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1.
Experimental Study of Sediment Incipience Under Complex Flows 总被引：1，自引：0，他引：1
Sediment incipience under flows passing a backward-facing step was studied. A series of experiments were conducted to measure
scouring depth, probability of sediment incipience, and instantaneous flow velocity field downstream of a backward-facing
step. Instantaneous flow velocity fields were measured by using Particle Image Velocimetry (PIV), and an image processing
method for determining probability of sediment incipience was employed to analyze the experimental data. The experimental
results showed that the probability of sediment incipience was the highest near the reattachment point, even though the near-wall
instantaneous flow velocity and the Reynolds stress were both much higher further downstream of the backward-facing step.
The possible mechanisms are discussed for the sediment incipience near the reattachment point.
Partially supported by National Natural Science Foundation of China (No.10602017), Maritime Research Center and DHI-NTU Center
of Nanyang Technological University, Singapore. 相似文献
2.
Yee-Meng Chiew 《天津大学学报(英文版)》2008,14(4):289-295
This paper examines scour and scour countermeasures at bridge piers and abutments. Abutment scour is by far more complex than its counterpart associated with piers because of the possibility of the presence of a floodplain. Notwithstanding this, the mechanism of scour at both piers and abutments is very similar; moreover, the failure mechanisms associated with both armoring and flow-altering countermeasures are not very different. In rivers with a floodplain, abutment scour becomes much more complex. In cases where the abutment ends at or near to the floodplain, it can initiate bank erosion, which clearly is an important erosion problem that is quite distinct from the customary scour at either an abutment in rivers without a floodplain or a pier. For this reason, abutment scour can be very site-specific while pier-scour is more generic in nature. To this end, the ability to identify the type of abutment scour that may form in a particular channel is closely related to an engineer＇s ability to propose devices for effective scour countermeasure.By summarizing research efforts on using riprap as a pier or abutment countermeasure over the past few decades, this paper highlights the deficiencies of riprap in arresting pier scour. To this end, different failure mechanisms are identified. They are shear failure, winnowing failure, edge failure, bedform-induced failure and bed-degradation induced failure. Each failure mechanism can singly or, more likely, combine to cause the eventual breakdown of the riprap layer. The study shows that a riprap layer is vulnerable to other failure mechanisms even though it is adequately designed against shear failure, rendering it ineffective in arresting scour. 相似文献
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4.
钢桥面铺装体系等效轴载换算方法 总被引：2，自引：0，他引：2
通过对钢桥面铺装主要病害的研究与分类,提出了桥面铺装结构设计的指标参数体系,并应用疲劳等效的原理,推导了轴载等效换算公式.根据室内试验和理论分析,分别研究了3种典型的铺装结构对应3种不同轴载类型的受力特性,并提出了各自轴载换算公式的参数的取值.3种轴载类型包括:单轴单轮组、单轴双轮组、双轴双轮组.通过对桥面铺装的影响因素包括气候与环境、交通、受力状态等使用条件的分析,提出的轴载等效换算公式与参数取值经过现场测试数据进行修正后,可以应用于新建桥梁桥面铺装的设计和已建桥梁桥面铺装使用状况的评价. 相似文献
5.
龚福洪 《长江工程职业技术学院学报》2000,(4)
以丹江口工程冲刷坑地质调查成果为例 ,阐述了岩体特征是影响冲刷形成的内在因素。根据三峡工程冲刷区丰富翔实的地质资料 ,分析了冲刷区岩体结构特征 ,进而与丹江口冲刷坑岩体抗冲性能进行类比分析并作了评价 ,为后续水力学试验和技术设计提供地质依据。 相似文献
6.
沥青混凝土铺装层各参数对铺装层力学性能的影响 总被引：4，自引：0，他引：4
影响正交异性钢桥面铺装层力学性能的重要参数古铺装层的厚度和沥青混凝土铺装层的模量．铺装层典型破坏的3个控制指标是铺装层的最大横向拉应力、钢板和铺装层间的最大剪切应力和铺装层的最大挠度．本建立正交异性钢桥面铺装体系分析模型，用有限元方法进行了铺装体系的受力分析，研究在高、低温季节沥青混凝土模量变化的情况下，不同铺装层厚度对三大控制指标的影响．研究结果对钢桥面铺装层厚度的确定提供了理论依据． 相似文献
7.
基于结构健康监测系统的悬索桥运行模态识别(英文) 总被引：2，自引：0，他引：2
介绍了联合应用峰值法和互谱法的模态参数识别方法,并提出了一种新的主梁振型优化方法.将上述方法应用于润扬大桥悬索桥的运行模态识别系统中,利用结构健康监测系统采集的振动响应数据获取结构的模态参数.作为应用实例,对台风麦莎作用下的主梁、主缆和桥塔振动响应数据进行了模态参数识别.结果表明:主梁部分振型的模态频率不仅能从主梁的振动响应识别出来,而且能够从主缆和桥塔振动响应中识别,主粱、主缆和桥塔之间存在较强的耦合振动.此外,将运行模态的识别结果和成桥之初的现场测试结果进行了对比,二者识别结果整体上吻合较好,但运行模态系统识别的部分振型模态频率,如L1和L2,发生了较明显的下降. 相似文献
8.
