共查询到19条相似文献，搜索用时 421 毫秒
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为了选择适用于复杂连续弯道的二次流修正方法,选取了线性方法中两种典型的计算模式,通过在正交曲线坐标系二维浅水动量方程中增加扩散应力项开发了考虑二次流影响的平面二维水流模型。基于不同复杂度的4个连续弯道试验的水位和流速分布资料,通过理论分析和数值试验对比定量评估了传统二维模型和两种二次流修正方法在连续弯道水流模拟中的效果。测试结果表明,Delft3D模型的二次流修正方法自由度较高,适用于不同复杂度的连续弯道水流模拟,而Lien模型二次流修正方法适用于微弯或中弯,应用于中弯时需要慎重选用,不适用于急弯连续弯道模拟。两种方法比较,建议连续弯道水流模拟中优选Delft3D模型的二次流修正方法。 相似文献
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河流泥沙模拟技术进展与展望 总被引：4，自引：1，他引：4
本文系统总结了河流模拟技术的发展过程和研究成果。河流模拟技术包括河流实体模型和泥沙数学模型两部分。在实体模型方面,已建立了一整套河工模型的相似理论、设计方法和试验技术,在模型变态、模型沙选择、高含沙水流模拟、模型测验等方面取得了重要的研究成果,并解决了大量的工程泥沙问题。在数学模型方面,建立了一维、二维和三维泥沙数学模型,并随着泥沙基本理论研究的不断深入与广泛的工程应用,在计算模式、数值计算方法、计算结果的后处理、参数选择、高含沙水流问题处理等方面均取得了重要进展。本文还展望了河流模拟技术今后的发展方向。 相似文献
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为研究河型转化过程机理,建立了考虑弯道二次流影响与边岸崩塌过程的平面二维河流数学模型,包括水流模型、泥沙模型和边岸崩塌模型。通过在水流动量守恒方程中增加弥散应力项以考虑弯道二次流的影响,并采用室内水槽实验结果对水流模型进行了验证;利用上荆江沙市至石首天然长河段的水沙过程和河道演变资料,对泥沙模型进行了验证;结果表明本模型数值计算量合适,有较好的适应范围。模型中提出了边岸崩塌过程的模拟技术,相对于传统平面二维水沙模型而言,可以更好地模拟天然河道的横向摆动以及洲滩消长过程。 相似文献
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采用DynaRICE二维河冰模型模拟弯道及其取水口附近的水面冰运动和堆积过程,探讨弯道取水口导冰筏的优化设计。该模型耦合了水动力方程和冰动力方程,分别采用有限元法和光滑粒子流体动力学法对水动力方程和冰动力方程进行求解。模拟得到弯道取水口处水流水力特性、不同角度导冰筏下河冰运动规律及其受力情况。结果表明河冰靠弯道凹岸一侧运动,并在取水口附近及其下游堆积,横向环流对河冰运动影响可忽略,取水口上游设置角度和长度合理的导冰筏可有效阻止河冰进入引水渠。但是,下游也需设置导冰筏来防止河冰在取水口下游堆积及向上游延伸到取水口。 相似文献
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采用DynaRICE二维河冰模型模拟弯道及其取水口附近的水面冰运动和堆积过程,探讨弯道取水口导冰筏的优化设计。该模型耦合了水动力方程和冰动力方程,分别采用有限元法和光滑粒子流体动力学法对水动力方程和冰动力方程进行求解。模拟得到弯道取水口处水流水力特性、不同角度导冰筏下河冰运动规律及其受力情况。结果表明河冰靠弯道凹岸一侧运动,并在取水口附近及其下游堆积,横向环流对河冰运动影响可忽略,取水口上游设置角度和长度合理的导冰筏可有效阻止河冰进入引水渠。但是,下游也需设置导冰筏来防止河冰在取水口下游堆积及向上游延伸到取水口。 相似文献
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为了更好地把握溃坝洪水风险,减小因溃坝洪水而造成的人员生命和财产损失,建立了基于Godunov格式的一维、二维溃坝水流耦合数学模型。一维溃坝水流模型采用HLL格式的有限体积法求解,二维溃坝水流模型采用基于非结构网格的Roe格式离散求解,在一维、二维模型的链接处采用重叠计算区域的方法实现一维模型和二维模型之间的水力要素信息交换。经弯道溃坝算例和断面突变溃坝算例验证,该耦合模型具有良好的可靠性和适用性,验证后的耦合模型为大尺度的溃坝水流数值模拟打下了基础。 相似文献
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通过分析不同长度的过渡段对连接连续弯曲河道后弯水流的影响,探讨航道整治工程设计中过渡段长度的确定依据。在模型试验资料验证的基础上,采用RNG k-ε湍流模型和VOF方法处理自由水面的水气两相流数学模型,对连续弯道水流进行模拟计算。对比不同过渡段长度条件下后弯水流特征的变化情况,发现增加过渡段长度可以减弱前弯对后弯水流的影响。当相对过渡段长度大于一定数值后,后弯的特征水流情况保持稳定,增加过渡段长度所引起的减弱前弯水流对后弯水流影响的效应基本丧失。以后弯水流条件趋于稳定为特征定义临界过渡段长度,可作为航道尺度设计中过渡段长度取值的计算基础。 相似文献
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John M. MacDonald John Wheeler Simon L. Harley Elisabetta Mariani Kathryn M. Goodenough Quentin Crowley Daniel Tatham 《Contributions to Mineralogy and Petrology》2013,166(1):21-41
Zircon is a key mineral in geochemical and geochronological studies in a range of geological settings as it is mechanically and chemically robust. However, distortion of its crystal lattice can facilitate enhanced diffusion of key elements such as U and Pb. Electron backscatter diffraction (EBSD) analysis of ninety-nine zircons from the Lewisian Gneiss Complex (LGC) of northwest Scotland has revealed five zircons with lattice distortion. The distortion can take the form of gradual bending of the lattice or division of the crystal into subgrains. Zircon lattices are distorted because of either post-crystallisation plastic distortion or growth defects. Three of the five distorted zircons, along with many of the undistorted zircons in the population, were analysed by ion microprobe to measure U and Pb isotopes, Ti and REEs. Comparison of Th/U ratio, 207Pb/206Pb age, REE profile and Ti concentration between zircons