Calculation of derivative of complex modes using classical normal modes

In this paper, a method to calculate derivatives of eigenvectors of damped discrete linear dynamic system with respect to the system parameter is presented. Due to the non-proportional nature of the damping, the eigenvectors become complex, and as a consequence, the derivatives also become complex. The derivatives are calculated using small damping assumption, and the method avoids using the state-space approach. The results are obtained in terms of complex modes and frequencies of the second-order system, which in turn are related to the eigensolutions of the undamped system using perturbation method. Based on the derivatives, an expression for total change of the complex eigenvectors is obtained for a more general case when all the elements of mass, stiffness and damping matrices are varying. Application and accuracy of the derived expressions are demonstrated by considering numerical examples.     

含间隙弹簧振动系统的非线性模态特性

针对含间隙的两自由度弹簧-质量分段振动系统的非线性模态开展了研究.首先,解析确定了分段保守自治系统发生同相和反相模态运动的初始位移,并采用加权平均方法确定了分段振动系统的模态频率,及其在位形空间模态曲线.然后,采用数值方法求解了系统的非线性模态曲线和模态频率,与本文获得的解析模态频率比较,说明本文的结果较等效模态频率有更好的精度.研究结果表明:在一定的参数条件下,系统的非线性模态个数会高于系统的自由度数目,系统可能发生内共振,而产生多余模态.多余模态运动是两振子同向振动中含有异向振动,说明多余模态是在同相模态运动和反相模态运动之间转换的模态.     

Discrete-time control of continuous systems with approximate decentralized fixed modes

In this paper, the discrete-time control of decentralized continuous-time systems, which have approximate decentralized fixed modes, is studied. It is shown that under certain conditions, discrete-time controllers can improve the overall performance of the decentralized control system, when a linear time-invariant continuous-time controller is ineffective. In order to obtain these conditions, a quantitative measure for different types of approximate fixed modes in a decentralized system is given. In this case, it is shown that discrete-time zero-order hold (ZOH) controllers, and in particular, that generalized sampled-data hold functions (GSHF), can significantly improve the overall performance of the resultant closed-loop system. The proposed sampled-data controller is, in fact, a linear time-varying controller for the continuous-time system.     

克希霍夫积分偏移在探地雷达中的应用及实现

详细分析和论述了克希霍夫积分偏移原理及其在探地雷达成像中的应用,针对单目标和多目标做了仿真实验.实验结果证明:将克希霍夫积分偏移原理应用在探地雷达成像中具有精度和效率较高、算法简单等优势.     

Rotation of spherical microobjects in the hyper-geometric beams

We numerically calculate forces acting upon a spherical microobject in a new family of laser beams. When propagated in homogeneous space, these beams retain their structure up to scale. It is numerically shown that when the mode’s azimuth number remains unchanged, while the radial number changes severalfold, the force exerted upon the microbead of diameter less than the width of the mode’s bright diffraction ring changes in nearly the same proportion. Experimental results on the rotation of the spherical microobject in the hypergeometric beam are presented. The text was submitted by the authors in English.     

Enabling design and interactive selection of haptic modes

The ever increasing size and complexity of volumetric data in a wide range of disciplines makes it useful to augment volume visualization tools with alternative modalities. Studies have shown that introducing haptics can significantly increase both exploration speed and precision. It is also capable of conveying material properties of data and thus has great potential to improve user performance in volume data exploration. In this paper we describe how recent advances in volume haptics can be used to build haptic modes—building blocks for haptic schemes. These modes have been used as base components of a toolkit allowing for more efficient development of haptic prototypes and applications. This toolkit allows interactive construction, configuration and fine-tuning of both visual and haptic representations of the data. The technology is also used in a pilot study to determine the most important issues and aspects in haptic volume data interaction and exploration, and how the use of haptic modes can facilitate the implementation of effective haptic schemes.     

Equivalence of characterizations of fixed modes

In this paper an equivalent property of two matrix rank conditions of a family of matrices is established. This equivalent property is then used to show that two well-known characterizations of fixed modes are mutually derivable from each other when a minor condition is satisfied.     

