Numerical simulation of flow field deposition and erosion characteristics around bridge-road transition section

Wind-sand flow generates erosion and deposition around obstacles such as bridges and roadbeds, resulting in sand damage and endangering railway systems in sandy regions. Previous studies have mainly focused on the flow field around roadbeds, overlooking detailed examinations of sand particle erosion and deposition patterns near bridges and roadbeds. This study employs numerical simulations to analyze the influence of varying heights and wind speeds on sand deposition and erosion characteristics at different locations: the bridge-road transition section(side piers), middle piers, and roadbeds. The results show that the side piers, experience greater accumulation than the middle piers. Similarly, the leeward side of the roadbed witnesses more deposition compared to the windward side. Another finding reveals a reduced sand deposition length as the vertical profile, in alignment with the wind direction, moves further from the bridge abutments at the same clearance height. As wind speeds rise, there’s a decline in sand deposition and a marked increase in erosion around the side piers, middle piers and roadbeds. In conclusion, a bridge clearance that’s too low can cause intense sand damage near the side piers, while an extremely high roadbed may lead to extensive surface sand deposition. Hence, railway bridges in areas prone to sandy winds should strike a balance in clearance height. This research provides valuable guidelines for determining the most suitable bridge and roadbed heights in regions affected by wind and sand.

Structural Design of Roadbed and Pavement in Transition Section of Roads and Bridges

As the lifeline of social development,road and bridge projects are the main channel to realize resource transportation and economic circulation.Ensuring the quality of road and bridge project construction is crucial for the development of society,the economy,and people’s livelihoods.This paper studies the design of roadbed pavement structures in road and bridge transition sections.It aims to provide technical references and significance for China’s road and bridge engineering design and construction units,promoting scientific and standardized design in these actions.This will contribute to the safety and stable operation of road and bridge projects,offering effective technical support.Furthermore,it seeks to foster the sustainable and healthy development of China’s road and bridge engineering on a macro level.

Finite element analysis on impact of foundation treatment in bridgehead transition section upon bridge piles

In order to decrease relative settlement, foundation treatment plays an extremely important role in bridgehead transition section, especially, the situation of building the bridge piles firstly, and then processing piles. On the basis of engineering practice, the authors analyzed the influence of foundation treatment on bridge piles in bridgehead transition section by finite-element method (FEM). This research has positive significance in predicting displacement of bridge pile, directing construction of foundation treatment, and improving quality of engineering and so forth.

Fine-grained gravity flow sedimentation and its influence on development of shale oil sweet sections in lacustrine basins in China

The geological conditions and processes of fine-grained gravity flow sedimentation in continental lacustrine basins in China are analyzed to construct the model of fine-grained gravity flow sedimentation in lacustrine basin,reveal the development laws of fine-grained deposits and source-reservoir,and identify the sweet sections of shale oil.The results show that fine-grained gravity flow is one of the important sedimentary processes in deep lake environment,and it can transport fine-grained clasts and organic matter in shallow water to deep lake,forming sweet sections and high-quality source rocks of shale oil.Fine-grained gravity flow deposits in deep waters of lacustrine basins in China are mainly fine-grained high-density flow,fine-grained turbidity flow(including surge-like turbidity flow and fine-grained hyperpycnal flow),fine-grained viscous flow(including fine-grained debris flow and mud flow),and fine-grained transitional flow deposits.The distribution of fine-grained gravity flow deposits in the warm and humid unbalanced lacustrine basins are controlled by lake-level fluctuation,flooding events,and lakebed paleogeomorphology.During the lake-level rise,fine-grained hyperpycnal flow caused by flooding formed fine-grained channel–levee–lobe system in the flat area of the deep lake.During the lake-level fall,the sublacustrine fan system represented by unconfined channel was developed in the flexural slope breaks and sedimentary slopes of depressed lacustrine basins,and in the steep slopes of faulted lacustrine basins;the sublacustrine fan system with confined or unconfined channel was developed on the gentle slopes and in axial direction of faulted lacustrine basins,with fine-grained gravity flow deposits possibly existing in the lower fan.Within the fourth-order sequences,transgression might lead to organic-rich shale and fine-grained hyperpycnal flow deposits,while regression might cause fine-grained high-density flow,surge-like turbidity flow,fine-grained debris flow,mud flow,and fine-grained transitional flow deposits.Since the Permian,in the shale strata of lacustrine basins in China,multiple transgression-regression cycles of fourth-order sequences have formed multiple source-reservoir assemblages.Diverse fine-grained gravity flow sedimentation processes have created sweet sections of thin siltstone consisting of fine-grained high-density flow,fine-grained hyperpycnal flow and surge-like turbidity flow deposits,sweet sections with interbeds of mudstone and siltstone formed by fine-grained transitional flows,and sweet sections of shale containing silty and muddy clasts and with horizontal bedding formed by fine-grained debris flow and mud flow.The model of fine-grained gravity flow sedimentation in lacustrine basin is significant for the scientific evaluation of sweet shale oil reservoir and organic-rich source rock.

