The random vibration workflow

A controller run in, a compliance report out. A random test is judged against a band: the specification says what the control PSD must be, warning and abort lines say how far it may stray, and the report's job is to show where the run sat inside that band, channel by channel.

The walkthrough is the demonstration plate's own random test — eight control channels against four shakers, controlled to a shaped specification by a real Rattlesnake run — photographed at every step. The run ships with the repository (testdata/plate/random.nc4), so every step can be followed exactly.

Step	In the app	In a script
Import the run	drag the controller's .nc4 onto the window	project = visualdynamics.random_vibration_run(path)
Say what it is for	(the run says — the type switches itself)	project.project_type == 'Random Vibration'
Control PSDs	Compute PSDs in the averaging view	project.compute_psds('Time History')
The octave-band view	Octave Bands on the PSD's bar	project.compute_octave('Time History PSDs')
Multiple coherence	Multiple Coherence in the averaging view	project.compute_multiple_coherence('Time History')
Compare against the spec	select PSD and specification together	plot_comparison(psds, spec)
Geometry and photos	drag them in, link them	project.add(...), project.link(...)
Report	Generate Report on the bar, the project row selected	project.generate_report('random')
Export	Export HTML…	project.export_report(name, path)
Save	Save Project As…	project.save('random.vdyn')

In the app, step by step

1. Import the run

Drag the controller's save onto the window. A Rattlesnake random run brings the control time histories, the specification with its warning and abort lines, and the channel table in one file — and says which environment drove it, so the project type switches to Random Vibration by itself. The tree's grey slots then say what a finished report still needs.

2. Compute the control PSDs

Compute PSDs in the time history's averaging view averages over the run's own frame length and framing — the numbers the controller used, read from the file, not guessed — and the view shows exactly those frames before the button is pressed.

3. Band onto sixth octaves

The octave-band PSD is a standing deliverable of a random report, not an option. Octave Bands on the PSD's bar previews the banded steps over the narrowband as the spacing is set (a sixth is the usual answer) and the panel's own button bands conserving area — the octave PSD is still a PSD, drawn as bars because its bandwidth says so.

4. Multiple coherence

How much of each response the drives account for — Multiple Coherence, beside the PSDs in the averaging view, so it reads the same frames. This is the figure that later separates "the article exceeded" from "the cable did" — a channel the drives explain (coherence near one) exceeded because the article did.

5. Compare against the specification

Select the control PSDs and the specification together. One channel draws at a time — the drop-down reaches the rest — with the tolerance zones shaded and every line that went outside the abort band striped red or blue for which way it went. The table below the plot accounts for every channel at once; the plot shows the ones you pick in it.

Two things to notice in the bar above the plot. The Scaling field is the comparison's dB offset — detected from the data in whole decibels, for runs captured below the 0 dB requirement; this run was at full level, so it reads 0. And the status bar notes the records that had no specification to answer to: the drive force PSDs share DOF names with control channels, and the comparison filters them out rather than judging newtons against an acceleration band.

6. Geometry, photos, report

Drag the article's geometry in and declare its units; drop the setup photographs beside it; link them into the group. Then the project's row's Generate Report builds the random report — the measured data, the specification comparison read three ways (spectra, RMS error bars, lines-out bars), the coherence beside the compliance so the reader can ask why a channel exceeded. Export HTML writes one self-contained file.

The same run, headless

And the script never has to be reconstructed by hand: the console tab along the bottom of the window writes it live as you click — every act of the session as the line that replays it. Expand it, copy the stretch you want, and it runs as-is.

The whole thing is one call when the defaults are right:

import visualdynamics

visualdynamics.random_vibration_report('random.nc4', 'report.html')

…and the same call written out when the project should live on. It is condensed from examples/random_workflow.py, which the test suite executes; the step numbers match the walkthrough.

import visualdynamics
from visualdynamics.plot import plot_bars, plot_coherence_map, plot_comparison

# 1-4. import and work up: PSDs over the run's own frames, the
# sixth-octave banding, the coherence — one verb does the sequence
project = visualdynamics.random_vibration_run('random.nc4')
assert project.project_type == 'Random Vibration'

history = project.time_history
spec = project.specification
psds, octave = project.psds        # the specification is not among them

# 5. the comparison, drawn headless
plot_comparison(psds, spec, path='control.png', show=False)
plot_comparison(octave, spec, path='control_octave.png', show=False)
plot_bars(psds, spec, 'error', path='error.png', show=False)
plot_bars(psds, spec, 'lines', path='lines.png', show=False)
plot_coherence_map(project.coherence, path='coherence.png', show=False)

# 6. geometry, photos, report
project.add('Geometry', visualdynamics.import_file('geometry.npz'))
project.geometry.define_units('m')
project.link(*project.names)
project.set_basis(*project.names)
project.generate_report('random')
project.export_report(project.report, 'random_report.html')
project.save('random.vdyn')

Where judgement lives

• Whether an exceedance is the article or the instrumentation. The multiple coherence map answers it: a channel whose response the drives explain exceeded because the article did; a channel low on coherence may be a mounting or a cable. The report puts the map beside the compliance bars for exactly this reading.
• Whether the comparison scale is right. A run captured below the requirement is compared scaled up to the 0 dB specification — standard practice — and the scale is detected only when the data supports it: every channel at or above a corroborated offset. Type a number in the Scaling field to hold it (0 holds it unscaled), clear the field to detect again. The data itself is never changed.
• What the run was allowed to do. The warning and abort lines come from the specification; whether a brush against the warning line matters is the test engineer's sentence to write in the conclusions.