基于信息融合技术的多传感器大气波导探测研究

结合我国大气波导探测技术发展的实际情况,引入了信息融合技术,介绍并分析了采取多传感器大气波导探测的可行性和必要性,提出了信息融合中的关键技术。结合GNSS探测大气波导和气象水文模型计算大气波导2种方法的特点,初步建立了多传感器大气波导探测系统的信息融合体系结构。     

一种适于大气波导探测的空降气象仪设计

大气波导现象对舰艇作战应用有着重要的影响,探明大气波导的性质和位置具有重要的作用。传统气象测量系统对大气波导探测的针对性、准确性和实时性都不强。为此,设计了一种适于大气波导探测的空降式气象仪系统,用于提高大气波导探测的针对性、准确性和实时性。通过对大气波导形成的气象条件进行模型推导,获得影响大气波导形成的气象要素;在应用上对系统在功能进行了需求分析;提出了一种系统设计方法,针对形成大气波导的几个气象因素和需完成的功能对系统的组成和设计进行了初步的软硬件设计。     

海洋大气波导环境下反舰导弹作战效能评估

为有效评估反舰导弹在海洋大气波导环境下的作战效能,真实反映作战能力发挥,更好地服务于作战使用,针对大气波导会改变雷达电磁波传输途径的问题,研究分析了反舰导弹攻击水面舰艇和敌舰采取软硬对抗过程中,海洋大气波导对反舰导弹突防能力和制导能力的影响。并在此基础上,运用概率分析方法,引入大气波导影响因子,建立了海洋大气波导环境下反舰导弹作战效能评估模型。最后进行了该模型的实例计算,计算结果与海洋大气波导对反舰导弹作战效能有提升作用的实际情况相符,较好地反映了反舰导弹在海洋大气波导环境下作战效能发挥的实际情况,证明了该模型的合理性和实用性,为有效评估反舰导弹在海洋大气波导环境下的作战效能提供了新思路。     

蒸发波导对雷达探测距离的影响

电磁波在大气环境中传播受到各种因素的影响,引起电磁波出现异常传播现象,尤其在陷获折射条件下,形成大气波导传播。本文在介绍大气波导的分类基础上,重点论述了蒸发波导对雷达探测距离的影响。     

数字式大气波导测试仪设计

由于常规大气结构探测设备的误差较大,根据开口微波谐振腔的谐振频率随流过腔内介质不同而变化的原理,设计了一种数字式大气波导测试仪。实验证明：大气波导测试仪能够探测出气象仪器所无法获得的精细大气波导结构,具有精度高、响应速度快等特点。该仪器可为舰船雷达、通信系统实现超视距传播奠定基础。     

基于扰动理论的蒸发波导传播模态分析方法

蒸发波导足形成海上微波超视距传播的主要机制,波导模态理论用于研究微波在蒸发波导中的传播特性,但求解过程复杂,计算时间较长不适于实时应用.根据蒸发波导折射率垂直剖面情况,提出了扰动理论和波导模态理论结合的方法,简化了求解过程,提高了计算效率.应用所编制的模态分析程序,仿真计算了蒸发波导高度不同时低阶模态的传播常数,并与算例比较,验证了方法的计算精确性和快速性.同时进一步分析并给出了信号频率与蒸发波导特性参数及场分布之间的关系.     

海面蒸发波导信道的建模及仿真研究

针对海洋表面蒸发波导信道的时变、多径特性,根据海上环境下蒸发波导信道的特点及电磁波实现波导传播的必要条件,采用傅立叶分裂步进算法求解抛物线方程得出信号的传输损耗并进行功率设置,提出并建立了一个时变多径的蒸发波导信道模型,并进行了仿真.实验结果表明,提出的模型具有随机时变、多径衰落的特性,能够模拟北纬20°～ 25°、东经110°～115°海域中性层结条件下的蒸发波导信道,并在一定程度上为海上微波超视距通信系统的优化设计提供信道模型参考.     

