Numerical investigation of hydro-morphodynamic characteristics of a cascading failure of landslide dams

A cascading failure of landslide dams caused by strong earthquakes or torrential rains in mountainous river valleys can pose great threats to people’s lives,properties,and infrastructures.In this study,based on the three-dimensional Reynoldsaveraged Navier-Stokes equations(RANS),the renormalization group(RNG)k-εturbulence model,suspended and bed load transport equations,and the instability discriminant formula of dam breach side slope,and the explicit finite volume method(FVM),a detailed numerical simulation model for calculating the hydro-morphodynamic characteristics of cascading dam breach process has been developed.The developed numerical model can simulate the breach hydrograph and the dam breach morphology evolution during the cascading failure process of landslide dams.A model test of the breaches of two cascading landslide dams has been used as the validation case.The comparison of the calculated and measured results indicates that the breach hydrograph and the breach morphology evolution process of the upstream and downstream dams are generally consistent with each other,and the relative errors of the key breaching parameters,i.e.,the peak breach flow and the time to peak of each dam,are less than±5%.Further,the comparison of the breach hydrographs of the upstream and downstream dams shows that there is an amplification effect of the breach flood on the cascading landslide dam failures.Three key parameters,i.e.,the distance between the upstream and the downstream dams,the river channel slope,and the downstream dam height,have been used to study the flood amplification effect.The parameter sensitivity analyses show that the peak breach flow at the downstream dam decreases with increasing distance between the upstream and the downstream dams,and the downstream dam height.Further,the peak breach flow at the downstream dam first increases and then decreases with steepening of the river channel slope.When the flood caused by the upstream dam failure flows to the downstream dam,it can produce a surge wave that overtops and erodes the dam crest,resulting in a lowering of the dam crest elevation.This has an impact on the failure occurrence time and the peak breach flow of the downstream dam.The influence of the surge wave on the downstream dam failure process is related to the volume of water that overtops the dam crest and the erosion characteristics of dam material.Moreover,the cascading failure case of the Xiaogangjian and Lower Xiaogangjian landslide dams has also been used as the representative case for validating the model.In comparisons of the calculated and measured breach hydrographs and final breach morphologies,the relative errors of the key dam breaching parameters are all within±10%,which verify the rationality of the model is applicable to real-world cases.Overall,the numerical model developed in this study can provide important technical support for the risk assessment and emergency treatment of failures of cascading landslide dams.

Enhanced picosecond terahertz wave generation based on cascade effects in a terahertz parametric generator

Enhanced terahertz wave generation via a Stokes cascade process has been demonstrated using picosecond pulse pumped terahertz parametric generation at 1 kHz repetition rate.Clear cascade saturation of terahertz output was observed,and the corresponding cascade-Stokes spectra were analyzed.The maximum terahertz wave average power was 22μW under a pump power of 30 W,whereas the maximum power conversion efficiency was 8×10^(-7)under a pump power of 21 W.The THz power fluctuation was measured to be about 1%in 20 min.This THz parametric source with a relatively stable output is suitable for a variety of practical applications.

Research on large-scale cascading failure of power systems using synergistic effect

This paper discusses the primary causes from the point of synergistic effects to improve power system vulnerability in the power system planning and safety operation. Based on the vulnerability conception in the complex network theory the vulnerability of the power system can be evaluated by the minimum load loss rate when considering power supply ability.Consequently according to the synergistic effect theory the critical line of the power system is defined by its influence on failure set vulnerability in N-k contingencies.The cascading failure modes are proposed based on the criterion whether the acceptable load curtailment level is below a preset value.Significant conclusions are revealed by results of IEEE 39 case analysis weak points of power networks and heavy load condition are the main causes of large-scale cascading failures damaging synergistic effects can result in partial failure developed into large-scale cascading failures vulnerable lines of power systems can directly lead the partial failure to deteriorate into a large blackout while less vulnerable lines can cause a large-scale cascading failure.

Conjugated microporous polymers-scaffolded enzyme cascade systems with enhanced catalytic activity

Enhancing catalytic activity of multi-enzyme in vitro through substrate channeling effect is promis-ing yet challenging.Herein,conjugated microporous polymers(CMPs)-scaffolded integrated en-zyme cascade systems(I-ECSs)are constructed through co-entrapping glucose oxidase(GOx)and horseradish peroxidase(HRP),in which hydrogen peroxide(H_(2)O_(2)) is the intermediate product.The interplay of low-resistance mass transfer pathway and appropriate pore wall-H_(2)O_(2) interactions facilitates the directed transfer of H_(2)O_(2),resulting in 2.4-fold and 5.0-fold elevation in catalytic activ-ity compared to free ECSs and separated ECSs,respectively.The substrate channeling effect could be regulated by altering the mass ratio of GOx to HRP.Besides,I-ECSs demonstrate excellent stabili-ties in harsh environments and multiple recycling.

