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A promising approach to improve the efficiency in manufacturing processes is to build digital twins of the main assets from the available data to estimate and predict important metrics such as the energy consumption of each machine. Such predictions can then be exploited in process optimization. However, generating the digital twins from data is challenging in Industry 4.0: the high dimensionality of the data and the complexity of the manufacturing process makes it difficult and time-consuming for a human to model all important assets in the line. To address this problem, this paper investigates the feasibility of a framework for automatic generation of digital twins from historical data, which incorporates automatic selection of variables and data-driven system identification. For that, different versions of an algorithm for variable selection were exhaustively combined with several data-driven system identification methods. The framework was applied in the generation of digital twins for an electrical motor in a state-of-the-art production line of wooden fibreboards. In the estimation and prediction of the motor power, several of the automatically-generated digital twins presented acceptable accuracy, performing similarly to a simple manually designed physics-based model. The results suggest that the automatic framework is feasible, deserving therefore further effort to enhance it and provide a more extensive validation. ispartof: International Conference on Control, Automation and Diagnosis ispartof: 2023 International Conference on Control, Automation and Diagnosis (ICCAD) location:Rome, Italy date:10 May - 12 May 2023 status: Published online

A novel approach is presented for the time-domain system identification of structural dynamic components exploiting the high spatial density of vision-based measurements. By using spatially dense measurements, the number of spatial measurement points is much larger than the dimensionality of the underlying dominant dynamics (i.e., the number of measurement points needed to meet observability of the targeted dynamics). This opens up the potential to develop new experimental identification methods that use this spatial overdetermination which were out of reach with conventional discrete sensors. The new approach presented in this paper directly extracts a relatively noise-free, low-order set of dynamic states by projecting the spatially dense time-domain measurements on a low-order dominant deformation motion basis. The basis is constructed by applying an over-complete singular value decomposition on the measurements. These dynamic states together with their numerically calculated first and second order time-derivatives are then used in a two-step identification of the structural dynamic parameters. Here, the structure of the model to identify is based on a-priori physical knowledge of the underlying set of partial differential equations, unlike a purely data-driven method. This approach has the benefits of providing a mathematical formulation that is straightforward to understand and implement and is time-efficient to solve. The presented approach is experimentally validated on a clamped plate as well as on a flexibly suspended plate which requires a correction of the rigid body motion. The identified models have shown to provide an accuracy up to 1 × 10-5 m with respect to the dominant measured motion components in both validation cases. ispartof: Mechanical Systems And Signal Processing vol:182 status: Published online

ispartof: Computer Methods In Applied Mechanics And Engineering vol:403 status: published

Periodic structures such as metamaterials and phononic crystals hold potential as promising compact and lightweight solutions for noise and/or vibration attenuation in targeted frequency ranges. The performance of these structures is usually investigated by means of dispersion curves. The input for dispersion curve computations is often a finite element model of the corresponding unit cell. Nowadays, the vibration and noise attenuation of the periodic structures are generally tackled as separate problems and their performance is investigated with either structural or acoustic dispersion curves, respectively. Recently, vibro-acoustic unit cell models have come to the fore which can exhibit simultaneous structural and acoustic stopbands. However, the vibro-acoustic coupling inside the unit cell is usually not taken into account during the dispersion curve computations. To consider this coupling during their performance assessment, the computation of vibro-acoustic dispersion curves is required. Although these dispersion curves provide valuable information, the associated computational cost rapidly increases with unit cell model size. Model order reduction techniques are important enablers to overcome this high cost. In this work, the Bloch mode synthesis (BMS) and generalized BMS (GBMS) unit cell model order reduction techniques are extended to be applicable for 2D and 3D periodic vibro-acoustic systems. Through a verification case, the methodologies are shown to enable a strongly reduced dispersion curve calculation time while maintaining accurate predictions. At the time of verification: no ISSN/ISBN on the publisher's site. ispartof: Proceedings of ECCOMAS 2022 ispartof: ECCOMAS 2022, 8th European Congress on Computational Methods in Applied Sciences and Engineering location:Oslo, Norway date:5 Jun - 9 Jun 2022 status: published

