1,720,956 research outputs found
Low-cycle Thermal Fatigue and High-cycle Vibration Fatigue Life Estimation of a Diesel Engine Exhaust Manifold
Full text linkThis paper aims at estimating the low-cycle and high-cycle fatigue life of a turbocharged Diesel engine exhaust manifold. First, a decoupled thermo-structural Finite Element analysis has been performed to investigate low-cycle fatigue phenomena due to the thermal loadings applied to the exhaust manifold. High/low temperature cycles causes stress-strain hysteresis loops in the manifold material whose related dissipated energy can be directly correlated to low-cycle thermal fatigue. Afterwards, a dynamic harmonic analysis has been performed aiming at investigating the existence of high-cycle fatigue phenomena due to vibrational loading applied to the exhaust manifold during the duty cycle. Three direction acceleration experimental loadings have been applied to the model. An ad-hoc methodology has been developed to superimpose thermo-structural results to dynamic harmonic analysis results. In particular, quasi-static thermo-structural results have been employed to identify the mean stress values of vibration fatigue cycles, while alternate stress values have been derived from harmonic analysis. Different combinations of frequencies and phases of the acceleration input signals have been considered to create different high-cycle fatigue loadings. Each cyclic load case has been processed employing the multiaxial Dang Van fatigue criterion
Influence of different temperature distributions on the fatigue life of a motorcycle piston
Full text linkIn this paper, finite element analyses are performed to evaluate the stresses and the strains in a motorcycle piston. Non-linear finite element models are employed to mimic the piston behaviour when subjected to different loading conditions. In particular, the gas forces, the inertial forces and the piston-to-cylinder contact forces are considered. Appropriate temperature distributions are applied to the model to include the thermal stresses and strains in the analyses. Two different thermal configurations are considered: the first has a standard design of the oil jet hitting the underside zone of the piston crown, while the second presents modified parameters able to increase the heat transfer coefficient appreciably. The different operating temperature distributions related to the two thermal configurations considered strongly influence the pistons thermomechanical behaviour. This paper aims to perform high-cycle fatigue analyses to show how the fatigue life and fatigue-critical points of the component change when moving from the standard configuration to the modified configuration
Influence of the temperature distribution on both high-cycle and low-cycle fatigue life of a motorbike piston
No full textFinite Element analyses are performed to evaluate stresses and strains in a motorbike
piston. Non-linear Finite Element models are employed to mimic the piston behaviour when
subjected to different loading conditions. In particular, gas forces, inertial forces, and piston-tocylinder
contact forces are considered. Temperature distributions formally evaluated and validated
against experimental evidences [1] are applied to the model to include thermal stresses and strains
into the analysis. Two different thermal configurations are considered: the first has a no-optimized
design of the oil jet hitting the underside zone of the piston crown, while the second presents
modified parameters able to appreciably increase the heat transfer coefficient. This aspect causes
different operating temperature distributions that strongly influence the piston behaviour. This
paper aims at performing both low-cycle and high-cycle fatigue analysis to show how the fatigue
life and fatigue-critical points change in the two considered thermal configuration
Numerical investigation of the cavitation damage in the wet cylinder liner of a high performance motorbike engine
No full textIn this paper a numerical methodology is proposed which aims at understanding the origin of a particular failure occurred in a two-cylinder high performance spark ignition engine for motorbike applications. A relevant cavitation damage/erosion has been detected at the water side of the engine cylinder liner during severe reliability bench tests, performed at the early stage of the engine design process. On the contrary, no damages have been registered during parallel high-load long runs of the motorbike. This contribution investigates in detail the differences between the bench test cooling circuit layout and the actual motorbike cooling circuit layout in order to find an explanation of the engine critical behaviour. In particular, CFD-CHT analyses of the water cooling jacket are performed, the computational domain covering both the coolant galleries and the surrounding metal components (head, block, gasket, valves, valve seats, valve guides, cylinder liner, spark plug). The contribution of a two-phase approach which takes into account the effect of a phase transition within the engine coolant is considered. Different engine operating conditions are investigated and a detailed analysis of different thermo-mechanical parameters influencing the engine behaviour is carried out. Results of the CFD simulations asses the methodology capability to correctly capture and understand the origin of the engine failure, thus providing a useful design tool for a faster and more effective design modification
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
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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