1,720,961 research outputs found
Acoustic radiation-based optimization of the placement of actuators for active control of noise transmitted through plates
No full textActive Structural Acoustic Control (ASAC) is mostly performed using a passive noise barrier, vibration actuators, sensors and a control system. ASAC reduces or alters the vibration of the barrier structure in a way that blocks the noise propagation through it. However, it is crucial that the actuators are appropriately arranged to be able to effectively control the vibration of the barrier. If the actuators were not optimally arranged, then certain modes of the structure may be uncontrollable, or require a very high control effort. Hence, the locations of the actuators should be determined by a careful optimization process employing a model of the structure. A common approach is to maximize the controllability of the system over a defined frequency range of operation. However, such an optimisation procedure often results in a solution that considers numerous vibration modes, only some of which are acoustically-relevant. That is, certain structural modes may vibrate considerably, but their contribution to the noise transmission and radiation would be negligible. Therefore, in the presented research a new acoustic radiation-based approach to the optimisation of the arrangement of actuators is proposed. A model of acoustic radiation is introduced and new cost functions are formulated to focus on modes that strongly contribute to noise transmission or radiation by the noise barrier. For the considered system, this enables an increase in the controllability measure of more than 5 dB for acoustically-relevant modes, which is similar to the level of improvement achieved when the number of actuators is doubled
Modelling vibro–acoustic response of lightweight square aluminium panel influenced by sound source locations for active control
No full textThis paper uses numerical approach to give insight into the structural–acoustic response of a lightweight square aluminium panel. It takes into consideration different locations of a primary sound source in an acoustic medium and how these locations influence the response of the structural panel. Finite element method as well as the first-order deformation theory are employed for constructing the numerical model. Experimental measurements of the mode shapes and velocity frequency response of the vibrating panel are used to validate the results of the finite element model. Furthermore, vibro-acoustic emission indexes such as sound transmission loss, sound pressure level and far-field directivity of sound pressure are obtained numerically. The results show that different locations of the primary sound source significantly influence the response of the structural panel to reduce noise. Sound source typically positioned close to the structural panel lowers the efficiency of the vibrating panel to reduce noise. Moreover, the sound distribution profiles at the radiated end of the vibrating panel for the different locations of the sound source are investigated. The study shows that the variation of the zones of quiet, vibro-acoustic emission parameters and sound distribution profiles obtained can provide vital information about the best positioning of structural source for both active vibration and noise control
Optimizing design of openings in vibrating plates for enhanced vibro-acoustic performance using a genetic algorithm approach
No full textOptimizing structural openings in vibro-acoustic systems is essential for balancing functional needs with acoustic performance in various engineering applications. This paper presents an efficient optimization approach for designing openings in plate structures within vibro-acoustic systems, aimed at enhancing acoustic performance while maintaining structural integrity. A genetic algorithm framework is developed to determine the optimal shapes and locations of openings simultaneously, utilizing an analytical model based on hyperbolic and trigonometric admissible functions within a master–slave software architecture. The proposed method accommodates a variety of opening requirements for different systems and employs a cost function that evaluates both the average and peaks of sound power responses to identify the designs with the highest fitness. This results in significant reductions in sound power levels compared to median and worst-case designs. Additionally, the method analyzes how variations in opening locations, numbers, and shapes impact acoustic performance, providing guidance for opening designs that avoid undesired acoustic outcomes and improve noise barrier performance in vibro-acoustic systems
Shaping of the frequency response of vibrating plates with openings for vibro-acoustic systems
No full textThe frequency response of vibrating plates with openings can be tailored through the shape and location of these openings in the mixed interfaces of vibro-acoustic systems. This paper introduces a novel method for designing the characteristics of openings in mixed interfaces to achieve the desired vibrational and acoustic responses. The core of this methodology is an analytical model that utilizes the Rayleigh-Ritz method, augmented by a radiation resistance matrix for precise estimation of sound power in a free field. This approach provides the essential flexibility to alter the shapes and locations of the openings. A Finite Element Method (FEM) is specifically employed to enhance the visualization of the interactions within the multiphysics domains of the vibro-acoustic systems. This FEM model, developed for the enclosure and coupled with the vibrating plate according to Kirchhoff's thin plate theory, is complemented by the Boundary Element Method (BEM) for the sound pressure calculations. The methodology is further substantiated by experimental validation, which confirms the theoretical predictions and enhances the credibility of the proposed models
Impact of Boundary Conditions on Shaping Frequency Response of a Vibrating Plate - Modeling, Optimization, and Simulation
No full textAbstractThe aim of this paper is to further develop the original method proposed by the authors in their previous publications and submitted as a patent to shape frequency response of a vibrating plate according to precisely defined demands. The method is based on modeling the plate together with additional masses and ribs, and applying a sophisticated optimization algorithm, which issues arrangement of the masses and ribs. It has a very high practical potential. It can be used to improve acoustic radiation of the plate for required frequencies or enhance acoustic isolation of noise barriers and device casings. It can be utilized for both passive and active control. For the latter case it allows at the same time to optimally arrange actuators and sensors.In the paper there are presented, compared and discussed simulation results of the method for a plate with different boundary conditions: simply supported, fully-clamped and elastically restrained against rotation (corresponding to a mounting in a real device casing). Proposed optimization criteria are followed from practical scenarios, where precise modification of a vibrating plate frequency response is desired. The application of the proposed method for active control is also shown. The important additional outcome of the paper are guidelines on designing device casings in terms of rigidity in order to obtain their required vibration and noise isolation features
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
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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