Fluid-film bearing · evidence-led screening

Journal-bearing Sub-synchronous Frequency Screening

Convert measured spectral lines to shaft order, project only a band documented by your procedure or model, and compare two operating speeds. The worksheet does not generate an oil-whirl or oil-whip diagnosis from RPM.

ISO 13373 scope disclosedNo universal 0.42–0.48× ruleDecimal point or comma

Run A shaft speed (r/min)

Run A measured line (Hz)

Must be measured and below shaft frequency.

Run B shaft speed (r/min, optional)

Run B measured line (Hz, optional)

Enter both Run B fields or leave both blank.

Documented candidate order — lower

Documented candidate order — upper

Documented lateral natural frequency (Hz, optional)

Use a validated modal/run-up/coast-down result for the same configuration.

Interpretation boundary

Source for candidate band, natural frequency and acceptance tolerances

Measurement evidence and configuration

Diagnostic boundary: a computed fractional-order line is not a defect frequency and cannot by itself prove oil whirl, oil whip, rub, looseness, misalignment or unbalance. Confirm repeatability, forward precession/orbit and phase where available, speed tracking or lock-on during run-up/coast-down, bearing condition, load, clearance, oil properties and the machine model before changing operation.

Run A shaft / measured order

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Entered candidate band at Run A

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Run A band comparison

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Run B shaft / measured order

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Entered candidate band at Run B

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Two-speed comparisons

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Natural-frequency proximity

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Einstufung

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Arithmetic performed

Menge	Equation	Bedeutung
Shaft frequency	f_Welle = n / 60	n in r/min; result in Hz.
Measured order	r = f_meas / f_Welle	Dimensionless. A line below 1× is sub-synchronous.
User-documented band	[r_lof_Welle, r_hif_Welle]	Only the entered source-specific order limits are projected.
Constant-order prediction	f_B,pred = f_A(n_B/n_A)	Comparison model for an order that tracks shaft speed.
Tracking residual	100\|f_B−f_B,pred\| / f_B,pred	No universal pass/fail threshold is applied.
Fixed-frequency change	100\|f_B−f_A\| / f_A	Comparison with a stationary line; not proof of lock-on.
Natural-frequency proximity	100\|f_meas−f_n\| / f_n	Reported only when a documented natural frequency is supplied.

Why the former automatic frequencies were removed

The old page generated a fixed 0.42–0.48× band from speed, labelled it an oil-whirl range and attached generic diagnoses to 0.5×, 1× and 2×. Those labels were not consequences of the arithmetic. Historical NASA material reports ranges such as 0.35–0.48× in a training context, while classic rotor-bearing analyses describe a forward-precessional component close to one-half speed and show that load, bearing design and supply/pressurization can change the ratio substantially. Therefore this worksheet has no default ratio and never calls a calculated line a defect frequency.

Standards and source scope

ISO 13373-2:2016, edition 2 is Published and under systematic review; it covers processing, analysis and presentation of vibration data, including time/frequency-domain and operational-change analysis. ISO 13373-3:2015, edition 1 is Published and was confirmed in 2026; it gives general diagnostic procedures. ISO 13373-4:2021, edition 1 covers diagnostic techniques for gas and steam turbines with fluid-film bearings and explicitly notes that actions depend on circumstances, confidence and safety. None of these official scope pages publishes a universal oil-whirl order band or a speed-only diagnosis.

Engineering background: NASA’s public Whirl and Whip — Rotor/Bearing Stability Problems discusses forward fractional-frequency whirl and speed-tracking/whip behaviour; Vibration Diagnostic Guide gives contextual 35–48% observations; and NASA TN D-4934 warns that externally pressurized bearings can differ considerably from the near-half-speed self-acting case. These are engineering references, not current normative acceptance limits.

Required diagnostic evidence

Use synchronized speed and spectra over more than one operating point; inspect direction/precession, orbit and phase where instrumentation permits; confirm sensor location, bandwidth, resolution and units; review bearing geometry, radial-versus-diametral clearance convention, load, alignment, lubricant viscosity at operating temperature and system natural frequencies. Apply only thresholds documented for the actual machine and procedure. The exact diagnostic clauses and acceptance limits remain NEEDS_LICENSED_SOURCE.