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通过动床试验,结合黄河下游细沙河床研究了大尺度缩窄河道时非恒定流桥墩的局部冲刷. 研究结果表明,非恒定流洪水过程中的桥墩局部冲刷与恒定流的情况相比,两者之间存在差 异而且有必然的联系. 通过影响因素和试验数据的分析,建立了两者之间的关系和相应的非 恒定流桥墩局部冲刷深度计算方法. 经与原型非恒定流洪水实测资料对比,结果合理且比较 符合实际情况.     

河渠冰水力学研究进展和趋势

从河渠冰水力学基本理论7个方面(水热循环机理、流冰形成输移扩散机理、锚冰岸冰形成发展释放、封河冰塞机理、开河冰坝机理、水工建筑物冰塞机理、水冰沙互馈作用机理)、河渠冰情预测预报及过程模拟、河冰关键参数观测技术与装备等层面介绍了国内外的河冰水力学研究的主要进展和动向,剖析了当前科学研究和工程应用研究中存在的难题,并从理论和技术角度阐明了相关原因并指出方向. 总结提出了河渠冰水力学未来需要重点开展的研究,如在河渠冰水力学基本理论拓展方面,应进一步完善现有河冰理论框架,尤其是河流锚冰生长和释放过程、卡冰和初始冰盖形成的热力-动力-地形特征影响的定量化机制、复式断面冰盖下水力特性和河冰运动与岸滩侵蚀过程中的水冰沙耦合作用机理等;在变化环境下的冰情预报方面,应多尺度结合,进一步探索中长期气候变化或短期极端情况对北方河流冰情的影响,尤其是研发不同尺度区域、长短期结合的水文-水力预测预报模型技术,对于科学研判河流冰情未来情势具有指导意义;在冰凌灾害全过程监测与防控技术装备方面,应进一步研发能反映冰塞内部渗流、冰塞内摩擦力以及冰塞冰坝内部反映其演化过程的关键监测传感器和装备,弥补现有观测的不足;在冰湖溃决模拟等方面,应加大观测力度并多学科交叉,注重开展低温条件下冰湖溃口演化的机理试验探索,尤其是研究水流冲蚀溃口冰碛土下切和坍塌过程等.      

一种新的往复流试验平台及其泥沙冲刷试验研究

本文提出一种可以模拟潮流运动的自动化控制水槽。该水槽可以时控制往复流两端的水位,实现流的往复运动,并可以按计算机要求实现水位的稳定或渐变。本文同时利用该水槽进行了圆柱开桥墩周围的测试数据、照片为基础、分析了不同水流条件下圆柱形桥墩周围的床面冲刷情况。试验发现在桥墩附近,水流的旋滚运动及旋涡系是造成床面冲刷的主要原因,另外对于往复流情况,桥墩附近床面受到的冲刷比固定水位冲刷时要严重,也更为复杂 。     

流体喷射条件下金属材料冲刷腐蚀的研究进展

综述了流体喷射条件下冲刷腐蚀试验装置、冲刷腐蚀机理的研究进展,总结和分析了流速、固相颗粒、攻角等因素对冲刷腐蚀的影响,最后指出了流体喷射下金属材料冲刷腐蚀研究中存在的问题,并展望了流体喷射条件下金属材料冲刷腐蚀的研究方向.     

传递矩阵法分析约束悬臂裂纹管道失稳临界流速

研究了自由端受线性弹簧支承和扭转弹簧约束的悬臂输流管道在含有圆周非贯穿裂纹时的失稳临界流速;根据梁模型模态函数的一般表达式和裂纹处的关联式以及传递矩阵法推导出含裂纹梁的模态函数;根据特征方程具体分析了裂纹位置、裂纹深度、裂纹圆周角等参数对系统失稳临界流速的影响,并进行了数值仿真分析。结果表明:由于裂纹的存在,系统的失稳临界流速下降,动态失稳临界流速下降的速率和幅值均比静态失稳临界流速下的大;临界流速与裂纹位置、深度和裂纹圆周角等参数密切相关,特别是对颤振失稳临界流速的影响更明显,在裂纹位置、裂纹非贯穿圆周角、裂纹深度等参数影响下,管道的失稳形态将从屈曲失稳转变为颤振失稳。     

局部径向载荷作用下外压薄壁圆筒稳定性分析

为简化真空塔器外挂件支撑区局部失稳分析,提炼出局部径向载荷作用下外压薄壁圆筒稳定性计算模型. 以易拉罐为薄壁圆筒试件,对不同外压下试件的局部径向临界载荷进行了测试. 利用有限元法对各实验模型进行了特征值屈曲分析,结果与实验数据能较好地吻合. 采用正交设计及参数化计算,得到了各结构参数及外压下的局部径向临界载荷经验公式. 实例计算表明,所得经验公式稍有保守,可用于真空塔器外挂件支撑件区的局部稳定性分析.     

