Jacques Cuenca

Inverse estimation of the elastic and anelastic properties of the porous frame of anisotropic open-cell foams

This paper presents a method for simultaneously identifying both the elastic and anelastic properties of the porous frame of anisotropic open-cell foams. The approach is based on an inverse estimation procedure of the complex stiffness matrix of the frame by performing a model fit of a set of transfer functions of a sample of material subjected to compression excitation in vacuo. The material elastic properties are assumed to have orthotropic symmetry and the anelastic properties are described using a fractional-derivative model within the framework of an augmented Hookes law. The inverse estimation problem is formulated as a numerical optimization procedure and solved using the globally convergent method of moving asymptotes. To show the feasibility of the approach a numerically generated target material is used here as a benchmark. It is shown that the method provides the full frequency-dependent orthotropic complex stiffness matrix within a reasonable degree of accuracy.

A general methodology for inverse estimation of the elastic and anelastic properties of anisotropic open-cell porous materials—with application to a melamine foam

This paper proposes an inverse estimation method for the characterisation of the elastic and anelastic properties of the frame of anisotropic open-cell foams used for sound absorption. A model of viscoelasticity based on a fractional differential constitutive equation is used, leading to an augmented Hookes law in the frequency domain, where the elastic and anelastic phenomena appear as distinctive terms in the stiffness matrix. The parameters of the model are nine orthotropic elastic moduli, three angles of orientation of the material principal directions and three parameters governing the anelastic frequency dependence. The inverse estimation consists in numerically fitting the model on a set of transfer functions extracted from a sample of material. The setup uses a seismic-mass measurement repeated in the three directions of space and is placed in a vacuum chamber in order to remove the air from the pores of the sample. The method allows to reconstruct the full frequency-dependent complex stiffness m...

Acoustic analysis of anisotropic poroelastic multilayered systems

The proposed method allows for an extended analysis of the wave analysis, internal powers, and acoustic performance of anisotropic poroelastic media within semi-infinite multilayered systems under ...

Derivation of the state matrix for dynamic analysis of linear homogeneous media

A method to obtain the state matrix of an arbitrary linear homogeneous medium excited by a plane wave is proposed. The approach is based on projections on the eigenspace of the governing equations matrix. It is an alternative to manually obtaining a linearly independent set of equations by combining the governing equations. The resulting matrix has been validated against previously published derivations for an anisotropic poroelastic medium.

Deterministic and statistical parameter characterization in resonant fluid-structure interaction problems

This research focuses on developing computational methods to estimate model parameters in resonant fluid-structure interaction problems over a wide frequency range by means of model inversion approaches. The considered problems are widely known to be subjected to local minima, which represent a major challenge in the field of parameter identification. In the proposed method, the frequency spectrum is divided into successive substeps allowing to efficiently guide the estimation towards the global minimum, i.e., the true model parameters. The estimation is performed through two frameworks, namely, the deterministic using gradient-based optimization and Bayesian using Markov chain Monte Carlo method. Proposed numerical examples illustrate the effectiveness and potential of the proposed stepwise scheme to find the global minimum and reduce the overall computational burden.This research focuses on developing computational methods to estimate model parameters in resonant fluid-structure interaction problems over a wide frequency range by means of model inversion approaches. The considered problems are widely known to be subjected to local minima, which represent a major challenge in the field of parameter identification. In the proposed method, the frequency spectrum is divided into successive substeps allowing to efficiently guide the estimation towards the global minimum, i.e., the true model parameters. The estimation is performed through two frameworks, namely, the deterministic using gradient-based optimization and Bayesian using Markov chain Monte Carlo method. Proposed numerical examples illustrate the effectiveness and potential of the proposed stepwise scheme to find the global minimum and reduce the overall computational burden.

