ON LONG-WAVES BREAKING Ⅱ.IN A HALF INFINITE CHANNEL WITH BOTTOM SLOPE

The propagation of long-waves, such as tidal waves from the coastal oceam into shallow estuarine waters,often produces asymmetries of veolcity and water level in time series resulting in long-wave breaking.Tian (1994) studied the mechanism of long-wave breaking in an infinite channel with constant depth,considering nth power bottom friction. This study is for the case of a half infinite channel with bottomslope, taking linear bottom friction into account. The wave breaking time and wave breaking location areestimated and the criteria for long-wave breaking in this particular case are obtained. The results obtainedcan also be e asily applied to the case considering wind stress.

EXPERIMENTAL STUDY OF DAM-BREAK FLOW IN CASCADE RESERVOIRS WITH STEEP BOTTOM SLOPE

Dam break can cause a significant disaster in the downstream, especially, in a valley with cascade reservoirs, which would aggravate the disaster extent. The experimental studies of the dam-break flow of cascade reservoirs are few and far between at the present, Most of related studies concern the failure of a single dam.. This article presents an experimental study of the characteristics of an instantly filled dam-break flow of cascade reservoirs in a rectangular glass flume with a steep bottom slope. A new method was used to simulate the sudden collapse of the dam. A series of sensors for automatic water-levels were deployed to record the rapid water depth fluctuation. The experimental results show that, the ratio of the initial water depth of the downstream reservoir to that of the upstream reservoir would greatly affect the flood peak water depth in the downstream reservoir area and in the stream channel behind the downstream dam, while the influence of the dam spacing is insignificant. In addition, the comparison between the single reservoir and the cascade reservoirs shows some difference in the dam-break flow pattern and the stage hydrograph at the corresponding gauging points.

Inverse problem of bottom slope design for aerator devices

Air entrainment is an effective approach to protect release works from cavitation damage. The traditional method of aerator device designs is that, for given flow conditions, the geometries of the aerator device are designed and then the effec（s are experimentally tested for cavitation damage control. The present paper proposes an inverse problem method of determining the bottom slopes in front of and behind an aerator if the requirements of air entrainment, flow conditions and some of aerator geometric parameters are given. An RBF neural network model is developed and the relevant bottom slopes are calculated in different conditions of flow and geometry on the basis of the data of 19 aerator devices from different discharge tunnels with safe operation. The case study shows that the methodology provides an effective way to design aerator devices under given target conditions.

Mild-slope equation for water waves propagating over non-uniform currents and uneven bottoms

A time-dependent mild-slope equation for the extension of the classic mild-slope equation of Berkhoff is developed for the interactions of large ambient currents and waves propagating over an uneven bottom, using a Hamiltonian formulation for irrotational motions. The bottom topography consists of two components the slowly varying component which satisfies the mild-slope approximation, and the fast varying component with wavelengths on the order of the surface wavelength but amplitudes which scale as a small parameter describing the mild-slope condition. The theory is more widely applicable and contains as special cases the following famous mild-slope type equations: the classical mild-Slope equation, Kirby's extended mild-slope equation with current, and Dingemans's mild-slope equation for rippled bed. Finally, good agreement between the classic experimental data concerning Bragg reflection and the present numerical results is observed.

砂箱模型中底板倾斜角度对承压含水层海水入侵的影响研究

滨海地区普遍存在向海倾斜的承压含水层,但含水层底板的倾斜角度对海水入侵的影响程度仍不清楚。本研究利用室内砂箱试验,并应用显色示踪技术,综合分析不同底板倾斜角度承压含水层海水入侵的动态过程,探究海平面高度、地下淡水流量和含水层岩性对向海倾斜的承压含水层海水入侵的影响。研究发现,底板倾斜角度对承压含水层的海水入侵有显著影响。在咸淡水界面稳定时,底板倾斜角度与咸水楔长度之间存在指数函数关系,咸水楔长度随倾斜角度的增加而减少。在定水头条件下,底板倾斜角度的增加导致地下淡水排泄量减少。在定流量边界条件下,尽管底板倾斜角度的变化不影响地下淡水排泄量,但咸水楔面积却随倾斜角度的增加而减小。当含水层岩性从粗砂变为细砂时,由于其渗透系数降低,咸水楔长度减少,尤其是在定流量条件下,其缩短更为显著。研究表明,对于向海倾斜的承压含水层,底板倾斜角度较小时,海平面升高和地下淡水流量减少对海水入侵的影响更加显著。

