Frequency response based sensor placement for the mid-frequency range

Abstract

Accurately characterizing mid-frequency vibrations is essential for structures that require ultra-quiet vibration environments. Selecting the proper sensor locations is an important step in the model verification and validation process. State-of-the-practice approaches to sensor placement are typically based on modes shapes of the pretest finite element model. However, these modal based techniques break down in the mid-frequency range due to the high modal density. The purpose of this work was to develop a sensor placement technique based directly on a structure's frequency response. The finite element model frequency response can be decomposed into principal directions and their corresponding singular values, which relate the principal directions to the system's energy. A system's response is usually dominated by a relatively small number of principal directions, even for frequency bands with high modal densities. Principal directions are always orthogonal, while mode shapes in general are not, which makes them more robust to modeling errors and experimental noise. The new method places sensors such that the independence and signal strength of the dominant principal directions are maintained.