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.

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.

一种新的非线性光学现象——Cascaded二级非线性光学效应

从Maxwell方程组出发 ,研究了一种新的非线性光学效应———Cascaded二级非线性现象 ,推导了依赖于光强的折射率变化———类克尔效应 ,分析了Cascaded非线性系数依赖于基波波长及波矢失配的变化规律

Lumped-equivalent circuit model for multi-stage cascaded magnetoelectric dual-tunable bandpass filter

A lumped-equivalent circuit model of a novel magnetoelectric tunable bandpass filter, which is realized in the form of multi-stage cascading between a plurality of magnetoelectric laminates, is established in this paper for convenient analysis.The multi-stage cascaded filter is degraded to the coupling microstrip filter with only one magnetoelectric laminate and then compared with the existing experiment results. The comparison reveals that the insertion loss curves predicted by the degraded circuit model are in good agreement with the experiment results and the predicted results of the electromagnetic field simulation, thus the validity of the model is verified. The model is then degraded to the two-stage cascaded magnetoelectric filter with two magnetoelectric laminates. It is revealed that if the applied external bias magnetic or electric fields on the two magnetoelectric laminates are identical, then the passband of the filter will drift under the changed external field; that is to say, the filter has the characteristics of external magnetic field tunability and electric field tunability. If the applied external bias magnetic or electric fields on two magnetoelectric laminates are different, then the passband will disappear so that the switching characteristic is achieved. When the same magnetic fields are applied to the laminates, the passband bandwidth of the two-stage cascaded magnetoelectric filter with two magnetoelectric laminates becomes nearly doubled in comparison with the passband filter which contains only one magnetoelectric laminate. The bandpass effect is also improved obviously. This research will provide a theoretical basis for the design, preparation, and application of a new high performance magnetoelectric tunable microwave device.

Theoretical analysis and experimental validation of radial cascaded composite ultrasonic transducer

A radial cascaded composite ultrasonic transducer is analyzed.The transducer consists of three short metal tubes and two radially polarized piezoelectric ceramic short tubes arranged alternately along the radial direction.The short metal tubes and the piezoelectric ceramic short tubes are connected in parallel electrically and in series mechanically,which can multiply the input sound power and sound intensity.Based on the theory of plane stress,the electro-mechanical equivalent circuit of radial vibration of the transducer is derived firstly.The resonance/anti-resonance frequency equation and the expression of the effective electromechanical coupling coefficient are obtained.Excellent electromechanical characteristics are determined by changing the radial geometric dimensions.Two prototypes of the transducers are designed and manufactured to support the analytical theory.It is concluded that the theoretical resonance/anti-resonance frequencies are consistent with the numerical and experimental results.When R_(2) is at certain values,both the anti-resonance frequency and effective electromechanical coupling coefficient corresponding to the second mode have maximal values.The radial cascaded composite ultrasonic transducer is expected to be used in the fields of ultrasonic water treatment and underwater acoustics.

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。

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.

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。

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%。

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。

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。

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。

Enhancing wood efficiency through comprehensive wood flow analysis:Methodology and strategic insights

Wood,an essential natural resource in human civilization,remains widely used despite advances in technology and material substitution.The surge in greenhouse gas emissions and environmental concerns accentuates the need for optimizing wood utilization.Material flow analysis is a powerful tool for tracking material flows and stocks,aiding resource management and environmental decision-making.However,the full extent of its methodological dimensions,particularly within the context of the wood supply chain,remains relatively unexplored.In this study,we delve into the existing literature on wood flow analysis,discussing its primary objectives,materials involved,temporal and spatial scales,data sources,units,and conversion factors.Additionally,data uncertainty,data reconciliation and crucial assumptions in material flow analysis are highlighted in this paper.Key findings reveal the significance of wood cascading and substitution effects by replacing non-wood materials,where they can reduce greenhouse gas emissions more than the natural carbon sink of forests and wood products.The immediate impact of short-term wood cascading might not be as robust as the substitution effect,with energy substitution showcasing better results than material substitution.However,it's crucial to note that these conclusions could experience significant reversal from a long-term and global perspective.Strategies for improving wood efficiency involve maximizing material use,advancing construction technologies,extending product lifespans,promoting cascade use,and optimizing energy recovery processes.The study underscores the need for standardized approaches in wood flow analysis and emphasizes the potential of wood efficiency strategies in addressing environmental challenges.