FE Analysis of Longitudinal Dynamic Response of Subgrade in Bridge-Subgrade Transition of Heavy Haul Railway

With the increase of axle load and the train speed, dynamic interaction of train-track system becomes so exacerbated that the deformation and dynamic response of subgrade are more aggravated. The differential settlement will be created in bridge-embankment transition section under such dynamic action, and an adverse effect on the train operation safety can be caused. Meanwhile, differential settlement will produce additional dynamic effect when high-speed trains go through the transition between bridge-embankment. Such dynamic action will aggravate the differential settlement and subgrade damage. This paper applies the methods of field test and finite-element to systematically study the dynamic response characteristics of subgrade in bridge-embankment transition section of heavy haul railway under dynamic load for the first time. This research is focused on the analysis of influence of the different axle load, train speed, filled soil modulus, etc.. At last, the dynamic response rules are systematically summarized.

Load Transferring Mechanism on Transition Section of Composite Bucket Foundation for Offshore Wind Turbines

The composite bucket foundation (CBF) is a new kind of foundation which has been applied in the offshore wind industry. A reasonable connection pattern between the tower and the CBF top cover is crucial for load transmissions from the superstructure. Therefore, it is essential to choose an optimum structure type for the transition section. The line type and the arc transition section models were established by ABAQUS, and the internal forces of cross section were extracted along the height direction. Specifically, the force transfer mechanism for different types of the transition sections was investigated comparatively with monotonic as well as composite loadings. The results show that the curved transition structure exhibits the better mechanical characteristics under the monotonic and composite loadings, and the reason can be illustrated that its specific arc-shape structure can effectively convert the tremendous bending moment from the turbine tower into the limited tensile and compressive stresses downwards, without the occurrence of force concentration. © 2017, Tianjin University and Springer-Verlag Berlin Heidelberg.

Modeling and Analysis of Transitional Tube with Constant Sectional Area along Derivative Central Route

Firstly, sample square-circular transition tube along straight central route was modeled on CATIA software. The parameters are as follows： let the tube length is L, and the constant cross section area is S, and S = πR^2 = a2, in which R stands for the circle radius on one end, and a the square side length on the other end; set up the coordinate system with OX axis on the central route in which the origin O is on centroid of the square end and assume the cross section size at x as the square shaped with all four comers filleted in radius r which is proportional to x, that is, the linear slope of r is R/L, thus, both values r and square side length ax can be attained on the constant cross section area assumption. Secondly, some sample polygonal-circular transition tubes along straight, circular and helical central route were implemented similarly. Thirdly, numerical analysis of stress and displacement of these tubes were carried out on MSC/PATRAN software which are important to the distribution of turbulent flow and the layout of these transitional tube structures.

Design Strategy of Highway Speed Transition Section

In this paper,combined with the relevant speed theory and characteristics of the law,the current highway speed transition design problems are studied and analyzed.In the process of specific analysis,mainly combined with the characteristics of different types of highway speed changes and road section design requirements,this paper studies and analyzes the design methods of different types of highway speed transition section.And on this basis,according to the design principles and requirements of highway operation speed transition section,the paper summarizes the matters needing attention in the design of highway operation speed transition section,in order to provide certain reference value for relevant personnel.

The Research of Urban Rail Transit Sectional Passenger Flow Prediction Method

This paper studies the short-term prediction methods of sectional passenger flow, and selects BP neural network combined with the characteristics of sectional passenger flow itself. With a case study, we design three different schemes. We use Matlab to realize the prediction of the sectional passenger flow of the Beijing subway Line 2 and make comparative analysis. The empirical research shows that combining data characteristics of sectional passenger flow with the BP neural network have good prediction accuracy.

