Flume experiments to study fine-grain migration and its impact on slope stability

Fine grains migration is a primary cause of landslides and debris flows.This study investigates the effect of fine-grain migration on slope failure through flume experiments,focusing on the spatiotemporal characteristics and mechanisms of slope stability.A series of artificial rainfall flume experiments with varying rainfall intensities and slopes were conducted using soil samples collected from Wei Jia Gully.The experiments monitored pore-water pressure,grain migration,and failure sequences.Grain-size distribution parameters(μand Dc)were analyzed to understand the migration path and accumulation of fine grains.The experiments reveal that fine-grain migration significantly alters soil structure,leading to random blockage and interconnection of internal pore channels.These changes result in fluctuating pore-water pressure distributions and uneven fine-grain accumulation,critical factors in slope stability.Slope failures occur randomly and intermittently,influenced by fine-grain content in runoff and resulting pore-water pressure variations.This study highlights that fine-grain migration plays a vital role in slope stability,with significant implications for predicting and mitigating slope failures.The stochastic nature of fine-grain migration and its impact on soil properties should be incorporated into predictive models to enhance their accuracy and reliability.

基于改进的Flume实时数据采集系统应用研究

通过对Apache Flume日志采集系统的实时数据采集方案进行比较,并针对Flume现有的实时数据采集方案进行分析,提出了一种基于Flume改进的实时数据采集方案。实验证明,改进后的实时数据采集方案具有可行性。

A proposed directional function and wind-wave directional spectrum

A directional function for frequencies equal to and larger than the peak frequency of a wind-wave frequency spectrum is constructed by fitting the angular spreading based on the analytically derived directional spectrum of Wen et al. (1993, Journal of Oceanography, 49(2), 131～147, 149～172). For frequencies smaller than the peak frequency, the directional function is obtained by comparing and analyzing existing formulas. The nondimensional wind-wave frequency spectrum of Wen et al. (1994, Progress in Natural Seience, 4(4). 407～427;4 (5), 586～596) has been used together with the directional function just mentioned to obtain the directional spectrum for easier application.

Examination of wind-wave interaction source term in WAVEWATCH Ⅲ with tropical cyclone wind forcing

Results of drag coefficient（CD） from field observations and laboratory wave tank experiments indicate that the operational wave model can overestimate wind energy input under high wind conditions. The wind-wave interaction source term in WAVEWATCH Ⅲ has been modified to examine its behavior with tropical cyclone wind forcing. Using high resolution wind input,numerical experiments under idealized wind field and tropical cyclone Bonnie（1998） were designed to evaluate performance of the modified models. Both experiments indicate that the modified models with reduced CD significantly decrease wind energy input into the wave model and then simulate lower significant wave height（SWH） than the original model. However,the effects on spatial distribution of SWH,mean wavelength,mean wave direction,and directional wave spectra are insignificant. Due to the reduced wind energy input,the idealized experiment shows that the modified models simulate lower SWH than the original model in all four quadrants. The decrease in the front quadrants is significantly larger than that in the rear quadrants;it is larger under higher winds than lower winds. The realistic experiment on tropical cyclone Bonnie shows that the modified model with the various downward trends of CD in high winds creates a simulation that agrees best with scanning radar altimeter observations.

Dependence of sea surface drag coefficient on wind-wave parameters

The relationships between sea surface roughness z 0 and wind-wave parameters are analyzed,and spurious self-correlations are found in all of the parameterization schemes.Sea surface drag coefficient C D is fitted by four wind-wave parameters that are wave age,wave steepness,windsea Reynolds number R B and R H ,and the analyzed data are divided into laboratory,field and combined data sets respectively.Comparison and analysis of dependence of C D on wind-wave parameters show that R B can fit the C D most appropriately.Wave age and wave steepness are not suitable to fit C D with a narrow range data set.When the value of wave age has a board range,R H is not suitable to fit C D either.Three relationships between C D and R B are integrated into the bulk algorithm COARE to calculate the observational friction velocity,and the results show that the relationship between C D and R B which is fitted with field data set can describe the momentum transfer in the open ocean,under low-moderate wind speed condition,most appropriately.

