Using Spline element (NURBS) in SOFA

[bhagath555]

Hello Caribou Community,

This is Bhagath. I am implementing Isogeometric analysis IGA (Spline based FEM) in caribou (SOFA v 21.06).

Let me give you a brief introduction of developments.

1. NurbsSurf - Equivalent to FEM Element with few extra variables.
2. CoreNurbs - Spline geometry processor, similar to VTK module.
3. NurbsReaders - Equivalent to VTKReader.
4. SplinePatch - does the function of Mesh and Domain
5. CaribouSplineTopology - Equivalent to CaribouTopology
6. CaribouSplineForcefield - Equivalent to CaribouForcefield.
7. and finally, ElasticSplineForcefield.

We have validated the working of most of the code with unit-tests. However, When we tried to write unit-test of ElasticSplineForcefield with the inspiration of HyperElasticsplineForcefield. It prompted many errors. What are the possible changes I should make?

1. In the below test using RegularGridTopology and HexahedronSetTopologyContainer as input parameters of createObject function. If I am not wrong, these types are not part of Caribou but part of SOFA. How could I make it work for my case.
2. In “BocROI”, what should I used instead of {"quad", "@surface_topology.quad"} in case of NurbsSurf.

Note: In this test I would like to specify the geometry file path (which is in caribou/build/bin/mesh)

Code snippet : for full code see test_hyperelasticforcefield.cpp

TEST(HyperelasticForcefield, Hexahedron_from_SOFA) {
    MessageDispatcher::addHandler( MainGtestMessageHandler::getInstance() ) ;
    EXPECT_MSG_NOEMIT(Error);

    setSimulation(new sofa::simulation::graph::DAGSimulation());
    auto root = getSimulation()->createNewNode("root");
    createObject(root, "DefaultAnimationLoop");
    createObject(root, "DefaultVisualManagerLoop");
#if (defined(SOFA_VERSION) && SOFA_VERSION >= 201200)
    createObject(root, "RequiredPlugin", {{"pluginName", "SofaBoundaryCondition SofaEngine"}});
#else
    createObject(root, "RequiredPlugin", {{"pluginName", "SofaComponentAll"}});
#endif
#if (defined(SOFA_VERSION) && SOFA_VERSION > 201299)
    createObject(root, "RequiredPlugin", {{"pluginName", "SofaTopologyMapping"}});
#endif
    createObject(root, "RegularGridTopology", {{"name", "grid"}, {"min", "-7.5 -7.5 0"}, {"max", "7.5 7.5 80"}, {"n", "3 3 9"}});

    auto meca = createChild(root, "meca");
    // Create the ODE system
    createObject(meca, "StaticODESolver", {{"newton_iterations", "10"}, {"correction_tolerance_threshold", "1e-5"}, {"residual_tolerance_threshold", "1e-5"}});
    createObject(meca, "LDLTSolver");
    createObject(meca, "MechanicalObject", {{"name", "mo"}, {"src", "@../grid"}});

    // Complete hexahedral topology container
    createObject(meca, "HexahedronSetTopologyContainer", {{"name", "mechanical_topology"}, {"src", "@../grid"}});

    // Mechanics
    createObject(meca, "SaintVenantKirchhoffMaterial", {{"young_modulus", "3000"}, {"poisson_ratio", "0.499"}});
    auto ff = dynamic_cast<SofaCaribou::forcefield::HyperelasticForcefield<caribou::geometry::Hexahedron> *> (
        createObject(meca, "HyperelasticForcefield").get()
    );

    // Fix the left side of the beam
    createObject(meca, "BoxROI", {{"name", "fixed_roi"}, {"quad", "@surface_topology.quad"}, {"box", "-7.5 -7.5 -0.9 7.5 7.5 0.1"}});
    createObject(meca, "FixedConstraint", {{"indices", "@fixed_roi.indices"}});

    // Apply traction on the right side of the beam
    createObject(meca, "BoxROI", {{"name", "top_roi"}, {"quad", "@surface_topology.quad"}, {"box", "-7.5 -7.5 79.9 7.5 7.5 80.1"}});
    createObject(meca, "QuadSetTopologyContainer", {{"name", "traction_container"}, {"quads", "@top_roi.quadInROI"}});
    createObject(meca, "TractionForcefield", {{"traction", "0 -30 0"}, {"slope", "0.2"}, {"topology", "@traction_container"}});

    getSimulation()->init(root.get());

    // EXPECT_EQ(ff->number_of_elements(), 32);
}

Let me know, if any additional information required.
Thanks in advance.
Have a nice weekend.

