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View, Edit, and Delete Boundary Conditions

View Boundary Conditions

A PDE model stores boundary conditions in its BoundaryConditions property. To obtain the boundary conditions stored in the PDE model called model, use this syntax:

BCs = model.BoundaryConditions;

To see the active boundary condition assignment for a region, call the findBoundaryConditions function.

For example, create a model and view the geometry.

model = createpde(3);
importGeometry(model,'Block.stl');
pdegplot(model,'FaceLabels','on','FaceAlpha',0.5)

Set zero Dirichlet conditions for all equations and all regions in the model.

applyBoundaryCondition(model,'dirichlet','Face',1:6,'u',[0,0,0]);

On face 3, set the Neumann boundary condition for equation 1 and Dirichlet boundary condition for equations 2 and 3.

h = [0 0 0;0 1 0;0 0 1];
r = [0;3;3];
q = [1 0 0;0 0 0;0 0 0];
g = [10;0;0];
applyBoundaryCondition(model,'mixed','Face',3,'h',h,'r',r,'g',g,'q',q);

View the boundary condition assignment for face 3. The result shows that the active boundary condition is the last assignment.

BCs = model.BoundaryConditions;
findBoundaryConditions(BCs,'Face',3)
ans = 
  BoundaryCondition with properties:

           BCType: 'mixed'
       RegionType: 'Face'
         RegionID: 3
                r: [3x1 double]
                h: [3x3 double]
                g: [3x1 double]
                q: [3x3 double]
                u: []
    EquationIndex: []
       Vectorized: 'off'

View the boundary conditions assignment for face 1.

findBoundaryConditions(BCs,'Face',1)
ans = 
  BoundaryCondition with properties:

           BCType: 'dirichlet'
       RegionType: 'Face'
         RegionID: [1 2 3 4 5 6]
                r: []
                h: []
                g: []
                q: []
                u: [0 0 0]
    EquationIndex: []
       Vectorized: 'off'

The active boundary conditions assignment for face 1 includes all six faces, though this assignment is no longer active for face 3.

Delete Existing Boundary Conditions

To remove all the boundary conditions in the PDE model called pdem, use delete.

delete(pdem.BoundaryConditions)

To remove specific boundary conditions assignments from pdem, delete them from the pdem.BoundaryConditions.BoundaryConditionAssignments vector. For example,

BCv = pdem.BoundaryConditions.BoundaryConditionAssignments;
delete(BCv(2))

Tip

You do not need to delete boundary conditions; you can override them by calling applyBoundaryCondition again. However, removing unused assignments can make your model more concise.

Change a Boundary Conditions Assignment

To change a boundary conditions assignment, you need the boundary condition’s handle. To get the boundary condition’s handle:

  • Retain the handle when using applyBoundaryCondition. For example,

    bc1 = applyBoundaryCondition(model,'dirichlet', ...
                                       'Face',1:6, ...
                                       'u',[0 0 0]);
  • Obtain the handle using findBoundaryConditions. For example,

    BCs = model.BoundaryConditions;
    bc1 = findBoundaryConditions(BCs,'Face',2)
    bc1 = 
    
      BoundaryCondition with properties:
    
               BCType: 'dirichlet'
           RegionType: 'Face'
             RegionID: [1 2 3 4 5 6]
                    r: []
                    h: []
                    g: []
                    q: []
                    u: [0 0 0]
        EquationIndex: []
           Vectorized: 'off'

You can change any property of the boundary conditions handle. For example,

bc1.BCType = 'neumann';
bc1.u = [];
bc1.g = [0 0 0];
bc1.q = [0 0 0];
bc1
bc1 = 

  BoundaryCondition with properties:

           BCType: 'neumann'
       RegionType: 'Face'
         RegionID: [1 2 3 4 5 6]
                r: []
                h: []
                g: [0 0 0]
                q: [0 0 0]
                u: []
    EquationIndex: []
       Vectorized: 'off'

Note

Editing an existing assignment in this way does not change its priority. For example, if the active boundary condition was assigned after bc1, then editing bc1 does not make bc1 the active boundary condition.

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