Parameters in wind-wave frequency spectra and their bearings on spectrum forms and growth

The spectrum variance m0, peak frequency ω0 and peakness factor p are expressed in terms of nondimensional fetch and duration by making use of relations which are derived through comparing and analyzing existing empirical formulas for the growth of significant wave height and period. The main features of spectrum growth as specified by these parameters agree with those of the JONS-WAP experiments. For given wind speed and fetch, the high frequency parts beyond the peaks of shallow water spectra almost coincide with that of the corresponding deep water spectrum, whereas the low frequency parts differ appreciably. The method developed in this paper predicts smaller significant wave height as well as smaller wave period for shallow water spectra in contrast to the theoretical result of Kitaigorodskii ef al, in which the peak frequency, and consequently the significant wave period, remains basically unchanged for different water depths. Spectra are further reduced to a form in which only significant wave height and period are left as parameters, the peakness factor being replaced by the wave steepness through an empirical relation between them. Spectra in this form have been verified by observations.

EFFECT OF WATER DEPTH ON WIND-WAVE FREQUENCY SPECTRUM I. SPECTRAL FORM

Wen et al.'s method developed to obtain wind-wave frequency spectrum in deep water was used to derive the spectrum in finite depth water. The spectrum S(ω) (ω being angular frequency) when normalized with the zeroth moment m0 and peak frequency ω0, contains in addition to the peakness factor P= ω0S(ω0)/m0, a depth parameter ω= (2πm0)1/2/d (d being water depth), so the spectrum behavior can be studied for different wave growth stages and water depths.

EFFECT OF WATER DEPTH ON WIND-WAVE FREQUENCY SPECTRUM Ⅱ. VERIFICATION AND COMPARISON

The spectrum derived in Part 1 of the presert paper is here systematically verified with field data andcompared at some length with that obtained by multiplying the deep-water spectrum with theKitaigorodskii factor.

Effects of Wind-Wave Misalignment on a Wind Turbine Blade Mating Process:Impact Velocities,Blade Root Damages and Structural Safety Assessment

Most wind turbine blades are assembled piece-by-piece onto the hub of a monopile-type offshore wind turbine using jack-up crane vessels.Despite the stable foundation of the lifting cranes,the mating process exhibits substantial relative responses amidst blade root and hub.These relative motions are combined effects of wave-induced monopile motions and wind-induced blade root motions,which can cause impact loads at the blade root’s guide pin in the course of alignment procedure.Environmental parameters including the wind-wave misalignments play an important role for the safety of the installation tasks and govern the impact scenarios.The present study investigates the effects of wind-wave misalignments on the blade root mating process on a monopile-type offshore wind turbine.The dynamic responses including the impact velocities between root and hub in selected wind-wave misalignment conditions are investigated using multibody simulations.Furthermore,based on a finite element study,different impact-induced failure modes at the blade root for sideways and head-on impact scenarios,developed due to wind-wave misalignment conditions,are investigated.Finally,based on extreme value analyses of critical responses,safe domain for the mating task under different wind-wave misalignments is compared.The results show that although misaligned wind-wave conditions develop substantial relative motions between root and hub,aligned wind-wave conditions induce largest impact velocities and develop critical failure modes at a relatively low threshold velocity of impact.

Flume Experiment Investigation on Propagation Characteristics of Tidal Bore in A Curved Channel

Tidal bore is a special and intensive form of flow movement induced by tidal effect in estuary areas, which has complex characteristics of profile, propagation and flow velocity. Although it has been widely studied for the generation mechanism, propagation features and influencing factors, the curved channel will complicate the characteristics of tidal bore propagation, which need further investigation compared with straight channel. In this study, the flume experiments for both undular and breaking bores’ propagation in curved channel are performed to measure the freesurface elevation and flow velocity by ultrasonic sensors and ADV respectively. The propagation characteristics,including tidal bore height, cross-section surface gradient, tidal bore propagation celerity, and flow velocity are obtained for both sides of the curved channel. And three bore intensities are set for each type of tidal bores. The freesurface gradients are consistently enlarged in high-curvature section for undular and breaking bores, but have distinct behaviors in low-curvature section. The spatial distributions of tidal bore propagation celerity and flow velocity are compared between concave and convex banks. This work will provide experimental reference for engineering design of beach and seawall protection, erosion reduction and siltation promotion in estuary areas with the existence of tidal bores.

