系统仿真技术在控制系统中的应用

系统仿真技术是一种以对实际系统建立正确的数学模型为基础，以计算机为工具的对实际系统进行模拟的技术。计算机技术的高速发展，使系统仿真技术在各个领域中都得到了广泛的应用。以化工及工业锅炉自动控制系统中水箱系统的液位控制问题为例，阐述了系统仿真技术在自动控制领域中的应用。     

线性调频信号检测方法的研究

在线性调频信号体制雷达的数字脉冲压缩系统中对数字脉压后的脉冲串进行DFT相参处理时，若采样时刻偏离脉压回波的峰值时刻，不同的采样频率使得DFT相参积累后的信噪比会有不同程度的损失。本文详细分析了采样频率分别为20MHz和10MHz时对信号相参积累的影响，并对幅值检测和M／N检测两种检测方法的检测性能进行了比较，仿真结果表明，M／N检测优于幅值检测。     

一种新的多径相关瑞利信道的数学模型：理论分析及仿真比较

产生统计独立的多径相关瑞利信道是无线信道仿真的一个基本问题.Jakes模型得到了广泛应 用,但它在统计独立性方面还存在一些问题.该文提出一种新的相关瑞利信道的数学模型.理论分析和仿真 比较表明它在计算复杂度和统计独立性方面比最初的Jakes模型及其近来发现的改进模型更加简单有效.     

溶质运移理论的发展

关于土壤或地下水受到污染的问题,其实质是可溶性污染物在水流作用下在土壤或含水层中的运移结果,研究此问题而兴起的一门学科就是溶质运移理论。介绍了溶质运移模型、溶质运移的室内外试验研究成果和溶质运移数值模拟方法的研究现状。     

主动雷达终端实时仿真软件的设计与实现

在主动雷达数据回放显示的基础上,通过使用D irectDraw和Intel IPP技术,设计了主动雷达终端实时仿真软件,包括信号处理、数据处理及终端显示等模块,极大地提高了软件的执行效率,使得整个仿真过程具有良好的实时性。本文介绍了该软件的设计及实现。     

A stochastic model for localized disturbances and its applications

A stochastic model for local disturbances, particularly for a temporal harmonic with random modulations in amplitude and/or phase, is proposed in this paper. Results for the second moment responses of a linear single-degree-of-freedom system to this type of stochastic loading demonstrate a significant change in response characteristics due to a small uncertainty. A local phenomenon may last much longer and resonance may be smeared to a broad range. Integrated with wavelet transform, the proposed approach may be used to model a random process with non-stationary frequency content. Especially, it can be effectively used for Monte Carlo simulation to generate large size of samples that have similar characteristics in time and frequency domains as a pre-selected mother sample has. The technique has a great potential for the case where uncertainty study is warranted but the available samples are limited.     

Quantifying and characterizing contemporary riparian sedimentation

Fluvial processes of erosion, sediment transport and deposition determine the changing form and sedimentary structure of naturally adjusting riparian zones. Riparian sediment storage has both scientific and management importance in relation to: (i) the quantities of sediment that are involved; (ii) the quality of the sediment; and (iii) the dispersal of biological materials, notably the vegetation propagules that are transported and deposited in association with the sediment. After discussing the significance of riparian sedimentation processes, this paper reviews methods for quantifying contemporary sediment deposition within water bodies and their margins. Methods for investigating contemporary riparian sedimentation are given particular emphasis, and the extent to which different methods provide comparable estimates and have been used to support the analysis of different physical and chemical properties of the sediment are outlined. The importance of the following are stressed: (i) selecting a sampling method that is suited to the sedimentation environment; (ii) incorporating careful cross‐calibration if measurements from different methods are to be combined; and (iii) replicating measurements to give more robust estimates if small traps are employed. It is concluded that artificial turf mats provide a useful design of sediment trap across a range of environmental conditions because: (i) their surface roughness reduces problems of sediment removal by flood waters or rainfall; (ii) their pliability permits installation on irregular surfaces; (iii) they can be securely attached to the ground with metal pins to resist high shear stresses from river flows; (iv) they are robust and light and so easily manipulated in the field and laboratory; (v) it is possible to fully recover the deposited sediment to accurately determine the amount of sediment deposited and to support a range of other analyses. Results are presented to illustrate how artificial turf mats can be used to estimate the quantity and quality of deposited sediment and to explore the associated deposition of viable seeds. This provides one example of the important hydroecological role of riparian sedimentation processes and of the potential for the development of innovative, interdisciplinary research on riparian sediment dynamics. Copyright © 2003 John Wiley & Sons, Ltd.     

伶仃洋三维潮流输沙的数值模拟

作者使用垂向坐标变换技术，结合有限差分方法建立了三维潮流输沙的数学模型。为了增加模型的稳定性和减少数值耗散，对悬沙对流扩散方程中的水平对流项采用三阶迎风格式离散。应用本模型对伶仃洋的枯季和洪季的潮流输沙的悬沙场进行了数值模拟，将模拟结果与实测资料进行比较，二者吻合较好。模拟结果分析表明：伶仃洋悬沙运动主要集中在西滩，对伶仃航道影响不大；洪季水体含沙浓度高于枯季；水体含沙浓度沿水深存在浓度梯度，且洪季的浓度梯度明显大于枯季。     

带通采样在数据采集中的应用研究

在数据采集中采用带通采样，可大大降低采样率，但系统中的抗混叠滤波器会造成相位的非线性。采用对滤波后的信号进行带通采样，然后再用FRR滤波器校正相位的非线性，从而不失真地还原原信号，最后在Matlab中进行仿真，验证了该方法的有效性。