1,721,263 research outputs found
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
A Kalman-based identification approach for distributed aerodynamic loads on a rotating blade
No full textThe rotating blades of the helicopter are constantly interacting with the external fluid generating vibratory loads. These excitations are then transmitted to the rotor hub and can lead to failures in the main rotor system. The knowledge or prediction of the aerodynamic loads become thus of great importance for design and failure prevention. Several experiment-based and model-based techniques have been presented in literature, but given the complexity in helicopter modelling, high accuracy can only be reached if a large amount of sensor data and/or a high-fidelity numerical model is available. This contribution focuses on the usage of the Kalman filtering technique for rotor load estimation. The filter presents two main advantages: i) usage of a minimum set of sensors; ii) compensation of a low-fidelity model by accounting for sensor and model uncertainties. The problem of state and load estimation is addressed in this paper on a rotating helicopter blade through a numerical example. Numerical results show an accurate state reconstruction with respect to the selected sensor layout and model uncertainties. The distributed aerodynamic loads can be accurately reconstructed in post-processing
Simulazione di prove di “pass-by noise” su veicolo nelle medie frequenze attraverso il metodo Fast Multipole BEM
No full textPredicting vibration levels on an experimental test case by using invariant loads (e.g. Blocked forces) as source characterization
No full text© Proceedings of ISMA 2018 - International Conference on Noise and Vibration Engineering and USD 2018 - International Conference on Uncertainty in Structural Dynamics. All rights reserved. Component-based TPA is a relatively new TPA approach that allows to characterize a structureborne source component independently from the receiver structure (as opposed to classical TPA) and to predict its behavior when coupled to different receivers. This approach would allow to frontload the development process and considerably increase the flexibility during the design process. However, there are a number of challenges affecting its applicability, such as a proper modelling of the coupling degrees of freedom at the interface, the difficulty to access the interface connection points and the conditioning of the equations. A number of innovative methods were developed to address these issues, that will be investigated by means of measurements on a laboratory test bench. A systematic analysis will be performed through which the accuracy and applicability of the component-based TPA will be analyzed and assessed.sponsorship: The authors gratefully acknowledge the European Commission for its support of the Marie Sklodowska Curie program through the ETN PBNv2 project (GA 721615). (European Commission|GA 721615)status: Publishe
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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
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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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