CNTSTB

Bulk Data Entry Defines parameters for stabilization control of surface-to-surface contact and large displacement node-to-surface contact.

A CNTSTB Bulk Data Entry should be referenced by a CNTSTB Subcase Information entry to be applied in a particular subcase globally.

Format

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
CNTSTB	`ID`		`APSTB`	`LMTGAP`		`S0`	`S1`
	`SCALE`	`TFRAC`

The following continuation line (beginning with the CNTINT flag) is used to define another set of stabilization parameters, which overrides the set of parameters above, and applied locally on a specific contact interface (CTID). It can be repeated as required.

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
	`CNTINT`	`CTID`	`APSTB`	`LMTGAP`		`SO`	`S1`
	`SCALE`	`TFRAC`

The continuation line can also be used to define a set of stabilization parameters for CGAP/CGAPG elements with gap property (PID).

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
	`GAPINT`	`PID`	`APSTB`	`LMTGAP`		`SO`	`S1`
	`SCALE`	`TFRAC`

CNTINT and GAPINT continuation lines can coexist in one CNTSTB card. CTID and PID can be identical in one CNTSTB card, as well.

Example

(1)	(2)	(3)	(4)	(7)	(8)
CNTSTB	99		NO
	CNTINT	51	YES
		0.01
	CNTINT	52	YES
	10.0	0.01
	GAPINT	52	YES
	1.0E4	0.25
	GAPINT	58	YES	1.0	0.001
	1.0E4	0.05

Definitions

Field	Contents	SI Unit Example
`ID`	Each CNTSTB Bulk Data Entry should have a unique identification number. No default (Integer > 0)
`APSTB`	Head flag indicating if contact stabilization is activated. YES Contact stabilization effect is activated. NO (Default) Contact stabilization effect is deactivated. Note: All the fields following `APSTB` should be blank, if `APSTB` is set to NO.
`LMTGAP`	Contact opening threshold for stabilization. Stabilization becomes zero when contact opening is greater than or equal to this value. blank (Default) The threshold is calculated automatically based on characteristic edge lengths at the contact surfaces. The default threshold is 1.0 for the `GAPINT` continuation line. (Real > 0.0 - specified threshold value)
`S0`	Scale factor for stabilization coefficient at the start of a subcase. Default = 1.0 (Real ≥ 0.0)
`S1`	Scale factor for stabilization coefficient at the end of a subcase. Default = 0.0 (Real ≥ 0.0)
`SCALE`	Stabilization coefficient scale factor. Default = 1.0 (Real ≥ 0.0)
`TFRAC`	Factor for scaling tangential stabilization with respect to normal stabilization. Default = 0.1 (Real ≥ 0.0)
`CNTINT`	Defines the start of a continuation line used to specify another set of stabilization parameters, which overrides the set of parameters defined above, for a specific contact interface (`CTID`). It can be repeated as required.
`CTID`	Contact interface identification number. No default (Integer > 0)
`GAPINT`	Defines the start of a continuation line used to specify another set of stabilization parameters, which overrides the set of parameters defined above, for specific CGAP/CGAPG elements (`PID`). It can be repeated as required.
`PID`	Gap property identification number. No default (Integer > 0)

Comments

The CNTSTB Bulk Data Entry is selected by the CNTSTB Subcase Information Entry.
When APSTB is YES, the contact normal stabilization stiffness $K_{CSTB}^{normal}$ is calculated as:(1)
$K_{CSTB}^{normal} = {\begin{matrix} SCALE \cdot f (t^{*}) \cdot K_{CREF} & if contact opening < LMTGAP \\ 0 & if contact opening \geq LMTGAP \end{matrix}$

Where, $K_{C R E F}$ is automatically calculated reference stiffness (10^-5 times the contact penalty stiffness) for contact stabilization, and $f (t^{*})$ is the time-dependent scale factor.

For time, $t$ in a subcase, $t^{*}$ is calculated as:(2)
$t^{*} = (t - t_{0}) / (t_{1} - t_{0})$

Where,

$t_{0}$

Time at the start of the subcase

$t_{1}$

Time at the end of the subcase

$f (t^{*})$ is calculated using S0 and S1 as $f (t^{*}) = S 0 \cdot (1 - t^{*}) + S 1 \cdot t^{*}$ .
When APSTB is YES, the contact tangent stabilization stiffness $K_{CSTB}^{tangent}$ is calculated as:(3)
$K_{CSTB}^{tangent} = TFRAC \cdot K_{CSTB}^{normal}$

The defaults and priority information in conjunction with PARAM,EXPERTNL,CNTSTB for different contact types are:

Table 1. Contact Stabilization. Stabilization is not applicable to FREEZE or TIE Contact
	Model without LGDISP Analysis		Model with LGDISP Analysis
	N2S	S2S/CGAP/ CGAPG	N2S for LGDISP	S2S/CGAP/ CGAPG
PARAM,EXPERTNL,CNTSTB	Effective ²	Effective ¹	Effective ¹	Effective ¹
CNTSTB (Bulk card referenced by Subcase Entry)	Ineffective	Effective	Effective	Effective
PARAM,EXPERTNL,CNTSTB + CNTSTB (Bulk card referenced by Subcase Entry)	Stabilization with the PARAM is effective ²	For the subcase that references CNTSTB (Bulk Data), stabilization with the Bulk card is effective; For other subcases, stabilization with the PARAM is effective. ¹	For the subcase that references CNTSTB (Bulk Data), stabilization with the Bulk card is effective; For other subcases, stabilization with the PARAM is effective. ¹	For the subcase that references CNTSTB (Bulk Data), stabilization with the Bulk card is effective; For other subcases, stabilization with the PARAM is effective. ¹

When both CGAP/CGAPG elements and contact elements appear in a model together with CNTSTB applied globally, the global damping stabilization will not be applied on the CGAP/CGAPG elements, unless GAPINT is defined in CNTSTB card. When only CGAP/CGAPG elements appear in a model with CNTSTB applied globally, the global set of damping stabilization parameters will apply on the CGAP/CGAPG elements.
This card is represented as a load collector in HyperMesh.

¹ For Small Displacement S2S contacts/gaps and contacts/gaps in LGDISP, the stabilization activated with the PARAM is consistent with the stabilization activated with default settings of the CNTSTB Bulk Data Entry.

² For Small Displacement N2S, the stabilization can only be activated with the PARAM, and both normal and tangential stabilizations are non-zero, if the PARAM is specified in the model.