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1.
利用我们建立的三维分层线性理论计算模式和中尺度数值模式ARPS, 分别研究了三维分层流动过双山脉地形产生的三维线性和非线性山脉重力波和大气船舶的结构特征及其形成机制.线性理论计算结果表明三维三层流动过双山脉地形时，两个山脉各自强迫出一个发散模态的山脉背风波，在第二个山脉背风面，三维三层流动过双山脉地形可以强迫出两个发散模态的拦截背风波，大大加强了对大气环流的拖曳作用.非线性数值模拟结果表明，流动过山所产生的非线性山脉重力波和大气船舶完全不同于三维分层线性理论计算模式所产生的山脉重力波和大气船舶的结构和特征，由于分层流体之间的非线性相互作用，三维三层流动过双山脉地形时，可在第二个山脉背风面激发4个发散模态的拦截背风波. 三维三层流动过双山脉地形所强迫的山脉重力波和大气船舶，具有同三维三层流动过孤立山脉所产生的山脉重力波和大气船舶完全不同的结构和特征，三维流动过双山脉地形对两个山脉之间的距离表现出极大的敏感性.对于相距较远的两个山脉，流动过双山脉所强迫的山脉重力波表现为4个发散模态的拦截背风波，波动的能量相对于相距较近的两个山脉能传播到更高的高度. 相似文献
2.
通航渡槽与升船机是过坝的快速通道。通航渡槽具有墩高由高到低连续变化、升船机与相邻高墩区渡槽基本周期差异大的结构特点,属于地震下激烈碰撞易发结构。基于有限元模型,对通航渡槽进行碰撞特征、控制因素以及地震响应影响研究。研究结果表明:渡槽与升船机周期差异大是造成剧烈碰撞的主要因素,且此碰撞有明显的传递效应;具有大位移的高墩在相邻渡槽跨周期差异不大时也会造成剧烈的碰撞,是碰撞的另一主要控制因素;有别于桥梁结构中碰撞通常限制墩的位移,通航渡槽中靠近升船机的剧烈碰撞区域,出现了明显的槽墩位移放大现象;碰撞对支座剪力影响程度远大于墩底剪力、弯矩。 相似文献
3.
Tidal sand waves, also named tidal dunes, are large scale bedforms generated by the growth of perturbations of the sea bottom driven by tidal currents. Indeed, the interaction of an oscillatory tidal current with a bottom waviness gives rise to steady recirculating cells which tend to drag the sediment from the troughs towards the crests of the bottom perturbation. The net motion of the sediment towards the crests is opposed by gravity force and the growth of the perturbation is controlled by a balance between these two effects. In the literature, to determine the conditions which lead to the formation of sand waves and to determine the characteristics of the bedforms generated by this instability mechanism, both fully three-dimensional and shallow water approaches are employed. The shallow water approach is computationally less expensive than the fully three-dimensional one but, in many cases, it might be less accurate. This paper compares the quantitative predictions obtained by means of the two approaches and quantifies the range of the parameters such that the shallow water approximation provides reliable predictions. 相似文献
4.
根据重力地质法（GGM）,利用南中国海海域内63179个船测控制点水深将测高自由空间重力异常划分为长波参考场和短波残差场,并反演出了该海域112°E-119°E,12°N-20°N范围的1’×1’海底地形模型,该过程中使用的海水和海底洋壳密度差异常数1.32 g·cm-3通过实测水深估计得到.利用反演得到的GGM模型对剩余的10529个检核点船测水深插值计算后与实测水深进行比较,其较差结果的均值为-1.64 m,标准差为76.95 m,相对精度为4.06%.此外,根据船测点数量、分布和海底地形的不同,选择了三个海域进行统计,结果表明：在船测控制点分布均匀的海域,GGM模型精度优于ETOPO1模型,在控制点过于分散的海域其精度会有所下降,但好于船测水深的直接格网化结果.为进一步探究检核点的较差结果中出现较大数值的成因,本文对精度较差的点位进行了单独分析,选择了两条船测航迹剖面进行了研究,并分析了检核点的水深较差、相对精度与水深和重力异常的关系,结果表明：GGM模型精度受水深和重力异常的相关性影响较小,受海底地形复杂程度影响较大,地形坡度变化平缓海域的预测精度明显高于海山地区.最后,综合GGM模型和ETOPO1模型优势,利用所有船测水深作为控制,生成了综合的海底地形模型. 相似文献
5.
