Prin: 2010-2011

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Title of the Research Project

DYNAMICS, STABILITY AND CONTROL OF FLEXIBLE STRUCTURES

Scientific Coordinator: Professor Angelo Luongo

Abstract

The assessment of the bearing capacity of a structure is a primary objective of structural engineering: it is now a days made more challenging by the increasing use of innovative materials, new technologies of passive and semi-active control, and by the design of structures of a new generation, which have requests of performance highly demanding. These complex problems sometimes require the contribution of multi-disciplinary skills belonging to Material Technology and Mechanical Engineering.

Among the numerous factors that influence the behavior of a structure and complicate its analysis, many are detected in the fields of Dynamics, Stability and Control. The phenomena studied in these specialities, are often triggered and amplified by the Damage, and they cause the further spread of Damage in a complex mechanism of interaction, amplified by the presence of great structural flexibility.

Only some issues are here cited, limiting to those of interest to the present Project. (a) In Dynamics and Stability: effects induced by movement of masses not negligible with regard to the bearing structures; oscillations of great amplitude of guyed or suspended structures and pedestrian bridges caused by anthropic or environmental excitations; aeroelastic instability of suspended cables and beams, as well as airfoils; non-regular dynamics of impacting beams, with mono-lateral constraints or with complex constitutive laws, and of complex masonry structures, where the friction and the impact between the constituent elements play an essential role. (b) In the Control: the use of added devices whose dissipative capacity is inherently nonlinear, hence extending the concept of the classic Tuned Mass Damper, such as Nonlinear Energy Sinks, the parametric stabilization, the Liquid Column Dampers, the viscous non-Newtonian and fractional viscoelastic devices; the use of hysteretic, magnetorheological, or geometrically nonlinear dampers; the use of high-damping polymeric materials, including the effect of damage and loading history; the use of new isolation technologies, based on the friction, on the fractional viscoelasticity, on the impact or on the hysteretic behavior of shape memory alloys, especially in multiaxial state of stress. (c) In Damage Mechanics of multi-layered structures: the onset of fatigue cracking, the phenomena of wear caused byinter laminar abrasion, the partial detachment of the interface, the bilateral defect on constraints, the damage due to thermal changes or slow aging.

The study of all these phenomena requires the formulation of accurate, often non-smooth, models such as: moving boundary models, inverse problems, deterministic and random approaches, vagueness and imprecision stimates, perturbation methods, numerical methods; advanced models to study the damage, finalized to describing the behavior of the interface zone through the use of internal phenomenological variables, or through rational techniques of asymptotic analysis; multi-axial constitutive models, describing fractional viscous effects; multi-scale models designed to correlate the dissipation and thermo-mechanical response properties to the material properties. The investigation also requires the development of non-destructive techniques for the detection of damage, which often make use of the variations in the linear or nonlinear structural response, sometime caused by the addition of known masses to the structure. The realization of experimental tests, in reduced-scale or full-scale, for the validation and calibration of mathematical models, constitutes an added invaluable feature of the research in these fileds.

For the reasons exposed above there is a strong and topical scientific interest in conducting researches on the effects, independent or combined, of Dynamics, Control and Damage in flexible structures, and how these phenomena are able to influence the Stability of structures. This Project aims: (1) to analyze, through analytical, numerical and experimental models, the Dynamic response of flexible structures in the presence of geometric and constitutive nonlinearities, with particular attention to innovative materials; (2) to develop advanced strategies of semi-active or passive control for mitigation of dynamic and damage effects; (3) to investigate the interaction phenomena between Damage and Dynamics; (4) to implement monitoring and nondestructive damage detection techniques.

The Project is organized into the following Work Packages (WP). In WP-A the Dynamics and Stability of flexible structures will be analyzed. In WP-B the Control of oscillations will be studied. In WP-C the study of the interaction between Dynamics and Damagewill be dealt with.

Structure of the Project

The Project is organized in three Work Packages (A, B, C), each divided into Tasks (A.1, …), as shown below. Each task will be developed by the specified RUs.

A. DYNAMICS AND STABILITY OF FLEXIBLE STRUCTURES

A.1 Dynamics induced by moving masses

A.2 Dynamics and stability of strings and beams

A.3 Not-regular dynamics of systems with impact and friction

B. CONTROL OF OSCILLATIONS OF FLEXIBLE STRUCTURES

B.1 Passive control via added devices

B.2 Control via dissipation enhancement and experimental applications

B.3 Isolation via friction, impact and experimental applications

C. INTERACTION BETWEEN DYNAMICS AND DAMAGE

C.1 Models of multi-layered structures

C.2 Dynamics and damage of multi-layered structures

C.3 Non-destructive techniques for damage detection

C.4 Structural monitoring and experimental applicationsi

Research Units Inter-Unit Collaborations Collaborations with other Research Institutions