VALERIA SETTIMI

Pubblicazioni

VALERIA SETTIMI

 

38 pubblicazioni classificate nel seguente modo:

Nr. doc. Classificazioni
18 1 Contributo su Rivista
16 4 Contributo in Atti di Convegno (Proceeding)
4 2 Contributo in Volume
Anno
Risorse
2021
Global dynamics perspective on macro- to nano-mechanics
NONLINEAR DYNAMICS
Autore/i: Rega, G.; Settimi, V.
Classificazione: 1 Contributo su Rivista
Abstract: In about the last two decades, global nonlinear dynamics has been evolving in a revolutionary way, with the development of sophisticated techniques employing concepts/tools of dynamical systems, bifurcation, and chaos theory, and applications to a wide variety of mechanical/structural systems. The relevant achievements entail a substantial change of perspective in dealing with vibration problems and are ready to meaningfully affect the analysis, control, and design of systems at different scales, in multiphysics contexts too. After properly framing the subject within some main stages of developments of nonlinear dynamics in solid/structural mechanics, as occurred over the last 40 years, the article focuses on highlighting the role played by global analysis in unveiling the nonlinear response and actual safety of engineering systems in different environments. Reduced order models of macro-/micro-structures are considered. Global dynamics of a laminated plate with von Kármán nonlinearities, shear deformability, and full thermomechanical coupling allows to highlight the meaningful effects entailed by the slow transient thermal dynamics on the fast steady mechanical responses. An atomic force microcantilever is referred to for highlighting the severe worsening of overall stability associated with the application of an external feedback control and the importance of global dynamics for conceiving and effectively implementing a control procedure aimed at enhancing engineering safety. The last part of the article dwells on the general role that a global dynamics perspective is expected to play in the safe design of real systems, in the near future, focusing on how properly exploiting concepts and tools of dynamical integrity to evaluate response robustness in the presence of unavoidable imperfections, and to improve the system’s actual load carrying capacity.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290325 Collegamento a IRIS

2021
Nonlinear dispersion properties of one-dimensional mechanical metamaterials with inertia amplification
INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES
Autore/i: Settimi, V.; Lepidi, M.; Bacigalupo, A.
Classificazione: 1 Contributo su Rivista
Abstract: Architected metamaterials offering superior dynamic performances can be conceived by inducing local mechanisms of inertia amplification in the periodic microstructure. A one-dimensional cellular lattice characterized by a pantograph mechanism in the tetra-atomic cell is proposed as minimal physical realization of inertially amplified metamaterial. A discrete model is formulated to describe the undamped free dynamics of the cell microstructure. The ordinary differential equations of motion feature quadratic and cubic inertial nonlinearities, induced by the indeformability of the pantograph arms connecting the principal atoms with the secondary atoms, serving as inertial amplifiers. An asymptotic approach is employed to analytically determine the dispersion properties governing the free propagation of harmonic waves in the pantographic metamaterial. First, the linear wavefrequencies and waveforms are obtained by solving the eigenproblem governing the lowest asymptotic order. An invariant parametric form is achieved for the pass and stop band structure, corresponding to propagation and attenuation branches of the dispersion spectrum in the plane of complex wavenumbers. The major effects due to the mass ratio of the inertial amplifiers are discussed. Particularly, the existence conditions, amplitude and centerfrequency of the band gap separating the acoustic and optical pass bands are determined analytically. Second, the nonlinear wavefrequencies and waveforms are obtained by solving the hierarchical linear problems governing the higher asymptotic orders. Analytical, although asymptotically approximate, functions are achieved for the nonlinear wavefrequencies and waveforms, which show quadratic dependence on the oscillation amplitudes. The mechanical conditions for the softening/hardening behaviour of the nonlinear wavefrequencies and the different topological properties of the invariant manifolds associated to the nonlinear waveforms are discussed. Finally, numerical simulations are provided to validate the analytical results.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/291929 Collegamento a IRIS

