MODCHG

Bulk Data Entry

MODCHG – Parameters for Removing and/or Reactivating Contact Interfaces and/or Elements

Description

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	...
		TYPE	CHANGE	OPT
	CTID10/SID10	CTID11/SID11	CTID12/SID12	CTID13/SID13	CTID14/SID14	CTID15/SID15	CTID16/SID16	CTID17/SID17
	CTID18/SID18	...
		...

(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

Field	Contents
ID	Any MODCHG bulk data entry should have a unique ID. No default (Integer > 0)
TYPE	Type of the entities to be removed or reactivated. <CONTACT, ELMSET> No default. CONTACT – the entities are contact interfaces. ELMSET – the entities are element SETs.
CHANGE	Flag indicating that entities are either to be removed or to be reactivated. <REMOVE, ADD> No default. REMOVE – the entities are to be removed. ADD – the entities are to be reactivated.
OPT	Flag indicating whether to recalculate strain when reactivating stress/displacement elements. <WOSTRN, WISTRN> WOSTRN – strain-free reactivation for stress/displacement elements. WISTRN – strain-recalculated reactivation for stress/displacement elements. Defaults: If TYPE=ELSET 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 to be removed or reactivated, with TYPE=ELMSET. 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).

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,

o	if the subcase does not have a preceding subcase, the contact constraint is active;

o	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 element sets is not allowed nonlinear transient analysis.

•	Since the initial configuration should not be reset in small-displacement nonlinear static analysis, strain-free reactivation of elements is not allowed for small-displacement nonlinear static analysis.

•	Removal of element sets is not allowed, if multi-point constraints (MPC) or Rigid body elements are defined with the grids of any elements that are modified.

•

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.	This card is represented as a loadcollector in HyperMesh.