The shock workflow

A shock test specifies a response spectrum. The article must see an event whose SRS falls inside a tolerance band around the required curve, and the waveform that produces it is up to the shock machine. The report therefore leads with the transients, since how long each event lasted and how it rang down is only visible in the trace, and answers the spectral question after.

The walkthrough uses the demonstration plate's shock series, four half-sine events stepped up to level and recorded on six accelerometers and a drive channel, with a screenshot at every step. The recording ships with the repository (testdata/plate/shock.nc4).

Step	In the app	In a script
Import the recording	drag the .nc4 onto the window	project.import_file(path)
Say what it is for	right-click the root → Set Project Type → Shock	project.project_type = 'Shock'
The events	Detect in the Shocks view marks each event	project.detect_shocks('Time History')
Filter and integrate (optional)	Apply Filter in the Filter view; Integrate on the bar	project.filter_data(name), project.integrate(name)
Compute the SRS	Compute SRS in the Shocks view	project.compute_srs('Time History')
The required SRS	import it, with its tolerance	ShockSpecification(...) from visualdynamics.core.data
Compare	select SRS and specification together	plot_series([srs, spec]), plot_bars(srs, spec, 'srs') from visualdynamics.plot
Judge the tolerance	Points Rule on the bar, with SRS and specification selected	srs_tolerance(spec, srs) from visualdynamics.core.compliance, plot_srs_tolerance(srs, spec)
Geometry and photos	drag them in, link them	project.add(...), project.link(...)
Report	Generate Report on the bar, with the project row selected	project.generate_report('shock')
Or all of it at once	Automatic on the tree bar, once the project has its type	project.work_up()
Export	Export → HTML…	project.export_report(name, path)
Save	File → Save Project As…	project.save('shock.vdyn')

In the app, step by step

1. Import the recording, and say what it was

Drag the recording onto the window. At the file level a shock recording cannot be told from a transient one (both are one stream of events), so the run is imported as Transient and you declare it: right-click the project root and choose Set Project Type → Shock. The tree adds the slots a shock report draws from. There is no coherence slot, because a shock is a single event and coherence describes a stationary average.

Select the time history and choose Shocks on its bar. Press Detect to find the events; the view does not detect them until you ask, and Compute SRS detects them for you if you go straight to it. A record that is already read as frames (a controller's save of a transient run, whose playings are its frames) keeps its own. The time view shades each event on the trace, and Add and Remove in the view add a window the detector missed or drop one.

Detected windows share one length by default, the longest any event needs from its peak to a settled ringdown, so every event is analyzed over the same window. Dragging a window's body moves that one event. Dragging an edge resizes it, and while Same length for all is ticked, resizing one window resizes the whole series, stopping before any window would overlap its neighbor. Clear the box to resize windows one at a time.

2. Filter and integrate (optional)

The shock project has optional slots for a filtered record and for velocity and displacement integrated from it. Choose Filter on the time history's bar, set the filter, and press Apply Filter; the event windows are copied onto the filtered record. Integrate on the bar then gives velocity, and integrating that gives displacement. When a filtered record is present, compute the SRS from it, so the spectra, the motion and the scalogram in the report all describe the same signal. Automatic on the tree bar works in this order: it filters the record, computes the SRS from the filtered record, and integrates twice.

The Integrate act removes a drift below 2 Hz, which suits a record's motion and not a stroke estimate: a compensated pulse's displacement is content at a few hertz. To see whether a pulse fits on the shaker, choose Stroke on the bar instead. It integrates the record raw and reads the peak velocity, the travel with the shaker body counted and the force against the shaker's shock ratings; Will a pulse fit on the shaker says how to read it.

3. Compute the shock response spectra

Before computing, read the velocity check under the SRS settings in the Shocks view: every acceleration channel integrated to velocity with nothing removed, over every window. A record whose velocity does not come back to rest carries a zero shift or an offset, and its spectrum is false at the low end; Checking a shock record before its spectrum says how to read it.

Press Compute SRS in the Shocks view. It computes one SRS per channel per event, at the Q (10 by default, 5 % damping), Peak (maximax, positive or negative) and Per octave spacing (12 by default) set in the view. A shock test is judged on the worst event, so a recording holding four events gives four spectra rather than an average. For one spectrum over the whole record, set a single window over the whole record. The plot shows every event at one channel, so a stepped-up series reads as a family of curves rising to level, and the drop-down on the bar reaches the other channels.

