Browsing by Author "Oliveira, Kellie"
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- Controlo semi-ativo da suspensão de um veículo automóvelPublication . Oliveira, Kellie; Braz-César, M.T.; Paula, António MiguelOs sistemas passivos representam a solução convencional para o controlo de vibrações em suspensões de veículos. Embora este sistema seja uma tecnologia comprovadamente fiável e económica, os seus parâmetros não podem ser modificados em função das condições do piso. Os sistemas ativos permitem um controlo contínuo do movimento da suspensão exigindo, no entanto, um atuador complexo que normalmente consome uma elevada quantidade de energia. Os sistemas semi-ativos e baseiam-se na modificação do amortecimento da suspensão e constituem uma tecnologia recente com elevado potencial no controlo de vibrações. Esta característica permite obter a adaptabilidade dos sistemas ativos mas com um menor consumo de energia, constituindo uma opção fiável, eficiente e económica para o controlo de vibrações em suspensões de veículos pelo qual têm vindo a ser objeto de uma forte investigação e desenvolvimento. O trabalho elaborado nesta dissertação pretende avaliar o desempenho e a eficiência de um sistema de suspensão com controlo semi-ativo utilizando um amortecedor magneto-reológico na redução da resposta de um veículo e o consequente aumento do conforto dos passageiros comparativamente a um sistema passivo. A análise é feita através de simulações numéricas em ambiente Matlab/Simulink considerando o modelo de suspensão de ¼ de veículo com dois graus de liberdade para um sistema passivo e um sistema semi-ativo com um controlador ótimo e um controlador difuso. Neste estudo foi imposta uma excitação do tipo impulsiva de forma a avaliar o desempenho de cada controlador. Os resultados das simulações mostraram que o sistema de suspensão semi-ativo permite obter uma maior redução da resposta comparativamente ao sistema de controlo passivo.
- Development of an optimal and fuzzy semi-active control system for vehicle suspensionPublication . Oliveira, Kellie; Gonçalves, José; Braz-César, ManuelThis paper aims to evaluate the performance of a semi-active controlled suspension system using a magneto-rheological (MR) damper to provide better ride comfort and safety to vehicle passengers than an uncontrolled or passive suspension system. Passive systems represent a conventional solution for vibration control of suspension systems. Although this system is a proven, reliable and economic technology, their parameters cannot be modified according to the road conditions. On the other hand, active systems allow a continuous control of the suspension motion, but require a complex and energy demanding actuator. The proposed suspension system has the adaptability of active systems with lower energy consumption, which constitute an economic and efficient option for vibration control in vehicle suspensions. The analysis was carried out with a set of numerical simulations in Matlab/Simulink using a 1/4 vehicle suspension model with two degrees of freedom for a passive system and two semiactive control modes based on fuzzy and optimal controllers.
- Fuzzy based control of a vehicle suspension system using a MR damperPublication . Oliveira, Kellie; Braz-César, Manuel; Gonçalves, JoséVehicle suspension systems are usually based on passive actuators and control modes in which the damping and stiffness parameters are predefined and kept constant for all road profiles and vehicle response. A different approach is to use active systems to monitor and control the suspension motion in order to improve the vehicle handling and comfort. However, these systems have a complex design requiring a relatively high power source to operate. Semi-active systems are also capable to modify the properties of the vehicle suspension but with low power requirements making them a promising technology for demanding vibration control systems. This paper presents the findings of a numerical simulation involving a simplified model of a vehicle suspension system equipped with a MR actuator. The system is designed to improve the behavior (comfort and handling) of the vehicle compared with a traditional passive suspension system. A simple fuzzy logic controller is used to decide the control action in accordance with the measured system response.
