Rotating Frame

Centrifugal, Coriolis, and Euler forces are “fictitious” volume forces that need to be introduced in a rotating frame of reference, since it is not an inertial system. Use a node to add the effect of these forces. The forces are generated by all selected features in the physics interface having a density, mass, or mass distribution. You select objects having the highest geometrical dimension of the interface, and all objects with a lower dimensionality that belong to the selection are automatically included.

The idea when using a rotating frame is that the observer rotates with the structure. All results, such as displacements are thus relative to the rotating frame.

The node is only available with some COMSOL products (see https://www.comsol.com/products/specifications/). is available in 3D, 2D, and 2D axisymmetry.

Shell Properties


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

Rotating Frame

Select an — , , , or . For enter a rbp and eax.

Select a — or . The rotational direction does not make any difference for a centrifugal force.

Select a — , , , or


	The option Rigid body is only available in the Solid Mechanics and Multibody Dynamics interfaces.

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For enter a value for the angular velocity magnitude Ω.

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For , enter an RPM value.

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For , enter an , M, and an , Ω0. In this case, the angular speed is variable over time, and computed by using time integration of the angular acceleration caused by the applied moment.

It is assumed that axis of orientation is kept fixed. The moment of inertia around the axis of rotation, Iax, is automatically computed from the mass properties if the selection.

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For , enter the α in radians as function of time (the variable t).

In the case of a geometrically nonlinear analysis, the displacements computed in the Solid Mechanics interface are used to define the spatial frame. When a rotating frame is used, there are two possible interpretations.

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The default is that the spatial frame is also interpreted as corotating, that is only the displacements relative to the rotation are defining the spatial frame.

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Select to add also the rotation to the definition of the spatial frame. For other physics interfaces, this is similar to specifying a Rotating Domain, but with the displacements added. This approach must be used if there are a mix of stationary and rotating domains.


	When Define spatial frame rotation is selected, the actual angle of rotation becomes important. If the angular speed is nonconstant, you must then enter an expression for the angle as function of time explicitly using the User defined option. For the two other input options, the angle of rotation is assumed to be α0 + Ωt.

Frame Acceleration Effect

For 3D and 2D components, use the , , or check boxes to determine which effects of a rotating frame that are to be incorporated in the analysis. Only is selected by default.

For 2D axisymmetric components, the only effect from a rotating frame is the centrifugal force, which is then always included.

The check box is selected by default. When including spin-softening effects, an extra contribution to the centrifugal force from deformation is taken into account. The check box is only available if or is selected.


	For more information, see Frame Acceleration Forces in the Structural Mechanics Theory chapter.


	You can assign this load to a load group. See Load Cases in the Structural Mechanics Modeling chapter.

Location in User Interface

Context Menus

Ribbon

Physics tab with or selected:

Physics tab with , , or selected:

Physics tab with selected:

Physics tab with , , or selected: