考虑区域地质构造特征的概率性海啸灾害评估

确定性海啸灾害评估通常考虑极端情况下的海啸灾害情况,而考虑到实际地震海啸发生时各种参数的不确定性,概率性海啸灾害评估(Probabilistic Tsunami Hazard Assessment, PTHA)可以给出某个地区海啸波高的概率分布,逐渐成为目前的研究热点。现有的PTHA研究中通常假设地震震源在空间上是均匀分布的。而实际地震的发生位置受到岩石属性和板块应力等地质构造特征的影响,通常是不均匀的。该文以马尼拉俯冲带为例,构造了震源空间位置的非均匀分布模型,对中国沿海地区在未来2000年内遭受的海啸灾害进行概率性评估。结果显示,非均匀分布模型得到的海啸波高的超越概率相比均匀模型差异最高可达20%。因此,考虑地震位置空间分布的不均匀性对PTHA的研究有重要影响。     

南海海啸反问题预报模式

通过COMCOT海啸模型计算南海马尼拉海沟潜在震源区单元板块单位滑动产生的海啸波在区域内传播过程,将计算结果组成相应南海海啸波数据库.采用浮标监测数据与数据库结合通过最小二乘法构建南海海啸预报模式.以假想马尼拉海沟发生8.3级地震海啸为案例,应用预报模式对华南地区进行海啸预测,采用30 min和60 min监测数据分别反演计算,在三个近岸验证点的波高和正问题结果比较误差分别在25％和17％之内,到达时间及相位基本一致,预报的计算时间在2 min以内.     

某近海核电站海啸洪水演进数值模拟研究

为了应对可能出现的海啸洪水对于核电厂的安全级蓄电池、应急柴油发电机组及应急配电装置的破坏,本文通过数值模拟研究核电厂厂区洪水演进过程及其影响。首先,确定"防洪设计基准潮位"及"超设计海啸洪水参数",作为数值模拟的计算依据。其次,构建平面二维海啸洪水数学模型,模型计算采用基于无结构网格的有限体积法,以应对海啸洪水及核电厂区地形复杂等特点。再次,按设计基准洪水位与可能的超设计海啸洪水组合形成数学模型超设计洪水计算方案,开展不同极端工况下核电厂区的洪水演进情况及其对厂区重要建筑影响的数值模拟。海啸参数研究结果表明,该核电厂址可能最大海啸增水为1.16 m,最大风暴潮增水为5.30 m,海啸模拟中超设计基准海啸采用2.71 m和5.28 m两种代表波高组合。数值模拟结果进一步表明,当考虑最高天文潮位与可能的海啸增水与可能的风暴潮增水组合工况时,各方案海啸洪水最大波高高于厂址防洪水位7.20 m,海啸洪水可能威胁核电站厂区防洪安全;在海啸洪水淹没厂区过程中,不同方案海啸洪水进入厂区至整个厂区淹没所需时间长短相差不大,约144～169 s;当洪水流至核岛厂房附近时,厂房周围流速伴随着海啸洪水涨、退...     

基于Boussinesq方程的陡峭礁坪上波浪传播变形数值模拟

为了探究应用基于二阶完全非线性Boussinesq方程开发的Funwave-TVD波浪模型模拟波浪在陡峭礁坪上传播变形的可行性,在采用试验及已有文献成果进行可行性验证的基础上,利用该模型模拟了波浪在陡峭礁坪上的传播变形过程,分析了不同波浪要素及不同水深情况下波浪在陡峭礁坪上的传播规律。结果表明:当波高与水深的比值超过一定值时,波浪发生破碎,波高迅速减小;对于深水情况下的陡峭礁坪地形,当波浪离开礁坪坡脚的水平距离为4倍入射波长及更远时,礁坪上的平均波高可降低为稳定值。     

基坑开挖长宽比对临近管道变形影响研究

基坑开挖通常会对周围管道造成影响,为研究基坑开挖长宽比对临近管道地表变形的影响,采用MIDAS/GTS数值模拟建立三维数值计算模型,研究了开挖深度为16 m的基坑对应5种长宽比下的地表变形规律。结果表明：(1)基坑在开挖过程中,对地表影响的范围约为2.40倍的基坑开挖深度,此外,基坑侧方是否存在管道对地表变形影响不显著;(2)基坑开挖长宽比的变化对地表位移和支护结构的侧移影响趋势基本一致,即两者均随基坑开挖长宽比增大而显著增大;(3)当基坑开挖长宽比小于0.80时,沉降最大值的比值随基坑长宽比增大而线性增大,当长宽比大于0.80时,沉降最大值的比值随基坑长宽比增大而保持不变。     

