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.

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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.

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Compliant mechanisms have been applied successfully in many quasi-static applications. However, the dynamics of these mechanisms remain largely unexplored. In particular, dynamic problems hinder the implementation of compliant mechanisms in the field of power transmission systems. To realize this, here we present theoretical and experimental dynamics of a statically balanced compliant rotational power transmission mechanism, designed based on kinematics of the Oldham coupling. A fast and flexible generic model is proposed based on multi-body dynamics, which facilitates the design and implementation of this compliant transmission couplings in dynamic applications. In order to make the model applicable for the whole design family, the compliant embodiment is parametrized using a minimum set of design parameters. Furthermore, a case study is performed on an existing design and the method is validated experimentally. Predictions can be given of (i) the maximum attainable velocity before instability due to centrifugal forces, (ii) the lower resonance modes, and (iii) the characteristics of the resulting velocity transmission error. The proposed methodology is not only applicable to the compliant transmission couplings between parallel rotational axes but furthermore provides opportunities for the modeling of other compliant mechanisms applied in dynamic environments.@en

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.

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Component-based Transfer Path Analysis allows us to analyse and predict vibration propagation between an active source and passive receiver structures. The forces that characterise the active source are determined using sensors placed on the connected passive substructure. These source characterisation forces, often called blocked or equivalent forces, are an inherent and unique property of the source, allowing to predict vibration levels in assemblies with different connected passive structures. In order to obtain a unique and accurate characterisation, accurate measurements are of key importance. The success of the characterisation is not only dependent on the hammer skill of the experimentalist, but also relates to sensor placement, overdetermination and matrix conditioning. In this paper the effects of each of these influences are studied using theoretical approaches, numerical studies and measurements on a benchmark structure designed for in-situ source characterisation. An assembly of two substructures is tested, representing an active substructure with a source and a passive substructure. In order to determine a criterion for the placement of indicator sensors, the effect of the various influences on the in-situ characterisation is compared. Using the results, a structured approach for the use of indicator sensors for in-situ blocked force TPA is proposed.@en

During a rocket launch a spacecraft is, among other loads, exposed to a potentially damaging acoustic load. Prior to space flight, ground tests are performed to determine whether a spacecraft, or a specific part thereof, can withstand the acoustic load. In a reverberation room, a typical sound pressure field is generated to simulate a rocket launch. An acoustic feedback control algorithm shapes a noise signal in order to achieve a given spectral pattern. The sound pressure levels are controlled in third octave bands. A downside of feedback control in this particular case finds its origin in the time delay of the different subsystems. Especially excitation of the reverberation room results in a delayed response. Consequently, controlling the sound pressure level might lead to inaccuracies, because the influence of previous control actions cannot be observed instantly. Since the delay caused by this transient behaviour gains significance as the change in excitation increases, the feedback algorithm especially lacks efficiency when the test is started. To bring the sound pressure level faster to the desired level, a different approach is studied. In contrast to feedback control algorithm, a feedforward control algorithm can operate efficient on a system with a delayed response. The main advantage is of this approach is that by reducing the sound build-up time, energy is saved. However, identification of the system characteristics is, to an even greater extent, required for this approach. Therefore, for instance, non-linear acoustic phenomena that appear in high energy sound fields are quantified. When the desired sound pressure level is approached, feedback control assures that the sound pressure levels remain constant. The knowledge acquired in the more thorough system identification can also be used to improve the feedback control. A stable sound pressure level throughout the test increases the reliability of the test as the chance of undertesting is minimized. What’s more, unnecessary damage is prevented as the risk of overtesting is decreased.@en

Transfer Path Analysis (TPA) designates the family of test-based methodologies to study the transmission of mechanical vibrations. Since the first adaptation of electric network analogies in the field of mechanical engineering a century ago, a multitude of TPA methods have emerged and found their way into industrial development processes.
Nowadays the TPA paradigm is largely commercialised into out-of-the-box testing products, making it difficult to articulate the differences and underlying concepts that are paramount to understanding the vibration transmission problem. The aim of this paper is to derive and review a wide repertoire of TPA techniques from their conceptual basics, liberating them from their typical field of application. A selection of historical references is provided to align methodological developments with particular milestones in science. Eleven variants of TPA are derived from a unified framework and classified into
three categories, namely classical, component-based and transmissibility-based TPA.
Current challenges and practical aspects are discussed and reference is made to related fields of research.@en

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.

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