2020
Modeling and nonlinear dynamics of thermomechanically coupled composite plates
INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES
Autore/i: Rega, G.; Saetta, E.; Settimi, V.
Classificazione: 1 Contributo su Rivista
Abstract: An overview of extended research recently pursued on unified continuous/reduced-order modeling and nonlinear dynamics of thermomechanical composite plates of interest in aerospace, mechanical and civil engineering is presented. Reduced models exhibit the fundamental features of geometrical nonlinearity and thermomechanical coupling of the underlying continua. The role of multiphysics coupling and the main features of nonlinear response obtained with variably refined minimal models is highlighted. Besides transverse mechanical excitation and mechanically or thermally-induced buckling, a variety of active thermal excitations, of body or boundary nature, are considered. Features of thermal response obtained with variably refined thermal assumptions are compared, in view of detecting cheap, yet reliable, models to be used for systematic numerical investigations. The effects of two-way thermomechanical coupling on local and global nonlinear dynamics are addressed through bifurcation diagrams, phase portraits and planar cross sections of 4D basins of attraction, highlighting the important role played by the slow transient thermal dynamics solely detectable with coupled models in the steady outcome of the swifter mechanical response. Conditions allowing to utilize partially coupled models or even the uncoupled mechanical one with prescribed steady temperature are discussed.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290324 Collegamento a IRIS

2020
Minimal thermal modeling of two-way thermomechanically coupled plates for nonlinear dynamics investigation
JOURNAL OF THERMAL STRESSES
Autore/i: Saetta, E.; Settimi, V.; Rega, G.
Classificazione: 1 Contributo su Rivista
Abstract: Minimal thermal modeling of two-way thermomechanically coupled plates is addressed in the framework of a unified formulation of the underlying continuum problem. Variably refined reduced-order models are considered, and some main features of the relevant transient and steady responses to a variety of active thermal sources are investigated, by properly reconstructing 3D temperature configurations and energy balances. In comparison with a richer reduced model and available analytical solutions, a model with assumed cubic temperature distribution along the thickness has the advantage of being the minimal one still allowing to consider a wide set of boundary and body thermal excitations, while showing a comprehensive capability to reliably describe the thermal response. This appears of particular interest also in view of further pursuing a systematic, yet computationally demanding, investigation of the nonlinear dynamics of the coupled plate, in the cheapest possible way from both the mechanical and thermal viewpoint.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290312 Collegamento a IRIS

2020
Nonlinear dynamics of a third-order reduced model of thermomechanically coupled plate under different thermal excitations
MECCANICA
Autore/i: Settimi, V.; Saetta, E.; Rega, G.
Classificazione: 1 Contributo su Rivista
Abstract: Thermoelastic analysis of a shear deformable reduced model of laminated plates with von Kármán nonlinearities and cubic temperature along the thickness is presented. Parametric investigation of the response is accomplished by means of bifurcation diagrams, phase portraits and planar cross sections of the four-dimensional basins of attraction, in order to describe the local and global dynamical behavior of the model. Different scenarios induced by the boundary conditions are highlighted, along with the effect of a different modeling of temperature distribution (constant/dome-shape) on the system response.The effects of diverse (boundary/body) thermal sources are also comparatively explored. In all examined cases, proper consideration of system global dynamics is shown to be essential for reliably unveiling transient to steady effects due to thermomechanical coupling.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290323 Collegamento a IRIS

2020
Unveiling Transient to Steady Effects in Reduced Order Models of Thermomechanical Plates via Global Dynamics
IUTAM Bookseries
Autore/i: Settimi, V.; Rega, G.; Saetta, E.
Editore: Springer
Classificazione: 2 Contributo in Volume
Abstract: A reduced model of third-order shear deformable plate with cubic temperature is used to investigate the system nonlinear dynamic response in a full thermomechanical coupling framework. Numerical investigations of local and global dynamics allow to highlight distinct response features as occurring under different (constant or dome-shaped) prescribed spatial temperatures on the plate surfaces. In both cases, the important role played by global analysis for unveiling meaningful transient to steady effects in the system dynamics clearly comes out.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290326 Collegamento a IRIS

