Benchmarking of two three-dimensional numerical models in time/space domain to predict railway-induced ground vibrations

In the last 30 years,the scientific community has developed and proposed different models and numerical approaches for the study of vibrations induced by railway traffic.Most of them are formulated in the frequency/wave number domain and with a 2.5D approach.Three-dimensional numerical models formulated in the time/space domain are less frequently used,mainly due to their high computational cost.Notwithstanding,these models present very attractive characteristics,such as the possibility of considering nonlinear behaviors or the modelling of excess pore pressure and non-homogeneous and non-periodic geometries in the longitudinal direction of the track.In this study,two 3D numerical approaches formulated in the time/space domain are compared and experimentally validated.The first one consists of a finite element approach and the second one of a finite difference approach.The experimental validation in an actual case situated in Carregado(Portugal)shows an acceptable fitting between the numerical results and the actual measurements for both models.However,there are some differences among them.This study therefore includes some recommendations for their use in practical soil dynamics and geotechnical engineering.

Remaining Useful Life Prediction of Rolling Element Bearings Based on Different Degradation Stages and Particle Filter

A method is proposed to improve the accuracy of remaining useful life prediction for rolling element bearings,based on a state space model(SSM)with different degradation stages and a particle filter.The model is improved by a method based on the Paris formula and the Foreman formula allowing the establishment of different degradation stages.The remaining useful life of rolling element bearings can be predicted by the adjusted model with inputs of physical data and operating status information.The late operating trend is predicted by the use of the particle filter algorithm.The rolling bearing full life experimental data validate the proposed method.Further,the prediction result is compared with the single SSM and the Gamma model,and the results indicate that the predicted accuracy of the proposed method is higher with better practicability.

Agricultural Land Suitability of Production Space in the Taihang Mountains, China

The contradiction between the shortage of land for agriculture due to rapid expansion of industrialization and urbanization and increasing population pressure is projected to impose great threats to future food security.Agricultural land suitability evaluation is an effective approach to improve the utilization of land resources for crop production and thus enhance the capacity of food provision.In this study, we evaluated the land suitability for agriculture of the production space in the Taihang Mountains by three steps: establishing indicator system, determining weights for indicators, and constructing a fuzzy matter-element model to assess the grades of suitability.Results showed that the land suitability had a significant linear correlation with potential crop yields, indicating our evaluation was effective to predict crop production.The spatial pattern of land suitability for crop production demonstrated that land with higher suitability was generally located in piedmont plains and basins, while land with lower suitability was mostly situated in mountainous areas.The area of highly, moderately, marginally suitable and unsuitable land for agriculture was 32.13%, 28.58%, 37.49% and 1.80% of the production space, respectively.However, the correlation degree analysis indicated that the requirements of these four suitability grades were currently not satisfied but could be potentially fulfilled.In terms of indicator weights, soil properties were much more important than topography and location conditions to influence the grades of suitability.Among all indicators, slope, soil organic matter, soil texture and soil depth were the most influential factors, so slope farming prevention and organic fertilization were most likely to improve land suitability for agriculture.Compared the outputs of our land suitability evaluation model with the distribution of the existing croplands, we found that about 66.52% of marginally suitable and 54.55% of unsuitable land for agriculture were currently used for croplands.Therefore, de-farming policy should be implemented in areas of these two suitability grades.In contrast, cropland expansion was encouraged in the land that was highly or moderately suitable for agriculture.Our evaluation of agricultural land suitability is beneficial for future land use planning and decision-making in the Taihang Mountains.