基于小波分析的数字地形刃形消除

地形起伏特征是影响海上雷达探测性能的重要因素。基于幂级数多项式拟合、三角函数的FFT和一级Daubechies小波分解的理论分析以及数字地形的数值仿真,结果表明:FFT近似地形的精确程度与坡度取决于横向距离谱宽度,距离谱越窄,地形坡度越小,但地形失真也越严重;一级Daubechies小波分解地形的精度最高,且在整个横向距离内坡度均小于10°~15°。小波分析方法有效消除了海上复杂地形的刃形结构,极大地扩展了大气波导环境中基于修正抛物型方程进行精确数值分析的雷达探测范围。     

PJ蒸发波导模型在沿海岸应用的分析研究

PJ蒸发波导模型根据气象数据和海表温度预测蒸发波导高度及其修正折射率的垂直分布,目前对该模型预测可靠性的验证多数使用开阔海洋的气象数据,而较少使用沿海岸的气象数据.在介绍了PJ蒸发波导模型基本理论方法的基础上,利用实测的沿海岸气象数据和海上微波超视距传播实验中的传播损失观测值分析了PJ蒸发波导模型在沿海岸的适用性.结果表明,PJ蒸发波导模型使用沿海岸表面层气象数据计算出的波导高度高于实测波导高度,当实际的波导高度很低时,模型计算出的波导高度与实测高度相差很大,并且模型对海表温度的测量误差很敏感.     

三种常用蒸发波导预测模型精度比较北大核心

利用蒸发波导效应实现舰船雷达超视距探测是扩大其作用范围的有效方法之一。针对蒸发波导实际测量困难的现状,利用预测模型对蒸发波导剖面进行描述是较好的实用方法。通过对常用单参数预测模型、双参数预测模型和三参数三种蒸发波导预测模型在大气修正折射率剖面描述、对雷达电波射线描述等情况与实测蒸发波导参数的比较,证明了在描述蒸发波导剖面和利用蒸发波导参数进行电波传播分析等方面,双参数预测模型都具有较好的精度。     

基于海情和蒸发波导的舰船目标 RCS 研究

由于海面自身的条件及随机多变的特性,目标雷达散射回波会受到不同程度的影响。分别研究了不同海情、蒸发波导以及两种情况共同制约的状态下,舰船目标雷达散射回波情况,并进行了理论分析和岸-舰情况仿真。结果表明：①随海情等级的增加,目标 RCS 减小;②随着波导高度的增加,目标 RCS 增大,且大气湿度对蒸发波导传播有一定影响;③海面的粗糙度会影响蒸发波导传播,随粗糙度的增大,目标 RCS 会变小。研究结果为海面雷达侦测提供了参考依据。     

Flow simulation in Electro-Static-Precipitator (ESP) ducts with turning vanes

Flow simulation in inlet ducts along with several turning vanes used in electrostatic precipitator (ESP) are analysed to understand the flow pattern at its exit locations. The geometry of inlet duct has been extracted from the Plant Design Manufacturing System (PDMS) and refined with turning vanes placed at several locations. The domain of duct geometry around turning vanes are decomposed with several volumes and filled with hexahedral elements with the help of stat-of-art mesh generator - Hypermesh. The resulting computational grid has been used in TASCflow solver to predict its flow pattern in the duct. Simulation for the specified conditions predicts uneven flow distribution in the ESP inlet duct. Due to large flow recirculation and turbulent losses in the duct, non-uniform averaged mass flow rates are noticed at duct exit locations. Simulation results suggest that the improvement of flow distribution in the duct through optimization can be tried by placing more turning/splitter vanes in the inlet duct. In order to ensure that the results obtained from TASCflow are meaningful and in right direction, in the absence of measurement data, simulation was benchmarked with other industry standard commercial flow solvers. The observations made from these popular solvers confirm the findings obtained using the TASCflow solver. The analysis with multiple solvers indicates that Fluent provides quick results, while better visualization can be made using CFX solver. The Star-CD solver, which captures the turbulent losses accurately takes more time for convergence provides alternatives.     

Multi-leak detection and isolation in fluid pipelines

A multi-leak detection system for pipelines is designed and tested. The multi-leak detection problem is solved using only sensors of flow and pressure at the extremes of the duct, and using the analytical redundancy given of these measurements. The leak detection design is based on a distributed pipeline model that is discretized in space and assumes a set of leaks distributed through the duct. Leak location is accomplished by evaluating the residuals of a bank of unknown input observers that are robust against one leak and sensitive to the rest. Simulation and experimental results are reported to demonstrate the effectiveness of the proposed approach when two leaks appear simultaneously.     

