A New Technique of High-performance and Fast Tensioning Prestressed Anchorage CableEI北大核心

Research purposes: The large-span transition section tunnel of the Badaling Great Wall station on the Beijing-Zhangjiakou high-speed railway with the maximum excavation width of 32.7 m, and the largest excavation area of 494.4 m 2 , is the world's biggest traffic tunnel in the world with the largest excavation width and excavation area, which has difficult construction and high security risks. The initial support system of tunnel is mainly realized by prestressed bolt, prestressed cable and shotcrete. After test, anchor cable tension using the traditional anchor cable construction technology can't meet the design requirements, at the same time, it takes about 30 days to achieve prestressed tensioning. Therefore, we need to study the high-performance fast tensioning prestressed anchor cable technology, to effectively control surrounding rock deformation, to ensure the safety of construction, improve construction efficiency. Research conclusions:(1) The traditional anchor cable construction technology is adopted. The anchor cable tension value is mainly controlled by the grip force between the anchor rope and grouting body and the cohesive force between grouting body and surrounding rock. (2) The grip force between the anchor rope and the grouting body can be increased by about 2 times by increasing the "barb"; The cohesive force between the grouting body and the surrounding rock can be increased by 1.5 times by 6 ~ 7 MPa high-pressure grouting process. (3) The modified sulphoaluminate cement slurry can reach more than 30 MPa within 1 day of the slurry strength, so as to realize fast anchor cable tension within 1 day after grouting completion. (4)The research results can be used for reference in similar prestressed anchorage cable construction projects. © 2018, Editorial Department of Journal of Railway Engineering Society. All right reserved.     

基于模糊逻辑异步电动机间接矢量控制传动系统及其性能分析

文章提出了一种新颖的采用模糊逻辑控制的异步电动机(IM)转速控制方法.模糊逻辑控制器(FLC)是基于间接矢量控制系统设计的.模糊逻辑转速控制器用于外层回路.针对实验室1 hp鼠笼式IM采用DS-1102数字信号处理器插件板,对基于FLC的IM矢量控制传动系统进行了实验研究.对文章提出的基于FLC的IM传动性能进行了研究,从理论和实验两个方面,在诸如指令转速突变、负载阶跃变化等不同的动态工作条件下,与基于传统的比例积分(PI)控制器的传动系统作了比较,结果表明使用FLC更优越.因此该方法适用于高性能工业传动系统,以取代传统PI控制器的方法.     

消除三相电压不平衡引起的电压源逆变器直流环节电压脉动的控制方法

研究和分析了用于消除电网不平衡时电压源逆变器直流母线脉动电流的补偿控制方法.脉动电流不仅影响传动装置的运行性能,而且降低逆变器的电源品质.控制参数范围的选择取决于变流器抵抗电压不平衡的能力和系统参数.文中讨论和分析了在控制参数范围内控制方法对每相的功率因数和电流幅值的影响,重点分析了功率因数和前端整流器输入端电流不平衡问题,并提供系统在无补偿控制和补偿控制两种状态下的数值仿真和实验测量结果.     

PACDIN statement of methods

PAntograph–Catenary Dynamic Interaction (PACDIN) is a code developed by the vehicle technology research centre (CITV) of the Universitat Politècnica de València in collaboration with the railway company Talgo S.L. The model of the catenary is a finite element model using absolute nodal coordinates. It is based on a general formulation that can be applied for analysing a wide range of catenary configurations, including stitch wire, transitions or non-straight path tracks. The formulation is fully non-linear and includes large deformations, dropper slackening and contact interaction. The model is linearised when deformations are small, as in the case of the benchmark dynamic analysis. The results of the PACDIN code show a good agreement with the average results of other benchmark codes.     

A two-layer model of the Rhine plume

The outflow of Rhine water into the shallow Southern Bight of the North Sea leads to almost discontinuous vertical density distributions and sharp frontal structures around the river mouth. Strong tidal motion, wind and baroclinic effects have large influence on the dynamics and dispersion of river water. A three-dimensional tidal model, including advective and diffusive transport of salinity, is used in the two-layer mode for simulation of Rhine water outflow to quantify the interaction of the different processes and the effect on dispersion and mixing of river water. Layer depths are adjusted in a way that no advective transports between upper and lower layer take place in case of sufficiently stable stratification. In case of weak or no stratification the upper layer depth is fixed, and advective transports between layers are computed. Model results show frontal eddy development and (limited) growing internal waves due to baroclinic instability. Comparisons with observational data are presented.     

