MACEC can be used for experimental, operational, and combined modal testing of structures. When a modal test is performed in operational conditions, and when in addition to the operational excitation, one or several measured, artificial forces are applied, it is called a combined experimental-operational or an OMAX test (Operational Modal Analysis with eXogenous inputs). In Operational Modal Analysis (OMA), only the responses are recorded and the modal characteristics are extracted from the output-only data. In Experimental modal analysis (EMA), a structure is excited by one or several measured forces, the response of the structure to these forces is recorded, and the modal characteristics are extracted from the input-output data. In the second step, the modal characteristics of the identified model are calculated and divided into true (physical) modes and spurious modes, that appear due to measurement noise, modelling errors, harmonics, etc.ĭepending on the type of structure and the application for which the modal characteristics will be used, experimental, operational, or combined experimental-operational modal testing is needed. In the first step, a model of the structure is identified from the data, e.g., a state-space model or a non-parametric frequency response function. Unfortunately, modal characteristics (eigenfrequencies, damping ratios, mode shapes and modal scaling factors) can not be measured directly, but they have to be extracted from measured vibration data (accelerations, strains, forces. Modal testing of civil and mechanical structures is recieving considerable interest in an increasing range of applications such as design validation, (ambient) vibration monitoring, damage identification, determination of modal damping, fluid-structure interaction, etc. Modal testing of civil and mechanical structures
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