Using the irrotational intensity field to study vibration energy paths in automotive structures

International audience ; Although structural intensity was introduced in the 80’s, thisconcept never found practical applications, neither for numericalnor experimental approaches. Quickly, it has been pointed out thatonly the irrotational component of the intensity offers an easyinterpretation of the dynamic behavior of structures by visualizingthe vibration energy flow. This is especially valuable at mid andhigh frequency where the structure response understanding can bechallenging. A new methodology is proposed in order to extract thisirrotational intensity field from the Finite Element Model ofassembled structures such as Bodies In White. This methodology ishybrid in the sense that it employs two distinct solvers: a dynamicsolver to compute the structural dynamic response and a thermalsolver to address a diffusion equation analogous to the thermalconduction built from the previous dynamic response. The fieldseparation is based on the Helmholtz-Hodge theorem, which ensuresthe computation’s full consistency. The methodology is firstimplemented and validated in the case of a plate assembly, usingcommercial FE software. This first approach immediately highlightsa bias in the current power flow computations, leading to erroneoustransmission path understanding. It also shows a remarkablestability of the irrotational intensity patterns regardingfrequency. As one would expect, transmission path only makes sensewhen they stand for a broad enough frequency range. The methodologyis then applied to an automotive structure, introducing specificmodeling of the mechanical connections between stamped steel parts(spot welds, bolts, bids…). Again the method applies well and showsfully consistent results.