Experimental System Identification

The goal of the project is to develop methodologies and algorithms for the COUPLE software in collaboration with Dutch SME  Vibes Technology B.V. and the BMW Group. COUPLE uses frequency-based substructuring to determine how actively vibrating components transfer energy through damping elements (rubber bushings) to passive components to reach the target (e.g., driver's ear). Frequency-based substructuring divides an assembly into substructures, which are then modeled separately. The models of these substructures are combined using force and displacement equilibrium constraints to predict the response of the overall system.
When using substructuring, the individual components can be modeled using two approaches: computational and test-based. The computer-based modeling is relatively simple, but its results are not good enough to be used in real practical applications. Test-based modeling (used by COUPLE in combination with computational modeling) is much more accurate, but there are major technical challenges to apply it to complicated structures in practice. In the last decade, test-based substructuring has mostly been performed in academic settings on simple structures, in well-controlled environments, and with a validation measurement as a reference. These studies have demonstrated the enormous potential of test-based modeling. The next step is to work with industry partners to bring the method to the maturity required by industry.

The goal is to offer practical, robust and reliable finite element models for two types of connection elements, namely bolted connections and rubber mountings, in order to predict the vibrational behaviour of the system for different contact types and characteristics. For the rubber the focus is more on the constitutive modeling of the material, while for the bolted connection the contact itself represents the critical element. In both cases, the complexity lies in modelling the non-linear behaviour and parameter dependencies that characterise the connection under certain operating conditions. The modeling approaches range from a white box to a black box description, on the basis of the experimental tuning required to describe the dynamic behaviour of the joint. The former implies a full understanding and predictivity of the multi-scale and multi-physics phenomena underlying the joint dynamics. The latter indicates the knowledge of the only input/output dynamic representation of the connection element. In any case, it is required both a strategy for the characterization of the joint parameters and a practical and efficient implementation of the associated models in classic finite element codes.

In the automotive industry, Noise, Vibration, and Harshness (NVH) is becoming increasingly important to meet customer expectations for acoustic performance. To this end, methods are being developed to predict and improve NVH problems. One broad group of diagnostic tools for analyzing noise and vibration is transfer path analysis (TPA). Theoretically, it should be possible to characterize vibrations from active (source) and passive (receiver) structures independently. This will allow prediction of structure-borne noise for a structure with an excitation source (e.g., engine-transmission unit) on any coupled receiver structure (e.g., car body including rubber mounts). Within the scope of this project, existing methods for the characterization of the active structure shall be further developed. Furthermore, the assumption of unchanged excitations in different test rigs shall be investigated to allow the transferability of equivalent forces. A method that eliminates the contribution of non-measurable operating forces in the measured signals is called the Operational System Identification (OSI) method. This should be further developed to provide a reference excitation signal that is measurable. Combine this with the in-situ blocked force TPA approach, and this may lead to a promising measurement method that allows rubber bearings to be kept in a specific operating condition. In addition, methods for characterizing rubber bearings are to be further developed. Here, the dependent factors such as static preload, temperature, frequency and amplitude will be investigated in more detail. A major challenge can be the nonlinear behavior of rubber bearings. An investigation of how nonlinear effects of rubber bearings can be integrated into the FBS method is therefore also planned.
Project partner

This project is supported in part by Hyundai Motor Company (HMC) including its subsidiary Kia Motors Coroperation - 12, Heolleung-ro, Seocho-gu, Seoul, 06797, Korea.

The continuous development of experimental techniques in the field of dynamic substructuring and vibration analysis requires extensive investigation and experimental research. In addition to the efforts made for measurement campaigns, experimental setup, and experimental acquisitions, appropriate post-processing of the acquired data is necessary to improve the quality and reliability of experimental substructuring predictions. Uncertainty quantification, regularization, noise filtering, and data selection are some of the topics addressed in this research project. Here, current scientific and industrial challenges will be investigated in more detail. The goal is to develop a deep understanding of the errors that affect substructuring results and ultimately provide practical and robust strategies and tools for improved handling of experimental data.