Multi-batch OBMA technique for large structures under rotational excitation

Abstract

Operation Modal Analysis (OMA) is a viable option for structures where Experimental Modal Analysis (EMA) is challenging to apply. However, large structures may sometimes be measured in batches due to limitations in sensor quantity, which may result in incorrect scaling of mode shapes. This paper introduces a multi-batch Order Based Modal Analysis (OBMA) technique for large structures under rotational excitation, this technique uses common reference points, and the classic auto- and cross-powers will be replaced by the auto- and cross-power spectrum based on the angle domain. For comparison and validation, this technique was applied to a compressor rotor test rig, the first six modes of its casing obtained through OBMA, EMA and FEA are presented. It is concluded that multi-batch OBMA is a promising technique when confronting with large structures under rotational excitation, it can identify modal parameters under real boundary conditions with limited sensor quantity.