横向冲击作用下高桥墩的几何非线性动力稳定性

考虑大变形的影响,建立了高桥墩在横向冲击荷载作用下的非线性动力学基本方程式;通过位移形函数假设,采用伽辽金积分方法得到了时间变率的动力学控制方程;对时间变率的非线性微分方程进行数值求解,给出了不同冲击荷载作用下不同柔度高桥墩的位移响应曲线以及其从产生横向振动到失稳的全过程,得到了横向冲击时高桥墩失稳的临界冲击荷载和失稳时刻;通过数值算例比较了三角形和矩形冲击荷载作用下高桥墩的荷载-位移响应曲线;分析了横向冲击力幅值、冲击区域大小、冲击持续时间、高桥墩柔度、桥面质量大小对位移幅值响应曲线、临界冲击荷载、失稳时刻的影响。结果表明:无论是在矩形还是三角形形式横向冲击作用下,随着冲击区域的增大高桥墩的振动幅值变大;桥面简化质量越大,高桥墩失稳的临界冲击载荷越小;柔度越大时,高桥墩失稳的临界冲击荷载幅值越小;对于矩形冲击,当冲击持续时间大于1s后,冲击持续时间的增加对高桥墩的稳定性无明显影响;对于三角形冲击荷载,随着冲击持续时间的增大高桥墩的振动幅值变大。     

开口薄壁压杆考虑剪滞效应和几何非线性的临界荷载

针对上翼缘和下翼缘, 假设不同的剪力滞翘曲位移函数, 导出了薄壁压杆的能量泛函. 基于最小势能原理, 对开口薄壁压杆考虑剪力滞效应和几何非线性的稳定性进行了分析, 推导了压杆的特征方程, 并求出了简支压杆考虑剪力滞效应的临界荷载以及欧拉公式的修正系数, 讨论了翼缘宽度、厚度和压杆长度以及几何非线性对临界荷载修正系数的影响, 说明了欧拉临界荷载公式的适用条件.     

局部削弱压杆的稳定性实验研究

因为缺乏相关的理论和实验研究,局部削弱压杆的临界载荷通常按无削弱压杆处理.工程中,局部削弱压杆的使用极为普遍.对局部削弱压杆的稳定性的定量研究结果,无论是工程中,还是材料力学教学中都是迫切需要的.本文在前人理论研究的基础上,对局部削弱压杆的临界载荷作了定量的实验研究.试验结果表明,对细长压杆,即使削弱部分的刚度下降达到38.9%,对失稳临界载荷的影响仍可忽略;试验结果与黄玉珊提出的对局部削弱压杆稳定性的定量计算方法也比较接近.研究结果对部分工程问题和材料力学教学都具有一定的指导意义.     

床面上直立圆柱的三维湍流数值模拟

从数值预报桥墩等结构物床面局部冲刷的角度发展绕直立圆柱的三维湍流的数值模拟技术. 基于Wilcox的k-ω两方程湍流模式，采用基于有限体积法的压力修正SIMPLE算法, 计算了绕床面直立圆柱的三维湍流流场，分析了光滑和粗糙床面两种情况下的流动情况. 通过系列的验证计算，表明该计算模型能够比较准确地反映不同外来流条件下绕直立圆柱的流场. 计算结果揭示了床面粗糙度对绕圆柱的湍流流动的影响.     

Numerical modelling of ice jam resistance to main channel flow

In northern countries, subfreezing temperatures during the winter season result in the formation of ice covers on most rivers. Towards the end of the winter season, during the spring break-up period, stationary ice covers become weak in strength and break up. The resulting broken ice pieces or ice floes are significantly larger in thickness and have a rougher undersurface relative to sheet ice and impose higher hydraulic resistance. The downstream movement of the ice floes may be arrested under conditions such as an intact ice cover, bridge piers or channel constrictions, among others, thereby initiating a break-up ice jam. These ice jams most often have been observed to cause very high water stages. Detrimental effects caused by these high water levels encompass those of operational and design-related problems such as the flooding of communities due to ice-jam-induced backwater, flood risk assessments, altering of the open water flow regime, bed scour and flooding of bridges. The ability to predict the influence of an ice jam on the main flow is of considerable importance in river engineering and can be viewed upon by its effects on the variation in the water surface levels. All other information is dependent on the foregoing. The ice jam influence on the main flow can be regarded with respect to local and global standpoints. The primary objective of this study is to formulate the influence of the ice jam on the main channel flow. The formulation is then coupled with a two-dimensional numerical model for the simulation of the water flow regime. The data from different laboratory experiments on ice jams are reproduced numerically. Various simulations are then carried out to compute the water surface levels and velocities in channels under ice jam conditions. The numerical results are then compared with the laboratory data. Results show that the mathematical formulation developed to predict the water surface levels and velocities along the ice jam length as well as upstream and downstream of its leading and trailing edges respectively gives satisfactory predictions.     

