Analysis of Summer Cold Vortex Activity Anomalies in Northeastern China and Their Relationship with Regional Precipitation and Temperature

The Northeastern China cold vortex(NCCV)is one type of strong cyclonic vortex that occurs near Northeastern China(NEC),and NCCV activities are typically accompanied by a series of hazardous weather.This paper employed an automatic algorithm to identify the NCCVs from 1979 to 2018 and analyzed their circulation patterns and climatic impacts by using the defined NCCV intensity index(NCCVI).The analysis revealed that the NCCV activities in summer exhibited a strong inter-annual variability,with an obvious periodicity of 3-4 years and 6-7 years,but without significant trends.In years when the NCCVI was high,NEC experienced negative geopotential height anomalies,cyclonic circulation,and cooler temperature anomalies,which were conducive to the maintenance and development of NCCV activities.Furthermore,large amounts of water vapor converged in NEC through two transportation routes as the NCCVs intensified,leading to a significant positive(negative)correlation with the summer precipitation(surface temperature)in NEC.The Atlantic sea surface temperature(SST)anomalies were closely related to summer NCCV activities.As the Atlantic SST rose,large amounts of surface sensible and latent heat flux were transported into the lower troposphere,inducing a positive geopotential height anomaly that occurred on the east side of the heat source.As a result,an eastward diverging flow was formed in the upper troposphere and propagated downstream,i.e.,the eastward propagating Rossby wave train,which eventually led to a coupled circulation in the Ural Mountains and NEC,as well as more intensive NCCV activities in summer.

Study on the Wake Shape behind a Wing in Ground Effect Using an Unsteady Discrete Vortex Panel Method

The unsteady evolution of trailing vortex sheets behind a wing in ground effect is simulated using an unsteady discrete vortex panel method. The ground effect is included by image method. The present method is validated by comparing the simulated wake roll-up shapes to published numerical results. When a wing is flying in a very close proximity to the ground, the optimal wing loading is parabolic rather than elliptic. Thus, a theoretical model of wing load distributions is suggested, and unsteady vortex evolutions behind lifting lines with both elliptic and parabolic load distributions are simulated for several ground heights. For a lifting line with elliptic and parabolic loading, the ground has the effect of moving the wingtip vortices laterally outward and suppressing the development of the vortex. When the wing is in a very close proximity to the ground, the types of wing load distributions does not affect much on the overall wake shapes, but parabolic load distributions make the wingtip vortices move more laterally outward than the elliptic load distributions.

The Micro-Scale Mechanism of Metal Mine Tailings Thickening Concentration Improved by Shearing in Gravity Thickener

Higher concentration is beneficial for the Paste and Thickened Tailings(PTT)operation in metal mine.Partial paste thickeners are produced lower density underflow.Flocculated tailings are intended to form a water entrapped network structure in thickener,which is detrimental to underflow concentration.In this study,the continuous thickening experiment was carried out for ultra-fine tungsten tailings to study the influence of rake shearing on underflow.The micro pores structure and seepage flow in tailings bed before and after shearing are studied by CT and simulation approach to reveal the shearing enhancement mechanism of thickening process.The results shown that,the underflow concentration is increased from 61.4 wt%to 69.6 wt%by rake shearing in a pilot scale thickener,the porosity decreased from 46.48%to 37.46%.The entrapped water discharged from sticks structure more than sphere spaces.In items of seepage,after shearing,the seepage flow channel of tailings underflow is becoming longer,which caused the decreasing average flow rate decreases and absolute permeability.The absolute permeability is negatively correlated with tortuosity.The rake shearing can destroy the flocs structure;change the effective stress to increase the concentration.Higher underflow concentration improves the waste recycling and water recovery rate,especially for arid areas.

