1,721,032 research outputs found
Applicability and Limitations of Ru’s Formulation for Vibration Modelling of Double-Walled Carbon Nanotubes
Full text linkIn this paper, a comparison is conducted between two different formulations of the van der Waals interaction coefficient between layers, as applied to the vibrations of double-walled carbon nanotubes (DWCNTs); specifically, the evaluation of the natural frequencies is achieved through Ru’s and He’s formulations. The actual discrete DWCNT is modelled by means of a couple of concentric equivalent continuous thin cylindrical shells, where Donnell shell theory is adopted to obtain strain-displacement relationships. In order to take into account the chirality effect of DWCNT, an anisotropic elastic shell model is considered. Simply supported boundary conditions are imposed and the Rayleigh–Ritz method is used to obtain approximate natural frequencies and mode shapes. A parametric analysis considering different values of diameters and numbers of waves along longitudinal and circumferential directions is performed by adopting Ru’s and He’s formulations. From the comparisons, it is evident that Ru’s formulation provides unsatisfactory results for relatively low values of diameters and relatively high numbers of circumferential waves with respect to the more accurate He’s formulation. This behaviour is observed for every number of longitudinal half-waves. Therefore, Ru’s formulation cannot be used for the vibration modelling of DWCNTs in a large range of diameters and wavenumbers
Nonlinear vibrations of functionally graded circular cylindrical shells subjected to harmonic external load
No full textThe nonlinear vibrations of functionally graded (FGM) circular cylindrical shells are analysed. The Sanders-Koiter theory is applied in order to model the nonlinear dynamics of the system. The shell deformation is described in terms of longitudinal, circumferential and radial displacement fields. Simply supported boundary conditions are considered. The displacement fields are expanded by means of a double mixed series based on Chebyshev polynomials for the longitudinal variable and harmonic functions for the circumferential variable. Both driven and companion modes are considered. Numerical analyses are carried out in order to characterize the nonlinear response when the shell is subjected to a harmonic external load. A convergence analysis is carried out to obtain the correct number of axisymmetric and asymmetric modes describing the actual nonlinear behaviour. The influence of the material distribution on the nonlinear response is analysed considering different configurations and volume fractions of the constituent materials. The effect of the companion mode participation on the nonlinear response of the shell is analysed
Nonlinear vibration of functionally graded cylindrical shells: effect of constituent volume fractions and configurations
No full textIn this paper, the nonlinear vibration of functionally graded (FGM) cylindrical shells under different constituent volume fractions and configurations is analyzed. The Sanders-Koiter theory is applied to model nonlinear dynamics of the system in the case of finite amplitude of vibration. The shell deformation is described in terms of longitudinal, circumferential and radial displacement fields. Simply supported boundary conditions are considered. Displacement fields are expanded by means of a double mixed series based on harmonic functions for the circumferential variable and Chebyshev polynomials for the longitudinal variable. Both driven and companion modes are also considered, allowing for the travelling-wave response of the shell. The functionally graded material considered is made of stainless steel and nickel, properties are graded in the thickness direction according to a real volume fraction power-law distribution. In the nonlinear model, shells are subjected to an external radial excitation. Nonlinear vibrations due to large amplitude of excitation are considered. Specific modes are selected in the modal expansions; a dynamical nonlinear system is then obtained. Lagrange equations are used to reduce nonlinear partial differential equations to a set of ordinary differential equations, from the potential and kinetic energies, and the virtual work of the external forces. Different geometries are analyzed; amplitude-frequency curves are obtained. Convergence tests are carried out considering a different number of asymmetric and axisymmetric modes. The present model is validated in linear field (natural frequencies) by means of data present in the literature
Nonlinear vibrations of functionally graded cylindrical shells