Metamaterials have recently emerged and shown great potential for noise and vibration reduction in specific frequency ranges, called stop bands. To predict stop bands, their often periodic nature is exploited and dispersion curves are calculated based on a single representative unit cell, typically modeled using the finite element method. Since their sub-wavelength nature and often intricate design can lead to large unit cell models, model reduction methods such as the Generalized Bloch Mode Synthesis have been proposed to greatly accelerate dispersion curve calculations. In order to calculate forced vibro-acoustic responses of finite periodic elastic metamaterial plates composed of an assembly of unit cells, however, full order finite element models rapidly become computationally unaffordable. Therefore, in this work the Generalized Bloch Mode Synthesis is incorporated in a sub-structuring approach, which enables fast forced vibration response calculations of finite elastic metamaterial plates based on a single reduced order unit cell model. The main advantage as compared to a regular Craig-Bampton approach is the additional local reduction of unit cell boundary degrees of freedom, whereby a compatible basis for the identical neighboring unit cells is incorporated. In addition, by combining this Generalized Bloch Mode Synthesis based sub-structuring approach with the Elementary Radiator Approach, efficient sound transmission loss computations of finite periodic metamaterial plates are enabled. The performance of the proposed approach for fast vibro-acoustic response predictions is demonstrated for different cases. ispartof: Frontiers in Mechanical Engineering vol:8 status: published

no ISBN/ISSN ispartof: Proceedings of TECNIACUSTICA 2022 ispartof: TECNIACÚSTICA 2022 location:Elche, Spain date:2 Nov - 4 Nov 2022 status: Published online

In recent years, periodic structures such as metamaterials and phononic crystals have come to the fore in the search for innovative lightweight and compact noise and vibration solutions. The vibro-acoustic performance of these structures is often analyzed by means of dispersion curves and/or sound transmission loss calculations, using unit cell modeling. However, the link between these two performance indicators is not always straightforward. Recently, a first step to bridge this gap was taken by Yang et al. who proposed a method which allows decomposing the sound transmission of infinite in-plane homogeneous media into a sum of wave mode contributions. Despite providing useful insights in the sound transmission of homogeneous structures, this method is limited to meshes with corner degrees-of-freedom only and hence not readily applicable to arbitrarily complex, inhomogeneous periodic structures. To expand the potential of this method towards identifying the most important transmission mechanisms in periodic media, this work extends the method towards periodic inhomogeneous structures represented by unit cells with arbitrarily complex meshes. The proposed methodology is applied to a periodic double panel partition thereby demonstrating its ability to provide new insights into the sound transmission mechanisms of periodic media/structures. ispartof: pages:734-742 ispartof: Recent Trends in Wave Mechanics and Vibrations, Proceedings of WMVC 2022 vol:125 pages:734-742 ispartof: WMVC, 10th international conference on wave mechanics and vibrations location:Lisbon, Portugal date:3 Jul - 5 Jul 2022 status: published

Metamaterials, i.e. artificial structures with unconventional properties, have shown to be highly performant lightweight and compact solutions or the attenuation of noise and vibrations in targeted frequency ranges, called stop bands. In order to analyze the performance of these metamaterials, their stop band behavior is typically predicted by means of dispersion curves, which describe the wave propagation in the corresponding infinite periodic structure. The input for these calculations is usually a finite element model of the corresponding unit cell. Most common in literature are 2D plane metamaterials, which often consist of a plate host structure with periodically added masses or resonators. In recent literature, however, full 3D metamaterials are encountered which are periodic in all three directions and which enable complete, omnidirectional stop bands. Although these 3D metamaterials have favorable vibro-acoustic characteristics, the computational cost to analyze them quickly increases with unit cell model size. Model order reduction techniques are important enablers to overcome this problem. In this work, the Bloch Mode Synthesis (BMS) and generalized BMS (GBMS) reduction techniques are extended from 2D to 3D periodic structures. Through several verifications, it is demonstrated that dispersion curve calculation times can be strongly reduced, while accurate stop band predictions are maintained. ispartof: pages:2102-2113 ispartof: Proceedings of Internoise 2021 pages:2102-2113 ispartof: Internoise 2021, 50th International Congress and Exposition on Noise Control Engineering location:Virtual/ Washington DC date:1 Aug - 5 Aug 2021 status: published