Vectorial spin-orbital Hall effect of light upon tight focusing and its experimental observation in azopolymer films

Hall effect of light is a result of symmetry breaking in spin and/or orbital angular momentum(OAM)possessing optical system and is caused by e.g.refractive index gradient/interface between media or focusing of a spatially asymmetrical beam,similar to the electric field breaking the symmetry in spin Hall effect for electrons.The angular momentum(AM)conservation law in the ensuing asymmetric system dictates redistribution of spin and orbital angular momentum,and is manifested in spin-orbit,orbit-orbit,and orbit-spin conversions and reorganization,i.e.spin-orbit and orbit-orbit interaction.This AM restructuring in turn requires shifts of the barycenter of the electric field of light.In the present study we show,both analytically and by numerical simulation,how different electric field components are displaced upon tight focusing of an asymmetric light beam having OAM and spin.The relation between field components shifts and the AM components shifts/redistribution is presented too.Moreover,we experimentally demonstrate,for the first time,to the best of our knowledge,the spin-orbit Hall effect of light upon tight focusing in free space.This is achieved using azopolymers as a media detecting longitudinal or z component of the electrical field of light.These findings elucidate the Hall effect of light and may broaden the spectrum of its applications.

Role of grain boundary networks in vortex motion in superconducting films

We study the vortex dynamics of the polycrystalline superconductors in the presence of both random point defects and the generated grain boundary(GB) networks with Voronoi diagram. The synergistic effect of adjacent GBs on restricting the vortex motion in intragranular region is proposed and the corresponding intensity factor of the synergistic effect which characterizes the strength of the synergistic restriction of adjacent grain boundaries is also determined in the present work.The interconnected GBs offer easy-flow channels for vortices in addition to pinning effects on the vortices. The combined channels and the vortex flow patterns in the superconducting film are analyzed in detail from molecular dynamics simulations. Furthermore, it is discovered that the critical current increases with the decrease of magnetic field intensity,temperature, and the average grain size. The large number of vortices results in the enhanced repulsive interaction forcing the vortices to move out from the GBs. The thermal depinning from GBs leads to the lower Lorentz force range. The increase of the grain size causes the number of GBs to decrease. In summary, these effects leads the critical current to become a decreasing function of magnetic field, temperature, and grain size.

3D Effects on Vortex-Shedding Flow and Hydrodynamic Coefficients of A Vertically Oscillating Cylinder with A Bottom-Attached Disk

Vortex-shedding flow induced by the vertical oscillation of a cylinder with bottom-attached disks of different diameter ratio Dd/Dc and thickness ratio td/Dc is studied by a 3D （three-dimensional） numerical model developed in this paper, and compared with the results obtained through 2D （two-dimensional） numerical model. The high-order upwind scheme is applied to stabilize the computation, and convergence is accelerated by the multi-grid method. Qualitative and quantitative analyses of the differences between the 2D and 3D simulation results reveal the 3D effect on the flow field characteristics and hydrodynamic coefficients of the vertically oscillating cylinder with a bottom-attached disk. The 3D effect on the fluid field is mainly reflected in the significance of three vortex-shedding patterns： ωx has a greater effect on the flow fields around the sharp edges relative to the vortices generated in the 2D simulation. In the slice along the axial orientation, the vortex effect of ωy along the radial axis is smaller than that of ωx along the circumferential direction, indicating the radial effect on the velocity more pronounced than the circumferential effect around the sharp edges of the disk. The rotational interaction ωz of the fluid in the horizontal plane during the heave motion is insignificant. Based on the 2D and 3D simulation results, the turning points that separate the increasing regimes of the added mass coefficient and damping ratio are identified. The dependence of the turning point on the diameter ratio Dd/Dc and thickness ratio td/Dc are discussed in detail.