2019
Dynamical properties of a composite microcracked bar based on a generalized continuum formulation
CONTINUUM MECHANICS AND THERMODYNAMICS
Autore/i: Settimi, Valeria; Trovalusci, Patrizia; Rega, Giuseppe
Classificazione: 1 Contributo su Rivista
Abstract: The dynamical behavior of a mono-dimensional bar with distributed microcracks is addressed in terms of free and forced wave propagation. The multiscale model, derived from a generalized continuum formulation, accounts for the microstructure by means of a microdisplacement variable, added to the standard macrodisplacement, and of internal parameters representing density and length of microcracks. The influence of coupling between micro- and macrodisplacement overall response on the system is discussed, as well as the effect of the damage parameters on the propagating waves.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290281 Collegamento a IRIS

2018
High order asymptotic dynamics of a nonlinearly coupled electromechanical system
JOURNAL OF SOUND AND VIBRATION
Autore/i: Settimi, V; Romeo, F
Classificazione: 1 Contributo su Rivista
Abstract: A nonlinearly coupledmathematicalmodel of an electro-magneto-mechanical systemis studied via the multiple scale approach in order to investigate its weakly nonlinear dynamics and analytically predict its salient features. The obtained amplitude modulation equations up to the third order perturbation allow to analytically describe the mechanical and electrical responses in terms of frequency-response curves and stability scenarios. A critical threshold of Hopf bifurcation is detected and analyzed as a function of the main system parameters. The subsequent extension of the asymptotic scheme up to the fifth order proves to grasp also the post-critical behavior, providing with the accurate identification of the amplitude of the quasiperiodic responses characterizing the unstable region of the ordinary differential equations system.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290277 Collegamento a IRIS

2018
Avoiding/inducing dynamic buckling in a thermomechanically coupled plate: a local and global analysis of slow/fast response
PROCEEDINGS OF THE ROYAL SOCIETY OF LONDON. SERIES A
Autore/i: Settimi, V; Rega, G; Saetta, E
Classificazione: 1 Contributo su Rivista
Abstract: The nonlinear response of a reduced model of an orthotropic single-layered plate with thermomechanical coupling is investigated in the presence of thermal excitations, in addition to mechanical ones. Different issues are addressed via accurate and extended local and global analyses. (i) Assessing the possible occurrence, disappearance or modification of mechanical buckling as a result of thermal aspects; (ii) exploiting global dynamics to unveil the effects of coupling; (iii) highlighting the crucial role played by the slow thermal transient evolution in modifying the fast steady mechanical response; (iv) framing the influence of coupling and underlining the need to use a thermomechanical model to grasp the actual plate dynamics; and (v) getting hints of technical interest as to the outcome robustness with respect to variations in the external/internal thermal parameters.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290284 Collegamento a IRIS

2018
Dynamic regimes of a nonlinearly coupled electromechanical system
INTERNATIONAL JOURNAL OF NON-LINEAR MECHANICS
Autore/i: Settimi, V; Romeo, F
Classificazione: 1 Contributo su Rivista
Abstract: The dynamics of a nonlinearly coupled electro-magneto-mechanical system is numerically investigated with the aim to obtain a comprehensive description of its behavior in strongly nonlinear regime. Bifurcation diagrams and stability charts as a function of the main system parameters allow to detect several multistable and unstable regions, characterized by coexistence of low-amplitude and high-amplitude responses, and by the presence of wide ranges of chaotic motions, which have been connoted by computing the relevant Lyapunov characteristic exponents.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290291 Collegamento a IRIS

2018
Local and global nonlinear dynamics of thermomechanically coupled composite plates in passive thermal regime
NONLINEAR DYNAMICS
Autore/i: Settimi, V; Saetta, E; Rega, G
Classificazione: 1 Contributo su Rivista
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290296 Collegamento a IRIS

2018
Local versus global dynamics and control of an AFM model in a safety perspective
Global Nonlinear Dynamics for Engineering Design and System Safety
Autore/i: Settimi, V.; Rega, G.
Classificazione: 2 Contributo in Volume
Abstract: The role of local and global dynamics to assess a system robustness and actual safety in operating conditions is investigated, by also studying the effect of different local and global control techniques on the nonlinear behavior of a noncontact AFM. Firstly, the nonlinear dynamical behavior of a single-mode model of noncontact AFM is analyzed in terms of stability of the main periodic solutions, as well as attractors robustness and basins integrity. To the same AFM model, an external feedback control is inserted during its nonlinear continuum formulation, with the aim to keep the system response to an operationally suitable one. The dynamical analysis of the controlled system is developed to investigate and verify the effects of control into the system overall behavior, which could be unexpectedly influenced by the local nature of the control technique. A different control technique is finally applied to the AFM model, acting on global bifurcation events to obtain an enlargement of the systems safe region in parameters space. The analytical procedure, based on Melnikov method, is applied to the homoclinic bifurcation involving the system hilltop saddle, and its practical effects as regards possibly increasing the system overall robustness are numerically investigated by means of a dynamical integrity analysis. Then, a fully numerical procedure is implemented to possibly control global bifurcations involving generic saddles. The method proves to succeed in delaying the drop down of the erosion profile, thus increasing the overall robustness of the system during operating conditions.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290272 Collegamento a IRIS

