Hybrid actuation is an expanding field in which several systems, such as a mechanical, electrical, hydraulic, pneumatic, and/or thermal, among others, are integrated in order to combine certain aspects of each system, and achieve a better and more efficient performance under certain operating conditions. The concept of piezohydraulic actuation takes advantage of the high force capabilities that piezoceramics have and combines it with the operation at high frequencies, in order to achieve the hydraulic actuation of a system under a specified stroke and force. High frequency rectification translates the low stroke of a piezoelectric stack into a desired amount of stroke per unit time. Thus, the low displacement, oscillatory motion of the piezoelectric device (coupled with a high frequency operation) is translated into a unidirectional motion of a hydraulic cylinder. As part of this research, a benchtop piezohydraulic unit has been developed and the concept of piezohydraulic actuation has been demonstrated. The effective bidirectional displacement of a hydraulic cylinder through the actuation of a piezoelectric stack has been achieved. A lumped parameter model is developed in order to simulate the dynamics of the hydraulic system and of the entire piezohydraulic unit. The model did approximate the response of the piezohydraulic unit under a one-sided operation. Time response analysis is performed through the frequency spectrum comparison of the measured and the simulated data. Then a two-stage cycle simulation is used to model the pumping operation of the unit. Discrepancies were obtained between the model and the actual system for the single-ended piezohydraulic unit, nonetheless, a good approximation has been achieved for the pumping operation of the double-ended unit under certain conditions. Furthermore, several factors have been identified that may limit the operation of the piezohydraulic unit. First, the need of high displacement actuators often comes with the requirement of high voltage operation along with high current consumptions. Thus, the amplifier becomes the first limitation to overcome. Second, is the response of the controlled valves. The highest valve operating frequency and their time response will set the limit on the piezohydraulic unit. And finally, once these limitations are overcome, the unit is eventually limited by the dynamics of the fluid and the hydraulic system itself. Attenuation in the frequency response, or the operation near resonance and the possibility of cavitation, are some of the aspects that eventually will limit the operation of the piezohydraulic unit. A custom made, high displacement stack is used along with a custom made switching amplifier. The current system is being limited by the second factor, the solenoid valves. Nonethelss the analysis performed has addresed the relevant issues required for the design and use of another set of controlled valves. Finally, the eventual limitation from the hydraulic system has been determined through the analysis of the fluid dynamics of the system. The analysis does not account for potential cavitation, and future operations at high frequencies should take it into account. / Master of Science

Made available in DSpace on 2014-06-11T19:27:14Z (GMT). No. of bitstreams: 0 Previous issue date: 2005-10-31Bitstream added on 2014-06-13T19:55:36Z : No. of bitstreams: 1 carvalhal_r_me_ilha.pdf: 892699 bytes, checksum: 6654a8de1bfad0655527d3268f00f2f1 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Este trabalho apresenta o desenvolvimento analítico da modelagem de estruturas flexíveis do tipo treliça com o objetivo de atenuação de vibrações através do uso de técnicas de controle ativo. Atuadores de pilha piezelétricos são usados para exercer as forças de controle na estrutura, os quais substituem barras inteiras ou somente uma parte delas. Estes tipos de atuadores, também, satisfazem a necessidade de obtenção de estruturas leves. O posicionamento ótimo desses atuadores e de sensores é encontrado através da norma Hx, que é usada como função objetivo. Como técnica de controle é aplicado o Controle no Espaço Modal Independente (IMSC), no qual os estados são estimados por um estimador modal e são realimentados de acordo com a teoria de controle ótimo, o Regulador Linear Quadrático (LQR). O IMSC é eficiente computacionalmente mesmo aplicado a sistemas de alta ordem e também reduz os efeitos de spillover. Uma melhoria do IMSC, o Controle Modal Eficiente (EMC) também é apresentado com o propósito de reduzir as amplitudes das forças de controle. O modelo matemático da estrutura inteligente é obtido a partir do Método dos Elementos Finitos (MEF) considerando o acoplamento eletromecânico entre os atuadores de pilhas piezelétricos e a estrutura base. O projeto de uma treliça espacial, o posicionamento ótimo dos atuadores e sensores e o controle ativo de vibração são apresentados em simulações numéricas. Os resultados mostram que ambos os controladores aumentam o amortecimento da estrutura e, ainda, o EMC reduz as amplitudes das forças de controle. / This work presents the analytic development of the modeling of flexible truss structures with the aim to suppress the mechanical vibration using active control techniques. Piezoelectric stack actuators are used to produce control force in the structure, which can replace an entire bar or can be coupled to structural members. They also satisfy the necessity to obtain lighter structures. The optimal placement of actuators and sensors is found through the Hã norm as objective function. As control technique is presented the Independent Modal Space Control (IMSC), in which a modal estimator is used and the Linear Quadratic Regulator (LQR) feedback the estimated states according the optimal control theory. IMSC is computationally efficient also applied in high order system and reduces the negative effects of the control and observer spillover. An improvement in the IMSC is the Efficient Modal Control (EMC) that is proposed to reduce the amplitudes of control forces. The mathematical model of the intelligent structure is obtained from Finite Elements Method (FEM) considering the electromechanical coupling between the piezoelectric stack actuators and the base structure. The design of a space truss structure, the optimal placement of active members and the active damping vibration control is numerically implemented. Two control techniques are tested and compared: IMSC and EMC. Results show that the controllers increase the damping of the structure noticeably. The EMC controller provides better performance, reducing the amplitudes of control forces.