Kwang Sup Kim 《Pure and Applied Geophysics》2013,170(3):473-478
The analysis of the seismic and infrasound data recorded at the time of the Cheonan incident led Kim and Gitterman (this journal, published on line August 2012) to conclude that a non-contact underwater explosion had sunk the ship. They also concluded that one of the mines deployed by the South Korean Navy many years ago in the area and then abandoned sank the ship. Their mine theory that is based on the explosive charge weights they calculated by means of two methods using the bubble period determined by their analysis, however, appears to be invalid. Although the incident had occurred in a shallow sea with a depth of less than 50m, the authors used the methods that are applicable only to free-field underwater explosions. The consideration of the influence on the bubble period of the nearby sea surface and bottom and the nearby ship’s hull would double the calculated weights. In addition, the authors ignored several evidences that support the torpedo theory. One of them is aluminum-containing white powder found in large quantities at certain substrates in the retrieved Cheonan. However, the conclusion of the official investigation group that the torpedo was made in North Korea is based on a circumstantial evidence and is yet to be proven with other more direct evidences. 相似文献
6.
《国际泥沙研究》2021,36(6):736-746
In order to optimize ship navigation in the macrotidal Gironde Estuary, a recent project funded by the port of Bordeaux aims at better understand and forecast hydrodynamic and fine sediment transport within the estuary. In the framework of this project, a two-dimensional hydro-sedimentary model is built. The model includes hydrodynamic forcings, mixed-sediment transport, and consolidation processes. The harmonic analysis of the astronomical tides reveals a strong distortion of the tidal wave inducing the growth of overtide constituents and the non-significant effect of tide-surge interactions in annual-scale prediction. Depending on hydrological conditions, river discharge can considerably alter the model accuracy due to the migration of the turbidity maximum zone modifying the bottom roughness. Comparison with measurements shows the ability of the model to reproduce suspended-sediment concentrations in the central Estuary. Sensitivity of the model to sediment features has also been discussed in regard of suspended-sediment concentrations and fluid mud deposits. The model will be further coupled with ship squat predictions and a morphodynamic model. 相似文献
7.
本文基于SKUA-GOCAD三维建模软件平台的构造-地层实体建模流程,通过整合研究区大量地质、地球物理资料和数据利用地质时间域坐标系转换和离散光滑插值（DSI）技术,并结合非定量化的地质基础利用地质网格功能建立了郯庐断裂带江苏段新生界的三维地质构造模型,该模型包括地表、第四系底部、新近系底部和基岩顶部等四个层面的地层模型和断层模型。该模型定量化地给出了研究区第四系、新近系底界的三维结构和特征,并刻画了主要活动断裂的三维空间分布,通过该模型可以更直观地显示研究区新生代地层单元和断裂的变化规律,对深入分析活动断裂带的沉积与构造具有重要的意义。 相似文献
8.
A bottom photographic and temperature study was carried out in the Dead Sea using a miniature version of the unmanned camera system ANGUS (mini-ANGUS). Due to the low transparency of the Dead Sea water, the bottom photographs provide very poor results. Only in a very few locations was the floor visible and in those cases it was found to be a white undulating sedimentary surface.The bottom temperature measurements, which were made continuously along the ship track, indicate the presence of a large zone of temperature anomalies. This zone is located in the deep part of the north basin at a water depth of over 330 m. The anomalies occur above a portion of an east-west fault which cuts through the Dead Sea suggesting the presence of hydrothermal activity. 相似文献
9.
Effects of bottom bracings on torsional dynamic characteristics of horizontally curved twin I-girder bridges with different curvatures 总被引：1，自引：0，他引：1
Curved twin I-girder bridges (CTIGBs) have low torsional stiffness that makes them vulnerable to dynamic loads.This study investigates the effects of bottom bracings on the torsional dynamic characteri... 相似文献
10.
11.