2018
High order asymptotic dynamics of a nonlinearly coupled electromechanical system
JOURNAL OF SOUND AND VIBRATION
Autore/i: Settimi, Valeria; Romeo, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: A nonlinearly coupled mathematical model of an electro-magneto-mechanical system is studied via the multiple scale approach in order to investigate its weakly nonlinear dynamics and analytically predict its salient features. The obtained amplitude modulation equations up to the third order perturbation allow to analytically describe the mechanical and electrical responses in terms of frequency-response curves and stability scenarios. A critical threshold of Hopf bifurcation is detected and analyzed as a function of the main system parameters. The subsequent extension of the asymptotic scheme up to the fifth order proves to grasp also the post-critical behavior, providing with the accurate identification of the amplitude of the quasiperiodic responses characterizing the unstable region of the ordinary differential equations system.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290294 Collegamento a IRIS

2018
Thermomechanical coupling and transient to steady global dynamics of orthotropic plates
Problems of Nonlinear Mechanics and Physics of Materials
Autore/i: Settimi, Valeria; Rega, Giuseppe
Editore: Springer Verlag
Classificazione: 2 Contributo in Volume
Abstract: Different reduced order models of thermomechanically coupled von Kármán shear indeformable plate with prescribed linear temperature along the thickness are comparatively investigated in terms of local and global dynamics exhibited in active thermal regime, under harmonic transverse and constant axial mechanical excitations. Two-d.o.f. one-way coupled models are then used for “economical” yet reliable numerical investigation of the nonlinear dynamic response in terms of the mechanical variable and of the dominant (membrane or bending) thermal variable, under the corresponding thermal excitations inducing variably rich scenarios of buckled mechanical response. Attention is focused on the important role played by global dynamics in unveiling the meaningful effects entailed on the structure steady mechanical response by the variably slow thermal transients taken into account by the thermomechanically coupled model.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290276 Collegamento a IRIS

2017
Effects of the thermomechanical coupling on the nonlinear dynamics of a reduced order model of composite plate
AIMETA 2017 - XXIII Congresso Associazione Italiana di Meccanica Teorica e Applicata
Autore/i: Settimi, V; Saetta, E; Rega, G
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290292 Collegamento a IRIS

2017
Passive/active thermal dynamics in the coupled nonlinear vibrations of laminated plates
ENOC 2017: 9th European Nonlinear Dynamics Conference
Autore/i: Settimi, V; Saetta, E; Rega, G
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290275 Collegamento a IRIS

2017
Nonlinear dynamics and control in macro/micro-mechanics: some computational issues
22nd International Conference on Computer Methods in Mechanics. Short papers
Autore/i: Rega, Giuseppe; Settimi, Valeria
Editore: Lublin University of Technology
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: Computational issues in the global dynamics of two systems in micro- and macro-mechanics, with different dimensionality, are addressed. Attention is focused on calculation of integrity measures, determination of saddle manifolds undergoing global bifurcations, implementation of a control procedure for delaying basins erosion, selection of 2D cross-sections of multidimensional basins of attraction for understanding the role of transient dynamics in the global scenario of coupled steady responses.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290278 Collegamento a IRIS

2017
Nonlinear vibrations of symmetric cross-ply laminates via thermomechanically coupled reduced order
PROCEDIA ENGINEERING
Autore/i: Saetta, E; Settimi, V; Rega, G
Classificazione: 1 Contributo su Rivista
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290293 Collegamento a IRIS

