ctc_utils

SDT-nlsim Contents Functions

ctc_utils

Purpose

High level contact handling in SDT/NL and SDT/contact module.

Generate, GenerateContactPair

This command generates contact data necessary to perform computation of observation and tangent matrices, and possible feplot displays (when using p_contact this command is handled with the syntax

ctc_utils('Generate',model,data)

model is a standard SDT model, data is a structure or a cell array of structures defining contact interactions. data has the fields

name Optional. The interaction name.
master an element selector string which result generates the Face set of the master surface, see sdtweb FindElt. The master is necessarily associated with elements in the model. One can also directly provide an element matrix containing the contact elements.
slave An element selector string which result generates the Face set of the slave surface (for master/slave convention see section 3.2), see sdtweb FindElt.

The following fields are optional, and only required for tangent matrix computations. xxx why not set

contact A string providing the contact law, or the corresponding integer, among the following list. 1: linear; 2: exponential; 4: tabular.
Fu A string providing the contact law parameters.
friction A string providing the friction law or the corresponding identifier, among the following list. 0: none ; 1 or 11: coulomb strict ; 2 or 12: coulomb reg ; 3 or 13: coulomb arctan ; 4 or 14 coulomb scaledreg.
Fv A string providing the friction law parameters.
ProId to specify the target ProId.

If sequentially called for a single model, Generate will concatenate the contact data model with new data. Command option -reset resets the contact data and only keeps the result from the last call.

For SDT/NL models,

Command GenerateContactPair allows a direct generation of contact elements in the model.
generating the minimal contact data model outside the global one for visualization optimization, command option Obs can be used.

Set SetPro

This command handles high level contact/friction laws assignments

model=ctc_utils('setcontId par val',model)'

contId is an identifier of the contact law to define. One can either use ctcnamename, with name the contact interaction name (corresponding to the model stack entry), or proidval with val the contact elements ProId attached to the contact law.

One can then assign any property par to val regarding contact and friction data in the command string. Accessible parameters are ContactLaw, FrictionLaw, Fu, Fv, TangStick, Euler, and other fields relative to contact are supported.

The alternative command setEdit allows editing fields Fu and Fv by only specifying the varying parameters instead of redefining the full sub-property.

The following examples illustrate the syntax use for a model with contact property my_ctc and ProId 1001:

% two equivalent calls to assign a linear contact property 
% of stiffness 1e10 and fixed jacobian value to 1e9
model=ctc_utils('set ctcname"my_contact" ContactLaw"linear" Fu"Kc 1e10" KcLin 1e9',model);
model=ctc_utils('set ProId 1000  ContactLaw 1 Fu"Kc 1e10" KcLin 1e9',model);
% call to assign a friction law with tangent sticking property
model=ctc_utils('set ProId 1000 FrictionLaw11 Fv"mu 0.3 kappa 1e5" TangStick 1',model);
% two equivalent calls to modify kappa in the friction law prop Fv
model =ctc_utils('set ProId1000 Fv"mu 0.3 kappa 1e3"',model); % need to specify the full Fv
model=ctc_utils('setEdit ProId 1000 Fv"kappa 1e3"',model); % with edit no need to specify all Fv param

Definition of customized local orientation MAPs is possible using further arguments,

MAP=struct('dir',{{0,1,0,'v3x','v3y','v3z'}},...
           'lab',{{'v1x','v1y','v1z','v3x','v3y','v3z'}});
model=ctc_utils('set',model,'MAP',MAP);

remove

This command allows removing contact elements and/or properties in the model, and the contact coupling superelement tgtctc.

model=ctc_utils('RemovecontId',model);

The following command options are available:

all allows removing all contact elements at once.
SEinModel allows removing the tangent contact superelement tgtctc generated by command TangentMdlinModel.
obs allows removing the minimal contact observation data in an SDT/NL model generated with command GenerateObs.
-keepSE allows keeping the coupling superelement tgtctc in the model.
-keepStackSE removes the superelement declaration but keeps the stack entry SE,tgtctc.

GetCPro

This command recovers contact properties in the model. The base syntax is [cproid,cil,cpro]=ctc_utils('GetCPro',model)
model is an SDT model with contact elements. The outputs are cproid a column vector providing the ProId of contact elements in the model, cil an ElProp matrix of p_contactentries corresponding to cproid and cpro stack entries of type pro associtated to the contact properties.

The following command options are available

slide to recover contact elements with sliding friction only (Euler property activated).
-zt to also recover elements with p_zt properties.
-ztOnly to only recover elements with p_zt properties.

GetObs

This command outputs data necessary to perform gap observations and generalized force projections for external computations, and feplot selections to display contact fields data.

data=ctc_utils('GetObs',model)
data=ctc_utils('GetObs ProIdi',model) data=ctc_utils('GetObs Name''val''',model) data=ctc_utils('GetObs',model,def)
model is a standard SDT model, on which command Generate was performed, or which contains contact elements.

