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81.
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多维平差问题粗差的局部分析法 总被引:1,自引:0,他引:1
用一个水准网说明了依据改正数进行粗差处理可能导致错误,而且粗差能够被正确处理与其所处的位置有关。为了解决这个问题,本文提出了局部分析法。局部分析法从多维平差问题的函数模型出发,根据设计矩阵得到一个被观测量的多个独立观测,包括被观测量的观测值和其他观测值的函数,并且给出了根据平差问题的设计矩阵搜索这些函数的方法。根据独立观测的数目即可判断被观测量的观测值能否容忍粗差。在此基础上提出了一种根据真误差判断被观测量的独立观测所涉及到的观测值是否含有粗差的方法。最后用一个测角网说明局部分析法和粗差探测方法的过程。 相似文献
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对土石坝心墙掺砾黏土开展模拟心墙单元小主应力方向加载的真三轴试验,首先对试样进行不同围压条件下等向固结,然后保持小主应力恒定,通过调整大主应力和中主应力,以模拟土石坝竣工后的初始三向应力状态。试验过程中保持大主应力和中主应力恒定,从小主应力方向单向加载,以模拟土石坝蓄水过程中心墙单元所经历的应力路径。试验结果与常规三轴试验以及复杂应力条件下大主应力方向真三轴加载试验结果都有显著不同。不同初始应力条件下,不同主应力方向的初始切线模量和初始切线泊松比的变化规律非常复杂,应力–应变显现出明显的各向异性。在心墙堆石坝施工过程及蓄水过程中,心墙单元所经历的应力路径明显不同,合理的土体本构模型应该对这种由于加荷路径不同所引起的不同方向模量和泊松比进行合理描述。 相似文献
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为了研究复杂应力条件下非饱和原状黄土的非线性本构模型,通过考虑真三轴条件下中主应力和吸力对大主应变的影响,提出了一个考虑中主应力影响的非饱和原状黄土的非线性本构模型。该模型包含12个参数,均可由常含水率非饱和土真三轴试验确定。研究了中主应力对土体变形和强度的影响,探讨了模型参数的变化规律。初始吸力一定时,土体的黏聚力随着中主应力的增大而增大,而内摩擦角随着中主应力的增大呈线性减小趋势。当吸力小于162 kPa时,吸力摩擦角等于21.8°;当吸力大于162 kPa时,吸力摩擦角等于5.5°。初始吸力相同时,不同中主应力条件下土体的体积模量可取为常数。利用该模型预估了常含水率真三轴等向固结试验的吸力变化规律,理论结果与试验结果比较接近。但是对于真三轴剪切试验吸力的预估还需要进行深入探讨。 相似文献
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利用真三轴岩爆试验系统,开展了不同饱水度红色粗晶花岗岩的岩爆试验,分析了不同饱水度下岩爆破坏岩样的强度与变形特征、破坏与弹射特征、声发射特性等,探讨了岩石饱水度与岩爆弹射动能的定量关系以及水对岩爆的影响机制。研究结果表明:(1)当岩样的相对饱水度超过0.3,其峰值应力和屈服应力较天然状态的明显降低;(2)岩样饱水度的增加使得岩爆过程中小颗粒弹射减少、小岩片剥落增多、岩板外鼓现象减弱,且岩爆坑体积减小、岩爆碎块的粒径分布由连续分布变为不连续分布;(3)随饱水度的增加,岩爆发生前夕声发射撞击数显著下降的平静期的总历时呈缩短趋势,岩爆发生时刻的声发射撞击数呈增大趋势,且累积绝对能量呈减小趋势、能量释放速度呈放缓趋势,表明岩样塑性破坏特性有所增强;(4)岩爆弹射动能随饱水度的增大而显著减小,二者呈单调线性的负相关关系,水对岩石的作用主要是软化和水楔作用,水的黏性也会对碎块弹射产生影响。 相似文献
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Two models of masonry infilled reinforced concrete frame buildings were tested at the shaking table. Models were built in the reduced scale 1:4 using the materials produced in accordance to modelling demands of true replica modelling technique. The first model represented a one‐storey box‐like building and the second one the two‐stories building with plan shaped in the form of a letter H. Models were shaken with the series of horizontal sine dwell motions with gradually increasing amplitude. Masonry infills of tested models were constructed of relatively strong bricks laid in weak mortar. Therefore, typical cracks developed and propagated along mortar beds without cracking of bricks or crushing of infill corners. Data collected from tests will be used in future evaluation, verification and development of computational models for prediction of in‐plane and out‐of‐plane behaviour of masonry infills. The responses of tested models can be well compared with global behaviour of real structures using the modelling rules. The similarity of local behaviour of structural elements, e.g. reinforced concrete joints, is less reliable due to limitations in modelling of steel reinforcement properties. The model responses showed that buildings designed according to Eurocodes are able to sustain relatively high dynamic excitations due to a significant level of structural overstrength. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
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Amplitude versus offset information is a key feature to seismic reservoir characterization. Therefore amplitude preserving migration was developed to obtain this information from seismic reflection data. For complex 3-D media, however, this process is computationally expensive. In this paper we present an efficient traveltime based strategy for amplitude preserving migration of the Kirchhoff type. Its foundations are the generation of traveltime tables using a wavefront-oriented ray-tracing technique, and a generalized moveout relation for 3-D heterogeneous media. All required quantities for the amplitude preserving migration are computed from coarsely gridded traveltime tables. The migration includes the interpolation from the coarsely gridded input traveltimes onto the fine migration grid, the computation of amplitude preserving weight functions, and, optionally, the evaluation of an optimized migration aperture. Since ray tracing is employed for the traveltime computation the input velocity model needs to be smooth, i.e. velocity variations of spatial dimensions below the wavelength of the considered reflection signals are removed. Numerical examples on simple generic models validate the technique and an application to the Marmousi model demonstrates its potential to complex media. The major advantage of the traveltime based strategy consists of its computational efficiency by maintaining sufficient accuracy. Considerable savings in storage space (105 and more for 3-D data with respect to no interpolation at all) can be achieved. The computational time for the stack can be substantially reduced (up to 90% in 3-D) with the optimized migration aperture since only those traces are stacked which really contribute to the image point under consideration. 相似文献
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We report here new geochronological and paleomagnetic data from the 802±10 Ma Xiaofeng dykes in South China. Together with existing data, these results suggest that Rodinia probably spread from the equator to the polar region at ca. 800 Ma, followed by a rapid ca. 90° rotation around an axis near Greenland that brought the entire supercontinent to a low-latitude position by ca. 750 Ma. We propose that it was the initiation of a mantle superplume under the polar end of Rodinia that triggered an episode of true polar wander (TPW) which brought the entire supercontinent into equatorial latitudes. An unusually extensive emerged land area at the equator increased both atmospheric CO2 drawdown and global albedo, which, along with waning plume volcanism led directly to the low-latitude Sturtian glaciation at ca. 750–720 Ma. 相似文献