1,720,998 research outputs found
Structural Control of a Wind Turbine Accounting for Second Order Effects
Full text linkThe negative impact of the use of fossil fuels on the environment has lead to a boom in the production of wind turbines. The progressively increasing turbines' height, decided to take ad-vantage of the smoother winds at higher altitude, has led to an increased demand to control tower forces. The proposed work is focused on the application of a semi-active (SA) control system to limit bending moment demand at the base of a wind turbine by relaxing the base restraint of the turbine's tower, without increasing the top displacement. The proposed SA control system reproduces a variable restraint at the base that changes in real time its mechanical properties according to the instantaneous response of the turbine's tower. This smart restraint is made of a central smooth hinge, elastic springs and SA magnetorheological dampers driven by a properly designed control algorithm. A commercial 105 m tall wind turbine has been considered as a case study. Several numerical simulations have been performed with reference to two extreme loads, different one each other for intensity, duration, frequency content, so as to understand if a unique optimal configuration of the controller can be defined for both of them. The proposed study is also focused on understanding whether and how to reduce the residual top displacement due to the possible incremental base rotation that may happen during a wind load history, especially when it is long lasting
Semi-Active Control of Precast RC Columns under Seismic Action
No full textThis work is inspired by the idea of dissipating seismic energy at the base of prefabricated RC columns via semi-active (SA) variable dampers exploiting the base rocking. It was performed a wide numerical campaign to investigate the seismic behaviour of a pre-cast RC column with a variable base restraint. The latter is based on the combined use of a hinge, elastic springs, and magnetorheological (MR) dampers remotely controlled according to the instantaneous response of the structural component. The MR devices are driven by a SA control algorithm purposely written to modulate the dissipative capability so as to reduce base bending moment without causing excessive displacement at the top. The proposed strategy results to be really promising, since the base restraint relaxation, that favours the base moment demand reduction, is accompanied by a high enhancement of the dissipated energy due to rocking that can be even able to reduce top displacement in respect to the "fixed base rotation" conditions
Experimental verification of semi-active magneto-rheological dampers for earthquake structural control
No full textMechanical behaviour, promptness and dissipative capability of variable dampers for semi-active control
No full textThe definition of smart devices for semi-active structural control is well represented by semi-active magnetorheological (SA MR) dampers. SA MR dampers can be used as reactive force generators, when the control algorithms adopted to drive the devices are derived in the framework of the control theory, or as smart dampers, when the real-time change of their mechanical properties has the aim to provide, at any time, the optimal amount of damping in a structure. The two approaches have different requirements in modelling the SA MR devices. On the base of the results of an experimental campaign on 2 prototype devices manufactured in Europe, the present paper compares the effectiveness of numerical models presented in the literature and analyzes their response time and dissipative capability
Bidirectional shaking-table tests of unbonded recycled-rubber fiber-reinforced bearings (RR-FRBs)
No full textThis paper describes the results of bidirectional shaking-table tests performed on novel, low-cost, and eco-friendly recycled-rubber fiber-reinforced bearings (RR-FRBs). The research aims to demonstrate the adequacy of square bearings made of recycled rubber when it comes to performing a base isolators in low-rise residential buildings in developing regions of the world. The results of shear tests on RR-FRBs are described in this paper as well as the response of a base-isolated prototype building under bidirectional ground-motion excitation. Compared with the results of a fixed-base structure, the peak drift ratio, peak base shear, and peak acceleration on the different floors are significantly reduced for the base-isolation system of the RR-FRBs. The results of this work confirm the option of adopting RR-FRBs as base isolators in real structures, with the stability of the devices under major bidirectional excitation requiring further investigation
A semi-active rocking system to enhance the seismic dissipative capability of precast rc columns
