TIME value (optional for static analyses)

NLGEOM,ON

! Turns large-deflection effects on

NROPT,FULL

! You must explicitly set the Newton-Raphson option

ESTIF,...

! Sets non-default reduction factor (optional)

ESEL,...

! Selects elements to be deactivated in this load step

EKILL,...

! Deactivates selected elements

ESEL,S,LIVE

! Selects all active elements

NSLE,S

! Selects all active nodes

NSEL,INVE

! Selects all inactive nodes (those not attached to any

 

! active elements)

D,ALL,ALL,0

! Constrains all inactive DOFs (optional)

NSEL,ALL

! Selects ALL nodes

ESEL,ALL

! Selects ALL elements

D,...

! Adds constraints as appropriate

F,...

! Adds nodal loads to active DOFs as appropriate

SF,...

! Adds element loads as appropriate

BF,...

! Adds body loads as appropriate

SAVE

 

SOLVE

 

13.4.2.2. Define Subsequent Load Steps

In the remaining load steps, you can deactivate and reactivate elements as desired. As before, be sure to apply and delete constraints and nodal loads as appropriate.

To deactivate and reactivate elements, issue the EKILL and EALIVE commands, respectively.

13.4.2.2.1. Sample Input for Subsequent Load Steps

The following simplified input listing demonstrates how you might deactivate and reactivate elements:

! Second (or subsequent) load step:

TIME,...

 

ESEL,...

 

EKILL,...

! Deactivates selected elements

ESEL,...

 

EALIVE,...

! Reactivates selected elements

...

 

FDELE,...

! Deletes nodal loads at inactive DOFs

D,...

! Constrains inactive DOFs

...

 

F,...

! Adds nodal loads as appropriate to active DOFs

DDELE,...

! Deletes constraints from reactivated DOFs

SAVE

 

SOLVE

 

13.4.3. Review the Results

Typically, you will follow standard procedures when postprocessing an analysis containing deactivated or reactivated elements.

 

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of ANSYS, Inc. and its subsidiaries and affiliates.