Multiple Plasmonic Resonances and Cascade Effect in Asymmetrical Ag Nanowire Homotrimer

Plasmonic Ag nanowire homotrimer with asymmetrical radii and separations, which exhibits characteristics of multiple plamonic resonances and different electric field distributions, is systematically investigated by means of 2D finite element method. It was found that the dark and bright modes appear in asymmetrical nanowire homotrimer. In addition, when the dark modes appear between the smaller radii of the nanowires, the cascade effect results in enhanced electric field between the smaller radii nanowires. As a result of the appearance of the bright modes between the smaller radii of the nanowires, the restriction of the cascade effect generates enhanced electric field between the bigger nanowires.

Science Letters:Model for cascading failures in congested Internet

Cascading failures often occur in congested networks such as the Internet. A cascading failure can be described as a three-phase process： generation, diffusion, and dissipation of the congestion. In this account, we present a function that represents the extent of congestion on a given node. This approach is different from existing fimctions based on betweenness centrality. By introducing the concept of ＇delay time＇, we designate an intergradation between permanent removal and nonremoval. We also construct an evaluation fimction of network efficiency, based on congestion, which measures the damage caused by cascading failures. Finally, we investigate the effects of network structure and size, delay time, processing ability and packet generation speed on congestion propagation. Also, we uncover the relationship between the cascade dynamics and some properties of the network such as structure and size.

Effects of Mountain Rivers Cascade Hydropower Stations on Water Ecosystems

China is rich in hydropower resources,and mountain rivers have abundant water resources and huge development potential,which have a profound impact on the pattern of water resources allocation in China.As the main way of water resources and hydropower development,the construction of cascade hydropower stations,while meeting the requirements of water resources utilization for social development,has also brought adverse effects on river ecosystems.Therefore,the impact of the construction of cascade hydropower stations on mountainous river ecosystems,where the minimum ecological flow of rivers must be ensured and reviewed.In addition,this paper proposed the deficiencies and outlooks for cascade hydropower stations based on previous research results.

考虑质量传导的项目调度与人员配置集成优化

研究表明,质量问题是项目返工的主要原因之一,而人员技能水平是影响项目活动完成质量的关键因素。基于一般性的多技能资源受限项目调度问题,综合考虑人员技能水平以及活动间质量传导作用对活动完成质量的影响,进一步数学表达级联作用下的返工子网以及重构的项目网络,并结合一个大型船舶制造项目案例进行实验分析。对比实验结果表明:所提出的模型可有效平衡有限人力资源在不同活动间的分配,有利于减少返工风险的级联,缩短项目总工期。进一步,通过质量评估区间和人员技能水平参数波动的随机实验,验证模型对两类参数波动具有一定的鲁棒性。

高负荷涡轮叶栅风洞流动周期性研究

为设计符合要求的平面叶栅试验段以开展跨音速高负荷平面叶栅气动试验,以高负荷涡轮转子叶栅为研究对象,采用数值模拟方法研究了不同来流攻角和不同出口等熵马赫数对高负荷涡轮平面叶栅进口流场的均匀性与叶栅通道流场周期性的影响.结果表明:平面叶栅进口流场沿周向呈现出不均匀的波动分布,靠近吸力面侧壁的三个通道的来流均匀性和准确性普遍较差,叶栅中部和靠近压力面侧壁的通道进口均匀性和准确性较好;进口流场品质直接影响着叶栅通道内流场的周期性,而来流攻角对叶栅进口流场品质的影响比出口等熵马赫数更明显,在正攻角下,攻角偏差极限值约为0.7°,不同叶栅通道进口流场均匀性和准确性较好;从亚音速流动到超音速流动,靠近试验件吸力面侧壁的叶栅通道产生强激波,致使叶片80%轴向弦长处压力误差值增大,叶栅通道流场周期性下降.

