FreeTO

Freeform 3D topology optimization in MATLAB using structured meshes with smooth boundaries

FreeTO

FreeTO stands for Freeform Topology Optimization (3D topology optimization through a structured mesh with smooth boundaries) and is an open-source Matlab code for initializing, optimizing, and post-processing free-form 3D topology optimization problems.

Syntax

• FreeTO(file, force1, MeshControl, volfrac, 'PropertyName', VALUE,...) Performs topology optimization on the STL domain provided in file with the load-carrying STL subdomain provided in force1, MeshControl to create a structured hexahedral mesh, volfrac for the required volume fraction, property names and values (support conditions and force magnitudes are essential), and other default parameters. The property name-value inputs are given in Table 1.

Table 1: Name-value inputs

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Name-value	Description	Default value
fixed	Mesh file (.stl) of the regions in domain with a Dirichlet displacement boundary condition fixed in all three directions	-
xfixed, yfixed, zfixed	Type of topology optimization approach	-
force2 – force10	Mesh files (.stl) of regions in domain that carry up to 9 additional load cases	-
keepdom	Mesh file (.stl) of regions in domain that should remain unchanged throughout the optimization	-
keep_BC	Specify if the load and support (fixed in all directions) regions should be included in the optimized structure	Yes
keep_BCx, keep_BCy, keep_BCz	Specify if the support regions fixed in x, y, and z directions, respectively, should be included in the optimized structure	No
YoungsModulus	Specify the Young’s Modulus of the material
PoissonsRatio	Specifies the Poisson’s ratio of the material	0.3
optimization	Specify the optimization method (SIMP or SEMDOT)	SIMP
Fmagx, Fmagy, Fmagz	Indicates the x, y, and z components of the loads	0, 0, 0
modelName	Indicates the name of the mesh file (.stl) generated from the optimized structure	-
loadtype	Indicates if a load should be applied at a point (center node) or distributed across all nodes in a load case	distributed
Symmetry1, Symmetry2, Symmetry3	Indicates a symmetry plane to mirror the optimized topology. Symmetry can be indicated a maximum of 3 times.	-
direction1, direction2, direction3	Indicates whether the mirror should occur to the left or right of the symmetry plane. It can be invoked the same number of times as Symmetry	Right

Table 2: Outputs

Variable	Description
comp	Compliance of optimized topology
finalvol	Volume fraction of optimized topology
eleden	Element density array
gridden	Grid density array
elenum1	Number of active elements in the optimization
elenum2	Total number of elements (active + passive)
	Display of the optimized topology
	Display of the compliance and volume fraction histories
	STL file (optional)

Examples:

The following examples show how FreeTO is used. Input STL files of the sample design problems have been prepared and are in the STLs folder in this repository. The input file preparation is shown in a video for Example 1 here.

• Example 1: Optimize a GE bracket given the freebody diagram on the left of Figure 1

  • FreeTO('STLs\GE_domain.stl','STLs\GE_force.stl',80,0.3,'fixed','STLs\GE_fixed.stl','force2','STLs\GE_force.stl','Fmagy',[0 -2000],'Fmagz',[1500 0],'YoungsModulus',210e9)

• Example 2: Optimize one half of an airplane bracket

  • FreeTO('STLs\air_domain.stl','STLs\air_force.stl',90,0.2,'fixed','STLs\air_fixed.stl','zfixed','STLs\air_zfixed.stl','force2','STLs\air_force.stl','force3','STLs\air_force.stl','Fmagx',[1000 1324 0],'Fmagy',[0 -1324 -2500],'YoungsModulus',210e9,'Symmetry1',"x-y",'direction1',"right",'optimization','SEMDOT','modelName','STLs\air_brack_TO.stl')

• Example 3: Optimize a human hand model with loads on the fingertips

  • FreeTO('STLs\hand_domain.stl','STLs\hand_force1.stl',90,0.3,'fixed','STLs\hand_fixed.stl','force2','STLs\hand_force2.stl','force3','STLs\hand_force3.stl','force4','STLs\hand_force4.stl','force5','STLs\hand_force5.stl','Fmagz',2e3*ones(1,5),'YoungsModulus',210e9)

• Example 4: Optimize the quarter of a quadcopter

  • FreeTO('STLs\quad_domain.stl','STLs\quad_force1.stl',70,0.3,'fixed','STLs\quad_fixed.stl','xfixed','STLs\quad_xfixed.stl','yfixed','STLs\quad_yfixed.stl','force2','STLs\quad_force2.stl','force3','STLs\quad_force3.stl','Fmagz',[-1500 -1500 -1000],'YoungsModulus',2e9,'Symmetry1','y-z','Symmetry2','z-x','direction1','right','direction2','left','modelName','STLs\quad_TO.stl','keep_BCz','yes')

Supporting Open-Source Codes

FreeTO utilizes other open-source codes such as intriangulation.m by Johannes Korsawe, and modifications to top3D.m by Liu and Tovar, SEMDOT.m by Fu et al., and phi2stl.m by Vogiatzis et al. FreeTO on this repository uses the optimality criteria method (OCM) but works much better with the Method of Moving Asymptotes (MMA) as optimizer. The implementation of MMA is given in SIMP.m and SEMDOT.m but the lines are commented out as the codes are not on this repository and the user should request them from Prof. Krista Svanberg by email. If using MMA, comment out lines 79 to 84, 135, 137 and uncomment lines 44 to 56, 86 to 99 in SEMDOT.m and SIMP.m. Furthermore, in SEMDOT.m and SIMP.m, tolx = tol_thresh = 1e-3, beta = ER = 0.5 are recommended values for MMA.

To Cite

If you find this code helpful in your work, please cite this open access paper