[bhagath555]

@Ziemnono @Sidaty1 and @hugtalbot, Could you please look into it.

[Ziemnono]

Hi @bhagath555 ,

1. Instead of using the RegularGridTopology and HexahedronSetTopologyContainer you should use your NurbsSurf to create your geometry and then the topology using your CaribouSplineTopology. In this example, even though it is in Python, you should be able to create your NURBS element and create the topology based on this.
2. For the BoxROI, if I remember well you do not need to precise a topology only a BoxSize, and the engine will find your indices inside the Box. You can find many examples in Python, such as sofa/src/examples/Components/engine/BoxROI_2d.scn.
   Let me know if it helped!

[bhagath555]

@Ziemnono , I tried but no luck. Here is the code snippet and error messages

Modified code

createObject(root, "NurbsSurf", {{"name", "nurbs"}});
auto meca = createChild(root, "meca");
// Create the ODE system
createObject(meca, "StaticODESolver", {{"newton_iterations", "10"}, {"correction_tolerance_threshold", "1e-5"}, {"residual_tolerance_threshold", "1e-5"}});
createObject(meca, "LDLTSolver");
createObject(meca, "MechanicalObject", {{"name", "mo"}, {"src", "@" + executable_directory_path + "/meshes/splines/xy_rectangle.txt"}});

//  Complete Nurbs topology container
createObject(meca, "CaribouSplineTopology", {{"name", "mechanical_topology"}, {"src", "@" + executable_directory_path + "/meshes/splines/xy_rectangle.txt"}});

// Mechanics
createObject(meca, "ElasticMaterial", {{"young_modulus", "3000"}, {"poisson_ratio", "0.499"}});
auto ff = dynamic_cast<SofaCaribou::forcefield::ElasticSplineForcefield<caribou::geometry::NurbsSurf<caribou::_2D>> *> (
        createObject(meca, "ElasticSplineForcefield").get()
    );

List of error messages

[ERROR]   [DAGNode(root)] Component 'nurbs' of type 'NurbsSurf' failed:  
 Object type NurbsSurf<> was not created  
 The object is not in the factory.  

/home/bhagath/code/plugins/caribou_IGA/unittest/SofaCaribou/Forcefield/test_elasticsplineforcefield.cpp:35: Failure
Failed
A message of type 'Error' was not expected but it was received. 
====================== Messages =======================
[DAGNode]: 
    Message type   : Error
    Message content: Component 'nurbs' of type 'NurbsSurf' failed:  
 Object type NurbsSurf<> was not created  
 The object is not in the factory.  

    source code loc: /home/bhagath/code/sofa/SofaKernel/modules/SofaSimulationGraph/src/SofaSimulationGraph/SimpleApi.cpp:90
      component: DAGNode(root)
===============================================================

[ERROR]   [MechanicalObject(unnamed)] Source object "@/home/bhagath/code/plugins/caribou_IGA/build/bin/meshes/splines/xy_rectangle.txt" NOT FOUND.
/home/bhagath/code/plugins/caribou_IGA/unittest/SofaCaribou/Forcefield/test_elasticsplineforcefield.cpp:35: Failure
Failed
A message of type 'Error' was not expected but it was received. 
====================== Messages =======================
[MechanicalObject]: 
    Message type   : Error
    Message content: Source object "@/home/bhagath/code/plugins/caribou_IGA/build/bin/meshes/splines/xy_rectangle.txt" NOT FOUND.
    source code loc: /home/bhagath/code/sofa/SofaKernel/modules/SofaCore/src/sofa/core/objectmodel/BaseObject.cpp:135
      component: MechanicalObject(unnamed)
===============================================================

