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101.
This paper is concerned with computing an L2-optimal reduced-order model for a given stable multivariable linear system in the presence of input and output frequency weightings. By parametrizing a class of reduced-order models in terms of an orthogonal projection and using manifold techniques as tools, both continuous and iterative algorithms are derived and their convergence properties are established. As an application, we show that an L2 optimal reduced-order filter in the closed-loop sense can be computed using these algorithms. 相似文献
102.
The robust H∞ control problem for discrete-time uncertain systems is investigated in this paper. The uncertain systems are modelled as
a polytopic type with linear fractional uncertainty in the vertices. A new linear matrix inequality (LMI) characterization
of the H∞ performance for discrete systems is given by introducing a matrix slack variable which decouples the matrix of a Lyapunov
function candidate and the parametric matrices of the system. This feature enables one to derive sufficient conditions for
discrete uncertain systems by using parameter-dependent Lyapunov functions with less conservativeness. Based on the result,
H∞ performance analysis and controller design are carried out. A numerical example is included to demonstrate the effectiveness
of the proposed results.
This work was partially supported by RGC Grant 7103/01P and the open project of the state key Laboratory of intelligent and
Systems, Tsinghua University (No.0406). 相似文献
103.
Robust stability and stabilization of discrete singular systems: an equivalent characterization 总被引:3,自引:0,他引:3
This note deals with the problems of robust stability and stabilization for uncertain discrete-time singular systems. The parameter uncertainties are assumed to be time-invariant and norm-bounded appearing in both the state and input matrices. A new necessary and sufficient condition for a discrete-time singular system to be regular, causal and stable is proposed in terms of a strict linear matrix inequality (LMI). Based on this, the concepts of generalized quadratic stability and generalized quadratic stabilization for uncertain discrete-time singular systems are introduced. Necessary and sufficient conditions for generalized quadratic stability and generalized quadratic stabilization are obtained in terms of a strict LMI and a set of matrix inequalities, respectively. With these conditions, the problems of robust stability and robust stabilization are solved. An explicit expression of a desired state feedback controller is also given, which involves no matrix decomposition. Finally, an illustrative example is provided to demonstrate the applicability of the proposed approach. 相似文献
104.
H. C. Lam W. W. Ki A. L. S. Chung P. Y. Ko A. C. Y. Lai S. M. S. Lai P. W. Y. Chou & E. C. C. Lau 《Journal of Computer Assisted Learning》2004,20(2):114-123
Effective teaching should focus the attention of learners to its essential aspects. It follows that instructional software can be designed in such a way that allows learners to experience the important variations in the critical aspects of the content to be learned. This paper reports on the experience of designing such special kinds of instructional learning objects for the learning of Chinese characters. The design of these learning objects takes into consideration not only what Chinese characters are all about but also how learners commonly make errors while they learn to write the characters. Out of the analysis of these learners' errors, variations in the structural features of Chinese characters were pulled out and embodied in the design of the learning objects. Learners tinkering with the learning objects can thus implicitly develop a sense of the structural features or regularity of Chinese characters, which most importantly should prepare the learners to learn more new characters in the future. The main proposal of this paper is the notion of this variation‐affording instructional software that allows learners to attend to the essential aspects of what is to be learned. Furthermore, the idea of the learning object also differs from other instructional software in its small, self‐contained and reusable nature, such that teachers can flexibly embed the learning objects into their own teaching materials. 相似文献
105.
Particles in initially well-mixed suspensions subject to inhomogeneous shear flows will migrate and establish a particle concentration gradient and a non-Newtonian velocity profile. In this study, a phenomenological diffusive flux model coupled with flow equations was employed to describe the shear-induced particle migration in a concentrated suspension. The focus of the paper is on the determination of the two phenomenological constants in the diffusive flux model kc and kη. They were determined inversely by employing a least square analysis on the experimental pressure data with different capillary die ratios of length to diameter of the die. The pressures and the flow patterns of the non-Newtonian concentrated suspension were predicted in terms of these two phenomenological constants. The results indicated that particle migration should be accounted for to properly characterize the rheological behaviour of concentrated suspensions. 相似文献
106.
Elastic fracture is governed by the material's strain energy released rate and depends on the applied loads and the stiffness
of the structure. The effect of stiffness on fracture as a function of structural size is typically modeled using strain-based
elastic fracture mechanics, but recent experimental evidence indicated that when the size of the structure is on the order
of the higher order material length scale parameters, elastic strain gradients would stiffen the structure. In this paper,
the higher order J-integral and energy-released rate for the analysis of fracture of strain gradient stiffened structures are developed. The
effects of beam size on the fracture behaviors of strain gradient stiffened cantilevers on a substrate were analyzed using
the higher order J-integral and the energy-released rate. Analyses revealed that the fracture load is elevated to more than 1.4 times of the
un-stiffened case when the bending stiffness is doubled by strain gradient stiffening. Elastic fracture is shown to have an
added dependence on the size of the structure when strain gradient stiffening is non-negligible. 相似文献
107.
E. A. Johnson H. F. Lam L. S. Katafygiotis J. L. Beck 《Canadian Metallurgical Quarterly》2004,130(1):3-15
Structural health monitoring (SHM) is a promising field with widespread application in civil engineering. Structural health monitoring has the potential to make structures safer by observing both long-term structural changes and immediate postdisaster damage. However, the many SHM studies in the literature apply different monitoring methods to different structures, making side-by-side comparison of the methods difficult. This paper details the first phase in a benchmark SHM problem organized under the auspices of the IASC–ASCE Structural Health Monitoring Task Group. The scale-model structure adopted for use in this benchmark problem is described. Then, two analytical models based on the structure—one a 12 degree of freedom (DOF) shear-building model, the other a 120-DOF model, both finite element based—are given. The damage patterns to be identified are listed as well as the types and number of sensors, magnitude of sensor noise, and so forth. MATLAB computer codes to generate the response data for the various cases are explained. The codes, as well as details of the ongoing Task Group activities, are available on the Task Group web site at 〈http://wusceel.cive.wustl.edu/asce.shm/〉. 相似文献
108.
Guo M Jiang XP Lam KH Wang S Sun CL Chan HL Zhao XZ 《The Review of scientific instruments》2007,78(1):016105
In this article, a multilayer piezoelectric transformer based on lead-free Mn-doped 0.94(Bi(12)Na(12))TiO(3)-0.06BaTiO(3) ceramics is presented. This piezoelectric transformer, with a multilayered construction in the thickness direction, is 8.3 mm long, 8.3 mm wide, and 2.3 mm thick. It operates in the second thickness extensional vibration mode. For a temperature rise of 20 degrees C, the transformer has an output power of >0.3 W. With a matching load resistance of 10 Omega, its maximum efficiency approaches 81.5%, and the maximum voltage gain is 0.14. It has potential to be used in low voltage power supply units such as low power adapter and other electronic circuits. 相似文献
109.
This paper focuses on the state observer design problem as well as the observer-based stabilization problem for linear neutral delay systems. The purpose of the former problem is to design an observer that guarantees the asymptotic stability of the estimation error dynamics. The existence condition for such an observer is established. The latter problem, which is the main problem studied in this paper, aims at designing an observer-based feedback controller, such that the closed-loop system is asymptotically stabilized. It is shown that the desired controller can be easily designed if there are solutions to several linear matrix inequalities. Finally, two simulation examples are given to demonstrate the validity and effectiveness of the proposed approach. 相似文献
110.