Model of Universe as Described by Dynamic Universe Model

In this paper we will see the model of Universe according to Dynamic Universe Model of Cosmology by visualizing various processes that are happening in the Universe as per experimental evidences. For simplifying the matter here, we will see in part 1: about the Galaxy life cycle, where the birth and death of Galaxies discussed. Probably Universe gives guidance for the movement of Galaxies. We call this Part 1: Thinking and Reproducing Universe or Mindless Universe? (Galaxy life cycle). We see every day Sun, Stars, Galaxies etc., dissipating enormous energy in the form of radiation by the way of fusion of Hydrogen to helium. So after sometime all the Hydrogen is spent and Universe will die, is it not? … Dynamic Universe Model says that the energy in the form of electromagnetic radiation passing grazingly near any gravitating mass changes in frequency and finally will convert into neutrinos (mass). Hence Dynamic Universe Model proposes another process where energy will be converted back into matter and the cycle energy to mass to energy continues, sustaining the Universe to maintain this present status for ever in this form something like a Steady state model without any expansion. This we will see in Part 2: Energy - Mass - Energy Cycle. After converting energy into mass “how various elements are formed and where they are formed?” will be next logical question. Dynamic Universe Model says that these various particles change into higher massive particles or may get bombarded into stars or planets and various elements are formed. Here we bifurcate the formation of elements into 6 processes. They are for Elementary particles and elements generated in frequency changing process, By Cosmic rays, By Small stars, By Large Stars, By Super Novae and Manmade elements By Neutron Stars. This we will discuss in Part 3: Nucleosynthesis.

基于TLE数据的大气密度反演与校正

用于航天器轨道预报的热层密度模型普遍存在30%左右的误差,影响LEO卫星的精密轨道确定和载荷控制。基于低轨航天器平运动变化与大气密度的关系,使用GRACE(gravity recovery and climate experiment)卫星TLE数据反演2003、2007年沿轨大气密度,通过比较反演值、模型值和实测值的关系分析误差产生原因,使用对数正态分布拟合密度比值。通过分析太阳辐射、地磁指数对大气密度变化的影响,提出一种基于空间环境指数的热层大气密度模型校正与预报方式。使用该方法对2003、2004、2007、2008年的MSIS86模型计算密度进行修正,将模型平均相对误差从33.33%~59.62%降低到11.55%~15.13%,太阳活动低年改进量是高年的1.5~2倍。对2009年经验模型结果进行预报校正,将预报误差降低36.49%,提高了模型精度。

BIM技术辅助空间异型薄壁混凝土结构施工技术

为高效且精确地完成现浇空间异型薄壁混凝土结构的施工,以熊猫基地扩建工程熊猫门建筑施工为载体,分析了BIM技术在施工过程中的应用。利用BIM建立空间曲面薄壁结构三维模型,并对曲面弧形结构进行有限元划分;通过建立模板支撑体系三维模型,导入MIDAS GEN后应用有限元分析计算,优化支架搭设方式,实现支撑体系的深化设计。结果表明:利用BIM技术辅助空间异型薄壁混凝土结构施工,提高了混凝土施工效率,节约了施工时间与成本。

海上油气井测试射孔峰值压力预测方法

为有效降低海上油气井射孔测试联作施工安全风险,以东海常用套管、油管、射孔枪、射孔弹组合为参考,建立了射孔管柱有限元数值模型。利用控制变量法,结合射孔峰值压力数值模拟结果,分析了总装药量、井筒初始压力、井筒爆炸空间等参数与射孔峰值压力的相关性,在此基础上,通过多元非线性回归建立了射孔峰值压力的计算公式。利用2口井射孔实测压力结果对公式进行验证,射孔峰值压力相对误差分别为6.1%和9.8%,在合理误差范围内。该公式可用于射孔作业前的峰值压力预测,为现场及时作出安全决策提供指导和支持。

针尖-样品距离对扫描微波显微成像的影响分析

随着芯片制备工艺的不断完善,半导体集成电路朝着小型化、集成化的方向不断发展,给近场微波成像技术带来了新的挑战。本文建立了探针-样品三维电磁耦合模型,并利用有限元数值分析法研究了探针针尖与样品之间的电磁相互作用。在不同探针-样品间距下,对硅基芯片表面结构进行扫描微波成像。成像结果与仿真结果相一致,随着针尖-样品间距的增加,扫描微波测试系统的灵敏度和分辨率降低。对于由原子力显微术结合微波测量技术发展而来的扫描微波显微镜的改进与产业化具有重大意义。