At present, black-box and simulation-based optimization problems with multiple objective functions are becoming increasingly common in the engineering context. In many cases, the functional relationships that define the objective and constraints are only known as black-boxes, cannot be differentiated accurately, and may be subject to unexpected failures. Directional direct search techniques, in particular the direct multisearch (DMS) methodology, may be applied to identify Pareto fronts for such problems. In this work, we propose a mechanism for adaptively selecting search directions in the DMS framework, with the goal of reducing the number of black-box evaluations required during the optimization. Our method relies on the concept of simplex derivatives in order to define search directions that are optimal for a local, linear model of the objective function. We provide a detailed description of the resulting algorithm and offer several practical recommendations for efficiently solving the associated subproblems. The overall performance in an academic context is assessed via a standard benchmark. Through a realistic case study, involving the bi-objective design optimization of a mechatronic quarter-car suspension, the performance of the novel method in a multidisciplinary engineering setting is tested. The results show that our method is competitive with standard implementations of DMS and other state-of-the-art multi-objective direct search methods. ispartof: Optimization And Engineering vol:23 issue:3 pages:1411-1437 status: accepted

In general, multibody models are described with a set of redundant coordinates and additional constraints. Their dynamics is thus expressed through differential algebraic equations. As an alternative, the minimal coordinate formulation permits to describe a rigid system with the minimal number of variables leading to ordinary differential equations which can be employed in a coupled state/input estimation scheme. However, in some cases the explicit relation between the full-system coordinates and the minimal coordinates may not be available or analytically obtainable, as for closed-loop mechanisms. In this work, a previously presented deep learning framework to find the non-linear mapping and reduce a generic multibody model from redundant to minimal coordinates is employed. The resulting equations are then exploited in an extended Kalman filter where the unknown inputs are considered as augmented states and jointly estimated. The necessary derivatives are given and it is shown that acceleration measurements are sufficient for the estimation. The method is experimentally validated on a slider–crank mechanism.

O presente trabalho tem por objetivo, a partir da conceituação do contrato de conta corrente, delimitar o alcance dessa operação quando realizada entre empresas do mesmo grupo econômico, especialmente para definir se a incidência do imposto sobre operações de crédito, prevista no artigo 13 da Lei nº 9.779, de 19 de janeiro de 1999, pode alcançar toda e qualquer operação de remessa de valores, além das operações de mútuo legalmente previstas. Uma vez fixado esse entendimento, busca-se extrair uma recomendação geral acerca do uso, bastante comum, desse relevante instrumento jurídico na atividade dos grupos empresariais, apesar das dificuldades e obstáculos que vêm sendo impostos pelo fisco nos últimos anos. Também se faz um confronto desse instituto com o chamado cash pooling, adotado, em especial, pela União Europeia. Ainda, aborda-se o conceito e características envolvidos nos contratos de mútuo, de modo a traçar sua distinção em relação ao contrato de conta corrente, concluindo pela não incidência do IOF/Crédito sobre as operações de conta corrente. Como resultado, apresenta-se o impacto prático do posicionamento proposto e as condutas recomendáveis para empresas que já utilizam ou pretendem utilizar esse tipo específico de operação. This dissertation aims at studying the nature of checking account contract, carried out among companies of a same economic group, differentiating such an account from an ordinary credit transaction that is subject to taxation by Tax on Credit Transactions (“IOF/Credit”) established by in article 13 of the Law No. 9,779, of January 19th, 1999. Such differentiation is essential to demonstrate that checking account contract between related parties cannot be deemed as credit transaction and, consequently, cannot be subject to IOF/Credit. Also, it is covered the main aspects to be observed in a checking account agreement to avoid any questions on the nature of such agreements, and comparison of checking account contract with the so-called cash pooling, adopted by companies located in the European Union. Another point treated in this dissertation refers to disputes against tax authorities who, oftentimes, intend to treat checking account contracts as credit transactions, imposing on taxpayers IOF/Credit assessments, including penalties and arrears interest. In summary, this dissertation discusses concepts and characteristics of financial contracts, especially loan agreement, to conclude that IOF/Credit is not levied on checking account transactions, with identification of practical impacts of such an understanding, and points to be observed by companies already using or intending to use this checking account contract within entities of an economic group.

