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31.
A simplified analytical model including the coupled effects of the wheel–rail–soil system and geometric irregularities of the track is proposed for evaluation of the moving train load. The wheel–rail–soil system is simulated as a series of moving point loads on an Euler–Bernoulli beam resting on a visco-elastic half-space, and the wave-number transform is adopted to derive the 2.5D finite element formulation. The numerical model is validated by published data in the literature. Numerical predictions of ground vibrations by using the proposed method are conducted at a site on the Qin-Shen Line in China. 相似文献
32.
L. G. Taff 《Experimental Astronomy》1990,1(4):237-266
There are two guiding modes of the Hubble Space Telescope used for the acquisition of astronomical data by one of its six scientific instruments. The nominally more precise one is called Fine Lock and the other is known as Coarse Track. Two of the three Fine Guidance Sensors are locked onto Guide Stars, in one of these two modes, thus maintaining the spacecraft's line of sight to a few milli-arc seconds (nominally 7 milli-arc seconds for Fine Lock and 17 milli-arc seconds for Coarse Track). In this paper I report on the most realistic and extensive simulations to date of the Coarse Track guidance mode. These simulations clearly show that the precision of Coarse Track is influenced by one adjustable parameter and that for default operating conditions its precision is 12 milli-arc seconds. A factor of two improvement should be possible by modifying the key parameter which governs the precision of Coarse Track. The importance of this for the scientific mission on the Hubble Space Telescope is that the use of Coarse Track in place of Fine Lock will result in a 1/3 reduction of engineering overhead per scientific target acquisition.See text for a full explanation. 相似文献
33.
Sensitivity experiments are conducted for three cases of cyclones for investigating the impact of different vortex initialization
schemes on the structure and track prediction of the cyclone using India Meteorological Department’s Limited Area Model. The
surface wind and pressure profiles generated using Holland and Rankine initialization schemes differ from each other. These
different generated profiles are compared with the actual data and the root mean square error (RMSE) was calculated between
them. In case of the Holland vortex, ‘b’ is found to be equal to 1.5 and 2.0 respectively for two cases of very severe cyclonic storms in the Arabian Sea, namely
6–10 June 1998 and 16–20 May 1999 and 2.25 for the severe cyclonic storm in the Bay of Bengal. The ‘α’ parameter in Rankine’s
scheme was found to be 0.5 for two cases and 0.4 for the third system. This shows that cyclones differ even if they attain
the same intensity. The values of these parameters i.e. ‘b’ and ‘α’ are used for generating the synthetic wind data for individual cyclones and the same is used in the data assimilation
system. The analysis and forecast generated for the above cases using the Holland scheme show that the simulated structure
has characteristics closer to the actual storm; however, the Rankine scheme shows a weaker circulation. The mean track error
for three cases in the Holland scheme is 93, 149, 257 and 307 km in 12-, 24-, 36- and 48-h forecast. The mean track errors
for the Rankine scheme are 152, 274, 345 and 327 km, respectively, for the same period. 相似文献
34.
轨道交通工程联系测量方法的应用 总被引:3,自引:0,他引:3
结合北京城市轨道交通建设中测量的实际经验,通过对联系测量应用实例的介绍和隧道贯通测量数据的统计,对影响隧道工程安全贯通的重要环节一联系测量的方法和手段进行了总结,供测量工作者参考。 相似文献
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37.
为了探究冬季(12~2月)北大西洋地区风暴轴与海温异常的关系,利用伴随AO(Arctic Oscillation)出现的"三核型"海温异常对大气环流模式CAM3.0进行强迫,将模拟结果与NCEP/NCAR再分析资料做对比,发现CAM3.0在该SSTA强迫下可以再现伴随AO异常出现的风暴轴与急流异常,结论可概括为:海温正(负)异常时,北大西洋风暴轴增强(减弱),北美急流出口区向北(向南)摆动;"三核型"海温异常作为外强迫源,可能通过2种途径影响风暴轴的强度:首先通过热力作用改变中纬度低层大气斜压性来直接影响风暴轴,其次通过影响北美急流出口区的南北摆动来间接影响风暴轴;另外,海温正(负)异常可以增强(减弱)瞬变波与基本气流之间的正反馈效应。 相似文献
38.
Shuguang Zhang Xinbiao Xiao Zefeng Wen Xuesong Jin 《Soil Dynamics and Earthquake Engineering》2008,28(8):662-673
The paper reviews some important published papers on the effects of railway track imperfections on track dynamic behavior, and investigates the effect of unsupported sleepers on the normal load of wheel/rail in detail through a numerical simulation. The numerical simulation is based on a coupling dynamic model of vehicle–track. In the model, the vehicle is modeled as a multi-body system, and the track is considered as a 3-layer model with rails, sleepers, and ballast masses. Each rail of the track is modeled with a Timoshenko beam resting on discrete sleepers. The lateral, vertical, and torsional deformations of the beam are taken into account. The sleepers are assumed to move backward at a constant speed to simulate the vehicle running along the track at the same speed, and therefore such a track model can consider the effect of the discrete support by sleepers on the coupling dynamic behavior of the vehicle and track in the simulation. In calculating the coupled vehicle and track dynamics, Hertzian contact theory and the theory by Shen et al. are, respectively, used to calculate the normal forces and the creep forces between the wheels and the rails. The motion equations of the vehicle–track are solved by means of an explicit integration method. A nonlinear spring and a nonlinear damper are used to simulate a gap between the unsupported sleeper and the ballast mass. The numerical results obtained indicate that the gaps between the unsupported sleepers and ballast masses have a great influence on the normal load of the wheel and the rail. 相似文献
39.
2009年夏季西太平洋台风路径和强度的多模式集成预报 总被引:6,自引:3,他引:3
基于TIGGE资料中的中国气象局、欧洲中期天气预报中心、日本气象厅和英国气象局等四个中心的2009年5月1日-8月31日台风预报资料,利用多模式集合平均、消除偏差集合平均和加权消除偏差集合平均等方法,对2009年8月1-31日预报期的西太平洋的台风路径和强度(中心气压)进行24~ 72 h预报时效的多模式集成预报,并对0907号台风“天鹅”和0908号台风“莫拉克”进行个例分析.结果表明:各中心对于不同时效的预报,预报技巧有明显差异.消除偏差集合平均与加权消除偏差集合平均显著地减小了预报误差,预报效果优于最好的单个中心预报和多模式集合平均.对于24 ~ 72 h预报,加权消除偏差集合平均方法始终表现出最好的预报性能. 相似文献
40.
Charles W. Helm Julien Benoit Adrienne Mayor Hayley C. Cawthra Cameron R. Penn-Clarke Renee Rust 《Proceedings of the Geologists' Association. Geologists' Association》2019,130(5):541-558
Compared with other parts of the world, the study of geomythology in southern Africa, and the associated documentation of non-western awareness of palaeontological and geological phenomena, is in an early phase. We focus on examples of rocks and fossils as items of special interest and curiosity, and we search for evidence of an indigenous palaeontology and geology. We review twenty-one sites or cases for which published accounts exist, and we describe a newly identified trilobite manuport site. In combination these sites provide various levels of evidence of palaeontological and geological awareness exhibited by non-western cultures in southern Africa, and how these cultures incorporated this knowledge into their understanding of their world. We anticipate that in time a diverse heritage of such ‘natural knowledge’ may become evident in southern Africa, aided in part by recognition of the possibility that rock art images may be associated with awareness of body fossils and trace fossils. We suggest ways in which further analysis may bolster this contention. 相似文献