江苏东台潮滩沙纹形态特征及其演变过程的数值模拟研究

主要研究了江苏东台潮滩下部沙纹形态特征及其主要影响因素。基于潮滩下部水深、流速、沙纹形态的观测及表层沉积物的粒度数据,分析了研究区沙纹形态特征及其与潮汐水动力条件、沉积物粒度间的关系。并建立了地貌动力学模型,模拟了不同沉积物粒度和不同水深变化条件下沙纹尺度(波长、波高)的变化和沙纹的演化过程。研究结果表明:潮滩表面主要形成尺度较小的不对称沙纹,其形态的主要影响因素是流速和沉积物粒度,在一定范围内,流速越大,沉积物颗粒越细,沙纹尺度越大。在一个潮周期内沙纹形态经历以下过程:平底→不对称性指示涨潮方向的沙纹→平底→不对称性指示落潮流方向的沙纹。     

明渠沙纹床面湍流结构实验研究

沙纹的形成会显著地影响床面附近的湍流结构。论文通过水槽实验,模拟了天然河流中沙纹的形成,并针对最终形成的稳定沙纹形态,利用声学Doppler测速仪采集了沙纹床面不同位置处的高频流速过程数据,继而对脉动强度、雷诺应力、湍流动能及自相关函数等湍流特征量进行了计算,并分析了沙纹床面湍流结构和特点,为进一步的理论和数值研究提供了有价值的参考数据和依据。     

风成沙纹形成过程模拟与形态分析

通过简单的跃移模型、蠕移模型和稳定模型对风成沙纹的形成过程进行了二维数值模拟研究。模拟结果表明沙纹波长和波高与床面蠕移沙粒的移动距离成正比，沙纹的波高随着床面的冲击密度的增加而增大，沙纹的稳定形态与蠕移距离大小有关。     

风成沙纹的波高控制机理

采用数值模拟的方法研究了风成沙纹的波高控制机理，并与风洞实验测量结果进行了对比。在数值模拟的蠕移模型中考虑了空气动力控制因子对沙粒蠕移距离的影响。结果表明，随着空气动力控制因子数值的增大，沙纹波高和波长都先增大后减小；在特定的空气动力控制因子数值条件下，数值模拟结果可与风洞实验结果相比较，其吻合程度较好。     

扰动对明渠湍流结构及床面稳定性影响的实验研究

本文通过在水槽实验中采集的流速过程数据,定量地研究了沙纹阶段明渠水流在不同形式扰动作用下的湍流结构,以及湍流结构对泥沙运动和床面演化的影响。实验发现,扰动附近水流紊动大大增强,扰动促使局部泥沙在断面平均流速低于平床起动流速的情况下起动,并促使床面失稳形成沙纹。另外,不同的扰动形式、位置及尺度对泥沙运动以及床面稳定性的影响各不相同,实验中进行了深入的比较和分析。     

破碎波作用下床面形态研究及泥沙受力分析

破碎带水体强烈紊动对床面形态影响甚大,基于波浪水槽试验对沙质斜坡上破碎带床面形态以及泥沙受力进行研究。分析床面形态发现,同一断面处沙纹沙坝的形态与波浪形态基本一致,波高和周期决定沙纹沙坝的尺寸,波高越大,沙纹沙坝越高;周期越长,沙纹沙坝越长。通过对波浪破碎区的近底流速及砂床内孔隙水压力进行测量,将计算得到的表层上举力与超静孔隙水压力进行对比分析,发现其上举力与床面超静孔隙水压力大小相同。同时观察波浪破碎带床面高程,进一步研究上举力与超静孔隙水压力与床面高程的关系,发现表层上举力随着床面高程增加而变大,随着床面高程的降低而减小,而超静孔隙水压力与床面高程之间的关系则相反。     

