Contact problem between 2 plates

[Hoangn06]

Hello everyone,

I'm testing a contact simulation between 2 plates like this photo. The upper plate will go down and collide with the lower plate.

The XML Script is under my questions.

When i set the ContactDistance =0. The contact can be detected but the contact still can not be created when the 2 plates collide. The upper plate just go right through the lower plate and i received the notification in the terminal like this "[WARNING] [MinProximityIntersection(Proximity)] Null distance between contact detected"

On the third try, i changed the ContactDistance to 4e-5 and now the contact can be detected and created.

My question is why can't i let the ContactDistance to 0 ?

Thank you all and have a great day!!!

---

The XML Script

<?xml version="1.0" ?>

<Node name="root" dt="0.01" gravity="0 0 0">

    <Node name="plugins">
        <RequiredPlugin name="Sofa.Component.IO.Mesh"/> <!-- Needed to use components [MeshGmshLoader] -->  
        <RequiredPlugin name="Sofa.Component.LinearSolver.Iterative"/> <!-- Needed to use components [CGLinearSolver] -->  
        <RequiredPlugin name="Sofa.Component.Mass"/> <!-- Needed to use components [MeshMatrixMass] -->  
        <RequiredPlugin name="Sofa.Component.MechanicalLoad"/> <!-- Needed to use components [ConstantForceField] -->
        <RequiredPlugin name="Sofa.Component.StateContainer"/> <!-- Needed to use components [MechanicalObject] -->  
        <RequiredPlugin name="Sofa.Component.ODESolver.Backward"/> <!-- Needed to use components [EulerImplicitSolver] -->  
        <RequiredPlugin name="Sofa.Component.SolidMechanics.FEM.Elastic"/> <!-- Needed to use components [TetrahedronFEMForceField] -->  
        <RequiredPlugin name="Sofa.Component.Topology.Container.Dynamic"/> <!-- Needed to use components [TetrahedronSetGeometryAlgorithms, TetrahedronSetTopologyContainer] -->  
        <RequiredPlugin name="Sofa.Component.Visual"/> <!-- Needed to use components [VisualStyle] -->  
        <RequiredPlugin name="Sofa.GL.Component.Rendering3D"/> <!-- Needed to use components [OglModel] -->  
        <RequiredPlugin name="Sofa.Component.Constraint.Projective"/> <!-- Needed to use components [FixedProjectiveConstraint] -->  
        <RequiredPlugin name="Sofa.Component.Topology.Container.Constant"/> <!-- Needed to use components [MeshTopology] -->  
        <RequiredPlugin name="Sofa.Component.Collision.Detection.Algorithm"/> <!-- Needed to use components [BVHNarrowPhase,BruteForceBroadPhase,CollisionPipeline] -->  
        <RequiredPlugin name="Sofa.Component.Collision.Detection.Intersection"/> <!-- Needed to use components [MinProximityIntersection] -->  
        <RequiredPlugin name="Sofa.Component.Collision.Geometry"/> <!-- Needed to use components [LineCollisionModel] -->  
        <RequiredPlugin name="Sofa.Component.Collision.Response.Contact"/> <!-- Needed to use components [CollisionResponse] -->  
        <RequiredPlugin name="Sofa.Component.Mapping.Linear"/> <!-- Needed to use components [IdentityMapping] -->  
        <RequiredPlugin name="Sofa.Component.Topology.Mapping"/> <!-- Needed to use components [Tetra2TriangleTopologicalMapping] -->  
    </Node>

    <DefaultAnimationLoop computeBoundingBox="false"/>
    <VisualStyle displayFlags="showForceFields" />
    <MeshGmshLoader name="meshLoaderPlaque1" filename="plaque_bas.msh" />
    <MeshGmshLoader name="meshLoaderPlaque2" filename="plaque_haut.msh" />

    <CollisionPipeline />
    <BruteForceBroadPhase/>
    <BVHNarrowPhase/>
    <MinProximityIntersection name="Proximity" alarmDistance="1e-2" contactDistance="0"/>
    <CollisionResponse name="Response" response="PenalityContactForceField"/>

  
    <Node name="Plaque_bas">
        <EulerImplicitSolver />
        <CGLinearSolver iterations="200" tolerance="1e-09" threshold="1e-09"/>

        <TetrahedronSetTopologyContainer name="Container" src="@../meshLoaderPlaque1" />
        <TetrahedronSetTopologyModifier />
        <TetrahedronSetGeometryAlgorithms template="Vec3d" name="GeomAlgo" />