反倾销嵌入全球生产网络的级联效应仿真研究

本研究将复杂网络理论应用于投入产出模型并将其引入宏观经济学生产函数理论模型,对反倾销嵌入全球生产网络的内在机理与其产生的级联效应展开探讨与仿真模拟分析.研究发现:基于网络视角与投入产出关系,反倾销冲击对中间产品的贸易抑制作用要明显大于最终产品,多次跨境的中间品将会累积增加反倾销带来的贸易成本;反倾销带来的行业引致需求量降低与出口贸易受到抑制以及行业与国家总产出水平的波动等影响,会沿着以中间品贸易为基础的全球生产网络中的投入产出关系进行传播,从而产生显著的级联效应,并且该效应会随着不同国家-部门节点之间的联系紧密程度(贸易量)的降低而衰减;反倾销产生的级联效应不仅涉及全球生产网络中直接关联节点即涉案国(调查国与被调查国)的国内上下游行业,而且波及间接关联节点即非涉案国的第三方国家和地区,进而影响全球多边贸易发展,同时,级联效应也阻碍了网络节点参与全球价值链生产分工,导致了节点隶属国(地区)的国内价值链被拉长;反倾销嵌入全球生产网络后,会通过整个生产网络产生总量波动效应,从而改变全球生产网络的拓扑结构,即全球生产网络变的相对稀疏、节点间网络距离拉长等.

考虑零碳航线的集装箱运输网络抗毁性研究

随着世界各国对航运碳排放的重视,零碳航线作为减少碳排放的创新方式备受关注。集装箱运输过程可以利用复杂网络拓扑的形式呈现,虽然零碳航线的加入不会改变航运网络的结构,但由于零碳航线上港口的独特性质和作用,会对集装箱运输网络产生一定影响。本文根据港口实际数据构建引入零碳航线的集装箱运输网络模型,以网络效率、最大联通子图规模、绿色港口抗毁性指数这3个指标衡量网络的抗毁性能。通过模拟实验选择蓄意攻击触发网络级联效应,分析容量参数、绿色港口数、负载分配系数对集装箱运输网络抗毁性的影响。结果表明,零碳航线的加入对集装箱运输网络抗毁性能影响较大;25%的港口为绿色港口时,能兼顾网络的三方面抗毁性能,包括网络全局效率、绿色港口抗毁性指数和最大连通子图规模;负载分配系数为4时能够提高运输网络的抗毁性能,削弱零碳航线加入造成的影响。重要节点受到攻击后,网络效率、最大联通子图规模均大幅度下降。

基于水循环全过程的旱涝级联效应研究框架

气候变化与人类活动影响加剧背景下,亟须实现旱涝灾害风险精准防控。从孕育机理、传播机制、事件评价、风险评估、影响效应等方面回顾了旱涝事件研究现状,明晰了当前在旱涝事件演变机理和评价指标构建方面存在的不足。从水循环全过程视角,分析了干旱和洪涝事件在坡面、河道、流域和区域4个尺度与水量和效应2个层面的本质内涵、影响效应及评价方式。基于地表-土壤-地下、坡面-河道、支流-干流及水网工程间的水力联系,分别从水量和效应层面分析了不同空间尺度上干旱和洪涝的内在联系,明确了干旱、洪涝及旱涝级联过程本质上受流域调蓄作用的影响。从旱涝级联效应的内涵、类型、表现形式和关键技术等方面,提出了旱涝级联效应的研究框架。未来应从流域调蓄作用的视角量化不同空间尺度各要素调蓄能力变化,分层调蓄防范化解旱涝风险。

金沙江下游水电站梯级开发对下游水温的影响

金沙江下游梯级水电开发导致下游水温沿程变化,对鱼类产卵繁衍和生长发育产生了重要影响。基于下游向家坝、朱沱、宜昌和大通4个水文站2002—2022年表层水温监测数据,对比分析了梯级水电建设期、运行期下游江段水温沿程的变化规律。结果表明:①溪洛渡和向家坝两级水电联合运行期,向家坝水文站多年平均最低水温较天然状态升高约1.4℃,最低水温出现时间较天然状态滞后约35 d;②乌东德、白鹤滩、溪洛渡和向家坝四级水电站联合运行期,向家坝、朱沱、宜昌和大通4个水文站年最低水温分别较溪洛渡和向家坝两级水电站联合运行期升高约2.0、1.1、0.8、0.7℃,年最低水温出现时间较天然状态分别滞后约42、29、11、18 d。研究成果可以为金沙江下游梯级水电站水温生态调度和下游水生态保护提供参考依据。

新兴的生态危机——“空气富营养化”

存在于水生态系统和陆地生态系统中的藻类可以通过各种自然和人为的过程溢出到大气中,形成空气中的藻类。随着水体和陆地富营养化、空气污染、气候变暖和人造夜间灯光等各种因素的加剧,各因素之间交互作用将可能进一步刺激空气中藻类及其毒素的繁殖和扩散,最终形成“空气富营养化”级联效应.并且这一新兴级联效应将可能会对人类健康和生态系统构成严重威胁.