Theoretical analysis of the optical rotational Doppler effect under atmospheric turbulence by mode decomposition

The optical rotational Doppler effect associated with orbital angular momentum provides a new means for rotational velocity detection.In this paper,we investigate the influence of atmospheric turbulence on the rotational Doppler effect.First,we deduce the generalized formula of the rotational Doppler shift in atmospheric turbulence by mode decomposition.It is found that the rotational Doppler signal frequency spectrum will be broadened,and the bandwidth is related to the turbulence intensity.In addition,as the propagation distance increases,the bandwidth also increases.And when C_(n)^(2)≤5×10^(-15)m^(-2/3)and 2z≤2 km,the rotational Doppler signal frequency spectrum width d and the spiral spectrum width d_(0)satisfy the relationship d=2d_(0-1).Finally,we analyze the influence of mode crosstalk on the rotational Doppler effect,and the results show that it destroys the symmetrical distribution of the rotational Doppler spectrum about 2l·Ω/2π.This theoretical model enables us to better understand the generation of the rotational Doppler frequency and may help us better analyze the influence of the complex atmospheric environment on the rotational Doppler frequency.

Dynamic Properties of Steel Catenary Riser near Touchdown Point Under Coplanar Vessel Heave and Vortex Induced Vibration

The present study establishes a simple numerical model for the coupled response of a steel catenary riser(SCR) subjected to coplanar vessel motion and vortex-induced vibration(VIV). Owing to the large deflection of the SCR, the geometric nonlinearity is considered in this model. The hydrodynamic force comprises the excitation force and hydrodynamic damping, where the excitation force that only exists when the non-dimensional frequency is located in the lock-in range, is associated with the VIV. The hydrodynamic force model is validated based on the published VIV test data.As for the seabed resistance at the touchdown zone(TDZ), integrated with an initial seabed trench, the hysteretic feature is modeled. Based on the model, the study emphasizes on the coupled response characteristics near the touchdown point(TDP) induced by coplanar vessel heave and VIV, and analyzes the sensitivity of the coupled response to the heaving amplitude and frequency. It is found that with the increase of the heave amplitude and frequency, the VIV can be obviously mitigated, but the heave-related response in the coupled analysis seems to be close to that in the heave-only simulation. Finally, the fatigue damage near TDP is parametrically investigated based on the separate analysis and the coupled analysis. The results demonstrate that the coupled effect plays a significant role in the fatigue assessment near TDP. Besides, the proportion of the coupled effect accounting for the total fatigue damage decreases with the increasing seabed stiffness, while increases with the increasing seabed trench depth.

A Thermal Analogue of the Zel’Dovich Effect

We analyze in this work anisotropic heat conduction induced by a harmonically oscillating laser source incident on rotating conductors, exploiting an analogy with an effect discovered long ago, called the Zel’dovich effect. We re-covered the main results of a recently published paper that predicts the translational Doppler frequency shift of a thermal wave induced on a sample moving with uniform rectilinear motion. We extend then this framework to take into account the frequency shift of a thermal field propagating on a rotating platform. We show that it coincides with the rotational frequency shift which has been recently observed on surface acoustic waves and hydrodynamic surface waves, called rotational superradiance. Finally, we use an analogy with the Tolman effect to deduce a simple estimate of the average temperature gradient induced by rotation, showing the existence of a new cooling effect associated with heat torque transfer.

旋涡空化水动力学特性研究进展与展望

涡空化作为一种在推进器叶顶涡心处产生的空化现象,在推进器原型上往往最早出现,其一旦发生将会严重影响舰艇的声隐身性能(噪声增加10 dB以上),在很大程度上限制了舰艇临界航速的进一步提升,因而长期以来一直是空化水动力学领域研究的重点与难点课题之一.本文首先简要介绍了旋涡空化流动相较于其他形式空化流动的特点,并以梢涡空化为主要对象,系统阐述了旋涡空化初生、发展的演变行为与流动机理研究,从空化三要素的角度深入讨论了其影响因素与作用机制.在此基础上,本文分别对旋涡空化流动中尺度效应、流动控制等关键问题的相关研究进展进行了回顾,较为系统地梳理了旋涡空化尺度效应的内在原因以及旋涡空化流动控制方法与控制思路.最后,本文针对目前旋涡空化研究领域关注的重点与难点问题,对旋涡空化流动研究中采用的实验测量及数值模拟技术进行了总结与展望.

