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971.
972.
针对执行器发生部分失效故障的漂浮基空间机器人系统,提出了一种自适应H∞分散容错控制算法。利用拉格朗日第二类方程建立了系统的动力学模型。根据分散原理将系统分解为以基座或臂杆为单元的多个子系统,并将表示执行器控制能力的有效因子融入到每个子系统,使得单个子系统的执行器故障不会影响相邻执行器的正常运行。通过对每个故障子系统设计形式一致的自适应容错算法实现对整个系统的容错控制。仿真结果表明,与现有某非奇异终端滑模容错算法相比,本文算法具有更快的跟踪速度和更高的跟踪精度。 相似文献
973.
入射电子被中性原子散射过程中的库仑波描述 总被引:1,自引:0,他引:1
在前期工作的基础上,给出了有效电荷Zeff的解析形式.研究发现:有效电荷Zeff与入射电子的能量和散射角有关.我们早期工作的一个重要缺陷是:对于初、末通道,分别使用了解析的平面波和库仑波,而现有的波函数与早期工作之间的一个重要差别在于:在初通道,现有的波函数包含有入射电子与中性原子之间的短程相互作用效应,而早期文章则没有这种效应.这里使用的末态波函数与以前是相同的.当入射电子处在有效电荷库仑场的情形下,我们计算了电子入射离化氦原子的三重微分截面,并发现现有的理论计算与实验结果很好的一致. 相似文献
974.
975.
O. C. Valdiviezo-Mijangos V. M. Levin F. J. Sabina 《Archive of Applied Mechanics (Ingenieur Archiv)》2009,79(1):51-67
This paper deals with the problem of multiple scattering by a random distribution of spherical solid particles in a solid.
The material properties of both media are taken as thermoelastic. The radii of the inclusions may be different. The self-consistent
method in its variant of the effective medium is used to find the dispersion and attenuation of quasi-elastic, quasi-thermal
and shear waves. The single scattering problem required by this technique is solved approximately by means of the Galerkin
method applied to an integral equation using the Green function. Numerical results display a characteristic resonance phenomena
which appears in the interval where the results are approximately valid, that is, for very long waves down to wavelengths
about twice the largest diameter of the spheres. Examples are shown, for composites with two sets of inclusions, which have
either a very similar or dissimilar size. Comparisons are made with the elastic counterpart. Among the material properties,
the mass density ratio, inclusion to matrix, seems to play an important and simple role. Frequency intervals are distinguished
and shown to depend on that ratio, where the attenuation and dispersion of quasi-elastic and P-waves are either very close
to each other or not at all. The same applies to shear waves in either composite. The mass density ratio also displays a simple
monotonic decreasing behaviour as a function of the frequency at the first attenuation maximum and velocity minimum. These
results may be of interest for the nondestructive testing characterization of particulate composites. 相似文献
976.
Orthotropic materials weakened by a doubly periodic array of cracks under far-field antiplane shear are investigated, where the fundamental cell contains four cracks of unequal size. By applying the mapping technique, the elliptical function theory and the theory of analytical function boundary value problems, a closed form solution of the whole-field stress is obtained. The exact formulae for the stress intensity factor at the crack tip and the effective antiplane shear modulus of the cracked orthotropic material are derived. A comparison with the finite element method shows the efficiency and accuracy of the present method. Several illustrative examples are provided, and an interesting phenomenon is observed, that is, the stress intensity factor and the dimensionless effective modulus are independent of the material property for a doubly periodic cracked isotropic material, but depend strongly on the material property for the doubly periodic cracked orthotropic material. Such a phenomenon for antiplane problems is similar to that for in-plane problems. The present solution can provide benchmark results for other numerical and approximate methods. 相似文献
977.
Based on both the spring layer interface model and the Gurtin-Murdoch surface/interface model, the anti-plane shear problem is studied for piezoelectric composites containing coated nano-elliptical fibers with imperfect interfaces. By using the complex function method and the technique of conformal mapping, the exact solutions of the electroelastic fields in fiber, coating, and matrix of piezoelectric nanocomposites are derived under far-field anti-plane mechanical and in-plane electrical loads. Furthermore, the generalized self-consistent method is used to accurately predict the effective electroelastic moduli of the piezoelectric nanocomposites containing coated nano-elliptical fibers with imperfect interfaces. Numerical examples are illustrated to show the effects of the material constants of the imperfect interface layers, the aspect ratio of the fiber section, and the fiber volume fraction on the effective electroelastic moduli of the piezoelectric nanocomposites. The results indicate that the effective electroelastic moduli of the piezoelectric nanocomposites can be significantly reduced by the interfacial debonding, but it can be improved by the surface/interface stresses at the small scale, which provides important theoretical reference for the design and optimization of piezoelectric nanodevices and nanostructures. 相似文献
978.
Contact transformation is an operator transformation method in time-independent perturbation theory which is used successfully
in molecular spectroscopy to obtain an effective Hamiltonian. Floquet theory is used to transform the periodic time-dependent
Hamiltonian, to a time-independent Floquet Hamiltonian. In this article contact transformation method has been used to get
the analytical representation of Floquet Hamiltonian for quadrupolar nuclei with spin I = 1 in the presence of an RF field and first order quadrupolar interaction in magic angle spinning NMR experiments. The eigenvalues
of contact transformed Hamiltonian as well as Floquet Hamiltonian have been calculated and a comparison is made between the
eigenvalues obtained using the two Hamiltonians. 相似文献
979.
基于定性分析的方法,提出了有效累计时间的概念,建立了一种基于遗传算法的人力资源优化配置模型,为人力资源的优化配置提供了一种新的量化管理的具体方法,并进行了算例分析,证明了模型的有效性、实用性. 相似文献
980.
Arguments are provided which show that extension of renormalizability in quantum field theory is possible. By an appropriate choice of effective Lagrangian, a dressed Feynman propagator is obtained. In this scheme, higher order Feynman diagrams become self-convergent and nonrenormalizable interactions become renormalizable. As an example, the vacuum fluctuation effects on ρ meson mass for the vector-tensor coupling model is discussed. It is found that the result can agree with the experimental value when coupling constant is adjusted. 相似文献