Equilibrium sediment transport in lower Yellow River during later sediment-retaining period of Xiaolangdi Reservoir

The Xiaolangdi Reservoir has entered the later sediment-retaining period, and new sediment transport phenomena and channel re-estab- lishing behaviors are appearing. A physical model test was used to forecast the scouring and silting trends of the lower Yellow River. Based on water and sediment data from the lower Yellow River during the period from 1960 to 2012, and using a statistical method, this paper analyzed the sediment transport in sediment-laden flows with different discharges and sediment concentrations in the lower Yellow River. The results show that rational water-sediment regulation is necessary to avoid silting in the later sediment-retaining period. The combination of 3 000 m^3/s 〈 Q 〈 4 000 m^3/s and 20 kg/m^3 〈 S 〈 60 kg/m^3 （where Q is the discharge and S is the sediment concentration） at the Huayuankou section is considered an optimal combination for equilibrium sediment transport in the lower Yellow River over a long period of time.

A Higher-Efficient Non-Hydrostatic Finite Volume Model for Strong Three-Dimensional Free Surface Flows and Sediment Transport

In order to accurately simulate strong three-dimensional （3-D） free surface flows and sediment transport, the fully 3- D non-hydrostatic pressure models are developed based on the incompressible Navier-Stokes equations and convection-diffusion equation of sediment concentration with the mixing triangle and quadrilateral grids. The governing equations are discretized with the unstructured finite volume method in order to provide conservation properties of mass and momentum, and flexibility with practical application. It is shown that it is first-order accurate on nonuniform plane two-dimensional （2-D） grids and second-order accurate on uniform plane grids. A third-order approximation of the vertical velocity at the top-layer is applied. In such a way, free surface zero stress boundary condition is satisfied maturely, and very few vertical layers are needed to give an accurate solution even for complex discontinuous flow and short wave simulation. The model is applied to four examples to simulate strong 3-D free surface flows and sediment transport where non-hydrostatic pressures have a considerable effect on the velocity field. The newly developed model is verified against analytical solutions with an excellent agreement.

Two-Dimensional Mathematical Model of Tidal Current and Sediment for Oujiang Estuary and Wenzhou Bay

A 2-D mathematical model of tidal current and sediment has been developed for the Oujiang Estuary and the Wenzhou Bay. This model accomodates complicated features including multiple islands, existence of turbidity, and significant differ-ence in size distribution of bed material. The governing equations for non-uniform suspended load and bed load transport are presented in a boundary-fitted orthogonal curvilinear coordinate system. The numerical solution procedures along with their initial conditions, boundary conditions, and movable boundary technique are presented. Strategies for computation of the critical condition of deposition or erosion, sediment transport capacity, non-uniform bed load discharge, etc. are suggested. The model verification computation shows that, the tidal levels computed from the model are in good agreement with the field data at the 18 tidal gauge stations. The computed velocities and flow directions also agree well with the values measured along the totally 52 synchronously observed verticals distributed over 8 cross sections. The coraputed tidal water throughputs through the Huangda'ao cross section are close to the measured data. And the computed values of bed deformation from Yangfushan to the estuary outfall and in the outer-sea area are in good agreement with the data observed from 1986 to 1992. The changes of tidal volumes through the estuary, velocities in different channels and the bed form due to the influence of the reclamation project on the Wenzhou shoal are predicted by means of this model.

Electronic transport properties of lead nanowires

Lead nanowire occupies a very important position in an electronic device. In this study, a genetic algorithm（GA）method has been used to simulate the Pb nanowire. The result shows that Pb nanowires are a multishell cylinder. Each shell consists of atomic rows wound up helically side by side. The quantum electron transport properties of these structures are calculated based on the non-equilibrium Green function（NEGF） combined with the density functional theory（DFT）,which indicate that electronic transport ability increases gradually with the atomic number increase. In addition, the thickest nanowire shows excellent electron transport performance. It possesses great transmission at the Fermi level due to the strongest delocalization of the electronic state. The results provide valuable information on the relationship between the transport properties of nanowires and their diameter.

