The paper presents a methodology for evaluating the effective stiffness of unidirectional composite materials with shape memory alloy (SMA) fibers in the presence of matrix cracks. The solution is obtained for the cas...
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The paper presents a methodology for evaluating the effective stiffness of unidirectional composite materials with shape memory alloy (SMA) fibers in the presence of matrix cracks. The solution is obtained for the case where SMA fibers in the intact composite are in the austenitic phase. However, elevated stresses in the sections of SMA fibers adjacent to the crack planes cause the martensitic transformation affecting the stiffness of the material. The solution has to account for thermal residual stresses in SMA and `ordinary' fibers and in the matrix. The order of magnitude of these stresses is calculated in the paper for two representative composite systems. As follows from the numerical examples, thermal residual stresses in the SMA fibers increase proportionally to their volume fraction but remain relatively small. However, thermal stresses in the matrix may reach rather high values reducing the strength of the matrix by a significant factor.
In this work the control of vibration in an elastic plate, by piezoelectric transducers, is considered. The model of the plate is that presented in [2]. An approximation of the optimal controller by a derivative parti...
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In this work the control of vibration in an elastic plate, by piezoelectric transducers, is considered. The model of the plate is that presented in [2]. An approximation of the optimal controller by a derivative partial operator is given. It is based on a development in series of the Riccati operator with respect to the reverse of the stiffness. Its implementation in term of distributed analog electronic circuits, is developed. Numerical simulations, obtained by the coupling of Finite Elements code and a circuit simulator, Alecsis, are presented. To improve the preceding result an iterative algorithm of approximation of the optimal controller, being able to be implemented by an electronic circuit, is developed. The algorithm is inspired by the approach of [4].
In this work, refined finite element models based on higher order displacement fields have been developed to study the mechanical and electrical behavior of laminated composite plate structures with embedded and/or su...
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In this work, refined finite element models based on higher order displacement fields have been developed to study the mechanical and electrical behavior of laminated composite plate structures with embedded and/or surface bonded piezoelectric actuators and sensors. Sensitivity analysis and optimization techniques are also applied in order to maximize the piezoelectric actuator efficiency, improve the structural performance and/or minimize the weight of the structure. To show the performance of the proposed models several illustrative and simple examples are presented.
Wavelets provide a new tool in vibration, identification and control. By their properties wavelets transform are stronger than FEM and FFT. We dispose to several wavelets family as Haar, Daubechies, Morlet, Mallat, et...
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Wavelets provide a new tool in vibration, identification and control. By their properties wavelets transform are stronger than FEM and FFT. We dispose to several wavelets family as Haar, Daubechies, Morlet, Mallat, etc. and use the filter banks for vibration analysis. This paper deals with the problem of controlling the bending oscillations of a thin walled cantilever beam with arbitrary cross section. The control is achieved via the action of a bending moment applied at a tip of structure. A possibility to generate the control bending moment at the wing tip is via the implementation into the structure of piezoactuators. The velocity feedback control allows the possibility to generate damping through the feedback gain coefficient. Feedback law where the bending moment at a tip is proportional to the velocity is included into matrix wavelet implementation. Numerical examples for PDE are computed and compared with other examples for particular cases included in earlier paper of Librescu, Na. The paper uses the Haar wavelet transform to algebrize PDE leading to a powerful and general method to study the nonlinear problems with more flexibility and localization of peak resonance in comparison with other procedures.
The systems theory approach to the feedback stabilization of finite-amplitude disturbances in plane Poiseuille flow results in high-order system models to accurately represent the disturbance dynamics. From a practica...
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The systems theory approach to the feedback stabilization of finite-amplitude disturbances in plane Poiseuille flow results in high-order system models to accurately represent the disturbance dynamics. From a practical standpoint, a controller developed for a specific flow control task will often have to be implemented in real-time. The need for the synthesis of rigorous control theory and experimental methods has been noted by several researchers over the years. A key step to this synthesis is the development of low dimensional descriptions of flow dynamics for control synthesis. This paper examines the use of the optimal projection method for reduced-order controller synthesis for flow disturbance model systems with relatively high order (greater than 40).
This paper proposes a new space telescope design in which the classical truss structure of the telescope is replaced by a tensegrity structure. A tensegrity structure is a prestressed structure whose structural shape ...
