nl_mesh

SDT-rotor Contents Functions

nl_mesh

Purpose

Integrated mesh modifications and case handling for non-linear applications

Description

Integrated case handling for constraint penalization and coupling component splitting hare implemented in this function.

Some non-linearities require surface/volume remeshing (e.g. definition of conforming interfaces for contact) or adaptations (generation of thin interface layers). This function regroups such functionalities. Mesh generation are performed by fe_gmsh(interface to gmsh) and fe_tetgen (interface to tetgen, see help fe_tetgen).

Conform

The Conform call is an integrated call to generate conforming meshes between two facing interfaces. The command generates a conforming surface mesh of the face to replace, merges it with the conform mesh of the second interface, replaces the model face mesh and remeshes the model volume to yield a new equivalent volume with a conform face mesh.

mo1=nl_mesh('conform eltsel"FindElt"',model,sel);
% sel={eltSelToReplace eltSelForReplacement;...}

model is a standard SDT model. sel is a cell array containing in each line two FindElt commands specifying the element selection face to remesh and the element selection face to use for the conforming interface for replacement.

Command option eltsel allows specifying in a string a FindElt command restraining the working area in the original model.
Command option smartSize allows generating a conforming mesh with a coherent mesh characteristic length.
Command option gmsh allows using gmsh to mesh the final volume.
Command option tetgen allows using tetgen to mesh the final volume (by default).
Command option output asks to output the generated mesh in a .mat file.
Command option OrigContour asks to keep original positions of mid-nodes of the quadratic faces delimiting the volume to remesh. This may however yield mesh wrapping problems when the face to remesh is much coarser than the mesh trace to place for conformity.
Command option mergeTo allows specifying a FindElt selection command in a string to replace the mesh on another model selection than the one used to generate the conforming interface (which uses eltsel.
It is also possible to provide additional arguments, which will be passed the the nl_meshcover call performed in the procedure.

Limitations: The Conform call only supports generation of conforming interfaces when one interface contour fully contains the other interface contour. Handling of more complex contour configurations has not been implemented. Besides, this function has been designed to handle planar surfaces. Additional operation to work on non planar surfaces are left to the user (e.g. pre/post projections of the surfaces on a plane).

Contour

Call ContourFrom generates SDT beam1or beam3 contour models for CAD definitions. All formats readable by gmsh can theoretically be used. Only the .geo, .stp and .igs are tested.

Since .geo files can contain geometric yet non discretized objects, a 1D meshing pass is performed with gmsh to provide an SDT contour model. This is not supported for other file types.

model=nl_mesh('contourFrom','file.stp'); % not specifying the type

Call Contour generates an SDT face mesh from an SDT beam1or beam3 contour.

 model=nl_mesh('contour',model);

model is an SDT beam model defining a closed contour.

Command option lcval allows specifying a characteristic length for Gmsh.
Command option lcminval allows specifying a minimal characteristic length for Gmsh.
Command option quad allows generating quadratic meshes.
Command option keepNode asks to keep the original contour NodeId for the contour command.
Command option diag asks to output the Gmsh log file for diagnostic problems.
Command option single tells nl_mesh that a single contour is defined. This is useful when several closed contours are defined since it is impossible to automatically decide whether each contour is independent or if they define a single complex contour.
Command option groupval is used in combination to the single command option. This allows specifying which contour group will be meshed, while other possible contours will define holes.
Command option algo”val” allows specifying which algorithm gmsh must use (this depends on the gmsh version, report to the gmsh documentation for more details).
Command option AllowContourMod allows gmsh adding nodes on the contour provided. By default gmsh is forced not to add nodes to the lines defining the contour to mesh.

Cover

The Cover call is designed to mesh the interstice between two closed planar contours, when one fully contains the other. The call is performed as

[newModel,opt,largeContour]=nl_mesh('cover',model,{eltsel_large,eltsel_small});

model is a standard SDT model. Variables eltsel_large and eltsel_small are FindElt calls defining the element selection of the respectively large surface and small surface (the small being contained in the large).

The output newModel is the mesh generated from the surface contours.

opt outputs additional information about the mesh generation, it is a struct containing fields .NodeAdd specifying the potential nodes added in the interstice space meshed,.nodeEdgeSel1 specifying the NodeId of the nodes located on the eltsel_large contour, .nodeEdgeSel2 specifying the NodeId of the nodes located on the eltsel_small contour, and .tname the name of the temporary file containing the generated mesh.

largeContour provides the original contour in beam elements of the eltsel_large selection.

The following command options are available

merge allows merging the interstice mesh with the inner mesh of the eltsel_small selection.
quad allows generating proper quadratic meshes.
smartSize allows generating an interstice mesh with a characteristic length in coherence with the contour mesh length.
lcval allows setting the characteristic length to Val to the interstice mesher.
algo“name” allows specifying the meshing algorithm name to the gmsh mesher. See the gmsh documentation for more information.

Hole[,Groups,Diff,Drill,Gen]

The Hole command series aims at handling hole detection on surfaces and bore drilling generation. The following functionalities are avaiable

Command HoleGroups detects holes on a closed surface and outputs a contour model with element groups relative to each isolated contour. A second output provides the GroupId corresponding to detected holes.