[ERROR]   [CaribouSplineTopology(unnamed)] Source object "@/home/bhagath/code/plugins/caribou_IGA/build/bin/meshes/splines/xy_rectangle.txt" NOT FOUND.
/home/bhagath/code/plugins/caribou_IGA/unittest/SofaCaribou/Forcefield/test_elasticsplineforcefield.cpp:35: Failure
Failed
A message of type 'Error' was not expected but it was received. 
====================== Messages =======================
[CaribouSplineTopology]: 
    Message type   : Error
    Message content: Source object "@/home/bhagath/code/plugins/caribou_IGA/build/bin/meshes/splines/xy_rectangle.txt" NOT FOUND.
    source code loc: /home/bhagath/code/sofa/SofaKernel/modules/SofaCore/src/sofa/core/objectmodel/BaseObject.cpp:135
      component: CaribouSplineTopology(unnamed)
===============================================================

[WARNING] [CaribouSplineTopology(mechanical_topology)] Template '' incorrect, used NurbsSurf in the list:
	* NurbsSurf
	* NurbsSurf_2D
[ERROR]   [DAGNode(meca)] Component 'ElasticSplineForcefield' of type 'ElasticSplineForcefield' failed:  
 Object type ElasticSplineForcefield<> was not created  
 The object is in the factory but cannot be created.  
Requested template : None  
Used template      : None  
Also tried to create the object with the template 'NurbsSurf_2D' but failed for the following reason(s):  
    1. Cannot find a topology in the current context from which the template 'NurbsSurf_2D' can be deduced.  
  

/home/bhagath/code/plugins/caribou_IGA/unittest/SofaCaribou/Forcefield/test_elasticsplineforcefield.cpp:35: Failure
Failed
A message of type 'Error' was not expected but it was received. 
====================== Messages =======================
[DAGNode]: 
    Message type   : Error
    Message content: Component 'ElasticSplineForcefield' of type 'ElasticSplineForcefield' failed:  
 Object type ElasticSplineForcefield<> was not created  
 The object is in the factory but cannot be created.  
Requested template : None  
Used template      : None  
Also tried to create the object with the template 'NurbsSurf_2D' but failed for the following reason(s):  
    1. Cannot find a topology in the current context from which the template 'NurbsSurf_2D' can be deduced.  
  

    source code loc: /home/bhagath/code/sofa/SofaKernel/modules/SofaSimulationGraph/src/SofaSimulationGraph/SimpleApi.cpp:90
      component: DAGNode(meca)

[Ziemnono]

@bhagath555 , not sure how it works by calling with the cpp but did you create the Python binding associated?

[bhagath555]

@Ziemnono. Yeah, almost done. I am testing bindings of CaribouSplineForcefield and ElasticSplineForcefield. I'll let you know.

[Ziemnono]

@bhagath555 , you should also make them for your NurbsSurf and SplineTopology

[bhagath555]

Yes, those are completed.

[Ziemnono]

OK, I think I understand what you're trying to do. You cannot create a NurbsSurf like this, as it is not a "proper" SOFA object. The best is to directly create your CAribouSplineTopology indicating the template NurbsSurf and to precise the positions of the patch nodes, indices, knot span, etc..

[hugtalbot]

Hey @bhagath555

How is it going on your end? I see you closed this issue.
We would love to have an update from you
Cheers 🙌

[bhagath555]

Dear @hugtalbot ,

Almost all the formulation is implemented and visualization part completed yesterday :).

• Elasticity,
• Hyper-elasticity,
• Traction force field,
• Mass,
• Visualization.

However, I still need to validate the implementation, and there are few minor issues regarding NURBS geometry reader and python binding of Data<sofa::type::vector<sofa::type::vector<PointID>>> for indices. I tried to figure out the issues, but no luck. I am waiting for @jnbrunet response at Implementation challenges in Spline based FEM (Isogeometric analysis) in Caribou.

Meanwhile I am looking for some benchmark problems to validate the implementation and other features I can work on.

Thanks, Have a nice day,
Bhagath