土岩交错地层隧道爆破施工的振动响应及空洞效应分析

以汕湛高速揭博段水墩隧道为工程背景,运用数值模拟计算的方法,建立上软下硬地层下爆破振动的有限元计算模型,对爆破荷载作用下上部初期支护和围岩的振动响应及空洞效应进行研究。结果表明： 1）掌子面下部基岩爆破施工的振动荷载主要通过支护结构传递给拱顶围岩,而掌子面上部前方围岩（未成洞区）和后方围岩（成洞区）振动分布并不对称,其中成洞区围岩的振动速度和振动范围远大于未成洞区,说明上软下硬地层隧道爆破振动存在空洞效应; 2）成洞区单向约束是造成振动加剧的根本原因,围岩振动的纵向最不利位置为掌子面后方约2 m处,径向为软硬交界结构面与隧道外轮廓的切点处; 3）振动方向以径向为主,即拱顶围岩振动以竖向振动为主,初期支护拱脚以水平振动为主; 4）距离掌子面1倍(洞径)范围的拱顶围岩及初期支护拱脚是控制爆破振动的关键部位。     

High-frequency random vibration analysis of a high-speed vehicle–track system with the frequency-dependent dynamic properties of rail pads using a hybrid SEM–SM method

A hybrid Spectral Element Method (SEM)–Symplectic Method(SM) method for high-efficiency computation of the high-frequency random vibrations of a high-speed vehicle–track system with the frequency-dependent dynamic properties of rail pads is presented. First, the Williams-Landel-Ferry (WLF) formula and Fractional Derivative Zener (FDZ) model were, respectively, applied for prediction and representation of the frequency-dependent dynamic properties of Vossloh 300 rail pads frequently used in China's high-speed railway. Then, the proposed hybrid SEM–SM method was used to investigate the influence of the frequency-dependent dynamic performance of Vossloh 300 rail pads on the high-frequency random vibrations of high-speed vehicle–track systems at various train speeds or different levels of rail surface roughness. The experimental results indicate that the storage stiffness and loss factors of Vossloh 300 rail pad increase with the decrease in dynamic loads or the increase in preloads within 0.1–10,000?Hz at 20°C, and basically linearly increase with frequency in a logarithmic coordinate system. The results computed by the hybrid SEM–SM method demonstrate that the frequency-dependent viscous damping of Vossloh 300 rail pads, compared with its constant viscous damping and frequency-dependent stiffness, has a much more conspicuous influence on the medium-frequency (i.e. 20–63?Hz) random vibrations of car bodies and rail fasteners, and on the mid- (i.e. 20–63?Hz) and high-frequency (i.e. 630–1250?Hz) random vibrations of bogies, wheels and rails, especially with the increase in train speeds or the deterioration of rail surface roughness. The two sensitive frequency bands can also be validated by frequency response function (FRF) analysis of the proposed infinite rail–fastener model. The mid and high frequencies influenced by the frequency-dependent viscous damping of rail pads are exactly the dominant frequencies of ground vibration acceleration and wheel rolling noise caused by high-speed railways, respectively. Even though the existing time-domain (or frequency-domain) finite track models associated with the time-domain (or frequency-domain) fractional derivative viscoelastic (FDV) models of rail pads can also be used to reach the same conclusions, the hybrid SEM–SM method in which only one element is required to compute the high-order vibration modes of infinite rail is more appropriate for high-efficiency analysis of the high-frequency random vibrations of high-speed vehicle–track systems.     

高桩码头结构加固改造常用方案

结合具体工程实例,对国内高桩码头结构加固改造常用方案进行分析,总结每种改造方案的适用条件和优缺点,供高桩码头结构加固改造方案选择和设计参考。     

Mechanical Behavior of a Glass-fiber Reinforced Composite to Steel Joint for Ships

The use of a glass-fiber reinforced composite in marine structures is becoming more common, particularly due to the potential weight savings. The mechanical response of the joint between a glass-fiber ...     

雷达训练系统目标回波信号模拟方法研究

对光学区扩展目标的散射特性进行分析,建立了基于多散射中心及线性调频体制宽带雷达的目标回波模型,同时给出了雷达回波数据的存储模型及处理方法。在此基础上对扩展目标作径向和非径向匀速直线运动两种情况下的回波信号进行模拟仿真为验证回波模型的正确性,对仿真的回波数据分别进行脉冲压缩和多普勒处理,得出的目标的一维距离像和速度维正确地反映出目标特征,表明模型可行有效,为后续的目标特征提取、目标识别奠定了基础。     

浅析高职院校加强公务车辆管理的对策

高职院校的公务车辆管理是学校基础管理的重要组成部分,加强车辆管理工作是服务师生员工的重要内容,其服务质量的高低直接影响到学院的教学科研、行政后勤管理和公务活动等各项工作的正常开展。文中从提高对车辆管理重要性的认识、建立健全管理运行机制、实行内部成本核算和培养高素质的驾驶员队伍等四个方面,提出了加强公车管理的具体对策,以供相关院校参考借鉴,进一步提高公车管理水平。     

基于ARMA的桥梁监测信息预测技术研究

为解决桥梁结构健康监测中长期累积的海量监测数据处理问题,采用数据挖掘中的时间序列分析方法,利用自回归移动平均(ARMA)技术对桥梁历史静态监测量进行分析,直接得出关于其过去行为的有关结论,进而推断其未来发展趋势。与基于因果关系的结构式模型预测法不同,ARMA无需明确模型结构或边界条件,而是直接从统计学的角度预测变量未来发展情况。采用该技术对西安白蛇峪大桥应变监测数据进行分析,试验结果显示出较高的预测精度;采用该技术对重庆偏岩子大桥的应变、挠度、裂缝、倾斜监测量进行预测,试验统计结果表明,ARMA单步预测误差小于10%的置信度在97%以上,在工程实际中具有可实用性,可为桥梁结构的安全预警提供重要参考依据。     

沥青路面热再生混合料疲劳性能研究

采用三分点加载疲劳试验研究了100、200、250、300共4个应变水平、30%、40%,50%共3种RAP掺量下沥青路面热再生混合料的抗疲劳性能,揭示了热再生混合料的疲劳变化规律,同时建立了疲劳方程。研究结果表明随着RAP掺量的增加热再生混合料的疲劳寿命提高,同时热再生混合料的疲劳寿命对应变水平的变化敏感程度增加。考虑到我国的气候分区和不同掺量热再生混合料路用性能的变化规律,本文建议热再生混合料最大RAP掺量的选择应考虑道路所在的气候分区。     

灰土挤密桩处理湿陷性黄土地基的应用研究

灰土挤密桩主要通过对桩间土的挤密、侧向约束及桩体的承载作用来提高复合地基的承载力;通过重型击实和无侧限抗压强度试验,确定采用灰土比为2∶8、含水率为20%的灰土进行灰土桩的施工;桩身和桩间土现场取样检测结果表明,灰土挤密桩能够有效改善湿陷性黄土的力学性能,提高地基承载能力。     

载机舰船初步甲板风包络的一种建立方法

研究提出一种甲板风包络建立方法,包括流场相似性要求,CFD数值模拟、风洞缩比模型试验、海上实船测试,以及数据的对比,验证和安全甲板风包络的绘制,以某型舰船为例,给出了方法的具体实现示范.该种甲板风包络可以用来指导下一步实际起降飞行试验,降低实际起降飞行试验的成本,提高实际起降飞行试验的安全性,加快最终正式包络线的生成.