Linearly Accelerated Frame
When you add a Linearly Accelerated Frame node, inertial forces are applied to all selected features in the physics interface with 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 Linearly Accelerated Frame node is only available with some COMSOL products (see https://www.comsol.com/products/specifications/).
Shell Properties

Coordinate System Selection
The Global coordinate system is selected by default. The Coordinate system list contains any additional coordinate systems that the model includes. It can be used when prescribing the direction of the frame acceleration.
Linearly Accelerated Frame
Enter the components of the linear Frame acceleration, af. The force is computed as f = −ρaf and acts in a fixed spatial direction.
Time-Dependent Study
For a time-dependent study, you can compute the absolute velocity and absolute displacement postprocessing variables by checking the corresponding check boxes.
For more information, see Frame Acceleration Forces in the Structural Mechanics Theory chapter.
Only features that have a geometrical selection contribute to the mass forces. The Mass and Moment of Inertia nodes are global features and will not get any contribution from Linearly Accelerated Frame. You may need to add extra force contributions if such nodes are present.
You can add a Harmonic Perturbation subnode for specifying a harmonic variation of the values of the prescribed acceleration.
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 Solid Mechanics or Multibody Dynamics selected:
Physics tab with Shell, Layered Shell, or Membrane selected:
Physics tab with Plate selected:
Physics tab with Beam, Truss, or Wire selected: