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Robustness of compliant mechanism topology optimization formulations

Proceedings of SPIE - The International Society for Optical Engineering 1999年 3667卷 244-254页

作者： Hetrick, Joel A. Kikuchi, Noboru Kota, Sridhar Univ of Michigan Ann Arbor United States

Compliant mechanisms are devices which utilize elastic deformation to emulate the behavior of conventional rigid mechanisms. Structural optimization techniques represent a relatively new approach for automating topology synthesis of compliant mechanisms. A cantilever beam model is presented in order to examine the solution behavior of various objective functions intended for compliant mechanism optimization. The model reveals that objective functions which attempt to simultaneously maximize the flexibility and stiffness of a compliant mechanism can be formulated such that they are not well-bounded. Topology optimization problems using these types of objective functions may exhibit heightened convergence sensitivity with respect to the lower design variable bound. The cantilever beam model is also used to develop a new objective function based on maximizing the energy throughput of a compliant mechanism pushing against an external spring. The objective function shows a well-bounded solution to the simple beam model and consequently exhibits more robust optimization convergence. A simple numerical example is given which demonstrates the heightened robustness of the formulation.

关键词： Intelligent structures

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Probabilistic characterization of the performance of actively controlled smart structures

Probabilistic characterization of the performance of activel...

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smart structures and materials 1999 Conference

作者： Akpan, UO Orisamolu, IR Martec Ltd Res & Emerging Technol Dept Halifax NS B3J 3J8 Canada

ISBN: (纸本)0819431419

smart materials and structural systems are increasingly attracting attention from the engineering community because of their importance in current and future high performance structural applications. As these new structural systems emerge, there is an important need to have capabilities that can be employed for assessing their performance with reference to the primary functional requirement of structural integrity and control robustness as well as reliability. Furthermore, it is desirable to establish adequate performance metrics (which account for inherent or environmental uncertainties) that can be used as a quantitative basis for the comparative evaluation of various design options or for assessing the state of such systems that are already in service. In this study, two measures that can be used for probabilistic characterization and assessment of the performance of actively controlled smart structures are developed. The framework is based on the use of the probabilistic finite element strategy for modelling the parent (host) structure as well as the piezoelectric materials that are employed for sensing and actuation in the assembled system. The uncertainties inherent in the parent structure and the piezoelectric materials are propagated through the probabilistic finite element model. This enables rational and realistic characterisation of the performance measures. The probabilistic models are based on the use of advanced reliability analysis algorithms which utilize fast probability integration algorithms that are robust and computationally more efficient than Monte Carlo simulation schemes. To facilitate efficient computation, an adaptive response surface methodology is employed for the approximation of the probabilistic finite element response quantities. Example problems are used to illustrate the robustness and usefulness of the proposed, methodology.

关键词： probabilistic characterization uncertainties finite elements smart structures active control

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control system design for structural systems under statistical parametric uncertainty

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Proceedings of SPIE - The International Society for Optical Engineering 1999年 3667卷 219-230页

作者： Huerta-Ochoa, Ruben Johnson, Stanley H. Lehigh Univ Bethlehem United States

This paper presents a statistical approach to the controller design process for structural systems represented by uncertain models. The plant model uncertainty is here accounted for in terms of first- and second-order statistics of uncertain parameters. The basic idea is to make the closed-loop system stability as robust as possible to statistical variations of uncertain plant model parameters. First, an approximate expression for the root variance of an uncertain polynomial is derived as a function of second-order statistics of the polynomial coefficients. The expression is specialized to the case of an SISO closed-loop system characteristic polynomial, where the uncertainty is due to statistical variability of model parameters. Uncertainty cost functions intended to represent the uncertainty of the closed-loop pole locations are then constructed. By parameterizing the set of controllers that yield a desired characteristic polynomial, the uncertainty cost function minimization is converted into a constrained optimization problem. This scheme is illustrated with an SISO seismic control system previously studied in the literature. By comparing the predicted closed-loop pole variance to numerical results obtained from Monte Carlo simulations, it is concluded that the expression developed here provides an excellent approximation, with the advantage of being an analytical expression that is suitable for use in multi-objective optimization design algorithms.