2017
Response robustness and safety against jump to contact in AFMs controlled via different techniques
PROCEDIA IUTAM
Autore/i: Settimi, V; Rega, G
Classificazione: 1 Contributo su Rivista
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290269 Collegamento a IRIS

2016
Global dynamics-based control of a noncontact atomic force microcantilever
6th International Conference on Nonlinear Vibrations, Localization and Energy Transfer
Autore/i: Settimi, V; Rega, G; Lenci, S
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290297 Collegamento a IRIS

2016
Response robustness and safety against jump to contact in AFMs controlled via different techniques
IUTAM Symposium on Nonlinear and Delayed Dynamics of Mechatronic Systems
Autore/i: Settimi, V; Rega, G
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290299 Collegamento a IRIS

2016
Control of global bifurcations in a noncontact atomic force microcantilever
International Conference on Structural Nonlinear Dynamics and Diagnosis
Autore/i: Settimi, V; Rega, G; Lenci, S
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290271 Collegamento a IRIS

2016
Global dynamics and integrity in noncontacting atomic force microscopy with feedback control
NONLINEAR DYNAMICS
Autore/i: Settimi, Valeria; Rega, Giuseppe
Classificazione: 1 Contributo su Rivista
Abstract: Dynamical integrity of a noncontact AFM model with external feedback control is investigated to evaluate the effects of such local control procedure on the erosion of the basins of attraction of the system bounded solutions. Two-dimensional cross sections of the five-dimensional basins of attraction have been systematically constructed, and the relevant erosion profiles are obtained for the parametrically excited system. The outcomes, summarized by the so-called isointegrity curves (i.e., frequency-dependent thresholds with constant residual integrity which actually represent the system practical safety), highlight that around the resonance frequencies, the system undergoes a worsening of its practical stability, with respect to variations in the forcing amplitude and the tip–sample distance, as well, thus underlining the importance of a global analysis to assess the system actual safety in operating conditions.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290300 Collegamento a IRIS

2016
Exploiting global dynamics of a noncontact atomic force microcantilever to enhance its dynamical robustness via numerical control
INTERNATIONAL JOURNAL OF BIFURCATION AND CHAOS IN APPLIED SCIENCES AND ENGINEERING
Autore/i: Settimi, V; Rega, G
Classificazione: 1 Contributo su Rivista
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290289 Collegamento a IRIS

2016
Influence of a locally-tailored external feedback control on the overall dynamics of a non-contact AFM model
INTERNATIONAL JOURNAL OF NON-LINEAR MECHANICS
Autore/i: Settimi, V; Rega, G
Classificazione: 1 Contributo su Rivista
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290273 Collegamento a IRIS

2015
Global dynamics effects of a feedback control of noncontact atomic force microscopy
Proceedings of the ASME 2015 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference - IDETC/CIE 2015
Autore/i: Settimi, V; Rega, G
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290295 Collegamento a IRIS

2015
Global control of a noncontact atomic force microcantilever
AIMETA 2015 - XXII Congresso Associazione Italiana di Meccanica Teorica e Applicata
Autore/i: Settimi, V; Rega, G; Lenci, S
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290290 Collegamento a IRIS

2015
External feedback control of a noncontact AFM and its effects on global dynamics
AIMETA 2015 - XXII Congresso Associazione Italiana di Meccanica Teorica e Applicata
Autore/i: Settimi, V; Rega, ; G,
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290283 Collegamento a IRIS

2015
Dynamical integrity of noncontact AFM with external feedback control
Euromech Colloquium 562 – Stability and Control of Nonlinear Vibrating Systems
Autore/i: Settimi, V; Rega, G
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290287 Collegamento a IRIS

2015
Global dynamics effects of a feedback control of noncontact atomic force microscopy
Proceedings of the ASME 2015 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference - IDETC/CIE 2015
Autore/i: Settimi, Valeria; Rega, Giuseppe
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: Dynamical integrity of a noncontact AFM model with external feedback control is investigated to evaluate the effects of such local control procedure on the erosion of the basins of attraction of the system bounded solutions. The outcomes highlight that around the resonance frequencies the system undergoes a worsening of its practical stability, with respect to variations of the forcing amplitude and the tip-sample distance, as well, thus underlining the importance of a global analysis to assess the system actual safety in operating conditions.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290280 Collegamento a IRIS