Command HoleDiff provides surface elements that are inside the holes of a given contour. You should better exploit lsutilto get a robust result.

Command HoleGen generates a planar surface with a ruled mesh featuring a hole and controlled radial positions.

.len length of plate
.wid width of plate
.rAnulus radii for base positions
.ND angular refinement
.NRext external to bolt radius refinement
.MatId assign mat/pro id to meshed part
.noExt remove exterior side
.Center
.normal

Command HoleDrill generates cylindrical drills in a model with the possibility to integrate a ruled bolt mesh.

Replace

The call Replace is designed to replace parts of a model mesh with new given meshes, mesh parts conformity is assumed. It is performed as

model=nl_mesh('replace',model,nodesToReplace,NewModel,nodeIDtoKeep)

model is a standard SDT model. nodesToReplace is a cell array containing vectors of NodeId specifying the areas to be replaced. NewModel is a cell array containing the new models which will be merged to the mesh in coherence with the removed elements (specified by nodesToReplace). nodeIDtoKeep is an optional argument specifying NodeId of the original model for nodes whose NodeId must not change in the transformation.

Control of nodeIDtoKeep per NewModel part is possible by providing a cell array of NodeId list of the same size than NewModel.

The following command options are available

setMat allows defining a specific MatId to the output mesh.
setPro allows defining a specific ProId to the output mesh.
eltsetFindEltString can be provided to provide an element selection for MatId and ProId assignment.
keepNoCheck in combination with the use of a third argument nodeIDtoKeep assumes the nodes numbering is correct and forces the nodes original numbering without check.
-jAll asks to join all elements per type, then separated by MatId
-inSet asks to maintain coherence with EltId sets. EltId sets for which the totality of a given removed part belonged to will be updated to contain the EltId of the replacement mesh.

Rivet

This command generates rivet drills in a specified contour. A model containing a beam contour can be provided, or an EltSel string generating a surface selection (see section and the selface option) on a bigger model. A data structure providing the origins, and rivet radius and washer (or rivet head radius). The mesh generated between both radius is structured.

The data structure must contain fields

Orig providing the rivet centers in an [x y z;...] matrix.
radHole providing the rivet hole radius, either a scalar if all rivets have the same radius, or a line vector providing each rivet radius separately.
radWash providing the rivet washer (or head) radius, either a scalar if all rivets have the same washer radius, or a line vector providing each rivet washer radius separately.

and can optionally contain fields

plane To directly provide the contour plane normal to define the drilling, in an [nx ny nz; ...] matrix.
Ns To define the number of mesh segments in the rivet to washer radius area (default 10), either a scalar if all rivet heads have the same properties, or a line vector defining the property for each rivet separately.
Nr To define the number of mesh radial nodes in the rivet to washer radius area (default 2), either a scalar if all rivet heads have the same properties, or a line vector defining the property for each rivet separately.

Command option MatIdval allows setting the modified mesh MatId to val.
Command option ProIdval allows setting the modified mesh ProId to val.
Command option -fill outputs in second argument a compatible mesh of the rivet bores.
Command option -allQuad outputs the remeshed model with elements only.

Following example meshes a rectangular contour with a few rivet drilling inside.

% Generate a global contour
model=struct('Node',[...
 1 0 0 0  0  0 0;
 2 0 0 0 10  0 0;  
 3 0 0 0 10  2 0
 4 0 0 0  0  2 0], 'Elt',[]);
model.Elt=feutil('ObjectBeamLine 1 2 0 2 3 0 3 4 0 4 1',model);
model=feutil('refinebeam .2',model);
%feplot(model)

% define rivet positions, eventually planes
RO=struct('Orig',[ 3 1 0;6 1 0;9 1 0],...
 'radHole',[.2;.2;.2],...
 'radWash',[.8;.8;.8]);

model=nl_mesh('Rivet',model,RO);
cf=feplot(model);

GmshVol

This call integrates the generation of a volume mesh from a face mesh with gmsh.

model=nl_mesh('GMSHvol',model);

model is a standard SDT face mesh model.

Command option setmat allows specifying a specific MatId to the output mesh.
Command option setpro allows specifying a specific ProId to the output mesh.
Command option keepFaces asks to keep original NodeId of the nodes located on the face mesh.
Command option lc specifies a characteristic length for gmsh.
Command option clmin specifies a minimal mesh length for gmsh.
Command option clmax specifies a maximal mesh length for gmsh.

ExtrudeLayer

This command generates a non trivial extrusion of a face mesh following the face normal at each node, to generate a volume layer.

model=nl_mesh('ExtrudeLayer thick Val',model);

model is an SDT model with shell elements (a surface definition).

Command option thick specifies the extrusion thickness. Command option setmat allows specifying a specific MatId to the output. Command option setpro allows specifying a specific ProId to the output.

StackClean

This call cleans up a model stack when mesh modifications have been performed. It cleans up stack entries definition that became incoherent with some mesh modifications.

model=nl_mesh('StackClean',model);

Command option rmuns removes stack entries that could not be sorted out. Command option rmmod removes stack entries affected by the model modifications.