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ELASTOHYDRODYNAMIC LUBRICATION IN ELASTOMERIC RECIPROCATING SEALS. PART 2 - THEORETICAL-EXPERIMENTAL AND NUMERICAL METHODS
No full textStick-slip transition and dynamic cyclic response of friction damped systems
Full text linkThis thesis is subdivided into two parts: in the first we analyze the transition from static to dynamic friction with some emphasis on the implication of using more refined friction laws (with respect to the simple Coulomb model) while in the second part we study the cyclic response of dynamical systems that experience friction. Particularly, in the first part we will take inspiration from some recent experiments from the group of Prof. Fineberg to tackle some partial slip contact problems, with the idea in mind of providing analytical models that can, in some extent, interpreter some of the numerous experimental evidences that came from the direct observation of the sliding phenomena. In the chapters 1-2 a brief introduction of the equations that govern the contact of elastic bodies and the experimental test rig used in the experiments is presented. In chapter 3 the partial slip problem of a flat square-ended punch pressed against an half-plane and tangentially loaded above the contact interface is studied, then a FEM of the Prof. Fineberg experimental test rig will be proposed to avoid the hypothesis of half-plane elasticity, with good agreement between numerical and experimental results. In chapter 4 the implications of using a slip weakening friction law instead of the classical Coulomb law are discussed and an energetic criterion for slip inception is derived, which we will call "Griffith friction model". In chapter 5, using this "Griffith friction", the partial slip problem for different plane geometries (power law punches and sinusoidal profile) is solved.
In the second part of the thesis we will focus our attention on the dynamic response of mechanical systems subjected to friction. In chapter 7 a very simple model of structure subjected to dry friction is studied, constituted by a single degree of freedom system subjected to a periodical tangential excitation and a (possibly) varying normal load. First we compare the quasi-static solution with the dynamic solution in the limit of very low excitation frequency, then we study (in the bounded regime) how the peak displacement and dissipation is related to the phase shift between the normal and the tangential load. In chapter 8 the dynamical behavior of a mass-spring-viscous damper structure linked to a massless Coulomb damper is studied with attention to the regime that minimize the vibration amplitude of the mass. Finally in chapter 9, we study a friction-excited nonlinear oscillator chain, where a polynomial nonlinearity is introduced in the system. We focus our attention on the multiplicity of solutions that are proven to exist in certain parameter rangeS which leads to a bifurcation pattern similar to the snaking bifurcations. In the end conclusions and possible developments of the present work are proposed
ON THE INCOMPATIBILITY BETWEEN THE EQUIVALENT SHEAR FORCE CONCEPT AND THE INTEGRAL FORMULATION OF CONTACT PROBLEMS BETWEEN KIRCHHOFF PLATES AND IRREGULAR LINEAR SUPPORTS
No full textIt is shownthat, when employing the integral formulation to describe contact problemsbetween Kirchhoff plates and irregular linear supports, the equivalent shear force concept maybe incompatible with the integral approach. In such circumstances the equivalent shear forceconcept has to be abandoned in favour of an equivalent twisting moment approach. A classicalexample of an infinite plate resting on a linear central segment is revisited in the light of theequivalent twisting moment concept, where all the computations are carried out in exact form.An additional example is developed to show that the usefulness of an integral approach basedupon the equivalent twisting moment concept remains valid even when the equivalent twistingmoment is applied at a plate border along which the twisting moment must be null, as it occursin a partially clamped border. The reaction singularity at the endpoints of a linear support isexamined with theWilliams asymptotic method. Finally, a physical interpretation is proposed forthe adoption of a distributed twisting moment among the contact reaction
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
Singular integral equations and contact problems in Kirchhoff plates resting on irregular linear supports
No full textThe construction of (boundary) singular integral equation formulations of contact problems for Kirchhoff (thin) plates is addressed. In particular, the need to forecast the singularity strength of the contact reaction is evidenced. It is shown that, when employing the integral formulation to describe contact problems between Kirchhoff plates and irregular linear supports, the equivalent shear force concept may be incopatible with the integral equation approach. In such circumstances the equivalent shear force concept has to be abandoned in favour of, or coupled with, an equivalent twisting moment approach. These concepts are described and applied to two particular contact problems
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
Progettazione integrata di componenti motore in lega di alluminio ottenuti per fusione e sollecitati a fatica ad alta temperatura
No full textSi presenta un progetto mirato allo sviluppo di una innovativa metodologia di progettazione di componenti motore ottenuti per colata di lega d’alluminio sollecitati termomeccanicamente, integrando aspetti progettuali/strutturali, metallurgici e tecnologici. Il contributo accademico al progetto è multidisciplinare e multisede
On the Bursting Mechanism in Rotating Rings
No full textThe bursting mechanism in rotating, bored discs is theoretically reviewed in the light of published experimentalinformation. In particular, the segmentation sequence in bursting wheels is analysed according to a curved barmodelling and to a quasi-static loading, where a dynamic correction factor is introduced which reconciles theory withexperiments. Finally, a diagram reporting the number of wheel fragmented pieces in terms of the ratio of ring inner toouter radii is presented, based upon available experimental data and theoretical interpretation
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