结构动态测试传感器优化配置的预试验技术

传感器配置是结构动态测试的一项重要的技术措施,其效果决定了结构的各阶主要测试模态的有效程度。由此,首先对结构仿真模型进行预先的主元素分析,优化传感器的布置。在结构有限元模型(FEM)中,对模型固有特性进行分析,确认重要的结构模态和结构动态测试目标。利用Guyan缩减方法对模型的自由度进行主从划分;选取感兴趣的结构振型的主自由度,对应从有限元模型中提取缩减的"试验模型"。针对提取的缩减模型重新开展模态分析,采用模态置信度(MAC)指标评估各阶振型之间的相关性,进而量化并直观显示传感器的配置效果。对某型号无人直升机机身结构进行地面振动试验。通过从仿真模型中选取合适的振型主元,改进传感器的配置,能保证试验中获得期望的结构测试模态,验证了利用结构仿真模型在动态测试之前预先进行传感器优化配置的效果。

Pre-test Technique for Optimization of Sensors Placement in Structure Dynamic Testing

Sensors placement is a key step in the dynamic testing of structures. Its effectiveness even determines whether the main test modes could be accurately derived or not. The preliminary master-elements analysis of structural simulation models is used to optimize the testing sensors placement. A detailed finite element model (FEM) of the structures was firstly prepared. Structural mode analysis was performed to have a deep insight into the importance modes and the objective of the dynamic testing of the structures. Master-slave degrees of freedom (DOFs) were then separated from the structural finite element model. The master DOFs for the interesting vibration modes were defined, which is corresponding to the extracted “reduced test model” from the aircraft finite element model. Modal analysis for the reduced model was repeated. Modal assurance criterion (MAC) was used to assess the correlation among the calculated modes shapes of the reduced model. The effects of optimal sensor placement were eventually quantified and clearly displayed. An actual example was demonstrated for the ground vibration test (GVT) of an unmanned helicopter fuselage. The optimal placement of testing sensors through selecting the suitable master vibration modes of FEM assured that the expected fuselage vibration modes from the GVT could be obtained. This verified the effectiveness of structural simulation model usage for the optimization of sensor placement in advance of the dynamic testing.