Paper: Application of Operational Modal Analysis for In-Situ Deflection Shape Analysis during Shaker Tests

Abstract

Shaker testing is an important step in evaluating the structural performance and fatigue of components and assemblies in many important areas like aerospace, automotive and electronic products. In many of these tests head expanders or slip tables are used for mounting the test specimen on the shaker. As these components may have significant impact on the overall dynamics of the system a basic understanding of their structural properties is essential. Otherwise depending on the positioning of the control transducers and the mounting points significant under or over testing may occur. Thus, it is important to understand the structural dynamics of the test assembly, shaker and head expander to achieve testing in accordance with specifications. Especially mounting the test specimen and the control accelerometers on nodes or anti nodes of the head expander has significant impact on the test results and the vibration control algorithm.

In this paper a shaker with a head expander model is analyzed using three different approaches. Initially the head expander’s mode shapes are examined via classical modal impact hammer testing. Additionally, Operational Deflection Shape (ODS) analysis and its applicability in evaluating the dynamic behavior of the vibrating system is investigated before the concept of Operational Modal Analysis (OMA) as an alternative method is introduced.