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.
Adaptive structures optimal design problems and solution methods are presented and discussed for the cases of shape control and active damping. A general method to solve simultaneously optimal placement and control pr...
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ISBN:
(纸本)0819431419
Adaptive structures optimal design problems and solution methods are presented and discussed for the cases of shape control and active damping. A general method to solve simultaneously optimal placement and control problems for active damping applications is outlined. This method is based on a finite element structural model and on the calculation of the closed-loop system poles. Numerical results are given to illustrate this method for the case of a beam with collocated PZT sensor/actuator pair and a direct velocity feedback controller.
This paper presents the design and experiment results of active position control of a shape memory alloy (SMA) wires actuated composite beam. The composite beam is honeycomb structured with shape memory alloy wires em...
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This paper presents the design and experiment results of active position control of a shape memory alloy (SMA) wires actuated composite beam. The composite beam is honeycomb structured with shape memory alloy wires embedded in one of its phase sheet for active actuation. The potential applications of this experiment include thermo-distortion compensation for precession space structure, stern shape control for submarines, and flap shape control for aeronautical applications. Shape memory alloy wires are chosen as actuating elements due to their high recovery stress (maybe >700 MPa) and tolerance to high strain (up to 8%). However, shape memory alloy wires are inherently nonlinear and pose a challenge for control design. A robust controller is designed and implemented to active control the tip position of the composite beam. The experiment setup consists of the composite beam with embedded SMA wires, a programmable current/voltage amplifier to actuate the SMA wires, an infrared laser range sensor to detect the beam tip displacement, and a real-time data acquisition and control system. Experiments demonstrated the effectiveness of the robust control.
Among the numerous studies published in the field of shape memory alloys (SMA), an important part is devoted to the thermomechanical properties of these materials. Few studies have been done in order to develop contro...
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ISBN:
(纸本)0819431419
Among the numerous studies published in the field of shape memory alloys (SMA), an important part is devoted to the thermomechanical properties of these materials. Few studies have been done in order to develop control laws of SMA actuators for temperature, position and force control with guaranteed stability and performances. The reason is that these materials have an highly non linear dynamic behavior (including hysteresis) because of the physical principle of motions which is a solid-solid phase transition (between an austenitic and a martensitic phase). It is then difficult to guaranty stable control and to predict the dynamic behavior in closed-loop (trajectory and effort). For this purpose, this paper is focused on control of such actuators. To obtain a control law for the closed-loop motion or force control, we use a non linear dynamic model performed in a previous work. With this dynamic model, we use non linear control techniques based on the Lie algebra to obtain the control laws for the position or the force closed-loop. Experimentation show that the proposed method is very useful for the control of SMA actuators.
A one-dimensional model for shape memory alloys is presented that permits the simulation of actuatoric behavior. It is an improved version of the Muller-Achenbach single crystal model and calculates the length change ...
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ISBN:
(纸本)0819431419
A one-dimensional model for shape memory alloys is presented that permits the simulation of actuatoric behavior. It is an improved version of the Muller-Achenbach single crystal model and calculates the length change as a response to electric heating. Based on this model, a polycrystalline version is developed, which is shown to be in excellent agreement with experimental results. Finally, as an illustrative application,a real-time control is calculated for an adaptive beam using SMA actuators.
Modeling of piezoelectric smartstructures including absorbing material was studied for cabin noise problems, The finite element method which uses a combination of three dimensional piezoelectric, flat shell and trans...
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ISBN:
(纸本)0819431419
Modeling of piezoelectric smartstructures including absorbing material was studied for cabin noise problems, The finite element method which uses a combination of three dimensional piezoelectric, flat shell and transition finite elements is adopted to model the piezoelectric active structure. The acoustic pressure in the cubic shaped cavity is represented in terms of modes of the cavity and the absorbing material is modeled using surface acoustic impedance. Finally, the effect of the cavity pressure is introduced in the finite element equations. The simulation result of sound pressure in the cavity is compared with an experiment and they show a good agreement. The cavity pressure is reduced in a wide frequency range except the resonance frequencies of the plate by applying absorbing material. It can be concluded that the piezoelectric smartstructures with absorbing materials can be a creative technology for cabin noise problems.
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