Rough Road Vehicle dynamics analysis for vehicle vibration assessment

Multibody dynamics analysis in vehicle development provides a few useful vehicle design guidelines in a few disciplines. The first discipline is vehicle handling simulation, where the major recommendation is suspension geometry and tuning of bushings, shocks and springs. The vehicle dynamics simulations on rough roads give insights about vehicle durability performance: vehicle components, subsystems, and the vehicle body systems. Almost all inputs to the vehicle systems come from tire to ground interactions, tire modeling is the most critical aspect in vehicle durability simulation, e.g. load prediction. The third discipline is the vehicle vibration performance assessment using vehicle dynamic simulations. This study is to demonstrate a vehicle dynamics simulation process to assess vehicle vibration performance. A vehicle dynamics model is simulated on ride roads, first. Hardware measurement can be done in a similar fashion to get the vehicle target performance or bench marking data. The final objective is acceleration response at the passenger locations in frequency domain. Body interface loads are recovered from the vehicle dynamic simulation on the ride roads. In the meantime, Frequency response function (FRF) of the body structure is ready in a fashion that input forces are applied to all body interface locations to the suspension and powertrains. Output acceleration points for the body structure FRF are driver and passenger locations. This will give acceleration sensitivity of the body structure to each body interface force input. The linear sum of body interface loads multiplied by FRF at each interface creates acceleration responses in frequency domain. A mid-size sedan model was used to demonstrate the process. A full vehicle dynamics model using Ansys Motion was simulated on a virtual ride road at a constant speed. The body loads were recovered in time domain and Fast Fourier Transformed (FFT) to convert them in frequency domain. The Body-In-white model was run a harmonic analysis to get body FRF. The multiplication process was accomplished by a python code. The vehicle acceleration performance at the passenger locations is plotted in frequency domain. This process successfully demonstrated vehicle vibration performance at driver positions in terms of suspension tuning and body structure designs. It has several recommendations not available in the 100% vehicle dynamics approach, where the accelerations from the passenger locations are obtained from the same vehicle dynamics simulation. Not mentioning acceleration performance in frequency domain, it can tell contributions of each load path from body interface points to the passenger locations. The contribution from each load path enables engineers to explore the design compromises: the most cost effective or the most timing effective or both.