Frontogenesis,Evolution and the Time Scale of Front Formation

Observational study shows that, in some cases, the frontal structure displays the features of gravitative flows. It seems that the formation of discontinuity is an important problem in the study of the frontogenesis which is usually defined as an increasing of the scalar gradient. In this paper, the characteristic features of air flow with initial imbalance between the wind and the density fields are studied. Much attention is paid on the condition for the formation of discontinuity and its time scale. It is found that the initial distribution of density plays an important role in the formation of the discontinuity which happens in short time duration.

Multi-relaxation-time lattice Boltzmann front tracking method for two-phase flow with surface tension

In this paper, an improved incompressible multi-relaxation-time lattice Boltzmann-front tracking approach is proposed to simulate two-phase flow with a sharp interface, where the surface tension is implemented. The lattice Boltzmann method is used to simulate the incompressible flow with a stationary Eulerian grid, an additional moving Lagrangian grid is adopted to track explicitly the motion of the interface, and an indicator function is introduced to update the fluid properties accurately. The interface is represented by using a four-order Lagrange polynomial through fitting a set of discrete marker points, and then the surface tension is directly computed by using the normal vector and curvature of the interface. Two benchmark problems, including Laplace＇s law for a stationary bubble and the dispersion relation of the capillary wave between two fluids are conducted for validation. Excellent agreement is obtained between the numerical simulations and the theoretical results in the two cases.

STABILITY OF TIME-PERIODIC TRAVELING FRONTS IN BISTABLE REACTION-ADVECTION-DIFFUSION EQUATIONS

This paper is concerned with the global exponential stability of time periodic traveling fronts of reaction-advection-diffusion equations with time periodic bistable nonlinearity in infinite cylinders. It is well known that such traveling fronts exist and are asymptotically stable. In this paper, we further show that such fronts are globally exponentially stable. The main difficulty is to construct appropriate supersolutions and subsolutions.

Three-dimensional multi-relaxation-time lattice Boltzmann front-tracking method for two-phase flow

We developed a three-dimensional multi-relaxation-time lattice Boltzmann method for incompressible and immiscible two-phase flow by coupling with a front-tracking technique. The flow field was simulated by using an Eulerian grid, an adaptive unstructured triangular Lagrangian grid was applied to track explicitly the motion of the two-fluid interface, and an indicator function was introduced to update accurately the fluid properties. The surface tension was computed directly on a triangular Lagrangian grid, and then the surface tension was distributed to the background Eulerian grid. Three benchmarks of two-phase flow, including the Laplace law for a stationary drop, the oscillation of a three-dimensional ellipsoidal drop, and the drop deformation in a shear flow, were simulated to validate the present model.

立式自吸泵前口环几何参数对其自吸性能的影响

为探究立式自吸泵前口环几何参数对其自吸性能的影响,以350WFB-1200-50型外混式无密封立式自吸泵为研究对象,在保证自吸泵其他参数不变的情况下,通过改变前口环间隙δ和前口环长度l的数值大小,共设计20种方案.利用数值计算和试验验证相结合的研究方法,通过定常数值计算得到不同方案外特性曲线图及前口环进出口压差图;通过非定常数值计算得到不同方案不同时刻中间截面气体体积分布云图、不同方案自吸泵出口含气率变化图及不同方案自吸完成时间曲线图来研究立式自吸泵前口环几何参数与其自吸性能的关系.研究发现:前口环间隙δ和前口环长度l对自吸泵自吸性能均有影响,适当减小前口环间隙δ和增大前口环长度l均能提高自吸泵自吸性能,且当前口环间隙δ过大时,其对自吸泵自吸性能的影响大于前口环长度l对自吸泵自吸性能的影响.