WAVE BOTTOM LAYERS DYNAMIC WITH SUSPENDED SEDIMENT OVER VORTEX RIPPLES

Vortex ripple is widely formed in the coastal region, and the dynamic of vortex is quite important because it is responsible for sediment transport. The flow structure around the vortex ripples can be modeled as 2D flow due to the geometry of the flow boundaries. In this paper, 2D Large-Ed-dy-Simulation (LES) method was used to predict the flow structure and the dynamic of vortex in the bottom layers under the action of the wave, the numerical simulation results show a completely process of vortex formation, evolvement and disappearance. Based on the study of flow structure, the suspended sediment transport was modeled in present paper. The simulated sediment concentrations were compared to measurements from the literature. The agreement between the time averaged simulated concentration profiles and measurements is satisfactory. For a high setting velocity, the suspended sediment is confined to the vicinity of the bed, and it is dominated by the local bottom shear stress. For a small setting velocity, the suspension is more dominated by the characteristic of vortex. There are two suspended sediment transport peaks observed in the cross-section at the trough and crest in the half period, the second peak is due to the separation bubble taking the sediment.     

沙纹床面涡量特性实验研究

沙纹的形成与水流流态密切相关,但对于其相互关系至今尚无确定的结论。采用PIV（Particle Image Velocimetry）测量设备对沙纹床面水流特性及涡量特性进行了实验研究。通过对平床与沙纹床面涡量场的比较,得到了沙纹床面的涡量分布区域。结果表明,涡量较大值主要集中在沙纹的背水坡面与迎水坡带,之外区域涡量值约为零。结论对研究沙纹的形成有积极意义。      

利用河流平衡理论检验推移质输沙函数的应用性

推移质输沙函数多根据试验资料建立,在实际应用中往往会给出相去甚远的预测,对河流平衡形态影响显著。本研究利用河流平衡理论检验推移质输移通式Φ=cb(τ0*-τ*c)β中各参数对河道平衡形态的影响,式中Φ为无量纲推移质输沙强度,τ0*为无量纲水流平均剪切应力,cb、τ*c和β为输沙参数,分别代表输沙系数、无量纲水流临界剪切力和输沙指数。引入河道过水断面的宽度与平均水深的比值作为表征断面形态的无量纲参数,基于变分原理的图形分析结果表明,输沙通式中指数β的选取是影响平衡河道形态的重要因素。结合长江中游监利河段河道形态实际观测数据,对比分析已有推移质输沙函数对河道平衡形态的定量影响,结果表明β=5/3时河流平衡理论具有很好的实际应用性。     

Ripple dynamics over various microtopographical roughness elements and their implications for river management

Specific problems in connection with the sediment regime have arisen in the granite and gneiss area in the northern part of Austria due to the increased sediment supply of coarse sand and fine gravel as a product of rock weathering. One of the physical characteristics of these sediments is their high mobility in form of ripple bedforms along the surface. In these rivers, the microtopographical structures of the bed surface are hydraulically active, especially in the initial stages when ripples have not overtopped the largest elements of the bed's roughness elements. There is a lack of detailed studies of the impacts of these microtopographical structures on ripple dynamics. Thus, the aim of the present study was to investigate the impact of various microtopographic roughness elements on ripple movement. This study was performed using a 1:1‐scaled physical laboratory experiment. The results showed, in all repetitions of the experiment with variable grain sizes, that the higher the microtopographical variability of the river substrate and turbulence was, the higher the measured transport velocities of the ripples were. The expected hidden impacts on sediment transport were not documented. Important implications for sediment management were discussed, as river sections with high accumulation rates of coarse sand and fine gravel are prone to additional degradation as downstream transport decreases over smooth ripple–dune morphologies. Additionally, structural elements such as exposed rocks may increase the downstream transport due to the increased variability in turbulence.     

