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May 28, 2026
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Final version toyota examples #160

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final version toyota example
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131 changes: 8 additions & 123 deletions iga/use_cases/toyota_3d_sbm/README.md
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# 3D Toyota SBM Example
# 3D Toyota SBM Examples

This use case demonstrates a 3D immersed-body fluid analysis with the Surrogate Boundary Method (SBM) in the Kratos IGA Application. The Toyota body is not discretized with a body-fitted fluid mesh. Instead, the car surface is provided as an immersed skin in `toyota_immersed_surface_sbm.mdpa`, while the fluid is solved on a structured Cartesian background NURBS volume generated in the JSON settings.
This directory contains the shared geometry for the Toyota SBM examples together with two split use cases:

## SBM Philosophy
- [steady_stokes/README.md](/home/nantonelli/Examples/iga/use_cases/toyota_3d_sbm/steady_stokes/README.md): steady-state-style 3D Stokes example
- [transient_navier_stokes/README.md](/home/nantonelli/Examples/iga/use_cases/toyota_3d_sbm/transient_navier_stokes/README.md): transient 3D Navier-Stokes example

The main idea of SBM is to decouple the geometry description from the analysis mesh:
The shared files stored in this parent folder are:

- the immersed body is described only by a surface mesh
- the analysis domain is a simple Cartesian background volume
- boundary conditions are imposed on a surrogate boundary built from the background mesh, rather than on a body-fitted mesh
- `toyota_immersed_surface_sbm.mdpa`: common immersed Toyota surface mesh used by both subcases
- `FluidMaterials.json`: common material definition

For this kind of problem, that is useful because the geometry can come from an external triangulated surface, for example an STL-like workflow prepared outside Kratos and then exported to `.mdpa`. The analysis mesh can then be changed independently by editing the background box and its resolution directly in the parameter files.

In this example, the no-slip condition on the immersed Toyota surface is imposed weakly on `IgaModelPart.SBM_Support_inner` with `SbmFluidConditionDirichlet`. The formulation includes skew-symmetric Nitsche terms, and the example is configured in penalty-free mode on the immersed surrogate boundary through `PENALTY_FACTOR: 0.0` in `FluidMaterials.json`.

## Geometry and Modelers

Both `ProjectParameters_3D_fluid.json` and `ProjectParameters_3D_fluid_steady_state.json` follow the same three-step geometry pipeline:

1. `import_mdpa_modeler` imports `toyota_immersed_surface_sbm.mdpa` into `initial_skin_model_part_in`.
2. `NurbsGeometryModelerSbm` creates the background 3D Cartesian NURBS volume.
3. `IgaModelerSbm` builds the fluid domain and the fitted/surrogate support conditions needed by the SBM formulation.

The main model parts created by the setup are:

- `IgaModelPart.FluidDomain`: background fluid volume
- `IgaModelPart.SBM_Support_inner`: surrogate boundary associated with the immersed Toyota body
- `IgaModelPart.SBM_Support_outer`: outer wall support surfaces of the background box
- `IgaModelPart.Support_inlet`: inlet support surface
- `IgaModelPart.SupportOuterPressure`: outlet pressure support surface

## What You Can Change in the JSON

The most important SBM geometry controls are in the `NurbsGeometryModelerSbm` block:

- `input_filename`: selects the immersed surface mesh to import
- `lower_point_xyz` and `upper_point_xyz`: define the background Cartesian box
- `polynomial_order`: defines the polynomial degree of the background NURBS volume
- `number_of_knot_spans`: defines the Cartesian resolution in each direction
- `lambda_outer`, `lambda_inner`, `number_of_inner_loops`: control the SBM surrogate-boundary construction

In practice, if you want to analyze another immersed geometry, the usual workflow is:

1. generate or export a triangulated surface externally
2. convert it to an `.mdpa` skin mesh
3. replace `toyota_immersed_surface_sbm.mdpa`
4. adapt the background box and the number of knot spans in the JSON files

## Physics in This Folder

This folder contains two related fluid setups:

- `ProjectParameters_3D_fluid.json`: transient monolithic 3D Navier-Stokes case with `NavierStokesElement` and a ramped inlet velocity
- `ProjectParameters_3D_fluid_steady_state.json`: steady-state-style 3D case using `StokesElement` and a constant inlet velocity

The boundary treatment is:

- inlet velocity prescribed on `IgaModelPart.Support_inlet`
- zero outlet pressure prescribed on `IgaModelPart.SupportOuterPressure`
- outer-box support conditions imposed weakly on `IgaModelPart.SBM_Support_outer`
- immersed no-slip condition imposed weakly on `IgaModelPart.SBM_Support_inner`

The material file uses a 3D Newtonian constitutive law. In the current setup:

- `IgaModelPart` uses `DENSITY = 1.0`, `DYNAMIC_VISCOSITY = 1e-3`, and `PENALTY_FACTOR = 1e3` for the fitted support terms on the background box
- `IgaModelPart.SBM_Support_inner` uses `PENALTY_FACTOR = 0.0` for the penalty-free immersed-boundary configuration

## Files

- `ProjectParameters_3D_fluid.json`: transient fluid setup
- `ProjectParameters_3D_fluid_steady_state.json`: steady-state fluid setup
- `FluidMaterials.json`: 3D Newtonian material data and SBM penalty settings
- `toyota_immersed_surface_sbm.mdpa`: immersed Toyota skin used by the SBM modeler
- `run_and_post_nurbs_time.py`: runs the transient case and generates postprocessed GIFs
- `run_and_post_nurbs_steady_state.py`: runs the steady case and generates final plots
- `plot_conditions.py`: visualizes the surrogate faces created by the geometry/modeler setup

## Python Dependencies

The post-processing scripts use:

- `numpy`
- `matplotlib`
- `imageio` for GIF writing in the transient script

If a `latex` executable is available, the plotting scripts can use Computer Modern style math text. Otherwise they fall back to standard matplotlib text rendering.

