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GPS坐标时间序列呈现显著的季节性变化,通常认为大气压、非潮汐海洋负载及水文负载(统称为地表质量负载)是引起测站谐波变化的主要因素.本文计算了不同地表质量负载造成的测站位移,以此修正中国区域11个IGS基准站的坐标时间序列.建立了地球物理现象与测站季节性变化及噪声特性之间的初步数值联系,认为其会造成测站的噪声特性变化,主要表现为带通及随机漫步噪声特征,且仅能减小测站U分量的周年运动,但并不是造成测站U分量半周年运动及水平方向周年运动的主要原因.深入分析了造成中国区域IGS基准站非线性变化的其他可能因素,重点探讨了周日(S1)、半周日(S2)大气潮汐对基准站周年振幅的贡献,由此提出S1、S2大气潮汐是造成中国区域IGS基准站周年运动,尤其是中南部测站垂向周年运动的主要因素之一. 相似文献
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现有海洋可控源电磁三维数值模拟方法大多基于电导率各向同性介质理论,不能模拟海底地层电导率各向异性的实际情况.本文给出了电导率各向异性三维介质中电性源海洋可控源电磁二次电场的边值问题以及相应的变分问题,采用长方体单元对研究区域剖分,将场分量定义在剖分单元的边上,利用矢量有限单元法求解变分问题,实现了电导率任意各向异性海洋可控源电磁三维矢量有限元数值模拟.这个新的正演方法可以计算电导率任意各向异性三维地电模型的海洋可控源电磁响应,基于二次场矢量有限元法直接求解电磁场,避免了传统有限元方法可能遇到的伪解问题和难于处理电场法向分量不连续的问题,提高了数值模拟计算精度.一维电导率各向异性模型电磁场数值解与解析解吻合得相当好,无论在源附近还是远离源处相对误差均不超过1%.电导率各向异性二维模型的计算结果与已有文献采用的非结构有限元模拟结果十分吻合.三维地电模型数值模拟结果显示,电导率各向异性张量电导率主轴分量和欧拉角对不同装置海洋可控源电磁响应均有着明显的影响. 相似文献
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地磁台站和地磁卫星能观测到饱含钠、氯离子运动海水切割地球主磁场产生的感应磁场数据.计算潮汐感应电磁场的三维高精度空间分布是从潮汐电磁数据中获得海洋底部电导率结构的关键,更是设计与优化地磁台站、电磁卫星轨道的重要依据.现有的潮汐(或运动海水)感应电磁场正演计算方法普遍存在难以精确模拟真实海岸线、不均匀陆地与海水表层、复杂地球深部结构影响的问题,从而降低潮汐感应电磁数据的解释水平.为解决此问题,本文开发了一种基于四面体单元的潮汐感应电磁场矢量有限元计算方法,具备精确模拟真实海岸线、不均匀陆地与海水表层、复杂地球深部结构影响的能力.首先,推导了运动海水感应电磁场满足的边值问题,结合四面体单元,利用矢量有限元计算方法求解了运动海水感应电磁场.然后,利用最新的海洋深度与海底沉积层模型,建立了包含真实海岸线、不均匀陆地与海水电导率分布的地球三维电导率模型,以M2潮汐激励源为例计算潮汐感应电磁场,通过与球谐有限元和积分方程结果的对比,来验证本文方法的正确性.最后,利用计算的高精度M2、N2和O1潮汐感应电磁场信号... 相似文献
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2008年11月10日在青海柴达木盆地北缘发生了大柴旦M_W6.3地震,为了研究该地震的区域地震波传播与地面运动特征,本文利用地质资料和地壳速度结构研究成果,构建了柴达木盆地及周边区域三维传播介质模型,采用有限差分方法模拟了大柴旦地震波场传播过程以及地面运动分布特征.结果表明,柴达木盆地对波场传播有明显影响,表现为地震波传入盆地后在边界产生次生面波,盆地沉积物对地震波具有围陷作用,地震地面运动在盆地内振幅增大、持时延长.模拟结果给出的地震地面运动峰值速度分布以及理论地震图均和观测结果符合较好,反映数值模拟较好地给出了观测地面运动的主要特征以及传播介质模型的合理性. 相似文献
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高精度、快速有效的正演模拟算法是三维电磁正反演的前提.为了提高海洋电磁三维数值模拟的精度和效率,本文提出利用基于Gauss-Lobatto-Chebyshev（GLC）基函数的谱元法进行海洋可控源三维电磁正演模拟.谱元法结合有限元法和谱方法的优点.我们通过应用伽辽金加权残差法离散二次电场矢量亥姆赫兹方程,在单元内选择混合阶GLC多项式的张量积作为高阶矢量插值基函数,在求解大型稀疏线性方程组时利用直接求解器进行快速求解,从而实现了三维海洋可控源电磁快速高精度正演模拟.一维和三维模型正演结果验证了本文算法的有效性和准确性.典型模型的数值结果表明谱元法是一种有效的三维海洋可控源电磁正演数值方法,能在稀疏网格剖分情况下获得精确的海洋电磁正演模拟响应. 相似文献
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基于活动断层的地震危害性综合评价可为城市规划和工程建设提供科学依据， 强地面运动数值模拟则是进行地震危害性预测和评价的重要方法， 而建立以第四系为主体的符合真实地层结构的三维物理模型是保证数值模拟结果可靠性的必要条件之一. 本文以昆明盆地为例， 综合利用地震地质、钻孔、地形地貌、DEM、地震勘探、波速测试等资料，以剪切波速为主要分层指标，参考地层层序， 结合ArcGIS等多种软件和相关的编程技术，采用将相邻介质分界面（层网）在深度方向上逐层叠加的方法建立三维物理模型；详细阐述了建立三维物理模型的主要技术思路和实现过程， 同时建立三维物理模型的数据库，为强地面运动数值模拟提供模型数据和参数. 文中还针对不同类型的探测、实验数据，总结了相应的技术处理方法和需要注意的问题. 相似文献
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本文基于显式有限元法研究了地震波垂直入射时三维复杂山谷地形对地震地面运动的影响,在数值分析中应用了三维化二维的解法和黏弹性人工边界的处理方法,实现了地震波垂直输入下三维复杂场地地震动数值模拟,并验证了该方法的合理性.以四川桃坪地区一山谷地形作为研究对象,基于地表高程数据分别建立了二维和三维场地模型,对比研究表明:在复杂地形情况下考虑二、三维模型时具有明显差异,三维模型能更真实地反映地形变化对地震动的影响,复杂地形条件下有必要考虑三维实际场地模型.本文对边界自由场的处理方法也可用于处理三维复杂场地地震动斜入射问题,为三维复杂地形场地地震效应研究提供参考. 相似文献
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L. Li D. A. Barry C. Cunningham F. Stagnitti J. -Y. Parlange 《Advances in water resources》2000,23(8):176
Previous studies on tidal dynamics of coastal aquifers have focussed on the inland propagation of oceanic tides in the cross-shore direction, a configuration that is essentially one-dimensional. Aquifers at natural coasts can also be influenced by tidal waves in nearby estuaries, resulting in a more complex behaviour of head fluctuations in the aquifers. We present an analytical solution to the two-dimensional depth-averaged groundwater flow equation for a semi-infinite aquifer subject to oscillating head conditions at the boundaries. The solution describes the tidal dynamics of a coastal aquifer that is adjacent to a cross-shore estuary. Both the effects of oceanic and estuarine tides on the aquifer are included in the