A Short Introduction to Modal Analysis

The dynamic behavior of a mechanical structure can be described uniquely by its modal parameters (natural frequency, mode shape and damping). Modal analysis is the process of identifying these modal parameters, either experimentally (Experimental Modal Analysis, Operational Modal Analysis) or analytical (Finite Element Analysis).

These findings can be used to reduce unfavorable sound and vibration conditions, which are usually associated with resonance phenomena. In the case of resonance, for example, the operating forces excite natural frequencies and corresponding natural modes to oscillate, which can lead to resonance catastrophe and material failure. Modal analysis is thus an important tool in the development process and for prototype construction to identify and specifically eliminate operationally critical or acoustically unfavorable vibration modes of the structure. Among other things, this approach is important for compliance with safety standards, e.g. in automotive, aerospace or civil engineering.

Result of an Experimental Modal Analysis

Figures 1 and 2 show the result of an experimental modal analysis performed on an aluminum steel rim. By applying a targeted impulse excitation to the structure and recording the system response at over 400 measurement points using laser Doppler vibrometry, it was possible to determine the structure's natural frequencies from the measurement data.

Figure 1 shows an example of the natural mode shape at 1215 Hz. Other vibration modes are shown in Figures 3 - 5.

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WaveImage: Experimental Modal Analysis of a car rim

An Experimental Modal Analysis was performed to determine the dynamic behavior of a car rim. This provides the identification of the structural modal parameters (natural frequency, natural mode and damping) from known system excitation and measured system response.