## Run

Transient case:

```bash
cd /home/nantonelli/Examples/iga/use_cases/toyota_3d_sbm
python3 run_and_post_nurbs_time.py
```

Steady-state case:

```bash
cd /home/nantonelli/Examples/iga/use_cases/toyota_3d_sbm
python3 run_and_post_nurbs_steady_state.py
```

Geometry / surrogate-condition plot:

```bash
cd /home/nantonelli/Examples/iga/use_cases/toyota_3d_sbm
python3 plot_conditions.py
```

## Outputs

Transient script:

- `particles_trails.gif`
- `cut_contour_x_lt_0.gif`
- `plane_x_eq_0_contour.gif`

Steady-state script:

- `steady_3d_velocity_pressure.png`
- `steady_plane_x0_velocity.png`
- `steady_plane_x0_pressure.png`

Geometry helper:

- `surrogate_faces_plot.png`
The split layout avoids duplicating the immersed `.mdpa` file while keeping the steady and transient examples documented separately.
11 changes: 2 additions & 9 deletions ...jectParameters_3D_fluid_steady_state.json → ...jectParameters_3D_fluid_steady_state.json
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Expand Up @@ -6,7 +6,6 @@
"echo_level": 1,
"parallel_type": "OpenMP",
"start_time": 0.0,
// "end_time": 9.0
"end_time": 5.0
},

Expand All @@ -17,7 +16,7 @@
"model_part_name": "IgaModelPart",
"domain_size": 3,
"model_import_settings": { "input_type": "use_input_model_part" },
"material_import_settings": { "materials_filename": "FluidMaterials.json" },
"material_import_settings": { "materials_filename": "../FluidMaterials.json" },
"linear_solver_settings": { "solver_type": "bicgstab", "tolerance": 1.0e-14, "max_iteration": 1000, "scaling": true, "preconditioner_type": "ilu0"},
// "linear_solver_settings":{
// // "solver_type": "LinearSolversApplication.sparse_lu"
Expand All @@ -44,7 +43,7 @@
"modeler_name" : "import_mdpa_modeler",
"kratos_module" : "KratosMultiphysics",
"Parameters" : {
"input_filename" : "toyota_immersed_surface_sbm",
"input_filename" : "../toyota_immersed_surface_sbm",
"model_part_name" : "initial_skin_model_part_in"
}
},
Expand Down Expand Up @@ -139,8 +138,6 @@
{
"variable_name": "BODY_FORCE",
"value": ["0", "0", "0"]
// NAVIER STOKES
// "value": ["(cosh(x)*sinh(x)*cosh(y)*cosh(y)*cosh(z)*cosh(z) + cosh(x)*sinh(x)*sinh(y)*cosh(z)*sinh(z-y) - cosh(x)*sinh(x)*sinh(y)*cosh(y)*cosh(z)*sinh(z)) + cosh(x) - 3*cosh(x)*cosh(y)*cosh(z)", "(cosh(x)*cosh(x)*cosh(y)*cosh(z)*sinh(z-y) - sinh(x)*sinh(x)*sinh(z-y)*cosh(z-y) - sinh(x)*sinh(x)*sinh(y)*cosh(z)*cosh(z-y)) + sinh(y) - 3*sinh(x)*sinh(z-y)", "(-cosh(x)*cosh(x)*cosh(y)*sinh(y)*cosh(z)*cosh(z) - sinh(x)*sinh(x)*sinh(z-y)*cosh(y)*cosh(z) + sinh(x)*sinh(x)*sinh(y)*sinh(y)*cosh(z)*sinh(z)) + cosh(z) + 3*sinh(x)*sinh(y)*cosh(z)"]
}
]
},
Expand All @@ -154,7 +151,6 @@
"0.0",
"0.0"
]
// "value": ["cosh(x)*cosh(y)*cosh(z)","sinh(x)*sinh(z-y)","-sinh(x)*sinh(y)*cosh(z)"]
}]
},
{
Expand All @@ -167,7 +163,6 @@
"0.0",
"2.0"
]
// "value": ["cosh(x)*cosh(y)*cosh(z)","sinh(x)*sinh(z-y)","-sinh(x)*sinh(y)*cosh(z)"]
}]
},
{
Expand All @@ -176,7 +171,6 @@
{
"variable_name": "PRESSURE",
"value": "0.0"
// "value": "sinh(x) + cosh(y) + sinh(z)"
},
{
"variable_name": "NORMAL_STRESS",
Expand All @@ -203,7 +197,6 @@
"0.0",
"0.0"
]
// "value": ["cosh(x)*cosh(y)*cosh(z)","sinh(x)*sinh(z-y)","-sinh(x)*sinh(y)*cosh(z)"]
}
}
],
Expand Down
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