Distress Characteristics in Embankment‑Bridge Transition Section of the Qinghai‑Tibet Railway in Permafrost Regions

The Qinghai-Tibet Railway has been operating safely for 16 years in the permafrost zone and the railroad subgrade is generally stable by adopting the cooling roadbed techniques.However,settlement caused by the degradation of subgrade permafrost in the embankment-bridge transition sections(EBTS)is one of the most representative and severe distresses.A feld survey on 440 bridges(including 880 EBTSs)was carried out employing terrestrial laser scanning and ground-penetrating radar for comprehensively assessing all EBTSs in the permafrost zone.The results show that the types of distresses of EBTSs were diferential settlement,upheaval mounds of the protection-cone slopes,subsidence of the protection-cone slopes,surface cracks of the protection cones and longitudinal and transverse dislocation of the wing walls.The occurrence rates of these distresses were 78.93,3.47,11.56,3.36,21.18 and 4.56%,respectively.The most serious problem was diferential settlement,and the average diferential settlement amount(ADSA)was 15.3 cm.Furthermore,the relationships between diferential settlement and 11 infuencing factors were examined.The results indicate that ADSA is greater on the northern side of a bridge than on the southern side and on the sunny slope than on the shady slope.It is also greater in the high-temperature permafrost region than in the low-temperature permafrost region and in the high-ice content area than in the low-ice content area.The EBTSs are more infuenced by ice content than by ground temperature.The ADSA increases when the embankment height increases,the particle size of subgrade soil decreases and the surface vegetation cover decreases.

Ab initio Calculations of Electron-Impact Excitation Cross Sections for N_2 Molecule

One of the great difficulties in understanding nitrogen plasma elementary processes is the lack of an available database of the cross-sections of electron-impact excitations and radiations. Ab initio calculations of vibrational excitation cross sections for electron collisions with nitrogen molecules in low-lying states using similarity function approach, such as a-a＇, a-w, B-B＇ and B-W transition systems, are reported here for the first time. In the meantime, the average excitation energies of neighboring levels of these systems have been calculated. In order to obtain the cross sections, accurate spectroscopic constants and transition dipole moments have been investigated. Potential energy curves and other electronic transition dipole moments for the low-lying states of N2 have been re-evaluated using complete active space self-consistent field （CASSCF） approach with aug-cc-pVqZ basis set. The calculated cross-sections could provide a database for studying the elementary processes and the properties in N2 plasma.

广东省二、三级医疗机构延续护理部门设立及运作现况调查

目的:了解广东省二、三级医疗机构延续护理部门的设立及运作情况,为医疗机构建设延续护理部门、开展延续护理提供参考和借鉴。方法:采用便利抽样法于2023年5月4日—19日选取广东省110所二、三级医疗机构的护理管理人员进行调查,调查其所在医疗机构延续护理部门的建立情况、运作情况、阻滞因素及相关建议。结果:110所医疗机构中有35所(31.82%)设立了延续护理部门,58所(52.73%)拟计划开展延续护理服务,17所(15.45%)暂无设立延续护理部门及开展延续护理的计划。已开展延续护理的35所医疗机构中,2010年前设立延续护理部门的有3所(8.57%),2010—2018年有9所(25.71%),2019年至今有23所(65.71%)。35所医疗机构延续护理运作情况良好,但在医疗收费、医院-社区联动及延续护理质量指标设置方面需进一步加强和完善。51所(46.36%)医疗机构认为设立延续护理部门开展延续护理服务无障碍,59所(53.64%)认为存在障碍,障碍因素主要包括人力资源短缺(79.66%)、经济效益受限(76.27%)、实施场地缺乏(54.24%)、不知如何开展(32.20%)、院领导不支持(23.73%)等。结论:因缺乏统一、规范的标准及指南,广东省二、三级医疗机构延续护理部门的设立及运作情况参差不齐且存在多方面争议、困惑及不足。建议从“相关政策制度、部门组织架构、信息共享与协调机制、服务收费与支付机制、延续护理质量评价指标、工作人员绩效”等方面完善延续护理部门的设立及运作,从而推进延续护理的发展,助力实施健康中国战略。