孤立波浅化过程的SPH数值模拟

本文应用光滑粒子流体动力学(SPH)方法建立了二维数值波浪水槽,研究了孤立波沿斜坡的传播、变形和破碎过程。通过数值计算分析了波浪沿斜坡传播过程中自由表面的变化特征,给出了斜坡上不同位置处波面变化的历时曲线,并应用文献记录的试验结果对数模结果进行了验证。得到了波高的沿程变化趋势、破波点的位置和破碎波高以及不同破碎形态下波浪自由表面的变化特征,显示了SPH方法在处理较复杂自由表面流动问题方面的优越性。     

防护林分布条件下开敞水域堤前波浪要素计算分析

长乐滨海路路堤项目外海朝向开敞式海域,波浪在传播过程中不断发生浅水变形,采用理论的波浪变形条件难以取得满意的成果。工程设计时,在分析路堤堤前波高破碎因素,并充分考虑外海侧滩地地形条件和防护植物分布的情况下,对破碎波高进行数值分析计算,获得计算波高的准确数值,为优化堤顶高程和降低工程投资提供了技术依据。该文对此进行总结,可供类似工程参考。     

不同护坡条件下波浪溢流海堤内坡水动力特征

波浪溢流指强风暴潮引起堤前水位超过堤顶,海堤受到的越浪与溢流联合作用。波浪溢流一旦发生,极易引起大范围的海堤内坡侵蚀乃至溃堤,产生灾难性后果。基于1:1的大型水槽试验,分析了波浪溢流过程中不同海堤内坡护坡条件下(碾压混凝土、铰接式护坡砖和高性能加筋草皮)海堤内坡水力学特征;建立了相应的内坡平均水深和平均流速计算模型,计算结果表明波浪溢流过程中海堤内坡上的波高分布仍符合瑞利分布,并分析了内坡上的特征波高和特征峰值水深之间的换算关系;提出了波浪溢流过程中海堤内坡上的均方根波高和波速经验计算式。     

滩地刚性植物消浪作用特性研究

滩地植物有利于保障沿海地区的水安全,量化成熟期植物消浪作用是提升生态海岸韧性的基础。本文基于一般试验规律和两种波高消减模型,分析提出了新的滩地植物消浪系数计算方法,结合波高条件可计算林带消浪后波高,相关表达式由大量试验数据进行了验证,最后对比了由本文方法与规范方法计算的林带后波高。结果表明,阻尼因数及消浪系数能直观体现植物消浪作用特性,波浪传播方向上植物面积占横截面比例是影响植物消浪机理的关键无量纲参数。植物非淹没时,本文方法得到的林带后波高与规范方法接近;植物淹没时,本文方法能更准确描述植物消浪作用。相较于规范方法,本文方法考虑了植物淹没情况,直观揭示了林带密度、宽度、高度,植物平均直径,水深等参数的影响,适用于更多工况。基于植物消浪作用的模型可快速研判相关参数变化对植物消浪效果的影响,为生态海堤滩地刚性植物规划设计及数模研究提供科学和技术支撑。     

一种考虑震源与传播路径的重力坝地震响应分析的新方法

本文提出一种新的重力坝地震输入方法,基于地震学理论,综合考虑了震源、传播路径和结构响应全过程,相对于传统输入方法,本文给出更加合理和科学的空间非均匀地震波波场。本文使用谱元法程序SPECFEM2D计算了弹性波从震源到近场的传播过程;用有限元方法计算近场重力坝的地震响应,计算结果表明,传播介质以及震源与重力坝相对位置对大坝动力反应都具有显著的影响,在工程设计中应该予以考虑,同时提供了一种计算大坝地震响应输入参数的新思路。对类似工程研究具有参考价值。     

2D numerical modelling of bed profile changes due to tsunami effects on near shore coasts: Kadikoy case study.

This study was aimed at the investigation of tsunami effects on the seabed profile as these may be important for coastal structures, like sea outfalls or breakwaters. Tsunamis are well known with huge wave heights and destructive effects on the coastal region. A 2D numerical model was set using the software, COSMOS to calculate the cross-shore sediment transport and to evaluate profile changes in the coastal seabed. The study area is Kadikoy region, a densely populated industrial coastal area in South East Istanbul. The model was run for different kinds of tsunami waves. Not only the bed profile changes, but also the wave heights, breaker depths, peak wave bottom orbital velocities, wave set-up and cross-shore sediment transport rates were determined. The results indicated that, at a water depth around 40-50 m, some tsunamis were found to have a wave height of order of 15 m, which became about 5 m at a depth of 10 m. The wave set up near the coast was about 1.5-2 m. The results also implied that tsunami waves, with their destructive nature, could lead to dramatic vertical changes of the seabed.     