solution. The analytical prediction of the head fluctuations is verified by comparison with numerical solutions computed using a standard finite-difference method. An essential feature of the present analytical solution is the interaction between the cross- and along-shore tidal waves in the aquifer area near the estuary’s entry. As the distance from the estuary or coastline increases, the wave interaction is weakened and the aquifer response is reduced, respectively, to the one-dimensional solution for oceanic tides or the solution of Sun (Sun H. A two-dimensional analytical solution of groundwater response to tidal loading in an estuary, Water Resour Res 1997;33:1429–35) for two-dimensional non-interacting tidal waves. 相似文献
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Tidally induced upwelling off Yangtze River estuary and in Zhejiang coastal waters in summer 总被引：4，自引：0，他引：4
L 《中国科学D辑(英文版)》2007,50(3):462-473
MASNUM wave-tide-circulation coupled numerical model (MASNUM coupled model, hereinafter) is de-veloped based on the Princeton Ocean Model (POM). Both POM and MASNUM coupled model are ap-plied in the numerical simulation of the upwelling off Yangtze River estuary and in Zhejiang coastal waters in summer. The upwelling mechanisms are analyzed from the viewpoint of tide, and a new mechanism is proposed. The study suggests that the tidally inducing mechanism of the upwelling in-cludes two dynamic aspects: the barotropic and the baroclinic process. On the one hand, the residual currents induced by barotropic tides converge near the seabed, and upwelling is generated to maintain mass conservation. The climbing of the residual currents along the sea bottom slope also contributes to the upwelling. On the other hand, tidal mixing plays a very important role in inducing the upwelling in the baroclinic sea circumstances. Strong tidal mixing leads to conspicuous front in the coastal waters. The considerable horizontal density gradient across the front elicits a secondary circulation clinging to the tidal front, and the upwelling branch appears near the frontal zone. Numerical experiments are de-signed to determine the importance of tide in inducing the upwelling. The results indicate that tide is a key and dominant inducement of the upwelling. Experiments also show that coupling calculation of the four main tidal constituents (M2, S2, K1, and O1), rather than dealing with the single M2 constituent, im-proves the modeling precision of the barotropic tide-induced upwelling. 相似文献
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Prediction and prevention of the impacts of sea level rise on the Yangtze River Delta and its adjacent areas 总被引：4，自引：0，他引：4
The Yangtze River Delta region is characterized by high density of population and rapidly developing economy. There are low lying coastal plain and deltaic plain in this region. Thus, the study area could be highly vulnerable to accelerated sea level rise caused by global warming. This paper deals with the scenarios of the relative sea level rise in the early half period of the 21st century in the study area. The authors suggested that relative sea level would rise 25 50 cm by the year 2050 in the study area, of which the magnitude of relative sea level rise in the Yangtze River Delta would double the perspective worldwide average. The impacts of sea level rise include: (i) exacerbation of coastline recession in several sections and vertical erosion of tidal flat, and increase in length of eroding coastline; (ii) decrease in area of tidal flat and coastal wetland due to erosion and inundation; (iii) increase in frequency and intensity of storm surge, which would threaten the coastal protection works; (iv) reduction of drainage capacity due to