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Modal Testing of Harvester Structure

The modal testing experiment presented here is performed by a university research laboratory using ModalVIEW software and National Instruments DSA hardware as the modal testing and analysis tool. The analysis result provides instructive guidance of structure design on their new harvester prototype.

Experiment scenario

The testing object is a harvester head structure:

To identify closed spaced modes with large damping of this complex structure, accurate modal analysis method of poly-reference, multiple DOF, global fitting is required. ModalVIEW modal analysis software provides advanced modal analysis method based on mode stabilization diagram to extract modes from poly-reference FRF measurements, which meet testing requirements. National Instruments 24-bit portable module PXI-4498 is used to guarantee the accurate measurement of weak vibration signal of measured points far away from excitation point. The portable NI DSA hardware is suitable for field modal testing experiment.  

System configuration

In this modal testing experiment, the following software and hardware are used

1.ModalVIEW R2 Software.

2.NI DSA System (PXI Chassis PXI-1042 Controller PXI-8106, 16 channel DSA module PXI-4498)

Analysis results

Modal analysis for the structure is finished with ModalVIEW’s advanced mode estimation method based on mode stabilization diagram. The following figure shows the clear mode stabilization diagram from 92 measured FRF data.

The closely spaced modes can be selected from stabilization diagram. The real modes are kept with mathematical or faked modes being discarded. Part of the picked meaningful modes are listed in following table :

Index Frequency (Hz) Damping (%)
1 34.5674 0.303602
2 87.5461 0.454995
3 107.576 0.524794
4 118.731 0.230154
5 119.057 0.68687
6 138.546 0.550448

Part of the mode shapes are displayed as following :

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Last updated April 28th, 2018