金沙江下游梯级联合调度对川渝河段防洪效果评价

金沙江下游四级梯级水库联合调度为长江川渝河段提供了防洪安全保障,对其防洪调度效果进行评价,可以科学衡量与评估川渝河段防洪调度效果,促进流域洪水资源化利用。基于金下四级联合防洪调度方案,建立防洪、发电、生态和航运4个准则下的评价指标体系,采用改进的层次分析法和熵权法,构建川渝河段梯级水库防洪调度效果评价模型,综合考虑防洪和兴利效益,评估不同来水频率和不同起调水位的梯级水库防洪调度效果;对比溪-向两库联合调度与金下四级联合调度效果,分析乌东德、白鹤滩水库建成投产对于川渝河段防洪调度及洪水资源化利用的综合效果。结果表明:①随着乌-白两库起调水位升高,金下四级防洪调度效果系数呈现先升高后降低的趋势。②对于20,30,50 a一遇和100 a一遇洪水,乌东德和白鹤滩水库分别从(965 m和795 m)、(975 m和790 m)、(955 m和790 m)、(952 m和795 m)起调时,金下四级防洪调度效果系数最大,梯级水库联合防洪调度方案最优。③乌东德、白鹤滩水库建成投产后,川渝河段洪水资源化利用效果提升。研究成果可用于多功能、多保护对象的梯级水库防洪调度效果评价,为地区防洪调度决策提供依据。

跨声速叶栅尾缘激波对层板冷却的影响研究

采用数值模拟与实验验证相结合的方法针对跨声速叶栅尾缘激波影响下叶片吸力面侧层板冷却结构内外耦合流动传热特性展开研究,获得了来流热力参数和主要结构参数对层板冷却效率及压力损失等的影响规律。研究结果表明:斜激波入射形成的逆压梯度易使得吸力面边界层流动分离;冷却气射流的引入对流动分离有抑制效果,但局部的分离也使层板热侧表面形成局部热斑,冷却效率发生突降(本研究范围内降幅达27.83%);吹风比增大可明显提高冷却效率,但相对压力损失也随之增大;压比由1.89增大到3.67时,叶栅通道内激波作用位置后移,平均冷效提升40.98%,对冷却性能起改善作用。随着气膜孔直径的增大,冷却效果逐渐提升,相对压力损失逐渐增大;冲击孔直径的增大削弱了综合冷却效果,相对压力损失有所下降;在本研究范围内,改变扰流柱直径与高度则对流动换热规律则影响较小。

基于质量谱模型评估捕捞对蜈支洲岛海洋牧场鱼类群落的影响

基于生态系统的渔业管理的理念已得到广泛认同,但其在海洋牧场建设中的应用仍非常少见。本研究根据2020−2021年在蜈支洲岛海域开展的渔业资源底拖网调查数据,构建了海洋牧场鱼类群落的质量谱模型(SSM),反映了海洋牧场中食物网的复杂结构以及种间相互作用,以评估捕捞对海洋牧场鱼类群落的影响。研究通过对两种管理策略(单物种管理和多物种管理)的模拟,分析特定种类的捕捞死亡系数变化对鱼类群落产生的影响,并利用群落总生物量、质量谱斜率、平均最大质量、平均质量和大型鱼类指数5种群落生态指标监测了鱼类群落的特征状态。单物种管理策略结果显示,蜈支洲岛海洋牧场生态系统呈现下行控制效应,肉食性鱼类对浮游生物食性鱼类存在着强烈的调控作用。捕捞死亡系数变化后,不同物种间竞争捕食等复杂的相互作用会产生营养级联效应。多物种管理策略结果显示,灰海鳗(Muraenesox cinereus)的捕捞死亡系数对群落质量谱斜率影响最大,大头狗母鱼(Trachiocephalus myops)和灰海鳗的捕捞死亡系数对鱼类群落生物量和群落结构及功能的影响最大。研究结果对于保护和维持鱼类群落稳定方面具有重要意义,能够帮助管理者更好地了解捕捞死亡系数变化对鱼类群落产生的潜在影响,从而根据物种对渔业的重要性制定可行且有效的保护和管理策略。