Tide simulation using the mild-slope equation with Coriolis force and bottom friction

Since the mild-slope equation was derived by Berkhoff （1972）,the researchers considered various mechanism to simplify and improve the equation,which has been widely used for coastal wave field calculation.Recently,some scholars applied the mild-slope equation in simulating the tidal motion,which proves that the equation is capable to calculate the tide in actual terrain.But in their studies,they made a lot of simplifications,and did not consider the effects of Coriolis force and bottom friction on tidal wave.In this paper,the first-order linear mild-slope equations are deduced from Kirby mild-slope equation including wave and current interaction.Then,referring to the method of wave equations’ modification,the Coriolis force and bottom friction term are considered,and the effects of which have been performed with the radial sand ridges topography.Finally,the results show that the modified mild-slope equation can be used to simulate tidal motion,and the calculations agree well with the measurements,thus the applicability and validity of the mild-slope equation on tidal simulation are further proved.

考虑底坡影响的U形渠道量水槽流量公式研究

渠道底坡是影响输水能力的重要因素,但量水槽流量公式往往忽略渠道底坡。为了探究渠道底坡对流量公式的影响,以三角形量水槽为研究对象,在6种底坡的U形渠道上开展田间试验。应用能量方程式推求了流量的理论公式,基于量纲分析法分别建立不包含和包含渠道底坡的流量公式,探讨渠道底坡影响流量公式的范围。流量的理论公式表明渠道底坡是影响量水槽流量公式的因素之一。与不包含渠道底坡的流量公式相比,包含渠道底坡的流量公式测流精度显著提高,平均相对误差从2.92%降低至1.65%,最大相对误差从12.22%减小至7.37%,相对误差绝对值小于5%的比例从80.94%提升至95.89%。渠道底坡影响三角形量水槽流量公式的范围界定为1100~1/1200,当渠道底坡小于11200时可以忽略。量水槽流量公式应考虑渠道底坡的影响。

泄洪洞变底坡掺气坎掺气特性研究

针对高水头小底坡泄洪洞采用常规挑(跌)坎存在的空腔回水现象严重、稳定性差、水头变幅适应性差等问题,通过模型试验的方法,结合如美水电站放空洞,对“挑坎+平缓坡+陡坡”的变底坡形式掺气坎进行系统研究,揭示了变底坡掺气坎各部位(挑(跌)坎、平缓坡段以及陡坡段)对掺气空腔的影响机理。结果表明:在水位大幅变化过程中,变底坡掺气坎对应的空腔充满回水的临界水头值为73.5 m,比常规掺气坎提高了29.4 m。研究结果可为高水头小底坡泄洪洞的掺气设施布置提供参考。

基于底摩擦试验的缓倾边坡滑移拉裂破坏过程研究

顺层边坡一旦失稳,具有规模大、危害性强的特点。针对缓倾顺层边坡滑移—拉裂型破坏,采用底摩擦物理模型试验,结合PIV粒子成像技术以及MATLAB后处理方法,分析了缓倾顺层边坡滑移—拉裂型破坏过程中的宏微观特征。研究结果表明:PIV和MATLAB的后处理所得结果与宏观观察结果相吻合,计算结果能够反映出不同边坡结构下的位移矢量特征,并对变形特征进行分区;滑移—拉裂式破坏过程分为三个阶段,裂缝产生阶段、裂缝扩展阶段和破坏阶段。裂缝产生阶段边坡后缘首先产生竖向张拉裂隙,裂缝扩展阶段裂缝向深部扩展,破坏阶段边坡上部岩体沿层面中的软弱结构面滑动。对缓倾边坡滑移拉裂破坏过程的研究成果,能够为类似边坡的滑动机制分析提供一定参考。

考虑地下水影响的基坑边坡土钉墙支护效果研究

【目的】为了验证基坑边坡支护方案的合理性,保证施工安全,以晋江某基坑边坡为例,研究分析其边坡支护效果。【方法】建立基坑边坡三维网格模型和地下水位模型,采用有限差分法计算地下水影响情况下,该基坑边坡未支护和土钉墙支护时天然工况和暴雨工况下的稳定性系数和位移量分布。【结果】计算结果表明,土钉墙支护下该边坡在天然工况和暴雨工况下的稳定性系数分别为2.85和2.60,与未支护情况下的2.35和1.51相比有了大幅提升,位移量也明显减少。【结论】土钉墙支护明显提升了边坡的整体稳定性,并且改变了基坑边坡的位移分布模式,降低了边坡的坍塌风险。研究成果对类似的基坑边坡稳定性分析和支护方案设计和验证具有一定的参考价值。

