Harmonic Perturbation — Exclusive and Contributing Nodes
A physics node that is exclusive has a Harmonic Perturbation subnode. This subnode adds harmonic perturbations to the right-hand-side contributions of its parent node (for example, a Boundary Load on the Solid Mechanics interface or a Terminal node on the Electric Currents interface). In the Settings window, the perturbation is entered for these contributions, which is only used when you solve for a Frequency Domain Perturbation study type. The parent node defines the stationary value for the contribution, which is not present for the Frequency Domain Perturbation study.
Harmonic perturbation nodes have a tilde over the top of the node, as in this example of a boundary level node ().
Nodes that are contributing (typically sources) can add their contributions as a harmonic perturbation. To define the stationary value for the contribution, you can add another node of the same type with the harmonic perturbation setting cleared.
For exclusive loads, there is only one way of doing it due to the exclusivity — as a subnode. This subnode cannot, in general, be a full copy of the original node because only some subsets of data can be changed.
As an example (prescribed displacement in structural mechanics), the prescribed displacement must have the same local system and the harmonic perturbation can only be applied to degrees of freedom already prescribed in the parent node.
Also, all contributing nodes are free to use the full set of settings. A static point load can be at one point in the global direction, and a local system for the harmonic contribution can be used.
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Physics Exclusive and Contributing Node Types
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For different plot settings made available, see Small-Signal Analysis, Prestressed Analysis, and Harmonic Perturbation Plot Settings.
Vibrating MEMS structures are often prestressed. For example, a cantilever structure could be prestressed by applying a DC voltage bias between the cantilever and a nearby ground plane; then vibrations could be driven at resonance by applying an additional AC bias. Another common example would be a clamped-clamped beam with a residual thermal stress.