COMSOL 6.3 - Edge Load

Edge Load

Add an as a force or moment distributed along an edge (for the Plate interface add it to boundaries). The load is defined in the given coordinate system.

Coordinate System Selection

Select the coordinate system to use for specifying the load. From the list select from:

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(the standard global coordinate system).

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	For details about the definition of local edge systems, see Local Edge System.

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Any additional user-defined coordinate system.

Face Defining the Orientations

This setting is used in conjunction with and . When the load is applied to an edge which is shared between boundaries, the coordinate system can be ambiguous. Select the boundary which should define the edge system. The default is .


	This section is available only for edges in the Shell interface and is only visible if the selected coordinate system is Local edge system or Shell Local System.

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.

If a selected edge is connected to boundaries having different thicknesses, then the result of specifying or is not well defined.

Force

Select a — , , , , , or .

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For and , the traction components are given explicitly.

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For and , the given traction components are multiplied by the thickness of the shell in order to give the edge load.

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For , COMSOL Multiphysics divides the total force by the length of the edges 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 , 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.


	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
Force per reference length	fL	N/m	edges boundaries	3D 2D
Force per deformed length	fl	N/m	edges boundaries	3D 2D
Force per reference area	fA	N/m2	edges boundaries	3D 2D
Force per deformed area	fa	N/m2	edges boundaries	3D 2D
Total force	Ftot	N	edges boundaries	3D 2D
Resultant	F, M	N, N m	edges	3D

Moment

Select a to define the moment load — , , , , or . Enter values or expressions for mA, ma, mL, ml, or Mtot.

This section is available only in the Shell and Plate interfaces. It is not present when is selected as the .


Load Type	variable	SI unit	Geometric Entity Level	Space Dimension
Moment per reference area	mA	N	edges boundaries	3D 2D
Moment per deformed area	ma	N	edges boundaries	3D 2D
Moment per reference length	mL	N	edges boundaries	3D 2D
Moment per deformed length	ml	N⋅m/m2	edges boundaries	3D 2D
Total moment	Mtot	N⋅m	edges boundaries	3D 2D

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.