Ship-generated waves and return currents are capable of re-suspending significant quantities of bottom and bank sediments.However,most of the previous studies done on the subject do not show how and where sediment is re-suspended by the wakes and the directions of net transport.In this paper,a 3D numerical model based on hydro-sedimentary coupling is presented to search the relationship between the sediment movement,and the pattern of ship-generated waves around and far away from the vessel and the return currents around the ships.The hydrodynamic model is based on 3D Navier-Stokes equations including the standard k-ε model for turbulence processes,and the sediment transport model is based on a 3D equation for the re-suspended sediment transport.The computation results show that the areas of sediment concentration and transport(whether by resuspension or by the bedload) depend mainly on the position,the speed of the ship in the waterways,the kinematics of ship-generated waves and on the return flows.Thus,a map of sediment distribution and the modes of sediment transport generated by the passage of the ship are presented. 相似文献
12.
Jianguo Sang 《中国科学D辑(英文版)》1997,40(6):592-598
The analytical solutions of the atmospheric internal ship waves induced by three-dimensional terrain are obtained by solving the atmospheric wave equation. The solutions show that the waves consist of the untrapped and trapped parts. The patterns of the diverging wave and transverse wave in the untrapped parts are mainly determined by the shape and orientation of the terrain. This kind of wave may transport the wave energy to the upper atmosphere. The patterns of trapped lee waves are decided by the atmospheric conditions such as stratification, mean wind speeds and wind shear. 相似文献
13.
《Continental Shelf Research》1999,19(9):1161-1170
A vessel-towed camera platform with unique design features, developed to photograph seafloor habitat types on the continental shelf off southeastern Australia, is described. Photographic images contributed to the evaluation of the importance of habitat types to demersal fishery productivity. The significant features of the towed automatically compensating observation system (TACOS) are: it is a towed system that enables collection of photographic data along transects of several kilometres in length; it provides real-time video to the ship which permits fine operational control and real-time capture of images and data; it maintains a constant height above the bottom, and can traverse a range of bottom types including high-relief reefs. It is a low-cost system, relative to remotely operated vehicles (ROVs) or submersible camera platforms, based on an easily fabricated framework and commercially available components. The system has been successfully field tested to depths of 190 m in exposed open-ocean conditions. 相似文献
14.
In this paper SST imagery and a three-dimensional numerical model of a river plume were employed to detect upwelling induced by tidal straining in the Rhine ROFI (region of fresh water influence). Previous studies have shown that the Rhine ROFI in the North Sea exhibits strong cross-shore density gradients that compete with tidal and wind mixing to establish stratification. During neap periods with low mixing energy an area measuring 30 km offshore by 100 km alongshore becomes stratified. When the ROFI is stratified strong cross-shore currents are observed, with surface currents rotating anti-cyclonically and bottom currents rotating cyclonically. The cross-shore currents interact with the cross-shore density gradients to produce a semi-diurnal cycle of stratification. Due to continuity requirements imposed by the proximity of the coast, the offshore-directed surface currents and onshore-directed bottom currents should lead to coastal upwelling. 相似文献
15.
本文对采用顶底角钢连接的半刚性钢梁柱连接节点进行了精细的三维非线性有限元分析,在与实验数据对比的基础上,对影响该连接性能的主要参数如角钢厚度、柱翼缘连接螺栓与梁翼缘间的距离等进行了分析,得到了其弯矩-转角曲线。 相似文献
16.
为提升预制节段拼装桥墩的抗震性能,采用碳纤维增强复合材料(CFRP)对预制节段拼装桥墩在地震中易损伤部位进行加固。基于既有试验,建立缩尺的预制节段拼装桥墩三维实体有限元模型,分析预制节段拼装桥墩在循环往复荷载情况下的恢复力特性以及破坏情况。分别采用箍筋加密和外包CFRP布对预制节段拼装桥墩底部节段进行加固,对比两种加固方式对预制节段拼装桥墩抗震性能的影响。研究结果表明,CFRP包裹桥墩底部节段能够增强桥墩整体刚度和承载能力,并且使得桥墩的刚度退化更加平缓,有利于预制节段拼装桥墩在地震作用下保持自身力学特性的稳定,确保桥梁整体的安全。 相似文献
17.