ispartof: pages:522-534 ispartof: ISMA-USD conference proceedings ispartof: ISMA2022 location:Leuven, Belgium status: accepted

ispartof: pages:1-15 ispartof: Proceedings of ISMA 2022 ispartof: ISMA 2022 location:Leuven status: published

no ISBN/ISSN ispartof: Proceedings of ISMA-USD 2022 ispartof: ISMA 2022 location:Leuven date:12 Sep - 15 Sep 2022 status: Published online

In the search for lightweight and compact partitions with both favorable vibro-acoustic characteristics and load-carrying capacity, an increasing trend towards double-leaf panels with structural metamaterial cores is emerging. Generally, these partitions are designed and analyzed by only considering the attenuation along the structural path, disregarding the influence of the air inside. This work investigates the impact of the air in these partitions on their performance, which reveals that the acoustic path needs to be included during the design phase. ispartof: pages:562-563 ispartof: Proceedings of META 2022 pages:562-563 ispartof: META 2022, the 12th International Conference on Metamaterials, Photonic crystals and Plasmonics location:Torremolinos, Spain date:19 Jul - 22 Jul 2022 status: Published online

Over the years, metamaterials have shown their potential in a wide range of different disciplines, e.g. optics, electromagnetics, dynamics etc. Metamaterials are, often periodic, engineered structures made of conventional materials but which exhibit properties not encountered in nature. In the field of noise and vibration, metamaterials have received increasing interest since they can obtain frequency ranges of high noise and vibration attenuation, called stop bands. Their performance is often investigated by means of dispersion curves, which are calculated based on a single unit cell and assuming a structure of infinite periodic extent. Nowadays, the attenuation of acoustic and structural waves is commonly tackled as two separate problems, whereby either acoustic or structural dispersion curves are used. Recently, vibro-acoustic unit cell designs have come to the fore which can exhibit appealing characteristics, such as simultaneous structural and acoustic stop bands. To consider the vibro-acoustic coupling in these unit cell designs during the performance predictions, vibro-acoustic dispersion curve calculations are thus required. However, these computations are typically cumbersome to perform due to the associated high computational cost and therefore, often, uncoupled dispersion curves are used during the performance assessment. Although several unit cell model order reduction approaches have recently been proposed to accelerate the dispersion curve computations, such as the Bloch mode synthesis (BMS) and Generalized Bloch mode synthesis (GBMS), they are not readily applicable to vibro-acoustic unit cells. To accelerate vibro-acoustic dispersion curve calculations, this work extends the BMS and GBMS techniques towards 2D and 3D periodic vibro-acoustic systems. To balance accuracy versus speed, the extended BMS reduction basis is constructed using a split set of vibro-acoustic coupled modes, while the extended GBMS reduction basis uses the uncoupled modes. Several verification cases demonstrate that strongly accelerated vibro-acoustic dispersion curve computations are achieved whereby the vibro-acoustic coupling inside the unit cell is accurately accounted for. ispartof: Frontiers in Mechanical Engineering vol:8 status: published

ispartof: Computer Methods In Applied Mechanics And Engineering vol:397 status: published

ispartof: Aiaa Journal vol:60 issue:6 pages:3593-3602 ispartof: location:ELECTR NETWORK status: published