压电作动器在基于声辐射模态的ASAC中的应用

控制作动器的选取和设计是实现主动结构声学控制的关键一环。利用压电材料的逆压电效应,选择矩形压电片作为控制作动器应用于基于声辐射模态的主动结构声学控制中,提出了基于声辐射模态的压电作动器主动控制策略,并得到了最佳控制电压的获取方法。以简支板为例,通过压电作动器控制效果分析,揭示了压电作动器控制的内在规律;通过与单点力控制效果的比较分析,验证了压电作动器控制策略的优越性。     

Asymptotic non-linear normal modes for large-amplitude vibrations of continuous structures

Non-linear normal modes (NNMs) are used in order to derive accurate reduced-order models for large amplitude vibrations of structural systems displaying geometrical non-linearities. This is achieved through real normal form theory, recovering the definition of a NNM as an invariant manifold in phase space, and allowing definition of new co-ordinates non-linearly related to the initial, modal ones. Two examples are studied: a linear beam resting on a non-linear elastic foundation, and a non-linear clamped–clamped beam. Throughout these examples, the main features of the NNM formulation will be illustrated: prediction of the correct trend of non-linearity for the amplitude-frequency relationship, as well as amplitude-dependent mode shapes. Comparisons between different models—using linear and non-linear modes, different number of degrees of freedom, increasing accuracy in the asymptotic developments—are also provided, in order to quantify the gain in using NNMs instead of linear modes.     

Control of parallel-plate modes in microstrip antennas fed by conductor-backed coplanar waveguides

This paper evaluates the substrate characteristics allowing the control of parallel-plate modes (PPMs) in microstrip antennas fed by conductor-backed coplanar waveguides. The ratio between the radiated power and the power lost in PPMs is correlated with return loss measurements. General rules based on the calculation of the power ratio are given to avoid spurious effects due to PPMs. © 1998 John Wiley & Sons, Inc. Int J RF and Microwave CAE 8: 398–404, 1998     

Stabilization and tracking in the nonholonomic integrator via sliding modes

In this paper we use an approach based on sliding mode control to design a feedback which stabilizes the origin for the so-called nonholonomic integrator or Heisenberg system, a particular case of a canonical class of nonlinear driftless control systems of the form

which fail Brockett's necessary condition for the existence of a smooth stabilizing feedback.     

Characterizations of decentralized fixed modes for interconnected systems

A study of the characterization of decentralized fixed modes for large-scale interconnected systems is made. This is done by obtaining a recursive characterization of decentralized fixed modes, in which the existence of fixed modes of a ν-control agent system is expressed in terms of the existence of fixed modes of ν ? 1 control agent systems. An interpretation of these conditions is then made in the frequency domain. Simple conditions, in terms of the controllability of the system's subsystems, are then found for a composite system consisting of ν interconnected subsystems to have no decentralized fixed modes. This result clarifies some recent discussion on the fixed modes of interconnected systems; in particular, it proves that Fessas's conjecture is true for systems with two control agents, but false for systems with more than two control agents.     

A graph-theoretic characterization of structurally fixed modes

A characterization of structurally fixed modes in linear systems is given in the graph-theoretic framework. The characterization results in a computationally efficient test for stabilizability of systems under feedback structure constraints.     

Smart utilization of tertiary instructional modes

This empirical research surveys first year tertiary business students across different campuses regarding their perceived views concerning traditional, blended and flexible instructional approaches. A structural equation modeling approach shows traditional instructional modes deliver lower levels of student-perceived learning quality, learning experience and learning skills. A combination of on-line and face-to-face learning approaches, embedded across each course, yields far higher levels of total learning effects, and to explain differences in instructional approaches, a ‘Cone of Learning’ continuum is presented and discussed. Theoretical and practical research implications, and the measurement, theoretical and management aspects of future research options are presented. Tertiary institutions can adopt the approaches herein to assist in the development and build of smart targeted learning solutions – ones more in-line with the perceived needs of their respective student year levels and groups.