Full text linkIn this paper, the nonlinear vibrations of functionally graded (FGM) circular cylindrical shells are analysed. The Sanders–Koiter theory is applied to model the nonlinear dynamics of the system in the case of finite amplitude of vibration. The shell deformation is described in terms of longitudinal, circumferential and radial displacement fields. Simply supported, clamped and free boundary condi- tions are considered. The displacement fields are expanded by means of a double mixed series based on Chebyshev orthogonal polynomials for the longitudinal variable and harmonic functions for the circumferential variable. Both driven and companion modes are considered; this allows the travelling- wave response of the shell to be modelled. The model is validated in the linear field by means of data retrieved from the pertinent literature. Numerical analyses are carried out in order to characterise the nonlinear response when the shell is subjected to a harmonic external load; a convergence analysis is carried out by considering a variety of axisymmetric and asymmetric modes. The present study is focused on determining the nonlinear character of the shell dynamics as the geometry (thickness, radius, length) and material properties (constituent volume fractions and configurations of the constituent materials) vary
Manuale per la lean excellence. Guida alla trasformazione aziendale ed all'applicazione pratica del pensiero snello
No full textWhen I wrote the original Toyota Way in 2003 I was trying to correct a major
misunderstanding. Most books about lean were describing a litany of tools. Do 5S, set
up cells, design a kanban system, install an Andon system to stop the line for quality problems, and more. Every new idea became a tool. Hoshin Kanri automatically
meant fill out an X-matrix. Standardized work meant find the proper form and fill in
the steps and times. Even an organizational design change like work groups were
something to install. In fact many companies still judge the “leanness” of an operation by auditing relative to a checklist of lean tools. The message was do these things
and you will be lean. And the goal was to do them as quickly as possible as broadly as
possible. “Lean conversions” meant that you had installed all this lean stuff and got a
good grade on the checklist.
In the meantime I had been studying Toyota for almost twenty years and the
message they gave was the exact opposite. The Toyota Production System is not
about implementing tools, but about developing people to strive for excellence, by
experimenting and learning. One-piece flow is an ideal to strive for-perfect, uninterrupted flow to the customer without waste. People must learn to set high, even seemingly unachievable goals in that direction and be persistent in working to achieve
them. Along the way various tools will be useful but the specific ones, their timing,
and their sequence will vary depending on the situation. You do not send a carpenter
out to first do a bunch of hammering, and then go through and screw in a bunch of
things in for a while, and hope the result is a house. Similarly the TPS house cannot be
build by poorly trained people whose main skill is they learned how the tool works
from a book or short course. They need a level of mastery of the art of lean to achieve
the critical goals of the organization, whatever those are
Quantitative methods for quality management
No full textThis book is intended to offer a theoretical support and a practical guide to understand and use a wide set of quantitative tools for Quality Management. The most common tools and methods are first explained and then applied in industrial examples: Basic Statistics, Graphical Approach, Pareto, Hypothesis Testing, ANOVA, DoE, Control Chart, Acceptance Sampling are some of the covered topics. The goal of this book is to provide the readers both with theory recall and examples of application to understand the approach and master the application. Thus the book is projected to be a useful resource for both students and practitioners in manufacturing and service operations. Students will find the ideal support and guidance for getting confident with the subject, while practitioners will be provided with theoretical and practical insights to deeply understand the ground on which most of commonly used quality tools are built on. The book will explain the topics starting from the easiest-to-understand, gradually increasing the level of complexity in the tools and in the numerical examples. This third edition of the book has widened the theory support and re-organized the topics. This new organization will both support a deeper understanding of the statistical basics and facilitate the mastering of the more complex quality tools
Manuale Six Sigma per le Green Belt
Full text linkLa gestione della qualità passa per il miglioramento dei processi aziendali. Il Six Sigma si è dimostrato essere uno dei sistemi più efficaci per raggiungere l’eccellenza operativa, grazie ai risultati raggiunti sia dalle grandi multinazionali, sia dalle aziende più piccole pronte al cambiamento. Grazie alla rivoluzionaria combinazione di organizzazione, metodo, gestione dei progetti, strumenti qualitativi e strumenti quantitativi, il Six Sigma ha definito un organismo vincente innovazioni dei processi e la gestione del miglioramento. Questo manuale offre una panoramica completa sul Six Sigma, una guida pratica utilizzo del metodo email e degli strumenti per la risoluzione dei problemi e innovazione dei processi ed una serie di casi aziendali esemplari per toccare con mano i risultati ottenuti in diversi settori. Per la vastità e la completezza dei temi trattati il manuale è un valido supporto per contenimento della certificazione Green Belt
