Iyer, G., Mohan, S., Rao, N., and Unnithan, S., "Evaluation of Dynamic Characteristics of an Automotive Exhaust System using Operational Modal Analysis (OMA) and Experimental Modal Analysis (EMA)," SAE Technical Paper 2013-01-2903, 2013, doi:10.4271/2013-01-2903.
NVH refinement has gained increased importance in the automotive industry especially in the last two decades, due to increased global competition and customer requirements. Furthermore, owing to the stringent legislative requirements on the radiated noise levels have also put additional demands on the automotive industry from the NVH perspective. Engineers have been constantly focusing on improving NVH evaluation techniques and test methodologies to improve the quality of test data, ease of measurement and productivity.The traditional input/output technique based modal analysis has always been an NVH engineer's favorite tool, for identifying the dynamic behavior of the component / BIW / vehicle in whole. The knowledge of a structure's modes and mode shape gives sufficient information of the component with respect to the system's modal alignment, for further optimization of performance, weight and for updating the CAE model. The alternative technique for dynamic characteristics extraction which is the output only technique or the OMA has also gained increased significance in the past few years as it has no consideration of the input excitation measurement, which allows the dynamic characterization under actual operating condition of the component.Details discussed in this work includes, evaluation of dynamic characteristics of an automotive exhaust system using both OMA and EMA. The dynamic behavior of an exhaust system on vehicle level is influenced due to presence of multiple decoupling elements, temperature gradient and also the gas flows. This paper tries to identify the correlation of the dynamic characteristics between the two modal analysis methodologies, and correlation of the shape vectors using MAC comparison for various described test conditions related to EMA. The study also includes the influence of temperature effect on the measured modal parameters of the exhaust system. The paper also tries to explore the advantage of OMA in terms optimization, time and a more realistic representation of vehicle level behavior.