1,720,973 research outputs found
Nieuwe reductietechnieken voor externe vibro-akoestische modellen en hun toepassing in modelgebaseerde metingen en identificatie
No full textThe physical interaction between vibrating structures and acoustics is of paramount importance in modern society. It is encountered in many products of daily use, such as vehicles, home appliances, and musical instruments but also in industrial environments, such as an assembly line in a factory. On the one hand, sound can be considered pleasant or useful in the context of music or communication. On the other hand, undesired sound, or noise, can cause health issues and is hence regarded as a problem.
The physical principles behind sound waves and their mathematical description are known since a long time, but the analytical solution for problems with a moderate to high geometrical complexity is too difficult to obtain. Therefore, engineers make use of numerical computer models that approximately solve the underlying physics to predict and prevent the resulting noise from a vibrating structure.
Besides the assessment of acoustic comfort, additional fields of application arise for vibro-acoustic models that are combined with physical measurements. For example, material properties and boundary conditions, or the health of a structure can be derived by doing an inverse identification. Another possibility is to combine them in a state-estimator to get an accurate prediction of the unmeasured field variables, thus to create a virtual vibro-acoustic sensor.
For low-frequency noise and vibration modeling deterministic element based numerical approximation schemes, such as the finite element method, are most often used. The expectations and desires from academia and industry on what should be calculated with these models have increased throughout the years. Thus, although the available computing power is larger than before, solving such models remains a demanding task. Especially when a series of solutions is desired, for example when an optimization is performed, or when simulation results are desired in near-real time, the required time and calculation resources might be unacceptable.
Therefore, this dissertation's main focus is on model order reduction techniques. Its main contributions are split into two parts. The first part is focused on the advancement of model order reduction techniques for vibro-acoustic systems to reduce the calculation complexity of these models. Specifically, the focus is on exterior vibro-acoustic problems in the time domain. Since they require the inclusion of the Sommerfeld radiation condition to correctly model the wave propagation to infinity, which is not included in the weak form of the finite element method, an additional stable boundary condition has to be introduced. Therefore, a conjugated infinite element description is chosen and it is shown how the resulting model can be reduced in size effectively with several examples. Furthermore, a parametric model order reduction scheme is derived that allows for low-rank parametric changes in the reduced order model of the second order system without sampling of the parameter space. A potential disadvantage of the shown algorithm is that it can lead to large reduced order models when an extensive set of parameters is considered. Hence, the first part concludes with the derivation of an automatic reduction algorithm for second order systems with many inputs, where the aim is to arrive at a model of acceptable size.
The second part of this dissertation investigates the possibilities to use the aforementioned model order reduction techniques for efficient vibro-acoustic sensing and modeling. The effectiveness of the derived reduced order models is shown by constructing a virtual sensor that accurately estimates both the pressure and acoustic intensity of a complex radiating structure with the inclusion of only a small amount of measurements. Additionally, it is shown with an experimental setup how the derived parametric model order reduction scheme can be used for fast inverse identification of structural boundary conditions. The required reduced order model is obtained with the proposed automatic reduction algorithm. The potential of this algorithm is also assessed in a substructuring context, which could be beneficial for the modeling of unit cells, for example to evaluate the performance of metamaterials. The second part concludes by presenting a time reversed version of the conjugated infinite element description that works as an acoustic sink, which can be used in a time reversal simulation for scatterer and source identification.status: Publishe
Physics-based sound radiation estimation from multiple speakers by combined lumped parameter and reduced-order finite element modeling
