[MappingApplication] Proper Implementation of a Radial Basis Function Mapper for FEM-FEM and IBRA-FEM #13981

juancamarotti · 2025-11-19T10:35:09Z

This PR extends the MappingApplication to support Radial Basis Function (RBF) mapping, enabling flexible, mesh-independent transfer of scalar and vector fields between non-matching geometries.

Overview

Introduces an RBFMapper for scalar and vector field transfer across arbitrary point sets
Supports multiple RBF kernels (Gaussian, multiquadric, inverse multiquadric, thin-plate spline) with optional polynomial augmentation.
Implements bi-directional mapping using consistent interpolation matrices. (Note: Consistent mapping is supported from IBRA → FEM domains or between FEM domains.)
Fully integrated with the CoSimulationApplication for FSI and other multi-physics couplings.
Supports conservative mapping, ensuring energy and load consistency.

Implementation Notes

The mapper allows selecting N closest support points to build each local interpolation system.

"search_settings" : {
      "use_all_rbf_support_points": false, 
      "required_rbf_support_points": 10,
      "max_num_search_iterations"     : 10
 }

Precomputing the mapping matrix is available through precompute_mapping_matrix and recommended for repeated coupling steps and mandatory for IGA setups.
The algorithm includes a local-search termination criterion to avoid redundant InterfaceInfo creation (at the end we only have just one InterfaceInfo per LocalSystem). Each InterfaceInfo has a RBFSupportAccumulator which is the data structure in charge of accumulating the support points for each local system

Tests

Validated with analytical scalar and vector mapping benchmarks.
Verified on FSI benchmarks, including FSI Mok and FSI Turek, demonstrating accuracy and robustness.

Multivariate interpolation for fluid-structure-interaction problems using RBF.pdf

FYI @matekelemen @sunethwarna

…nts to control points

…garding naming

…into mapping/rbf_mapper_proper_implementation

…d classes

…erface info

… can be used from outside the class

juancamarotti · 2025-11-24T11:26:18Z

FYI @philbucher

philbucher

great work, I think conceptually its very good

I had mostly implementation detail questions and remarks

philbucher · 2025-12-01T23:55:27Z

applications/MappingApplication/custom_searching/interface_communicator.cpp

-        "echo_level"                    : 0
+        "echo_level"                    : 0,
+        "required_rbf_support_points"  : 0,
+        "use_all_rbf_support_points": true


why not define "max_support_points`?

Also, this should be settings of the RBF local system and interface info, its not even used here

philbucher · 2025-12-01T23:57:56Z

applications/MappingApplication/custom_utilities/mapper_utilities.cpp

    rModelPartCommunicator.SynchronizeNonHistoricalVariable(INTERFACE_EQUATION_ID);
 }

+void AssignInterfaceEquationIdsOnConditions(Communicator& rModelPartCommunicator)


Ideally you would generalize the function that works on nodes, maybe by passing a range, or iterator start and end

philbucher · 2025-12-01T23:58:21Z

applications/MappingApplication/custom_utilities/mapper_utilities.h

+/**
+* @brief Assigning INTERFACE_EQUATION_IDs to the conditions, with and without MPI
+* This function assigns the INTERFACE_EQUATION_IDs to the conditions, which
+* act as EquationIds for the MappingMatrix in the case of IGA. This work with and without MPI,


Suggested change

* act as EquationIds for the MappingMatrix in the case of IGA. This work with and without MPI,

* act as EquationIds for the MappingMatrix. This work with and without MPI,

philbucher · 2025-12-01T23:59:00Z

applications/MappingApplication/custom_utilities/mapper_utilities.h

+* act as EquationIds for the MappingMatrix in the case of IGA. This work with and without MPI,
+* in MPI a ScanSum is performed with the local number of nodes
+* @param rModelPartCommunicator The Modelpart-Communicator to be used
+* @author Juan I. Camarotti


Suggested change

* @author Juan I. Camarotti

we dont do fct based authorship => thats what we have git for

there are also authorship rules in the wiki somewhere

philbucher · 2025-12-01T23:59:20Z

applications/MappingApplication/custom_utilities/mapper_utilities.h

+* @brief Assigning INTERFACE_EQUATION_IDs to the conditions, with and without MPI
+* This function assigns the INTERFACE_EQUATION_IDs to the conditions, which
+* act as EquationIds for the MappingMatrix in the case of IGA. This work with and without MPI,
+* in MPI a ScanSum is performed with the local number of nodes


wrong comment

philbucher · 2025-12-02T00:13:59Z

applications/MappingApplication/custom_mappers/radial_basis_function_mapper.h

+              mRBFTypeString(RBFType),
+              mRBFTypeEnum(ParseRBFType(RBFType)),


whats the difference? Why isnt the enum enough?

