Identify a structure’s response to excitation with modal analysis. The Modal Testing software collects responses, calculates averages, and generates transfer functions. From there, export the data to a modal analysis software.
Engineers seek to understand the natural vibration frequencies of a structure and its response to excitation. If an external vibration aligns with the structure’s natural vibration, resonance will occur. If unaccounted for, the natural vibration will be amplified and result in structural fatigue or damage.
When a structure is excited at its natural frequency, the resulting vibration creates different shapes. These mode shapes help to describe the vibration.
Modal Test Setup
Modal analysis can be experimental or operational. Engineers most often use experimental analysis, where a mechanical device excites the structure, and the response is recorded.
A modal test setup includes a device to generate the excitation, transducer(s), and a data acquisition system. The structure is subject to an impact, the transducers attached to the structure record the response, and the output signal is sent to a dynamic signal analyzer such as the ObserVR1000.
Record Responses & More
Capture transient events with an ObserVIEW/ObserVR1000 system, and access a comprehensive suite of features for additional data recording, editing, and analysis.
The ObserVIEW Modal Testing module is compatible with a modal impact hammer for excitation. The ObserVR1000 records the impulse via the hammer’s force sensor and the structure’s output via the response accelerometers. The user can capture data using the roving hammer or roving accelerometer method.
The ObserVIEW software also employs automatic double-hit detection. If there is a second peak in the input that is a certain percentage of the main peak value, it is considered a double hit and rejected automatically. The user defines the percentage value per their own requirements.
Modal Testing in ObserVIEW
In ObserVIEW, the Modal Testing software collects responses to excitation with an impact hammer. The program calculates an average response for each hit location and generates a smooth transfer function (FRF). From there, the data can be exported to a modal software such as MEscope for further analysis.
ObserVIEW reads RPC® and RSP time waveform files and supports pasted traces. Organized transfer function data are exported to a UFF or another modal data format.
With Modal Testing in ObserVIEW:
Manage table of hits per location and review hits
Average multiple data acquisitions
Calculate decay rate from transient ring-down events
Manage the acquisition channel using a large, interactive display
Assess the Stability of a System
Add a Nyquist plot to view transfer function data as a scatter plot.
Transfer Function (FRF)
After the data are acquired, the time response of the structure can be converted to the frequency domain by using a Fourier transform. The frequency response of all the modes of the system is known as the frequency response function or transfer function. The coherence plot can be used to validate the transfer function graph.