No full textIn this paper a virtual sensor is derived that can perform full field estimation of the sound field radiating from a number of loudspeakers in the time domain. The virtual sensor scheme contains two parts: Firstly, a time-domain physics-based numerical system level model that includes both the electro-mechanical behavior of the loudspeaker and the resulting wave propagation. Secondly, a Kalman filter in which the numerical model and a limited set of microphone measurements are combined to perform full field estimation. The loudspeaker dynamics are captured in a lumped parameter model and the resulting wave propagation is captured in a finite element model. To reduce the calculational complexity of the system level model, Krylov subspace based reduced order modeling is applied on the finite element model, leading to a significant reduction of the number of states. The system level model is brought to a discrete time state–space format, which allows for efficient implementation in the Kalman filter. The method is validated using two setups that use both vented and closed box loudspeakers, leading to improved estimation results as compared to pure simulation results, thus showing the merits of the virtual sensor. Furthermore, the importance of including the lumped parameter speaker model in the system level model is shown by comparing the estimation results with and without the inclusion of the lumped parameter model.sponsorship: The research of S. van Ophem (fellowship no. 1277021N) is funded by a grant from the Research Foundation-Flanders (FWO) , Belgium. The Research Fund KU Leuven is gratefully acknowledged for its support. This research was partially supported by Flanders Make, the strategic research center for the manufacturing industry. Furthermore, VLAIO (Flanders Innovation & Entrepreneurship Agency), Belgium is also acknowledged for its support. (Research Foundation-Flanders (FWO), Belgium|1277021N, Research Fund KU Leuven, Flanders Make, the strategic research center for the manufacturing industry, VLAIO (Flanders Innovation & Entrepreneurship Agency), Belgium)status: Published onlin
An efficient time-domain approach for coupled multibody-vibroacoustic simulations with stationary sound-radiating components
No full textThe accurate prediction of noise emissions from mechanical systems with moving flexible bodies is crucial for a wide range of engineering applications. This study introduces a novel time-domain methodology for simulating systems where components with significant rigid body motion excite vibrations in stationary components, which in turn radiate sound Traditional approaches, which couple time-domain flexible multibody dynamic simulations with frequency-domain vibroacoustic simulations, are often limited by high computational costs, complexity in handling transient phenomena, and cumbersome workflows. Our methodology addresses these challenges by integrating high-order finite element methods for transient acoustics with flexible infinite elements for modeling non-reflecting condition. These modeling techniques are combined with Krylov model order reduction, offering significant improvements in computational efficiency. The introduction of an efficient time-domain vibroacoustic model within this methodology allows to develop a unified multibody-vibroacoustic formulation that integrates multibody dynamics and vibroacoustic simulations into a single solver, greatly simplifying the modeling process. This novel formulation is validated with a simplified gearbox model and an academic test case featuring large-amplitude motion. Moreover, the performance of the newly introduced time-domain methodology is benchmarked against the traditional frequency-domain approach for simulating the noise radiated from a higher-fidelity gearbox model. The results from these numerical tests underscore the efficiency of the proposed method
Parametric model order reduction without a-priori sampling for low rank changes in vibro-acoustic systems
No full textA parametric model order reduction scheme is presented for second order systems that does not require a-priori sampling of the parameter space. The proposed scheme \revi{transfers} the parameter dependence to the throughput matrix of the dynamic system by using an auxiliary input matrix. The resulting model can thus be reduced with non-parametric model reduction techniques. Furthermore, it allows for independent low rank changes in the stiffness, damping and mass matrix of the system. It is shown that in combination with the tangential iterative rational Krylov algorithm, a high number of low rank changes can be parametrized, while keeping the reduced model accurate and of moderate size. Also, a scheme is proposed to further reduce the model size, by a frequency limited post-processing step. The methodology is illustrated with two numerical examples: A purely structural example that simulates an unknown defect by locally reducing the stiffness and damping, and a fully coupled vibro-acoustic example that demonstrates how the method can be used to simulate added mass loading, due to for instance the placement of sensors/actuators.sponsorship: The Research Fund KU Leuven is gratefully acknowledged for its support. The research of E. Deckers is funded by a grant from the Research Foundation Flanders (FWO). The computational resources and services used in this work were provided by the VSC (Flemish Supercomputer Center), funded by the Research Foundation - Flanders (FWO) and the Flemish Government - department EWI. (Research Fund KU Leuven, Research Foundation - Flanders (FWO), Flemish Government - department EWI, Research Foundation Flanders (FWO))status: Publishe
