1,720,957 research outputs found
Ottimizzazione Strutturale nell’Analisi agli Elementi Finiti: Applicazioni in Ambito Automotive per Missioni NVH
No full textI miglioramenti nella progettazione di componenti strutturali sono spesso raggiunti con approccio iterativo guidato dall’esperienza del progettista. Nonostante questo sia un aspetto fondamentale dell’iter progettuale, un approccio completamente fondato sull’esperienza rischia di portare a miglioramenti solo marginali e in tempi generalemente lunghi. Un approccio complementare è quello rappresentato dai metodi di ottimizzazione strutturale per le simulazioni a elementi finiti. In generale, queste tecniche non si prefiggono l’obiettivo di arrivare al prodotto nella sua forma definitiva, ma forniscono suggerimenti concettuali molto utili in vista del suo sviluppo e della sua ingegnerizzazione.
In questo lavoro di tesi tali metodi vengono approfonditi e alcune applicazioni industriali sono presentate e discusse. In particolare, sono stati studiati e ottimizzati singoli componenti e sottostrutture telaistiche prestando particolare attenzione alle prestazioni NVH (Noise, Vibration and Harshness).
Inizialmente viene presentata una metodologia di modellazione agli elementi finiti per materiali smorzanti tramite correlazione numerico-sperimentale. La modellazione proposta ha permesso di testare diverse strategie per ottimizzare la distribuzione di materiale smorzante e la forma delle nervature su un pannello parafiamma (avvalendosi anche di tecniche di sottostrutturazione e di analisi stocastica). Le prove sperimentali condotte hanno inoltre permesso di effettuare un confronto fra il comportamento di alcuni materiali viscoelastici in diverse condizioni di lavoro.
Successivamente, strategie e algoritmi di ottimizzazione strutturale sono stati valutati e confrontati su strutture più complesse, sempre con l'obiettivo di migliorare le prestazioni NVH. In primo luogo, è proposta un'analisi critica dei casi di carico dinamico-lineari considerati come dimensionanti per uno studio di ottimizzazione topologica su telaio completo. Viene quindi presentata una campagna di simulazioni sulla struttura plancia di una vettura a motore posteriore arrivando al confronto tra differenti strategie e domini di ottimizzazione. Le considerazioni raccolte vengono quindi trasferite su casi di interesse industriale: in particolare, tecniche topometriche, parametriche e di sensitività sono state utilizzate al fine di migliorare il comportamento dinamico (frequenze proprie e rigidezza dinamica) dei supporti motore e degli attacchi sospensione di una vettura a motore posteriore: allestimenti diversi del veicolo (telaio, “Body in White” e “Trimmed Body”) e vincoli di manufatturabilità sono stati presi in considerazione e diverse soluzioni progettuali sono state proposte.Improvements in structural components design are often achieved on a trial-and-error basis guided by the designer know-how. Despite the designer experience is a fundamental aspect in design, such an approach is likely to allow only marginal product enhancements. A complementary approach is the one represented by structural optimization methods linked with finite elements analyses. On a general basis these techniques do not deliver the final shape of the product, but they give very useful hints to the designer in view of the product development and engineering.
In the present work, these methods have been deepened and some industrial applications are presented and discussed. In particular, car body structures have been studied and optimized giving particular attention to the NVH (Noise, Vibration and Harshness) performance.
In the beginning, a methodology for tuning a finite elelment damping material model, by means of numerical-experimental correlation, is presented. The simplified modelling obtained has allowed to test different strategies for the optimization of damping material distribution and beads pattern on a vehicle rear bench (making also use of dynamic reduction and robust analysis techniques). The modal tests conducted have also allowed a comparison between the behaviour of different viscoelastic materials in several working conditions.
Subsequently, structural optimization strategies and algorithms have been evaluated and compared dealing with larger structures, always with the aim of improving the NVH performance. Firstly, a critical analysis of the linear dynamic loadcases considered as dimensioning in a full chassis topology optimization is proposed. Then, an extensive campaign of structural optimization simulations involving a car dashboard is reported: a comparison between different strategies and design spaces has been obtained and the lessons learned have been transferred on real industrial cases. In particular, topometry, size and sensitivity techniques have been used in order to improve the behaviour of engine mounts and suspensions attachements of a rear-engine car in terms of natural frequencies and dynamic stiffness: different car configurations (chassis, Body in White and Trimmed Body) and design constraints have been taken into account and several design solutions have been proposed
OPTIMIZATION METHODOLOGY FOR INNOVATIVE AUTOMOTIVE CRASH ABSORBERS
No full textThe simulation of vehicle crash impacts requires accurate and computationally expensive Finite Element analysis. An effective procedure consists in considering and establishing which improvement can be made on an equivalent sub-model of the full vehicle. In this way, all the analysis can be performed on smaller models, thus saving computational time. A full vehicle simulation is required only at the end of the design process to validate the results of the sub-model analysis.A software based on a genetic optimization algorithm has been developed in order to optimize the geometrical parameters of a variable-thickness crash absorber. A numerical study on the folding of thin-walled aluminum tubes with variable-thickness has been performed in order to achieve the maximum energy absorption-to-mass ratio. Moreover, the performance in terms of folding length and crush load peaks have been considered.Different optimization strategies have been implemented to find out which solution guarantees the achievement of the optimization target with the lowest computational cost.The results show how the approach proposed by the authors allows an efficient variable-thickness crash absorber to be obtained. In fact it performs better in term of crash behavior and energy dissipation-to-mass ratio, with respect to the original constant_thickness model
A Sensitivity-Based Approach to Improve Efficiency of Automotive Chassis Architecture
No full textThe strong competition of the automotive market brings the industries to look continuously for more challenging comfort and performance standards. These requirements often contrast with the need for weight reduction related to the restrictive emissions limits. In this scenario, the investments aimed at increasing the structure efficiency (stiffness-to-weight ratio) become fundamental. The objective of this work is to propose a methodology that allows to identify the most important chassis areas in terms of efficiency: The design and research efforts could then be focused on the real determinant parts. This is done through a sensitivity process that works on frame subsystems and then on each component, first varying the material properties and then the thickness (and so the mass). The designing loadcases considered are the torsional stiffness, bending stiffness, modal analysis and frequency response analysis. The results show which are the most important subsystems and components that affects the chassis efficiency and that will have to be re-designed in order to improve the current architecture
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
Simplified modeling technique for damping materials on light structures: Experimental analysis and numerical tuning
No full textSpecific polymeric and asphaltic materials are widely used for NVH automotive applications. If patches of such materials are properly collocated on vehicle's panels, they are able to improve significantly noise and vibration performance by modulating damping and stiffness. This work presents a methodology for tuning a FE composite model, using optimization techniques to improve the correlation with the experimental modal tests performed. In particular, plain and ribbed aluminum plates have been considered for several covering ratios of three damping materials. The correlation between numerical and experimental data is achieved by monitoring dynamic parameters such as natural frequencies, mode shapes, and frequency response functions (FRFs). The optimization strategy consists of two steps and makes use of evolutionary and gradient-based algorithms. LMS Virtual.Lab® is used in this part of the work as an environment for correlation and optimization. In order to verify the reliability of the correlation, modal tests are performed on a particular vehicle's panel. Copyright © 2013 by ASME
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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