Experimental Modal Analysis of Automotive Exhaust Structures

Experimental modal analysis (EMA) provides many parameters that are required in numerical modeling of dynamic and vibratory behavior of structures. This paper discusses EMA on an exhaust system of an off-road car. The exhaust structure is tested under three boundary conditions: free-free, supported with two elastomeric mounts, and mounted to the car. The free-free modal parameters are compared to finite element results. The two-mount tests are done with the mounts fixed to a rigid and heavy frame. The rigidity of the frame is verified experimentally. The on-car test is done with realistic boundary conditions, where the exhaust structure is fixed to the engine manifold as well as the two elastomeric mounts. The two-mount and the on-car tests result in highly complex mode shapes.

Details discussed in the paper include obtaining the measurement point coordinates, a method to attach triaxial accelerometers to align with coordinate axes, methods to ensure rigidity of the mounting frame, and the effects of non-proportional damping from the elastomeric mounts. Results from EMA provide data and validation to numerical models such as finite element models.