Multi-objective control optimization for semi-active vehicle suspensions

In this paper we demonstrate a method for determining the optimality of control algorithms based on multiple performance objectives. While the approach is applicable to a broad range of dynamic systems, this paper focuses on the control of semi-active vehicle suspensions. The two performance objectives considered are ride quality, as measured by absorbed power, and thermal performance, as measured by power dissipated in the suspension damper. A multi-objective genetic algorithm (MOGA) is used to establish the limits of controller performance. To facilitate convergence, the MOGA is initialized with popular algorithms such as skyhook control, feedback linearization, and sliding mode control. The MOGA creates a Pareto frontier of solutions, providing a benchmark for assessing the performance of other controllers in terms of both objectives. Furthermore, the MOGA provides insight into the remaining achievable gains in performance.     

Passive control of chaotic system with multiple strange attractors

In this paper we present a new simple controller for a chaotic system, that is, the Newton--Leipnik equation with two strange attractors: the upper attractor (UA) and the lower attractor (LA). The controller design is based on the passive technique. The final structure of this controller for original stabilization has a simple nonlinear feedback form. Using a passive method, we prove the stability of a closed-loop system. Based on the controller derived from the passive principle, we investigate three different kinds of chaotic control of the system, separately: the original control forcing the chaotic motion to settle down to the origin from an arbitrary position of the phase space; the chaotic intra-attractor control for stabilizing the equilibrium points only belonging to the upper chaotic attractor or the lower chaotic one, and the inter-attractor control for compelling the chaotic oscillation from one basin to another one. Both theoretical analysis and simulation results verify the validity of the suggested method.     

Development of multiple drywall with high sound insulation performance

Experimental studies for the development of multiple drywalls with a high sound insulation performance are performed. Firstly, a means of preventing the sound insulation deterioration due to the coincidence effect at high frequencies is investigated by layering two plasterboards with different physical characteristics. Based on the results, a double drywall with a sound insulation performance of R_w = 61 is developed. Further more, a double drywall of R_w = 64 , a triple drywall of R_w = 86 and a quadruple drywall of R_w = 90 are developed.     

Optimization of laser butt welding parameters with multiple performance characteristics

This paper presents a study carried out on 3.5 kW cooled slab laser welding of 904 L super austenitic stainless steel. The joints have butts welded with different shielding gases, namely argon, helium and nitrogen, at a constant flow rate. Super austenitic stainless steel (SASS) normally contains high amount of Mo, Cr, Ni, N and Mn. The mechanical properties are controlled to obtain good welded joints. The quality of the joint is evaluated by studying the features of weld bead geometry, such as bead width (BW) and depth of penetration (DOP). In this paper, the tensile strength and bead profiles (BW and DOP) of laser welded butt joints made of AISI 904 L SASS are investigated. The Taguchi approach is used as a statistical design of experiment (DOE) technique for optimizing the selected welding parameters. Grey relational analysis and the desirability approach are applied to optimize the input parameters by considering multiple output variables simultaneously. Confirmation experiments have also been conducted for both of the analyses to validate the optimized parameters.     

多基阵联合的无源纯方位目标运动分析研究

研究基于两声呐基阵的方位数据融合的目标运动分析方法,给出了伪线性处理、扩展卡尔曼滤波、最大似然估计等算法的模型,进行了仿真实验,比较和分析了仿真结果。计算结果表明,所给出的多基阵联合的无源纯方位目标运动分析方法,不仅克服了单基阵纯方位目标运动分析需要本舰机动的限制,而且提高了参数估计算法的稳定性和全局性。     

Improved power distribution in diffuse Indoor Optical Wireless systems employing multiple transmitter configurations

Power distribution plays a vital role in the performance of diffuse indoor optical wireless systems. Commonly used single-transmitter diffuse systems result in non-uniform power distribution patterns. We propose the use of multiple transmitters, suitably placed at different locations on the ceiling, as a technique to obtain fairly uniform power distribution on the floor. In this paper we use an extension of the recursive method developed by J.R. Barry and J.M. Kahn (IEEE Sel. Area Commun. 1 367, 1993), to compute multi-path impulse response and power distribution. We show that placement of the transmitters is crucial in achieving near uniform power distribution. Effect of the number of transmitters on power distribution and the channel bandwidth are also examined.     