Radiation mean free path for non-LTE fully ionized medium

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Photon-assisted electronic and spin transport through two T-shaped three-quantum-dot molecules embedded in an Aharonov-Bohm interferometer

We investigate the time-modulated electronic and spin transport properties through two T-shaped three-quantum-dot molecules embedded in an Aharonov-Bohm（A-B） interferometer. By using the Keldysh non-equilibrium Green＇s function technique, the photon-assisted spin-dependent average current is analyzed. The T-shaped three-quantum-dot molecule A-B interferometer exhibits excellent controllability in the average current resonance spectra by adjusting the interdot coupling strength, Rashba spin-orbit coupling strength, magnetic flux, and amplitude of the time-dependent external field.Efficient spin filtering and multiple electron-photon pump functions are exploited in the multi-quantum-dot molecule A-B interferometer by a time-modulated external field.

放射性核素生态运移与辐射剂量评价研究现状及趋势

放射性核素在生态环境中的输运和转移(简称运移)长期以来受到辐射环境保护领域的特别关注。本文将系统梳理放射性核素在生态环境中的运移机制和模型及参数、人类和非人类生物剂量评价方法,以及在核设施发生事故情况下放射性核素非平衡态运移模型及参数等相关研究现状,并从计算模型、评价方法和参数等多维度探讨放射性核素在生态环境中的运移行为,重点针对放射性核素海洋运移、非人类物种剂量评价、短期事故排放的动态模型、人工智能技术应用等方面开展进一步研究并提出建议,为核与辐射应急响应、环境监测与风险评估等提供科学依据和技术支持。

不平衡输沙条件下河道断面形态调整规律试验研究

21世纪以来,受气候变化与人类活动共同影响,进入黄河下游河道的水沙条件发生显著变化,下游河道长期处于不平衡输沙状态,横断面形态调整剧烈,直接影响河势稳定,威胁下游防洪安全。基于2001—2021年黄河下游白鹤镇—高村河段实测断面资料,在分析原型河道横断面形态参数演变特征的基础上,选取黑岗口—柳园口河段开展物理模型试验,以定量揭示不平衡输沙条件下横断面形态调整规律。原型实测资料分析发现,相对于黄河下游其他河段,花园口—夹河滩河段断面形态变化相对较大。选择花园口—夹河滩河段中典型河段为原型,采用水平比尺600、垂直比尺60构建物理模型,保持相同的初始河道边界条件,开展了2000、3000、4000、5000 m^(3)/s四级流量,不同进口含沙量条件下断面形态调整试验。试验结果表明,各测验断面基本呈现进口含沙量较小时主槽冲刷、面积增大、河相系数减小,进口含沙量较大时主槽淤积、面积减小、河相系数增大的规律。对比原型资料与试验数据发现,不平衡输沙条件下,河段尺度的断面形态参数与来沙系数相关性较好,其中主槽面积与来沙系数成指数负相关,河相系数与来沙系数成二次函数关系。

典型非均匀推移质输沙率公式适用性比较

基于等中值粒径的“单、双峰型级配”推移质输沙试验以及“驼峰”输沙率试验数据,选择Einstein、吴伟明、Wilcock和吴保生等4种典型非均匀推移质输沙率公式计算“单、双峰型级配”推移质输沙率,将两种级配的输沙率比值及曲线形态与试验成果对比分析。结果表明:吴伟明公式在反映“单、双峰型级配”推移质输沙差异上表现最好,这4种公式均无法反映“驼峰”输沙率现象。基于多参数考虑的Patel公式较这4种公式能更好地反映上述两种现象。充分考虑床沙级配对分组沙起动切应力和输沙有效Shields数的影响,是提高非均匀推移质输沙率公式精度和适用性的关键。

