1,721,010 research outputs found
Analysis of enclosures and anti vibration devices for electronic equipment for space applications
No full textAn interpolated FFT algorithm for full-field nonlinear modal testing with a 3D-SLDV
No full textThe measurement of full-field dynamics of a light-weighted structure can be challenging due to its low mass-to-area ratio, complex spatial deformation shapes and geometrical nonlinear behaviours under harsh loadings. In this paper, a Three-dimensional Scanning Laser Doppler Vibrometer (3D SLDV) is used to capture the full-field, multi-harmonic shapes of a vibrating blade in a laboratory environment. The wellknown disadvantages of the 3D SLDV such as its long testing duration, coarse frequency resolution and severe spectral leakage are countered by a Multi-step Interpolated Fast Fourier Transform (Multi-step IFFT) procedure in combination with a phase resonance testing strategy. A numerical example featuring ten harmonics is firstly presented, highlighting the accuracy of the proposed procedure before it is applied to the test of a wide-chord fan blade. To the best of authors’ knowledge, the full-field, multi-harmonic shapes for such an industrial large-scale, geometrically complex and nonlinear structure are experimentally measured for the first time
On an improved adaptive reduced-order model for the computation of steady-state vibrations in large-scale non-conservative systems with friction joints
No full textJoints are commonly used in many large-scale engineering systems to ease assembly, and ensure structural integrity and effective load transmission. Most joints are designed around friction interfaces, which can transmit large static forces, but tend to introduce stick-slip transition during vibrations, leading to a nonlinear dynamic system. Tools for the complex numerical prediction of such nonlinear systems are available today, but their use for large-scale applications is regularly prevented by high computational cost. To address this issue, a novel adaptive reduced-order model (ROM) has recently been developed, significantly decreasing the computational time for such high fidelity simulations. Although highly effective, significant improvements to the proposed approach is presented and demonstrated in this paper, further increasing the efficiency of the ROM. An energy-based error estimator was developed and integrated into the nonlinear spectral analysis, leading to a significantly higher computational speed by removing insignificant static modes from the stuck contact nodes in the original reduced basis, and improving the computational accuracy by eliminating numerical noise. The effectiveness of the new approach was shown on an industrial-scale fan blades system with a dovetail joints, showing that the improved adaptive method can be 2–3 times more computationally efficient than the original adaptive method especially at high excitation levels but also effectively improve the accuracy of the original method
Comparison of contact parameters measured with two different friction rigs for nonlinear dynamic analysis
Full text linkThe accurate measurement of contact interface parameters is of great importance for nonlinear dynamic response computations since there is a lack of predictive capabilities for such input parameters. Several test rigs have been developed at different institutions, and a series of measurements published, but their reliability remains unknown due to a lack of direct comparisons. To somehow address this issue, a Round-Robin test campaign was performed including the high frequency friction rigs of Imperial College London and Politecnico di Torino. Comparable hysteresis loops were recorded on specimen pairs manufactured from the same batch of raw stainless steel, for a wide range of test conditions, including varying normal loads, sliding distances and nominal areas of contact. Measurements from the two rigs were compared to quantify the level of agreement between the two very different experimental setup, showing a reasonably good matching in the results, but also highlighting some differences. Results also demonstrated that loading conditions can strongly affect the contact parameters, and consequently their effect must be included in future nonlinear dynamic simulations for more reliable predictions
A Wireless Vibration Control Technique for Gas Turbine Blades Using Piezoelectric Plates and Contactless Energy Transfer
No full textMultifunctional structure technologies for satellite applications
No full textConventional spacecraft subsystems are designed and manufactured separately, and are integrated only during the final stages of satellite development. This requires containers for the subsystems' hardware, mechanical interfaces, panels, frames, bulky wire harnesses, etc., which add considerable mass and volume. As all subsystems are generally secured to the structure, the multifunctional structure approach aims at merging these elements into the structure, so that the structure also carries out some of the typical functions of the subsystems (e.g. electrical energy storage). The main advantages are as follows: (i) removal of the bolted mechanical interfaces and most of the subsystems' containers; (ii) reduction of the satellite structure mass, as the strength of the parts of the subsystem imbedded into the structure are exploited, and substitute purely structural parts; (iii) reduction of the overall satellite volume, as elements such as battery packs or electronic harnesses can be built into the structure's volume. There are still issues that need to be addressed to allow a wider utilization of multifunctional structures. However, the development of concurrent engineering approaches, to carry out an integrated design of the spacecraft, together with advances in the subsystems' disciplines, will help to promote the further diffusion of multifunctional structures. © 2007 SAGE Pulications
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
Optimal placement of piezoelectric plates to control multimode vibrations of a beam
No full textDamping of vibrations is often required to improve both the performance and the integrity of engineering structures, for example, gas turbine blades. In this paper, we explore the possibility of using piezoelectric plates to control the multimode vibrations of a cantilever beam. To develop an effective control strategy and optimize the placement of the active piezoelectric elements in terms of vibrations amplitude reduction, a procedure has been developed and a new analytical solution has been proposed. The results obtained have been corroborated by comparison with the results from a multiphysics finite elements package (COMSOL), results available in the literature, and experimental investigations carried out by the authors
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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