Spectral Characteristics of Wind-Waves in Laboratory

Spectral characteristics of wind-generated waves in labortaory are presented on the basis of a systematic measurement in a large-scale wind-wave channel and compared with those in the field. A marked characteristics of the measured spetra is the existence of secondary spectrum-peak. The dependence of spectral peak-frequency, peak-value and zeroth-order moment on wind speed and fetch are presented and found roughly similar to those in the field represented by the JONSWAP spectrum, regardless of the differences in coefficient. The spectral slope beta at high-frequencies are found somewhat greater than those of field wind-waves in both cases of deep and shallow waters. Except for the low-frequency part, the spectral forms measured in different wind conditions are similar and fit for the JONSWAP spectrum with gamma = 6 and beta = 5.5. Some relevant problems are discussed.

Overtopping Discharge of Wind-Waves on Simple Slope Dikes

An empirical formula for estimating the overtopping discharge of wind-waves on a smooth-impermeable-simple slope dyke is derived through model tests in this paper, it can be adopted by related design departments in the determination of the crest elevation of the dyke.

基于Flume和Flink的轨道交通智能运维数据接收解析系统

随着轨道交通智能运维技术的不断发展,越来越多的车载设备将数据通过车载无线通信设备下发至地面服务器进行存储、分析以及可视化显示。通过研究相关大数据技术,提出一种基于日志收集框架Flume和流数据处理引擎Flink的智能运维数据接收解析系统,可在高吞吐量的基础上保证稳定性与实时性。

Flow Structure and Short-Term Riverbed Evolution in Curved Flumes

River bending is the major effect responsible for bed topography and bank changes.In this study,fluid velocity(measured by a three-dimensional Doppler advanced point current meter)and bed topographical data have been collected in 40 sections of an experimental model.The whole flume was composed of an organic glass bend,upstream and downstream water tanks,two transition straight sections,a circulation pump,and a connection pipeline.Each section has been found to be characterized by a primary circulation and a small reverse circulation,with some sections even presenting three more or more circulation structures.The minimum circulation intensity has been detected in proximity to the top of the curved channel,while a region with small longitudinal velocity has been observed near the concave bank of each bend,corresponding to the flat bed formed after a short period of scouring.The maximum sediment deposition and scour depth in the presence of a uniform distribution of living flexible vegetation within 10 cm of the flume wall have been found to be smaller than those observed in the tests conducted without vegetation.

分支河流体系沉积学工作框架与流程

基于现有的研究成果和存在的问题,探讨了分支河流体系(DFS)研究中的关键科学问题、主要研究内容、研究方法和工作流程。研究结果表明:①DFS研究中最关键的3个科学问题是明确河网结构和河型演变规律、构建沉积标志和沉积模式、分析其形成和分布的控制因素。②DFS研究的主要内容包括建设形态沉积学数据库、现代沉积机理研究、分类研究、建立沉积模式、储层建模与储层预测等5个方面。③DFS研究中的关键技术包括基于遥感图像的形态数据采集、形成机理的水槽和模拟实验、河网重构、顶点位置预测与河道分汊点自动生成方法、储层建模知识库平台等。④DFS研究的基本工作流程是先建立形态沉积学数据库,搭建数据库软件平台,在此基础上选择具有代表性的DFS进行现代沉积解剖,然后综合现代沉积调查、露头解剖和模拟实验成果,形成分类体系,总结各类DFS的识别标志和沉积模式,分层次建立储层预测模型,形成沉积结构储层预测模型的建模软件平台,从而预测沉积体系中有利储层的分布。

随机风-浪联合传播数值模拟及分析

海洋风、浪往往同时传播,同步传播过程中风、浪之间具有显著的相互耦合作用。针对海洋脉动风和随机波浪同步传播的数值仿真需求,基于程序开发平台MATLAB和计算流体动力学(computational fluid dynamics,CFD)软件平台Fluent,提出了一种随机风场和随机波浪联合传播数值模拟方法,基于该数值方法构建了随机风-浪联合传播数值水槽,并对该数值水槽单独随机风、单独随机波浪以及随机风-浪联合传播的数值模拟效果进行了试算和验证分析。结果显示该水槽数值模拟脉动风速与对应理论计算风速相吻合,水槽数值模拟随机波浪与对应理论计算随机波浪相吻合,水槽风-浪联合数值模拟显示了风、浪之间显著耦合作用效应。建立的随机风-浪联合数值水槽在随机风和随机波浪同步传播的数值仿真上具备可靠性及可应用性。研究内容为海上风、浪环境要素耦合效应研究及海洋工程结构风-浪联合作用相关研究提供了平台基础。

