Practical techniques for scaling of optically measured operating deflection shapes

Abstract

Operational Modal Analysis (OMA) is used to identify vibration patterns of large structures under unknown operating conditions. However, operating data extracted from output-only measurements is not scaled and cannot be used for Structural Dynamic Modification (SDM), frequency response function (FRF) synthesis, force estimation and structural response simulation. Therefore, developing an algorithm that is able to extract scaled mode shapes using measured operating data is desirable. In the current paper, two different scaling techniques including drive point scaling as well as mass sensitivity scaling are employed to scale optically measured operating deflection shapes (ODS). To evaluate the capability of each scaling technique, the scaled optically measured operating shapes are compared to mode shapes extracted using input– output measurements (reference mode shapes). Additionally, the scaled operating shapes are used in structural dynamic modification to demonstrate the benefits and drawbacks associated with the mass sensitivity technique. The results reveal that both mass sensitivity and drive point scaling techniques are capable of effectively scaling optically measured operating deflection shapes of the structure.