The optimization problems arising in modern engineering practice are increasingly simulation-based, characterized by extreme types of nonsmoothness, the inaccessibility of derivatives, and high computational expense. While generating set searches (GSS) generally offer a satisfying level of robustness and convergence to stationary points, the convergence rates may be slow. In order to accelerate the solution process without sacrificing robustness, we introduce (simplex) gradient-informed generating set search (GIGS) methods for solving bound-constrained minimization problems. These algorithms use simplex gradients, acquired over several iterations, as a guidance for adapting the search stencil to the local topography of the objective function. GIGS is shown to inherit first-order convergence properties of GSS and to possess a natural tendency for avoiding saddle points. Numerical experiments are performed on an academic set of smooth, nonsmooth and noisy test problems, as well as a realistic engineering case study. The results demonstrate that including simplex gradient information enables computational cost savings over non-adaptive GSS methods. ispartof: Computational Optimization And Applications vol:79 issue:1 pages:35-65 status: published

Multi-material topology optimization has become a popular design optimization discipline since it allows to go a step further in topology optimization of the design of lightweight components and structures. However, it also presents additional challenges in terms of managing a higher complexity in the optimization problem, reliably estimating the manufacturing cost taking into account the cost of joining dissimilar materials, or assessing the manufacturability of the design. This paper proposes a set of methods that solve generic multi-material topology optimization problems, while including several novel aspects such as a comprehensive cost model, specific design rules for multi-material design, and model order reduction techniques to improve the computational efficiency. Two different examples, consisting of a sitting bench and a car cowling, have been solved in order to support the benefits of the approach.

The current interest in sustainable aviation is motivating the development of aircraft with better environmental performance. Within this context, advanced turboprops offer higher fuel efficiency compared to conventional turbofan engines. However, the cabin noise levels of propeller driven aircraft are significantly higher than those in common fanjets. The dominant noise sources in turboprop aircraft are the turbulent boundary layer noise, which is generated by the turbulent airflow exciting the fuselage, and the propeller induced noise caused by the periodic pressure fluctuations produced by the propeller blades passing near the fuselage. This paper presents the design of an innovative noise generation system that will be able to replicate, with a set of loudspeakers, the dynamic excitation given by both the turbulent boundary layer noise and the blade passing noise on a fuselage. The novelty of this system is the use of MIMO feedback controllers to simultaneously achieve desired sound pressure levels and spatial correlations at specific fuselage locations. The aim of the CONCERTO project (GA886836) is to develop cabin noise testing equipment that will be used to evaluate the interior noise of regional aircraft and to aid the development of noise reduction solutions. Firstly, a preliminary analysis of the noise generation system is carried out for a small-scale noise generation set-up. The system components are investigated and MIMO feedback control strategies are introduced. MIMO random control is used to replicate the random pressure field generated by the turbulent boundary layer excitation. The tonal components of the propeller induced excitation are then added to the broadband noise using a time waveform replication technique. The preliminary results for the small-scale set-up show that the power spectral densities of the measured microphone signals converge to those of the references within acceptable tolerance (±1.5 dB). Finally, the design of the modular mechanical structure for the full-scale innovative noise generation system is discussed. Proceedings can be found here: https://iiav.org/content/archives_icsv_last/2021_icsv27/indexbd58.html?va=viewpage&vaid=410 ispartof: pages:1-8 ispartof: "Advances in Acoustics, Noise and Vibration – 2021" Proceedings of the 27th International Congress on Sound and Vibration pages:1-8 ispartof: 27th International Congress on Sound and Vibration location:Virtual date:11 Jul - 16 Jul 2021 status: published