philbucher · 2025-12-02T00:14:56Z

applications/MappingApplication/custom_mappers/radial_basis_function_mapper.h

+    {
+        // backward compatibility
+        if (mMapperSettings.Has("search_radius")) {
+            KRATOS_WARNING("Mapper") << "DEPRECATION-WARNING: \"search_radius\" should be specified under \"search_settings\"!" << std::endl;


please dont introduce deprecated stuff in new code

philbucher · 2025-12-02T00:15:04Z

applications/MappingApplication/custom_mappers/radial_basis_function_mapper.h

+        }
+
+        if (mMapperSettings.Has("search_iterations")) {
+            KRATOS_WARNING("Mapper") << "DEPRECATION-WARNING: \"search_iterations\" should be specified as \"max_num_search_iterations\" under \"search_settings\"!" << std::endl;


philbucher · 2025-12-02T00:15:51Z

applications/MappingApplication/custom_mappers/radial_basis_function_mapper.h

+    void AddInterfaceInfo(MapperInterfaceInfoPointerType pInterfaceInfo) override 
+    {
+        mInterfaceInfos.clear();
+        mInterfaceInfos.push_back(pInterfaceInfo);
+    }


can you please explain why you override?

philbucher · 2025-12-02T00:20:19Z

applications/MappingApplication/custom_utilities/mapper_interface_info.h

+    * @brief Returning the results of the neighbour search for the RBF mapper
+    * @author Juan I. Camarotti
+    */
+    virtual const RBFSupportAccumulator& GetRBFSupportAccumulator() const


please dont add a special interface

I solved basically the same issue with static_cast, see here:

Kratos/applications/MappingApplication/custom_mappers/barycentric_mapper.cpp

Line 278 in 1290106

const BarycentricInterfaceInfo& r_info = static_cast<const BarycentricInterfaceInfo&>(*mInterfaceInfos[i]);

Its not the greatest solution either, but I think in this case its cleaner

juancamarotti added 30 commits May 13, 2025 14:52

First draft of the RBF Mapper

aea9c5a

Creating a matrix of destination coordinates

07ce71d

Adding the functionality to tranform the mapping from integration poi…

5be0815

…nts to control points

Changes for the VLM solver

f687181

changing the definition odf the TPS

b270b2e

Adding new parameters to the mapper

e344117

changing some types

d7b201b

error correction

22377f1

adding some new functions in the rbf mapper

9b848b3

minor changes and creation of some new functions

da7cc7a

changing typedef to using and adding some new function

ea6aec0

Reimplementing some methods in the RBF mapper

a01d093

Change comparison for the thin_plate_spline rbf

994dfac

Refactoring of the RBF Mapper

c7098fa

Merge branch 'master' into mapping/rbf_based_mapper

61e7fc5

Short explanation for a function

3e45bc0

Test for the RBF Mapper

2fad679

small changes and adding error messages

62ab6c4

correcting the test

f7a2a4d

Changint the rbf type to an enum class and also some minor changes re…

b10cb87

…garding naming

Merge remote-tracking branch 'origin' into mapping/rbf_based_mapper

8d36f20

first commit

a250955

adding rbf utilities (other PR)

340b316

Initial creation of the new rbf mapper

bfe526a

Merge branch 'master' of https://github.com/KratosMultiphysics/Kratos …

3a10cb1

…into mapping/rbf_mapper_proper_implementation

Fixing some old tests

0d075ff

Changing the RBF Test

53233bb

solving a bug in the RBF utilities

113865f

solving bug

ffb4ad4

adding BuildMappingMatrixRBFMapper to the mapping matrix utilities

ef2b099

juancamarotti added 6 commits November 19, 2025 11:13

adding AssignInterfaceEquationIdsOnConditions to the MapperUtilities

841b5ad

new parameters for the search

42fe081

making AddInterfaceInfo virtual so that it can be overriden is derive…

8b12985

…d classes

creating a method called GetRBFSupportAccumulator() inside mapper int…

db5ef77

…erface info

creation of the rbf mapper for FEM-FEM and IGA-FEM scenarios

9f4327a

Merge branch 'master' into mapping/rbf_mapper_proper_implementation

a9828e2

juancamarotti requested a review from philbucher November 19, 2025 10:35

juancamarotti self-assigned this Nov 19, 2025

juancamarotti requested review from a team as code owners November 19, 2025 10:35

juancamarotti added C++ CoSimulation Mapping labels Nov 19, 2025

reverting the changes in the rbf utilities in the core

426df72

juancamarotti requested a review from rickyaristio November 19, 2025 10:38

juancamarotti added 7 commits November 19, 2025 11:40

making CalculateInverseMultiquadricShapeParameter() public so that it…

c149291

… can be used from outside the class

reverting the changes in the interpolative mapper

89db329

reverting changes in interpoaltive base mapper

5fec50f

solving small bug

1af1275

correction in the mapper tests

f4d1771

small bug

b0eeb1d

erasing a non-used member function

1290106

philbucher reviewed Dec 2, 2025

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[MappingApplication] Proper Implementation of a Radial Basis Function Mapper for FEM-FEM and IBRA-FEM #13981

[MappingApplication] Proper Implementation of a Radial Basis Function Mapper for FEM-FEM and IBRA-FEM #13981

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	* act as EquationIds for the MappingMatrix in the case of IGA. This work with and without MPI,
	* act as EquationIds for the MappingMatrix. This work with and without MPI,

		mRBFTypeString(RBFType),
		mRBFTypeEnum(ParseRBFType(RBFType)),

[MappingApplication] Proper Implementation of a Radial Basis Function Mapper for FEM-FEM and IBRA-FEM #13981

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[MappingApplication] Proper Implementation of a Radial Basis Function Mapper for FEM-FEM and IBRA-FEM #13981

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juancamarotti commented Nov 19, 2025 •

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