CNCHECK, Option, RID1, RID2, RINC, InterType, TRlevel, CGAP, CPEN, IOFF
Provides and/or adjusts the initial status of contact
pairs.
OptionOption to be performed:
DETAIL | — | List all contact pair properties (default). |
SUMMARY | — | List only the open/closed status for each contact pair. |
POST | — | Execute a partial solution to write the initial contact configuration to the Jobname.RCN file. |
ADJUST | — | Physically move contact nodes to the target in order to close a gap or reduce penetration. The initial adjustment is converted to structural displacement values (UX, UY, UZ) and stored in the Jobname.RCN file. |
MORPH | — | Physically move contact nodes to the target in order to close a gap or reduce penetration, and also morph the underlying solid mesh. The initial adjustment of contact nodes and repositioning of solid element nodes due to mesh morphing are converted to structural displacement values (UX, UY, UZ) and stored in the Jobname.RCN file. |
RESET | — | Reset target element and contact element key options and real constants to their default values. This option is not valid for general contact. |
AUTO | — | Automatically sets certain real constants and key options to recommended values or settings in order to achieve better convergence based on overall contact pair behaviors. This option is not valid for general contact. |
TRIM | — | Trim contact pair (remove certain contact and target elements). |
UNSE | — | Unselect certain contact and target elements. |
RID1, RID2, RINCFor pair-based contact, the range of real constant
pair ID's for which Option will be performed.
If RID2 is not specified, it defaults to RID1. If no value is specified, all contact pairs in
the selected set of elements are considered.
For general
contact (InterType = GCN), RID1 and RID2 are section
IDs associated with general contact surfaces instead of real constant
IDs. If RINC = 0, the Option is performed between the two sections, RID1 and RID2. If RINC > 0, the Option is performed among all
specified sections (RID1 to RID2 with increment of RINC).
InterTypeThe type of contact interface (pair-based versus general contact) to be considered; or the type of contact pair to be trimmed/unselected/auto-set.
The following labels specify the type of contact interface:
(blank) | — | Include all contact definitions (pair-based and general contact). |
GCN | — | Include general contact definitions
only (not valid when |
The following labels specify the type of contact pairs
to be trimmed/unselected/auto-set (used only when Option = TRIM, UNSE, or AUTO, and only for pair-based contact definitions):
ANY | — | All types (default). |
MPC | — | MPC-based contact pairs (KEYOPT(2) = 2). |
BOND | — | Bonded contact pairs (KEYOPT(12) = 3, 5, 6). |
NOSP | — | No separation contact pairs (KEYOPT(12) = 2, 4). |
INAC | — | Inactive contact pairs (symmetric contact pairs for MPC contact or KEYOPT(8) = 2). |
TRlevelTrimming level (used only when Option = TRIM, UNSE, or MORPH):
(blank) | — | Normal trimming (default): remove/unselect contact and target elements which are in far-field. |
AGGRE | — | Aggressive trimming: remove/unselect contact and target elements which are in far-field, and certain elements in near-field. |
The remaining arguments, CGAP, CPEN, and IOFF, are parameters that control initial contact adjustment.
They are only valid when Option = ADJUST
or MORPH.
CGAPControl parameter for opening gap. Close the opening
gap if the absolute value of the gap is smaller than the CGAP value. CGAP defaults
to 0.25*PINB (where PINB is the pinball radius) for bonded and no-separation
contact; otherwise it defaults to the value of real constant ICONT.
CPENControl parameter for initial penetration. Close the
initial penetration if the absolute value of the penetration is smaller
than the CPEN value. CPEN defaults to 0.25*PINB (where PINB is the pinball radius) for any
type of interface behavior (either bonded or standard contact).
IOFFControl parameter for initial adjustment. Input a
positive value to adjust the contact nodes towards the target surface
with a constant interference distance equal to IOFF. Input a negative value to adjust the contact node towards the target
surface with a uniform gap distance equal to the absolute value of IOFF.
The CNCHECK command provides information
for surface-to-surface, node-to-surface, and line-to-line contact
pairs (element types TARGE169, TARGE170, CONTA171, CONTA172, CONTA173, CONTA174, CONTA175, CONTA176, CONTA177). All contact
and target elements of interest, along with the solid elements and
nodes attached to them, must be selected for the command to function
properly. For performance reasons, the program uses a subset of nodes
and elements based on the specified contact regions (RID1, RID2, RINC) when executing the CNCHECK command.
CNCHECK is available in both the PREP7 and SOLUTION processors, but only before the first solve operation (that is, only before the first load step or the first substep).
If the contact and target elements were generated through mesh commands (AMESH, LMESH, etc.) instead of the ESURF command, you must issue MODMSH,DETACH before CNCHECK. Otherwise, CNCHECK will not work correctly.
The following additional notes are available:
Option = POSTThe command CNCHECK,POST solves the initial contact configuration in one substep. After issuing this command, you can postprocess the contact result items as you would for any other converged load step; however, only the contact status, contact penetration or gap, and contact pressure will have meaningful values. Other contact quantities (friction stress, sliding distance, chattering) will be available but are not useful.
Because Option = POST forces a solve
operation, the PrepPost (PP) license does not work with CNCHECK,POST.
If CNCHECK,POST is issued within the solution processor, the SOLVE command that solves the first load step of your analysis should appear in a different step, as shown in the following example:
/SOLU CNCHECK,POST FINISH . . . /SOLU SOLVE FINISH . . .
