Frequency Domain Perturbation
The Frequency Domain Perturbation () study step is used for studying small oscillations about a biased solution (small-signal analysis).
This study step is useful for small-signal analysis (AC/DC), prestressed analysis (structural mechanics), and harmonic perturbation (fluid flow) types of analyses.
This study step is part of some two-step studies (see below).
When this study step is added to the Model Builder as part of a two-step study, the first step is usually a Stationary study step that computes the stationary (or bias) solution. The second step is the Frequency Domain Perturbation step, which computes a perturbed solution of the linearized problem around the linearization point (or bias point) computed in the first step. The settings are the same as those for the Stationary and Frequency Domain nodes.
Values of Linearization Point
Use the settings under Values of linearization point to specify a linearization point.
From the Settings list, choose Physics controlled (the default) to use linearization point settings controlled by the physics interfaces. Choose User defined to specify the linearization point using the Method list. Select:
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 Initial expression to use the expressions specified on the Initial Values nodes under a specific physics interface as a linearization point.
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 Solution to use a solution as a linearization point.
Use the Study list to specify which solution to use from the available studies. Select:
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 Zero solution to use a linearization point that is identically equal to zero.
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Any other available solution to use it as a linearization point. It can be the current solution in the sequence, or a solution from another sequence, or a solution that was stored with the Solution Store node. You select a stored solution by changing Use to the name of the stored solution. Choose a solution using the Selection list (see Values of Dependent Variables under Common Study Step Settings).
This study step is available for a variety of interfaces and licenses:
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As a study step with the AC Impedance, Stationary and AC Impedance, Time Dependent studies, which require the Battery Design Module or the Electrodeposition Module.
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As a study step with the Frequency Domain, Prestressed study, which requires the Structural Mechanics Module, Geomechanics Module, MEMS Module, or Acoustics Module (depending on which physics interface you use it for).
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As a study step for the Small-Signal Analysis, Frequency Domain study, which requires the AC/DC Module or MEMS Module.
Harmonic Perturbation, Prestressed Analysis, and Small-Signal Analysis
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With the AC/DC Module, see Small-Signal Analysis of an Inductor, Application Library path ACDC_Module/Devices,_Inductive/small_signal_analysis_of_inductor.
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With the Acoustics Module and AC/DC Module, see Loudspeaker Driver — Frequency-Domain Analysis: Application Library path Acoustics_Module/Electroacoustic_Transducers/loudspeaker_driver.
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With the Fuel Cell & Electrolyzer Module, see Electrochemical Impedance Spectroscopy in a Fuel Cell, Application Library path Fuel_Cell_and_Electrolyzer_Module/Fuel_Cells/ac_fuel_cell.
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With the MEMS Module, see Frequency Response of a Biased Resonator — 2D, Application Library path MEMS_Module/Actuators/biased_resonator_2d_freq.
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With the Structural Mechanics Module, see Bracket — Frequency-Response Analysis, Application Library path Structural_Mechanics_Module/Tutorials/bracket_frequency.