Units and conventions

VANE follows OpenFAST’s SI conventions on input and states the units of what it reports.

Quantities and units

Quantity

Unit

Notes

Rotor speed (input)

rad/s

As written in the .lin header (LinFile.rotor_speed).

Rotor speed (reported)

rev/min

rotor_speed_rpm = rad/s × 30/π (MBC result, modal solution, Campbell axis).

Azimuth

rad (input), deg (reported)

MBCResult.azimuths_deg; wrapped to [0, 360) deg for the sweep checks.

Natural / damped frequency

Hz

natural_frequencies_hz, damped_frequencies_hz.

Angular frequency

rad/s

Used in theory expressions; ω = 2π f.

Damping ratio

dimensionless

ζ in [0, 1) for an underdamped mode; negative for an unstable one.

Wind speed

m/s

Mean hub-height; 0 when InflowWind is absent.

Excitation harmonic

integer

The nP line, n × rpm / 60 Hz; n a positive integer.

Sign and normalization conventions

  • Eigenvalues: of each complex-conjugate pair, the eigenvalue with positive imaginary part is kept.

  • Damping: ζ = -Re(λ)/|λ|; positive for a stable (decaying) mode. The solution separately counts unstable (positive-real-part) and over-damped (stable real) eigenvalues in n_unstable and n_overdamped.

  • Mode shapes: complex, phase-normalized so the dominant component is real and positive. Correlations (MAC) are invariant to per-mode complex scaling, so the normalization does not affect identification.

  • Whirl direction: for the dominant cosine/sine pair of a blade triplet, the sign of Im(q_s · conj(q_c)) sets the direction: positive is regressive (the lower-frequency ω0 - Ω line) and negative is progressive, calibrated against the Coleman split (see Mode identification). A pair whose normalized circularity is below WHIRL_CIRCULARITY_THRESHOLD (0.2) in magnitude is a standing "cyclic" pattern with no whirl direction.

Confidence and uncertainty

All confidence values are dimensionless and lie in [0, 1], with 1 the most trusted, but they measure different things:

  • ModeLabel.confidence is the share of a mode’s participation carried by the category that names it.

  • ModeTrack.confidence is the weakest link correlation (MAC) along a track.

  • unified_mode_confidence() combines conditioning, degeneracy, azimuth spread and tracking into one per-mode value.

The azimuth-spread standard deviations (AzimuthSpread) are in the units of the underlying quantity: Hz for frequency, dimensionless for damping. See Mode identification.

Tabular export

vane.export writes the modal and Campbell tables with the column names and units above (for example natural_frequency_hz and damping_ratio). The operating-parameter column of the Campbell table is named after the diagram’s parameter (rotor_speed_rpm or wind_speed).