Improvements on bed‐shear stress formulation for pier scour computation

This paper introduces an improved formula for the bed‐shear stress by applying the vorticity effect and its application in a 3D flow and sediment model to estimate scouring around bridge piers. Up to now, the sediment transport formulae used for computing pier scour were developed based on the general scouring in unobstructed flow. The capability for numerical models to predict local scour around bridge piers was severely restricted by the sediment transport formulae. The new formula introduced in this paper can take into account vortices that affect the local scour process by adding some terms into the classic bed‐shear stress equation. The 3D numerical model system used in this study consists of three modules: (a) an unsteady hydrodynamic module; (b) a sediment transport module; and (c) a Fation module. The hydrodynamic module is based on the 3D RANS equations. The sediment transport module is comprised of semi empirical models of suspended load and non‐equilibrium bed load. The bed‐deformation module is based on the mass balance for sediment. The model was used to simulate pier scour in tree different test cases: (1) a circular pier; (2) a square pier; and (3) a rectangular pier, by applying the ordinary sediment equation and the newly introduced sediment equation. Results of both numerical simulations were compared against laboratory measured data and also in case 1 with result of Olsen and Melaaen (J. Hydraul. Eng. 1993; 119 (9):1048–1054). Comparisons show that the new sediment formula could predict the scour more accurately than the ordinary one. Copyright © 2010 John Wiley & Sons, Ltd.     

Down-flow and horseshoe vortex characteristics of sediment embedded bridge piers

The flow around bridge structures is a recent research topic, given the significance of bridges as basic engineering infrastructures. This study investigates the internal flow features around circular bridge piers by Particle Image Velocimetry applied both in the horizontal and vertical planes and therefore allowing for a quasi-spatial visualization of the velocity field. The temporal evolution of the vertical deflected flow at the pier front and the horseshoe vortex inside the increasing scour hole were explored resulting in the velocity and vorticity profiles. This work, therefore, provides novel insight into the complex and fascinating two-phase flow around circular bridge piers placed in loose sediment and provides an experimental data basis for advanced numerical simulation.     

Flow Field Around Single and Tandem Piers

The present study provides a comparison between the flow pattern around two circular piers in tandem and a single pier set up on a moderately rough flat bed in a laboratory flume. Velocities are measured by an Acoustic Doppler Velocimeter (ADV). The contours of the time-averaged velocity components, Reynolds shear stresses, turbulence intensities and turbulence kinetic energy at different planes are presented. Streamlines and vectors are used to study the flow features. The analysis of power spectra around the piers is also presented. The results show that the presence of downstream pier changes the flow structure to a great extent, particularly in the near-wake region. Within the gap between the two piers, a stronger and substantial upflow is shaped. However, a weaker transverse-deflection is formed in comparison with that in the single pier. Near the bed, the velocity of flow approaching the downstream pier decreases to 0.2–0.3 times of the approach mean velocity (U ₀) due to the sheltering effect of the upstream pier. In the wake of downstream pier, the flow structure is completely different from the one in the wake of single pier. In comparison with the single pier, the values of turbulence kinetic energy and turbulence intensities show a considerable decrease around the tandem piers. In tandem piers, the high values of turbulence characteristics are found near the downstream pier. There is a recirculation zones just upstream of the sheltered pier close to the bed and another behind that pier near the free surface. The results show a decrease in the strength of vortical structure in the wake of tandem piers in comparison with single pier. It is shown that the formation of flow with different Reynolds number along the flow depth due to the effect of bed roughness, as well as pier spacing, can influence the type of flow regime of tandem case. In addition to enhancing the flow structure indulgence, the present detailed measurements can also be used for verification of numerical models.     

