Modal and spectral-based hybrid experimental-analytical synthesis technique for analyzing structural dynamic interactions

The vibration characteristics of powertrain substructures and the nature of their dynamic interactions with the support brackets and body structures are critical to the overall vehicle system noise and vibration quality. This is because the fundamental modal properties of the stand-alone structural substructures tend to alter significantly due to their interactions with the dynamics of the attached structures (base). The substructure modes also affect the vibration transmissibilities across the connection points. However, it is often unrealistic and inaccurate to setup a single dynamic response model for the entire coupled system due to certain limitations inherent in the widely used finite element method. In addition, the vibration coupling between the substructures and base structures is not always known precisely. Traditional approach of designing a substructure in stand-alone free-free, constraint or other idealized state does not reliably represent the ultimate performance of the assembled system. The current dissertation examines an improvement in the modal synthesis approach using multi-point constraint equations in the context of a finite element scheme, and a proposed spectral-based approach to predict substructure modes in a coupled system state. In-depth error evaluation will be performed for both techniques.; This dissertation research explores the limitation and the range of applicability of both techniques. In general, the modal-based substructuring technique is found to work well for systems with lightly damped, well-separated modes. On the other hand, the spectral-based substructuring technique is suitable for analyzing structures with higher modal density and damping characteristics. To demonstrate the salient features of these proposed methodologies, an idealized beam-flange-plate example and a real-life supercharger-engine problem are analyzed. In these two applications, the effect of the differences between the FEM model of the primary substructure and actual hard crane on the final synthesized result is also evaluated. Based on these calculations, additional refinement work is performed. The results reveal a direct correlation between the trends of the system response and substructure FRFs or substructure modes.