ispartof: Journal Of Sound And Vibration vol:535 status: published

ispartof: SAE Technical Papers status: Published online

Experimental Modal Analysis (EMA) allows to assess the dynamical properties of a mechanical component or structure by estimating the modal parameters. Whereas EMA is usually based on local accelerometers or laser vibrometer data, in this paper we focus on camera-based EMA as cameras offer full field and contact-less data. However, besides few very specific controlled cases, camera-based EMA is limited by the low frame rate of the camera in comparison to accelerometers and vibrometers. In this paper we propose a novel acquisition scheme that allows to estimate modal parameters above the Nyquist-Shannon limit (i.e., half of the camera frame rate) by employing a random sampling scheme in time in combination with one accelerometer. With this information we reconstruct the Impulse Response Function (IRF) modal model through a nonlinear optimization problem, where the accelerometer ensures a global solution by providing an initial guess of the eigenfrequencies. We investigate numerically the accuracy of the methodology by simulating multiple damped sine waves. Furthermore, we present an experimental validation on a clamped-clamped beam excited by an impact hammer. Thereby, the displacement information is captured by a single camera triggered by random pulses, and computed by Lucas-Kanade (LK) optical flow. The complexity and modal assurance criterion (MAC) of the modes show that all modes whose amplitudes are higher than the noise level are measured successfully with only one excitation hit, where the highest mode, at 218 Hz, is measured with a random sampling scheme comparable to 50 fps (to reach 218 Hz, a regular sampling with 436 fps would be required). ispartof: Mechanical Systems And Signal Processing vol:170 status: published

Sparsity-based methods have recently come to the foreground of damage detection applications posing a robust and efficient alternative for traditional approaches. At the same time, low-frequency inspection is known to enable global monitoring with waves propagating over large distances. In this paper, a single sensor complex Group Lasso methodology for the problem of structural defect localization by means of compressive sensing and complex low-frequency response functions is presented. The complex Group Lasso methodology is evaluated on composite plates with induced scatterers. An adaptive setting of the methodology is also proposed to further enhance resolution. Results from both approaches are compared with a full-array, super-resolution MUSIC technique of the same signal model. Both algorithms are shown to demonstrate high and competitive performance. ispartof: Sensors vol:22 issue:8 ispartof: location:Switzerland status: Published online

Recently, the potential of metamaterials and phononic crystals to cope with conflicting requirements of obtaining lightweight structures with desirable noise and vibration properties has been demonstrated. These, often periodic, structures are commonly studied based on their representative unit cell of which the vibro-acoustic performance is examined by means of their wave propagation, visualized by dispersion curves. Typically, the unit cell is discretized using a finite element technique to capture the possibly complex geometry. This leads to a high computation cost for the dispersion curve calculation which can be strongly reduced by applying modal based model order reduction techniques such as the (generalized) Bloch mode synthesis. In this paper, the choice of the unit cell is shown to have an impact on the dispersion curve calculation time. Moreover, the efficiency of (generalized) Bloch mode synthesis strongly depends on the unit cell choice. The highest reduction in computation time is accomplished when the number of boundary degrees-of-freedom is limited. ispartof: Journal of Vibration and Acoustics vol:144 issue:2 status: Published online

ispartof: pages:1-9 ispartof: Proceedings of the 26th International Congress of Mechanical Engineering pages:1-9 ispartof: COBEM 2021 26th International Congress of Mechanical Engineering location:Virtual Conference (Brazil) status: Published online

ispartof: pages:1323-1332 ispartof: Proceedings of Euronoise pages:1323-1332 ispartof: Euronoise 2021 location:Madeira, Portugal - Online date:25 Oct - 27 Oct 2021 status: Published online

ispartof: pages:281-290 ispartof: Proceedings of the Euronoise 2021 Conference pages:281-290 ispartof: Euronoise 2021 location:Madeira, Portugal date:25 Oct - 27 Oct 2021 status: published