复杂环境下工程物流网络级联失效抗毁性研究

合理评估工程物流网络抗毁性有助于保障工程物资及时准确供应,为制定物资运输计划与交通中断疏通应急预案提供科学支撑。针对复杂环境下工程物流网络运输通道承载能力不足且风险多样的特征,在考虑路段状态的基础上提出了拥堵效应分配策略,选择与复杂环境下工程物流网络中断成因相对应的三种攻击方式进行级联失效模拟。构建了反映路段抗毁能力、网络结构完整性及网络服务能力的评价指标,评估了复杂环境下工程物流网络和路段的抗毁性。最后,以复杂环境下某交通基础设施建设工程物流网络为例,验证了模型的有效性和合理性。结果表明:当路段容差参数β和失效阈值参数λ取值为0.5时,工程物流网络抗毁能力提升最为经济合理;工程物流网络中的路段在面临不同规模级联失效时存活率排序稳定,需要对存活率较低的路段制定针对性保通策略;工程物流网络抵抗介数降序蓄意攻击的能力较弱,面对风险降序蓄意攻击时抗毁性较强;相较于传统负载重分配策略,所提出的拥堵效应分配策略可以使工程物流网络抗毁性提升约38%。

台风扰动下计及线路老化与连锁故障的输电网韧性评估

针对传统韧性评估方法对输电网老化效应及其诱发的连锁故障考虑不足的问题,以台风作为电力系统外部干扰的代表,提出一种台风扰动下计及输电线路老化与连锁故障的输电网韧性评估方法。首先,考虑老化效应对输电线路风致故障率和安全过载能力的影响,以故障自然演化时间为切入点,提出一种计及输电线路老化的输电网双时间维度故障演化模型,包括台风时间维度和连锁故障时间维度。其次,基于台风灾害下电网性能变化曲线,提出考虑时间分辨率的系统脆弱率和恢复率2个输电网韧性指标;基于电网性能和系统服役年限关联曲线,提出考虑不同服役年限的输电网韧性指标。然后,根据台风扰动下输电网性能演化特征,确定基于上述2类曲线评估输电网韧性的整体框架和流程。最后,在IEEE 39节点系统上进行算例仿真,结果表明所提方法能够有效评估不同服役年限输电网的韧性。

两级堰塞坝连溃过程数值模拟及溃口流量演化特征研究

在强震作用下,高山峡谷区易发生滑坡堵江形成串联的梯级堰塞坝,其中一级一旦溃决易引发梯级连溃。本文基于三维雷诺平均Navier-Stokes方程、湍流重正化群模型,以及悬移质和推移质冲蚀方程,并考虑溃口边坡的失稳坍塌,采用有限体积法建立了梯级堰塞坝连溃过程数值模拟方法,用于模拟连溃过程中的水动力特征及梯级堰塞坝的溃口形态演化过程。选择典型的两级堰塞坝连溃概化模型试验作为数学模型验证案例,对比实测值和计算结果发现,上下游堰塞坝溃口洪水流量过程和溃口形态演化过程基本一致,上下游堰塞坝溃口峰值流量、区间洪水演进时间等关键参数的相对误差小于±5%;比较上下游堰塞坝溃口洪水流量过程发现,梯级堰塞坝发生连溃时,溃坝洪水存在级联放大效应。选择上下游堰塞坝距离、河道坡度和下游坝坝高等三个关键参数,研究连溃洪水的放大效应及其影响因素,参数敏感性分析结果表明:下游坝溃口峰值流量随两坝间距和下游坝坝高的减小而增大,随河道坡度的增长呈先增大后减小的趋势;上游坝溃决洪水演进至下游坝时可能产生涌浪翻越并冲蚀坝顶,导致坝顶高程降低,并对下游坝发生溃决的时间以及溃口峰值流量产生影响,因此涌浪对下游坝溃决过程的影响与涌浪翻越坝顶的水量以及坝料冲蚀特性相关。选择小岗剑上、下两级堰塞坝连溃案例,通过对比计算和实测的溃口流量以及溃口形态发现,关键溃坝参数的相对误差小于±10%,验证了模型在实际案例中应用的合理性,本文提出的数值模拟方法可为梯级堰塞坝连溃风险评估和应急处置提供重要技术支撑。

