See how a design change shifts frequency response.

The engineering question

How does Variant A shift frequency response versus the Baseline?Frequency Compare is useful when a change in mass, suspension stiffness, suspension damping, or tire stiffness may move a resonance or change its magnitude. It complements Transient Compare; it does not replace a road-event study.

Both configurations use vehiclelab.quarter-car.linear-passive v0.2.0 and the existing vehiclelab.linear-frequency-response v0.1.0 direct complex solver. VehicleLab does not run an FFT or a long sequence of transient sine simulations for this production analysis.

Run a comparison

1. Choose Study → Frequency and complete a response.
2. Choose Compare a design change. Compare opens on Frequency, copies the current physical configuration to Baseline and Variant A, and initially inherits the Study frequency grid.
3. Edit one or more Variant A physical parameters.
4. Review the shared minimum frequency, maximum frequency, and point count.
5. Choose Run Frequency Compare.

The grid is logarithmically spaced and stored once by definition. The two completed studies must contain exactly equal Float64Array frequency samples; mixed or shifted grids are rejected rather than interpolated.

Read the evidence together

The completed record contains four Baseline-solid/Variant-dashed overlays:

• sprung displacement transmissibility;
• sprung acceleration per unit road displacement;
• suspension travel transmissibility; and
• dynamic tire deflection transmissibility.

The changed-parameter summary is derived from the immutable completed definitions. The peak table reports each configuration's interior peak frequency and magnitude plus absolute and relative shifts. If a bounded frequency interval contains no interior peak, VehicleLab reports no peak instead of inventing an endpoint peak or a delta.

The point inspector reads the nearest native stored frequency sample and reports both values and their absolute/relative deltas. It does not interpolate display data. A relative delta is left unavailable when its Baseline denominator is zero.

Preserve and export the result

One immutable FrequencyComparisonRecordV1 is the authoritative source for every completed comparison view and evidence export.

• Engineering Report in the Studio header creates a browser-local PDF from the active completed comparison, including four exact-array overlay figures.
• Data & project exports deterministic CSV with Baseline, Variant, absolute, and relative magnitude columns plus both phase columns.
• Each plot card directly renders a 1600 × 1000 PNG from the stored arrays.
• vehiclelab.project.v1 stores the Compare/Frequency selector, Baseline, Variant A, and shared grid definition—but no response arrays, peaks, or discovery history. Import always requires a fresh authoritative run.

Editing controls retains the last completed evidence and labels it stale. CSV, PNG, and PDF continue to describe that record; project JSON describes the current desired definition. Restoring the exact completed definition clears the rerun warning without recomputation.

Interpretation boundary

Responses are normalized by harmonic road-displacement amplitude and represent linear steady state. The analysis omits transient startup, finite road-event duration, nonlinear components, tire contact loss, geometry, controller behavior, uncertainty, and physical correlation. Phase is retained in CSV and the completed record; magnitude plots alone do not express timing relationships.

Frequency Compare is verified through exact repeatability, standalone-study correspondence, Worker/direct parity, completed-record integrity, and the browser workflow. The underlying frequency solver retains its independent state-space and RK4 harmonic cross-check evidence.