The use of photogrammetry to create meshes suitable for deterministic numerical methods is thought to be a promising approach for individual Head-Related Transfer Functions (HRTFs) ac-quisition. The validity of this HRTFs extraction technique is discussed in this paper. Photogram-metric methods are employed to reconstruct the shape of a Neumann KU100 dummy head from a set of pictures captured with a consumer-grade digital camera. The accuracy of the resulting sur-face information is analyzed by comparing it with a precise reconstruction obtained through laser scanning. Numerical HRTFs computed on these geometries are compared to a set of acoustic HRTFs measured on the same dummy head. The validity of the computed transfer functions is fur-ther assessed by means of a virtual perceptual model focusing on elevation perception on the sag-ittal plane. The results indicate that the adopted method is capable of providing accurate HRTFs in terms of binaural cues related to horizontal plane localization. However, the use of HRTFs derived from photogrammetry tends to hinder the elevation perception which relates to perceived realism in a complex virtual scene. This suggests that the photogrammetric method used in this paper lacks the precision needed for the acquisition of accurate HRTFs. ispartof: pages:1614-1617 ispartof: Fortschritte der Akustik - DAGA 2021 pages:1614-1617 ispartof: DAGA 2021 location:Vienna, Austria date:15 Aug - 18 Aug 2021 status: Published online

This paper presents a novel system‐level model order reduction scheme for flexible multibody simulation, namely the system‐level affine projection (SLAP). Contrary to existing system‐level model order reduction approaches for multibody systems simulation, this methodology allows to obtain a constant reduced order basis which can be obtained in a noninvasive fashion with respect to the original flexible multibody model. It is shown that this scheme enables an automatic joint constraint elimination which can be obtained at low computational cost through exploitation of the component level modes typically employed in flexible multibody simulation. The equations of motion are derived such that the computational cost of the resulting SLAP model is independent of the original model size. This approach results in a set of ordinary differential equations with a constant mass matrix and nonlinear internal forces. This structure makes the resulting model suitable for a range of estimation, control, and design applications. The proposed approach is validated numerically on a flexible four‐bar mechanism and shows good accuracy for a very low‐order SLAP model. ispartof: International Journal For Numerical Methods In Engineering vol:121 issue:14 pages:3083-3107 status: Published online

This paper investigates a metamaterial solution for efficient vibration attenuation and acoustic radiation reduction of an aluminum pipe. To this end, using unit cell predictions, locally resonant structures are designed to have a pronounced flexural resonance frequency at the vicinity of a dominant vibration mode of the pipe. A direct approach of the Bloch-Floquet theorem is adopted to provide the dispersion relation representing wave motion in an infinite metamaterial pipe. Using these wave dispersion relations, the frequency range of the stopband zone created by the metamaterial solution is predicted. The dynamic behavior of the finite counterpart is predicted using the Finite Element Method (FEM). The resonant structures are produced from polymethyl methacrylate (PMMA) panels and are added to the host structure. In order to properly characterize both the vibrational behavior of the metamaterial pipe and the acoustic radiation from its wall, impact tests using roving hammer technique is performed on the pipe and both accelerations and acoustic pressures are measured at different locations. The experimental results show a pronounced stopband zone created by the addition of a few rows of resonant structures. Moreover, comparisons between the measurements and numerical predictions show a good agreement. ispartof: Journal of Sound and Vibration vol:455 pages:96-117 status: published

© 2019 Elsevier Ltd A non-destructive testing strategy is proposed that combines microphone measurements and structural measurements in one array. The aim is to lower the total inspection time by reducing the number of structural sensors. This is possible by making use of the easier and faster installation of microphones as compared to structural sensors. Structural sensors are needed to limit the influence of background noise. The proposed algorithm is based on the theory of the Time-Reversal MUltiple SIgnal Classification (TR-MUSIC) algorithm. In addition to the novelty of using a vibro-acoustic array, this publication presents a strategy on how to select only the most ‘valuable’ regions of the frequency spectrum for the TR-MUSIC algorithm and an option to use the algorithm with a number of excitations below the theoretically necessary minimum. The proposed procedure is applied in an experiment that targets the localisation of loose or removed bolts in an assembly of aluminium beams and a honeycomb panel, mounted with rivets, bolts and double-sided tape. Although none of the bolts is in the line of sight of the sensor array, all introduced defects can be found in this experiment. This includes the localisation of multiple defects as well. By adding artificial measurement noise to the microphone measurements, it is demonstrated that a combined vibro-acoustic array can cope with a high ambient noise level, while the process fails if a comparable measurement error is also applied to the structural sensors. ispartof: MECHANICAL SYSTEMS AND SIGNAL PROCESSING vol:130 issue:130 pages:433-451 status: published

