Search

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.

This section highlights some specialized substructuring methods, such as methods for estimating the fixed-interface modes of a substructure from measurements of the free–free structure with a fixture attached at the interface, and also highlights some industrial examples. Transfer path analysis is reviewed, elaborating some of the similarities in the theoretical foundations. Most information about TPA has been obtained from van der Seijs et al. (2016), please refer to the original paper for a more elaborate discussion. — Chapter Authors: Maarten van der Seijs, Randall Mayes and Matt Allen.

There are several ways to formulate the dynamics of a substructure. The different domains in which the dynamics can be described will be reviewed since the manner in which substructures are characterized will later determine the substructuring methodology that can be applied. In addition to how the substructures are formulated, the way in which the coupling/decoupling problem is expressed will allow us in the subsequent chapters to develop different numerical and experimental techniques. Two conditions must be satisfied on the interface between substructures: a condition on the displacement field (compatibility) and on the interface stresses (force equilibrium). Those conditions can be accounted for following several different formulations, all mathematically equivalent, but each leading to different numerical methods, experimental approaches, and approximation techniques, as will be explained in the following chapters. In this chapter, we outline the basic concepts of the so-called three-field formulation, dual and primal assembly.—Chapter Author: Daniel Rixen

This chapter reviews common nonlinearities that are encountered in engineering structures, with a particular emphasis on geometric nonlinearity. Popular ways to construct reduced order models for geometrically nonlinear problems are discussed. The concept of nonlinear normal modes is presented to help understand the dynamics of these structures, and some recently presented substructuring methods are reviewed. —Chapter Authors: Matt Allen & Paolo Tiso.

The prior chapter presented rigorous theory and methods for nonlinear systems, which is necessary in general because many nonlinear systems exhibit strong modal coupling due to the nonlinearity; this is commonly the case for the geometrically nonlinear structures that were the focus of that chapter. However, one of the most common sources of nonlinearity in built-up structures is the joints, and in many cases, these introduce only a weak stiffness nonlinearity together with a significant damping nonlinearity. In this case, and in many others that are relevant to industry, one can obtain good estimates of the response of the structure using a weakly nonlinear model in which the linear modes of the structure are presumed to be preserved and coupling between modes is neglected. This chapter provides a brief introduction to these concepts.—Chapter Authors: Randall Mayes and Matt Allen

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.