2015
Asymptotic analysis of a noncontact AFM microcantilever sensor with external feedback control
NONLINEAR DYNAMICS
Autore/i: Settimi, V; Gottlieb, O; Rega, G
Classificazione: 1 Contributo su Rivista
Abstract: An external feedback control is inserted in a nonlinear continuum formulation of a noncontactAFM model. The aim of the feedback is to keep the system response to an operationally suitable one, thus allowing reliable measurement of the sample surface by avoiding possible unstable microcantilever sensor motions. The study of the weakly nonlinear system dynamics about the desired fixed point close to primary resonance is carried out via multiple-scale asymptotics, whose outcomes are validated via numerical simulations of the original system equations of motion. The latter include controllable periodic dynamics and additional periodic and distinct quasiperiodic solutions that appear beyond the asymptotic stability thresholds. The results highlight the effectiveness of the applied feedback control technique and also enable the derivation of a comprehensive system bifurcation structure highlighting the stability thresholds for robust controllable AFM dynamics.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290286 Collegamento a IRIS

2014
Controlling local and global dynamics of noncontact atomic force microscopes
Proc. ENOC 2014 - 8th European Nonlinear Dynamics Conference
Autore/i: Settimi, V.; Rega, Giuseppe
Editore: Horst Ecker, Alois Steindl, Stefan Jakubek
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: The strongly nonlinear dynamics of a noncontact AFM model with external feedback control is analyzed with the aim to achieve a description of its local and global dynamical behavior, and to realize a comparison with the results of the underlying uncontrolled system. As a result, the critical evaluation of the effectiveness of the control actuation is presented and the need to pursue an actually global control of the dynamics if solely bounded system responses are practically acceptable is highlighted.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290274 Collegamento a IRIS

2014
Numerical Analyses in the Nonlinear Dynamics and Control of Microcantilevers in Atomic Force Microscopy
Atti XX Convegno Nazionale di Meccanica Computazionale VII Riunione del Gruppo Materiali AIMETA
Autore/i: Settimi, V.; Rega, Giuseppe
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: It is well known in the literature that AFMs operating in dynamic mode can exhibit several nonlinear phenomena, such as bifurcations, in-well instability regions and eventually chaotic motion, that are common to many other dynamical systems and represent an undesirable behavior which restricts the operating range of many electronic and mechanical devices. The deep investigation of their dynamical bifurcation behavior as a function of the main system parameters is thus a topic of great theoretical and practical importance, not only to frame such systems in the literature scene, but also because its potentiality in enhancing performance, effectiveness, reliability and safety of systems is crucial to the aim of developing novel design criteria. In this perspective, the nonlinear response of a single-mode model of noncontact AFM has been analyzed by making use of several computational tools, in order to investigate the evolution of the main system periodic solutions and relevant basins of attraction under variations of the most significant system parameters. Different numerical simulations and continuation techniques have been employed (using Dynamics software and AUTO software) taking into account the presence of the horizontal parametric excitation and of the vertical external one, separately. Several bifurcation diagrams have been obtained in a large range of forcing frequencies which includes the fundamental (primary) and principal (subharmonic) parametric (external) resonances, whereby the main periodic solutions and local bifurcations have been detected thanks to the Floquet multipliers computation. The local bifurcation loci have been summarized in behavior charts, which report also the system stability threshold obtained as the envelope of local bifurcation escape thresholds in different parameter ranges. Moreover, erosion process of the basins of attraction of the various solutions, which is indeed a critical issue corresponding to system impending escape (corresponding to the unwanted jump-to-contact) and thus governing its practical safety, is investigated by applying the dynamical integrity concepts. Thanks to the analysis of basins of attraction evolution, and making use of specific computational tools such as the evaluation of different integrity measures (GIM and IF), several erosion profiles have been obtained as a function of the increasing excitation amplitude, with the aim to detect thresholds of residual integrity able to ensure acceptable safety targets established a priori according to the required system performances. The topic of controlling undesirable system dynamical responses is then addressed through the insertion in the AFM model of an external feedback control technique, with the aim to take the system response to a selected reference one. The periodic motion used as reference in the control procedure is chosen to be the response of the corresponding uncontrolled system, for which the previous analyses have already allowed to detect the main stability regions in various parameters planes. Upon checking the effectiveness of the procedure in the weakly nonlinear regime via a perturbation approach, the description of bifurcation/response scenarios of the controlled system under scan excitation up to the strongly nonlinear regime, and the critical comparison with the results related to the uncontrolled system permit to highlight the influence of the applied control on the overall dynamical behavior of the AFM system, and provide indications to refer to in practical applications.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290288 Collegamento a IRIS