Characteristics of wave amplitude and currents in South China Sea induced by a virtual extreme tsunami

This paper investigates the potential extreme tsunami hazards of the worst case scenario of the magnitude M_w=9.30 in South China Sea(SCS)as the Manila Trench is becoming one of the most hazardous tsunami source regions.Using nonlinear shallow water equations model,the time series of surface elevation,arrival time,spatial distributions of maximum wave amplitude and velocity distribution are presented.The characteristics of wave and currents are analyzed.The numerical results indicate that most of the energy of tsunami wave distributes in central and north part of SCS.The offshore regions around SCS will be influenced significantly by the tsunami currents generated by an earthquake in the Manila subduction zone.The maximum wave amplitude near Guangdong Province,Hainan Island,and Taiwan Island exceeds 4 m and velocities at the majority of measured locations near coast exceeds 2 m/s.Nested grid with high resolution is used to study the impacts of the tsunami on Hainan Island,Taiwan Island,and Lingding Bay.The regions with high hazard risk due to strong currents are identified.Finally,a fast tsunami warning method in SCS is developed and discussed,which can provide tsunami warning information in 5 min.     

聚焦波浪与直立圆柱作用的数值模拟

基于Fluent平台建立了可用于波浪传播模拟的数值计算水槽,利用不同波浪参数的线性规则波模拟分析了网格尺度L/Δx对产生波浪质量的影响,确定数值水槽的网格划分尺度,并验证了阻尼消波的有效性。在此基础上,用模拟频谱的方法对聚焦波浪的传播进行了数值模拟,通过数值模拟与物理试验不同位置处的聚焦波波面和聚焦点下水质点速度时间过程线对比,验证了模拟频谱方法数值计算的有效性。进一步对聚焦波浪与直立圆柱的作用进行了数值模拟,数值模拟聚焦波面过程、聚焦波浪水质点速度、圆柱周围波浪波动过程、圆柱上所受的波压力等,并与试验结果进行了对比,数值计算结果与试验结果吻合很好,验证了所建立的数值水槽的有效性。对聚焦波波面和压力特征值进行了误差分析,并分析了误差的产生原因,为进一步研究聚焦波浪与工程结构物的作用奠定基础。     

Combined effects of coastal forest and sea embankment on reducing the washout region of houses in the Great East Japan tsunami

Coastal vegetation is widely recognized for its ability to reduce tsunami damage; however, coastal forests in large areas of the Tohoku and Kanto districts of Japan were destroyed by the Great East Japan tsunami on 11 March 2011. To elucidate the tsunami-mitigating effect of a coastal forest during a destructive tsunami, the combined effects of sea embankment and coastal forest were analyzed using post-tsunami survey data of the damage and a nonlinear long wave equation model that includes the breaking or washout condition of trees. The numerical simulations estimated that a 600-m-long coastal forest reduced the washout region of houses due to a 10-m-high tsunami at the coast by approximately 100 m, and the reduction achieved by a sea wall of approximately 5.4–6.4 m in height was approximately 560–1520 m. The height of a sea embankment or wall with sand dunes greatly affects the breaking condition of trees behind it by changing the tsunami flux overflowing the sea wall and the sand dune. For the combination of a sea embankment and a coastal forest during a destructive tsunami, the tsunami mitigation function of the coastal forest has an optimum value when the fluid force on the trees is strong but not strong enough to break the trees under the condition at which the tsunami overflows the sea embankment. At the investigated site, the effect of the coastal forest was larger than that of the sea embankment under optimal conditions. Thus, a coastal forest on a sand dune should be designed as a mitigation measure behind a sea embankment and optimally designed to protect the houses that are not protected from a tsunami by the sea embankment alone.     

Run-up of non-breaking double solitary waves with equal wave heights on a plane beach

The evolution and run-up of double solitary waves on a plane beach were studied numerically using the nonlinear shallow water equations(NSWEs) and the Godunov scheme. The numerical model was validated through comparing the present numerical results with analytical solutions and laboratory measurements available for propagation and run-up of single solitary wave. Two successive solitary waves with equal wave heights and variable separation distance of two crests were used as the incoming wave on the open boundary at the toe of a slope beach. The run-ups of the first wave and the second wave with different separation distances were investigated. It is found that the run-up of the first wave does not change with the separation distance and the run-up of the second wave is affected slightly by the separation distance when the separation distance is gradually shortening. The ratio of the maximum run-up of the second wave to one of the first wave is related to the separation distance as well as wave height and slope. The run-ups of double solitary waves were compared with the linearly superposed results of two individual solitary-wave run-ups. The comparison reveals that linear superposition gives reasonable prediction when the separation distance is large, but it may overestimate the actual run-up when two waves are close.     

