# Thermo-elastic/Mechanical Topology Optimization/Simuation
![Screenshot from 2023-07-02 13-57-29.png](docs%2Fimgs%2FScreenshot%20from%202023-07-02%2013-57-29.png)
<b> (Optional) temperature limits, optimization of voxel mesh. </b>

This is the implementation of the paper [Thermo-elastic topology optimization with stress
and temperature constraints.](ref%2FThermo-elastic%20topology%20optimization%20with%20stress%0Aand%20temperature%20constraints.pdf)
By the way, this procedure realized the thermo-elastic TO(topology optimization)([Thermo-elastic topology optimization with stress
and temperature constraints.](ref%2FThermo-elastic%20topology%20optimization%20with%20stress%0Aand%20temperature%20constraints), mechanical TO([top3d.pdf](ref%2Ftop3d.pdf)) and corresponding simulations.

## Files
* `3rd/`: third-party library
* `assets/`: user-defined assets
* `examples/`: several teaching examples
   - `defined_model_writer`: User defined voxel mesh/model as TO/simulation input.
   - `clamped_model_writer`: Clamped to 0 or 1 of the optimized density.
   - `sim_mechanical`: Mechanical simulation.
   - `sim_thermoelastic`: Thermo-elastic simulation.
   - `top_mechanical`: Mechanical TO.
   - `top_thermoelastic`: Thermoelastic TO.
* `output/`: output directory
* `ref/`: reference material
* `src/`: source code
* `cmake/`: CMake files

## Dependencies
**Inside libraries**:
* [mma](3rd%2Fmma): constrained optimization algorithm
* [Eigen](https://eigen.tuxfamily.org/): linear algebra
* [libigl](https://github.com/libigl/libigl): basic geometry functions
* [AMGCL](https://github.com/ddemidov/amgcl): Linear solver. Optional.
* [json](https://github.com/nlohmann/json): parsing input JSON scenes
* [spdlog](https://github.com/gabime/spdlog): logging information
* OpenMP: CPU parallel processing. 
    ```bash
    sudo apt install libomp-dev
    ```
**The following dependencies require user installation**:
* [SuiteSparse](https://github.com/DrTimothyAldenDavis/SuiteSparse): Linear solver. Optional, NOTE: Use of the Intel MKL BLAS is strongly recommended.
* [CUDA Toolkit](https://developer.nvidia.com/cuda-toolkit): CUDA support. Optional (Strongly recommend).

**Select a Linear solver**

If your matrix has less than **50w** of freedom, then it is recommended to choose a direct solver (e.g. SuiteSparse):
1. install SuiteSparse.
2. Set `ENABLE_AMGCL` to `OFF` and set `ENABLE_SUITESPARSE` to `ON` in 
[CMakeLists.txt](CMakeLists.txt).

Otherwise, it is recommended to choose an iterative solver (e.g. AMGCL),in CPU:
1. install OpenMP and AMGCL.
2. Set `ENABLE_AMGCL` to `ON`, `ENABLE_AMGCL_CUDA` to `OFF` and `ENABLE_SUITESPARSE` to `OFF` in [CMakeLists.txt](CMakeLists.txt).

Further, CUDA can be used to speed up the iterative solver:
1. install OpenMP, CUDA Toolkit and AMGCL.
2. Set `ENABLE_AMGCL` to `ON`, `ENABLE_AMGCL_CUDA` to `ON` and `ENABLE_SUITESPARSE` to `OFF` in [CMakeLists.txt](CMakeLists.txt).

Finally, if all options are set to `OFF`, then the Eigen build-in iterative solver will be chosen.(not recommended).

## Build
1. set path in
   [CMakeLists.txt](CMakeLists.txt).
```cmake
set(CMAKE_CUDA_COMPILER "/path/to/nvcc") # set path to nvcc(if AMGCL_CUDA is ON)
```
2. 
```bash
mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=Release ..
make -j 16
```

## Usage
### updated: top and sim sequence
1. Use `example/defined_model_writer` to generate a user-defined voxel mesh/model as TO input.
2. Use `example/top_mechanical` to run mechanical TO. 
3. Use `example/top_thermoelastic` to run thermo-elastic TO.(`||Fth|| / ||Fm||` means the ratio of the thermal force to the mechanical force, the value suggested is `0.1-10`).
4. Use `example/clamped_model_writer` to clamp the optimized density to 0 or 1(select a suitable threshold) as SIM input.
5. Use `example/sim_mechanical` to run mechanical simulation.
6. Use `example/sim_thermoelastic` to run thermo-elastic simulation.
 
Note:
1. open `*.vtk` via [Paraview](https://www.paraview.org/download/).
2. Input 
   1. Set parameters in *.json. see comments in `assets/top-thermoelastic-*.json`(see comments in `assets/config_biclamed.json` and ref paper for MeTh parameters; see comments in `assets/top/config_Lshape.json`)
   2. Redirect in `main.cpp` or `main.cu` if ENABLE_AMGCL_CUDA is ON:
   3. `"//*"` in `config_*.json` file mean comments.
3. Output see `output/txt/${example_name}`, `output/txt/${example_name}/${clamed_example_name*}/` and `output/vtk/${example_name}/${clamed_example_name*}/`.
4. you can modify `OUTPUT_DIR` and `ASSETS_DIR` in `CMAKEList.txt`.
5. you can modify the linear solver arguments `prm.solver.tol` and `prm.solver.maxiter`  in `src/LinearSolver/Amgcl.h` or `src/LinearSolver/AmgclCuda.h`.
6. you should modify example content in `*.cpp` rather than `*.cu`, the latter is copied from the former by cmake.
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