Water masses and cyclonic circulation in Bay of La Paz, Gulf of California, during June 1998

The Bay of La Paz, a coastal and shallow basin of the Gulf of California (depth<420 m), exchanges mixed-layer waters with the Gulf of California predominantly through Boca Grande (Big Mouth), in the northeastern part of the bay. Equatorial Surface Water (ESW) flows from the gulf to the bay; once there, due to evaporation processes, this water increases its salinity above 35.00, therefore becoming Gulf of California Water (GCW) Mass. During June 1998, the baroclinic circulation in the bay was dominated by a cyclonic gyre. The hydrographic dome, related to this gyre, is depicted until approximately 150-m depth. However, the vertical mixing of water between the mixed-layer and the ones below practically does not occur because of the development of a sharp pycnocline. This fact and the isolation of the bottom of the bay by a bathymetric sill (approximately 250-m depth) at Boca Grande induce low oxygen content, particularly in the bottom-waters (O₂<0.1 ml/l). Chlorophyll values are higher and with larger vertical fluctuations within the Bay of La Paz than outside.     

The PROFILE project: an overview

The EC MAST project PROFILE (Processes in Regions of Freshwater Influence, ROFIs) aims to develop process understanding and tested numerical models for ROFIs. This includes the role of physical processes controlling water-property distributions, suspended sediments controlling the availability of light, nutrients and phytoplankton growth. The project comprises: (1) construction of a 3D nearshore model, with high resolution (1 h and one km approx.) and a framework coupling modules for hydrodynamics (tides, effects of winds and waves, currents, temperature, salinity, turbulence and diffusivity), sediments, plankton, nutrients and oxygen, (2) investigation of methods to include ROFI model detail in coarser shelf-wide models, (3) specific tests of model components against measurements, (4) tests of model calculations against measurements in contrasted ROFIs, (5) systematic observations suitable for these model tests (time-series over a seasonal cycle for dynamics and intermittency, good vertical resolution and spatial surveys) of the contrasted Rhine, Clyde and Thermaikos Bay ROFIs, complementing earlier measurements in the ROFI areas of the Rhine, German Bight and Po, (6) interpretation and comparison of the contrasted ROFIs' behaviour, (7) a defined set of observations, model code and output suitable for subsequent integration and promulgation as test data and a nearshore model for wider use.     

Baroclinic eddy formation in a Rhine plume model

A three-dimensional finite difference tidal model, including advective and diffusive transport of salinity, is used in the two-layer model for simulation of Rhine water outflow. Layer depths are adjusted in a way that no advective transports between upper and lower layer take place in case of sufficiently stable stratification.Model results show frontal eddy development related to (limited) growing internal waves in case of weak northeasterly to southeasterly winds. It is shown that baroclinically unstable conditions occur, related to vertical velocity shear, resulting in frontal meanders with wave lengths between 18 and 30 km. Satellite images of sea surface temperature show a comparable behaviour of the temperature front, which is strongly correlated with the salinity front of the Rhine plume.     

Characteristics and potential impacts of under-ice river plumes in the seasonally ice-covered Bothnian Bay (Baltic Sea)

The northernmost basin of the Baltic Sea, the Bothnian Bay, is ice-covered for about half the year. During this time, distinct under-ice river plumes develop, even seaward of the smallest rivers, that are substantially thicker and larger in extent than during the summer months. Wind mixing is negligible, and during late spring in April or May, the highest annual discharge occur while the sea is ice covered, thus providing conditions for the formation of extensive under-ice plumes. These plumes are characterised by high levels of trace elements (e.g., Al, Fe and Zn), organic matter (TOC and dissolved organic carbon [DOC]), nutrients and also optically active substances (colored dissolved organic matter, CDOM). The under-ice plumes provide an important pathway for undiluted transport of land-derived substances to the pelagic waters of the basin, affecting the salinity, chemistry and optical properties of coastal waters. Freshwater ice growth on the underside of an existing sea ice sheet also restricts the buildup of sea ice and under-ice algal communities, potentially in large areas along the coasts. Plume water influences the optical characteristics of coastal waters for a period of time after ice break-up, potentially affecting primary production in these areas. Furthermore, the formation of under-ice plumes potentially has a positive feedback on the ice season length due to freshening of the coastal waters (earlier freeze-up) and restricted oceanic heat flux (slower melting).     

Accessibility in the regional CGE framework: the effects of major transport infrastructure investments in Poland

Transportation - Since its EU accession, Poland has invested strongly in the development of fast road transport network. As a result, the total length of modern, high-speed roads has increased from...