高雷诺数下倒虹吸闸墩绕流水力特性

为研究倒虹吸出口闸墩绕流特性,以南水北调某典型倒虹吸为例,基于Flow3D软件建立倒虹吸模型,根据现场原型实测水位、流速进行模型验证;利用该模型模拟了雷诺数6.17×10^(6)~9.38×10^(6)范围下闸墩绕流特性。结果表明,高雷诺数条件下,随着雷诺数的增加,闸墩绕流造成的液面波动幅度增加,中墩液面波动显著大于边墩;闸墩后的尾涡量持续增加,雷诺数对斯特劳哈尔数影响不大;边侧闸墩受力的非对称性明显,边墩闸室间特征流速偏流比存在先增大再减小的变化规律,偏流效应造成的离心距不断增加。本研究可针对性改善输水工程水流流态。

双幅Π型叠合梁桥涡振特性的试验研究

采用弹簧悬挂节段模型风洞试验,研究了不同间距比和来流风攻角下双幅Π型叠合梁桥的涡激振动性能。通过对上、下游断面的涡激振动振幅、锁定区间、相位差等特性的详细分析,探究了双幅Π型叠合梁的涡激振动特性。结果表明:在各个攻角(α=±5°,±3°,0°)和间距比(L/D=6~8)下,双幅Π型叠合梁下游断面的涡激振动振幅因气动干扰的作用而被显著放大,而上游受干扰较小,其振幅较之单幅Π型叠合梁略小或接近;上、下游断面的涡激振动风速锁定区间以及涡脱频率几乎不受气动干扰效应的影响,与单幅桥基本一致,然而上、下游断面间的涡激振动存在显著的振动相位差,且其值随着振幅和风速的增大呈近似线性减小趋势。此外,与单幅Π型叠合梁涡激振动性能最不利发生在负攻角的特性不同,双幅Π型叠合梁的涡激振动振幅在正攻角下较大,导致其涡激振动最不利攻角发生在α=+5°。该文研究结果可为类似双幅桥梁的抗风设计提供有益参考。

Comparative Analysis of Energy Characteristics of Two Southwest Vortices in Sichuan Under Similar Circulation Backgrounds

Based on ERA5 reanalysis data,the present study analyzed the thermal energy development mechanism and kinetic energy conversion characteristics of two extreme rainstorm processes in relation to the shallow southwest vortex in the warm-sector during a“rain-generated vortex”process and the deep southwest vortex in a“vortex-generated rain”process.The findings were as follows:(1)During the extreme rainstorm on August 11,2020(hereinafter referred to as the“8·11”process),intense surface heating and a high-energy unstable environment were observed.The mesoscale convergence system triggered convection to produce heavy rainfall,and the release of latent condensation heat generated by the rainfall promoted the formation of a southwest vortex.The significant increase(decrease)in atmospheric diabatic heating and kinetic energy preceded the increase(decrease)in vorticity.By contrast,the extreme rainstorm on August 16,2020(hereinafter referred to as the“8·16”process)involved the generation of southwest vortex in a low-energy and highhumidity environment.The dynamic uplift of the southwest vortex triggered rainfall,and the release of condensation latent heat from rainfall further strengthened the development of the southwest vortex.The significant increase(decrease)in atmospheric diabatic heating and kinetic energy exhibited a delayed progression compared to the increase(decrease)in vorticity.(2)The heating effect around the southwest vortex region was non-uniform,and the heating intensity varied in different stages.In the“8·11”process,the heating effect was the strongest in the initial stage,but weakened during the vortex's development.On the contrary,the heating effect was initially weak in the“8·16”process,and intensified during the development stage.(3)The available potential energy of the“8·11”process significantly increased in kinetic energy converted from rotational and divergent winds through baroclinic action,and the divergent wind energy continued to convert into rotational wind energy.By contrast,the“8·16”process involved the conversion of rotational wind energy into divergent wind energy,which in turn converted kinetic energy back into available potential energy,thereby impeding the further development and maintenance of the southwest vortex.