雅砻江锦屏减水河段产漂流性卵鱼类早期资源及变化

分析雅砻江两河口和杨房沟水电站投产运行初期锦屏减水河段产漂流性卵鱼类早期资源及变化,为雅砻江中下游梯级水电开发的环境影响研究提供数据支撑。2022年5-7月在雅砻江干流锦屏二级减水河段凉山州冕宁县里庄断面设置采样点利用半圆弶网采集鱼类卵苗,同时测量网口流速、水温等环境因子,并结合径流量数据推断产卵场位置及规模。结果采集到鱼类卵苗12种,其中产漂流性卵鱼类4种,分别是中华金沙鳅、犁头鳅、长薄鳅和中华沙鳅。估算调查期间锦屏减水河段产漂流性卵径流量约为1019.07万粒,在5月下旬水温达到16℃以上开始繁殖,7月中上旬水温17℃以上达到繁殖高峰,较大规模的产卵场主要分布在九龙河口以下和爱、南河-青纳和里庄等3个江段。与2013年及2019-2020年调查相比,锦屏减水河段均以中华金沙鳅和犁头鳅为主要产卵种类,鱼卵密度低于2013年,高于2019-2020年,近年来繁殖规模总体呈现稳中有升的趋势,繁殖高峰期有所推迟。由于流水环境的存在,锦屏减水河段保留有雅砻江下游规模最大的产漂流性卵鱼类产卵场,建议继续加强河段水温观测、评估分层取水效果、优化生态调度方案以保护雅砻江下游鱼类资源。

清江梯级配合三峡水库对城陵矶防洪调度方式探究

为充分挖掘清江梯级水库10亿m^(3)防洪库容的防洪效益,构建了长江上游水库群与清江梯级水库联合防洪调度模型,定量分析了清江梯级水库配合三峡水库对荆江河段实施联合防洪调度的防洪作用和库容使用情况,探讨了清江梯级水库配合三峡水库对城陵矶联合防洪调度的必要性;在此基础上,开展了不同水库群联合防洪调度方案防洪效果的比较分析,提出了清江梯级水库配合三峡水库对城陵矶防洪调度的分级拦蓄方式。研究表明:提出的分级拦蓄方式为当来水小于4000 m^(3)/s,清江梯级水库各拦蓄流量为2500 m^(3)/s;当来水不小于4000 m^(3)/s,清江梯级水库各拦蓄流量为3000 m^(3)/s;拦蓄时机与三峡水库同步,在拦蓄过程中兼顾了发电因素。该方案可有效发挥清江梯级水库的防洪作用,减少长江上游水库群动用防洪库容。研究成果量化了清江梯级水库的防洪作用,可有力支撑长江水库群联合防洪调度方案编制。

侧向膨胀效应下激波与涡轮平面叶栅相互作用机理研究

爆轰燃烧具有更低的熵增率和更高的热循环效率,利用旋转爆轰燃烧室替代涡轮喷气式发动机的主燃烧室可以进一步提高其工作性能。为研究旋转爆轰波组合发动机内部的工作过程,建立激波管与涡轮平面叶栅耦合计算模型,考虑激波传播方向的影响,分析激波在侧向膨胀效应下与涡轮叶片相互作用机理,并在此基础上进一步开展可视化实验研究。结果表明:在侧向膨胀效应影响下,激波波阵面从竖直形状转变为弯曲形状,波后气流在直角台阶处形成一个三角形的局部超声速区域,随后弯曲激波与涡轮叶片的前缘处、压力面、吸力面和尾缘处相互作用,在叶栅通道内形成复杂的波系结构。静子叶栅和转子叶栅对压力和温度有着不同程度的抑制作用,当弯曲激波相对于叶片垂直时,叶栅的抑制更为明显。对比分析了实验与数值模拟获得的激波系在涡轮平面叶栅通道内的传播及演化过程,发现激波演化的时空特性高度一致,实验与数值模拟结果吻合良好。观测到弯曲激波在叶片尾缘处发生衍射,波阵面面积明显增大且激波传播方向改变,随着激波继续传播,叶片尾缘处伴随着脱落涡产生。