The modal analysis of a composite material spherical shell structure presented here is performed in a university lab for FEA verification using ModalVIEW software as the modal analysis tool. The analysis result provides instructive guidance on design of their structrual optimization design.

Experiment scenario

The testing object is a shallow spherical shell structure:

To identify this symmetric 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 PXI 1405 chasis and 24-bit PXI module NI PXI-4472 is used to guarantee the accurate measurement of weak vibration signal of measured points far away from excitation point. The scalability of NI DSA hardware also guarantees the investment of whole modal testing system.  

System configuration

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

1．ModalVIEW 2008 Software.

2．NI DSA System (High-performance chassis PXI-1405, 8 channel DSA module NI PXI-4472)

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

4．Accelerometer (Lance 501).

 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 47 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 :

Some mode shapes are displayed as following :

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