基于前端检测策略的集装箱超偏载检测系统设计

该文针对目前以龙门架和轨道衡进行超偏载检测的现状及其在检测过程中暴露的问题,将集装箱的超偏载检测流程前移,提出一种基于前端检测策略的集装箱超偏载检测系统。该系统采用基于半挂车的超偏载检测仪作为集装箱超偏载数据的采集器并实时发送数据至云端数据库服务器。半挂车司机通过手机APP端查看集装箱的超偏载信息,从而达到对集装箱超偏载状况的实时监测;货场调度中心通过Web应用端查看集装箱的超偏载信息,实现对集装箱超偏载状况的实时监测。该系统串联起来货场调度中心、货场调度员、半挂车、集装箱以及半挂车司机,形成一个完整的基于前端检测策略的公铁联运集装箱超偏载检测的闭环,推进集装箱超偏载检测的智能化。

基于遗传算法和分选识别需求的频段驻留时间优化设计

为有效提高信号接收系统前端截获概率并加快系统调试进度,提出了一种基于遗传算法和分选识别需求的频段驻留时间优化设计方法。该方法首先基于窗口函数模型获得前端截获概率计算公式,其次将优化频段驻留时间最大值问题抽象为约束条件下的非线性优化问题,并基于遗传算法进行迭代优化,最后结合辐射源信号正确分选和识别需求优化频段驻留时间最小值,从而得到最优频段驻留时间范围。结果表明,该优化设计方法可实现频段驻留时间范围的最优化,在提高系统前端截获概率的同时可解决现场调试费事费力问题,加快系统调试进度,适用于实际工程应用。

基于环境的三维激光实时去动态物体方法

为提高三维激光传入点云算法框架的点云质量,减少移动物体对点云地图精度的影响,提出一种能够在框架前端基于环境特征的实时去除动态物体的方法。将点云投影得到深度矩阵和高度矩阵(z值矩阵),并从z值矩阵中提取出环境特征;利用环境特征将前后帧点云快速对齐;利用对齐后的前后帧点云得到z值差分矩阵进行筛选,并标记动态点云;以动态点云为中心,利用深度矩阵进行聚类,并将聚类得到的未标记点云进行标记,传入后端时舍弃标记的点云。分别在Ours数据集上以及KITTI数据集上验证了该方法的效果。

一种基于前后台系统的CPU使用率计算方案

大多数小规模的嵌入式设备均不采用操作系统,而使用前后台系统进行功能设计开发。目前,在前后台系统下,尚无有效的方案实时反映任务及时性响应情况,无法监控功能偶发问题,导致功能缺陷出现。基于此,本文提出了一种基于前后台系统的CPU使用率计算方案,该方案通过统计周期内的触发次数、CPU使用率及极值实时反映任务及时性响应情况,并将该方案应用于GD32 MCU。结果表明,该方案能有效实时反映当前设备的整体运行状况,为设备功能的开发和测试提供有效支撑。

多画面实时监测系统在数字电视前端中的应用

随着科技的快速发展和人们生活水平的提高,数字电视已经成为现代家庭不可或缺的娱乐和信息来源。为确保数字电视节目的高质量传输和接收,电视前端系统的稳定性和可靠性至关重要。然而,传统的电视前端监控系统往往只能监测单个频道,无法满足现代数字电视前端同时监测多个频道的需求,而多画面实时监测系统的出现,则为数字电视前端的监控提供了新的解决方案。

Usage Count： A New Indicator to Detect Research Fronts

Purpose： Research fronts build on recent work, but using times cited as a traditional indicator to detect research fronts will inevitably result in a certain time lag. This study attempts to explore the effects of usage count as a new indicator to detect research fronts in shortening the time lag of classic indicators in research fronts detection. Design/methodology/approach： An exploratory study was conducted where the new indicator ＂usage count＂ was compared to the traditional citation count, ＂times cited,＂ in detecting research fronts of the regenerative medicine domain. An initial topic search of the term ＂regenerative medicine＂ returned 10,553 records published between 2000 and 2015 in the Web of Science （WoS）. We first ranked these records with usage count and times cited, respectively, and selected the top 2,000 records for each. We then performed a co-citation analysis in order to obtain the citing papers of the co-citation clusters as the research fronts. Finally, we compared the average publication year of the citing papers as well as the mean cited year of the co-citation clusters. Findings： The citing articles detected by usage count tend to be published more recently compared with times cited within the same research front. Moreover, research fronts detected by usage count tend to be within the last two years, which presents a higher immediacy and real-time feature compared to times cited. There is approximately a three-year time span among the mean cited years （known as ＂intellectual base＂） of all clusters generated by usage count and this figure is about four years in the network of times cited. In comparison to times cited, usage count is a dynamic and instant indicator. Research limitations： We are trying to find the cutting-edge research fronts, but those generated based on co-citations may refer to the hot research fronts. The usage count of older highly cited papers was not taken into consideration, because the usage count indicator released by WoS only reflects usage logs after February 2013. Practical implications： The article provides a new perspective on using usage count as a new indicator to detect research fronts.Originality/value： Usage count can greatly shorten the time lag in research fronts detection, which would be a promising complementary indicator in detection of the latest research fronts.