Model based virtual intensity measurements for exterior vibro-acoustic radiation
No full textIn this work a method for the virtual sensing of the acoustic intensity is derived for exterior vibro-acoustic radiation of a complex deepdrawn structure. The proposed method estimates the acoustic intensity and acoustic pressure resulting from structural excitation in the full acoustic domain, by utilizing a model-based state estimator in the form of a Kalman filter. The used model is a high fidelity, fully coupled vibro-acoustic finite element model with infinite elements to model the acoustic radiation to infinity. The model is reduced to about 0.1% of the original size by a Krylov based model order reduction technique that preserves the stability of the full model. This allows for the usage of the model in a Kalman filter. The effectiveness of the Kalman filter is demonstrated with several numerical experiments, in which both the measured pressure and the measured sound intensity are compared with the estimations from the filter at several locations. Furthermore, the robustness of the filter to changing acoustic environments is assessed.sponsorship: The Research Fund KU Leuven is gratefully acknowledged for its support. The research of E. Deckers is funded by a grant from the Research Foundation -Flanders (FWO). (Research Fund KU Leuven - Research Foundation -Flanders (FWO))status: Published onlin
Multi-channel Kalman filters for active noise control
Full text linkBy formulating the feed-forward broadband active noise control problem as a state estimation problem it is possible to achieve a faster rate of convergence than the filtered reference least mean squares algorithm and possibly also a better tracking performance. A multiple input/multiple output Kalman algorithm is derived to perform this state estimation. To make the algorithm more suitable for real-time applications, the Kalman filter is written in a fast array form and the secondary path state matrices are implemented in output normal form. The resulting filter implementation is tested in simulations and in real-time experiments. It was found that for a constant primary path the filter has a fast rate of convergence and is able to track changes in the frequency spectrum. For a forgetting factor equal to unity the system is robust but the filter is unable to track rapid changes in the primary path. A forgetting factor lower than 1 gives a significantly improved tracking performance but leads to a numerical instability for the fast array form of the algorithm. © 2013 Acoustical Society of America
Time-domain impedance boundary conditions for acoustic reduced order finite element simulations
No full textTransient responses impose additional restrictions concerning model order reduction of acoustic finite element systems. Time-stable model order reduction methods achieve model compaction while guaranteeing frequency domain models transform in a physically meaningful way. Efficiency and stability are of course of little consequence if the model is rendered inaccurate. Krylov subspaces inherently include system input and/or output behavior in the reduction basis making them ideal reduction bases for investigating system behavior outside of steady state. Realistic boundary conditions are demanded and must be preserved in the reduction basis. Frequency dependent impedance boundary conditions help in this regard but complicate both model reduction and time-integration strategies. Multiplications to enforce system damping in the frequency domain become time-domain convolutions. Recursively calculated minimal memory convolution formulations have long proven useful in lowering the associated computational burden. Complex frequency-dependent damping matrices create a challenge for Krylov subspace based model reduction due to the way the reduction basis is constructed. Arnoldi iterations implicitly match the moments of the system transfer function to span a Krylov subspace. This paper demonstrates how to maintain compatibility with such algorithms while including frequency dependent damping. This work proposes combining projection based model order reduction with an efficient time domain impedance boundary condition formulation. An important benefit of working in the time domain is the ability to directly output binaural audio signals. To this end, discrepancies are discussed in the perceptual context of audibility. A reduction of system degrees of freedom from NDOF = 13125 to RDOF = 63 and the inclusion of time-domain impedance boundary conditions are shown to enable computational speedups by a factor of 11–36 without introducing audible differences.sponsorship: European Commission|812719, Research Foundation (Flanders)|1277021Nstatus: Published onlin
A novel flexible infinite element for transient acoustic simulations