Orientador: Vicente Lopes Júnior / Banca: Luiz de Paula do Nascimento / Banca: Marcus Antonio Viana Duarte / Resumo: Este trabalho apresenta o desenvolvimento analítico da modelagem de estruturas flexíveis do tipo treliça com o objetivo de atenuação de vibrações através do uso de técnicas de controle ativo. Atuadores de pilha piezelétricos são usados para exercer as forças de controle na estrutura, os quais substituem barras inteiras ou somente uma parte delas. Estes tipos de atuadores, também, satisfazem a necessidade de obtenção de estruturas leves. O posicionamento ótimo desses atuadores e de sensores é encontrado através da norma Hx, que é usada como função objetivo. Como técnica de controle é aplicado o Controle no Espaço Modal Independente (IMSC), no qual os estados são estimados por um estimador modal e são realimentados de acordo com a teoria de controle ótimo, o Regulador Linear Quadrático (LQR). O IMSC é eficiente computacionalmente mesmo aplicado a sistemas de alta ordem e também reduz os efeitos de spillover. Uma melhoria do IMSC, o Controle Modal Eficiente (EMC) também é apresentado com o propósito de reduzir as amplitudes das forças de controle. O modelo matemático da estrutura inteligente é obtido a partir do Método dos Elementos Finitos (MEF) considerando o acoplamento eletromecânico entre os atuadores de pilhas piezelétricos e a estrutura base. O projeto de uma treliça espacial, o posicionamento ótimo dos atuadores e sensores e o controle ativo de vibração são apresentados em simulações numéricas. Os resultados mostram que ambos os controladores aumentam o amortecimento da estrutura e, ainda, o EMC reduz as amplitudes das forças de controle. / Abstract: This work presents the analytic development of the modeling of flexible truss structures with the aim to suppress the mechanical vibration using active control techniques. Piezoelectric stack actuators are used to produce control force in the structure, which can replace an entire bar or can be coupled to structural members. They also satisfy the necessity to obtain lighter structures. The optimal placement of actuators and sensors is found through the Hã norm as objective function. As control technique is presented the Independent Modal Space Control (IMSC), in which a modal estimator is used and the Linear Quadratic Regulator (LQR) feedback the estimated states according the optimal control theory. IMSC is computationally efficient also applied in high order system and reduces the negative effects of the control and observer spillover. An improvement in the IMSC is the Efficient Modal Control (EMC) that is proposed to reduce the amplitudes of control forces. The mathematical model of the intelligent structure is obtained from Finite Elements Method (FEM) considering the electromechanical coupling between the piezoelectric stack actuators and the base structure. The design of a space truss structure, the optimal placement of active members and the active damping vibration control is numerically implemented. Two control techniques are tested and compared: IMSC and EMC. Results show that the controllers increase the damping of the structure noticeably. The EMC controller provides better performance, reducing the amplitudes of control forces. / Mestre

This research investigates on-blade partial span active plain trailing edge flaps (TEFs)with an aim to alleviate the helicopter vibrations. Among all the available smart materials, piezoelectric stack actuator(PEA)has shown its strong candidature for full scale rotor systems. Although, PEAs are quite robust in operation, however, they exhibit rate dependent hysteresis phenomenon and can generate only very small displacements. Dynamic hysteresis is a complex phenomenon which, if not modeled, can lead to drift in the vibration predictions. In this research, a comprehensive experimental analysis is performed on a commercially available piezostack actuator, APA-500L, which is well suited for full scale applications. Rate dependent hysteresis loops are obtained for helicopter operational frequencies. Nonlinear rate-dependent hysteresis loops are modeled using conic section approach and the results are validated with experimental data. Dynamic hysteresis exhibited by the PEA is further cascaded with the helicopter aeroelastic analysis and its effect on helicopter vibration predictions is investigated. PEAs generate high force but are limited by small translational motions. A linear to rotary motion amplification mechanism is required to actuate the TEF for vibration alleviation. A smart flap is designed and developed using computer-aided-design models. A rotor blade test section is fabricated and a lever-fulcrum mechanism (AM-1) is developed for a feasibility study. Smart flap actuation is demonstrated on the rotor blade test section. The conventional motion amplification devices contain several linkages, which are potential sites for structural failure. A novel pinned-pinned post-buckled beam linear-to-rotary motion amplifier (AM-2) is designed and developed to actuate the flaps. A new design of linear-to-linear amplification mechanism (LX-4) is developed and is employed in conjunction with AM-2 to increase the flap angles by an order of magnitude. An analytical model is developed using Mathieu-Hill type differential equations. Static and dynamic tests are conducted on a scaled flap model. Helicopter aeroelastic simulations show substantial reduction in hub loads using AM-2 mechanism. To further enhance the flap angles, an optimization study is performed and optimal beam dimensions are obtained. A new technique is also proposed to actively bias the flaps for both upward and downward motion. Critical flap design parameters, such as flap span, flap chord and flap location influences the flap power requirement and vibration objective function significantly. A comprehensive parametric investigation is performed to obtain the best design of TEFs at various advance ratios. Although, parametric study equips the designer with vital information about various critical system parameters, however, it is a computationally expensive exercise especially when used with large comprehensive helicopter aero elastic codes. A formal optimization procedure is employed to obtain the optimal flap design and location. Surrogate models are developed using design of experiments based on response surface methodology. Two new orthogonal arrays are proposed to construct the second order polynomial response surfaces. Pareto analysis is employed in conjunction with a newly developed computationally efficient evolutionary multi-objective bat algorithm. Optimal flap design and flap locations for dual trailing edge flaps are obtained for mutually conflicting objectives of minimum vibration levels and minimum power requirement to actuate the flaps.