[SOLVED] creating_"skin"_of_mebrane_traingles

[ewpostek]

Hello,
I would like to cover a tetrahedral mesh with a “skin” made of triangular elements (membrane elements). The “skin” should match the nodes on the surface of the tetrahedrals, and it should have the thickness – th. The suitable mesh is done with gms. The *.msh file contains the triangles and the tetrahedrals.

Would you be so kind to give a hint “how to” ?
Is it possible to make with one loading ?

<MeshGmshLoader name=”meshLoader” filename=”mesh/x.msh” scale=”1″ createSubelements=”true” />

Some doubts: for example, in the

<triangularfemforcefield name=”FEM” youngModulus=”60″ poissonRatio=”0.3″ method=”large”></triangularfemforcefield>

I do not see a place for the thickness

best regards,
Elek

[Hugo]

Hi Elek,

Through the mapping mechanism, you can recover the surface of your tetrahedral mesh using a Tetra2TriangleTopologicalMapping (see example in examples/Components/topology/Tetra2TriangleTopologicalMapping.scn). Then you can have a surface representation of your object with mechanical properties on it.

Here is the scene file you need for an example with a columetric and surface representation of the liver, both with mechanical properties:

<?xml version="1.0" ?>
<Node name="lroot" gravity="0 -9.81 0" dt="0.02">
    <VisualStyle displayFlags="hideVisualModels showBehaviorModels hideCollisionModels hideBoundingCollisionModels hideMappings hideMechanicalMappings showForceFields hideInteractionForceFields"/>
    <DefaultPipeline name="CollisionPipeline" verbose="0" />
    <BruteForceDetection name="N2" />
    <DefaultContactManager name="collision response" response="default" />
    <DiscreteIntersection/>
	
    <Node name="Liver_Volume" gravity="0 -9.81 0">
        <EulerImplicitSolver name="cg_odesolver"  />
        <CGLinearSolver name="linear solver" iterations="25" tolerance="1e-09" threshold="1e-09" />
        <MeshGmshLoader name="meshLoader" filename="mesh/liver.msh" />
        <TetrahedronSetTopologyContainer name="topo" src="@meshLoader" />
        <MechanicalObject name="dofs" src="@meshLoader" />
        <TetrahedronSetGeometryAlgorithms template="Vec3d" name="GeomAlgo" />
        <DiagonalMass  name="computed using mass density" massDensity="1" />
        <TetrahedralCorotationalFEMForceField template="Vec3d" name="FEM" method="large" poissonRatio="0.3" youngModulus="3000" computeGlobalMatrix="0" />
        <FixedConstraint  name="FixedConstraint" indices="3 39 64" />
        <Node name="iver_Surface">
            <include href="Objects/TriangleSetTopology.xml" src="@" tags=" " />
            <Tetra2TriangleTopologicalMapping input="@../topo" output="@Container" />
            <TriangularFEMForceField name="FEM" youngModulus="60" poissonRatio="0.3" method="large" />
            <TriangularBendingSprings name="FEM-Bend" stiffness="300" damping="1.0" />
            <TrianglePressureForceField normal="0 0 1" dmin="0.9" dmax="1.1" pressure="0.4 0 0" />
            <TriangleSet />
        </Node>
        <Node name="Visu" tags="Visual" gravity="0 -9.81 0">
            <OglModel  name="VisualModel" fileMesh="mesh/liver-smooth.obj" />
            <BarycentricMapping name="visual mapping" input="@../dofs" output="@VisualModel" />
        </Node>
    </Node>
    
    <ClipPlane name="Clip" normal="1 0 0" position="-2 0 0"/>    

</Node>

And here is the result, you can see FEM triangles on the surface and tetra in the volume:

Hope this helps.
Cheers,

Hugo

[ewpostek]

Hi Hugo,
yes, it has helped, the triangles cover
the surface.
Just one concern.
Is it possible to identify the triangles on the surface
in the resulting *.vtu file (vtkExporter) ?
The total number of cells is
<Piece NumberOfPoints=”3009″ NumberOfCells=”65516″>
the tetrahedrals only – 15033;

cheers,
Elek

[Hugo]

Hi Elek,

In the scene I wrote above, you can find the triangles covering the surface in the component TriangleSetTopologyContainer (loaded by the Objects/TriangleSetTopology.xml). If you use your VTKExporter in this node, you should be able to export triangles on the surface only.

Does this answer your question?

Hugo

[ewpostek]

hi Hugo,
Thank you, I think we can close
the topic,
best, Elek

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