地铁隧道二次衬砌钢筋网防裂性能研究

为了定量分析防裂钢筋网提高隧道衬砌结构抗裂性能的机理和幅度,以地铁双线隧道二次衬砌结构为研究对象,采用荷载结构法和杆系有限元数值模拟方案,定量分析二次衬砌结构不设置与设置钢筋网这2种情况下的开裂临界荷载。其中素混凝土结构以达到极限拉应变为临界状态,衬砌结构增设钢筋网后以达到GB 50157-2013《地铁设计规范》允许的最大裂缝宽度0.2mm为临界状态。分析结果表明,配置防裂钢筋网后,Ⅲ级和Ⅳ级围岩衬砌结构抗裂性能可分别提高22.4%和19.3%,Ⅴ级围岩衬砌结构抗裂性能提高15.2%;Ⅲ级和Ⅳ级围岩二次衬砌结构的破坏形式由脆性破坏变为延性破坏,从而提高了其安全性能。     

考虑矿物各向异性的地聚物/集料界面静动态交互特征模拟

地聚物作为一种低碳环保、应用潜力广阔的无机结合料，其与不同表面构造集料的界面交互作用直接影响地聚物混凝土的力学性能和耐久性。充分考虑集料矿物晶向的各向异性，采用分子动力学模拟(Molecular Dynamics， MD)从原子分子层次的作用模式和强度分析，模拟了地聚物主要水化成分N-A-S-H、C-A-S-H和集料矿物化学成分SiO₂、CaCO₃不同晶面的静态界面相互作用，并采用单轴拉伸方法从纳米尺度下讨论了不同界面交互的动态力学行为。模拟结果表明：CaCO₃各晶面表现出比SiO₂更强的表面能和表面浸润性，并与C-A-S-H、N-A-S-H的界面相互作用势和拉伸应力更强，但CaCO₃晶面各向异性明显，性能稳定性不及SiO₂。地聚物与集料矿物的相互作用势主要由静电势提供，由于矿物界面静电作用及浸润特征，交互区水分子聚集，氢键作用明显，同时水分子与Ca²⁺、Na⁺进行配位形成水合离子，有助于离子在矿物表面迁移、沉淀与成核生长，增强界面空间位阻效应。在单轴拉伸模拟中，地聚物与集料矿物界面拉伸失效机制包括2个阶段：第1阶段(0 nm＜界面位移d＜0.15 nm)主要克服界面交互的静电作用，第2阶段(0.15 nm≤d≤0.3 nm)主要克服氢键作用。MD模拟有助于从分子尺度揭示地聚物与集料界面作用机制，为进一步研究地聚物混凝土材料优化、交互界面强化及损伤等提供了新方法和理论依据。     

Numerical study on the dynamic response of a truncated ship-hull structure under asymmetrical slamming

Dynamic response of ship-hull structure under slamming has tracked widespread attention in the marine structural design. However, our understanding on the dynamic characteristics largely relies on the symmetrical slamming cases. This paper presented a preliminary numerical investigation on the dynamic response of a truncated ship-hull structure under asymmetrical slamming based on the uncoupled CFD-FE method. Asymmetrical slamming loads were predicted through combining the seakeeping analysis and CFD method. In there, three kinds of motions (vertical, horizontal and roll motions) of 2D ship sections were obtained through the seakeeping analysis and then the slamming pressure was predicted through simulating the water entry with various motions based on CFD method. The dynamic response was analyzed through finite element method. Numerical predictions including ship motions, slamming loads and dynamic analysis were validated against published experimental data and numerical calculations. The characteristics of asymmetrical slamming loads were analyzed showing obvious asymmetry in space, and the dynamic characteristic of the ship bow structure was further clarified through discussing the deformation and stress distribution. These results are useful for readers for better understanding the dynamic characteristics of the bow structure under slamming.     