2013
Influence of the external feedback control on the bifurcation and escape scenario of a single-mode model of noncontact AFM
Proc. AIMETA 2013-XXI Congresso Associazione Italiana di Meccanica Teorica e Applicata
Autore/i: Settimi, V.; Rega, Giuseppe
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: The effects of the external feedback control on a single mode model of noncontact AFM in terms of modification of its nonlinear dynamical behavior are analyzed via several bifurcation analyses. Numerical simulations are carried out as a function of the excitation amplitude and of the feedback control parameter for different values of the forcing frequency, and allow one to detect the system stability boundary as the envelope of the obtained local escape thresholds. In particular, the interest is devoted to analyze the effect of the control on modifying the region of stability of the bounded solutions, and to make a comparison with the results obtained for the uncontrolled system, which has been already analyzed by the authors.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290282 Collegamento a IRIS

2013
Nonlinear dynamics of atomic force microscopy
Nonlinear Dynamics in Engineering: Modeling, Analysis and Applications
Autore/i: Rega, Giuseppe; Andreaus, Ugo; Placidi, L.; Settimi, V.
Editore: University of Aberdeen -Centre for Applied Dynamic Research
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: Atomic Force Microscopes (AFMs) are powerful devices used for surface analysis in nano-electronics, mechanics of materials and biotechnology, as they permit to topologically characterize surfaces up to micro and nano resolution levels. In a typical AFM, the topography is imaged by scanning a sharp tip, fixed to the free end of a microcantilever vertically bending over the sample surface, and by measuring the tip deflection through a laser technology. The tip-sample interaction modifies the beam dynamics and allows not only to image surfaces, but also to measure some physical properties of the sample. The most common operation modes of AFMs are the noncontact mode, in which there is absence of contact between the tip and the sample, and their interaction is governed by a solely attractive potential, and the tapping mode, in which the tip operates in both attractive and repulsive force regions and touches the surface only for short time intervals. In this lecture, both operation modes are addressed via a continuous beam model, with the interaction force being accounted for as a localized nonlinear field force. However, different continuous and Galerkin-reduced models are considered, and various aspects of nonlinear dynamics, typical of the two different AFM systems, are investigated and discussed in a somehow complementary way. In the noncontact AFM, whose cantilever tip has to maintain a design gap from the sample to ensure that the beam elastic restoring force is stronger than the atomic attraction, interest is mostly towards investigating conditions for possible occurrence of the unwanted phenomenon of jump to contact (escape), in phenomenological (dynamical) terms. To this aim, attention is systematically devoted to the strongly nonlinear dynamics of the system under beam vertical or scan horizontal excitation, which realize conditions of external or parametric resonance, respectively, by considering the relevant primary (fundamental) and subharmonic (principal) resonances of the dominant beam mode. Given the width of the bifurcation analyses, a minimal-order (single-mode) model of beam is considered, yet with the underlying continuous model consistently incorporating geometric nonlinearities, nonlinear atomic interaction, and generalized forces describing motion control of the microcantilever. In this way, a general platform to possibly conduct successive, more refined, multimodal investigations also accounting for the nonlinear coupling effects is realized. The nonlinear dynamic behavior of the single-mode model is analyzed in terms of attractors robustness and basins integrity. Local bifurcation analyses are carried out to identify the overall stability boundary in the excitation parameter space as the envelope of system local escapes. The dynamic integrity of periodic bounded solutions is studied, and basin erosion is evaluated by means of different integrity measures. The ensuing erosion profiles allow us to dwell on the possible lack of homogeneous safety of the stability boundary in terms of attractors robustness, and to identify practical escape thresholds ensuring an a priori design safety target. In contrast, in the tapping mode AFM, the interest is devoted to highlighting the effect of also higher order eigenmodes, with the relevant damping ratios, on the overall system dynamics, which is indeed addressed via a multimode approximation allowing to consider external excitation at primary or secondary resonance of different modes. In this case, a simple linear beam model is considered, with the dynamic response being investigated via numerical simulations of up to a three-mode reduced model, which appears indeed sufficient to catch the main nonlinear dynamic phenomena. Different bifurcation parameters are considered, namely the excitation frequency and the approach/retract separation between cantilever and sample. Typical features of tapping mode AFM response as nonlinear hysteresis, bistability, higher harmonics contribution, impact velocity and contact force are addressed. The analysis is conducted by evaluating damping of higher modes according to the Rayleigh criterion, which basically accounts for structural damping representative of the behavior of AFMs in air. However, nominal damping situations more typical of AFMs in liquids are also investigated, by considering sets of modal Q-factors with different patterns and ranges of values, and comparing the relevant responses. Variable attractive-repulsive effects are highlighted, along with the possible presence of a coexisting multi-periodic orbit when the system is excited at second resonance. The importance of considering excitation of also the second mode to the aim of evaluating possibly harmful tapping effects on the sample is discussed. References [1] G. Rega, V. Settimi: Bifurcation, response scenarios and dynamic integrity in a single-mode model of noncontact atomic force microscopy. Nonlinear Dynamics. (2013) DOI: 10.1007/s11071-013-0771-5. [2] U. Andreaus, L. Placidi, G Rega: Microcantilever dynamics in tapping mode atomic force microscopy via higher eigenmodes analysis. (2013) DOI: 10.1063/1.4808446.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290285 Collegamento a IRIS