        <MechanicalObject template="Vec3d" name="SDOF" showObject="1" showObjectScale="1" />
        <TetrahedronFEMForceField name="FEM" youngModulus="20e+10" poissonRatio="0.27"  method="large" />
        <UniformMass name="mass" totalMass="7.8e+3" />

               <Node name="Collision">
                  <!--<MeshTopology src="@../../meshLoaderPlaque1"/> -->
                  <TriangleSetTopologyContainer  name="Container" />
                  <TriangleSetTopologyModifier />
                  <Tetra2TriangleTopologicalMapping input="@../Container" output="@Container" /> 

                  <MechanicalObject name="CollisionDOF" rest_position="@../SDOF.rest_position"  />
                  <TriangleCollisionModel name="CollisionModel" />
                 <LineCollisionModel />
                 <PointCollisionModel />
                  <IdentityMapping name="MappingCollision" input="@../SDOF" output="@CollisionDOF"/>
               </Node>

    </Node>

    <Node name="Plaque_haut">
        <EulerImplicitSolver />
        <CGLinearSolver iterations="200" tolerance="1e-09" threshold="1e-09"/>

        <TetrahedronSetTopologyContainer name="Container" src="@../meshLoaderPlaque2" />
        <TetrahedronSetTopologyModifier />
        <TetrahedronSetGeometryAlgorithms template="Vec3d" name="GeomAlgo" />

        <MechanicalObject template="Vec3d" name="SDOF" showObject="1" showObjectScale="1" />
        <TetrahedronFEMForceField name="FEM" youngModulus="20e+10" poissonRatio="0.27"  method="large" />
        <UniformMass name="mass" totalMass="7.8e+3" />
        <ConstantForceField totalForce="0.1 0 0" /> 

                <Node name="Collision">
                  <!--<MeshTopology src="@../../meshLoaderPlaque1"/> -->
                  <TriangleSetTopologyContainer  name="Container" />
                  <TriangleSetTopologyModifier />
                  <Tetra2TriangleTopologicalMapping input="@../Container" output="@Container" /> 

                  <MechanicalObject name="CollisionDOF" rest_position="@../SDOF.rest_position"  />
                  <TriangleCollisionModel  />
                 <LineCollisionModel />
                 <PointCollisionModel />

                  <IdentityMapping name="MappingCollision" input="@../SDOF" output="@CollisionDOF"/>
               </Node>
            

    </Node>
</Node>

[hugtalbot]

Hi @Hoangn06

Could you remove both IdentityMapping of your collision nodes since you already have a Tetra2TriangleTopologicalMapping?

[Hoangn06]

Hello @hugtalbot

I tried to remove the IdentityMapping component. But when i launched, SOFA experienced a severe bug, displaying the error '[MinProximityIntersection(Proximity)] Null distance between contact detected' and requiring a force shutdown.

When I switched to NewProximityIntersection and removed the LineCollision and PointCollision components, the two plates disappeared from the scene, but contact was still being detected. What is causing this issue?

Thank you again for the help

[Hoangn06]

And in this example:

sofa/examples/Demos/SofaScene.scn

Line 107 in 7c6bddc

<Node name="Collision">

IdentityMapping still be used for Tetra2TriangleTopolocgicalMapping..

[Hoangn06]

Hello everyone and @hugtalbot,

I've test so many ways. Finer the mesh of the plates, or created a surface mesh for collision (not using Tetra2TriangleTopologicalMapping ), or turn the plates into rigid, or change the ContactStiffness, or test the another intersection methods,... but the contact can not be created between 2 plates when i set ContactDistance = 0 even though the contact can be detected.

I also tested FrictionalContact, but I encountered a strange interaction between two plates (the two plates were fractured into elements).

Do you have any suggestions how to solve this..?

Thank you and have a agreat day!

[hugtalbot]

Hi @Hoangn06

Sorry for the very late reply. We slowed down our forum activity in 2025 to focus on dev, we're now back here.

The configuration you are looking at is very specific. Two deformable objects colliding with their colliding faces which are co-planar. It is a ill-case for collision detection. To solve this, I would advise to use the LocalMinDistance which is a collision intersection method, filtering contact for such ill-case.

Regarding the remark about a zero contact distance, working with time stepping method as we do it is safer to always keep a safety collision offset (i.e. a small - but non-zero - collision distance)

I hope this helps
Cheers