Rita Greco

Bio: Rita Greco is an academic researcher from Instituto Politécnico Nacional. The author has contributed to research in topics: Tuned mass damper & Stochastic process. The author has an hindex of 21, co-authored 75 publications receiving 1169 citations. Previous affiliations of Rita Greco include University of Bari.

A comparison between different optimization criteria for tuned mass dampers design

Abstract: Tuned mass sampers (TMDs) are widely used strategies for vibration control in many engineering applications, so that many TMD optimization criteria have been proposed till now. However, they normally consider only TMD stiffness and damping as design variables and assume that the tuned mass is a pre-selected value. In this work a more complete approach is proposed and then also TMD mass ratio is optimized. A standard single degree of freedom system is investigated to evaluate TMD protection efficiency in case of excitation at the support. More precisely, this model is used to develop two different optimizations criteria which minimize the main system displacement or the inertial acceleration. Different environmental conditions described by various characterizations of the input, here modelled by a stationary filtered stochastic process, are considered. Results show that all solutions obtained considering also the mass of the TMD as design variable are more efficient if compared with those obtained without it. However, in many cases these solutions are inappropriate because the optimal TMD mass is greater than real admissible values in practical technical applications for civil and mechanical engineering. Anyway, one can deduce that there are some interesting indications for applications in some actual contexts. In fact, the results show that there are some ranges of environmental parameters ranges where results attained by the displacement criterion are compatible with real applications requiring some percent of main system mass. Finally, the present research gives promising indications for complete TMD optimization application in emerging technical contexts, as micromechanical devices and nano resonant beams.

Constrained reliability-based optimization of linear tuned mass dampers for seismic control

Abstract: This paper deals with the optimum design of vibration absorbers utilized to reduce undesirable vibrational effects which are originated in linear structures by seismic excitations. The single linear tuned mass dampers problem is treated and it is assumed that earthquake can be represented by a stationary filtered stochastic process. In the present problem, the objective is to minimize the maximum of the dimensionless peak of displacement of the protected system with respect to the unprotected one. Moreover, the constrained optimization problem is also analysed, in which a limitation of tuned probability of failure is imposed, where failure is related to threshold crossing probability by the maximum displacement over an admissible value. Examples are given to illustrate the efficiency of the proposed method. The variation of the optimum solution versus structural and input characteristics is analysed for the unconstrained and constrained optimization problems. A sensitivity analysis is carried out, and results are presented useful for the first design of the vibrations control strategy.

A comparison between different robust optimum design approaches: application to tuned mass dampers

Abstract: This paper is focused on the comparison between different approaches in structural optimization. More precisely, the conventional deterministic optimum design, based on the assumption that the only source of uncertainty concerns the forcing input, is compared to robust single-objective and multi-objective optimum design methods. The analysis is developed by considering as case of study a single-degree-of-freedom system with uncertain parameters, subject to random vibrations and equipped with a tuned mass damper device (TMD). The optimization problem concerns the selection of TMD mechanical characteristics able to enlarge the efficiency of the strategy of vibration reduction. Results demonstrate the importance of performing a robust optimum design and show that the multi-objective robust design methodology provides a significant improvement in performance stability, giving a better control of the design solution choice.

Robust optimum design of tuned mass dampers devices in random vibrations mitigation

Abstract: One of the most widely adopted and studied strategies for vibration control both in civil and in mechanical engineering is based on the use of tuned mass dampers (TMD) devices. Many conventional optimization criteria of mechanical parameters have been proposed, based on different approaches typically of a “conventional” type; in other words, they are based on the implicit assumption that all parameters involved are deterministically known. Removing this hypothesis means to convert a conventional optimization into a robust one, so that the solution must be able not only to minimize a performance but also to limit its variation induced by uncertainty in system parameters. In this work, a robust optimal design criterion for a single TMD device is proposed. The analyzed case concerns the structural vibration control of a main system subject to stochastic dynamic loads by a single linear TMD. The dynamic input is represented by a random base acceleration, modelled by a stationary filtered white noise process. It is assumed that not only mechanical parameters regarding main structure and TMD but also input spectral contents are affected by uncertainty. The problem is treated characterizing all uncertain parameters by a nominal mean value and a variance. It is also assumed that all these parameters are statistically independent. The protected main structure covariance displacement (dimensionless by dividing for the unprotected one) is adopted as the deterministic objective function (OF). Its mean and standard deviation are evaluated to perform the robust design. Robustness is formulated as a multiobjective optimization problem, in which both the mean and the standard deviations of the deterministic OF are minimized. Comparisons with a conventional approach based on the same OF show that the robust approach induces a significant improvement in performance stability.