关键词： Intelligent structures

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Nonlinear structural identification based on H∞ filter algorithm

Nonlinear structural identification based on H∞ filter algo...

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Proceedings of the 1999 smart structures and materials - mathematics and control in smart structures

作者： Sato, Tadanobu Qi, Kai Kyoto Univ Kyoto Japan

Dynamic behaviors of a 1-story and 4-story steel structures subject to multi-dimensional ground motion excitations were experimentally investigated by using a shaking table. Linear and nonlinear structural responses were obtained as observation data for the identification. Dynamics characteristics of the model structures were identified using the adaptive H∞ filter, which was developed for identifying structural systems with non-stationary dynamic characteristics by adding the function of memory fading (forgetting factor) for past observation data to the H∞ filter. Identification results show that the H∞ filtering technique are very efficient for identifying linear and nonlinear structural systems. Especially, the nonlinear behavior of the model can be traced effectively.

关键词： Steel structures

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Comparing direct model reference adaptive control with traditional feedback control in the area of damage mitigation

Comparing direct model reference adaptive control with tradi...

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smart structures and materials 1999 Conference

作者： Waters, DP USAF Acad Dept Mech Engn Colorado Springs CO 80840 USA

ISBN: (纸本)0819431419

The incorporation of an active control system into an aerospace structure as part of-a smart structure has raised the issue of: How does the controller respond when the structure is damaged? The answer is usually dependent on the answer to numerous: other questions regarding the type of controller, the type of damage, the application of the smart structure, etc. However, previous research has indicated that the Direct Model Reference Adaptive control (DMRAC) algorithm has potential in preventing the damaged smart structure from becoming unstable. Maintaining stability following an impact damage is of minimal usefulness if the controller can not also provide satisfactory performance before the damage event. This paper presents the simulation results of research comparing a velocity and position feedback controller with a DMRAC controller. The primary areas of concern were the undamaged performance (damping augmentation) and the damaged performance (stability and steady state response). The traditional controller design performed better before the damage occurred, but the DMRAC controller was significantly better after the damage occurred.

关键词： adaptive control damage mitigation active structures controller performance

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Collocated sensing and actuation for vibration control of adaptive anisotropic thin-walled beams

Collocated sensing and actuation for vibration control of ad...

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smart structures and materials 1999 Conference

作者： Song, O Kim, JB Librescu, L Chungnam Natl Univ Dept Mech Engn Taejon 305764 South Korea

ISBN: (纸本)0819431419

The problems of the mathematical modeling and dynamical response of thin-walled beam structures including a number of non-classical features and incorporating adaptive capabilities are considered. The theory of thin-walled beams as considered in this study encompasses non-classical features such as. anisotropy, transverse shear and secondary warping, whereas the adaptive capabilities are provided by a system of piezoelectric devices whose sensing and actuating functions are combined and which are bonded or embedded into the host structure. The synergistic implications of the application of both tailoring and collocated sensing-actuating capabilities upon the closed-loop dynamic response are presented and pertinent conclusions are outlined.

关键词： thin-walled beams adaptive materials feedback control collocated control flapping-lagging motion structural tailoring

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Roll maneuvering of flexible aircraft with distributed-parameter actuation via modal synthesis

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Proceedings of SPIE - The International Society for Optical Engineering 1999年 3667卷 46-58页

作者： Oz, Hayrani Khot, Narendra S. Bolz Hall Columbus United States

The focus is on obtaining and identifying optimal distributed-parameter-control equivalent actuation profiles for desired roll maneuvers by a modal synthesis approach. The solution for distributed-parameter-control of an aeroelastic system is developed by synthesis of modal-state-space controllers designed via the globally power optimal Independent Modal-Space control (IMSC) technique. The desired maneuver (set-point) control performance is achieved by a modal-performance-output synthesis (MPOS) approach. The MPOS approach requires that each independent modal controller be allocated a desired portion of the total desired output performance. In view of this, a modal performance-output allocation optimization problem is also defined, which minimizes a hybrid measure of control power and elastic strain energy of the structure during aeroelastic control. Insight to distributed-parameter-control equivalent actuation solutions are sought by considering the aeroservoelastic interactions among vehicle motion, aerodynamics, structural flexibility and control actuators from the perspective of work-energy, control power, and control loading requirements. The modal synthesis approach is illustrated for a flight vehicle wing design to achieve a 90 deg/sec roll-rate in a Mach 2 flight condition at altitude (20000 ft) via distributed-parameter equivalent actuation. The preliminary results indicate that such a roll-rate maneuver can be accomplished via distributed-parameter actuation with feasible levels of control power, work-energy, and control loadings through eliciting favorable aeroservoelastic interactions.

