Random-on-Random

Superimpose bands of random energy on a random background

In complex vibration environments, random vibration may present as both random background energy and narrow-band signals. Use Random-on-Random to run a controlled spectrum random vibration test. Random-on-Random is one of the three mixed-mode testing modules in VibrationVIEW.

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Random-on-Random Vibration Control

A Random-on-Random (RoR) test runs a complex test profile that contains two types of random signals: random background and narrow-band signals. This mixed-mode test reflects environments where the device under test experiences a broadband random signal and one or more random “tones,” such as:

Rocket launches: Engine vibration and narrowband structural resonances or control system vibrations.
Military vehicles: Rough terrain and rotating machinery or weapons systems.
Aircraft flight: Turbulence and engine or rotor harmonics.
Spacecraft launch or flight: Broadband acoustic loads and system-specific vibrations.

The swept or fixed frequency narrow-band signals are superimposed onto the base random energy profile. The random vibrations are performed simultaneously to simulate an environment where both modes are present.

Easy Test Entry

Use frequency/amplitude breakpoints or enter an endpoint and the desired dB/octave slope
Enter random frequency/amplitude breakpoints in an easy-to-read, tabular format or copy & paste a breakpoint table into the test
Enter over 9,999 breakpoints

Advanced Test Profile Configuration

Define up to 32 narrow spectral bands to superimpose on the background random spectrum and sweep between frequencies at a user-programmable rate. VibrationVIEW support individual sweep rates for each random tone. Enter up to 200 breakpoints, supporting virtually any test specification.

When to Use RoR?

Vibration in real life is unpredictable: your test profiles should match. Random vibration testing replicates real-world conditions by exciting all frequencies simultaneously, uncovering potential weaknesses and resonance interactions.

For more complex environments, tailor your random test profiles with RoR testing. RoR creates realistic stress profiles ideal for product qualification and fatigue testing, revealing design performance under operational loads.

Simulate an environment with broadband vibration and superimposed narrow-band sources
Target multiple failure modes for more comprehensive stress exposure
Represent operational loads that contribute to long-term material fatigue
Uncover nonlinear behavior or coupling between system resonances
Meet aerospace, military, and automotive standards
Customize tone frequencies, amplitudes, and sweep parameters to match use case

Additional Features

Configurable acceleration limits, line limits, and drive limits help protect the test article and shaker system. The control input is verified against shaker acceleration limits.
Tests can be scheduled to run for a user-defined length of time, and the spectrum level can be scaled by a specified decibel level, percentage, or RMS acceleration. Level schedules can be entered to run various durations at different acceleration levels.
Graph display options include power/acceleration spectral density (PSD), output voltage spectral density, and channel-to-channel transmissibility.

What is the Power Spectral Density (PSD)?

Random vibration is often analyzed with the power spectral density (PSD). The PSD represents the distribution of a signal over a defined frequency spectrum. It reveals resonances and harmonics that may not be visible in a time-history graph.

Normally distributed time-domain data is transformed into frequency-domain data (i.e., a PSD) using the fast Fourier transform. An understanding of the PSD will help engineers to determine the correct parameters to use when generating a PSD from a waveform. To learn more about generating a PSD, please enroll in our Random Testing course on VRU.