1,720,968 research outputs found
Active control of a tuned vibration absorber for use in metamaterial applications
No full textTuned Vibration Absorbers (TVAs) are an effective method of reducing vibration in a structure at the resonance frequency of the TVA. Unfortunately, TVAs are only effective across the narrow frequency bands to
which they are tuned. Recent work has broadened the effective bandwidth of control by combining arrays of
TVAs with different resonance frequencies to form a metamaterial. However, the tuning frequencies of these
passive metamaterials are still fixed after manufacture and, therefore, cannot effectively handle significant
uncertainty or changes in operating conditions. Active control can be used to alter the tuning frequencies of
the constituent TVAs and dynamically adjust the effective frequency range of control. This paper proposes
a novel active TVA, which incorporates piezoceramic actuators into the absorber and thus enables tuning of
the resonance frequency via modifications to the effective stiffness. The paper presents an investigation into
the design of the proposed active TVA and the limitations on its tunability using different control strategies
Experimental implementation of an actively controlled tuned vibration absorber using piezoelectric actuators
No full textTuned vibration absorbers (TVAs) are known to provide effective vibration control at their specific tuning frequency. They can effectively dissipate vibration energy from the host structure, making them useful for the control of both time invariant tonal excitation and structural resonances. However, they are ineffective away from their tuning frequency, making them unsuitable for applications where broadband vibration control is required or where there is significant variance in the system dynamics or the vibration spectrum. By incorporating some form of actuation and sensing into a TVA, active control can be used to vary the response of a TVA after production, tuning the TVA dynamics to the potential time varying application requirements. This paper explores the tunability of a specific TVA design, where the spring elements of the TVA are actuated using piezoelectric patch actuators. Previous work has studied thetheoretical limits of controlling the dynamics of this TVA design using feedback control strategies. The work presented in this paper extends this to an experimental implementation of active control on the proposed TVA design using commercially available piezoelectric actuators and sensors to establish thepractical limits on actively tuning the considered TVA design
Finite element modelling and optimisation of multi-material acoustic black holes
No full textGeometric acoustic black holes (ABHs) have been proven to be effective as a lightweight passive vibration control solution. However, the thin geometries associated with the design leaves them susceptible to damage. Multi-material ABHs have been proposed as an alternative, whereby the material properties and hence the acoustic impedance of the structure varies along the direction of wave travel as opposed to the geometry. Multi-material ABHs are produced through multi-material additive manufacturing, a relatively costly process which produces final components that cannot easily be altered after production. As such, an accurate numerical model is required to design and optimise the multi-material ABH configuration. This work investigates the best practices for finite element modelling and optimisation of a multi-material ABH design in a beam termination application. Considerations are made into accuracy, computational cost, and the potential effects of the additive manufacturing process on the effective material properties
Design of a multi-material acoustic black hole using geometric profile mapping
No full textSince their inception, acoustic black holes (ABHs) have taken on many forms. A wide range of profiles has been investigated for beam termination applications, including power laws and cosine profiles. However, all of these configurations have a common issue- the profiles have an inherent thin section at the end of the beam. This makes the profile susceptible to damage towards the tip, particularly through fatigue. Multi-material ABHs have been proposed as an alternative solution, maintaining a constant external geometry whilst varying the material properties along the length of the ABH termination. Previous work on multi-material ABHs has focused on optimising section lengths of each material based on a cost function, namely kinetic energy in the host beam. This work investigates the performance of multi-material ABH designs with section lengths chosen to approximate the effective impedance change of a range of geometric ABH terminations. The relative performance of each discretised gradient is compared through simulation in addition to comparison to an equivalent continuous gradient
Frequency dependent material property characterisation of inkjet printed polymers
No full textMulti-material additive manufacturing has rapidly advanced in recent years, enabling the construction of increasingly complex geometries with the potential for enclosed features of dissimilar materials. Several use cases for these processes in vibration control are currently being investigated, particularly in metamaterial applications where the increasingly complex geometries cannot be produced with traditional manufacturing techniques. Unfortunately, characterisation of the properties of the materials generally only focuses on the static material properties. As more applications for multi-material additive manufacturing in vibration control are investigated, it will become necessary to understand the frequency dependency of the materials used to aide in the design process. This work investigates the frequency dependency of the material properties of a range of photopolymers used in multi-material inkjet printing
Experimental validation of a multi-material acoustic black hole
No full textGeometric acoustic black holes (ABHs) have already been proven as an effective passive vibration control measure in plates and beams. However, the thin geometries inherent to the design raise concerns about the structure’s resistance to damage through fatigue. Multi-material ABHs (MMABHs) have been proposed as an alternative solution where by the material properties vary along the direction of wave propagation instead of the geometry. This, in theory, produces a change in acoustic impedance without the issues of fatigue seen in the geometric ABHs. Previous work has been performed on the design and modelling of polymer multi-material ABHs. This work discusses practices for experimental measurement and validation of multi-material ABHs produced through additive manufacturin
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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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