Manuale Six Sigma per le Black Belt
Full text linkIl Six Sigma è uno dei sistemi più efficaci per raggiungere l’operational excellence, che ha trasformato la gestione della qualità in un inesauribile centro di profitto per aziende grazie al miglioramento ed innovazione dei processi. Questo manuale completa quanto già affrontato nel precedente e complementare manuale Six Sigma per le Green Belt, presentando il Six Sigma come un modello organico di Change Management. La dotazione tecnica necessaria per raggiungere il livello di preparazione tipico delle Black Belt viene arricchita con strumenti di programma e Project Management, advanced root cause analysis, valutazione finanziaria, analisi quantitativa e statistica fino a toccare temi di leadership e soft skills. A compendio della trattazione teorica, vengono presentati alcuni casi aziendali particolarmente interessanti per complessità di implementazione e vastità dei risultati. Per la completezza dei temi ed il livello di approfondimento, il presente manuale è un valido supporto per contenimento della certificazione Black Belt
Effect of the geometry on the nonlinear vibrations of functionally graded cylindrical shells
No full textIn this paper, the effect of the geometry on the nonlinear vibrations of functionally graded (FGM) cylindrical shells is analyzed. The Sanders-Koiter theory is applied to model nonlinear dynamics of the system in the case of finite amplitude of vibration. Shell deformation is described in terms of longitudinal, circumferential and radial displacement fields; the theory considers geometric nonlinearities due to the large amplitude of vibration. Simply supported boundary conditions are considered. The displacement fields are expanded by means of a double mixed series based on harmonic functions for the circumferential variable and Chebyshev polynomials for the longitudinal variable. Both driven and companion modes are considered, allowing for the travelling-wave response of the shell. The functionally graded material is made of a uniform distribution of stainless steel and nickel, the material properties are graded in the thickness direction, according to a volume fraction power-law distribution.The first step of the procedure is the linear analysis, i.e. after spatial discretization mass and stiff matrices are computed and natural frequencies and mode shapes of the shell are obtained, the latter are represented by analytical continuous functions defined over all the shell domain. In the nonlinear model, the shell is subjected to an external harmonic radial excitation, close to the resonance of a shell mode, it induces nonlinear behaviors due to large amplitude of vibration. The three displacement fields are re-expanded by using approximate eigenfunctions, which were obtained by the linear analysis; specific modes are selected. An energy approach based on the Lagrange equations is considered, in order to reduce the nonlinear partial differential equations to a set of ordinary differential equations.Numerical analyses are carried out in order characterize the nonlinear response, considering different geometries and material distribution. A convergence analysis is carried out in order to determine the correct number of the modes to be used; the role of the axisymmetric and asymmetric modes carefully analyzed. The analysis is focused on determining the nonlinear character of the response as the geometry (thickness, radius, length) and material properties (power-law exponent and configurations of the constituent materials) vary; in particular, the effect of the constituent volume fractions and the configurations of the constituent materials on the natural frequencies and nonlinear response are studied.Results are validated using data available in literature, i.e. linear natural frequencies
Vibrations of Carbon Nanotubes: nonlinear models and energy distribution
No full textVibrations of Single-Walled Carbon Nanotubes for various boundary conditions are considered in the framework of the Sanders-Koiter thin shell theory. A double series expansion of displacement fields, based on the Chebyshev orthogonal polynomials and harmonic functions, is used to analyse numerically the natural frequencies of shells having free or clamped edges. A reduced form of the Sanders-Koiter theory is developed by assuming small circumferential and shear deformations; such approach allows to determine an analytical solution for the natural frequencies. The numerical model is validated with the results of molecular dynamics and finite element analyses present in literature. The analytical model is validated by means of comparisons with the numerical approach. Nonlinear vibrations and energy distribution of carbon nanotubes are then considered
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