非平衡热输运边界条件影响研究

当材料的特征尺寸小到与声子平均自由程相当,或特征时间短到与声子弛豫时间相当时,准平衡假设就不再有效,系统内会产生非局部效应。此时,边界条件将成为影响非平衡热输运的重要因素之一。超快速激光加热纳米薄膜是反映此类问题的典型案例,其传热过程中不仅热影响时间极短,而且作用区域还在纳米尺度。文章研究了不同边界条件对纳米硅薄膜非平衡热输运的影响,分析了声子从扩散状态向弹道状态转变的特性。结果表明:采用镜面边界条件与反弹边界条件具有相似的热输运过程,薄膜内部能量密度差异较小;对流边界条件下薄膜内部热量持续向外界流失,其能量密度最低;通过改变对流方式,发现强制对流相比于自然对流会带走更多的热量;随着薄膜尺寸减小,边界条件对热输运的影响会增大。

Non-canonical distribution and non-equilibrium transport beyond weak system-bath coupling regime： A polaron transformation approach

The concept of polaron, emerged from condense matter physics, describes the dynamical interac- tion of moving particle with its surrounding bosonic modes. This concept has been developed into a useful method to treat open quantum systems with a complete range of system-bath coupling strength. Especially, the polaron transformation approach shows its validity in the intermediate coupling regime, in which the Redfield equation or Fermi＇s golden rule will fail. In the polaron frame, the equilibrium distribution carried out by perturbative expansion presents a deviation from the canonical distribution, which is beyond the usual weak coupling assumption in thermodynam- ics. A polaron transformed Redfield equation （PTRE） not only reproduces the dissipative quantum dynamics but also provides an accurate and efficient way to calculate the non-equilibrium steady states. Applications of the PTRE approach to problems such as exciton diffusion, heat transport and light-harvesting energy transfer are presented.

基于客流博弈均衡的旅客列车双层开行方案优化

为提高旅客列车运行效益及旅客出行满意度,以铁路运营部门净收益、列车空座位走行公里最小化为上层0-1规划模型,以旅客出行满意度最大化为下层客流均衡模型,构建了纯整数非线性高速铁路旅客列车开行方案双层规划模型。针对下层客流均衡模型,通过划分博弈环境和分析旅客乘车出行选择行为,选取旅客同质群体作为局中人,构造各局中人合理赢得函数,对每个博弈环境均运用非合作博弈理论进行客流均衡分配。基于构建的模型特征分析,采用NSGA-Ⅱ算法求解上层停站方案模型,运用QPSO算法求解下层客流博弈均衡模型,并以兰新高速铁路为例验证了模型及算法的可行性。结果表明:该算法可获得使铁路运营部门与旅客双方均满意的Nash均衡解,由此得到的开行方案铁路旅客损失率为0%。

反旋转波相互作用对非平衡自旋玻色模型热输运性质的影响

随着实验技术的发展,量子系统中已经实现了强和超强自旋-腔、自旋-环境相互作用。很大一类光学腔和耗散环境可以用波色热库描述。在强系统-热库耦合条件下,之前适用于弱耦合条件下的旋波近似失效,需要考虑系统-热库的反旋转波相互作用对系统动力学演化和稳态行为的影响。使用正则变换和全计数统计方法,研究系统-热库反旋转波相互作用对热输运性质的影响。结果表明:在弱耦合情况下采用旋波近似时,稳态热流、噪声功率以及热力学不确定关系随温度单调增大。强耦合情况,反旋转波相互作用下,以上物理量呈非单调性:先增大后减小。在弱耦合情况下采用旋波近似时,热力学不确定关系与耦合强度无关。强耦合情况,反旋转波相互作用下,热力学不确定关系随着耦合强度的增大而减小,向热力学不确定关系的下限逼近。说明量子相干性有助于提高量子热机的性能,使其优于经典热机。

Resistant effect of non-equilibrium inter-particle collisions on dense solids transport

There exist big gaps between measurements and modeling predictions on solids holdup and pressure drop in dense solids transport, such as those occuring in the bottom sections of gas-solids risers. The inability of closing this gap by common modeling approaches indicates certain missing and/or misrepresentation of some controlling mechanisms in modeling the transport. Previous research efforts show that the gap can not be effectively narrowed by simply modifying the drag force formulations without inclusion of the collision effect. This paper explores the origin of some controlling mechanisms that might have been overlooked in previous modeling approaches, and recommends how to make the model dense solids transport better. Our analysis shows the presence of a resistant force arising from inter-particle collision when the solids are accelerated in dense-phase transport. This may be caused by non-equilibrium collision during solids acceleration, which differs from local-equilibrium assumptions on which the current kinetic theory modeling of granular particles is based. A complete modeling of this collision-induced resistance calls for a total revision of the kinetic theory, with the inclusion of non-equilibrium collisions and offcenter collisions in dense solids transport.

