并联同步发电机组振荡原因分析及处理

文章根据一例船舶同步发电机组并联运行时由于三相输出电流的严重不平衡而引起发电机组产生振荡,导致全船失电事故的实例,分析了发电机组振荡的原因,提出防范措施以确保船舶电站的安全运行。     

Three-dimensional numerical analysis of shipping water onto a moving ship using a particle method

The objective of this study was to develop a numerical analysis method based on the moving particle semi-implicit method for simulating shipping water on a moving ship. Towing tests of a very large crude carrier were numerically analyzed for three typical wavelengths. The ship was forced to move in order to express previously measured ship oscillations, and the calculated fluid behavior and the impact pressure on the deck were compared with the experimental results.     

Natural vibration characteristics of short-span submarine power cables with bending stiffness and sag

Based on a continuum model that governs the dynamics of submarine power cables, analytical solutions of the natural frequencies and modal shapes for free spanning cables are derived. The effects of sag, axial and bending stiffness are all included. The cable sag calculation has considered the effects of bending stiffness on the static profile. The accuracy of the derived solutions is validated by the results from a laboratory experiment. The applicable ranges of these solutions and that of Ricciardi (Ricciardi and Saitta, 2008) [15] are determined. Also, the effects of static profile, boundary conditions and non-dimensional parameters (ξ and λ²) on the cable natural frequencies and modal shapes are discussed. The results show that the static profile and boundary conditions have significant effects on the modal properties for free spanning submarine power cables. It must be noted that, for lower ξ values, the frequencies of the symmetric modes show a non-monotonic dependence on bending stiffness. The single-degree-of-freedom approach is adopted to further analyze the mechanisms of the non-monotonic behavior.     

衡水市冬季公交免费乘坐政策实施效果评估

优先发展公共交通,倡导绿色出行方式,可以缓解交通拥堵,减少交通污染。河北省衡水市在国内率先实施了冬季公交免费乘坐政策,政策出台的初衷是为了改善衡水市空气质量,经综合评估后,该政策在提高公交乘客满意度、增强公共交通吸引力和缓解交通拥堵等方面取得了明显成效,为国内三、四线城市的公共交通优先发展提供了有益的经验借鉴。     

高校思政课与网络文化的人本互动

实现人的自由全面发展是马克思主义的核心思想．高校思政课作为对大学生进行思想政治教育的主渠道,其根本目标是实现人的自由全面发展,而网络文化的最终目标也是实现人的自由全面发展;以实现人的自由全面发展为切入点,有利于高校思政课与网络文化两者的人本互动,从而更有效地促进大学生自由而全面的发展．     

轮胎在水平路面上的自由滚动接触分析

利用轮胎的模态参数直接对轮胎在水平路面上的滚动建立了便于解析计算的仿真模型。该模型可模拟轮胎稳态的滚动过程并可计算出不小同工况下的滚动特性、有效滚动半径、载荷与下沉量的关系以及印迹内变形和分布力。计算结果揭示了以往模型难以描述的微观现象,与以往文献的试验研究结果定性一致,充分显示了模型的合理性。     

自由设站放样测量在轨道交通连续刚构PC梁架设中的应用

芜湖轨道交通二号线是国内外首次采用跨坐式连续刚构PC梁的轨道交通项目,相较于国内外现有轨道交通项目的跨坐式简支PC梁,在梁体安装精度、线路平顺性控制、施工技术难度等方面均优于跨坐式简支PC梁。介绍了跨坐式连续刚构PC梁架设中自由设站放样测量控制网的测设原理、布点方法及布点形式,利用自由设站放样测量方法设站灵活、放样精度高等特点,结合自主研发的专用放样工装设备,解决了轻轨跨坐式连续刚构PC梁架设中测量精度不稳定、高程上桥困难、作业时遮挡严重、测量人员安全风险大、多榀梁连接平顺性差等测量难题,可将轨道梁中线偏差控制在3 mm以内,轨道梁中心变化率控制在1.5 mm/1.5 m以内,线路超高情况下的角度公差控制在±1/8°以内。实践证明:自由设站放样测量能够满足轨道PC梁精调施工定位的精度要求,且效率高、精度高、安全性高,在同类项目中具有推广和应用价值。     

Factors driving public support for road congestion reduction policies: Congestion charging,free public transport and more roads in Stockholm,Helsinki and Lyon

Based on an across-the-board survey conducted among residents of Stockholm, Helsinki and Lyon, we explore the opinions on three policy measures to combat road congestion: congestion charging, free public transport and building more roads. The support for the two latter policies is substantially higher than the support for congestion charging, which is only supported by a majority in Stockholm. Self-interest is important for the formation of the opinion to all three policies. However, fundamental values and general political views, indicated by four attitudinal factors, are even more important in forming opinions towards the three transport policies. Of all attitudinal factors, the one indicating environmental concern most influences the support for all policies. Equity concerns, however, increase the support for free public transport and opposition to taxation increases the support for building more roads.Our results further suggest that the opinions towards free public transport and building more roads can be mapped along the left–right political axis, where Environment and Equity are to the left and Pricing and Taxation are to the right. However, the opinion towards congestion charging cuts right through the political spectrum. The impact of the fundamental values and self-interest variables are similar for Stockholm and Helsinki, indicating that even if experience increases the overall support for charging, it does not change the relative strength of different political arguments to any major extent.     

Evacuation traffic dynamics

Historically, evacuation models have relied on values of road capacity that are estimated based on Highway Capacity Manual methods or those observed during routine non-emergency conditions. The critical assumption in these models is that capacity values and traffic dynamics do not differ between emergency and non-emergency conditions. This study utilized data collected during Hurricanes Ivan (2004), Katrina (2005) and Gustav (2008) to compare traffic characteristics during mass evacuations with those observed during routine non-emergency operations. From these comparisons it was found that there exists a consistent and fundamental difference between traffic dynamics under evacuation conditions and those under routine non-emergency periods. Based on the analysis, two quantities are introduced: “maximum evacuation flow rates” (MEFR) and “maximum sustainable evacuation flow rates” (MSEFR). Based on observation, the flow rates during evacuations were found to reach a maximum value of MEFR followed by a drop in flow rate to a MSEFR that was able to be sustained over several hours, or until demand dropped below that necessary to completely saturate the section. It is suggested that MEFR represents the true measure of the “capacity”. These findings are important to a number of key policy-shaping factors that are critical to evacuation planning. Most important among these is the strong suggestion of policy changes that would shift away from the use of traditional capacity estimation techniques and toward values based on direct observation of traffic under evacuation conditions.     

三维气泡运动的数值模拟

文章基于VOF模型,借助FLUENT软件,对单个三维气泡在近自由面运动进行了数值模拟。采用了VOF的PLIC界面重构方法,追踪气泡运动过程中气泡表面的变化。监测了气泡上升速度变化以及气泡运动对自由液面的影响。通过对直径不同的气泡数值模拟,得出了气泡运动的一些基本规律。本文数值模拟结果与实验值对比分析,三维数值模拟数据与试验结果吻合较好。