空基回收拖曳系统直线-盘旋转接段运动轨迹设计

针对气流扰动下空基回收拖曳系统在直线-盘旋转接段飞行过程中的拖曳浮标稳定问题,提出一种基于微分平坦理论的拖曳系统转接段运动轨迹的设计方法,通过设计母机运动轨迹间接地控制拖曳浮标沿着预设的转接轨迹安全、平稳、精准地转接飞行。采用质点-弹簧离散缆绳模型构建母机-缆绳-浮标组合体多体动力学模型;在证明拖曳系统具备微分平坦特性的基础上,以拖曳浮标三轴位置为平坦输出,所提方法以期浮标沿着预设安全转接段轨迹飞行;结合拖曳浮标直线飞行状态与盘旋飞行状态设计拖曳浮标转接段飞行轨迹。通过平静大气、多种常值风及阵风气流扰动场景下的仿真算例结果表明,所提方法能够实现拖曳浮标在直线-盘旋转接段的稳定飞行。

公路缓和曲线长度的合理取值分析

为给车辆由直线(圆曲线)驶入圆曲线(直线)提供合理的路径长度,确保驾驶员能以安全、舒适、自然的状态驶入目标曲线单元,通过对现行路线规范中缓和曲线长度取值规定的合理性分析,发现回旋线参数取值规定易存在曲线单元间长度分配均匀、取值长度过长、不易与地形地物相协调等问题。结合美国《绿皮书》对缓和曲线取值的相关规定,从汽车行驶轨迹、缓和曲线偏移值特征及超高过渡等方面对缓和曲线长度取值进行理论分析研究。结果表明:在设计速度一定的情况下,随着圆曲线半径的增加,缓和曲线长度取值应随之减小;随着设计速度的增加,缓和曲线长度取值也应随之增加,但增加值较小,可忽略不计;在设计速度和圆曲线半径均相同的情况下,随着缓和曲线长度的增加,驾驶员判断前方平曲线的曲率半径偏小,易驶入临近车道,不利于交通安全。另外,根据缓和曲线偏移值特征及超高过渡所需长度研究发现,通过控制缓和曲线偏移值1 m、缓和曲线长度200 m范围,圆曲线半径与缓和曲线之间的变化关系较为稳定,符合车辆行驶轨迹,基本满足超高过渡段设置的要求。经计算得出当圆曲线半径大于1666 m时,缓和曲线长度宜随圆曲半径的增大而减短。

基于DEM-FDM耦合的过渡段膨胀诱发钢轨上拱研究

研究目的:为分析涵洞过渡段地基膨胀引起的钢轨上拱响应,基于现场测试、室内膨胀试验数据,开展DEM-FDM耦合数值模拟,分析某涵洞附近路基土在膨胀范围为16 m,膨胀中心距离涵洞中心分别为0 m、5 m、10 m这三种工况下,不同膨胀率时基床填料的运动规律及钢轨的上拱响应。研究结论:(1)涵洞对于钢轨上拱位移的传递存在阻断作用,但会增大钢轨上拱的峰值,原位膨胀率下工况二的钢轨上拱峰值达到46 mm,当路基膨胀率为0.3%时钢轨上拱位移量达到无砟轨道钢轨可调节临界值(4mm);(2)过渡段钢轨上拱处同时产生轴向应力集中,其中原位膨胀率下工况二轴向应力峰值达到14.4 MPa;(3)对于膨胀区域位于涵洞下方的工况,钢轨轴向应力呈现出来的分布规律为钢轨上拱拱顶处为主拉应力状态,拱脚处为主压应力状态,因此一共包括三个压应力峰值点以及两个拉应力峰值点;(4)本文研究可为高铁涵洞过渡段路基膨胀病害解决方案的确定提供理论依据。

互联网+背景下虚拟教研室内涵建设

针对高校基层教学组织建设存在的一些问题,分析了虚拟教研室的成立背景、建设内涵,探讨了虚拟教研室的组织架构及保障条件,提出了以师资能力提升为导向,以课程建设为核心,以教学资源共享为途径,以开放课题研究为抓手的内涵建设途径。实践应用表明,通过加强虚拟教研室内涵建设,极大地提升了各参与高校的积极性,有效促进了各参与高校轨道交通信号与控制专业的专业建设水平,提升了人才培养质量。

