The modal testing experiment presented here is performed by a gearbox manufacturer using ModalVIEW software and National Instruments DSA hardware as the modal testing and analysis tool. The analysis result provides instructive guidance of their research on FEM model.

Experiment scenario

The testing object is a gearbox structure:

To identify closed spaced and conjugate modes of this symmetrical 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．ModalVIEW1.0 Software.

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

3．Hammer (Lance LC1302) and Charge amplifier (Lance LC0106).

4．Lance LC1301 accelerometer.

Analysis results

80 FRF data with 7 reference DOF are obtained in modal testing experiment, as the following figure shows.

Modal analysis for the structure is finished with ModalVIEW’s quick mode estimation method. The red synthesized FRFs from estimated modes are computed and overlaid with original FRFs. The synthesized FRFs match original FRFs well to indicate that estimated modes are accurate enough, as the following figure shows.

Part of the picked meaningful modes are listed in following table :

Part of the mode shapes are displayed as following :

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