Modal analysis and operational vibration

Modal analysis and operational vibration analysis

Information on vibrational behaviour is fundamental for both the dynamic interpretation and the failure analysis of a mechanical component. In the first step, the natural vibration behaviour is of primary interest as a structural property that is independent of excitation. Information on the modal parameters permits a description of the dynamic system behaviour and forms the basis of further structural dynamic tests.

In spite of advanced simulation technologies, the actual behaviour of a system can be determined only on the basis of experimental analyses. Experimental modal analysis (EMA) is one of the most important measurement methods in this regard.

Experimental modal analysis

The EMA determines the transmission functions of a system, i.e. the relationship between the reference force exciting a structure and the structural response. The structural response is traced back to the natural vibration behaviour of the structure using reference excitation forces. Natural frequencies and forms of natural vibration, which can be excited in resonance, as well as damping properties can, in turn, be derived from the above with adequate data processing.

Müller-BBM's measurement equipment offers diverse options for performing modal analyses. Electrodynamic shakers and impulse hammers in various sizes serve the purpose of excitation the structures. Load cells, accelerometers or laser measurement technology in combination with PC-based measurement systems for signal processing are available for signal acquisition.

Spatially animated results can be displayed with the help of visualisation models. These ensure that the basic information is available for evaluation, or for measures, with respect to load scenarios.

Operational vibration analysis

The actual behaviour under operating loads can also be specified with measurement techniques. The spectral composition of the structural response is also of interest, in addition to the absolute amplitude as a function of the operating load. In the operational vibration analysis (OVA), the signal is spectrally broken down into the temporal sequence of the operating load. This makes it possible to determine the frequency-based structural response at the measuring points at any points in time. The form of vibration thus determined is displayed as a form of spatially animated natural vibration with the help of a visualisation model. Other operating data such as temperature, pressure, or a GPS signal for vehicles, can be recorded simultaneously with the vibration response. The recording of a rotational speed signal also allows for order-based evaluations and displays.

We use the above methods to analyse mechanical structures of various types and sizes—from small parts such as printed circuit boards or brake components, to musical instruments, machine components, large diesel engines and large structures such as entire ships, or civil engineering structures such as bridges or building ceilings.

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