Selecting the proper set of degrees-of-freedom (DoFs) is essential in inverse blocked force calculation. Including too many degrees-of-freedom in the computation can lead to overfitting, resulting in inaccurate force estimations and poor prediction quality. The discrepancy arises from errors within the dataset, such as measurement noise or other artifacts. This article presents a solution to the overfitting problem, introducing the X-DoF procedure to automatically identify the relevant subset of blocked force degrees-of-freedom. Its effectiveness is showed through numerical and experimental validation and compared against regularization techniques.

Automotive OEMs have introduced a new development paradigm, modular architecture development, to improve diversity quality and production efficiency. It needs solid fundamentals of system-based performance evaluation and development for each system level and single component level. When it comes to NVH development, it is challenging to realize the modular concept because noise and vibration should be transferred through various transfer path consisting of many parts and systems, which interact with each other. It is challenging for a single system of interest to be evaluated independently of the adjacent parts and environments. In this study, a new system-based development process for a vehicle suspension was investigated by applying blocked force theory and FRF-based dynamic substructuring. The objective is to determine the better dynamic stiffness distribution of many bushes installed in a suspension system in the frequency range corresponding to road noise. The suspension force rig test methodology isolated the entire suspension system from the interaction with body structures. The blocked force outputs are measured directly on the suspension force rig. Dynamic substructuring is conducted to derive the transfer characteristics from tire wheel centers to multiple force outputs. Bush stiffness injection (BSI) method is developed through the dynamic substructuring of the system, by which suspension system-level blocked force differences by changes in multiple bush stiffnesses can be predicted without any actual bush-changing works. The BSI method enables a sensitivity analysis for each change in bush dynamic stiffness and an optimization study to determine the best combination of multiple bush dynamic stiffnesses.

Transfer path analysis (TPA) and source characterization using the in-situ blocked force methodology is becoming increasingly common in the automotive world. While robust techniques exist for this type of characterization in general, there are certain conditions where the analysis is more straight-forward than others. In this work, several techniques are presented to help improve the characterization across different frequency ranges. At the very low frequencies, where structures should behave rigidly, TPA results can be improved by filtering out any non-rigid body motion from a set of measured FRFs. In the mid-frequency range, testing can be simplified using a volume source to capture reciprocal FRFs and then predict sound levels at the driver’s ear. In the mid- and high- frequency ranges, the addition of rotational FRFs can help improve TPA predictions. These techniques are demonstrated using recent test results on various components and vehicles in this paper.

This paper introduces SEMM: a method based on Frequency Based Substructuring (FBS) techniques that enables the construction of hybrid dynamic models. With System Equivalent Model Mixing (SEMM) frequency based models, either of numerical or experimental nature, can be mixed to form a hybrid model. This model follows the dynamic behaviour of a predefined weighted master model. A large variety of applications can be thought of, such as the DoF-space expansion of relatively small experimental models using numerical models, or the blending of different models in the frequency spectrum. SEMM is outlined, both mathematically and conceptually, based on a notation commonly used in FBS. A critical physical interpretation of the theory is provided next, along with a comparison to similar techniques; namely DoF expansion techniques. SEMM's concept is further illustrated by means of a numerical example. It will become apparent that the basic method of SEMM has some shortcomings which warrant a few extensions to the method. One of the main applications is tested in a practical case, performed on a validated benchmark structure; it will emphasize the practicality of the method.

Prior to any structural system realization during the design phase, the structural dynamic should be characterized. Dynamic characterization provides the designers with local and global dynamic information which can be used to optimize the structures. To characterize the dynamic of too large and complex structures generally Dynamic Substructuring (DS) techniques are used. Experimental DS is one of these techniques and is recently more in use. Many researchers put effort in developing and evolving new concepts. The substructuring focus group at Society for Experimental Mechanics (SEM) uses a small-scale wind turbine, Ampair 600, in a combined effort to validate, classify and advance these techniques. In this paper the substructuring results, obtained with the LM FBS formulation applied to the wind turbines rotor are given. The Interface Deformation Mode (IDM) method is adopted and applied to overcome the lack of Rotational Degrees of Freedom (RDoF) and to minimize the measurement noise. To include the joint stiffness and damping a Substitute (Fixture) is used and two methods are proposed to model flexible and rigid Cyclic Symmetric Structures (CSS). The results obtained in this first substructure analysis of the rotor show that good results can be found in the lower frequency range.