本文对钢筋混凝土桥柔性桥面铺装的早期病害及其原因进行了分析与研究,在总结当前国内桥面铺装结构分析主要方法的基础上,通过理论分析,提出了用有限元进行结构分析时,需要重点研究的几个问题,指出了今后主要的研究方向。 相似文献
9.
拟定质量替代百分数分别为0%,15%,25%,40%,70%的碎石型陶粒环氧沥青混合料和圆型陶粒环氧沥青混合料,进行高温抗车辙性能、水稳定性及低温弯曲性能试验.采用有限元方法分析开启桥在行车和开启2种状态下的力学响应.最后成型含钢桥面板、防水黏结层及环氧沥青混凝土的复合结构试件来验证2451型环氧沥青黏结料的界面黏结强度.研究结果表明,质量替代百分数分别为0%,15%,25%,40%,70%的陶粒环氧沥青混合料均能满足钢桥面铺装的力学性能要求.替代百分数为70%的圆型陶粒环氧沥青混合料由于其在减轻铺装质量等方面的优势被推荐为开启桥桥面铺装用的首选材料.桥面铺装层间剪应力随着开启角度的增大而增大,并在开启角度达到最大值85°时达到峰值.通过室内试验结果可知,天津响螺湾立转式开启桥在桥面铺装铺筑完成并养生3d后可进行首次开启. 相似文献
10.
万德成 《上海大学学报(英文版)》1999,3(1):30-35
The interaction between regular water waves and a submerged obstacle in a channel is studied numerically. The fluid viscosity is taken into account and the volume of fluid method is used to deal with the free surface. The incident regular waves are generated by use of numerical absorbing wave maker paddle. The present method can be used to predict the nonlinear deformations of the transmitted regular waves, and to simulate the vortex flow near the obstacle and the shear flows beneath the free surface. 相似文献
11.
ＩＮＴＲＯＤＵＣＴＩＯＮＣａｂｌｅ ｓｔａｙｅｄｂｒｉｄｇｅｓａｒｅｗｉｄｅｌｙａｐｐｌｉｅｄｉｎｍｏｄｅｒｎｂｒｉｄｇｅｓｔｒｕｃｔｕｒａｌｓｙｓｔｅｍ .Ｔｈｅｌａｒｇｅｓｔｓｐａｎｏｆｃａｂｌｅ ｓｔａｙｅｄｂｒｉｄｇｅｉｓｃｌｏｓｅｔｏ 1 0 0 0ｍｗｈｅｎｍａｎｙｎｅｗｍａｔｅｒｉａｌｓａｎｄｔｅｃｈｎｏｌｏｇｉｅｓａｒｅａｐｐｌｉｅｄ.Ｔｈｅｓｔａｙｃａｂｌｅｓａｒｅｉｍｐｏｒｔａｎｔｂｒｉｄｇｅｓｔｒｕｃｔｕｒｅｃｏｍｐｏｎｅｎｔｓｍｏｓｔｐｒｏｎｅｔｏｅｘｈｉｂｉｔｈｉｇｈａｍｐｌｉｔｕ… 相似文献
12.
This paper presents a nonlinear dynamic model for simulation and analysis of a kind of parametrically excited vibration of
stay cable caused by support motion in cable-stayed bridges. The sag, inclination angle of the stay cable are considered in
the model, based on which, the oscillation mechanism and dynamic response characteristics of this kind of vibration are analyzed
through numerical, calculation. It is noted that parametrically excited oscillation of a stay cable with certain, sag, inclination
angle and initial static tension force may occur in cable-stayed bridges due to deck vibration under the condition that the
natural frequency of a cable approaches to about half of the, first model frequency of the bridge deck system. A new vibration
control system installed on the cable anchorage is proposed as a possible damping system to suppress, the cable parametric
oscillation. The numerical calculation results showed that with the use of this damping system, the cable oscillation due
to the vibration of the deck and/or towers will be considerably reduced.
Project supported by National Natural Science Foundation of China (No. 59978044) 相似文献
13.
用从河南省豫北地区大型种猪场发病猪群分离到的致仔猪黄痢、白痢6个大肠埃希氏菌优势血清型菌株O2,O139,O101,O138,O20,O60的两次培养物,经0.4%的福尔马林灭活48h,添加油乳佐剂充分乳化,制成地方性猪大肠埃希氏菌灭活苗,含菌量为150亿/mL.分别于产前30d和14d两次免疫妊娠母猪,剂量2mL头,使初生仔猪从母乳中获得较高含量的大肠埃希氏菌抗体,具有对抗黄痢、白痢发生的免疫力。 相似文献
14.