A series of measured shocks can also be the start of a requirement: Field Limit on the SRS's bar takes the envelope or a tolerance limit over the events and writes the straight-line envelope a shock specification is written from, at the spectra's own Q (see Deriving a specification from field data).

4. The requirement, and the comparison

A shock specification is an SRS with a tolerance band around it, the required curve with abort_upper and abort_lower. Import it, or write it once in a script and save it. Select the measured SRS and the specification together and the band is shaded around the spectra, still every event at one control channel. SRS Error on the bar shows the whole run as bars, one for every event at every control channel: the RMS deviation from the requirement in decibels, signed, shaded blue past −3 dB where the shock under-tested and red past +3 dB where it over-tested. The same 3 dB is used by the random workflow's RMS error bars.

The bars are an RMS summary and not the tolerance check, which counts the points of each spectrum inside the band and applies the test document's rule to the count. A spectrum with a narrow, deep dip can read well inside 3 dB on the bars and still fail it. That check is Points Rule on the bar, with its band and rule in the panel beside the plot; in a script it is srs_tolerance and its picture plot_srs_tolerance. Judging an SRS against its tolerance describes it.

A classical pulse (a half-sine, sawtooth or trapezoid) is judged in time rather than by its spectrum: Pulse Check on the time history's bar draws the record on the nominal pulse's tolerance envelope and reads its velocity change; Checking a classical pulse says how.

5. Geometry, photos, report

Drag the article's geometry in, declare its units, add the setup photographs, and link the group. Then select the project row and press Generate Report. The shock report starts with the front matter and the measured time histories, with the event windows shaded and numbered on them. How long each event lasted, how many there were, and whether the article was still ringing when the next event arrived are visible in the trace and not in the spectrum. When the project holds a filtered record or integrated motion, a section on the motion follows. Next is the scalogram of the filtered record (or of the measured record when there is no filtered one), which shows where in frequency each event's energy was and when, and is the way to find the source of an unexpected SRS peak. Then come the specification with its band, the measured SRS drawn over it as selecting both shows in the app, the signed deviation bars, and the conclusions. There is no PSD in a shock report: the level of a density computed from a transient recording depends on how much quiet time was recorded around the events, and the scalogram answers the frequency question with the time axis kept.

The same series, headless

The Console tab along the bottom of the window shows the session as Python while you work: every act as the line that replays it. Expand it, copy the lines you want, and they run as they are.

import numpy as np

import visualdynamics
from visualdynamics.core.data import ShockSpecification

project = visualdynamics.Project('Plate Shock Series')

# 1. import, and declare what the file cannot say
project.import_file('shock.nc4')
project.project_type = 'Shock'

# 2. one SRS per channel per event; the events are detected here
# because nothing else in the record says where they are
project.compute_srs(project.time_history)

# 3. the requirement: breakpoints with a tolerance band around them
srs = project.srs
frequencies = np.asarray(srs.abscissa, dtype=float)
level = ...                       # the required curve, from the test plan
project.add('Shock Specification', ShockSpecification(
    abscissa=frequencies, ordinate=level[None, :],
    response_dof=[srs.response_dof[0]],
    ordinate_dim='acceleration', ordinate_unit='m/s**2',
    q=srs.q, kind=srs.kind,
    abort_upper=level[None, :] * 10.0 ** 0.3,     # +6 dB: a factor of 2
    abort_lower=level[None, :] * 10.0 ** -0.3))   # -6 dB

# 4. 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('shock')
project.export_report(project.report, 'shock_report.html')
project.save('shock.vdyn')

Where judgment lives

• Which events count. The demonstration series was stepped up to level, as a real one usually is. The report shows every event's spectrum, and which events were qualification and which were rehearsal is for the engineer to write.
• The tolerance itself. The demonstration specification uses ±6 dB (+6 dB and −3 dB is a common convention). A real specification carries its own band, and the shading in every comparison comes from the specification object, not from a setting. The rule about how many points must lie inside it is the test document's, and is given to srs_tolerance as its arguments; the band it counts against is the specification's own unless one is given.
• Q, and what the spectrum means. An SRS is computed at one amplification: a spectrum at Q = 10 says nothing about what the same shock does to a Q = 50 article. The Q is stored on the spectrum and on the specification. Compute the SRS at the Q the specification names, because the deviation is computed from the two curves as they are, with no adjustment for a difference in Q.
• The window length. Once a window is long enough to hold the peak and its ringdown, the SRS changes very little with more length, which is why one shared length is a safe default. The judgment is whether each window reached that length: a ringdown cut short reads low at the article's own frequencies, and the shaded windows on the trace are where to check.