Command option Name"val" allows specifying a contact interaction name for which observation data are necessary.

data is a cell array containing as many lines as declared interactions. The first colum contains the type, here fixed as nl_contact, the interaction names, the third one contains contact data, in a structure format with fields

DOF The DOF vector on which observations are computed.
NORT Matrix [C_NOR]. This is the observation matrix of normal gaps at the contact points.
TANT Matrix [C_TAN]. This is the observation matrix of relative tangential displacements at the contact points. It is empty if no friction is asked.
wjdet The ponderation product J(x_i)ω_i for each contact point.
GaussCoor Coordinates of the contact points.
adof DOF vector corresponding to all contact data in the model, ordered as GaussCoor field , with DOF .50 for contact pressure, .51 for friction constraint along the first local direction, .52 (when existing) for friction constraint along the second local direction.
iNL Index vector of current contact data in vector adof
Sel A feplot selection for visualization purposes

By default, the observation is based on the constrained DOF (Case.DOF) of the global model.

Command option NoT To generate the observation on the full model DOF.
Command option NoPlace To generate the observation on the contact model.
Command option -NoSel Not to generate the feplot selection.
Command option -selOnly allows outputting the visualization mesh only.
It is possible to provide a deformation structure with field FNL as a third argument to adapt the observation to the deformation DOF.

GetFNL

This command allows computing a posteriori FNL field from a deformation field missing the non-linear data.

def=ctc_utils('GetFNL',model,def)'

GetWeight

This command output in a cell array for each asked ProId, a struct with fields EltId and wjdet with a center node integration rule to provide the weight, or surface associated to each contact element.

data=ctc_utils('GetWeight',model)'

ParInit

This command sets up parameter data in contact properties. They can be used to obtain a parametered tangent model with command ctc_utilsTangentMdl.

model=ctc_utils('ParInit',model,par);
model is a standard SDT model, on which command Generate was performed, or an SDT/NL model with contact elements. par is a parameter definition entry or a cell array of such entries. See .param field description in fe_range to obtain more information about these entries, the following restrictions apply

field .info is mandatory and must provide the parameter type and ProId using a formatted string as typ-proidval. Available types are
- Kn to apply proportional variations of the contact siffness.
- Mu to apply proportional variations of the friction coefficient.
- Omega to apply proportional variations of the sliding velocity with Euler formulation.
Only struct and string format definitions of parameter entries are accepted.

Zeto thickness elements are also supported. The same syntax can be used. Parameter types in field .infp are specific as

Kn to apply proportional variations of the normal siffness.
Kt to apply proportional variations of the planar siffness.
KnKt to apply both Kn and Kt at once.

TieSe

This command generates a surface elastic bonding superelement, that corresponds to TIE or GLUE notions in most codes. It takes the same input as a ctc_utilsGenerate call but will either output a coupling superelement with command TieSe or the model to which the superelement has been added with command TieSeAdd.

Syntax is SE=ctc_utils('TieSe',model,RA);
First input is a finite element model, second input is a struture RA with mandatory fields .slave and .msster providing surface selections on which contact will be formulated. RA can contain any contact property field handled by ctc_utilsGenerate, so that the assembled superelement can integrate the desired formulation.

Ctc2Zt

This command replaces contact elements with zero thickness elements. model=ctc_utils('Ctc2Zt',model).

The contact elements are replaced by zero thickness elements with p_zt properties. A fe_casegConnectionSurface constraint is applied between the zero thickness elements and the slave surface. If the underlaying mesh is second order the new elements are also unjoined from the master surface and a fe_casegConnectionSurface constraint is applied between the zero thickness elements and the master surface. This is required as p_zt properties are applied to first order element topologies.

For bilinear contact properties the same contact stiffness density is applied, for other cases an automated estimation is performed. Tangential coupling properties are by default based on the kappa values in p_contactlaws. No coupling is applied for models with no friction or no friction law.

The following command options are available

-proidval to only convert elements with the specified ProId.
-mtie to force unjoin and constraint the master surface side in all cases.

% Model with contact properties
model=d_contact('Cubes cbuild')
feutil('info',model)
% Convert to zt elements
model=ctc_utils('Ctc2Zt',model)
feutil('info',model)

MpcSe2Ctc

This command converts a coupling superelement based on a penalized fe_casegConnectionSurface constraint into a contact formulation. Contact elements are build on the master side of the constraint. By default contact properties are set as a bilinear contact with automatic stiffness density and a 2D sliding coulomb friction model with planar coupling for tangent models TangStick=1, contact states are evaluated on any present static state in the model stack curve,q0. It is possible to provide other properties.

The base syntax is model=ctc_utils('MpcSe2Ctc',model,list)
model is a model with superlements generated by penalized fe_casegConnectionSurface constraints (see feutilbCaseC2SE). list is a column cell array of superelement names to be converted. In option the second column of list can be a structure providing contact properties to be used as in GenerateContact command.

