8Subspace Processors for Physics‐Based Application

8.1 Subspace Identification of a Structural Device

Mechanical systems operating in noisy environments lead to low signal‐to‐noise ratios (SNRs) creating a challenging signal processing problem to monitor a structural device in real time. To detect/classify a particular type of device from noisy vibration data, it is necessary to identify signatures that make it unique. Resonant (modal) frequencies emitted offer a signature characterizing its operation. The monitoring of structural modes to determine the condition of a device under investigation is essential, especially if it is a critical entity of an operational system. The development of a model‐based scheme capable of the on‐line tracking of structural modal frequencies by applying both system identification methods to extract a modal model and state estimation methods to track their evolution is discussed. An application of this approach to an unknown structural device is discussed, illustrating the approach and evaluating its performance.

One approach is to recognize that unique modal frequencies (e.g. sinusoidal lines) appear in the estimated power spectrum that are solely characteristic of the device under investigation 1. Therefore, this study is based on constructing a “black‐box” model of the device that captures these physical features that can be exploited to “diagnose” whether the particular device subsystem is operating normally from noisy vibrational data. Measures ...

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