with and without lattice distortion suggests that the distortion is variably affecting the concentration of these trace elements and isotopes within single crystals, within samples and between localities. REE patterns vary heterogeneously, sometimes relatively depleted in heavy REEs or lacking a Eu anomaly. Ti-in-zircon thermometry records temperatures that were either low (~700 °C) or high (>900 °C) relative to undistorted zircons. One distorted zircon records apparent 207Pb/206Pb isotopic ages (?3.0 to +0.3 % discordance) in the range of ~2,420–2,450 Ma but this does not correlate with any previously dated tectonothermal event in the LGC. Two other distorted zircons give discordant ages of 2,331 ± 22 and 2,266 ± 40 Ma, defining a discordia lower intercept within error of a late amphibolite-facies tectonothermal event. This illustrates that Pb may be mobilised in distorted zircons at lower metamorphic grade than in undistorted zircons. These differences in trace element abundances and isotope systematics in distorted zircons relative to undistorted zircons are generally interpreted to have been facilitated by subgrain walls. Trace elements and isotopes would have moved from undistorted lattice into these subgrain walls as their chemical potential is modified due to the presence of the dislocations which make up the subgrain wall. Subgrain walls provided pathways for chemical exchange between crystal and surroundings. Only five per cent of zircons in this population have lattice distortion suggesting it will not have a major impact on zircon geochronology studies, particularly as three of the five distorted zircons are from strongly deformed rocks not normally sampled in such studies. However, this does suggest there may be a case for EBSD analysis of zircons prior to geochemical analysis when zircons from highly deformed rocks are to be investigated. 相似文献
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针对地形对电磁测量结果的影响,设计了一组带地形模型,采用有限差分法对其进行了正演模拟计算。对模拟结果进行了分析,总结了地形对电磁测量视电阻率的影响规律,即TM模式比TE模式易受地形影响,山顶比山谷易受地形影响。在此基础上,分析了常用地形校正方法的优缺点;理论模型和实测资料反演结果表明带地形的二维联合反演可有效消除地形影响。 相似文献
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章礼明 《中国地球化学学报》1993,12(1):92-96
By using the Lagrange‘s intermediate value theorem,it is derived mathematically that the structur-al distortion of a coordination polyhedron may lead to an increase in bond-valence sum of the cen-tral atom of ion .The applicabilities of the bond-valence model are discussed in the following two cases:the modeling of crystal structure ,and the indication of distortion degree of a coordination polyhedron.Also it is shown that a distorted polyhedron should be in favor of a longer average bond length or a smaller coordination number. 相似文献
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Two-dimensional electrical resistivity tomography data acquired on the crest of the embankment are distorted by the 3D effect of the embankment geometry, reservoir water level and abutment. The distortion affects seriously the final solution of the 2D inverse problem. By comparing the apparent resistivity pseudosections from a 3D and 2D electrical resistivity model of the embankment, the distortion degrees of the apparent resistivity pseudosections along the axis on the crest were estimated for the cases of reservoir and which does not contain water. The obtained results indicate that the distortion degree acquired in the case of