No full textThis article addresses the efficient solution of exterior acoustic transient problems using the Finite Element Method (FEM) in combination with infinite elements. Infinite elements are a popular technique to enforce non-reflecting boundary conditions. The Astley–Leis formulation presents several advantages in terms of ease of implementation, and results in frequency-independent system matrices, that can be used for transient simulations of wave propagation phenomena. However, for time-domain simulations, the geometrical flexibility of Astley–Leis infinite elements is limited by time-stability requirements. In this article, we present a novel infinite element formulation, called flexible infinite element, for which the accuracy does not depend on the positioning of the virtual sources. From a software implementation perspective, the element proposed can be seen as a specialized FEM element and can be easily integrated into a high-order FEM code. The effectiveness of the flexible formulation is demonstrated with frequency and time-domain examples; for both cases, we show how the flexible infinite elements can be attached to arbitrarily-shaped convex FE boundaries. In particular, we show how the proposed technique can be used in combination with existing model order reduction strategies to run fast and accurate transient simulations
A numerically stable, finite memory, fast array recursive least squares filter for broadband active noise control
Full text linkSummary For broadband active noise control applications with a rapidly changing primary path, it is desirable to find algorithms with a rapid convergence, a fast tracking performance, and a low computational cost. Recently, a promising algorithm has been presented, called the fast-array Kalman filter, which uses rotation matrices to calculate the filter parameters. However, when this algorithm is implemented, it can show unstable behavior because of finite precision error propagation. In this paper, a novel algorithm is presented, which exhibits the fast convergence and tracking properties and the linear calculation complexity of the fast-array Kalman filter but does not suffer from the mentioned numerical problems. This is accomplished by running two finite length growing memory recursive least squares filters in parallel and using a convex combination of the two filters when the control signal is calculated. A reset of the filter parameters with proper re-initialization is enforced periodically. The mixing parameters will be chosen in such a way that the total available information used for the calculation of the control signal will be approximately equal at every time instance. The performance of the filter is shown in numerical simulations and real-time lab experiments. The numerical experiments show that the algorithm performs better numerically than the fast-array sliding window recursive least squares filter, while achieving a comparable convergence rate and tracking performance. The real-time lab experiments confirm the behavior shown in the simulations. Copyright © 2015 John Wiley & Sons, Ltd
Stable model order reduction for time-domain exterior vibro-acoustic finite element simulations
No full textThis paper presents a novel method that enables model order reduction of a fully-coupled, exterior vibro-acoustic finite element model for time domain simulations. The method preserves the stability of the full model and reduces the amount of degrees of freedom significantly, with only a moderate amount of calculation complexity. Infinite elements are used on the finite element boundary to satisfy the Sommerfeld radiation condition. Two different strategies to calculate the reduced order model are compared. The first strategy works with a split reduced basis and can be applied on any fully stable model. The second strategy starts from a modified Everstine formulation and directly builds a reduced basis from the full model, leading to more compact reduced order models. Furthermore, a method is derived to perform explicit time integration on the reduced system, while avoiding the inversion of the mass matrix, which might not be possible due to the presence of the infinite elements. Also this method is shown to preserve the stability of the model and a computationally efficient way for implementation of the method is discussed. The effectiveness of the novel methodology is demonstrated with two numerical models.sponsorship: The research of S. van Ophem is funded by an Early Stage Researcher grant within the European Project ANTARES Marie Curie Initial Training Network (GA 606817). The research of E. Deckers is funded by a grant from the Fund for Scientific Research, Flanders (F.W.O). The Research Fund KU Leuven is gratefully acknowledged for its support. The computational resources and services used in this work were provided by the VSC (Flemish Supercomputer Center), funded by the Research Foundation, Flanders (FWO) and the Flemish Government, Department EWI. (Early Stage Researcher grant within the European Project ANTARES Marie Curie Initial Training Network|GA 606817, Fund for Scientific Research, Flanders (F.W.O), KU Leuven, Research Foundation, Flanders (FWO), Flemish Government, Department EWI)status: Publishe
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