时分复用射频前端高功率微波波形响应

为研究系统级射频设备高功率微波前门效应,采用注入法对某4G基站的滤波器、环形器、低噪放及功放构成的射频前端进行实验研究。结果表明,高功率微波脉冲上升沿和下降沿被射频前端滤波器强烈反射,脉冲平顶段反射很小。反射波形在上升沿及下降沿呈尖峰、在脉冲中部呈平底,显示高功率微波陡峭的上升沿和下降沿包含的丰富的滤波器带外频率成分被反射,导致通过滤波器的脉冲头尾被削弱。经滤波器后,高功率微波脉冲可由环行器进入上行通道低噪放,进而被反射,环行进入下行通道功率放大器,被再次反射,再环行从注入口输出。实验中监测到了经两次反射环行的高功率微波脉冲。说明在高功率脉冲条件下,原本由环形器隔离的下行通道功率放大器同样会承受上行通道进入的高功率微波脉冲损伤的风险。

基于计算前沿面的实时仿真数值积分并行构造及其数值模型解耦加速方法

数值仿真是先进智能计算的基础与底层核心技术,而计算速度是数值仿真的核心性能指标。然而,随着高开关频率功率器件在电机驱动等系统中的应用,短时间约束给实时及在线数值仿真的计算速度带来了严峻挑战。当前数字平台的计算结构朝着并行化的趋势发展,并行计算被视为短时间约束下优化计算速度的有效途径,但现有的数值模型和数值算法大多基于顺序计算的串行模式,缺乏可并行执行的冗余并行度。因此,该文研究了数值算法的求解核心数值积分的并行优化方法,提出了计算前沿面的优化思路,为数值积分算法构造冗余并行度以实现并行计算,分析了其在数值精度与数值稳定性方面的影响,并讨论了在多步与高阶数值积分法上的可拓展性。同时,利用计算前沿面构造的冗余并行度,设计了数值模型的并行解耦分割,并应用于电驱系统实现了元件级的数值加速。最后,在硬件在环的实时数值环境中验证了优化方法的可行性、数值性能以及加速效果。

基于预瞄时间自适应的爆胎车辆横向控制

针对汽车在高速行驶过程中突然爆胎极易引发严重交通事故的问题,文章提出一种基于预瞄时间自适应的爆胎车辆横向控制方法。在单点预瞄驾驶员模型的基础上,提出一种预瞄时间自适应算法,通过预测未来一段时间内不同预瞄时间的车辆运行状况,将道路边界约束添加为约束条件设计优化函数,选取合适的预瞄时间,提高车辆的行驶稳定性;采用滑模控制理论设计主动转向控制器,根据爆胎前、后横摆角速度偏差对车辆前轮转角进行补偿,以解决爆胎导致的车辆横向偏航问题。在CarSim与Simulink联合仿真平台下进行的仿真验证结果表明,该文提出的控制方法可以使爆胎车辆基本保持在原路径上行驶,有效提高了车辆的稳定性和安全性。

安徽小三线企业调迁刍议——以企业与城市互动为中心

1986年前后,安徽根据国家政策,立足省情,决定将大部分小三线企业调迁至城市。小三线布局弊病、城市若干优势、邻近地区三线调迁推动了安徽调迁决策形成。企业与城市双向选择受双方利益、职工籍贯、关系网络交织影响。调迁初期,大部分小三线企业力争以迁并路径搬迁至城市,实践中,拟合并双方企业利益平衡及小三线企业优势因素决定了迁并能否付诸实施。调迁中,小三线企业困难重重,接收城市在政策、组织、资金方面给予其帮助并推动省级层面优惠政策出台,这对安徽小三线调整战略实施具有重要意义。