激光焊接技术在轨道交通车辆中的应用

为解决轨道交通车辆不锈钢车体电阻点焊的外观质量差、密封性差、效率低等缺点,对部分熔透激光焊接工艺在不锈钢车体焊接中的应用开展了研究。研究包括:部分熔透激光叠焊原理、参数优化试验、显微组织分析、疲劳性能分析,以及激光焊接不锈钢车辆侧墙的结构改进。研究结果表明,不锈钢车体焊接中采用部分熔透激光叠焊工艺,可以获得高质量的表面状态及疲劳强度,车体结构强度高于EN12663标准中的要求。     

某平台机舱进排风口气流组织的CFD模拟

某自升式平台的机舱进、排风口位置比较接近,机舱排出的热气受大气风影响可能返回进风口,进而提高进风温度,成为一个设计隐患。文章应用CFD技术,通过模拟一定的大气环境条件下进排风口处的气流组织,找出最不利工况,并提出切实可行的改进建议。     

真空断路器用单稳态永磁机构概述

本文对单稳态永磁机构与传统机构以及双稳态永磁机构的特点进行了对比,对其结构与工作原理进行了简单说明,并对其发展前景进行了简要探讨。     

Strategic considerations behind the network–regional airline tie ups – A theoretical and empirical study

The paper examines the strategic vertical relationship between network and regional airlines. We develop a model to illustrate how network airlines can use the contractual relationship with regional airlines as an efficient tool to simultaneously drive out inefficient network airlines and also accommodate other cost efficient network airlines in any specific market. The model is tested on U.S. data using simultaneous and sequential choice models. We find that market size, cost differences between network airlines, as well as cost differences between network and regional airlines, are the chief determinants of the network airlines’ decisions on whether or not to serve a market with their own fleet, as well as how many regional airlines to contract with.     

Environmental lumping for efficient fatigue assessment of large-diameter monopile wind turbines

Fatigue damage is one of the governing factors for the design of offshore wind turbines. However, the full fatigue assessment is a time-consuming task. During the design process, the site-specific environmental parameters are usually condensed by a lumping process to reduce the computational effort. Preservation of fatigue damage during lumping requires an accurate consideration of the met-ocean climate and the dynamic response of the structure. Two lumping methods (time-domain and frequency-domain) have been evaluated for a monopile-based 10 MW offshore wind turbine, both based on damage-equivalent contour lines. Fatigue damage from lumped load cases was compared to full long-term fatigue assessment. The lumping methods had an accuracy of 94–98% for the total long-term fatigue damage and 90% for individual wind speed classes, for aligned wind and waves. Fatigue damage was preserved with the same accuracy levels for the whole support structure. A significant reduction of computational time (93%) was achieved compared to a full long-term fatigue assessment. For the cases with 30° and 60° wind-wave misalignment, there was a mean underestimation of approximately 10%. Variations in penetration depth did not affect the selection of the lumped sea-state parameters. This work presents a straightforward method for the selection of damage-equivalent lumped load cases, which can adequately preserve long-term fatigue damage throughout the support structure, providing considerable reduction of computational effort.     

Analysis of structural crashworthiness of double-hull ships in collision and grounding

A conceptual design framework for collision and grounding analysis is proposed to evaluate the crashworthiness of double-hull structures. This work attempts to simplify the input parameters needed for the analysis, which can be considered as a step towards a design-oriented procedure against collision and grounding. Four typical collision and grounding scenarios are considered: (1) side structure struck by a bulbous bow, (2) side structure struck by a straight bow, (3) bottom raking, (4) bottom stranding. The analyses of these scenarios are based on statistical data of striking ship dimensions, velocities, collision angles and locations, as well as seabed shapes and sizes, grounding depth and location. The evaluation of the damage extent considers the 50- and 90-percentile values from the statistics of collision and grounding accidents. The external dynamics and internal mechanics are combined to analyse systematically the ship structural damage and energy absorption under accidental loadings.     

基于ANSYS的三通道储罐结构加固及修复技术

以一台三通道储罐为分析对象,此储罐在轻微压力环境下即发生了局部开裂。以ANSYS有限元方法为基础,通过在内部合理布置T型钢加强筋的方式进行结构加固。并在确保结构强度的前提下,计算出了板制T型钢厚度的最优解。自加固修复后,此三通道储罐已安全运行2 a以上,这种基于ANSYS的结构加固及修复技术,体现了良好的工程实用性和经济性。