# CNTSTB

Bulk Data Entry Defines parameters for stabilization control of contact (S2S and N2S) and gap elements (CGAP/CGAPG). This entry is supported with nonlinear static and nonlinear transient analysis types for both small and large displacement cases.

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

## 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) (5) (6) (7) (8) (9) (10)
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 for CNTINT continuation line)
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.

There is no default for the GAPINT continuation line. You are required to provide a value for LMTGAP field, if the GAPINT continuation line is specified.

(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)

1. The CNTSTB Bulk Data Entry is selected by the CNTSTB Subcase Information Entry.
2. When APSTB is YES, the contact normal stabilization stiffness ${K}_{\text{CSTB}}^{\text{normal}}$ is calculated as:(1)
Where,
${K}_{\text{CREF}}$
Reference stiffness for contact stabilization.
Calculated as:
• For a contact interface: 10-4 times the raw stiffness of the base elements of the contact.
• For a CGAP/CGAPG element: 10-5 times the closed axial stiffness KA on PGAP.
$f\left({t}^{*}\right)$
Time-dependent scale factor.
For time, $t$ in a subcase, ${t}^{*}$ is calculated as:(2)
${t}^{*}=\left(t-{t}_{0}\right)/\left({t}_{1}-{t}_{0}\right)$
Where,
${t}_{0}$
Time at the start of the subcase.
${t}_{1}$
Time at the end of the subcase.

$f\left({t}^{*}\right)$ is calculated using $\text{S0}$ and $\text{S1}$ as $f\left({t}^{*}\right)=\text{S0}\left(1-{t}^{*}\right)+\text{S1}\left({t}^{*}\right)$ .

3. When APSTB is YES, the contact tangent stabilization stiffness ${K}_{\text{CSTB}}^{\text{tangent}}$ is calculated as:(3)
${K}_{\text{CSTB}}^{\text{tangent}}=\text{TFRAC}\cdot {K}_{\text{CSTB}}^{\text{normal}}$
4. The defaults and priority information in conjunction with PARAM,EXPERTNL,CNTSTB for different contact types are:
Table 1. Contact Stabililization. stabilization is not applicable to FREEZE or TIE Contact
LGDISP or (LGDISP+SMDISP) g SMDISP
N2S b/S2S CGAP/CGAPG N2S c

(CGAPG-core)

S2S CGAP/CGAPG
PARAM,EXPERTNL,CNTSTB Damping d Artificial Spring e Artificial Spring e Damping d Artificial Spring e
CNTSTB (Priority a)

(Bulk card referenced by Subcase Entry)

Damping

(‘CNTINT’ or the first line of CNTSTB Bulk card)

Damping f

(‘GAPINT’)

Damping

(‘CNTINT’ or the first line of CNTSTB Bulk card)

Damping

(‘CNTINT’ or the first line of CNTSTB Bulk card)

Damping f

(‘GAPINT’)

1. When both CNTSTB Subcase/Bulk Data pair and PARAM,EXPERTNL,CNTSTB are defined in a subcase, the CNTSTB Subcase/Bulk Data pair takes priority. For other subcases, the stabilization with the PARAM is effective.
2. When there are LGDISP subcases in a deck file, N2S contact will be converted to Internally generated contact (different from CGAPG), and the stabilization on N2S contact will be conducted in this category.
3. CGAPG-core N2S is generated, when N2S contact is defined and there is no LGDISP subcases defined in a deck file. The stabilization on N2S contact will be conducted in this category.
4. In this case, the stabilization activated with the PARAM is consistent with the stabilization activated with default settings of the CNTSTB Bulk Data Entry.
5. The artificial spring stiffness is determined by: (4)
${K}_{as}=\mathrm{max}\left\{0.01K\left({10}^{-6t}-{10}^{-6}\right),0.0\right\}$
Where,
${K}_{as}$
Artificial spring stiffness used to stabilize the gap elements.
$K$
Reference gap stiffness, generally it represents the stiffness of surrounding elements.
$t$
Global analysis time.
6. The data defined in the first line of this card does not apply on CGAP/CGAPG elements. In order to apply damping stabilization on these elements, continuation lines with ‘GAPINT’ flag must be defined and referenced.
7. SMDISP+LGDISP indicates models which contain both SMDISP subcases and LGDISP subcases in the same model.
5. Contact stabilization introduces artificial energy that can delay the open-to-close and close-to-open transitions, and it should be used with caution.
6. This card is represented as a load collector in HyperMesh.