陕南汉江盆地一次冷锋触发的短时强降水过程及预报检验

山区特殊地形下的强降水形成机理复杂、预报难度大,且此类强降水常导致严重的地质灾害。为提升特殊地形下强降水的预报能力,利用常规气象观测资料、欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)ERA5再分析资料、FY-4A卫星云图资料、多普勒雷达资料及多模式预报产品,对2022年6月3日夜间至4日清晨发生在陕南汉江盆地的局地短时强降水过程形成原因及模式预报性能进行检验分析。结果表明:(1)本次过程为一次锋面在盆地触发的短时强降水过程,由于对流不稳定层结浅薄、垂直风切变较弱,因此造成的强降水具有明显的局地性,但强度较大,12 h累计降水量多站超过50.0 mm,最大104.8 mm;(2)锋面两端受地形阻挡移动速度较慢并难以翻越高大山脉,因而不断在盆地内触发对流产生强降水,且在盆地近地层形成的次级环流可加强对流活动发展;(3)锋面前部形成的冷池在盆地不断触发新的对流单体后向传播形成列车效应,同时大于50 dBZ的强回波位于0℃层高度以下,具有较高的降水效率,且持续时间较长,因而带来最大62.6 mm·h^(-1)的短时强降水;(4)全球模式对此次短时强降水的预报能力有限,中尺度区域模式能够反映锋面对流的一些特征和降水,尤其是CMA-TRAM(Tropical Regional Atmosphere Model for the South China Sea)和CMA-GD(China Meteorological Administration-Guangdong)模式能较好地反映局地强对流的触发及发展趋势,但对锋前冷池造成的对流系统强度和组织性仍预报偏差较大。

雷电冲击电压波形仿真模型建立与应用

雷电冲击试验是耐压与绝缘试验中的重要项目,是判断电气设备是否满足高压工作要求的重要依据。为方便对冲击电压波形的参数进行定量调整,本文基于Simulink平台,建立雷电冲击电压发生器的仿真模型,并采用1600kV/80kJ雷电冲击电压发生器进行验证。实验证明:仿真波形与实际波形的电压峰值U_(m)、波前时间T_(1)与半峰值时间T_(2)之间的一致性误差未超过±3%,可快速、准确地调整冲击电压波形关键参数,提高日常实验效率,辅助实验设备的运维管理。

膨胀土边坡毛细覆盖层防渗特性试验研究

毛细覆盖层可借助粗-细层间毛细阻滞作用实现下覆地质体的防渗保湿,应用于膨胀土边坡时,可有效阻滞水分向坡体内部入渗,抑制膨胀土的胀缩变形和裂隙发育,维护坡体稳定性。为量化分析膨胀土边坡毛细覆盖层防渗特性,本文借助物理模型试验,对比分析了传统覆盖层与毛细覆盖层两种土质覆盖系统在降雨条件下的水分运移规律、导排渗漏量、突破时间以及储水量,在此基础上获取了毛细覆盖层较传统覆盖层的防渗效能增幅。结果表明:传统覆盖层储水量占降雨量的47%,底部入渗量占降雨量的46%,侧向导排量占降雨量的7%;毛细覆盖层储水量占降雨量的29%,底部入渗量占降雨量的9%,侧向导排量占降雨量的62%。较之传统覆盖层,毛细覆盖层侧向导排量提高16倍,底部入渗量降低67%,突破时间提高3.3倍,防渗效果显著提升。

基于固定时间非奇异终端滑模的汽车主动前轮转向系统控制

针对汽车主动前轮转向系统(active front steering,AFS)中的安全控制问题,提出一种基于固定时间非奇异终端滑模的主动前轮转向控制器.将固定时间终端滑模与幂次趋近律相结合设计一种新的固定时间非奇异终端滑模控制器,以实现系统的快速稳定控制和削弱系统稳态时的抖振,使得闭环系统的收敛时间仅取决于滑模面及控制器的参数设计,而与系统的初始值无关.基于Lyapunov稳定性理论验证了闭环系统的稳定性.仿真结果表明,所提固定时间终端滑模控制方法的快速性和稳定性均优于传统滑模控制和PI控制方法.