Time evolution of a squeezed chaotic field in an amplitude damping channel when used as a generating field for a squeezed number state

We investigate how an optical squeezed chaotic field（SCF） evolves in an amplitude dissipation channel. We have used the integration within ordered product of operators technique to derive its evolution law. We also show that the density operator of SCF can be viewed as a generating field of the squeezed number state.

Effects of the Reynolds number on the mean skin friction decomposition in turbulent channel flows

As the Reynolds number increases, the skin friction has been identified as the dominant drag in many practical applications. In the present paper, the effects of the Reynolds number on the mean skin friction decomposition in turbulent channel flows up to Reτ= 5 200 are investigated based on two different methods, i.e., the FukagataIwamoto-Kasagi(FIK) identity(FUKAGATA, K., IWAMOTO, K., and KASAGI, N.Contribution of Reynolds stress distribution to the skin friction in wall-bounded flows.Physics of Fluids, 14(11), L73–L76(2002)) and the Renard-Deck(RD) identity(DECK,S., RENARD, N., LARAUFIE, R., and WEISS, P.′E. Large-scale contribution to mean wall shear stress in high-Reynolds-number flat-plate boundary layers up to Reθ= 13 650.Journal of Fluid Mechanics, 743, 202–248(2014)). The direct numerical simulation(DNS) data provided by Lee and Moser(LEE, M. and MOSER, R. D. Direct numerical simulation of turbulent channel flow up to Reτ≈ 5 200. Journal of Fluid Mechanics,774, 395–415(2015)) are used. For these two skin friction decomposition methods, their decomposed constituents are discussed and compared for different Reynolds numbers.The integrands of the decomposed constituents are locally analyzed across the boundary layer to assess the actions associated with the inhomogeneity and multi-scale nature of turbulent motion. The scaling of the decomposed constituents and their integrands are presented. In addition, the boundary layer is divided into three sub-regions to evaluate the contributive proportion of each sub-region with an increase in the Reynolds number.

Critical transition Reynolds number for plane channel flow

The determination of the critical transition Reynolds number is of practical importance for some engineering problems. However, it is not available with the current theoretical method, and has to rely on experiments. For supersonic/hypersonic boundary layer flows, the experimental method for determination is not feasible either. Therefore, in this paper, a numerical method for the determination of the critical transition Reynolds number for an incompressible plane channel flow is proposed. It is basically aimed to test the feasibility of the method. The proposed method is extended to determine the critical Reynolds number of the supersonic/hypersonic boundary layer flow in the subsequent papers.

Effect of particles on turbulent thermal field of channel flow with different Prandtl numbers

The direct numerical simulation （DNS） of heat transfer in a fully developed non-isothermal particle-laden turbulent channel flow is performed. The focus of this paper is on the modulation of the particles on turbulent thermal statistics in the particle-laden flow with three Prandtl numbers （Pτ = 0.71, 1.5, and 3.0） and a shear Reynolds number （Reτ = 180）. Some typical thermal statistics, including normalized mean temperature and their fluctuations, turbulent heat fluxes, Nusselt number and so on, are analyzed. The results show that the particles have less effects on turbulent thermal fields with the increase of Prandtl number. Two reasons can explain this. First, the correlation between fluid thermal field and velocity field decreases as the Prandtl number increases, and the modulation of turbulent velocity field induced by the particles has less influence on the turbulent thermal field. Second, the heat exchange between turbulence and particles decreases for the particle-laden flow with the larger Prandtl number, and the thermal feedback of the particles to turbulence becomes weak.

Study on resistance coefficient in compound channels

This paper presents a further study of the Manning and Darcy-Weisbach resistance coefficients, as they play a significant role in assessing the cross-sectional mean velocity, conveyance capacity and determining the lateral distribution of depth mean velocity and local boundary shear stress in compound channels. The relationships between the local, zonal and overall resistance coefficients, and a wide range of geometries and different roughness between the main channel and the flood plain are established by analyzing a vast amount of experimental data from a British Science and Engineering Research Council Flood Channel Facility （SERC-FCF）. And the experimental results also show that the overall Darcy-Weisbach resistance coefficient for a compound channel is the function of Reynolds number, but the function relationship is different from that for a single channel. By comparing and analyzing the conventional methods with the experimental data to predict composite roughness in compound channels, it is found that these methods are not suitable for compound channels. Moreover, the reason why the conventional methods cannot assess correctly the conveyance capacity of compound channels is also analyzed in this paper.