An effective algorithm for simulating acoustical wave propagation

In this paper, the acoustical wave propagator scheme is implemented in Fortran for predicting sound propagation in a one-dimensional duct. Example calculations are performed for a semi-infinite duct and a duct with a solid blockage. Numerical accuracy of our results is examined and compared with the finite-difference time-domain method. This scheme is found to be highly accurate and computationally effective for describing the time-domain evolution of acoustic waves. Multiple reflections within the solid blockage and phase changes of the transmitting wave from solid back into air are illustrated through the implementation of this scheme.     

Direct numerical simulations of transverse and spanwise magnetic field effects on turbulent flow in a 2:1 aspect ratio rectangular duct

Magnetic fields are used extensively to direct liquid metal flows in material processing. Continuous casting of steel uses different configurations of magnetic fields to optimize turbulent flows in rectangular cross-sections to minimize defects in the solidified steel product. Realizing the importance of a magnetic field on turbulent flows in rectangular cross-sections, the present work is aimed at understanding the effect of a magnetic field on the turbulent metal flow at a nominal bulk Reynolds number of ∼5300 (based upon full duct height) (Re_τ = 170, based upon half duct height) and Hartmann numbers (based upon half duct height) of 0, 6.0 and 8.25 in a 2:1 aspect ratio rectangular duct. Direct numerical simulations in a non-MHD 2:1 aspect ratio duct followed by simulations with transverse and span-wise magnetic fields have been performed with 224 × 120 × 512 cells (∼13.7 million cells). The fractional step method with second order space and time discretization schemes has been used to solve the coupled Navier-Stokes-MHD equations. Instantaneous and time-averaged natures of the flow have been examined through distribution of velocities, various turbulence parameters and budget terms. Spanwise (horizontal) magnetic field reorganizes and suppresses secondary flows more strongly. Turbulence suppression and velocity flattening effects are stronger with transverse (vertical) magnetic field.     

Investigation on choking behavior of gas flow in microducts

In continuum regime, the large surface-to-volume ratio in microscale flow indicates stronger influence of boundary layer on internal flow, which is confirmed by the present study through quantitatively analyzing the in-duct choking and profile of boundary layer in a series of straight rectangular microducts with convergent entrances. The exit height and width of the microducts are 500 µm and 2500 µm. The number density distribution along the duct centerline is measured using a laser-induced fluorescence technique in underexpanded conditions for Reynolds numbers ranging from 745 to 6710. The experimental results show that an unexpected drop in number density emerges upstream of the duct exits. By numerically solving the 3-D Navier–Stokes equations, the computational results reveal that the build-up of boundary layer forms a virtual throat upstream of the duct exit, thus turns the straight duct into a convergent–divergent micronozzle. The location of Mach-number unity (choking) and the boundary-layer thickness are found affected by both duct configuration and Reynolds number at choking. In addition, location of the farthest in-duct choking from duct exit is found corresponding to a certain range of transition from laminar to turbulent at Re?～?2000. The 1-D analysis confirms that the in-duct choking phenomenon is related to the boundary-layer blockage rather than friction. The results of the present survey indicate the significance of reckoning boundary-layer blockage in micronozzle or microduct design.     

粗糙海面对微波蒸发波导超视距传播影响研究

蒸发波导是形成海上微波超视距传播的主要因素,但传播情况敏感于海面粗糙度.在模拟粗糙海面上的传播情况时,提出使用一个能包含粗糙海面阴影效应影响的表面反射系数,再利用抛物方程法和射线光学法计算路径损耗.仿真分析了微波在浪高服从高斯统计分布的海面上传播时,路径损耗与蒸发波导高度及风速之间的关系,并与使用不包含阴影效应影响的粗糙海面反射系数的计算结果进行了比较.结果表明来自粗糙海面的反射是计算微波沿粗糙海面蒸发波导传播路径损耗的不可忽视的重要因素.     

Energy-efficient system for automatic control of gas-air duct of heating boiler

A new energy-efficient technique to control the gas-air duct of a heating boiler is examined. The technique consists in simultaneous regulating the gas-air duct resistance by means of guiding devices (of the damper) and changing a frequency of the supply voltage of motors of the flue gas exhauster and blower. The implementation results are also considered.