findElements

Find mesh elements in specified region

Syntax

elemIDs = findElements(mesh,"region",RegionType,RegionID)

elemIDs = findElements(mesh,"box",xlim,ylim)

elemIDs = findElements(mesh,"box",xlim,ylim,zlim)

elemIDs = findElements(mesh,"radius",center,radius)

elemIDs = findElements(mesh,"attached",nodeID)

Description

elemIDs = findElements(mesh,"region",RegionType,RegionID) returns the IDs of the mesh elements that belong to the specified geometric region.

elemIDs = findElements(mesh,"box",xlim,ylim) returns the IDs of the mesh elements within a bounding box specified by xlim and ylim. Use this syntax for 2-D meshes.

elemIDs = findElements(mesh,"box",xlim,ylim,zlim) returns the IDs of the mesh elements located within a bounding box specified by xlim, ylim, and zlim. Use this syntax for 3-D meshes.

elemIDs = findElements(mesh,"radius",center,radius) returns the IDs of mesh elements located within a circle (for 2-D meshes) or sphere (for 3-D meshes) specified by center and radius.

elemIDs = findElements(mesh,"attached",nodeID) returns the IDs of the mesh elements attached to the specified node. Here, nodeID is the ID of a corner node. This syntax ignores the IDs of the nodes located in the middle of element edges.

For multiple nodes, specify nodeID as a vector.

Examples

Elements Associated with Particular Face

Find the elements associated with a geometric region.

Import and plot the geometry of the built-in function lshapeg.

gm = fegeometry(@lshapeg);
pdegplot(gm,FaceLabels="on",EdgeLabels="on")

Generate a mesh.

gm = generateMesh(gm,Hmax=0.5);

Find the elements associated with face 2.

mesh = gm.Mesh;
Ef2 = findElements(mesh,"region",Face=2);

Highlight these elements in green on the mesh plot.

figure
pdemesh(mesh,ElementLabels="on")
hold on
pdemesh(mesh.Nodes,mesh.Elements(:,Ef2),EdgeColor="green")

Elements Within Bounding Box

Find the elements located within a specified box.

Create a PDE model.

model = createpde;

Import and plot the geometry.

importGeometry(model,"PlateHolePlanar.stl");
pdegplot(model)

Generate a mesh.

mesh = generateMesh(model,"Hmax",2,"Hmin",0.4)

mesh = 
  FEMesh with properties:

             Nodes: [2×367 double]
          Elements: [6×163 double]
    MaxElementSize: 2
    MinElementSize: 0.4000
     MeshGradation: 1.5000
    GeometricOrder: 'quadratic'

Find the elements located within the following box.

Eb = findElements(mesh,"box",[5 10],[10 20]);

Highlight these elements in green on the mesh plot.

figure
pdemesh(model)
hold on
pdemesh(mesh.Nodes,mesh.Elements(:,Eb),"EdgeColor","green")

Elements Within Bounding Disk

Find the elements located within a specified disk.

Create a PDE model.

model = createpde;

Import and plot the geometry.

importGeometry(model,"PlateHolePlanar.stl");
pdegplot(model)

Generate a mesh.

mesh = generateMesh(model,"Hmax",2,"Hmin",0.4,"GeometricOrder","linear")

mesh = 
  FEMesh with properties:

             Nodes: [2×102 double]
          Elements: [3×163 double]
    MaxElementSize: 2
    MinElementSize: 0.4000
     MeshGradation: 1.5000
    GeometricOrder: 'linear'

Find the elements located within radius 2 from the center [5,10].

Er = findElements(mesh,"radius",[5 10],2);

Highlight these elements in green on the mesh plot.

figure
pdemesh(model)
hold on
pdemesh(mesh.Nodes,mesh.Elements(:,Er),"EdgeColor","green")

Elements Attached to Specified Nodes

Find the elements attached to a specified corner node.

Create a PDE model.

model = createpde;

Import and plot the geometry.

importGeometry(model,"PlateHolePlanar.stl");
pdegplot(model)

Generate a linear triangular mesh by setting the geometric order value to linear. This mesh contains only corner nodes.

mesh = generateMesh(model,"Hmax",2,"Hmin",0.4, ...
                          "GeometricOrder","linear");

Find the node closest to the point [15;10].

N_ID = findNodes(mesh,"nearest",[15;10])

N_ID = 
10

Find the elements attached to this node.

En = findElements(mesh,"attached",N_ID)

En = 1×3

    36    48    49

Highlight the node and the elements in green on the mesh plot.

figure
pdemesh(model)
hold on
plot(mesh.Nodes(1,N_ID),mesh.Nodes(2,N_ID),"or","Color","g", ...
                                           "MarkerFaceColor","g")
pdemesh(mesh.Nodes,mesh.Elements(:,En),"EdgeColor","green")

Input Arguments

mesh — Mesh object

Mesh property of a PDEModel object | output of generateMesh

Mesh object, specified as the Mesh property of a PDEModel object or as the output of generateMesh.

Example: model.Mesh

RegionType — Geometric region type

"Cell" for a 3-D model | "Face" for a 2-D model

Geometric region type, specified as "Cell" or "Face".

Example: findElements(mesh,"region","Face",1:3)

Data Types: char

RegionID — Geometric region ID

vector of positive integers

Geometric region ID, specified as a vector of positive integers. Find the region IDs by using pdegplot.

Example: findElements(mesh,"region","Face",1:3)

Data Types: double

xlim — x-limits of bounding box

two-element row vector

x-limits of the bounding box, specified as a two-element row vector. The first element of xlim is the lower x-bound, and the second element is the upper x-bound.

Example: findElements(mesh,"box",[5 10],[10 20])

Data Types: double

ylim — y-limits of bounding box

two-element row vector

y-limits of the bounding box, specified as a two-element row vector. The first element of ylim is the lower y-bound, and the second element is the upper y-bound.

Example: findElements(mesh,"box",[5 10],[10 20])

Data Types: double

zlim — z-limits of bounding box

two-element row vector

z-limits of the bounding box, specified as a two-element row vector. The first element of zlim is the lower z-bound, and the second element is the upper z-bound. You can specify zlim only for 3-D meshes.

Example: findElements(mesh,"box",[5 10],[10 20],[1 2])

Data Types: double

center — Center of bounding circle or sphere

two-element row vector for a 2-D mesh | three-element row vector for a 3-D mesh

Center of the bounding circle or sphere, specified as a two-element row vector for a 2-D mesh or three-element row vector for a 3-D mesh. The elements of these vectors contain the coordinates of the center of a circle or a sphere.

Example: findElements(mesh,"radius",[0 0 0],0.5)

Data Types: double

radius — Radius of bounding circle or sphere

positive number

Radius of the bounding circle or sphere, specified as a positive number.

Example: findElements(mesh,"radius",[0 0 0],1)

Data Types: double

nodeID — ID of corner node of element

positive integer | vector of positive integers

ID of the corner node of the element, specified as a positive integer or a vector of positive integers. The findElements function can find an ID of the element by the ID of the corner node of the element. The function ignores IDs of the nodes located in the middle of element edges. For multiple nodes, specify nodeID as a vector.

Example: findElements(mesh,"attached",[7 8 21])

Data Types: double

Output Arguments

elemIDs — Element IDs

positive integer | row vector of positive integers

Element IDs, returned as a positive integer or a row vector of positive integers.

Version History

Introduced in R2018a