A two-dimensional numerical model is applied to a coastal ocean wherein alongshore elevation and density gradients, normally calculated by a three-dimensional model, are instead supplied by climatologically averaged data for the California Current System between 25 and 40°N. Surface wind stress is also obtained from climatological data. Both surface and bottom boundary layers are resolved in the model calculations; a second moment turbulence closure submodel supplies vertical diffusivities. Near steady state solutions are possible when surface buoyancy flux is imposed at the surface.Model results are as follows: Southward wind stress produces a broad equatorward current with an embedded coastal jet in accordance with previous studies. Positive wind stress curl reduces the jet current and produces a poleward undercurrent which then surfaces as the curl is increased. The jet currents are reduced and poleward flow increases as bottom steepness increases; to a lesser extent, inclusion of the beta effect has a similar effect. The existence of near bottom, poleward or equatorward flow is explained rather simply in terms of the bottom stress resulting from the alongshore balance of surface wind stress and vertically integrated pressure gradient, the latter involving the alongshore surface elevation and density gradient. A further finding is that the upwelling circulation associated with wind stress is confined to the top 200 to 300 m of the ocean along the California coast. 相似文献
18.
The echo-amplitude of a 23-m-deep bottom-mounted acoustic Doppler current profiler (ADCP) shows regular spikes up to 30 dB above background level when a ship passes nearby, due to deep penetration of bubble clouds. This is evidenced from regularly occurring spikes in echo-data that are simultaneous with ferry crossings in a narrow sea-strait. The bubbles can nearly reach the bottom and are comparable in magnitude to near-bottom scattering off suspended material in vigorous tidal currents exceeding 1 m s−1 in magnitude. The bubble clouds mask the sea surface from the echo-amplitude, which hampers the use of an ADCP for estimating atmospheric parameters and near-surface currents, under such conditions. The echo-spikes associated with the ferry are confirmed with coinciding dips in bottom pressure up to 1200 N m−2 and with deviations up to 10° in the ADCP's heading due to pressure waves and magnetic field disturbances from under the ferry and from its rear, respectively. 相似文献
19.
为研究高速铁路路堤中WIB(波阻板)的减隔振效果,构建了简易的铁路路堤原理性试验模型,获得了在WIB底面与路堤顶面垂直间距不同时、在路堤面上的简谐荷载作用下引起的振动波在模型表面的传播衰减规律,分析了铁路路基中WIB底面与路堤顶面垂直间距不同时的减隔振效果;构建了高速铁路路基三维动力数值仿真分析模型,并进行对比分析,验证了模型试验的合理性。结果表明:在高速铁路路堤的基床底层中设置WIB,越靠近路堤顶面,减隔振效果越好;在基床底层的顶面设置WIB的减隔振效果优于在基床表层设置WIB。 相似文献
20.
A three-dimensional prognostic hydrodynamic model in cross sectional form is used to examine the influence of bottom friction,
mixing and topography upon the spin-down and steady-state circulation in a cold water bottom-dome. Parameters characteristic
of the Irish Sea or Yellow Sea cold water domes are used. In all calculations, motion is induced by specifying an initial
temperature distribution characteristic of the dome, and an associated along frontal flow. The spin-down of the dome is found
to be influenced by the coefficient of bottom friction, with a typical time scale of order 10 days, and in general to be independent
of the chosen initial vertical profile of along frontal flow. However, in the case in which the along frontal flow is such
that the near bed velocity is zero, then bottom stress is also zero, and there is no appreciable spin-down. Calculations showed
that the formulation of viscosity and diffusivity had a greater effect upon the steady-state circulation than topography,
suggesting that background mixing of tidal origin is important. The lack of topographic influence was due mainly to the formulation
of the initial conditions which were taken to be independent of topography. The steady-state circulation was characterized
by a cyclonic flow in the surface region, with an anti-cyclonic current near the bed, where frictional effects produced a
bottom Ekman layer and an across frontal flow. This gave rise to vertical circulation cells in the frontal region of the dome
with prevailing downwelling motion inside the dome. A detailed analysis of the dynamic balance of the various terms in the
hydrodynamic equations yielded insight into the processes controlling the steady-state circulation in cold water domes.
Responsible Editor: Phil Dyke 相似文献