Optimum design of Tuned Mass Dampers by displacement and energy perspectives

Abstract: Tuned Mass Dampers are extensively used for vibration control in many engineering fields, such as civil, mechanical and aeronautical. The present work focuses on the analysis of the effectiveness of this passive vibration control strategy. Its goal is to test the Tuned Mass Damper performance both from the energy and from displacement perspectives. For this purpose, a simple single degree of freedom system subject to a dynamic action and equipped with a Tuned Mass Damper is analyzed. The device performance is estimated by two indicators that are related to the reduction of the maximum displacement and dissipated energy into the primary system. These indices will be adopted as objective functions to perform an optimization procedure based on two different criteria, to obtain Tuned Mass Damper parameters, which give the best performances. Different circumstances, which reflect on various characterizations of the input and of the main system, are analyzed.

Recent advances in differential evolution – An updated survey

Abstract: Differential Evolution (DE) is arguably one of the most powerful and versatile evolutionary optimizers for the continuous parameter spaces in recent times. Almost 5 years have passed since the first comprehensive survey article was published on DE by Das and Suganthan in 2011. Several developments have been reported on various aspects of the algorithm in these 5 years and the research on and with DE have now reached an impressive state. Considering the huge progress of research with DE and its applications in diverse domains of science and technology, we find that it is a high time to provide a critical review of the latest literatures published and also to point out some important future avenues of research. The purpose of this paper is to summarize and organize the information on these current developments on DE. Beginning with a comprehensive foundation of the basic DE family of algorithms, we proceed through the recent proposals on parameter adaptation of DE, DE-based single-objective global optimizers, DE adopted for various optimization scenarios including constrained, large-scale, multi-objective, multi-modal and dynamic optimization, hybridization of DE with other optimizers, and also the multi-faceted literature on applications of DE. The paper also presents a dozen of interesting open problems and future research issues on DE.

Corrosion of steel by concrete

Abstract: The author details the reactions of various concretes on steel reinforcement. Although portland cements, slag cements and high alumina cements are all hydraulic binders, each possess special properties which are examined. The discussion of causes and methods of preventing the corrosion of steel reinforcement covers such aspects as galvanised steel reinforcement, effects of concrete composition, corrosion of steel reinforcments in concrete and prestressed reinforcement. It is concluded that the most significant influences on the corrosion of prestressing wire in concrete are: the presence of chloride; the presence of nitrates; the composition of the concrete; the degree of carbonation of the concrete; concrete compaction and, chlorides and sulphates should be used as far as possible when steel is embedded. (TRRL)

The Hysteresis Bouc-Wen Model, a Survey

Abstract: Structural systems often show nonlinear behavior under severe excitations generated by natural hazards. In that condition, the restoring force becomes highly nonlinear showing significant hysteresis. The hereditary nature of this nonlinear restoring force indicates that the force cannot be described as a function of the instantaneous displacement and velocity. Accordingly, many hysteretic restoring force models were developed to include the time dependent nature using a set of differential equations. This survey contains a review of the past, recent developments and implementations of the Bouc-Wen model which is used extensively in modeling the hysteresis phenomenon in the dynamically excited nonlinear structures.

Influence of extreme weather and climate change on the resilience of power systems: Impacts and possible mitigation strategies

Abstract: A key driver for developing more sustainable energy systems is to decrease the effects of climate change, which could include an increase in the frequency, intensity and duration of severe weather events. Amongst others, extreme weather has a significant impact on critical infrastructures, and is considered one of the main causes of wide-area electrical disturbances worldwide. In fact, weather-related power interruptions often tend to be of high impact and sustained duration, ranging from hours to days, because of the large damage on transmission and distribution facilities. Hence, enhancing the grid resilience to such events is becoming of increasing interest. In this outlook, this paper first discusses the influence of weather and climate change on the reliability and operation of power system components. Since modelling the impact of weather is a difficult task because of its stochastic and unpredicted nature, a review of existing methodologies is provided in order to get an understanding of the key modelling approaches, challenges and requirements for assessing the effect of extreme weather on the frequency and duration of power system blackouts. Then, the emerging concept of resilience is discussed in the context of power systems as critical infrastructure, including several defense plans for boosting the resilience of power systems to extreme weather events. A comprehensive modelling research framework is finally outlined, which can help understand and model the impact of extreme weather on power systems and how this can be prevented or mitigated in the future.