清水冲刷下顺直河道交错边滩演变过程试验研究

为进一步认识清水冲刷下顺直河道交错边滩的演变过程,基于长江中游典型边滩形态参数,采用概化水槽试验对不同流量条件下的交错边滩纵向、横向和平面冲淤变化进行了研究。结果表明:试验工况下,纵向上,沿程呈冲刷态势,流量越大,冲深越大(流量为215 L/s的深泓平均冲深约是流量为46.71 L/s的2.1倍),且大流量下深泓纵向比降变缓;横向上,边滩侧以冲刷为主,冲刷最大的位置在滩边附近,其它部位则呈冲刷—淤积—冲刷的变化规律(如流量为215 L/s时,2#断面边滩以外部分(0,2]h平均冲深约3.5 cm、(2,12]h平均淤高约0.5 cm、(12,21]h平均冲深约0.7 cm);平面上,边滩整体下移,变得细长,淤积主要发生在边滩下游1m范围内。此外,上游异岸边滩的存在初期会促使下游边滩淤积,而后加深下游边滩的冲刷,且对边滩坡脚影响最大。

立式双曲面网板水动力性能优化研究

为研究结构型式及尺寸对立式双曲面网板水动力性能的影响机理,基于计算流体力学方法,建立立式双曲面网板三维数值模型,计算分析其水动力性能,并通过设计制作缩比模型开展动水槽试验,验证数值结果的有效性。开展曲面板弯曲度、弯曲度位置、支撑板间距等不同结构参数对立式双曲面网板水动力性能的影响规律研究,以探究最优化的结构设计方案。研究结果表明:曲面板弯曲度的同步改变和单一改变均会对立式双曲面网板的水动力性能产生不同程度的影响。如果只考虑扩张效果,曲面板A、B的弯曲度均设置为20%左右,或曲面板A弯曲度设置为15%、曲面板B弯曲度设置为25%左右,均可在一定范围内将立式双曲面网板的最大升力系数提高到最大值;但从网板综合性能考虑,后一方案可获得更高的最大升阻比。当曲面板弯曲度位置同步设置为50%时,网板升力系数可达到最大值,此时扩张效果最佳,而当曲面板弯曲度位置同步设置为20%时,最大升阻比达到峰值,网板综合性能相对更好。支撑板间距对立式双曲面网板水动力性能的影响不明显,将支撑板间距设置为420 mm左右,可在小冲角范围内提升其最大升阻比。

不同等容粒径的泥沙暴露规律研究

采用概化模型试验对等容粒径的泥沙暴露规律进行初步研究,获得了500组试验数据,试验结果表明:当配比等容粒径的两组均匀沙粒径相差较大,且等容后泥沙粒径与较细均匀沙粒径接近时,床面不同高程的细沙暴露个数远多于粗沙暴露个数,且细沙暴露个数增加幅度比较均匀,粗沙暴露个数增加幅度迅速减小,其等容泥沙在床面表层的暴露个数明显多于表层以下;当配比等容粒径的两组均匀沙粒径相差较大,且等容后泥沙粒径与较粗均匀沙的粒径接近时,虽然细沙暴露的个数可能比粗沙少,但其暴露颗粒数的增加幅度比粗沙大,其等容后泥沙在床面表层的暴露个数多于表层以下;当配比等容粒径的两组均匀沙的粒径相差较小,且等容后泥沙粒径与两组沙的粒径均接近时,细沙暴露颗粒数的增加幅度与粗沙相当,其等容后泥沙在床面表层的暴露个数与表层以下相当。以上试验结果与天然卵石河床表层泥沙等容后的暴露个数多于深层的普遍现象相吻合。

台阶式沉井等效墩宽计算方法探究

桥梁工程中存在形状各异的桥墩,在研究不同截面桥墩的局部冲刷特性时,桥墩尺寸的定量描述非常重要。以台阶式沉井结构为研究对象,梳理并分析了国内外相关等效桥墩宽度计算方法,发现各类公式本质上为计算不同条件下的桥墩平均阻水宽度。开展了台阶式沉井局部冲刷试验研究,基于试验数据对比分析了各类等效墩宽计算方法的计算结果,发现Melville和Raudkivi的等效墩宽计算公式能够较好地估算考虑动床条件下台阶式沉井的平均阻水宽度;进一步收集了国内外193组台阶式沉井类结构的局部冲刷试验数据,数据集统计分析结果显示Melville和Randkivi的等效墩宽计算公式能够较为准确且保守地量化大多数台阶式沉井类结构的截面非均匀性;最后基于数据集冲深墩宽比统计结果对该公式近似方法的合理性进行了讨论。