珠江三角洲“9·7”极端暴雨精细观测特征及成因

2023年9月7—8日珠江三角洲出现极端特大暴雨(简称“9·7”极端暴雨)。应用多源资料分析该过程的精细化观测特征及成因,结果表明:“9·7”极端暴雨由高层辐散、中层弱引导气流、低层西南季风和台风海葵(2311)残涡共同造成,水平尺度约为100 km的带状中尺度对流复合体长时间维持,列车效应和暖云降水特征显著,雷达回波质心低,最强降水阶段不低于45 dBZ的强回波质心位于4 km高度以下,不低于30 dBZ的强回波在深圳持续时间长达21 h。该天气过程以中小雨滴为主且数浓度较大,当降水强度大于20 mm·h^(-1)时,雨滴粒径增大但数浓度明显降低。“9·7”极端暴雨持续时间、强度和落区与边界层低空急流脉动、急流核区位置对应很好,强降水出现在低空急流指数迅速加强后的1~2 h内,低空急流和低空急流指数变化对强降水具有重要指示意义。台风海葵(2311)残涡在珠江三角洲的长时间滞留是此次极端暴雨的天气尺度原因,深厚的边界层低空急流提供了良好的动力和水汽条件,对流风暴的持续生成和维持是此次极端暴雨的直接原因。

服务业综合改革与服务业企业员工配置效率

服务业体制机制滞后日趋成为影响产业高质量发展的掣肘,但既有研究对如何通过治理制度变革激发服务业新活力的讨论仍较为匮乏。借助中国上市企业匹配数据和双重差分法,考察国家服务业综合改革试点政策对服务业企业员工配置效率的影响。结果表明:服务业综合改革显著提升了服务业企业员工配置效率,且主要基于缩减企业员工冗余来实现。进一步地,服务业综合改革的政策效应在资本技术密集型企业、国有企业、拥有较大员工规模的企业、区域市场化程度低的企业、所处行业垄断程度高的企业、控股股东代理成本较低的企业和管理者短视程度较高的企业样本中更为明显。机制检验发现,服务业综合改革能通过缓解企业融资约束的润灌效应、促进技术进步的升级效应以及增强劳动力市场厚化效应来改善服务业企业的员工配置效率。制度创新变革赋能了企业员工配置结构优化,因此,应深化我国服务业供给侧结构性改革,提升服务业人力资源管理水平,形成服务业厚劳动力市场。

北京“23·7”极端强降雨特征和成因分析

利用北京地区加密气象站、补盲的北京市规划和自然资源委员会雨量站、双偏振雷达、风廓线雷达、GPS水汽等观测数据和ERA5再分析数据,对北京“23·7”极端强降雨阶段性特征和成因进行了分析。结果表明:“23·7”极端强降雨累计降水量(331 mm)和单点最大降水量(1025 mm)均打破历史纪录,最大雨强(126.6 mm·h^(-1))排名历史第二位,具有显著的极端性。强降雨可分为5个阶段,其中第Ⅱ和第Ⅳ阶段降水量分别占过程累计降水量的37.1%和39.7%,第Ⅳ阶段雨强更大,对应急流更强,高温、高湿特征也更明显。地形对降雨的增幅作用显著,降水量在海拔100~300 m山区迅速增加,极大值出现在海拔约400 m的山区,第Ⅱ(第Ⅳ)阶段山区平均降水量和小时雨强分别是平原的2.1(3.0)倍和2.0(2.7)倍;第Ⅱ阶段主要为地形对急流的直接抬升,第Ⅳ阶段为地形绕流辐合和直接抬升共同作用。7月31日上午(第Ⅳ阶段)边界层急流出口区与低空急流入口区耦合导致低层上升运动增强,促使西部山前β中尺度对流系统由块状发展成线状并有γ中尺度涡旋产生,该β中尺度对流系统北上时形成短暂的列车效应,引发了西部山区8个站次100 mm·h^(-1)以上的极端短时强降水。