城市地下空间内涝成因及污染风险预警研究

当地下空间内涝时,会使排水系统失效,废水难以顺利排除。这将导致污水在地下空间中滞留,引发废水中有机物、重金属、油脂和细菌的积累,对地下水质量和生态健康构成威胁。为此,提出了城市地下空间内涝成因及污染风险预警研究。构建区域排水模型来获得城市地下内涝模型,基于内涝模型对内涝成因展开分析,得到三个内涝成因作为评价指标,利用改进的物元可拓法对内涝污染风险等级展开评估,根据风险等级展开预警。实验结果表明,该方法的数据监测效果好、风险预警效率高,可以有效降低城市内涝污染现象发生频率。

异形空间钢楼梯结构设计

随着建筑日益向高品质方向发展,各种造型新颖的楼梯应运而生。结合启迪设计大厦六折空间曲桥楼梯和四折弹簧空间楼梯等,介绍了异形空间钢楼梯设计在边界条件的确定、结构布置、受力特性、分析方法、构造细节、中间约束和支座设计、舒适度验算等方面与普通楼梯的区别和特点,以及异形钢楼梯荷载试验,可供异形空间钢楼梯结构设计参考。

空间扭索面曲塔斜拉桥振动破损有限元仿真

为了提高斜拉桥的安全性和稳定性,提出空间扭索面曲塔斜拉桥振动破损有限元仿真方法。使用向量有限元模型研究桥梁的动态特性,得出空间扭索面曲塔斜拉桥每个质点的内力和外力分布情况,通过中心差分法计算出桥梁每个质点位置,得出斜拉桥的最大应力。扩展有限元模型,分别计算斜拉桥纤维拉伸失效、纤维压缩失效、基体拉伸失效以及基体压缩失效的四种空间扭索面曲塔斜拉桥破坏模式判定方式,实现斜拉桥破坏的有限元分析。仿真结果表明,所提方法的桥梁频率振动与实际结果拟合较好,计算步长少,损伤破坏分析效率较高。

城市装配式天桥施工技术与应用

为解决大跨度钢结构拼装人行天桥的施工精度、施工吊装等问题,通过BIM+Midas Gen有限元分析软件对钢结构天桥进行几何建模和网格划分,建立起三维空间模型,对结构进行分析、分段分节优化、安装方法优化等一系列措施,同时增加应用钢结构二维码追溯管理系统,建立钢结构和吊装构件模型,能够迅速、准确地完成结构分析和设计,使吊装受力分析快速化、准确化、可视化。结果表明:采用BIM+Midas Gen有限元分析软件建立三维空间模型可以得到钢结构天桥的几何构造特征,并通过控制三维坐标点,利用相贯线编程软件进行编程,生成相贯口的切割数据,将切割数据输入切割机进行管件的切割,提高钢管相贯线切割的精度。研究成果也可为跨径为30 m以上的人行天桥钢结构吊装、拼装及焊接施工提供新思路。

小间距双柱盖梁墩抗震性能研究

由于地形限制,双柱盖梁墩的间距受到严格的控制。通过SAP2000,对小间距双柱盖梁墩的建模进行空间有限元动力分析,可以得到其在地震荷载作用下的纵横向桥墩和桩基的地震响应。利用UCFyber软件,建立纤维单元模型,对桥墩和桩基截面进行抗弯能力分析(考虑轴力),从而检验小间距双柱盖梁墩在地震荷载作用下的桥墩和桩基的抗震力学性能,对今后相应结构的抗震性能分析具有一定的参考意义。

某泵站工程双排桩前后排桩不等距的研究与应用

双排桩基坑围护结构是由前、后排桩通过桩顶的连系梁形成一个超静定刚架的结构。目前关于如何计算双排桩前后桩不等距的研究相对较少。为此,以某排涝泵站工程为例,利用有限元Midas GTS NX软件建立三维模型,进行整体分析,并对双排桩结构进行受力分析及其对周围环境的沉降分析。研究发现:双排桩的前后桩受力状态不一致,可以据此进行分段配筋以节约造价;围护结构的连梁节点是其能否发挥作用的关键。