Capacity analysis of high-rank line-of-sight MIMO channels

Matrix perturbation theory is utilized to investigate high-rank line of sight multiple input multiple output channels in a microwave relay system. The upper and lower bounds of channel capacity are derived based on space time block codes technique and singular values decomposition. A useful constraint for designing LOS MIMO channels is developed by the use of the condition number of the MIMO channel matrix. The theoretical analysis of channel capacity is confirmed by the simulation. The results show that the proposed method is able to give a physical explanation of the high-rank LOS MIMO channel matrix characteristics.

LoRa扩频信道干扰与扩展性分析

为了提高LoRa通信系统节点的接入量,对LoRa通信系统的干扰及扩展性进行了详细分析。首先分析了LoRa相同扩频信道间和不同扩频信道间的干扰,得出相同扩频信道干扰严重的原因,以及不同扩频信道存在一定的干扰的情况,进而发现扩频信道间的码片间距越近干扰越严重;其次提出了一种LoRa不同扩频信道间的干扰消除算法,通过仿真验证了该算法能有效消除低扩频信道干扰的可行性;最后从理论上对LoRa原有调制解调算法进行了扩展性分析,结合LoRa技术的特点及干扰仿真结果得到LoRa技术新增扩频信道与相邻扩频信道的码片数之差大于等于128,并仿真验证了4条典型新增扩频信道的抗噪声性能、可行性,系统节点的可接入量能增加36.94%。

Unsteady Flow of a Dusty Visco-Elastic Fluid Through an Incliend Channel

The present discussion deals with the study of an unsteady flow of a dusty fluid through an inclined channel under the influence of pulsatile pressure gradient along with the effect of a uniform magnetic field. The analytical solutions of the problem are obtained using variable separable and Fourier transform techniques. The graphs drawn for the velocity fields of both fluid and dust phase under the effect of Reynolds number. The velocity profiles for the liquid and the dust particles decreases at different values of time t increases. As the visco-elastic parameter λ increases the velocity of the liquid and the dust particles deceases. When relaxation time parameter σ increases, the velocity of the liquid and dust particles decreases.

Run-Up Flow of a Maxwell Fluid through a Parallel Plate Channel

We consider the flow of an incompressible viscous Maxwell fluid between two parallel plates, initially induced by a constant pressure gradient. The pressure gradient is withdrawn and the upper plate moves with a uniform velocity while the lower plate continues to be at rest. The arising flow is referred to as run-up flow. The unsteady governing equations are solved as initial value problem using Laplace transform technique. The expression for velocity, shear stresses on both plates and discharge are obtained. The behavior of the velocity, shear stresses and mass flux has been discussed in detail with respect to variations in different governing flow parameters and is presented through graphs.

Uniform Flow of Molten Metals in Rectangular Open Channels

The flow of liquids in open channels has been studied since ancient Rome. However, the vast majority of published reports on flow in open channels are focused on the transport of drinking water and sewage disposal. The literature on the transport of molten metals in open channels is quite scarce. In this work, the uniform flow of pig iron and molten aluminum in rectangular open channels is studied. Specific energy curves are constructed and critical heights are analytically determined. The transition from subcritical to supercritical flow is analyzed as a function of the angle of inclination of the channel and the roughness of its walls. Manning’s equation is applied to the pig iron flow using data reported in the literature for molten aluminum. The need to correct the roughness coefficient for pig iron is observed in order to obtain results consistent with those previously reported.

Development of a new correlation to calculate permeability for flows with high Knudsen number

Flows with high Knudsen number play a prominent role in many engineering applications. The present study is an effort toward the simulation of flow with high Knudsen number using modified lattice Boltzmann method （LBM） through a porous medium in a channel. The effect of collision between molecules and solid walls, which is required to accurately simulate transition flow regime, is taken into account using a modified relaxation time. Slip velocity on the wall, which is another significant difficulty in simulating transition flow regime, is captured using the slip reflection boundary condition （SRBC）. The geometry of porous medium is considered as in-line and staggered. The results are in good agreement with previous works. A new correlation is obtained between permeability, Knudsen number and porosity for flows in transition flow regimes.