Early-stages comfort simulation of an e-aircraft

The electrification of transportation systems is increasingly taking place in our every-day landscape, including aviation applications. Besides obvious challenges in thrust generation and safety due to the powertrain changes, there is another aspect of the multi-physical behavior of an aircraft that can be affected: acoustic noise. It is important for an e-aircraft designer to comprehend the impact of the system-level design choices on the acoustic noise radiation of the e-aircraft, whether one relates to environmental noise pollution or passenger comfort. This paper proposes a functional modelling scheme to allow for the assessment of interior cabin noise in the early stages of the aircraft design process. This is accomplished by the combination of three source processes: the air-borne, wind and structural-borne contributions. The simulation results presented here are qualitatively compared to experimental data collected from a light one-propeller conventional aircraft modified with an electric motor, demonstrating the ability of the proposed approach to match the main features of the measured data.

Impact of electric propulsion on aircraft noise – all-electric light aircrafts case study

Aircraft electrification is on the verge of radically changing air transportation. Energy-efficient distributed propulsion, vertical take-off and landing capabilities and reduced emissions are some examples of the great possibilities that electric propulsion offers and how it could disrupt air travel and urban air mobility in the future. Next to the many technological challenges associated with such new concepts, important regulatory barriers still need to be overcome to make it come true. One aspect of particular attention is the impact on environmental noise. In this paper, the acoustic performance of two all-electric light aircrafts is assessed based on ground and in-flight measurements. The investigated aircrafts are the Magnus eFusion, first all-electric aerobatic training airplane in the world and the Extra 330LE, worlds first electric aircraft to tow a glider into the sky. For both airplanes, the actual impact of electric propulsion on exterior radiated noise during fly-over is quantified - for the first time - using two variants of the same aircraft, equipped with two different propulsion systems: in one case with a conventional piston engine, in the other case with an electric motor. Cabin noise is also assessed for the two aircraft variants. Sound quality metrics as well as sound source localization techniques are used to perform a detailed analysis of the interior and exterior aircraft noise and to get insight into the noise generation mechanisms. The manuscript details the complete set of measurement techniques which are available for acoustic engineers to develop quieter electric aircrafts in the future. It reports about the setup and execution of the test campaign; it describes the processing of the acquired data and discusses the major findings. Results highlight the different footprints of the two types of propulsion in terms of fly-over and cabin interior noise levels.

Eulerian frequency analysis of structural vibrations from high-speed video

An approach for the analysis of the frequency content of structural vibrations from high-speed video recordings is proposed. The techniques and tools proposed rely on an Eulerian approach, that is, using the time history of pixels independently to analyse structural motion, as opposed to Lagrangian approaches, where the motion of the structure is tracked in time. The starting point is an existing Eulerian motion magnification method, which consists in decomposing the video frames into a set of spatial scales through a so-called Laplacian pyramid [1]. Each scale — or level — can be amplified independently to reconstruct a magnified motion of the observed structure. The approach proposed here provides two analysis tools or pre-amplification steps. The first tool provides a representation of the global frequency content of a video per pyramid level. This may be further enhanced by applying an angular filter in the spatial frequency domain to each frame of the video before the Laplacian pyramid decomposition,...

Computing high frequency vibrations of polygonal plates by the Image Source Method

The aim of this paper is to show that the Image Source Method (ISM) can be used for predicting medium and high frequency vibrations of arbitrarily shaped polygonal plates with controllable precision. Modeling the vibrations of polygonal plates by ISM consists in superposing the contributions of elementary image sources, which allows the plate boundary conditions to be satisfied. For particular plate shapes leading to a spatially periodic pattern of image sources, it is shown that ISM allows the exact computation of the Greens function by means of a Poisson summation formula. For arbitrarily polygonal plates, a criterion for truncating the image source generation process is examined and used as a control parameter for the precision of the estimations. The given examples show that the results are in good agreement with exact analytical solutions for simple plate shapes and with results obtained by the finite element method for more complex shapes. The convergence towards reference solutions as the number o...