Scour Hole Influence on Turbulent Flow Field around Complex Bridge Piers

Experimental results of detailed flow measurements using an Acoustic-Doppler Velocimeter (ADV) around a complex bridge pier (CBP) are presented. The pier consists of a column, a pile cap (PC) and a 2×4 pile group. The time-averaged velocities, turbulence intensities, and Reynolds stresses are studied and presented at different horizontal and vertical planes. Streamlines obtained from the velocity fields are used to show the complexity of the flow around the pier. It is shown that the main feature of the flow responsible for the entrainment of the bed sediments is a contracted (pressurized) flow below the PC toward the piles. A deflected flow around the PC and a strong down-flow along its sides are observed and have been measured. It is shown that these flow patterns also cause sediment entrainment. Vortex flow behind the PC and amplification of turbulence intensity along its sides near the downstream region can be other reasons for the scour hole (SH) development. Turbulence intensities and Reynolds shear stresses are presented and discussed. A comparison is made between the flow field measured with the equilibrium SH and that measured on the fixed flat-bed. The results show that the flow field around the PC is considerably influenced by the development of the SH. The extent of the wake region at the rear of the PC is about 1.4 times larger for the fixed bed (FB) than for the scoured bed (SB). Moreover, the size of the core of high turbulent kinetic energy K, as well as the maximum values of K behind the column for the FB case is larger than that of the SB case. When a scour hole develops, the flow below the PC around the piles is considered to be the main cause of the scour. This is the first time that these observations about the flow and turbulence field around a complex bridge pier are reported and analyzed. In addition to improving the understanding of the flow structure, the present detailed measurements can also be used for benchmarking and verification of numerical models.     

爆炸冲击作用下预制节段拼装桥墩的动态响应与损伤分析

为研究爆炸冲击作用下预制节段拼装桥墩的动态响应与损伤，采用ANSYS/LS-DYNA建立圆形截面预制节段拼装桥墩受爆的三维实体分离式模型。通过与已有实验结果的对比分析，验证了该模拟方法的可靠性。基于该模型，研究了爆炸冲击作用下节段长细比、初始预应力水平及桥墩体系对圆形截面预制拼装桥墩动态响应与损伤的影响规律。结果表明:减小节段长细比使墩身由剪切破坏逐渐变为节段间相对位移，并减小墩身的整体侧向位移；提高初始预应力水平可以在一定程度上提高桥墩的抗爆性能；爆炸冲击作用下混合体系桥墩兼具完全节段和整体现浇桥墩的破坏特征。     

Computation of three‐dimensional flow around square and circular piers

The aim of the present study is to investigate, by numerical simulation, the three‐dimensional turbulent flow field around square and circular piers. The numerical model employs a finite volume method based on MacCormack's explicit predictor–corrector scheme to solve weakly compressible hydrodynamic equations for turbulent flow. Computed results are compared with Dargahi's experimental measurements to assess the validity of the proposed model. Very good agreements are obtained. The results of flow simulation indicate that near the upstream face of the pier there exists a downflow, which joins the separated flow to form the horseshoe vortex stretched around the pier. This horseshoe vortex interacts with the wake vortex to create the upflow behind the pier. These phenomena appear to be very important to the mechanism of scouring around the pier. In general, the flow patterns for the square and circular piers are similar. However, the strengths of the downflow and horseshoe vortex are greater in the case of the square pier. The position of the horseshoe vortex around the circular pier is closer to the front face than that around the square pier. In the meantime, the domain of the wake flow in the case of the square pier is greater than that in the case of the circular one. Copyright © 2000 John Wiley & Sons, Ltd.     

桥墩复合基频近似算法

在瑞利法和Southwell频率合成法的基础上导出了桥墩复合振动基频的计算公式,将基频表示成各惯性元和复原元所组成子系统的频率合成。然后用有限元建模来验证该方法,并分析了不同基础约束刚度和墩顶附加质量对桥墩基频的影响。计算结果表明本文导出的公式与有限元计算结果很接近。该方法适用于各种基础类型的桥墩和高耸结构基频的估算。     

圆柱绕流局部冲刷机制的实验研究

采用粒子图像测速技术和粒子图像识别技术研究了冲刷坑的演化过程及局部冲刷的流体动力机制。首先研究了动床条件下圆柱周围的床面演化过程，给出垂直对称面输沙率随时间变化以及圆柱下游垂直对称面的沙颗粒浓度和泥沙分布规律；其次针对典型冲刷坑形状固定底床，测量了圆柱下游的瞬时流场，并给出平均流场。结果表明尾流区平均剪应力较低，但垂向涡量和湍流强度较高。分析指出平均剪应力较低的尾流区域，局部冲刷的主要动力机制是尾涡和湍流的综合作用。