A Review of Similitude Methods for Structural Engineering

Similitude theory allows, through a set of tools known as similitude methods, to establish the conditions to design a scaled (up or down) model of a full-scale structure, usually defined as prototype. In the last years, to overcome the problems associated with full-scale testing, such as costs and setup, research on similitude methods has grown and their application has expanded in many branches of engineering. The aim of this paper is to provide a review as comprehensive as possible about similitude methods applied to structural engineering; after a brief historical introduction and a more deep analysis of the main methods, the article focuses on the applications classified by test articles

Numerical investigations about the sound transmission loss of a fuselage panel section with embedded periodic foams

Abstract The scope of this paper is to investigate the sound transmission loss of a typical fuselage panel section, as well as to propose solutions based on the inclusion of a periodic pattern inside its foam core, which aim at passively improving the acoustic performance in a mid-high range of frequencies. In detail, a new fuselage panel configuration is numerically studied, starting from the state of the art regarding the acoustic packages based on porous meta-materials. The main novelties of the present work are represented by the application of a meta-core solution inside an acoustic package of aeronautical interest, as well as a systematic investigation of the effects deriving from its geometrical parameters. In order to reach this goal, a numerical model of a fuselage panel section is studied, and the effect of several periodic patterns are simulated; more specifically, twelve configurations are taken into account, each with different radius of the inclusions and number of unit cells along the thickness. For each of these layouts, the mass increase of the so-called meta-core, compared to that of its classical homogeneous counterpart, is estimated, together with the associated mid-band frequency and amplitude of the sound transmission loss peak, which is caused by the additional acoustic modes excited by the periodic nature of the meta-core itself. Results are presented in terms of tables and graphs, which may constitute a good basis in order to perform preliminary design considerations that could be interesting for further generalizations

Similitude theory applied to plates in vibroacoustic field: a review up to 2020

Similitude methods are a set of tools which allow the design of scaled-up or scaled-down models of a full-scale structure called a prototype. In this way, the financial and temporal costs of experimental tests, and the problems associated with the set-up of too large (or small) test articles, may be overcome. This article provides a brief review of similitude methods applied to plates in a vibroacoustic field. Particularly, it is dedicated to a thorough analysis of similitude conditions and scaling laws for uncovering commonalities and differences, and physical interpretations, obtained from applying different scaling methods

Transmission Loss Analyses on Different Angular Distributions of Periodic Inclusions in a Porous Layer

The scope of this paper is to investigate the sound transmission loss of an acoustic package of glass wool with embedded periodic inclusions, considering the possibility to improve a standard configuration and inserting the innovative package in a practical configuration used in the aeronautic field for noise suppression. Periodic inclusions are introduced to enhance the sound transmission loss performance of the acoustic package in the mid-high range of frequencies. The main interest of the present work, with respect to the state of the art, is represented by the arrangement of the inclusions one respect to the others, then creating an inclusion pattern that improves the performance of the periodicity peak. To reach this goal, a numerical model of the package is studied, and the effect of the patterns of periodic inclusions is simulated. The pattern behavior is evaluated for eight configurations, which are different from each other for the cubic dimensions and the inclusion radii. Furthermore, an optimized configuration for aeronautical applications is designed starting from the studied acoustic package; then, the results in terms of mass and performance are discussed. Results are presented in terms of tables and graphs, which may constitute a good basis to perform preliminary design consideration that could be interesting for further generalizations

A Linear Transformation for the Reconstruction of the Responses of Systems in Similitude

Recent years have seen an increasing interest towards similitude methods. In fact, the possibility of testing a scaled model, instead of a full-scale prototype, leads to many advantages: financial and time savings, easier experimental setups, etc. However, similitudes have drawbacks, too, mainly due to non-scalable effects and partial similitude, which prevent from an accurate reconstruction of the prototype response. For these reasons, an alternative method which can bypass these limitations is needed. A new method, called VOODOO (Versatile Offset Operator for the Discrete Observation of Objects), is herein proposed: it is based on the definition of a transformation matrix which links the outputs of a given linear systems to those belonging to another system, which may be a scaled model. The responses are acquired on a discrete number of points for both the systems. This work aims at investigating the method’s strengths and limitations of the method. The results show that, although VOODOO exhibits some lack of accuracy in off-design conditions due to the loss of spatial correlation, it is able to overcome some major restrictions that affect all similitude methods

Gaussian-Based Machine Learning Algorithm for the Design and Characterization of a Porous Meta-Material for Acoustic Applications

The scope of this work is to consolidate research dealing with the vibroacoustics of periodic media. This investigation aims at developing and validating tools for the design and characterization of global vibroacoustic treatments based on foam cores with embedded periodic patterns, which allow passive control of acoustic paths in layered concepts. Firstly, a numerical test campaign is carried out by considering some perfectly rigid inclusions in a 3D-modeled porous structure; this causes the excitation of additional acoustic modes due to the periodic nature of the meta-core itself. Then, through the use of the Delany–Bazley–Miki equivalent fluid model, some design guidelines are provided in order to predict several possible sets of characteristic parameters (that is unit cell dimension and foam airflow resistivity) that, constrained by the imposition of the total thickness of the acoustic package, may satisfy the target functions (namely, the frequency at which the first Transmission Loss (TL) peak appears, together with its amplitude). Furthermore, when the Johnson–Champoux–Allard model is considered, a characterization task is performed, since the meta-material description is used in order to determine its response in terms of resonance frequency and the TL increase at such a frequency. Results are obtained through the implementation of machine learning algorithms, which may constitute a good basis in order to perform preliminary design considerations that could be interesting for further generalizations