路堤-桥梁过渡段车辆气动力风洞试验研究

为了探究路堤-桥梁过渡段处车辆的气动力,建立1:50的大比例尺路堤-桥梁过渡段和车辆试验模型,在桥梁和路堤段分别布置两种风屏障,并在车辆模型表面布置多个测压点,以研究不同防风措施下处于不同风向角的路桥过渡段车辆气动力。试验结果表明:与无防风措施相比,布置桥梁风屏障后最不利风向角会从-15°变为0°,此风向下过渡段处车辆的三分力最大;再进一步布置路堤风屏障后最不利风向角不变,但大幅度减小了0°风向角下车辆的侧力系数和力矩系数;布置路堤风屏障能有效减小车辆所受三分力;不同风向角下改变陆地风屏障参数产生的影响不同,针对路堤-桥梁过渡段布置防风措施时,应充分考虑其来流方向,以达到最优效果。

废弃橡胶轮胎在路桥过渡段沉降影响因素研究

为了研究废弃橡胶轮胎作为路基的加筋材料改善道路桥梁过渡段差异沉降的影响因素,建立了ABAQUS有限元数值模型。通过施加单一与交通荷载,对不同加筋层数、筋材特性、交通荷载的幅值、频率、循环次数等因素对土体沉降量的影响进行分析。结果表明,3层加筋效果优于2层,远优于1层。加筋后的桥头路基抵抗沉降的能力有显著提高,且随着模量的提高,效果更明显。在交通荷载作用下,随深度的增加,轮胎的影响深度逐渐减小;随荷载频率的增大,交通荷载作用在土层的次数增加,荷载的影响深度随之增大;随循环次数的增加,土体塑性位移递增。轮胎通过将软土层分层,提高了土体的整体性和连续性,减小了差异性沉降,使路桥的过渡段平稳过渡。

直流余热锅炉蒸发段长度和位置变动特性的仿真分析

在直流余热锅炉变工况运行过程中蒸发段长度和位置的改变会造成锅炉管壁温度分布、工质出口参数等产生较大的波动,影响锅炉安全运行。以某立式直流余热锅炉为研究对象,建立其动态仿真模型,研究锅炉烟气流量、入口烟温、高压给水流量和给水温度分别发生阶跃扰动后蒸发段长度及相变点位置的变化规律。仿真结果表明:余热锅炉在设计工况下运行,锅炉入口烟温对锅炉蒸发段长度的影响程度最大,入口烟温阶跃升高10℃后,蒸发段迅速缩短,相变点均向锅炉管内工质入口方向移动,蒸发段长度和相变点位置恢复稳定所需时间相对较短;烟气流量阶跃升高5%后,蒸发段长度迅速缩短而后缓慢增长,沸腾点向管内工质入口方向移动距离大于蒸干点,恢复稳定所需时间较长;给水流量阶跃升高5%后,蒸发段长度迅速增长而后缓慢缩短,蒸干点向管内工质出口方向移动距离大于沸腾点,恢复稳定所需时间最长;给水温度阶跃变化20℃对蒸发段长度和相变点位置的影响很小。

运营期纵连板式无砟轨道端刺结构位移特征

研究目的:Π型端刺锚固体系是纵连板式无砟轨道路桥过渡段限制轨道结构位移的关键部位。本文考虑轨道结构与桥梁及摩擦板、端刺与土体的非线性相互作用关系,建立轨道-桥梁-路基-端刺结构一体化计算模型,研究锚固结构服役状态下的位移特征,分析端刺与路基不同脱空位置对结构位移的影响,提出注浆填补层间脱空的增强方案,并对其可行性进行论证。研究结论:(1)端刺与路基完全脱空后,纵向位移相比脱空前大幅增加且超过了3 mm位移限值,脱空引起的路基对端刺结构摩阻力、锚固力下降会导致端刺产生超量位移;(2)摩擦板区域的脱空对端刺位移影响很小,主端刺区域脱空和完全脱空引起的端刺纵向位移只相差0.11 mm,所以主端刺区域路基脱空是引发结构超量位移的主因;(3)采用注浆方式对脱空区域路基进行加固整治后端刺的纵向位移降低了3.5 mm左右,端刺结构位移恢复到了与正常服役状况相近的程度;(4)本研究成果可为现场Π型端刺结构超量位移整治提供一定的理论依据。