大跨度斜拉桥与T构协作体系的动力特性分析

协作体系的动力特性主要包括体系的自振频率和主振型,它是协作体系结构动力分析的基础和前提。通过建立空间有限元模型,对金马大桥这种独特的协作体系结构进行了动力特征分析,给出了前20阶频率和相应的振型,并且对同等跨径的普通斜拉桥和剪力铰方案做了相应的动力特征比较分析,同时分别计算了各种结构参数变化对协作体系结构动力特性的影响,对其影响规律作了详细的讨论,本文的结果为协作体系的固有振动分析和抗震设计提供了理论依据。

空间飞网抛射展开动力学建模与仿真

空间飞网是由轻质绳索编织的在轨展开网状物体,主要用于在轨捕获。作为在轨服务的关键技术之一,飞网捕获技术受到国际空间技术领域越来越广泛的关注。当前国际上空间飞网的展开方式主要有三种:旋转展开、刚性构件支撑展开和直接抛射展开。其中,直接抛射展开方式的发射装置结构最为简单,但飞网的动力学行为最为复杂。本文针对飞网直接抛射展开的动力学过程,建立了正方形绳网、牵引质量块和发射器机构的力学模型,提出了飞网抛射效果的衡量标准,分析了影响飞网抛射效果的主要因素。为了分析飞网展开过程,建立了正方形空间飞网运动的解析模型;应用绝对节点坐标方法建立了正方形空间飞网的有限元模型,并在软件THUsolver上进行了数值仿真。本文选取多种不同工况,应用上述两类模型进行计算和仿真,并分析结果数据,得到主要因素对空间飞网抛射效果的影响。两类模型所得定性结论相一致。

空间飞网系统抛射参数优化研究

空间飞网由轻质绳索编织、通过抛射展开形成一定构型网,作为在轨服务的关键技术之一,在空间在轨服务、飞行器回收、轨道清理、空间拦截等领域具有巨大的应用潜力。本文采用ABAQUS建立不同折叠方式松弛飞网有限元模型并进行动力学仿真,提出了飞网展开效果衡量标准,比较了折叠方式对飞网展开性能参数的影响,对飞网的抛射参数:牵引质量块质量、抛射角度、抛射速度进行了优化设计。仿真表明,折叠方式的优劣是飞网有效展开的关键;在给定的参数范围内,得到了飞网抛射参数的最优值。

火灾下空间混凝土框架结构的反应分析与模拟

根据作者开发并经过试验验证的纤维梁单元模型和分层壳单元模型,通过考虑他们之间的协调关系,建立了考虑楼板的空间混凝土框架结构火灾反应数值模型,并通过作者开发的火灾反应分析系统RCF ire,实现了整体结构的火灾反应分析。纤维梁单元模型和分层壳单元模型均通过在截面上进行细分,从而考虑了不均匀温度场及材料非线性的影响。通过对一个具体框架火灾反应的分析,探讨了整体结构火灾反应的规律,为结构设计人员提高建筑结构的火灾安全提供参考。

虚拟作战空间环境及其数据描述与交换方法研究

虚拟作战空间环境(又称数字化作战空间环境)是重点研究对战争有重要影响的大气、海洋和太空环境现象变化规律和效应的建模与表现及其数字化产品制作的新技术领域。简述了作战空间环境的概念及其对战争的影响、虚拟作战空间环境的概念及其技术挑战;探讨了SEDRIS(综合环境数据描述与交换标准)在构建虚拟作战空间环境中的应用问题;以气象要素为例,阐述了基于SEDRIS标准对自然现象要素进行建模、仿真与可视化,以及自然现象要素与三维战场场景的合成方法。

梁-壳混合分析模型在客车骨架接头焊缝间距优化中的应用

运用基于超单元技术的梁-壳单元混合分析模型对客车侧围骨架接头局部特性进行分析,总结了接头处焊缝间距的大小对接头局部强度的影响,可为改进客车局部结构设计提供参考依据。