backwater effect in the Lixiahe lowland and the eastern lowland of Taihu Lake region, and exacerbation of flood and waterlogging disasters; and (v) increase in salt water intrusion into the Yangtze Estuary. Comprehensive evaluation of sea level rise impacts shows that the Yangtze River Delta and eastern lowland of Taihu Lake region, especially Shanghai Municipality, belong in the district in the extreme risk category and the next is the northern bank of Hangzhou Bay, the third is the abandoned Yellow River delta, and the district at low risk includes the central part of north Jiangsu coastal plain and Lixiahe lowland. 相似文献
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Estuarine environments are influenced by both river flows and oceanic tidal movement of water, sediment, and nutrients, often forming ecosystems that are rich in resources and biodiversity. The Yellow River once carried the world’s largest sediment load, but artificial structures have transformed its hydrodynamic processes. An annual Water-Sediment Regulation Scheme(WSRS) was introduced to flush accumulated sediment from the Xiaolangdi Reservoir, which provides flood control and water storage.Ho... 相似文献
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This study focuses on the medium scale morphodynamics of the tidal flat and channel system Fedderwarder Priel, located in the Outer Weser estuary (Wadden Sea, Germany). Tidal channels and adjacent flats are highly dynamic systems whose morphologic evolution are driven by tidal, wind, and wave forcings. These coastal environments are an important ecosystem and react to changes in hydrodynamic conditions in various spatial and temporal scales. Based on annual medium-resolution digital elevation models from 1998 to 2016, we describe changes in the surface area over depth with hypsometries and use vertical dynamic trends in order to analyze and visualize the morphologic evolution of the Fedderwarder Priel and adjacent tidal channels. It is shown that several intertidal flats rise in the order of 1.3 to 5.6 cm/year. The findings indicate that the Outer Weser estuary was not in an equilibrium state for the investigated period, and tidal flats accreted with a rate exceeding mean sea level rise. 相似文献
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A convection-conduction model for analysis of the freeze-thaw conditions in the surrounding rock wall of a tunnel in permafrost regions 总被引：1，自引：0，他引：1
The results of simulated tidal current field, wave field and storm-induced current field are employed to interpret the depositional
dynamic mechanism of formation and evolution of the radial sand ridges on the Yellow Sea door. The anticlockwise rotary tidal
wave to the south of Shandong Peninsula meets the following progressive tidal wave from the South Yellow Sea, forming a radial
current field outside Jianggang. This current field provides a necessary dynamic condition for the formation and existence
of the radial sand ridges on the Yellow Sea seafloor. The results of simulated “old current field (holocene)” show that there
existed a convergent-divergent tidal zone just outside the palaeo-Yangtze River estuary where a palaeo-underwater accumulation
was developed. The calculated results from wave models indicate that the wave impact on the topography, under the condition
of high water level and strong winds, is significant. The storm current induced by typhoons landing in the Yangtze River estuary
and turning away to the sea can have an obvious influence, too, on the sand ridges. The depmitional dynamic mechanism of formation
and evolution of the radial sand ridges on the Yellow Sea seafloor is “tidal current-induced formation—storm-induced chang—tidal
current-induced recovery”.
