addFace

Fill void regions in 2-D and split cells in 3-D geometry

Since R2020a

Syntax

h = addFace(g,edges)

[h,FaceID] = addFace(g,edges)

Description

h = addFace(g,edges) adds a new face to the geometry g. The specified edges must form a closed contour. For a 2-D geometry, adding a new face lets you fill voids in the geometry. For a 3-D geometry, adding a new face lets you split one cell into multiple cells.

You can add several new faces simultaneously by specifying their contours in a cell array. Each contour in the cell array must be unique.

Note

After modifying a geometry, always call generateMesh to ensure a proper mesh association with the new geometry.

[h,FaceID] = addFace(g,edges) also returns a row vector containing IDs of the added faces.

Examples

Fill Void Region in 2-D Geometry

Add a face to a 2-D geometry to fill an internal void.

Create a PDE model.

model = createpde();

Import the geometry. This geometry has one face.

gm = importGeometry(model,"PlateSquareHolePlanar.stl")

gm = 
  DiscreteGeometry with properties:

       NumCells: 0
       NumFaces: 1
       NumEdges: 8
    NumVertices: 8
       Vertices: [8x3 double]

Plot the geometry and display the face labels.

pdegplot(gm,"FaceLabels","on")

Zoom in and display the edge labels of the small hole at the center.

figure
pdegplot(gm,"EdgeLabels","on")
axis([49 51 99 101])

Fill the hole by adding a face. The number of faces in the geometry changes to 2.

gm = addFace(gm,[1 8 4 5])

gm = 
  DiscreteGeometry with properties:

       NumCells: 0
       NumFaces: 2
       NumEdges: 8
    NumVertices: 8
       Vertices: [8x3 double]

Plot the modified geometry and display the face labels.

pdegplot(gm,"FaceLabels","on")

Split Cells in 3-D Geometry

Add a face in a 3-D geometry to split a cell into two cells.

Create a PDE model.

model = createpde();

Import the geometry. The geometry consists of one cell.

gm = importGeometry(model,"MotherboardFragment1.stl")

gm = 
  DiscreteGeometry with properties:

       NumCells: 1
       NumFaces: 26
       NumEdges: 46
    NumVertices: 34
       Vertices: [34x3 double]

Plot the geometry and display the edge labels. Zoom in on the corresponding part of the geometry to see the edge labels there more clearly.

pdegplot(gm,"EdgeLabels","on","FaceAlpha",0.5)

xlim([-0.05 0.05])
ylim([-0.05 0.05])
zlim([0 0.05])

Split the cuboid on the right side into a separate cell. For this, add a face bounded by edges 1, 3, 6, and 12.

[gm,ID] = addFace(gm,[1 3 6 12])

gm = 
  DiscreteGeometry with properties:

       NumCells: 2
       NumFaces: 27
       NumEdges: 46
    NumVertices: 34
       Vertices: [34x3 double]

ID = 27

Plot the modified geometry and display the cell labels.

pdegplot(gm,"CellLabels","on","FaceAlpha",0.5)

Now split the cuboid on the left side of the board and all cylinders into separate cells by adding a face at the bottom of each shape. To see edge labels more clearly, zoom and rotate the plot. Use a cell array to add several new faces simultaneously.

[gm,IDs] = addFace(gm,{[5 7 8 10], ...
                        30, ...
                        31, ...
                        32, ...
                        33, ...
                        13})

gm = 
  DiscreteGeometry with properties:

       NumCells: 8
       NumFaces: 33
       NumEdges: 46
    NumVertices: 34
       Vertices: [34x3 double]

IDs = 6×1

    28
    29
    30
    31
    32
    33

Plot the modified geometry and display the cell labels.

pdegplot(gm,"CellLabels","on","FaceAlpha",0.5)

Input Arguments

g — Geometry

fegeometry object | DiscreteGeometry object | AnalyticGeometry object

Geometry, specified as an fegeometry object, a DiscreteGeometry, or an AnalyticGeometry object.

edges — Edges forming unique closed flat contour

vector of positive integers | cell array of vectors of positive integers

Edges forming a unique closed flat contour, specified as a vector of positive integers or a cell array of such vectors. You can specify edges within a vector in any order.

When you use a cell array to add several new faces, each contour in the cell array must be unique.

Example: addFace(g,[1 3 4 7])

Output Arguments

h — Resulting geometry

fegeometry object | handle

• If the original geometry g is an fegeometry object, then h is a new fegeometry object representing the modified geometry. The original geometry g remains unchanged.

• If the original geometry g is a DiscreteGeometry AnalyticGeometry object, then h is a handle to the modified object g.

FaceID — Face ID

positive number | row vector of positive numbers

Face ID, returned as a positive number or a row vector of positive numbers. Each number represents a face ID. When you add a new face to a geometry with N faces, the ID of the added face is N + 1.

Tips

• addFace errors when the specified contour defines an already existing face.

• If the original geometry g is a DiscreteGeometry or AnalyticGeometry object, addFace modifies the original geometry g.

• If the original geometry g is an fegeometry object, and you want to replace it with the modified geometry, assign the output to the original geometry, for example, g = addFace(g,[1 3 4 7]).

Version History

Introduced in R2020a

R2023a: Finite element model

addFace now accepts geometries specified by fegeometry objects.

R2021a: Face addition for analytic geometries

addFace now lets you fill void regions in 2-D AnalyticGeometry objects.