2013
Bifurcation, response scenarios and dynamic integrity in a single-mode model of noncontact atomic force microscopy
NONLINEAR DYNAMICS
Autore/i: Rega, Giuseppe; Settimi, Valeria
Classificazione: 1 Contributo su Rivista
Abstract: The nonlinear dynamical behavior of a single-mode model of noncontact AFM is analyzed in terms of attractors robustness and basins integrity. The model considered for the analyses, proposed in (Hornstein and Gottlieb in Nonlinear Dyn. 54:93-122, 2008), consistently includes the nonlinear atomic interaction and is studied under scan excitation (which appears as parametric excitation) and vertical excitation (which is prevalently external). Local bifurcation analyses are carried out to identify the overall stability boundary in the excitation parameter space as the envelope of system local escapes, to be compared with the one obtained via numerical simulations. The dynamical integrity of periodic bounded solutions is studied, and basin erosion is evaluated by means of two different integrity measures. The obtained erosion profiles allow us to dwell on the possible lack of homogeneous safety of the stability boundary in terms of robustness of the attractors, and to identify practical escape thresholds ensuring an a priori design safety target.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290298 Collegamento a IRIS

2012
Bifurcations, basin erosion and dynamic integrity in a single-mode model of noncontact atomic force microscopy
MATEC Web of Conferences
Autore/i: Settimi, Valeria; Rega, Giuseppe
Editore: E D P SCIENCES
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: The nonlinear dynamical behavior of a single-mode model of noncontact AFM is analyzed in terms of attractors robustness and basin integrity. The model considered for the analyses, proposed by Hornstein and Gottlieb [7], consistently includes the nonlinear atomic interaction and the scan control, which appears as parametric excitation. Local bifurcation analyses are carried out to define the overall stability boundary in the excitation parameter space as the envelope of system local escapes, to be compared with the one obtained via numerical simulations. The dynamical integrity of the periodic bounded solutions is studied, and basin erosion is evaluated by means of IF and GIM integrity measures. The obtained erosion profiles allow us to dwell on the possible lack of homogeneous safeness of the stability boundary in terms of attractors robustness and to identify practical escape thresholds ensuring an a priori design safety target.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290270 Collegamento a IRIS

2010
Nonlinearity in architecture versus science: borrowing the lexicon of complexity or exploiting its powerfulness?
Structures and Architecture
Autore/i: Rega, G.; Settimi, V.
Editore: Taylor & Francis Group
Luogo di pubblicazione: GBR
Classificazione: 2 Contributo in Volume
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/290279 Collegamento a IRIS




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