沙质河道冲刷不平衡输沙机理及规律研究

通过动床水槽试验,观测沙波运动,揭示了湍流扫荡河床使表层床沙产生频发的群体起动冲刷现象。据此,提出了床沙交换及冲刷粗化分二个层次的物理模式;分析了冲刷时表层床沙粗化的必然性,确定了悬移质扩散过程中适于非均匀沙河床的新的近底边界条件。依据所建立的不平衡输沙立面二维数学模型,计算了大量不同情况下的含沙量扩散恢复过程,据此总结出了冲刷时含沙量恢复饱和系数α的预报公式及变化规律。

不平衡输沙含沙量垂线分布研究

采用理论推导和数值计算的方法,进一步研究了不平衡输沙条件下的含沙量垂线分布,首次提出了非饱和泥沙通量的概念及其表达式,推导了不平衡输沙含沙量垂线分布的理论解,包括不平衡输沙含沙量垂线分布指数公式和幂函数公式,以及相应的底部含沙量确定方法。同时利用差分法求解剖面二维扩散方程,得到了不同参数的不平衡输沙含沙量垂线分布。其结果除少数误差稍大外,两种途径得出的含沙量垂线分布彼此符合良好。

非均匀悬移质输沙过程概化模型

对非均匀悬移质输沙过程进行了系统描述,建立了非均匀悬移质输沙的概化模型。讨论了概化模型的两种理想过程的解,基于实测数据对解式进行了验证,结果表明概化模型是合理的。指出了一类挟沙能力计算公式存在的问题,总结了非均匀沙实际输沙过程的一般规律。要揭示非均匀悬移质输沙机理,不仅要准确计算均匀沙平衡输沙的挟沙能力,而且应探求浑水中不同粒径泥沙自身的运动特性和颗粒间的相互影响。

非均匀悬移质恢复饱和系数的探讨

作者利用概率论的方法,分析了分组沙的恢复饱和系数与混合沙的平均恢复饱和系数之间的关系,得出了分组沙的恢复饱和系数与混合沙的平均沉速成正比,与该粒径组泥沙的沉速成反比的初步结论。文中给出了一个计算分组沙恢复饱和系数的半理论半经验关系式,并与现有研究成果进行了对比。

弯道三维水沙数值模拟中推移质输移方向的选取

在曲线坐标同位网格下,采用不平衡输沙方程建立了弯道三维水沙数学模型,并考虑了弯道处横坡与纵坡存在对泥沙起动的影响。模型采用有限体积法对方程进行离散,采用与动量插值技术相结合的SIMPLEC算法来进行模型求解。通过弯道试验的计算表明,模型能够有效地模拟出弯道处二次流及河床的冲淤变化情况,实测值与计算值吻合较好。在此基础上,进一步分析了弯道处推移质输移方向选取对冲淤模拟结果的影响,选取推移质输移方向与近底0.08倍水深处流速方向一致时,模拟效果较好。

河流冲刷过程中表层床沙粗化对不平衡输沙的影响

在分析前人的不平衡输沙研究成果的基础上 ,针对非均匀沙河床 ,提出了床沙交换速率的新物理概念 ,计算研究了不同床沙交换速率时表层床沙的粗化过程及非均匀沙含沙量恢复饱和过程。研究表明 ,由于较细泥沙的冲刷率总大于较粗泥沙 ,因此在床面薄层内泥沙随冲刷迅速粗化 ,致使挟沙力降低 ,不平衡输沙距离较均匀沙情况大大延长。床沙交换速率愈慢 ,则冲刷距离愈长。