- Neuro-fuzzy modelling of magneto-rheological dampersPublication . Braz-César, Manuel; Oliveira, Kellie; Barros, RuiNumerical modelling of magneto-rheological (MR) dampers based on parametric models constitutes one of the main methodologies to simulate the response of these actuators. However, the highly non-linear nature of these devices and also their inherent rheological behaviour make this modelling approach harsh and complicated hindering the development of simple numerical models. Usually complex parametric models comprising numerous parameters are required to achieve a reliable and accurate representation of the hysteretic behaviour of MR dampers. On the other hand, non-parametric models seems to be an alternative modelling approach that can deal with the complex non-linear behaviour of MR dampers without the need of to define or identify a large number of model parameters. In this context, this paper provides detailed information about a non-parametric technique based on an adaptive neuro-fuzzy inference system (ANFIS) to create neuro-fuzzy models for MR dampers. An ANFIS is used to optimize a fuzzy inference system by training a family of membership functions in accordance with a predetermined input and output data set related with the damper behaviour. This data optimization algorithm presents the advantage of providing automatic tuning of a fuzzy inference system to relate the device inputs (mechanical excitations and operating currents) to obtain the desired damping force output. Initially, the background and basic concepts of fuzzy modelling with an ANFIS algorithm are described. General guidelines are also provided to improve the optimization procedure with this type of modelling technique. A framework for modelling MR dampers with ANFIS was implemented and its effectiveness in simulating the response of a commercial MR damper was verified with both numerical training data. The results obtained with the resultant neuro-fuzzy model are compared with those of experimental tests and also with an established parametric model (i.e., the modified Bouc-Wen model).
- Neuro-fuzzy modelling of magneto-rheological dampersPublication . Braz-César, Manuel; Oliveira, Kellie; Barros, RuiNumerical modelling of magneto-rheological (MR) dampers based on parametric models constitutes one of the main methodologies to simulate the response of these actuators. However, the highly non-linear nature of these devices and also their inherent rheological behaviour make this modelling approach harsh and complicated hindering the development of simple numerical models. Usually complex parametric models comprising numerous parameters are required to achieve a reliable and accurate representation of the hysteretic behaviour of MR dampers. On the other hand, non-parametric models seems to be an alternative modelling approach that can deal with the complex non-linear behaviour of MR dampers without the need of to define or identify a large number of model parameters. In this context, this paper provides detailed information about a non-parametric technique based on an adaptive neuro-fuzzy inference system (ANFIS) to create neuro-fuzzy models for MR dampers. An ANFIS is used to optimize a fuzzy inference system by training a family of membership functions in accordance with a predetermined input and output data set related with the damper behaviour. This data optimization algorithm presents the advantage of providing automatic tuning of a fuzzy inference system to relate the device inputs (mechanical excitations and operating currents) to obtain the desired damping force output. Initially, the background and basic concepts of fuzzy modelling with an ANFIS algorithm are described. General guidelines are also provided to improve the optimization procedure with this type of modelling technique. A framework for modelling MR dampers with ANFIS was implemented and its effectiveness in simulating the response of a commercial MR damper was verified with both numerical training data. The results obtained with the resultant neuro-fuzzy model are compared with those of experimental tests and also with an established parametric model (i.e., the modified Bouc-Wen model).
- Response time analysis of a sponge type mr damperPublication . Braz-César, Manuel; Oliveira, Kellie; Barros, RuiThis paper presents the results of an experimental procedure carried out to determine the response time of a sponge type magnetorheological (MR) damper to electrical inputs. The promptness of an actuator is a fundamental requirement for real-time structural control applications, especially when bang-bang controllers are used to generate the control signal. This type of controllers are frequently used to change the operating current in the electromagnet of MR dampers in order to create a bi-state control mode by switching on and off the device between high and low damping states, respectively. Thus, bi-state control signals can be modelled as step inputs or square waveforms that must be reproduced as fast as possible by the driving electronics and the MR actuator. In this work a simplified methodology for response time estimation of a small sponge type MR damper to step current inputs with and without mechanical excitation is presented. The results obtained with the experimental tests are analyzed and discussed.
- Semi-active control of building structures using a neuro-fuzzy controller with acceleration feedbackPublication . Braz-César, Manuel; Oliveira, Kellie; Barros, RuiThe present paper investigates the effectiveness of a neuro-fuzzy controller to reduce the response of building structures subjected to seismic excitations. The proposed controller was developed using an Adaptive Neuro-Fuzzy Inference System (ANFIS) to train a fuzzy logic system. In this case, floor acceleration measurements are used to compute the desired control signal to command a MR damper. A numerical example involving a three degrees of freedom building structure excited by the El Centro earthquake is presented to demonstrate the effectiveness of the proposed semi-active control system in reducing the response under seismic loading. A comparison between uncontrolled and controlled structural responses are used to validate the performance and efficiency of the proposed semi-active controller.