Experimental investigation of the effects of contraction on tsunami-induced forces and pressures on a box section bridge

Many bridges that lie within possible tsunami inundation zones are critical links in transport networks. Some efforts have been made to determine the effects of tsunamis on bridges, but only a limited range of published design guidelines are available. Therefore, it is necessary to further investigate the effects of tsunamis on bridges. In the current study, physical modeling experiments were carried out to measure bore impact forces and pressures for various tsunami bore strengths on a bridge deck with different abutment types (wing wall and spill-through) and different opening and submergence ratios. The experiments were conducted in a wave flume with dimensions of 14 × 1.2 × 0.8 m (length × width × height), equipped with an automatic gate designed to generate a tsunami bore. The horizontal and vertical forces showed an increasing trend with increasing submergence ratio for both types of abutment. However, the horizontal force showed a decreasing trend as the opening ratio decreased, while the vertical force initially increased as the opening ratio decreased, until it reached a peak value, and then it started to decrease. The overall shapes of the results for both types of abutment are similar, with higher values for spill-through abutments due to their lower energy dissipation rates. Based on the experimental data, empirical equations are proposed for estimation of tsunami loads as a function of opening and submergence ratios.     

NUMERICAL SIMULATION OF SOLITARY WAVE RUN-UP AND OVER-TOPPING USING BOUSSINESQ-TYPE MODEL

In this article,the use of a high-order Boussinesq-type model and sets of laboratory experiments in a large scale flume of breaking solitary waves climbing up slopes with two inclinations are presented to study the shoreline behavior of breaking and non-breaking solitary waves on plane slopes.The scale effect on run-up height is briefly discussed.The model simulation capability is well validated against the available laboratory data and present experiments.Then,serial numerical tests are conducted to study the shoreline motion correlated with the effects of beach slope and wave nonlinearity for breaking and non-breaking waves.The empirical formula proposed by Hsiao et al.for predicting the maximum run-up height of a breaking solitary wave on plane slopes with a wide range of slope inclinations is confirmed to be cautious.Furthermore,solitary waves impacting and overtopping an impermeable sloping seawall at various water depths are investigated.Laboratory data of run-up height,shoreline motion,free surface elevation and overtopping discharge are presented.Comparisons of run-up,run-down,shoreline trajectory and wave overtopping discharge are made.A fairly good agreement is seen between numerical results and experimental data.It elucidates that the present depth-integrated model can be used as an efficient tool for predicting a wide spectrum of coastal problems.     

Numerical analysis of impacts of 2011 Japan Tohoku tsunami on China Coast

On the 11th of March, 2011, a subduction earthquake of magnitude Mw9.0 happened at the northeast of Japan, generating a tsunami which resulted in huge damage in Japan. Okada’s elastic fault model is used to generate the deformation of the sea bottom based on USGS sources and UCSB sources respectively. The shallow water equations are solved by the adaptively refined finite volume methods so that it can compute the propagation of tsunami in the Pacific Ocean efficiently. The computed time series of the surface elevation are compared with the measured data from NOAA real-time tsunami monitoring systems for model validation, and UCSB sources derive better results than USGS sources. Furthermore, one nested domain with fine grid and higher topography resolution is combined to compute numerically this tsunami spreading in the Bohai Sea, Yellow Sea, East China Sea, and North of South China Sea. The impacts on China Coast and seas are analyzed and discussed. The results show that the tsunami has almost no impact in the Bohai Sea and Yellow Sea. It has some kind impact on the East China Sea and South China Sea. However, maximum wave height on China Coast is smaller than 0.5 m. It is thus concluded that the 2011 Tohoku tsunami did not generate a significant influence on China Coast.     

海啸波作用下植被区海堤局部冲刷试验

近年来频发的海啸造成了沿岸建筑物周围剧烈的冲刷,而植物具有很好的减小海啸灾害的作用。采用PVC圆管概化模拟刚性植物,选取孤立波模拟海啸波,通过改变入射波高、植物带长度和密度、堤顶出水高度,研究植物对海啸波作用下海堤局部冲刷的影响,建立了海堤堤前冲刷坑、淤积沙坝、冲淤平衡点相对水平位置的尺度与植物带的长度和密度、波高、堤顶出水高度、泥沙比重以及岸滩坡度之间的关系式。试验结果表明:植物对海堤局部冲淤变化产生显著影响,植物带使得堤后近岸侧相对最大冲刷深度显著减小,堤前离岸侧冲刷位置由原堤脚处前移至植物带所在位置,冲刷范围大幅增加;堤前冲淤面积受入射波高和植物因素的共同影响,在同一植物模型下,冲刷坑面积和淤积沙坝面积都随入射波高的增大而增加;适当增大植物带密度,优化植物分布方式,可有效减弱海啸波对海堤的冲刷危害。