Viscous Effects on Wave Forces on A Submerged Horizontal Circular Cylinder

Numerical simulations are carried out for wave action on a submerged horizontal circular cylinder by means of a viscous fluid model, and it is focused on the examination of the discrepancies between the viscous fluid results and the potential flow solutions. It is found that the lift force resulted from rotational flow on the circular cylinder is always in anti-phase with the inertia force and induces the discrepancies between the results. The influence factors on the magnitude of the lift force, especially the correlation between the stagnation-point position and the wave amplitude, and the effect of the vortex shedding are investigated by further examination on the flow fields around the cylinder. The viscous numerical calculations at different wave frequencies showed that the wave frequency has also significant influence on the wave forces. Under higher frequency and larger amplitude wave action, vortex shedding from the circular cylinder will appear and influence the wave forces on the cylinder substantially.

Recent progress on the study of asymmetric vortex flow over slender bodies

The investigations of forebody vortex flow and its flow control have great importance in both academic field and engineering application areas. A large number of papers and many review papers have been published. However in this research field of forebody asymmetric vortices, three problems such as tip perturbation effect, Reynolds number effect and flow instability are less studied and thus not understood completely. So many researches are still working on the issues in recent years. The present paper attempts to provide a review of recent research progress on first two problems. The first problem is mainly concerned with how the vortex flow evolves after tip perturbation; how to solve the problem of repeatability and reproducibility of wind tunnel testing data; how to develop a conception of active flow control technique with tip perturbation based on the study of vortex flow response to tip perturbation. For the second problem one is mainly concerned that how the asymmetric vortices are developed with the increase of Reynolds number; how to classify the vortex flow patterns in different Reynolds number regimes; how to develop an appropriate boundary layer transition technique to simulate flows at high Reynolds number in the convention wind tunnels. Finally, some important ques- tions that deserve answers are proposed in the concluding remarks.

Propagation of Airy Gaussian vortex beams in uniaxial crystals

The propagation dynamics of the Airy Gaussian vortex beams in uniaxial crystals orthogonal to the optical axis has been investigated analytically and numerically. The propagation expression of the beams has been obtained. The propagation features of the Airy Gaussian vortex beams are shown with changes of the distribution factor and the ratio of the extraordinary refractive index to the ordinary refractive index. The correlations between the ratio and the maximum intensity value during the propagation, and its appearing distance have been investigated.

Seasonal Cumulative Effect of Ural Blocking Episodes on the Frequent Cold events in China during the Early Winter of 2020/21

Starting in mid-November,China was hit by several cold events during the early winter of 2020/21.The lowest temperature observed at Beijing station on 7 January reached−19.6°C.In this paper,we show that the outbreak of the record-breaking extreme cold event can be attributed to a huge merging Ural blocking(UB)ridge over the Eurasian region.The sea-ice cover in the Kara and East Siberia Seas(KESS)in autumn was at its lowest value since 1979,which could have served as a precursor signal.Further analysis shows that several successive UB episodes occurred from 1 September 2020 to 10 January 2021.The persistent UB that occurred in late September/early October 2020 may have made an important contribution to the October historical minimum of sea ice in the KESS region.Our results also show that,after each UB episode in winter,significant upward propagation of wave activity occurred around 60°E,which resulted in weakening the stratospheric vortex.Meanwhile,each UB episode also caused a significant reduction in sea-ice extent in KESS and a significant weakening of the westerly jet in mid-high-latitude Eurasia.Results suggest that the Arctic vortex,which is supposed to enhance seasonally,became weaker and more unstable than the climatic mean under the seasonal cumulative effects of UB episodes,KESS warming,and long-lasting negative-phase North Atlantic Oscillation(NAO-).Those seasonal cumulative effects,combined with the impact of La Niña winter,led to the frequent occurrence of extreme cold events.