A STUDY OF OSCILLATING FLOWS OVER PROPAGATING RIPPLES:PART Ⅱ. VORTICITY DYNAMICS

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＡｈｏｒｉｚｏｎｔａｌｂａｃｋ ａｎｄ ｆｏｒｔｈｍｏｔｉｏｎｐｒｏｄｕｃｅｄｎｅａｒａｓａｎｄｂｅｄｂｙ ｐｒｏｇｒｅｓｓｉｖｅｇｒａｖｉｔｙｗａｖｅｓｐｒｏｐａｇａｔｉｏｎｉｎｓｈａｌｌｏｗｗａｔｅｒｕｓｕａｌｌｙｇｉｖｅｓｒｉｓｅｔｏｎｅａｒｌｙｓｙｍｍｅｔｒｉｃａｌｂｅｄ ｆｏｒｍｓｃｏｍ ｍｏｎｌｙｋｎｏｗｎａｓｒｉｐｐｌｅｓ .Ｏｓｃｉｌｌａｔｉｎｇｆｌｏｗｓｏｖｅｒｐｅｒｉｏｄｉｃｒｉｐｐｌｅｓａｒｅｏｆｐｒａｃｔｉｃａｌａｓｗｅｌｌａｓｓｃｉ ｅｎｔｉｆｉｃ…     

A STUDY OF OSCILLATING FLOWS OVER PROPAGATING RIPPLES:PART I. STEADY STREAMING

1.　ＩＮＴＲＯＤＵＣＴＩＯＮＯｓｃｉｌｌａｔｉｎｇｆｌｏｗｓｏｖｅｒｐｅｒｉｏｄｉｃｒｉｐｐｌｅｓａｒｅｏｆｐｒａｃｔｉｃａｌａｓｗｅｌｌａｓｓｃｉｅｎｔｉｆｉｃｉｎｔｅｒｅｓｔｂｅｃａｕｓｅｏｆｔｈｅｉｒｒｅｌｅｖａｎｃｅｔｏｂｅａｃｈｐｒｏｃｅｓ...     

有压出流条件下突扩突跌掺气设施空腔长度研究

掺气减蚀措施可以减免高速泄水建筑物的空蚀破坏。采用突扩突跌掺气设施,会同时形成底空腔及侧空腔,获得较好的掺气减蚀效果,对建筑物底板及侧墙均起到良好的保护作用,在有压出流条件下,通过对突扩突跌掺气设施水工模型进行不同突扩宽度、跌坎高度、下游坡度、来流条件下的模型试验,初步确定了跌坎高度、突扩宽度、下游坡度对空腔长度的作用方式。结果表明,有压出流条件下,在其他条件相同时,底空腔长度与突扩宽度、跌坎高度均呈正相关关系,与下游坡度呈反相关关系;侧空腔长度与突扩宽度呈正相关关系,与跌坎高度及下游坡度均成反相关关系。最后通过量纲分析拟合出有压出流条件下,相对侧空腔长度与综合水力参数X的关系,得到在X<8时计算侧空腔长度的经验公式。     

NUMERICAL STUDY FOR EVOLUTION OF COHERENT VORTEX IN UNIDIRECTIONAL OSCILLATORY BOUNDARY LAYER OVER SAND RIPPLES

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＳｈｅａｒｆｌｏｗｓｐａｓｔｗａｖｙ ｌｉｋｅｂｏｕｎｄａｒｉｅｓｈａｖｅａｔ ｔｒａｃｔｅｄｃｏｎｓｉｄｅｒａｂｌｅａｔｔｅｎｔｉｏｎｉｎｒｅｃｅｎｔｙｅａｒｓｂｅ ｃａｕｓｅｏｆｔｈｅｃｅｎｔｒａｌｒｏｌｅｔｈｅｙ ｐｌａｙｉｎｓｅｖｅｒａｌｉｎ ｔｒｉｇｕｉｎｇ ｐｈｅｎｏｍｅｎａ ,ｓｕｃｈａｓｔｈｅ ｇｅｎｅｒａｔｉｏｎｏｆｗｉｎｄｗａｖｅｓｏｎｗａｔｅｒ ,ｔｈｅｆｏｒｍａｔｉｏｎｏｆｓｅｄｉｍｅｎｔａ ｒｙｒｉｐｐｌｅｓａｎｄｄｕｎｅｓｉｎｄｅｓｅｒｔｓａｎｄｒｉ…     