平面叶栅非定常响应函数及声辐射分析

[目的]针对叶栅在湍流中的脉动压力和声辐射问题,介绍并推导叶栅响应函数理论。[方法]该理论假设叶栅叶片无厚度,通过Wiener-Hopf方法求解叶栅散射场积分表达式,得到叶栅散射场速度势的解析表达式和叶栅表面非定常压力系数,再进一步得到叶栅外部流域的辐射声功率。采用解析公式计算叶栅的压力系数和辐射声功率,并与数值法进行对比,然后进一步将该函数推广应用至水下计算,对叶栅响应函数与Sears函数预报的叶栅表面非定常力进行比较。[结果]结果表明,采用解析法与数值法计算得到的结果吻合较好,叶栅响应函数与Sears函数计算得到的叶栅非定常升力系数频谱曲线趋势一致。[结论]在幅值上叶栅响应函数计算结果略低于Sears函数的结果,但相对于叶栅响应函数,单波数域的Sears函数无法考虑安放角、纵倾和侧斜对叶栅非定常升力的影响。

北方某村镇地区地热梯级利用供暖系统适宜性及运行效果分析

我国北方村镇地区冬季供暖能耗量大、能源利用率低、环境污染严重问题日益凸显。因此各地区都在推广清洁能源供暖、因地制宜地利用可再生能源,这对北方村镇地区冬季供暖具有重要意义。地热梯级利用供暖系统是一种清洁的供暖方式,其在村镇地区推广较少且具有一定的地域选择性。分析北方典型地区的清河县某村镇地区地热梯级利用供暖系统的适宜性和运行效果,对比不同供暖系统方案的适宜性,发现地热梯级利用供暖系统初投资较高,但运行成本较低,系统综合能效较高。经过适宜性综合评价得出:地热梯级利用供暖系统在北方村镇供暖具有优越性;分析地热梯级利用供暖系统的实际运行效果得出:系统实际运行费用为13.48元/m~2,运行能效比为4.49,系统运行状况良好;分析用户侧室内环境得出:在供暖季内,用户室内温度均高于设计温度,室内环境品质均达到标准要求,用户满意程度高。为推广地热梯级利用供暖系统在北方村镇地区的应用提供了重要参考。

青海祁连山区山水林田湖草生态保护修复工程生态成效评估

生态成效作为判定山水林田湖草生态保护修复工程有效性的重要途径,对加强工程总体布局和顶层设计、确保工程取得显著成效具有非常重要的意义。青海省祁连山区具有极其典型的“山水林田湖草”生命共同体特征,是中国第一批山水林田湖草生态保护修复工程试点之一。通过构建“生态干扰变化-生态系统格局变化-生态系统质量变化-生态系统功能变化-生态成效变化”逻辑框架,运用时空对比分析方法,对青海祁连山区山水林田湖草生态保护修复工程的生态成效进行了评估。结果表明:工程实施后,重要生态用地面积增长了0.1%、生态连通度降低了0.5%、植被覆盖度指数提升了10.1%、单位面积水源涵养量提高了31.5%,土壤保持量增加了3.1%,固碳量增加了2.8%,表明工程实施以来,生态干扰增加,部分类型生态系统破碎化有所加剧,但总体生态系统格局相对稳定,生态系统质量和各生态功能均有提升,修复成效显现。研究结果对青海祁连山区山水林田湖草生态保护修复工程的实施有一定的指导性作用,能为未来山水林田湖草生态保护修复工作提供先进经验,对科学指导中国更好地开展生态修复工作具有重要意义。