MODCHG

Bulk Data Entry Defines parameters for removing and/or reactivating contact interfaces and/or elements.

Format

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
MODCHG ID TYPE CHANGE OPT          
  CTID1/

SID1

 CTID2/

SID2

 CTID3/

SID3

 CTID4/

SID4

 CTID5/

SID5

 CTID6/

SID6

 CTID7/

SID7

 CTID8/

SID8

  
  CTID9/SID9 etc              
    TYPE CHANGE OPT          
  CTID10/

SID10

 CTID11/

SID12

 CTID12/

SID12

 CTID13/

SID13

 CTID14/

SID14

 CTID15/

SID15

 CTID16/

SID16

 CTID17/

SID17

  
  CTID18/

SID18

 etc              
    etc              

Example

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
MODCHG 99 CONTACT REMOVE            
  1 5 9            
    CONTACT ADD            
  2 3              
    ELMSET ADD WISTRN          
  11                
    ELMSET REMOVE            
  12                

Definitions

Field Contents SI Unit Example
ID Any MODCHG Bulk Data Entry should have a unique ID.

No default (Integer > 0)

  
TYPE Entity type to be removed or reactivated.
CONTACT
The entities are contact interfaces.
ELMSET
The entities are element SETs (SIDi pointing to SET Bulk Data with TYPE=ELEM).
RIGID
The entities are rigid SETs (SIDi pointing to SET Bulk Data with TYPE=RIGID).
No default 		 
CHANGE Flag indicating that entities are either to be removed or to be reactivated.
REMOVE
The entities to be removed.
ADD
The entities to be reactivated.

No default

 
OPT Flag indicating whether to recalculate strain when reactivating stress/displacement elements.
WOSTRN
Strain-free reactivation for stress/displacement elements.
WISTRN
Strain-recalculated reactivation for stress/displacement elements.

Defaults:

If TYPE=ELMSET and CHANGE=ADD, No default; otherwise, Default = Blank
Note: This option is only effective for TYPE=ELMSET and CHANGE=ADD.
  
CTIDi Identification number of a contact interface to be removed or reactivated, with TYPE=CONTACT.

No default (Integer > 0)

  
SIDi Identification number of an element SET or rigid SET to be removed or reactivated, with TYPE=ELMSET or TYPE=RIGID, respectively.

No default (Integer > 0)

  

Comments

  1. The MODCHG Bulk Data Entry is selected by the Subcase Information command MODCHG=option. It can only be referenced by nonlinear subcase(s). TYPE=CONTACT is additionally supported for optimization runs.
    Note: TYPE=ELMSET is not supported for optimization.

    MODCHG is not supported for CGAP/CGAPG elements and N2S contact in Small Displacement Nonlinear Static Analysis. (MODCHG is supported for N2S in Small Displacement Nonlinear Static Analysis only for cases where the model also contains LGDISP subcase).

  2. PARAM,HASHASSM,YES should be specified.
  3. For TYPE=CONTACT:
    • When a contact interface is removed from a nonlinear subcase, the contact constraint is inactive for the subcase. However, if the contact interface was active in the preceding subcase (the one referenced with CNTNLSUB by the current subcase), the corresponding contact nodal forces at the end of the preceding subcase are linearly ramped down to zero from the start to the end of the current subcase.
    • When a contact interface is reactivated in a nonlinear subcase, the contact constraint is active for the subcase. In large-displacement nonlinear analysis, contact elements are recreated with the deformed configuration when the contact is newly activated; in small-displacement nonlinear analysis, contact elements are not recreated when the contact is newly activated.
    • Contact constraint is effective immediately when the contact is activated. For FREEZE and TIE contacts, the reference configuration for the zero relative motion condition is the configuration when the contact is newly activated. For non-freeze contact, contact opening/penetration is calculated based on the deformed configuration.
    • A contact interface is neither removed nor reactivated in a nonlinear subcase,
      • if the subcase does not have a preceding subcase, the contact constraint is active;
      • if the subcase has a preceding subcase, the contact constraint may be active (depending on whether it is active in the preceding subcase).
    • The MUMPS solver should be specified.
  4. For TYPE=ELMSET:
    • Removal/reactivation of Solids, Shells, CBUSH, CONM2, JOINTG, CBAR, CBEAM, CROD, JOINTG, and Gasket elements (CGASK8, CGASK16, CGASK6, and CGASK12) is supported.
    • Removal/Reactivation of element sets is not allowed in nonlinear transient analysis.
    • Removal of all of the elements referencing a grid will also remove the grid.
    • Strain-free reactivation of elements is only supported for large-displacement nonlinear static analysis (LGDISP).
    • At the beginning of the removal step, OptiStruct calculates the forces that the elements to be removed exert on the remaining elements at the interface nodes between them. The forces are then treated as applied loads for the remaining elements and are gradually ramped down to zero at the end of the removal step. This means that the removal is not completed until the end of the step. The removed element sets are inactive in the succeeding subcase until they are reactivated.
    • Only the element sets removed in the preceding subcase can be reactivated. Additionally, only active element sets can be removed. Removal and reactivation of the same element set in a single subcase is not allowed.
    • For reactivation of the element set with OPT=WOSTRN, the specified elements are immediately activated with zero-stress and zero-strain. However, the initial configuration of the reactivated elements are reset so that they exert no forces at the beginning of the reactivation step. This type of reactivation is completed at the beginning of the reactivation step.
    • For reactivation of the element set with OPT=WISTRN, the specified elements are immediately activated with zero-stress and zero-strain. The initial configuration of the elements are inherited from the preceding removal subcase such that new virtual nodes for the reactivated elements are split from every common node between the reactivated elements and the inherited elements. In the analysis process, the virtual nodes are enforced to gradually merge with the corresponding common nodes at the end of the reactivation step.
  5. For TYPE = RIGID:
    • Removal/reactivation of RBE2 and RBE3 rigids is supported. The SIDi field(s) should reference SET Bulk Data Entry(ies) of TYPE=RIGID.
  6. This card is represented as a property in HyperMesh.