Wan Decheng 《上海大学学报(英文版)》1999,(1)
１ Ｉｎｔｒｏｄｕｃｔｉｏｎ Ｔｈｅｐｒｏｂｌｅｍｏｆｔｈｅｉｎｔｅｒａｃｔｉｏｎｂｅｔｗｅｅｎｒｅｇｕｌａｒｗａｔｅｒｗａｖｅｓａｎｄａｓｕｂｍｅｒｇｅｄｏｂｓｔａｃｌｅｉｓｒｅｌｅｖａｎｔｔｏｔｈｅｄｅｓｉｇｎａｎｄｏｐｅｒａｔｉｏｎｏｆｏｆｆｓｈｏｒｅａｎｄｃｏａｓｔａｌｓｔｒｕｃｔｕｒｅｓ．Ａｋｎｏｗｌｅｄｇｅｏｆｔｈｅｆｒｅｅｓｕｒｆａｃｅｄｅｆｏｒｍａｔｉｏｎｓａｎｄｖｏｒｔｅｘｆｌｏｗｉｓｎｅｃｅｓｓａｒｙｆｏｒｅｓｔｉｍａｔｉｏｎｏｆｄｒｉｆｔｆｏｒｃｅｓａｎｄｓｕｐｅｒｈａｒ… 相似文献
15.
为了确定正交异性钢桥面铺装受力状态并为设计提供参考,运用子模型有限元法分析了桥梁整体变形及局部轮载作用下铺装内部受力状态及应变分布特点.为优化设计铺装层结构,分析了铺装层模量对其应变状态影响.分析结果表明:大跨径钢桥整桥变形对铺装层受力状态影响很小,钢桥面铺装设计的控制受力因素是轮载局部作用下铺装层的横向应变,铺装层模量对铺装层的受力状态有显著影响,通过提高铺装层刚度过渡层的结构优化设计措施可以显著改善铺装层的受力状态,降低铺装层的应变水平.分别对环氧沥青混凝土、SBS改性沥青SMA和Rosphalt改性沥青混凝土的模量及疲劳性能进行了试验评价,可以为桥面铺装结构组合设计提供参考数据. 相似文献
16.
姜立军 《唐山师范学院学报》2005,27(2):44-46
电桥的灵敏度与检流计和电源所接的位置有关,通过数学推导和实验测量得出结论:当D>0检流计内接时,电桥灵敏度较高;当D<0检流计外接时,电桥灵敏度较高。 相似文献
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INTRODUCTION The cable-stayed-suspension (CSS) hybridbridge is developed from the traditional cable-stayedbridge and suspension bridge, and has some advan-tages of the two bridge types described as follows: 1. As compared with the suspension bridge of thesame span length, the suspension portion is greatlyshortened, so the tensional forces in the main cablesare greatly decreased, which helps to decrease theconstruction costs of the main cables and the massiveanchors, and the difficulty of… 相似文献
19.
桥面铺装早期病害问题的分析 总被引：1，自引：0，他引：1
钢筋混凝土桥面沥青混凝土铺装结构的早期破坏已成为影响高速公路使用功能和诱发交通事故的原因之一，造成钢筋混凝土桥面沥青混凝土铺装结构的早期破坏的原因是多方面的，本文从设计、铺装结构、材料、施工及气候等方面进行了分析，并提出了相应的处理措施。 相似文献
20.
YANG Chih Ted 《天津大学学报(英文版)》2008,14(4):235-247
GSTARS (Generalized Sediment Transport model for Alluvial River Simulation) is a series of computer models developed by the
U.S. Bureau of Reclamation while the author was employed by that agency. The stream tube concept is used in all GSTARS models
which allow us to solve one-dimensional equations for each stream tube independently and obtain semi-two-dimensional variation
of the hydraulic conditions along and across stream tubes for rivers and reservoirs. Sediment transport, scour, and deposition
processes are simulated along each stream tube independently to give us a semi-three-dimensional variation of the bed geometry.
Most sediment transport computer models assume that channel width is given and cannot change during the simulation process.
GSTARS models apply the theory of minimum stream power to the determination of optimum channel width and channel geometry.
The concepts of channel side stability, and active, inactive, and armoring layers are used in all GSTARS models for realistic
long-term simulation and prediction of the scour and deposition processes in rivers and reservoirs. GSTARS models have been
applied in many countries for solving a wide range of river and reservoir sedimentation problems. Case studies will be used
to illustrate the applications of GSTARS computer models.
YANG Chih Ted, Borland Professor of Water Resources and Director of Hydroscience and Training Center. 相似文献