a reservoir that contains water was much less than that in the case of the reservoir that does not contain water. In the case of reservoir that contains water, the apparent resistivity pseudosections of the P–P and ED–ED arrays had the largest distortion degree and of D–D, W–S and P–D arrays had the smallest distortion degree. In the case of the reservoir that does not contain water, the apparent resistivity pseudosection of P–P array had the smallest distortion among all arrays. Through modeling investigation, a correction process to reduce the distortion of the apparent resistivity pseudosection was proposed. The correction process was tested in the embankment model, and two field works were carried out in the To Lich River in Hanoi and Khuan Cat embankment in Lang Son province, Vietnam. It is possible to bring the distortion of the apparent resistivity pseudosection down to 2.8–13.9%, depending on the type of electrode arrays and the type of reservoirs, containing or does not contain water. The distortion correction of the apparent resistivity pseudosection is strongly recommended before doing the 2D inverse interpretation. 相似文献
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S. C. Kohn J. M. Charnock C. M. B. Henderson G. N. Greaves 《Contributions to Mineralogy and Petrology》1990,105(3):359-368
The structural environments of Mn2+ and Sr2+ at concentrations of 0.2–0.8 wt% in dry and hydrous silicate glasses have been studied using X-ray absorption spectroscopy (EXAFS and XANES). The environment of Mn in hydrous silica glasses containing 4.5 and 6.0 wt% H2O appears to be close to an undistorted octahedral site, whereas Mn in other compositions, both dry and hydrous, occupies either a distribution of octahedral and tetrahedral sites, or distorted, non-centrosymmetric sites. The fraction of non-centrosymmetric sites (including tetrahedral) or the average degree of distortion of the sites decreases with both increasing dissolved water concentration and number of non-bridging oxygens in the glass. For Sr the changes as a function of polymerisation and water concentration are less clear, but it appears that the average Sr-O distances are shorter than in crystalline silicates and decrease further with decreasing polymerisation. The structural data obtained in this study are not readily integrated with previous partitioning data for Mn, suggesting that changes in the first-shell coordination geometry of Mn do not play a direct role in controlling the melt compositional dependence of trace element partition coefficients. It is tentatively suggested that distortions of the framework resulting from the incorporation of Mn (i.e. a second shell effect) control the partitioning behaviour. 相似文献
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压剪应力条件下各向异性岩石损伤本构模型和渗流模型(Ⅰ)：理论模型 总被引：4，自引：4，他引：0
采用细观力学研究了岩石损伤变形过程和渗流过程。在本构模型中增加了对剪胀变形机理和渗流对变形影响的内容,同时按照微裂纹发展过程建立了考虑微裂纹扩展、变形和渗透压影响的岩石各向异性渗流模型,使得模型能够更好地表述岩石的变形特性和渗流特性。所建立的模型能够考虑微裂纹闭合摩擦滑移、微裂纹发生自相似扩展和微裂纹发生弯折扩展等过程。 相似文献
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中国大陆地壳和岩石圈化学成分模型可信吗? ——来自大地热流值的检验 总被引：3，自引：0，他引：3
大地热流值是大陆地壳和岩石圈U，Th,K丰度的直接约束；根据地球化学元素丰度值推算出的大地构造单元的区域地壳热流值，必定不能大于区域的平均热流值，根据700余个实测大地热流数据，对目前发表的中国大陆地壳和岩石圈的化学成分模型进行了检验，结果表明，多数模型不能满足大地热充约束，如黎彤等的关于中国大陆及其内部构造单元的地壳和岩石圈成分模型，倪守斌等提出的新疆北部地壳生热率模型，以及高山等提出的扬子地台北缘地壳成分模型，这些模型的U，Th,K丰度值不太可靠，其他强不相容元素的丰度值的可信程度亦值得怀疑，而迟清华，鄢明才提出的华北地台地壳成分模型和高山等建立的中国东部及华北地台和秦岭造山带的地壳成分模型通过了区域大地热流的检验。 相似文献