1,721,051 research outputs found
Optimal semi-active control and non-linear dynamic response of variable stiffness structures
No full textIn this paper we study the semi-active control of structural systems by means of variable stiffness devices, and the resulting non-linear dynamics of the controlled system. In particular, the study is applied to base-excited single-degree-of-freedom systems, controlled by variable ON-OFF elastic devices and subjected to simple motion conditions: free vibrations following initial conditions and stationary response to harmonic input. A performance index, which, in the case of base-excited structures, assumes an original dual formulation following the relative or absolute approaches, has been proposed for instantaneous optimal control. The Study includes both the optimal control design and the observation of the resulting non-linear dynamics of the controlled system. The dynamic behavior of the controlled non-linear system is studied with respect to the parameters which characterize the algorithms, the control device, and the input. In this way, also by means of significant (and original) analytical solutions of the equations of motion, the optimal formulation of the algorithms, some particular behaviors of the controlled systems, and the performances of the control approach are shown and explained for the different control strategies
Optimal semi-active control of adjacent structures
No full textThis paper deals of semi-active optimal control of adjacent structures, by studying the performances of optimized connections realized by ON-OFF magnetorheological devices. The model of structures and of connections represent an experimental set-up which is using in an shaking table tests campaign. For comparison purposes also the cases in which the magnetorheological connections operate as passive and the case of optimal passive elasto-plastic links are considered. An energy-based optimization procedure is used, and the comparison of the control performances shows that the semi-active connection guarantees good control performances also with respect to the other considered control cases
ALCUNE CONSIDERAZIONI SULLA RISPOSTA DINAMICA DI SISTEMI SEMI-ATTIVI A RIGIDEZZA VARIABILE
No full textSemi-active continuous control of base-excited structures: An exploratory study
No full textThe semi-active (SA) control techniques appear a realistic way to adopt active control in structural engineering. This paper reports an exploratory study on SA continuous control, where the mechanical parameters of the devices may continuously assume any value between the given limits.
First, a Lyapounov-based control strategy for SA continuous control is proposed and studied for base-excited structures. The obtained continuous control process is initially applied to a seismic-excited single-DOF structure with a variable stiffness device, in order to study the dynamics of the controlled system and the optimal configuration of the algorithm. Successively, the optimized control strategy is applied to single-DOF structures with more realistic SA elasto-plastic devices, and the performances of SA continuous control are compared with the ones of passive and SA ON–OFF control cases. Finally, the obtained results are verified and confirmed in the application to a 4-storey Multi-DOF-framed structure, equipped with continuously variable SA magnetorheological dampers.
The study shows the applicability and the possible advantages of the proposed control case, also in comparison with passive and SA ON–OFF cases. Generally it may be stated that the best performances in terms of structural displacements may be obtained by using ON–OFF SA control. Differently, continuous SA control significantly reduces the absolute accelerations and the total forces transmitted to the structures
Controllo passivo e semi-attivo della risposta sismica di strutture adiacenti
No full textNel presente lavoro si studia il controllo passivo e semi-attivo di strutture adiacenti con l’obiettivo di formulare una metodologia di progetto del collegamento e, quindi, verificare e confrontare l’efficacia dell’accoppiamento rispetto al caso di strutture non collegate. Saranno quindi formulate, in maniera ottimale e sulla base di grandezze energetiche, sia l’algoritmo di controllo da usarsi nel caso semi-attivo, sia la metodologia generale per la progettazione delle caratteristiche meccaniche dei dispositivi. Le metodologie saranno preliminarmente applicate ad un sistema a due gradi di libertà, per mezzo del quale si otterranno semplici ed interessanti indicazioni per la progettazione del dispositivo, e successivamente verranno applicate a sistemi a molti gradi di libertà
UN ALGORITMO PER IL CONTROLLO SEMI ATTIVO DI SISTEMI A MOLTI GRADI DI LIBERTÀ
No full textPaper n.SP_ST_4
Caratterizzazione di un dispositivo magnetoreologico mediante prove sperimentali
No full textThe paper approaches the problem of structural control by means of the semi active technology. The experimentation is on a prototype magnetorheological (MR) device, produced by Lord Corporation. Both passive and semi active tests are conducted on the MR damper applying respectively different constant voltage levels and variable voltage levels, by using an optimal control algorithm, to define damper’s mechanical characteristics. An identification is then conducted focusing attention on two models, known from literature: Bingham model and modified Bouc-Wen model. Moreover an estimate of electrical delays for the MR damper is carried out
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
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