CNCHECK,POST writes initial contact results to a file named Jobname.RCN. When postprocessing the initial contact state, you need to explicitly read results from this file using the FILE and SET,FIRST commands in POST1 to properly read the corresponding contact data. Otherwise, the results may be read improperly. The following example shows a valid command sequence for plotting the initial contact gap:
/SOLU CNCHECK,POST FINISH /POST1 FILE,Jobname,RCN SET,FIRST PLNSOL,CONT,GAP,0,1 FINISH . . .
Option = ADJUST or MORPHYou can issue CNCHECK,ADJUST to physically move contact nodes to the target surface. You can also issue CNCHECK,MORPH to physically move contact nodes to the target surface and then morph the underlying mesh to improve the mesh quality. See Physically Moving Contact Nodes Towards the Target Surface in the Contact Technology Guide for more information. Similar to the POST option, if CNCHECK,ADJUST or CNCHECK,MORPH is issued within the solution processor, the SOLVE command that solves the first load step of your analysis should appear in a different step:
/SOLU CNCHECK,ADJUST FINISH . . . /SOLU SOLVE FINISH . . .
After issuing the CNCHECK,ADJUST command, the initial adjustment is converted to structural displacement values (UX, UY, UZ) and stored in a file named Jobname.RCN. Similarly, the CNCHECK,MORPH command converts the initial adjustment of contact nodes as well as the morphing adjustment of solid element nodes to structural displacement values (UX, UY, UZ) and stores them in the Jobname.RCN file. You can use this file to plot or list nodal adjustment vectors or create a contour plot of the adjustment magnitudes via the displacements. When postprocessing the nodal adjustment values, you need to explicitly read results from this file using the FILE and SET,FIRST commands in POST1 to properly read the corresponding contact data. Otherwise, the results may be read improperly.
Note: The Jobname.RCN file contains information generated from the CNCHECK,POST, CNCHECK,ADJUST, or CNCHECK,MORPH command. If multiple commands are issued in the same analysis, the file is overwritten by the last CNCHECK command.
Option = RESETThe command CNCHECK,RESET allows you to reset
all but a few key options and real constants associated with the specified
contact pairs (RID1, RID2, RINC) to their default values. This
option is only valid for pair-based contact definitions.
The following key options and real constants remain unchanged when this command is issued:
Option = AUTOThe command CNCHECK,AUTO automatically changes certain default or undefined key options and real constants to optimized settings or values. The changes are based on overall contact pair behaviors. In general, this command improves convergence for nonlinear contact analysis. This option is only valid for pair-based contact definitions.
The tables below list typical KEYOPT and real constant settings implemented by CNCHECK,AUTO. The actual settings implemented for your specific model may vary from what is described here. You should always verify the modified settings by issuing CNCHECK,DETAIL to list current contact pair properties.
| KEYOPT | Description | Default (0 or blank) | CNCHECK,AUTO | |||
| 1 | Selects DOF set | Structural DOFs | Automatic selection based on DOFs of underlying elements. | |||
| 2 | Contact algorithm | Augmented Lagrange | 1- Penalty for rigid-rigid contact [1]. | |||
| 4 | Location of contact detection point | Gauss point | 2 - Normal to target surface if KEYOPT(2) > 1. | |||
| 5 | CNOF/ICONT adjustment | No adjustment | 1 - Auto CNOF if tiny gap exists. | |||
| 6 | Contact stiffness variation | Use default range |
| |||
| 7 | Element level time increment control | No control |
| |||
| 8 | Assymetric contact selection | No action | 2 - Auto selection if KEYOPT(2) > 1. | |||
| 9 | Effect of initial penetration or gap | Include all | 1 - Exclude if KEYOPT(5) = 1, or if ICONT was previously specified. | |||
| 10 | Contact stiffness update | Between load steps | 2 - Between iterations except when underlying elements are superelements. [2] |
| Real Constants | Description | Default | CNCHECK,AUTO | |
| No. | Name | |||
| 3 | FKN | Normal penalty stiffness factor | 1 | Set to 5 if KEYOPT(9) = 2 (ramp initial penetration) and KEYOPT(10) > 0. |
| 6 | PINB | Pinball region | see [1] | Cut in half if spurious contact is detected or contact searching is slow. |
| 14 | TCC | Thermal contact conductance | 0 | Calculated as a function of highest conductivity of underlying element and overall model size. |
| 19 | ECC | Electric contact conductance | 0 | Calculated as a function of highest permitivity or lowest resistivity of underlying element and overall model size. |
| 26 | MCC | Magnetic contact permeance | 0 | Calculated as a function of highest emissivity of underlying element and overall model size. |
PINB default depends on contact behavior (rigid vs. flexible target), NLGEOM,ON or OFF, KEYOPT(9) setting, KEYOPT(12) setting, and the value of real constant CNOF (see Defining the Pinball Region (PINB)).
CNCHECK,AUTO also sets PRED,OFF for the case of a force-distributed constraint defined via MPC contact.
Option = TRIM/UNSEL)You can issue CNCHECK,TRIM or CNCHECK,UNSEL to remove or unselect contact and target elements which are
in far-field (that is, open and not near contact), or even in near-field
if aggressive trimming logic is used (TRlevel = AGGRE).