No full textThis work is inspired by the idea of dissipating seismic energy at the base of prefabricated RC columns via semi-active (SA) variable dampers exploiting the base rocking. It was performed a wide numerical campaign to investigate the seismic behavior of a precast RC column with a variable base restraint. The latter is based on the combined use of a hinge, elastic springs, and magnetorheological (MR) dampers remotely controlled according to the instantaneous response of the structural component. The MR devices are driven by a SA control algorithm purposely written to modulate the dissipative capability so as to reduce base bending moment without causing excessive displacement at the top. The proposed strategy results to be really promising, since the base restraint relaxation, that favours the base moment demand reduction, is accompanied by an high enhancement of the dissipated energy due to rocking that can be even able to reduce top displacement in respect to the “fixed base rotation” conditions
Semi-Active Control of Precast RC Columns under Seismic Action
Full text linkThis work is inspired by the idea of dissipating seismic energy at the base of prefabricated RC columns via semi-active (SA) variable dampers exploiting the base rocking. It was performed a wide numerical campaign to investigate the seismic behaviour of a pre-cast RC column with a variable base restraint. The latter is based on the combined use of a hinge, elastic springs, and magnetorheological (MR) dampers remotely controlled according to the instantaneous response of the structural component. The MR devices are driven by a SA control algorithm purposely written to modulate the dissipative capability so as to reduce base bending moment without causing excessive displacement at the top. The proposed strategy results to be really promising, since the base restraint re-laxation, that favours the base moment demand reduction, is accompanied by a high enhancement of the dissipated energy due to rocking that can be even able to reduce top displacement in respect to the "fixed base rotation" conditions
Design and Retrofit of Multistory Frames with Elastic-Deformable Viscous Damping Braces
No full textThis paper provides an exhaustive treatment for the analysis of non-proportional damping structures equipped with elastically deformable viscous damping braces. A frequency domain approach is adopted for solving the equation of motion as a function of nondimensional parameters. Accounting for the brace flexibility, an optimal damping system is suggested in order to minimize the resonance peak of the top-story displacement response on the first vibration mode. The effect of variation of the dissipative bracing system is demonstrated not only in terms of provided equivalent viscous damping and maximum response, but also in terms of dominant frequency and mode shapes
Structural Monitoring and Dynamic Characterization of the Main Fire Station Building in Naples
No full textThe main Firemen Station of Naples is a steel–concrete composite building structure, that is peculiar due to its suspended configuration and to the seismic devices installed at the time of construction. The latters represents one of the first Italian applications of vibration control systems and the assessment of seismic performance according to current codes is strongly needed. The installation of a static and dynamic monitoring system of the structure and the performing of a rising test of one seismic bearing could allow to better understand the structural behaviour and to determine the best choice of seismic retrofit intervention of the building. A simplified structural model is developed to be used for predicting and evaluating the experimental results of dynamic shaking tests with vibrodine
Variable dampers to mitigate structural demand to wind turbines: The role of the monitoring system features for the effectiveness of the control strategy
Full text linkIn the last decade, some researchers and professionals have been engaged in the study of methods and techniques that can build high wind turbines while containing construction costs within the limits of economic convenience. Among the most promising solutions is that of using innovative devices to mitigate the structural demand for the towers. The reduction in the stress demand in the foundation makes the strategy particularly interesting for the repowering of existing plants, where it is convenient not to demolish and rebuild the foundation, but rather to reuse the existing one for the new plant. A semi-active vibration control strategy, based on the adoption of controllable dissipative devices, is presented herein. The proposed technique requires the tower to be equipped with a measurement system suitable for the real time monitoring of structural response. Performing reliable high-frequency measurements of the horizontal displacement of points located at heights of tens of meters is not simple. With the purpose of assessing the efficiency and feasibility of Global Navigation Satellite System (GNSS)-based systems for the control of wind turbine structures, the proposed paper tries to investigate the characteristics and data processing techniques that are able to make the GNSS useful for such applications. Several numerical simulations were carried out with reference to a case-study wind turbine to quantitatively assess how the performance of the control system changes as the features of the monitoring system worsen, and finally to draw conclusions and suggestions for the minimum performance that monitoring devices must have for an effective reduction in structural demand
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