Project supported by the National Natural Science Foundation of China (Grant No. 49236120). 相似文献
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Tidal straining effect on sediment transport dynamics in the Huanghe (Yellow River) estuary was studied by field observations
and numerical simulations. The measurement of salinity, suspended sediment concentration, and current velocity was conducted
during a flood season in 1995 at the Huanghe river mouth with six fishing boats moored at six stations for 25-h hourly time
series observations. Based on the measurements, the intra-tidal variations of sediment transport in the highly turbid river
mouth was observed and the tidal straining effect occurred. Our study showed that tidal straining of longitudinal sediment
concentration gradients can contribute to intra-tidal variability in sediment stratification and to asymmetries in sediment
distribution within a tidal cycle. In particular, the tidal straining effect in the Huanghe River estuary strengthened the
sediment-induced stratification at the flood tide, thus producing a higher bottom sediment concentration than that during
the ebb. A sediment transport model that is capable of simulating sediment-induced stratification effect on the hydrodynamics
in the bottom boundary layers and associated density currents was applied to an idealized estuary to demonstrate the processes
and to discuss the mechanism. The model-predicted sediment processes resembled the observed characteristics in the Huanghe
River estuary. We concluded that tidal straining effect is an important but poorly understood mechanism in the transport dynamics
of cohesive sediments in turbid estuaries and coastal seas. 相似文献
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SHEN Zhigang Department of Engineering Mechanics Shanghai Jiao Tong University Hua Shan Road Shanghai China. 《国际泥沙研究》2001,16(2)
SEDIMENT TRANSPORT IN TIIE YANGTZE RIVER ESTUARYSHEN Zhigang'ANSTa^CTThe hy~ntalc and the sedimen tranSport Patter'nS within the estUaIy of the YangtZe mver arecomPlex because of intemehon of fluvial and the hdal forCes, depending on freshwate discharge andhdal range. Based on the data measuIed in meent years, thes papo discusses the characterishcs of flowand sNnt movemen in the tw forer EstUaIy and their iIifluences on the evolution of theestuaryKey W: YangtZe mver… 相似文献
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《Advances in water resources》2007,30(4):851-865
Groundwater flow and chemical transport in subterranean estuaries are poorly understood despite their potentially important implications for chemical fluxes from aquifers to coastal waters. Here, a numerical study of the dynamics in a subterranean estuary subject to tidal forcing is presented. Simulations show that salt transport associated with tidally driven seawater recirculation leads to the formation of an upper saline plume in the intertidal region. Computed transit times and flow velocities indicate that this plume represents a more active zone for mixing and reaction than the dispersion zone of the lower, classical salt wedge. Proper conceptualisation of this surficial mixing zone extends our understanding of processes within the subterranean estuary. Numerical tracer simulations reveal that tidal forcing may reduce the threat of a land-derived contaminant discharging to the marine environment by modifying the subsurface transport pathway and local geochemical conditions. Mixing and stratification in the subterranean estuary are strongly affected by both inland and tidal forcing. Based on the estuarine analogy we present a systematic classification of subterranean estuaries. 相似文献
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High-frequency (HF) radar observations of surface currents were conducted for 3 months during summer 2002 in the Keum River estuary. A comparison between HF radar-derived currents and directly measured ones form a buoy showed that the regression slope is close to 1 and the correlation coefficient greater than 0.86, with an RMS difference less than 13 cm/s which is less than 17% of the tidal current. This fairly good agreement allows us to use HF radar observation in investigating the surface flow and circulation in this tidal-current-dominant coastal-plume area. To examine the spatial variation in tidal current characteristics, as well as currents associated with non-tidal forcing, the HF radar-derived currents were separated into tidal and sub-tidal frequency currents. The overall pattern of M2-current ellipse distribution in the study area showed a counterclockwise rotation, with the offshore maximum current direction to the northeast. Eccentricity, the direction of maximum current, and the phase of net motion of the ellipse changed near the estuary mouth and near the gap of the Saemangeum reclamation tide dyke due to the complex coastal geometry and the out-flowing jet during the ebb period. 相似文献