The Envelope: What It Is and Why It's Important
Every Spherene computation starts with an envelope. It is the single most important input you provide. This article explains what the envelope is, what it must look like, and why getting it right determines whether your computation succeeds.
What is the envelope
The envelope (abbreviated env) is the closed solid volume that defines the shape Spherene fills with ADMS geometry. Think of it as the mold: Spherene generates its minimal surface structure entirely inside this boundary and trims the result precisely to its surface.
The envelope can be any complex 3D shape: a lightweight bracket, a heat exchanger block, a shoe midsole, a bone scaffold. Whatever geometry you are designing, the envelope is the outer boundary of that volume.
Only one envelope is allowed per Spherene project or computation.
What makes a valid envelope
The envelope must be a closed, watertight, triangulated mesh. In practice this means:
- Closed: no open edges or holes in the surface. Every edge must be shared by exactly two faces.
- Watertight: the mesh fully encloses a volume. There are no gaps or missing faces that would allow the inside to connect to the outside.
- Triangulated: all faces are triangles. Quads and n-gons must be triangulated before use.
- Manifold: no non-manifold edges (edges shared by more than two faces) and no degenerate faces.
- Consistent normals: all face normals pointing outward from the enclosed volume.
Note: The density estimate has a precision of approximately +/- 10% when using a constant density field. This is a known algorithm characteristic, not an error in your setup.
Where your envelope comes from
The envelope can be prepared in any CAD tool and imported into Spherene as a mesh. Common sources:
- A solid body from parametric CAD (Fusion, SolidWorks, Creo), meshed and exported as STL or OBJ.
- A surface model from Rhino, converted to a closed solid and meshed.
- A Grasshopper-generated solid, meshed before wiring to the Spherene component.
- A topology-optimised form from nTop, thresholded and converted to a mesh.
- An imported scan or mesh body, repaired to watertight quality.
How to check and fix your envelope
Before computing, always verify the envelope mesh. Each plugin has its own tools:
|
Plugin |
How to check |
How to fix common issues |
|
Rhino |
Run the Check command on the mesh |
FillMeshHoles, UnifyMeshNormals, RebuildMeshNormals |
|
Grasshopper |
Wire to a Mesh Edges component and check for Naked Edges output |
Use Weld and Unify Normals mesh components before wiring to sphe_Single |
|
Fusion |
Inspect > Physical Properties (no volume = not closed) |
Inspect > Interference Detection, then repair in Fusion or export to Meshmixer |
|
nTop |
Mesh Analysis > Check Mesh blocks |
Smooth Mesh or Implicit Smooth, then re-mesh from the implicit body |
What happens if the envelope has problems
A non-watertight envelope is the most common cause of failed computations. The ADMS engine cannot generate geometry inside a volume it cannot fully define. Typical results of a bad envelope:
- Computation returns empty or incomplete geometry.
- Boolean errors during generation.
- ADMS fills only part of the volume.
Fix the envelope before trying to adjust density, DRT, or other parameters. The envelope is always the first thing to check when a computation fails.
The defeatured envelope (dfenv)
The dfenv is an optional simplified mesh that fully encloses the actual envelope. When a dfenv is assigned, the ADMS is generated inside the dfenv volume, then Boolean-trimmed to the actual env shape.
Use dfenv when:
- Sharp tips or thin fins in the envelope are not getting filled by standard generation.
- Complex concave regions leave areas underpopulated.
- You want to control the angle at which ADMS meets the envelope surface, so it connects at something other than perpendicular.
A convex hull or a slightly inflated bounding box of the envelope works well as a dfenv in most cases. See the DFENV article for a full guide.