关键词： Intelligent structures

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Design of an optimum smart wing to enhance roll performance

Design of an optimum smart wing to enhance roll performance

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smart structures and materials 1999 Conference

作者： Khot, NS USAF Res Lab AFRL VASD Wright Patterson AFB OH 45433 USA

ISBN: (纸本)0819431419

This paper is concerned with designing an optimum flexible wing structure to enhance roll maneuver capability at high dynamic pressures using embedded actuating system. A wing optimized to minimize the weight with constraints on strength for symmetric pull up maneuver and constraints on the frequency distribution was used for this study. Elastic twist and camber is achieved by providing a system of actuating elements distributed within the internal substructure of the wing to provide control forces. The equilibrium equations were developed for the steady roll maneuver of a wing subjected to aerodynamic loads and actuating forces. Optimal control design approach was used to determine the distribution of actuating forces. The total straing energy was calculated as a measure of power requirement to produce twist and camber, to achieve specified flexible roll rate at different Mach numbers.

关键词： Actuators Aerodynamics control systems control systems design smart materials Fourier transforms Mathematical modeling Platinum Aerospace engineering Embedded systems

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Nonlinear control of PZT actuated trailing edge flaps

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Proceedings of SPIE - The International Society for Optical Engineering 1999年 3667卷 380-393页

作者： Kurdila, A. Li, Jing Fulton, M. Webb, Glenn Mechanics and Engineering Science Gainesville United States

While PZT exhibits only mild nonlinear response at low voltage levels, it is well-known that the response can be profoundly nonlinear at high field strengths. Moreover, the use of mechanical linkages and structural design to amplify the stroke of PZT-based actuation likewise can couple with this material nonlinearity to yield a structural level nonlinearity that is non-negligible. In this paper, we investigate such a nonlinear response in a PZT actuated trailing edge flap attached to a scaled helicopter rotor blade. While the example studied in this paper is quite specific, the methodology derived is generally applicable. We extend the recent results of [18,19] for the derivation of closed loop control for active material actuated devices. In this technique, a compensator derived from an offline identification of a Krasnoselski-Pokrovski hysteresis operator is cascaded with the plant. We show that the methodology is well-posed for the class of problems under consideration; we derive closed loop stability and robustness conditions that can be associated with the prediction error in the identified hysteresis operator. We study the performance of our methodology in numerical examples and discuss relevant experimental results.

关键词： Actuators

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Design of flextensional transducers using the homogenization design method

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Proceedings of SPIE - The International Society for Optical Engineering 1999年 3667卷 232-243页

作者： Silva, Emilio C.N. Nishiwaki, Shinji Kikuchi, Noboru Universidade de Sao Paulo Sao Paulo Brazil

Flextensional transducers consist of a piezoceramic (or a stack of piezoceramics) connected to a flexible mechanical structure that converts and amplifies the output displacement of the piezoceramic. Among the applications, they can be used as actuators and sonars. The transducer performance in these applications depends on the distribution of mass, stiffness, and flexibility in the coupling structure domain, which is related to the coupling structure topology. By designing other types of coupling structures connected to the piezoceramic, we can obtain new types of flextensional transducers with enhanced performance for a desired application. In this work, we extended the method for designing flextensional transducers in static and low-frequency applications to dynamic applications by introducing the inertia effect in the optimization problem. The method applies topology optimization technique based on the homogenization design method, which consists of finding the optimal material distribution in a perforated design domain with infinite microscale voids. The problem is posed as the design of a flexible structure coupled to the piezoceramic that produces high output displacements in a specified point of the domain and direction, in a specified frequency. Therefore, it consists of designing a flexible structure with a specified mode shape in a desired resonance frequency. As a result, designs of flextensional transducers are presented.

关键词： Intelligent structures

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