COMSOL 6.3 - Face Load

Face Load

Add a to boundaries (for the Plate interface add it to domains), to use it as a pressure or tangential force acting on a surface. The loads are defined in the given coordinate system.

Coordinate System Selection

The is selected by default. The list contains all applicable coordinate systems in the model. Prescribed loads are specified along the axes of this coordinate system. See Coordinate Systems and in the COMSOL Multiphysics Reference Manual.

Through-Thickness Location

Select a surface — , , or . The default is that the load is applied at the midsurface. The effect of using another surface than the midsurface is twofold:

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For a curved boundary, the difference in area between the midsurface and the selected surface is taken into account.

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For a tangential load, the distance from the midsurface is used to compute an additional equivalent moment load.

To place the load at another distance from the midsurface, select the checkbox, and enter a value for the offset, zoffset.

If the material model is , there may physically not be a well-defined top and bottom surface. If the load is applied at such a surface, the thickness value used to compute the load is taken from the settings in the node.

Force

Select a — , , , , or . The last option is only available in the Shell interface, and only in 3D components.

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For and , the traction components are given explicitly.

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For , COMSOL Multiphysics divides the total force by the area of the boundaries where the load is active. Then the force is applied in the same way as for a . When working with curved boundaries or local coordinate systems, use this option carefully, as the result is not always intuitive.

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For , a scalar input is given, and the orientation of the load is given by the normal to the boundary. The pressure is positive when directed in the opposite direction of the normal to the shell. In a geometrically nonlinear analysis, the current surface normal and area are used.

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For , enter the and with respect to a point. Select the — , , or . For , the coordinates of the application point is the centroid of the selected boundaries. For , select a geometrical point in the section . For , enter the global coordinates of the , xa.


	For the load types Force per reference length and Total force, the load list normally only contains User defined. When combining with another physics interface that can provide this type of load, it is also possible to choose a predefined load from this list.


Load Type	variable	SI unit	Geometric Entity Level	Space Dimension (components)
Force per reference area	fA	N/m2	boundaries domains	3D (x, y, z) 2D axisymmetric (r, z) 2D (x, y, z)
Force per deformed area	fa	N/m2	boundaries domains	3D (x, y, z) 2D axisymmetric (r, z) 2D (x, y, z)
Total force	Ftot	N	boundaries domains	3D(x, y, z) 2D axisymmetric (r, z) 2D(x, y, z)
Pressure	p	Pa	boundaries domains	3D 2D axisymmetric 2D
Resultant	F, M	N, N m	boundaries	3D (x, y, z)

Moment

Select the — , , or . Enter values or expressions for mA, ma, or Mtot.

This section is not present when is selected as the .

Traction Field

This section is only shown when has been selected as . The distribution of the forces over the selected points is controlled by the settings here.

Select a — or .

When is selected, the force distribution approximately matches the stress distribution over a beam cross section.

For , you can write expressions for the force distribution. For 3D components enter expressions for the six dimensionless vector-valued distribution functions, 1, 2, 3, 4, 5, and 6. For 2D components enter expressions for 1, 2, and 4. Usually, the local coordinates of the loaded region would be used for this purpose, but there is no limitation on the form of the functions. The built-in variables for the local coordinates are named <physics_tag>.<load_tag>.x2 and <phys_tag>.<load_tag>.x3, for example solid.bndl1.x2. The default value is the distribution that is used when is selected as .

The local coordinates, x2 and x3, are defined in the following way:

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The origin is placed at the centroid of the selected points.

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The axis directions coincide with the principal axes of a virtual collection of points with unit mass.

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x2 is the axis around which the virtual principal area moment of inertia is larger.

When is selected, you can also select a — , , or . This function acts as a multiplier to the force distribution functions. When is selected, the weight function w = 1. For , enter a radius rw of a circle, outside of which no load is applied (w = 0). Inside the circle, w = 1. For , enter a weighting expression. Usually, the built-in local coordinates of the loaded region would be used for this purpose, but there is no limitation on the form of the function. A time- or parameter-dependent function can, for example, be used to model a moving load.

The traction distribution functions have the property that the forces are distributed as

where the coefficients ci are chosen so that the given force and moment resultants are obtained.

Symmetry

This section is only shown when has been selected as . If the resultant force is applied in a symmetry or antisymmetry plane, this fact needs to be taken into account when creating the corresponding force distribution.

Select a symmetry type — , , or . When one of the types of symmetry is chosen, specify the symmetry plane by entering a , nsym, and a , xsym, located in the plane.

When specifying a resultant load in a symmetry plane, you still provide the full value of force and moment, as if there were no symmetry in the model. Any components of the given load that do not fulfill the selected type of symmetry will be discarded.