Planar Decomposition
Planar decomposition divides a 3D compliant mechanism design problem into multiple 2D cross-sectional solves by defining cutting planes through the part. Each plane produces an independent 2D design optimization, and the results combine to form the full 3D mechanism. This approach bridges 2D solve speed with 3D design intent.
When to use planar decomposition
Use Planar Decomposition when:
- You have a 3D mechanism design but want to leverage fast 2D solvers.
- The mechanism can be reasonably approximated as a stack of 2D cross-sections.
- You want to explore how different cutting orientations affect the optimized design.
- The full 3D solver is too slow for your iteration needs.
Do not use planar decomposition when:
- The mechanism requires true 3D design (loads and motion that cannot be captured by any set of 2D planes). Use Compliant Mechanism 3D instead.
- The design is purely 2D. Use Compliant Mechanism 2D directly.
Decomposition planes
The core concept of planar decomposition is the cutting plane. Each cutting plane has the following properties:
| Property | Type | Description |
|---|---|---|
| Position | Vector3 | Location of the plane center in world space (mm). |
| Normal | Vector3 | Normal vector defining the plane orientation. |
| Rotation | Quaternion | Orientation of the plane. |
| Thickness | Number (mm) | Rib thickness centered on the plane. Controls how much 3D volume each 2D slice represents. |
| Force Projection Mode | Project or Override | How forces from 3D preserves are projected onto the 2D plane. Project projects the 3D force vector onto the plane. Override uses a custom direction. |
| Force Override Direction | Vector3 (optional) | Custom force direction used when Force Projection Mode is set to Override. |
At least one cutting plane must be defined before running the solver.
Adding and positioning planes
Planes are added through the editor and positioned in the 3D viewport. Each plane slices through the design domain, and the solver extracts the 2D cross-section at that location for optimization.
The force projection mode determines how boundary conditions from 3D input/output preserves translate to each 2D plane. In Project mode, the 3D force vector is automatically projected onto the plane's coordinate system. In Override mode, you specify the exact 2D force direction to use for that plane.
Boundary conditions
Planar decomposition uses standard input, output, and fixed preserves, the same as compliant mechanism analysis:
| Condition | Object type | Purpose |
|---|---|---|
| Input | Input Preserve + Path | Force application point and direction |
| Output | Output Preserve + Path | Desired motion point and direction |
| Fixed | Fixed Preserve or Boundary Fixed Preserve | Anchoring condition |
Obstacles and preserve pairs are also supported.
The solver projects these 3D boundary conditions onto each cutting plane, producing per-plane 2D boundary conditions that drive independent design optimizations.
Solver parameters
Optimization
| Parameter | Default | Description |
|---|---|---|
| Iterations | 30 | Maximum optimization steps per plane. |
| Volume Fraction | 0.3 | Target material fraction (0.05 -- 0.95). |
| Element Size | 2.0 mm | Mesh element size. Smaller values increase resolution. |
| Thickness | 1.0 mm | Out-of-plane thickness for 2D plane-stress assumption. |
| Penalization | 7.0 | Controls design sharpness (higher values produce crisper solid-or-void designs). |
| Filter Radius | 1.5 | Feature size control radius. |
| Convergence Tolerance | 0.01 | Early-stop threshold. |
| Force Preserve Density | true | Force preserve areas to full density (not adjustable in the UI). |
Design domain
The design domain mode is always automatic. The solver computes the domain from preserve positions with optional padding. There is no manual dimension mode for planar decomposition.
| Parameter | Description |
|---|---|
| Padding | Fractional padding around preserves (automatic mode). |
Formulation and analysis
| Parameter | Options | Description |
|---|---|---|
| Formulation | Robust / Nuanced (Compliance) | Solver formulation mode. |
| Material Model | Linear Plane Stress, SVK, Neo-Hookean, Yeoh | Material model for the analysis substep. |
| Nonlinear analysis | Checkbox | Enable geometric and material nonlinearity for more accurate simulation. |
| Stress Constraint | Checkbox | Enable von Mises stress constraint with configurable yield strength and factor of safety. |
Symmetry
Per-plane symmetry constraints can be applied:
| Parameter | Description |
|---|---|
| Vertical mirror | Enforce left/right symmetry. |
| Horizontal mirror | Enforce top/bottom symmetry. |
Running the solve
The properties panel for a planar decomposition analysis shows a Run Planar Decomposition button. The button is disabled when:
- No cutting planes have been added.
- The scene is read-only.
- A solve is already running.
The plane count is shown above the solver settings (for example, "2 cutting planes").
Related pages
- Compliant Mechanism 2D -- the underlying 2D solver used per plane
- Compliant Mechanism 3D -- full 3D alternative
- Solver Parameters -- general parameter reference
- Object Types -- cutting plane type reference