In recent years reduced order modeling techniques for vibro-acoustic systems that are modeled with numerical techniques, such as the finite element method, have been established as a key technology in digital twin design. By reducing the order of the system, the complexity of the model can be alleviated to such a degree that the model can be run in a (near-)real time environment, allowing for integration of the model on an embedded system included with the physical asset, e.g. for state estimation. This paper demonstrates how to create a state space model of a vibro-acoustic finite element model including frequency dependent impedance boundary conditions. These systems are difficult to convert to a state space representation for two reasons: Firstly, the frequency dependency has to be preserved in the reduced order model. Secondly, the state space form only takes the previous time step into account, while the frequency dependent damping behavior would result in a convolution operation. This paper aims to solve both issues by approximating the frequency dependency using a digital filter bank approach, in which the individual filter banks use a frequency independent damping matrix. The filter bank is designed such that a near perfect reconstruction is achieved. Furthermore, it allows for banks with different frequency bandwidths to fine-tune the filter where the impedance changes rapidly as function of frequency. The frequency independent vibro-acoustic models in the filter banks are reduced using a Krylov subspace projection method. The resulting filter bank is converted to a state space form by converting the reduced order model to first order form and rewriting the finite impulse response filters in state space format. A second reduction is performed on these filters, due to the large number of filter coefficients, leading to a small and stable system level state space model. ispartof: Proceedings of the 27th International Congress on Sound and Vibration ispartof: The 27th International Congress on Sound and Vibration location:Online date:11 Jul - 16 Jul 2021 status: Published online

This paper presents the development of a cabin noise testing equipment that will be used to evaluate the interior noise of regional aircraft as well as to aid the development of noise reduction techniques. The innovative noise generation system consists of three loudspeaker arrays positioned around the fuselage circumference to synthesize a pressure field that is similar to the pressure field seen by the fuselage during a flight. The acoustic pressure field generated by the loudspeakers is measured by a number of microphones scattered on the fuselage surface. These microphone signals are then fed back to the controller with the purpose of minimising the error between the target pressure field and the measured one by means of an iterative learning approach. The number and location of the microphones used in the control loop are selected through a pre-test optimisation analysis, which aims to reduce the time and cost of the set-up. A small-scale electroacoustic demonstrator has been built to develop the feedback control approach. A frequency domain multi-input multi-output feedback controller is used to replicate the random pressure field generated by the turbulent boundary layer excitation. The multiharmonics of the propeller induced excitation are then added to the time histories of the broadband noise using a time waveform replication technique. Different arrangements of the driving signal distribution are investigated, and the results are then presented in terms of accuracy of the pressure field reproduction.

ispartof: pages:1-11 ispartof: SAE Technical Papers pages:1-11 status: Published online

Locally resonant metamaterials have recently emerged and gained attention in the field of noise control engineering. The addition of resonant structures to a flexible partition on a sub-wavelength scale enables a targeted frequency range of strongly reduced vibration and sound transmission. These structures have been widely studied and are typically analyzed using infinite periodic structure theory. The implications of nonsub-wavelength resonator spacing on the sound transmission loss of metamaterial partitions as well as on the representativeness of the infinite periodic structure modeling are, however, less well known. In this technical brief, it is shown that, although a shifted sound transmission loss peak can be predicted for partitions with nonsub-wavelength resonator spacing when using infinite periodic structure modeling, the sound transmission loss enhancement is not guaranteed for their finite structure counterparts.

ispartof: AIAA 2021 proceedings ispartof: AIAA 2021 AVIATION FORUM location:Virtual status: Published online