轨底坡对轮轨接触行为及动力响应的影响的分析

轨底坡的大小直接影响轮轨接触点的位置和轮轨力的作用方向及大小,适当地调整内外轨的轨底坡可改善轮轨之间的接触状况,使轮轨接触点发生变化而有利于轮对通过曲线。基于Simpack仿真软件,建立车辆系统动力学模型,设计不同曲线通过条件,分析了内外轨轨底坡相同和不同的情况下对轮轨接触行为及动力响应的影响。

基于DEM的露天煤矿坡顶线与坡底线的提取研究

以黑岱沟露天煤矿0.5 m分辨率DEM为例,运用ArcGIS软件,提出一种基于高分辨率DEM的露天煤矿坡顶线与坡底线提取方法。通过计算DEM中坡顶和坡底的平面曲率,利用矿山DEM在坡顶、坡底的平面曲率与坡面、平盘的平面曲率存在差别,从而分离坡顶线和坡底线。该方法操作简便,精度较高,为我国露天煤矿地理信息生产提供了技术支持。

High-Order Models of Nonlinear and Dispersive Wave in Water of Varying Depth with Arbitrary Sloping Bottom

High-order models with a dissipative term for nonlinear and dispersive wave in water of varying depth with an arbitrary sloping bottom are presented in this article. First, the formal derivations to any high order of mu(= h/lambda, depth to deep-water wave length ratio) and epsilon(= a/h, wave amplitude to depth ratio) for velocity potential, particle velocity vector, pressure and the Boussinesq-type equations for surface elevation eta and horizontal velocity vector (U) over right arrow at any given level in water are given. Then, the exact explicit expressions to the fourth order of mu are derived. Finally, the linear solutions of eta, (U) over right arrow, C (phase-celerity) and C-g (group velocity) for a constant water depth are obtained. Compared with the Airy theory, excellent results can be found even for a water depth as large as the wave legnth. The present high-order models are applicable to nonlinear regular and irregular waves in water of any varying depth (from shallow to deep) and bottom slope (from mild to steep).

A General Linear Wave Theory for Water Waves Propagating over Uneven Porous Bottoms

Starting from the widespread phenomena of porous bottoms in the near shore region, considering fully the diversity of bottom topography and wave number variation, and including the effect of evanescent modes, a general linear wave theory for water waves propagating over uneven porous bottoms in the near shore region is established by use of Green's second identity. This theory can be reduced to a number of the most typical mild-slope equations currently in use and provide a reliable research basis for follow-up development of nonlinear water wave theory involving porous bottoms.

An Extended Mild-Slope Equation

On the assumption that the vortex and the vertical velocity component of the current are small, a mild-slope equation for wave propagation on non-uniform flows is deduced from the basic hydrodynamic equations, with the terms of (V(h)h)(2) and V(h)(2)h included in the equation. The terms of bottom friction, wind energy input and wave nonlinearity are also introduced into the equation. The wind energy input functions for wind waves and swells are separately considered by adopting Wen's (1989) empirical formula for wind waves and Snyder's observation results for swells. Thus, an extended mild-slope equation is obtained, in which the effects of refraction, diffraction, reflection, current, bottom friction, wind energy input and wave nonlinearity are considered synthetically.

EFFECTS OF SLOPING BOTTOM ON THE DEEPCROSS-EQUATORIAL BOUNDARY CURRENT

This paper reports study focusing on the effects of sloping bottom on the deep cross-equatorial boundary current, and discusses model and laboratory experiment results showing that the southward that the southward intrusion distance and flow speed of the western boundary current depend on the bottom slope variation rate,the difference between and and are the current thickness at eastward edge and westward edge, respectively), and the net mass transport.

