This presentation was made at the 2019 NAFEMS World Congress in Quebec Canada

Resource Abstract

The industry of off-road vehicles has grown widely in the past decade with the arrival of side-by-side vehicle as a new major player in the market. The very competitive industry of recreational vehicles always seeks for engineering improvement to keep an edge on competitors and Noise-Vibration and Harshness of a structure (NVH) issues are becoming even more important as sophistication of these products get better. To achieve that goal, the use of a structural finite element model along with modal (Nastran SOL103) and sine analyses (SOL111) allows to predict the vehicle entire frame NVH issues under internal combustion engine excitation. The engine unbalance forces and moments as well as weight and mass moment of inertia are input on the engine CG modeled with RBE2 and CONM2 elements and are determined using GT Crank simulation software. The engine is connected to the frame through its engine mounts modeled with CBUSH elements referenced by PBUSHT tables to account for their frequency dependent behavior. To capture the behavior of the vehicle throughout the entire engine operational range from idle to maximum rpm, SOL111s are performed accounting for a specific DLOAD which represents the frequency content of the engine. This procedure allows to output the nodal accelerations at hand, feet and seat rest and compare different frame configurations, engine mounts characteristics and positions as well as engine architectures to ultimately take the best decisions at optimizing the end-user vibration comfort. Based on modal analysis, the procedure was first experimentally correlated on single components such as the frame by impact hammer testing. The reproduction results by simple modal analysis allow to ensure strong basis for upcoming frequency response analysis. Next, a working prototype was equipped with accelerometers and slow ramp-up measurements with rpm tracking allowed to correlate the forced response procedure for two different internal combustion engines architecture. The analyses presented herein would eventually lead to the prediction of radiated noise for a structure under engine excitation. Such approach made possible the correlation of the numerical model at the different stages of the analysis process.