1,721,009 research outputs found
Wave propagation with long-range forces and mistuning effects
No full textThe present paper investigates the effects induced by long-range connections embedded within a classical D’Alembert waveguide, characterized by the number of connections and the distance between the linked sections of the structures. This new connectivity pattern induces unconventional effects, such as wave-stopping and negative group velocity, which can be adjusted by the features of the superstructure. Furthermore, a mistuning effect is met as consequence of the perturbation of the long-range connection distance. This perturbation may produce the amplification of the nonconventional propagation phenomena, even when the other physical and geometrical properties are unchanged
Variational control approach to energy extraction from a fluid flow
Full text linkEnergy harvesting from the environment is an important aspect of many technologies. The scale of energy capturing and storage can involve the power range from mWatt up to MWatt, depending on the used devices and the considered environments (from ambient acoustic and vibration to ocean wave motion, or wind). In this paper, the wind turbine energy harvesting problem is approached as an optimal control problem, where the objective function is the absorption of an amount of energy in a given time interval by a fluid-flow environment, that should be maximized. The interest relies on outlining general control models of fluid-flow-based extraction plants and identifying an optimum strategy for the regulation of an electrical machine to obtain a maximum-efficiency process for the related energy storage. The mathematical tools are found in the light of optimal control theory, where solutions to the fundamental equations are in the frame of Variational Control (the basis of the Pontryagin optimal control theory). A special problem, named Optimally Controlled Betz’s Machine OCBM-optimal control steady wind turbine, is solved in closed form, and it is shown that, in the simpler steady case, it reproduces the maximum efficiency machine developed in Betz’s theory
Wave propagation phenomena in nonlinear elastic metamaterials
Full text linkThe present chapter provides a general method to deal with nonlinear integro-differential equations, based on statistical linearization and Fredholm's approach. In this context, the elastic metamaterial is characterized by long-range nonlocal interactions besides a nonlinear short-range constitutive relationship. Results are analytically obtained and unveil the birth of unconventional propagation
Numerical simulations in nonlinear elastic metamaterials with nonlocal interaction
No full textThe paper presents a numerical investigation of an elastic metamaterial, i.e., a one-dimensional elastic waveguide, equipped with nonlocal (long-range) and nonlinear interactions. The dynamic behavior of the newly defined structure is described by nonlinear integro-differential equation of motion. Numerical simulations, comparing the linearized model and the nonlinear one, unveil the arising of wave-stopping and backward propagation phenomena
Optimal control theory based design of elasto-magnetic metamaterial
Full text linkA method to design a new type of metamaterial is presented. A two-step strategy to define an optimal long-range force distribution embedded in an elastic support to control wave propagation is considered.
The first step uses a linear quadratic regulator (LQR) to produce an optimal set of long-range interactions. In the second step, a least square passive approximation of the LQR optimal gains is determined. The paper investigates numerical solutions obtained by the previously described procedure. Finally, we discuss physical and engineering implications and practical use of the present study
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
Twin-waves propagation phenomena in magnetically-coupled structures
Full text linkThe use of magnetic dipoles embedding in an elastic support introduces long-range interaction forces. This is a completely new paradigm in structural mechanics, classically based on local short-range particle interaction. The features of long-range forces produce very new mechanical coupling effects. This paper examines the case in which two identical rod-like structures, each with a dipole distribution embedded, vibrate side by side. Waves generated in one of the rods propagate also in the second and vice versa creating a new effect we name twin-waves. The present investigation unveils the existence of an infinite number of propagation modes even in one-dimensional infinite structures, a new and unus al behaviour in classical waveguides. The physics behind this phenomenon is further investigated also by numerical simulations
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
Machine learning and sensor swarm for structural health monitoring of a bridge
No full textThe present work proposes an unsupervised early-stage damage detection method, which relies on the combined application of the Principal Component Analysis, for features extraction and dimensionality reduction, and Symbolic Data Analysis, for automatically cluster different patterns. The structure considered is a Warren truss bridge, which is numerically simulated by a Finite Element Model. It is excited by a thermal cycle and a static load; the damage is modelled as a sudden reduction of the area of the section. The validity of the proposed algorithm is numerically tested over one month of vibration data. The damage is properly identified by some PCAs; furthermore, Symbolic Data Analysis allows an effective clustering of damaged and undamaged PCA samples. Robustness of the algorithm is tested at different noise level, timing of damage, damage position and depth, the influence of the sensors' number is also tested
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