泥石流龙头的形成及特征研究

泥石流龙头的高度反映了泥石流的规模,是防治工程的重要参数之一。陡峻的地形、大量松散固体物质、丰富的水源构成了泥石流发生的三大要素,同时也是影响泥石流龙头高度的重要因素。通过采用均质沙及宽级配沙进行水槽实验,探究泥石流运动过程中龙头高度与沟道物质级配、流量、坡度之间的关系,提出泥石流龙头高度随流量、坡度、平均粒径、细沙含量的增加,呈先上升后下降的趋势。利用回归分析方法,采用水流功率的概念,建立了泥石流龙头高度计算模型,并采用其他科学家的试验数据进行了验证,可为预测不同条件下泥石流规模提供科学依据。     

Transient peristaltic diffusion of nanofluids: A model of micropumps in medical engineering

Peristaltic micro-pumps offer an excellent mechanism for delivery of a variety of medicines including drugs, corneal solutions etc. The surge in deployment of nanoparticles in medicine has provided new potential for such pumps. In light of this we investigate the time-dependent peristaltic flow of nanofluids with diffusive effects through a finite non-uniform channel, this geometry being more representative of real micro-pumps. Creeping flow is taken into account(inertial forces are small compared with viscous forces) i.e., Reynolds number is low(Re 1) and wavelength is also taken to be very large. The Buongiorno formulation for nanofluids is employed with an Oberbeck-Boussinesq approximation. Closed-form solutions are developed for the non-dimensional governing equations subject to physically realistic boundary conditions. Mathematica symbolic software is employed to evaluate the evolution of nanoparticle fraction, temperature, axial velocity, transverse velocity and pressure difference distribution along the length of the pump channel with variation in thermal Grashof number, basic-density(species i.e., mass) Grashof number, Brownian motion parameter and thermophoresis parameter.     

EXPERIMENTAL STUDY ON BED FORMS AND FLOW RESISTANCE OF LIGHT－WEIGHT MATERIALS WITH DIFFERENT DENSITIES

ＥＸＰＥＲＩＭＥＮＴＡＬＳＴＵＤＹＯＮＢＥＤＦＯＲＭＳＡＮＤＦＬＯＷＲＥＳＩＳＴＡＮＣＥＯＦＬＩＧＨＴ－ＷＥＩＧＨＴＭＡＴＥＲＩＡＬＳＷＩＴＨＤＩＦＦＥＲＥＮＴＤＥＮＳＩＴＩＥＳ￥ＤｕａｎＧｕｏ－ｈｏｎｇ；ＷａｎｇＧｕｉ－ｘｉａｎ（Ｄｅｐｔ．ｏｆＨｙ...     

沙纹床面上波流共同作用的数值模拟

海滨地区广泛存在涡动沙纹,它很大程度上决定着波浪衰减和泥沙运动。本文建立了描述波浪、水流共同作用下底层流动特性的立面二维数值模型。模型成功模拟了波浪、水流共同作用下底层分离涡随时间、空间变化的动力特性,文中还进一步对波浪、水流不同对比情况下的涡动力特性及分离涡尺度和紊动特性进行了讨论。     

从大型实验室波浪泥沙输运实验得到的启示

展示了一些用于测量波浪输沙过程的基本特征的大型实验的关键结果。这些实验是在Delft水力研究所的大型振荡水槽中进行,还有一些是在阿伯丁振荡流隧道中进行,这一系列实验覆盖了各种水流与泥沙条件。在紊流区和层流区的结果都在这里进行介绍,揭示出在每个实验中的一些重要机理。论述的重点是在波浪输沙中的内部不稳定性。     

DISSIPATION OF WAVE ENERGY ON VERY MILD SLOPE

1.　INTRODUCTIONOffshoreareasarewherepeoplefrequentlyengagevariouskindsofhumanactivities,forexamples,portbuilding.seawallconstruction,installationofoildrillingplatformandseashorepowerstation,etc.Whenstructuresplacedinshallowwateraredesigned,thedesignwaveheightalwaystakesthecriticalwaveheight-breakingwaveheight.ThecriticalwaveheightadoptedinChineseCodeisdeterminedbyGoda′smethod,whichiswidelyusedinmanycountries.Thismethodisbasedonthestudyofregularwavesonbottomslopei≥1/50.Themaximumwavehe…