基于状态矢量融合的多基地无源目标运动分析

在多基地独立观测估计的基础上,采用对状态矢量进行数据融合的方法对无源目标运动分析(以下简称TMA)问题进行了研究。在双基地的条件下,讨论了当双基地的无源声呐匀采用容易得到的目标方位角、频率的数据测量为输入时的无源TMA问题。利用伪线性方法或扩展Kalman滤波方法作预处理后,将所得到的各状态矢量的预估计送入融合中心再进行数据融合,最后实现对目标的最终估计。计算机仿真结果表明:状态矢量融合的方法能够进一步提高对目标运动参数的估计精度,能有效地实现无源TMA问题的估计。     

Passive combination of multiple beams in an optical fiber via stimulated Brillouin scattering

We demonstrate passive combination of multiple beams in an optical fiber via stimulated Brillouin scattering (SBS). Four off-axis beams are combined in a long multimode optical fiber using a novel all-optical mount. The combined beam has the high spatial coherence properties of the LP(01) mode owing to the beam cleanup properties of SBS. The threshold for SBS when off-axis pumps are used is shown to be a factor of 13 times higher than for on-axis pump beams. We propose this method would improve the brightness of an array of fiber amplifiers.     

Convection in colloidal suspensions with particle-concentration-dependent viscosity

The onset of thermal convection in a horizontal layer of a colloidal suspension is investigated in terms of a continuum model for binary-fluid mixtures where the viscosity depends on the local concentration of colloidal particles. With an increasing difference between the viscosity at the warmer and the colder boundary the threshold of convection is reduced in the range of positive values of the separation ratio y \psi with the onset of stationary convection as well as in the range of negative values of y \psi with an oscillatory Hopf bifurcation. Additionally the convection rolls are shifted downwards with respect to the center of the horizontal layer for stationary convection (y \psi > 0 and upwards for the Hopf bifurcation (y \psi < 0 .     

带经济器的热泵型纯电动客车空调系统结霜特性研究

针对热泵型纯电动客车空调系统在冬季低温供热运行时车外换热器易结霜问题,设计并搭建一套带经济器、有三种不同补气方式的热泵空调系统实验台。通过实验研究并对比分析该系统在不同补气方式下运行时车外微通道平行流换热器的结霜性能,发现车外环境温度为-15℃工况时,在中压补气方式下结霜运行时系统COP、制热量、蒸发温度均明显最高,此时系统可高效运行。     

机动车空气动力测试风洞的声学设计

测试、鉴定并研究高速机动车对环境及在车内所产生的噪声，必须有“安静”的风洞，抑制风洞内的气流噪声，将它的本底噪声降低到车辆噪声以下，测试大厅中有足够低的以上获得应有的自由声场范围，所有的声学处理措施不影响风洞的空气动力性能；吸声构件中不含矿物性纤维材料；具有相应的阻燃性能并易于清洁，本文介绍了满足以上所有要求的斯图加特大学空气动力实验室风洞的声学设计和所采用的新型吸声材料，给出了构造大样及实测结果     

无人机载多光谱侦察效能研究

光谱成像探测技术将成像技术和光谱技术结合在一起,能够提供丰富的目标场景信息。对多光谱成像探测技术进行了详细研究,针对迷彩伪装目标侦察设计了无人机载多光谱摄像机,重点分析了多光谱侦察探测、识别的计算方法。通过试验验证,多光谱侦察效能提高20%~50%。     

Passive imaging with pulsed ultrasound insonations

Previously, passive cavitation imaging has been described in the context of continuous-wave high-intensity focused ultrasound thermal ablation. However, the technique has potential use as a feedback mechanism for pulsed-wave therapies, such as ultrasound-mediated drug delivery. In this paper, results of experiments and simulations are reported to demonstrate the feasibility of passive cavitation imaging using pulsed ultrasound insonations and how the images depend on pulsed ultrasound parameters. The passive cavitation images were formed from channel data that was beamformed in the frequency domain. Experiments were performed in an invitro flow phantom with an experimental echo contrast agent, echogenic liposomes, as cavitation nuclei. It was found that the pulse duration and envelope have minimal impact on the image resolution achieved. The passive cavitation image amplitude scales linearly with the cavitation emission energy. Cavitation images for both stable and inertial cavitation can be obtained from the same received data set.     