过渡流道对串联高速离心泵空化特性的影响

为分析不同结构的过渡流道对串联高速离心泵空化特性的影响,以某型串联高速离心泵的第2级为研究对象,基于ANSYS Fluent中Zwart-Gerber-Belamri空化模型,采用RNG k-ε双方程湍流模型对同一工况下环形和螺旋形过渡流道在不同空化数下的增压值、叶片空化面积、流道内空泡体积进行了对比分析.结果表明:采用螺旋形过渡流道的次级离心泵在流量区间32000~64000 L/h增压值提升约8.5%,大流量工况(qV>52000 L/h)下效率提升3%~6%.次级叶轮发生完全空化时,相比环形过渡流道,螺旋形过渡流道次级叶轮叶片背面空化面积和流道内空泡体积均有所下降.由此可见,螺旋形过渡流道抑制了叶轮叶片空化气泡的产生,提升了次级叶轮的抗空化性能.

NACA0021和NACA4822翼型肋通道中环境空气流动传热特性的实验研究

针对超燃冲压发动机在更高Mach数飞行时,主动再生冷却技术面临换热能力不足的瓶颈问题,拟利用翼型肋加强再生冷却通道的传热性能.为了从原理上验证翼型肋通道的强化传热效果,搭建了环境空气在NACA0021对称翼型肋和NACA4822非对称翼型肋通道(横截面尺寸50 mm×50 mm)中的流动传热实验测试平台,基于稳态液晶技术得到受热表面的Nusselt数.通过实验研究发现:NACA0021对称翼型肋通道和NACA4822非对称翼型肋通道的传热强度分别被提升了0.17%~17.1%和18.4%~52.1%,50 m^(3)/h流量下的PEC(performance evaluation criteri-on)分别为1.04和1.24;大流量条件下,NACA4822非对称翼型肋通道可强化中间受热面的传热性能;翼型肋通道中的流动压降也会相应增大,其中NACA4822翼型肋通道中的压降最大,翼型肋的非对称性使得流动湍流强度不断积累造成下游压降存在明显升高.该研究将有助于进一步开展翼型肋通道内超临界流体的流动传热特性研究,拓宽超燃冲压发动机主动再生冷却技术的应用温区.

面向6G通感一体化的多频带信号恢复系统设计

通感一体化(ISAC)被视为实现基于6G的星地一体化的核心技术。调制宽带转换器(MWC)在信号处理过程中能够同时完成频谱定位和信息通信任务,从而提高频谱的使用效率,减轻硬件设备的压力,并提高信息处理效率,以满足ISAC的各项功能需求。然而,该系统在确定信号处理通道数量方面存在困难,因此提出了一种能自动调节通道数量的自适应宽带频谱感知系统。该系统还引入了基于稀疏度估计的指数变步长自适应匹配跟踪(ES-EVss AMP)算法,并与混叠MWC(AMWC)系统相结合,以实现自适应宽带频谱感知。仿真结果证实了该改进结构的优势。

U型渠道中直角三角形量水槽体型设计

量水槽体型设计是量水槽应用于灌区的重要环节,目前尚无完善的体型设计标准可依。为解决直角三角形量水槽实际应用中的体型设计问题,提出以淹没度、壅水高度和上游弗劳德数的限制条件为标准的量水槽体型设计准则。在2种型号、3种坡度的U型渠道上,利用钢模板修建5座直角三角形量水槽进行灌区试验;建立了包含渠道坡度的流量公式,拟合了淹没阈值、壅水高度和上游弗劳德数的经验公式。研究表明:含有坡度的流量公式精度较高,平均相对误差仅为1.88%,相对误差的最大值为5.56%,相对误差在±5%范围以内的数据比例为98%;拟合得到的3个经验公式描述了淹没阈值、壅水高度和上游弗劳德数与量水槽喉口宽度之间的定量关系,可用于量水槽体型设计。基于体型设计准则和经验公式,建立了最大流量和最小流量下淹没度小于相应淹没阈值、最大流量下壅水高度小于渠道岸顶超高、最小流量下上游弗劳德数小于0.5的直角三角形量水槽体型设计方法。研究成果可为类似量水槽体型设计提供参考。

