COMSOL 6.4 - The Solid Rotor, Fixed Frame Interface

The interface (

) is found under the > branch (

) when adding a physics interface. It is intended for the analysis of rotating 3D structural components that are symmetric about their axis. As opposed to the interface, the quantities are defined as seen by an observer sitting in a space-fixed frame. With this interface, you can compute displacements, velocities, accelerations, and stresses. The journal and thrust bearing features provided in this interface can be used to model different type of bearings. You can also model the effect of a bearing mounted on a foundation.

The Linear Elastic Material is the default material model. It adds the equations for the displacements in a linear elastic rotor and has a Settings window to define the elastic and inertia properties of a material. The equations in this feature also account for the frame acceleration forces — for example centrifugal, Coriolis, and Euler accelerations — that arise due to the rotation of the rotor.

When the Solid Rotor interface is added, the following default nodes are added to the — ; (a domain feature to specify the axis of rotation, and the rotational velocity of the rotor); (a boundary condition where boundaries are free, with no loads or constraints); ; and (a reference surface where axial rotation relative to the rigid rotation of the rotor is zero). From the toolbar, you can add additional features to your model in order to implement other rotor properties. You can also right-click the interface to select physics features from the context menu.

The is the default physics interface name.

The is used primarily as a scope prefix for variables defined by the physics interface. Refer to such physics interface variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different physics interfaces, the name string must be unique. Only letters, numbers, and underscores (_) are permitted in the field. The first character must be a letter.

The default (for the first physics interface in the model) is srotf.

To display this section, click the button (

) and select in the dialog. Normally these settings do not need to be changed.

You can choose how extra ODE variables added by some features are grouped in the node of a generated solver sequence.

The selection made in the section can be overridden by the settings in the section of the Rigid Material or Gear features.

In the Solid Rotor, Fixed Frame interface, you can choose not only the order of the discretization, but also the type of shape functions: Lagrange or serendipity. For highly distorted elements, Lagrange shape functions provide better accuracy than serendipity shape functions of the same order. The serendipity shape functions will however give significant reductions of the model size for a given mesh containing hexahedral or prism elements.

The default is to use shape functions for the . Using shape functions will give what is sometimes called constant stress elements. Such a formulation will for many problems make the model overly stiff, and many elements may be needed for an accurate resolution of the stress.

The physics interface uses the global spatial components of the u as dependent variables in the rotor domain. The default names for the components are (u, v, w).

You can change both the field name and the individual component names. If a new field name coincides with the name of another displacement field, the two fields (and the interfaces that define them) share degrees of freedom and dependent variable component names.

A new field name must not coincide with the name of a field of another type (that is, it must contain a displacement field), or with a component name belonging to some other field. Component names must be unique within a model except when two interfaces share a common field name.