1,721,002 research outputs found
Wave finite element analysis of fluid-filled pipes
No full textNumerical computation of wave characteristics in fluid–filled pipes is obtained using a Wave Finite Element method. Axisymmetric properties of the system are exploited, resulting in a very low order FE model to which theory of wave propagation in periodic structures is applied. The method takes advantage of commercial FE packages capability of modelling acoustic fluid, structure and fluid–structure interaction. The formulation leads to a general approach which is neither limited to low frequency analysis nor thin–wall theory. The method is described and illustrated by application to isotropic and laminated sandwich pipes filled with non–viscous fluid. Complex dispersion curves are presented and discussed. Results are found straightforwardly and at negligible computational cost. The method could be easily implemented in a commercial finite element code
Wave Propagation in Laminated Cylinders with Internal Fluid and Residual Stress
Full text linkNumerical computation of wave propagation in laminated cylinders with internal fluid and residual stress is obtained using a Wave Finite Element formulation for 2D waveguides. Only a very small segment of the system is modelled, resulting in a very low-order finite element (FE) model to which the theory of wave propagation in 2D periodic structures is applied. The method uses standard FE formulations and exploits the capability of commercial FE software to model both fluid and structure and their interaction, resulting in a very large reduction in computational time. The presented approach is general, and can be applied without the need to make assumptions related to shell theory or low-frequency analysis. In particular, the laminated structure is discretised using 3D solid elements, thus representing the through-thickness dynamics with high accuracy. Residual radial and hoop stresses are included in the model by adding the FE pre-stress stiffness matrix to the original stiffness matrix of the system. The method provides simultaneously a very substantial reduction of computational cost, accurate solutions up to very high frequency and prediction of the dispersion curves for selected circumferential orders without the need for any further analysis. Here, the formulation of the method is introduced and its application to laminated cylinders filled with an acoustic fluid is presented. A composite, reinforced rubber cylinder, pre-stressed by a circumferential tension, is also shown as an example of a laminated pipe for high-pressure applications
Un Nuovo Metodo del Simplesso per il Problema di Complementarità Lineare Mista in Sistemi Multibody con Vincoli Unilateri
No full text
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
Wave propagation in helically orthotropic elastic cylindrical shells and lattices
No full textA use of orthotropic materials such as fibre-reinforced composites can introduce into vibro-acoustic performance of cylindrical structures effects that are not feasible when an isotropic material is used. In this paper, free and forced wave propagation in cylindrical structures with helically orthotropic material properties is analysed to demonstrate these effects. Two models, a thin cylindrical shell and a cylindrical beam lattice, are considered and two methods, an analytical method of the thin shell theory and a numerical Wave Finite Element method, are used. For both models, the symmetry break effect concerned with the location of dispersion curves is captured by means of these methods and explained. The influence of the helix angle and of the material parameters on the location of dispersion curves is investigated. The Green's matrix is formulated for rotating forces and the forcing problems are solved to highlight some unusual waveguide properties of the helically orthotropic cylindrical structures. The results are discussed in view of a possible application for control of energy flow in piping systems exposed to rotating excitation
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
Numerical Analysis of Vibration Attenuation and Bandgaps in Radially Periodic Plates
Full text linkObjectivePeriodic configuration of mechanical and civil structures has shown great potential for noise and vibration reduction. However, the use of Cartesian coordinates in studying periodicity effects in elastic structures overlooks the benefits of radially periodic configurations when dealing with wave propagation in large flexible plates disturbed by a small source area. This paper presents an easy-to-use numerical approach to predicting bandgap characteristics in polar coordinates.MethodologyTo demonstrate the vibration-attenuation effect, we consider a circular radially periodic plate model. We use an adapted Wave Finite-Element method in numerical experiments to demonstrate the existence of the attenuation effect. To verify the numerical results, we apply an adapted Floquet theory to polar coordinates.Results and ConclusionsOur findings indicate that theoretical and numerical results are in excellent agreement considering a new parameter that introduces the distance from the origin. The adapted Wave Finite-Element approach and Floquet theory presented here demonstrate their potential to model more complex structures in polar coordinates
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