窄缝通道内低雷诺数蒸汽流动换热特性数值模拟研究

为探究窄缝通道在大破口失水事故下再淹没过程中低雷诺数(Re_(in)=1 881~10 348)过热蒸汽的流动换热特性,采用计算流体力学(computational fluid dynamics, CFD)方法,基于优选出的湍流模型,探究加热面热流、压力条件和入口速度对低雷诺数过热蒸汽流动换热特性的影响规律。对比了Gnielinski关联式与Dittus-Boelter关联式,并对Dittus-Boelter经验关联式进行修正。计算结果表明:雷诺时均(Reynolds average Navier-Stokes, RANS)湍流模型中SST k-ω的模拟结果与大涡模拟(large eddy simulation, LES)的模拟结果最为接近,且计算量小;过热蒸汽对流换热能力随压力和入口流速的增加而增强,随加热面热流增加而减弱;相对于数值模拟结果,Dittus-Boelter和Gnielinski经验关联式预测的Nu数偏低,修正后的新关联式误差在15%以内,可为再淹没过程低雷诺数过热蒸汽的流动换热分析程序开发提供参考。

基于PSENet区域分割的列车车厢号定位研究

针对自然场景中行驶列车的车厢号采用现有文本定位方法容易存在严重畸变,从而导致漏检率高的问题,提出一种基于区域分割的列车车厢号精确定位方法。该方法所采用的网络模型基于PSENet,首先采用引入通道域注意力的ResNet50网络提取特征,使模型更加关注卷积通道信息,从通道域的角度对权重进行再分配,提高车厢号的定位精度;然后采用特征金字塔和自底向上路径增强模块融合多尺度特征图,将浅层网络中的强定位特征传播到深层网络,以从复杂环境中准确定位车厢号区域,降低车厢号的漏检率;最后采用基于广度优先算法的渐进尺度扩展模块对融合的特征图进行目标区域的从小尺度到大尺度的拓展分割,使用结合集合相似度度量Dice系数的损失函数对分割结果进行分类回归,输出定位结果。实验结果表明:通过在真实列车车厢号图像数据集上进行训练验证,本文提出的网络模型在铁路货运列车车厢号定位精度达到97.47%,召回率为94.14%,综合F1分数为95.78%,预测单张图约需0.2 s。相比于基础PSENet对车厢号的定位精确率提升3.78%,召回率提升1.71%,总体上车厢号的F1分数提升2.73%。研究成果可为列车车厢号自动检测识别系统提供一种高精度的车厢号检测定位方法。

改进的YoloV3轻量化多目标检测算法

为有效解决轻量化目标检测网络降低参数量导致的检测精度损失问题,设计一种轻量化多目标检测网络MSPF-YoloV3,可以通过低分组数、低内存占用的通道混洗结构,达到与高分组数同样的信息交流的效果;将位置信息丰富的浅层特征与深层特征进行融合,提高对不同大小目标的检测精度。经过实验验证了该方法的有效性与实时检测的能力。该网络在PASCAL VOC07+12数据集上的mAP达到86.31%;在COCO2014数据集中提取出与PASCAL VOC07+12数据集相同的20个类别,mAP达到67.71%;权重文件大小为46.8 MB,相较于YoloV3降低了198.2 MB;检测速度达到44 FPS。

基于AD8184的视频多路复用芯片测试装置设计

在现代监控系统中,出于全天候监控的需要,多同时配备夜视仪和可见光监控设备,2种监控设备共用一套显示设备,2路视频信号通过四选一视频多路复用芯片AD8184进行切换。为了满足芯片AD8184功能测试的需要,设计了一体式芯片AD8184测试装置。采用模块化设计方式,将信号产生电路、通道编号显示电路等各种功能电路模块单独设计,最终组成一个测试装置,对AD8184芯片进行功能检测。在AD8184芯片测试装置制作完成后,对其进行测试。结果表明,测试装置达到了预定的设计指标。由于AD8184芯片测试装置自带信号产生电路和通道编号显示电路,可以节省信号发生器等昂贵设备,同时,可视化操作设计也提高了测试效率。

提高煤矿微震定位精度的最优通道个数的选取

根据煤矿实际条件和震动波传播特点,建立了最优通道个数的确定原则,构建了用于定位精度评价模型中P波波速和P波到时标记精度的方差函数,符合两个参数随距离、纵波幅值阻尼系数和纵波波速变异系数增大而波动性增强的特点。现场数值试验结果表明:当震源激发探头个数足够多时,不断地增加定位通道个数并不能有效提高震源的定位精度,在台网布设较优时,6个通道就可以保证震源的定位精度;台网布设较差区域对误差的抵抗能力较弱,增加探头反而降低震源定位精度;提高震源定位精度,应首先从优化台网布设入手,然后再利用最优通道个数选取原则确定最优通道个数。