Narrow-Band Topology Optimization on SPGrid

[Paper] [Video]

Narrow-Band Topology Optimization on a Sparsely Populated Grid, ACM Transactions on Graphics (SIGGRAPH Asia 2018).

By Haixiang Liu (University of Wisconsin-Madison),

Yuanming Hu (MIT CSAIL),

Bo Zhu (Dartmouth College),

Wojciech Matusik (MIT CSAIL),

Eftychios Sifakis (University of Wisconsin-Madison).

Installation (Tested on Ubuntu 16.04/18.04/Arch Linux. Windows/OS X not supported.)

• Install taichi (legacy branch) first and put this in the projects folder.
• Build the FEM solver: cd solver && make (Note: this needs Intel icc and mkl. Please install if you don't have it.)
• Set the following environment variables according to your machine. For example,

export TC_MKL_PATH=/opt/intel/compilers_and_libraries_2018.0.128/linux/mkl/lib/intel64_lin/
export CUDA_ARCH=61 # or 0 if there is no CUDA
export TC_USE_DOUBLE=1 #

TC_MKL_PATH is for libmkl_rt.so.

• ti build in shell and wait for the build to finish.
• Pick a script under the scripts folder and run with python3. Some scripts have extremely high resolution (see Table 2 in our paper). If you run out of memory, you may want to use a smaller n.

TopoOpt.init

• res: resolution say (64, 64, 64)
• volume_fraction: default=0.1
• use_youngs: Use Young's modulus and Poisson's ratio for material description
  • E: 1e6
  • nu: 0.3
• penalty: SIMP penalty, default=3
• minimum_density: minimum_density in topology optimization, default=0
• minimum_stiffness: default=1e-9
• grid_update_start: default=5
• fraction_to_keep: default=1.0, keep only this fraction of SPGrid blocks during optimization. The blocks with highest density sum will be selected.
• wireframe: default=False
• wireframe_grid_size: default=32
• wireframe_thickness: default=4
• fix_cells_near_force: default=False
• fix_cells_at_dirichlet: default=False
• progressive_vol_frac: default=0 (Solver parameters:)
• cg_tolerance: default 1e-4
• active_threshold: default 1e-6
• cg_max_iterations: default=50
• defect_correction_iter: default=10
• verbose_snapshot: default=False
• defect_correction_cg_iter: default=3
• boundary_smoothing_iters: default=3
• smoothing_iters: default=1 (interior smoothing iterations)
• mg_bottom_size: default=64
• mg_level: default=adaptively choose a value s.t. the coarsest level has resolution <= mg_bottom_size
• explicit_mg_level: default=1
• restart_iterations: default=0
• print_residuals: default=False
• jacobi_damping: default=0.4 (not useful when using GS. Do we need a parameter to switch between GS and jacobi?)
• connectivity_filtering: default=True
• objective_threshold: default=0.5
• exclude_fixed_cells: default=True
• fixed_cell_density: default=1
• step_limit: default=0.2
• exclude_minimal_compliance: default=false

TopoOpt.populate_grid

• domain_type: a container used to populate the SPGrid.

• box: ...
• cylinder: ...
• sphere:
  • inner_radius=0.4
  • outer_radius=0.5
  • upper_only=False

• uniform_bc: Set Dirichlet on all nodes? A string of axis (e.g. 'xy'). default = ""

Set Boundary Conditions

• add_dirichlet_bc(center, radius=0.03, axis='xyz', value=(0, 0, 0))
• add_load(center, force)
• add_plane_load(force, axis_to_search=0/1/2, extreme=+1/-1, bound1=(-0.5, -0.5, -0.5), bound2=(0.5, 0.5, 0.5))
• add_plane_dirichlet_bc(axis_to_fix, axis_to_search, extreme)

Utilities

• Solve a single tcb (e.g. 00002.tcb)

ti run fem_solve 00002.tcb

• Convert binary tcb to human-readable formats (for inspecting boundary conditions, solver parameters e.t.c.)

# Without density field
ti run convert_fem_solve 00002.tcb
# With density field (can be huge)
ti run convert_fem_solve 00002.tcb --with-density

Visualization

ti vd [mode] [file/folder name]

mode can be fem (default, contains BCs, solver parameters and density field only) or snapshots (basically everything). vd stands for visualize_density.

This can be called directly at the output folder (say, bridge_v6_r1024), or the fem, or snapshots folder (bridge_v6_r1024/snapshots), or a single tcb file (bridge_v6_r1024/fem/00001.tcb).

Use H and L to switch between frames. Use J and K to change threshold in voxel rendering. Transparent volume rendering is also supported, press T (for a while, like 1 second) and R to switch.

From snapshots (generated with verbose_snapshot=True), press C to switch channels between density, sensitivity, smoothed_sensitivity, and displacement.

For symmetric domain, press 1, 2, 3 to mirror x, y, z axes.

Bibtex

Please cite our paper if you use this code for your research:

@article{liu2018narrow,
  title={Narrow-Band Topology Optimization on a Sparsely Populated Grid},
  author={Liu, Haixiang and Hu, Yuanming and Zhu, Bo and Matusik, Wojciech and Sifakis, Eftychios},
  journal={ACM Transactions on Graphics (TOG)},
  volume={37},
  number={6},
  year={2018},
  publisher={ACM}
}