An extended time-dependent numerical model of the mild-slope equation with weakly nonlinear amplitude dispersion

In the present paper, by introducing the effective wave elevation, we transform the extended elliptic mild-slope equation with bottom friction, wave breaking and steep or rapidly varying bottom topography to the simplest time-dependent hyperbolic equation. Based on this equation and the empirical nonlinear amplitude dispersion relation proposed by Li et al. （2003）, the numerical scheme is established. Error analysis by Taylor expansion method shows that the numerical stability of the present model succeeds the merits in Song et al. （2007）＇s model because of the introduced dissipation terms. For the purpose of verifying its performance on wave nonlinearity, rapidly varying topography and wave breaking, the present model is applied to study： （1） wave refraction and diffraction over a submerged elliptic shoal on a slope （Berkhoff et al., 1982）; （2） Bragg reflection of monochromatic waves from the sinusoidal ripples （Davies and Heathershaw, 1985）; （3） wave transformation near a shore attached breakwater （Watanabe and Maruyama, 1986）. Comparisons of the numerical solutions with the experimental or theoretical ones or with those of other models （REF/DIF model and FUNWAVE model） show good results, which indicate that the present model is capable of giving favorably predictions of wave refraction, diffraction, reflection, shoaling, bottom friction, breaking energy dissipation and weak nonlinearity in the near shore zone.

坡底饱和型黄土滑坡离心模拟试验

黄土极具结构性和水敏性,人类活动及自然因素作用下的水致地质灾害备受关注,其中坡底饱和型黄土边坡极易失稳破坏并造成危害。基于离心模拟手段,采用未扰动原状黄土制作模型,自主设计模型后缘渗水装置,模拟坡底饱和型黄土边坡的失稳过程;通过模型顶部视频监测、侧面粒子图像测速(particle image velocimetry,简称PIV)分析、底部孔隙水压力及土压的联合监测手段,分析其失稳破坏特征,并结合现场滑坡演化特征进行验证对比。主要得出以下结论:加速度达80g时,模型底部饱和,前缘出现滑移、后缘发生塌陷及内部湿陷,呈多元破坏形式;模型侧面位移表现为滑移前的表层张拉变形、底部湿陷变形及后缘塌陷前的顶部沉降变形;模型底部高孔隙水压力区分布于大面积滑移和塌陷区域下方,表征了坡底高水位对破坏的影响及底部水渗流的不均匀性;模型滑移破坏与现场滑坡具相同演化进程:坡底饱和-张拉裂缝-后退式小型滑移-水位抬升-后退式大型滑移。研究成果可为原状黄土的模型试验研究思路及原位滑坡的多元破坏机制研究提供借鉴。

科尔沁沙地流动沙丘优势物种的点格局分析

植被恢复与重建在保护水土资源、防止生态退化和荒漠化扩大等方面发挥着重要作用,成为防治荒漠化的主要措施和方法。一定尺度内优势物种的格局反映了植被恢复的过程。通过在科尔沁沙地流动沙丘迎风坡底部建立了20 m×20 m样方,调查了流动沙丘3种优势物种的位置和高度信息,采用点格局分析的方法,对优势物种格局、过程与尺度的关系进行分析。经研究发现:沙蓬在该样方内,r<5 cm尺度上均匀分布,5 cm<r<50 cm尺度上表现为均匀分布与聚集分布交替出现的格局;狗尾草和差巴嘎蒿在0<r<50 cm尺度上表现为随机分布,但狗尾草在r=10 cm尺度上聚集分布和r=18 cm尺度上均匀分布。在r<5 cm尺度内,沙蓬和狗尾草表现为负相关,随着尺度的增大,出现正相关,但整体尺度以正相关为主且随着尺度增加相关性减弱。同质性条件下种子扩散模型不能解释沙蓬与狗尾草的空间格局,由于流动沙丘异质性较强,推测环境异质性是导致优势物种格局的主要原因。

山城道路路基高边坡防护中锚杆框架梁技术应用研究

以忠县银山安置点连接道一路项目为例,对锚杆框架梁技术在路基高边坡防护中的应用展开论述,该项目路基高边坡分三线:即A线K1+260~460,边坡最大高度为38.8 m;B线K0+400~K0+460,边坡最大高度为37.46 mm;C线K0+200~K0+260,边坡最大高度为40.7 m。均按1∶1.25放坡设置锚杆框架,因为边坡高度大且位于山区,边坡开挖及支护难度大,故通过开挖一级防护一级、工厂预制锚杆、锚孔孔底返浆法、现浇框架等技术措施进行锚杆框架梁施工,最终取得了预期效果。