Hybrid WDMA/OCDM system with the capability of encoding multiple wavelength channels by employing one encoder and one corresponding optical code

<正>A hybrid wavelength division multiple access(WDMA)/optical code division multiplexing(OCDM) system is proposed,where the optical code is not the same as the address of every optical network unit(ONU); rather,the code is a virtual fiber of hybrid passive optical network(PON).To our knowledge,this is the first report analyzing a single encoder/decoder with a single corresponding optical code being exploited to encode/decode multiple wavelength signals simultaneously.This system enables OCDM to become transparent to ONU so that the existing wavelength division multiplexing(WDM) PON can be upgraded. Thus,redesigning the optical line terminal and ONU can be easily accomplished,and greatly decreasing the number of encoder/decoder becomes possible.In experiment,we only employ two encoder/decoder pairs to combine two WDM-PONs in one fiber.Simulation results confirm the feasibility of the proposed system.     

Facile synthesis of nanostructured n-type SiGe alloys with enhanced thermoelectric performance using rapid solidification employing melt spinning followed by spark plasma sintering

SiGe alloy is widely used thermoelectric materials for high temperature thermoelectric generator applications. However, its high thermoelectric performance has been thus far realized only in alloys synthesized employing mechanical alloying techniques, which are time-consuming and employ several materials processing steps. In the current study, for the first time, we report an enhanced thermoelectric figure-of-merit (ZT) ∼ 1.1 at 900 °C in n-type Si₈₀Ge₂₀ nano-alloys, synthesized using a facile and up-scalable methodology consisting of rapid solidification at high optimized cooling rate ∼ 3.4 × 10⁷ K/s, employing melt spinning followed by spark plasma sintering of the resulting nano-crystalline melt-spun ribbons. This enhancement in ZT > 20% over its bulk counterpart, owes its origin to the nano-crystalline microstructure formed at high cooling rates, which results in crystallite size ∼7 nm leading to high density of grain boundaries, which scatter heat-carrying phonons. This abundant scattering resulted in a very low thermal conductivity ∼2.1 Wm⁻¹K⁻¹, which corresponds to ∼50% reduction over its bulk counterpart and is amongst the lowest reported thus far in n-type SiGe alloys. The synthesized samples were characterized using X-ray diffraction, scanning electron microscopy and transmission electron microscopy, based on which the enhancement in their thermoelectric performance has been discussed.     

Passive quantum error correction with linear optics

Recently it was proposed by Kalamidas in [D. Kalamidas, Phys. Lett. A 343 (2005) 331] an optical set-up able to correct single qubit errors using Pockels cells. In this work, we present a different set-up able to realize error correction passively, in the sense that none external action is needed.     

Passive mode locking with slow saturable absorbers

We give a comprehensive overview on passive mode locking of solid-state lasers with slow saturable absorbers, based on analytical and numerical calculations. For picosecond lasers, we present a simple equation to estimate the obtained pulse duration and compare the results to those for mode locking with fast saturable absorbers. We also discuss how much shorter the pulse duration can be compared to the absorber recovery time and present a simple rule. The effect of self-phase modulation is found to be qualitatively different compared to the case of a fast saturable absorber, and the effect of phase changes in the absorber is also discussed. Finally, we discuss various issues concerning soliton mode-locked lasers. Received: 20 July 2001 / Revised version: 28 September 2001 / Published online: 7 November 2001     

Passive T-bus with asymmetrical 4-port couplers

A newly designed 4-port coupler in planar technology is described. The axes of the coupling fibers are mutually offset as before, but the input fiber is thinner than the other three, and its diameter is matched to the emitting surface area of the light source serving as a transmitter. Low insertion loss and high coupling efficiency are realized through the choice of favorable dimensions. Graphs show the output coupling efficiency, input coupling loss, and insertion loss with step-index fibers as a function of the axial offset. The maximum number of terminals that can be connected to the T-bus is calculated for various conditions. The number of terminals is found to be about 40% higher than is possible with the coupler with four identical fibers.     

多无人机协同的稳定控制机理研究

多无人机协同系统的过度扩散会引起协同失效, 对系统进行规模控制是解决该问题的一种潜在方法. 首先抽象出多无人机协同搜索系统的宏观运动特征, 进而建立平台的运动方程, 然后通过构造合适的李雅普诺夫函数, 获得该系统的稳定控制规律及其控制参数. 仿真结果表明: 1)本文所提的稳定控制机制不仅能够使多无人机系统实现有效的协同, 还能确保系统的稳定性; 2)在系统稳定时, 通过调整相关控制参数可以有效地控制系统规模. 关键词： 无人机 协同系统 稳定控制