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This paper proposes a new space telescope design in which the classical truss structure of the telescope is replaced by a tensegrity structure. A tensegrity structure is a prestressed structure whose structural shape is guaranteed by the interaction between elastic members in tension (tendons) and a set of rigid members (bars). A nonlinear dynamical model of a two stage tensegrity telescope is derived. Static analysis is performed for tensegrity telescopes composed of two stages. The performance specifications for the control system are formulated in terms of the peak value (L∞ norm) of the pointing and alignment errors. The control system is designed to minimize a certain upper bound on this peak value subject to a peak value constraint on the external disturbances. Evaluations of the design are performed through numerical simulations of the closed loop system.
This paper presents a methodology to suppress the vibration of thin rectangular plate clamped all edges. Intelligent materials such as the piezoelectric ceramic are used as actuators and sensors. The experimental mode...
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This paper presents a methodology to suppress the vibration of thin rectangular plate clamped all edges. Intelligent materials such as the piezoelectric ceramic are used as actuators and sensors. The experimental modeling technique, i.e., the state-space frequency domain identification, is introduced to model the complex shaped structures bonded with noncollocated actuators/sensors. This method is much free from the Multi-Input Multi-Output (MIMO) model order problem caused at the digital implementation and also reduces distortion of the signal. In control scheme, the adaptive feedforward with feedback control algorithm is adopted since it is robust for both the transient and persistent external disturbances. The adaptive feedforward control uses the well known Multiple filtered-x LMS (least mean square) algorithm. The MIMO error path dynamics is controlled by the feedback loop which is constructed by multivariable digital LQG (Linear Quadratic Gaussian) controller composed of the regulator and Kalman filter. Experiment results demonstrate the effective reduction of the vibration label and the robustness for both the transient and persistent external disturbances.
Analytical formulations are presented which account for the coupled mechanical, electrical, and thermal response of piezoelectric composite shell structures. A new mixed multi-field laminate theory is developed which ...
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Analytical formulations are presented which account for the coupled mechanical, electrical, and thermal response of piezoelectric composite shell structures. A new mixed multi-field laminate theory is developed which combines `single layer' assumptions for the displacements along with layerwise fields for the electric potential and temperature. This laminate theory is formulated using curvilinear coordinates and is based on the principles of linear thermopiezoelectricity. The mechanics has the inherent capability to explicitly model both the active and sensory responses of piezoelectric composite shells in thermal environments. Finite element equations are derived and implemented for an eight-noded shell element. Numerical studies are conducted to investigate both the sensory and active responses of piezoelectric composite shell structures subjected to thermal loads. Results for a cantilevered plate with an attached piezoelectric layer are compared with corresponding results from a commercial finite element code and a previously developed program. Additional studies are conducted on a cylindrical shell with an attached piezoelectric layer to demonstrate capabilities to achieve thermal shape control on curved piezoelectric structures.
The paper first presents a general purpose finite element based simulation tool for piezoelectric controlled smartstructures. In addition to the standard finite elements, this tool contains a number of coupled electr...
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ISBN:
(纸本)0819431419
The paper first presents a general purpose finite element based simulation tool for piezoelectric controlled smartstructures. In addition to the standard finite elements, this tool contains a number of coupled electromechanical finite elements as well as numerical tools to simulate controlled structures in statics and dynamics. The effectiveness of a smart structure decisively depends on the amount and distribution of active materials across the passive structure and on the controller design. To solve this design problem automatically, a discrete optimization technique and ideas from topology optimization are presented. The control parameters are considered as continuous design variables. Mathematical solution algorithms for nonlinear, mixed continuous and discrete-valued optimization techniques are used to solve the optimization problem. As a test example the distribution of piezoelectric wafers over a beam structure is presented. Finally, tis paper gives an outlook for new developments in this field.
A study of optimal vibration control of aircraft wings carrying externally mounted stores and exposed to blast loading is presented. The wing structure is modelled as a thin-wailed beam of closed cross-section contour...
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A study of optimal vibration control of aircraft wings carrying externally mounted stores and exposed to blast loading is presented. The wing structure is modelled as a thin-wailed beam of closed cross-section contour, and a number of non-classical features such as transverse shear, secondary warping, and anisotropy of the constituent materials are included. The wing structure can carry underwing and/or tip stores. The control is achieved via the use of actuating and sensing capabilities provided by piezoelectric devices which are bonded or embedded into the host structure. The cases of piezoactuators spread over the entire span of the structure, or in the form of a patch are considered, and issues related with the influence of patch location and size upon the vibration control efficiency of wings carrying external stores axe discussed. Other issues related with the minimization of the required input power and of those generated by the inclusion/discard in the quadratic performance index of time-dependent external excitations are also addressed.
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