The following command options are available

-useDOF to restrain original selections to elements that were effectively matched for the constraint.
-flipSel to revert slave and master sides for contact in comparison to the constraint selections.
-nocqinit not to setup the constact state estimation based on static states.

% Model to couple
model=d_contact('Cubes');
% Generate a penalized connection surface constraint
model=fe_caseg('ConnectionSurface -dens -KpAuto -MaxDist1e-6',model,'tie',...
 'group1 & selface & innode{z==1}','group2 & selface & innode{z==1}');
% compute modes
d1=fe_eig(model,[5 10 1e3]);
% convert penalized constraint to contact coupling
model=ctc_utils('MpcSe2Ctc',model,{'tie'});
% compute modes and check frequencies
d2=nl_solve('ModeSkip-fullDOF',model,[5 10 1e3]);
[d1.data d2.Mode.data(:,1)]

Zt2Ctc

This command converts zero thickness elements to contact elements. This is currently a partial implementation for normal contact without friction and hexa8 based surface only. Please report to SDTools if a broader application case is necessary. A bilinear contact model based on p_zt properties is setup.

model=ctc_utils('Zt2Ctc',model);

TangentMdl

This command outputs a coupling superelement containing the tangent contact friction stiffnesses.

SE=ctc_utils('TangentMdl',model,def);
model=ctc_utils('TangentMdl inModel',model);

model is a standard SDT model, on which command Generate was performed, or an SDT/NL model with contact elements. def is a standard SDT deformation curve see sdtweb def which will be used to compute tangent coupling matrices. def should have a single column if a static state is provided. An optionally second column can be provided to specify a velocity.

The following command options allow specific use of the command

inModel asks to output the input model with added coupling superelement relative to the tangent state, with name tgtctc.
-clean combined with inModel, removes the contact elements and properties in the model, so that the output model only features an equivalent tangent coupling instead of contact.
-sepKj asks to output the superelement with coupling matrices respectively split for contribution.
-setPar for use in models with parametered contact and in conjunction with inModel to output a parametered tangent model.
-real to generate a superelement with conservative matrix types only (adapted to real mode computations).
-evalFNL to update non-linear static states based on stack entry curve,q0 prior to generate the tangent model. This option is mandatory if the static state does not have a .FNL field.

Show

This commands performs visualization operations to display contact fields in the FEM. Contact fields are expressed at Gauss points, so that a triangulation of the contact Gauss points is necessary. This is performed by the GetObs command. If this was not performed earlier, Show will perform it itself. It can be noted that for SDT/NL models, this information may be precomputed (and stored in def.FNL.NL) by assigning parameter Sel to 1 in the contact parameter.

By default, the display units are MPa for pressures, and µm for lengths.

Command Show allows visualizing standard contact fields generated by SDT/contact module or SDT/NL, which are the following

Pn Contact pressure, identified by the DOF .50.
Ft1 Friction constraint in first local direction, identified by the DOF .51.
Ft2 Friction constraint in second local direction, identified by the DOF .52.
G Gap, identified by the DOF .54.
W Sliding velocity, identified by the DOF .55.
Pta Friction constraint norm, computed using Pt1 and Pt2.
LMu Local Mu, computed as the ratio of Pta to Pn.

It must be noted that the model has to be contained in an feplot figure to allow display. If argument def is omitted, cf.def will be used.

The following command options can be used

ProIdval allows specifying the contact element of ProId val to be displayed. By default all groups are displayed.
InMesh allows visualizing the contact fields in the full mesh in transparency. By default only the surfaces supporting contact data are displayed.
unitID allows specifying a unit different from the default one. The user must then specify the unit system ID (e.g. SI, or TM) in which the data has to be displayed.
EltSelEltSel_String, in combination with InMesh allows specifying a mesh sub-selection in which the contact surfaces will be displayed, using a string EltSel_String that will be exploited by feutil('findEltEltSel_String,cf.mdl);.
-reset Asks to reset the feplot display from scratch instead before generating the new display.
Rel Asks to display the field variation relative to its initial state (first deformation column). This is useful to display small variations from a static state.
Vel Asks to display the field velocity, computed by numerically deriving the provided field.

The following command lines illustrate how Show can be used

% display contact pressure
ctc_utils('showPn-reset',cf.mdl,def);
% display first direction firction constraint in the full mesh
ctc_utils('showFt1 InMesh',cf.mdl,def);
% display the friction constraint norm relative to its initial state
ctc_utils('ShowPta Rel -reset',cf.mdl,def);
% display the gap field in mm rather than in micrometers
ctc_utils('ShowG unit"MM"',cf.mdl,def);

Examples

Examples are provided in function d_contact.

A simple cube model and a simple disc brake models are available, respectively using the commands d_contact('cubes') and d_contact('DiscBrake').

Application examples are then available in the script command section:

% contact handling demonstration
d_contact('script Cube_Basic')
% disc brake with polar friction basis and convection observation
d_contact('script Brake Polar')
% simple static resolution
d_contact('script Brake')