1,720,971 research outputs found
Numerical approach for the acoustic connection of nonconforming meshes by transfer matrices
No full textAcoustic behaviour of elliptical mufflers with single-inlet and double-outlet
No full textExpansion chambers with single-inlet and double-outlet are used in the exhaust system of internal combustion engines since they provide noise attenuation similar to simple chambers (single inlet/outlet), and reduce the flow noise and back pressure. This work presents a detailed analysis of the acoustic attenuation performance of elliptical expansion chambers with single-inlet and double-outlet. First, the finite element method (FEM) is considered in order to obtain a reference solution. Then, the mode-matching method (MMM) is applied at the area discontinuities of the muffler, considering a circular inlet pipe, a central elliptical chamber and two circular outlet pipes. This method reduces the computational requirements and enables to couple the acoustic fields within each region, described by means of Mathieu functions in the elliptical chamber and Bessel functions in the circular pipes. The solution given by this analytical approach is compared with finite element results and experimental measurements for a selected configuration, showing a good agreement. The acoustic behaviour is then analysed in detail as a function of the chamber length, the . eccentricity of the elliptical cross-section and the position of the inlet and outlet pipes. Some potential means to improve the acoustic performance are proposed
Error estimation for the finite element evaluation of G<sub>I</sub> and G<sub>II</sub> in mixed-mode linear elastic fracture mechanics
No full textA discretization error estimator for the finite element evaluation of the strain energy release rates (SERRs) I, GII is presented for mixed-mode bidimensional problems of the linear elastic fracture mechanics (LEFM). The estimator is related to one of the most efficient energetic methods: the equivalent domain integral method (EDI). A continuum approach of the shape design sensitivity analysis (SDSA) is applied to the fracture mechanics problem in combination with the field decomposition technique to obtain separate estimates of the discretization error for each mode. The error estimator enables an a posteriori improvement of I, GII for a given finite element mesh. The improvement is achieved by adding the estimated errors to the previously calculated values of GI, GII by means of the discrete analytical stiffness derivative method (DASD). This is verified through numerical examples based on the Westergaard's problem and a finite domain problem
Error estimation and <em>h</em>-adaptive refinement in the analysis of natural frequencies
No full textThis paper deals with the estimation of the discretization error and the definition of an optimum h-adaptive process in the finite element analysis of natural frequencies and modes. Consistent and lumped mass matrices are considered. In the first case, the discretization error essentially proceeds from the stiffness modelization, so it is possible to apply the same error estimators than those considered in static problems. On the other hand, the error associated with the modelization of the inertial properties must be taken into account if lumped mass matrices are used. As far as h-adaptivity is concerned, it is usually interesting to obtain meshes with a specified error for each mode. However, traditional criteria for static problems consider only one load case. Defining the optimum mesh as the one that gets the desired error with the minimum number of elements, a method is proposed for the h-adaptive process taking into account a set of natural modes simultaneously. The proposed methods have been validated by applying them to bi-dimensional test problems
Acoustic modelling of exhaust devices with nonconforming finite element meshes and transfer matrices
Full text link[EN] Transfer matrices are commonly considered in the numerical modelling of the acoustic behaviour associated with exhaust devices in the breathing system of internal combustion engines, such as catalytic converters, particulate filters, perforated mufflers and charge air coolers. In a multidimensional finite element approach, a transfer matrix provides a relationship between the acoustic fields of the nodes located at both sides of a particular region. This approach can be useful, for example, when one-dimensional propagation takes place within the region substituted by the transfer matrix. As shown in recent investigations, the sound attenuation of catalytic converters can be properly predicted if the monolith is replaced by a plane wave four-pole matrix. The finite element discretization is retained for the inlet/outlet and tapered ducts, where multidimensional acoustic fields can exist. In this case, only plane waves are present within the capillary ducts, and three-dimensional propagation is possible in the rest of the catalyst subcomponents. Also, in the acoustic modelling of perforated mufflers using the finite element method, the central passage can be replaced by a transfer matrix relating the pressure difference between both sides of the perforated surface with the acoustic velocity through the perforations. The approaches in the literature that accommodate transfer matrices and finite element models consider conforming meshes at connecting interfaces, therefore leading to a straightforward evaluation of the coupling integrals. With a view to gaining flexibility during the mesh generation process, it is worth developing a more general procedure. This has to be valid for the connection of acoustic subdomains by transfer matrices when the discretizations are nonconforming at the connecting interfaces. In this work, an integration algorithm similar to those considered in the mortar finite element method, is implemented for nonmatching grids in combination with acoustic transfer matrices. A number of numerical test problems related to some relevant exhaust devices are then presented to assess the accuracy and convergence performance of the proposed procedure.Authors gratefully acknowledge the financial support of Ministerio de Ciencia e Innovacion and the European Regional Development Fund by means of the Projects DPI2007-62635 and DPI2010-15412.Denia, F.; Martínez-Casas, J.; Baeza, L.; Fuenmayor, F. (2012). Acoustic modelling of exhaust devices with nonconforming finite element meshes and transfer matrices. Applied Acoustics. 73(8):713-722. https://doi.org/10.1016/j.apacoust.2012.02.003S71372273
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
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