Prescribed Displacement

The node adds a condition where the displacements are prescribed in one or more directions to the geometric entity (domain, boundary, edge, or point).

If a displacement is prescribed in one direction, this leaves the solid free to deform in the other directions.

You can also define more general displacements as a linear combination of the displacements in each direction.


	If a zero displacement is applied in all directions, this is the same as a Fixed Constraint.


	For details, see Prescribed Displacements, Velocities, and Accelerations.

Shell Properties


	This section is only present in the in the Layered Shell interface, where it is described in the documentation for the Prescribed Displacement node.

Interface Selection


	This section is only present in the in the Layered Shell interface, where it is described in the documentation for the Prescribed Displacement, Interface node.

Coordinate System Selection

The constraints are applied in the axis directions of the coordinate system selected in this section. You should only use a coordinate system which has fixed spatial directions.

Prescribed Displacement

Select a — or .

Standard Notation

To define the displacements individually, click the button.

Select one or all of the ,, and for 3D components, check boxes. Then enter a value or expression for u0, v0, and for 3D components, w0. For 2D axisymmetric components, select one or both of the and check boxes. Then enter a value or expression for u0 and w0.

General Notation

Click the to specify the displacements using a general notation that includes any linear combination of displacement components. For example, for 2D components, use the relationship

For Hmatrix H select , , , or and then enter values as needed in the field or matrix. Enter values or expressions for the Rvector R.

For example, to achieve the condition u = v, use the settings

which force the domain to move only diagonally in the xy-plane.

Constraint Settings

To display this section, click the button (

) and select in the dialog box.

In the COMSOL Multiphysics Reference Manual:

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Constraint Reaction Terms

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Weak Constraints

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Constraint Settings

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Excluded Surfaces, Excluded Edges, and Excluded Points


	When Individual dependent variables is selected in the Apply reaction terms on list, the constraint forces are applied directly on the degrees of freedom, which are the displacements along the global coordinate axes. If you use this setting together with a local coordinate system, the results will be inconsistent since the constraint forces will not match the constraint orientation.

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You can add a Harmonic Perturbation subnode for specifying a harmonic variation of the values of the prescribed displacements in a frequency domain analysis of perturbation type.

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You can activate and deactivate this boundary condition by assigning it to a constraint group. See Load Cases in the Structural Mechanics Modeling chapter.

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You can assign the value of the prescribed displacement to a load group. See Load Cases in the Structural Mechanics Modeling chapter.

Location in User Interface

Context Menus

Ribbon

Physics tab with selected: