A Note on Tsunami Bore Front

A note is presented on tsunami bore front. This tsunami bore front is an old dynamical problem but also a new problem to be understood. The tsunami event on 2004 December 26 has raised this is an urgent problem. The author introduces here a model in order to see a hydrodynamical specific property of the tsunami bore front. This modeling gives us a new understanding about what mechanics is for the interested tsunami bore front, especially, around a coastal zone. This work adds a new understanding about mechanics of water motions as the tsunamis generated by the earthquake undersea at a distant area from the coast. The model in this work points out a specific transitional pattern as a function of time and space of tsunami bore front. This modeling gives what is essential at considering tsunami bore front.     

黄海西部沿岸锋多年平均特征统计分析

根据黄海1939-1999年海洋实测数据集和2010年黄海成山头附近海域海试资料,统计分析了黄海西部沿岸锋温度分布结构、平均强度、宽度、位置分布等特征。实测数据统计分析结果表明,黄海西部沿岸锋具有明显的季节变化特征:春季开始形成并逐步加强,夏季处于强盛期,秋季海洋锋逐渐减弱,冬季相比秋季略有增强的趋势,初春季节海洋锋消亡。海试资料表明2010-08该锋位于20m等深线以西5nmile至以东30nmile之间的海域,且位于40m等深线以西20nmile至以东20nmile之间的海域。     

Experimental investigation of tsunami bore impact pressure on a perforated seawall

Catastrophic failures of many tsunami barriers along the affected coasts during the 2011 Tohoku earthquake tsunami has prompted extensive investigation into improving and revising design codes for tsunami defence structures. To date, researchers and coastal engineers are investigating to understand the failure mechanisms and to find solutions so that the structures merely remain intact in the extreme event such as tsunami. Thus, the present work is motivated to experimentally study tsunami-induced bore pressures exerted on vertical seawalls; a solid vertical wall and a porous vertical seawall that consisted of a perforated front wall and a solid rear wall. Bores with various heights and velocities were generated by using the dam-break method. A porous seawall with 20% porosity of perforated front wall was used in this study. Bore pressures exerted on the solid rear wall and chamber oscillations that occurred in the experiments were also discussed. The experimental results showed that multiple peak pressures were observed during bore run-up phase in the time series of bore impacts. A predictive equation to estimate the maximum bore pressure on a perforated seawall was developed using multiple regression analysis. The proposed equation was also compared with previous empirical formulas.     

涌潮冲击丁坝的数值计算

鉴于钱塘江涌潮水流复杂多变和带有自由表面的情况,采用VOF方法追踪自由表面,考虑各向异性,用修正的K吨模型封闭Reynolds方程,用施主一受主法求解流体体积函数控制方程,计算了涌潮冲击丁坝时的压力场和自由面状况,并与现场实测值进行了比较,取得了良好的效果,为涌潮的小尺度数值模拟提供了借鉴的经验。     

海洋锋区的一种声速计算模式及其在声传播影响研究中的应用

利用穿过海洋锋区断面的实测CTD数据,确定了锋面的宽度、所在的位置以及陡度等特征参数,建立了海洋锋区声速计算理论模式。结果表明,此模式可以用来描述选定断面的锋面特性。将理论计算结果与实测数据进行比较,二者符合较好。进而利用二维PE模型,研究了通过海洋锋面的声传播特性。结果表明,在声源深度为50m和发射频率为150 Hz的情形下,对不同接收深度,有锋面与无锋面时传播损失的差别最大约为20 dB左右。     

Modeling of 500-year tsunamis for probabilistic design of coastal infrastructure in the Pacific Northwest

This paper describes the development of tsunami scenarios from the National Seismic Hazard Maps for design of coastal infrastructure in the Pacific Northwest. The logic tree of Cascadia earthquakes provides four 500-year rupture configurations at moment magnitude 8.8, 9.0, and 9.2 for development of probabilistic design criteria. A planar fault model describes the rupture configurations and determines the earth surface deformation for tsunami modeling. A case study of four bridge sites at Siletz Bay, Oregon illustrates the challenges in modeling of tsunamis on the Pacific Northwest coast. A nonlinear shallow-water model with a shock-capturing scheme describes tsunami propagation across the northeastern Pacific as well as barrier beach overtopping, bore formation, and detailed flow conditions at Siletz Bay. The results show strong correlation with geological evidence from the six paleotsunamis during the last 2800 years. The proposed approach allows determination of tsunami loads that are consistent with the seismic loads currently in use for design of buildings and structures.     

韩国海岸港口工程概况

简要介绍了韩国海岸和海洋环境、港口发展、海岸和港口工程的有关机构和团体，并综述其近年来海岸动力方面研究的课题和成果。内容包括海洋动力因素、海岸波浪观测和设计波浪的确定、波浪的传播变形、不规则波理论、非线性波和波浪破碎、波浪与建筑物相互作用、泥沙运动、海岸演变和环境影响分析等方面。     

Analysis of the Tsunami of December 26, 2004, on the Kerala Coast of India—Part I: Amplitudes

The Indian Ocean tsunami of December 26, 2004, not only affected the Bay of Bengal coast of India but also part of the Arabian Sea coast of India. In particular, the tsunami caused loss of life and heavy damage on some parts of the Kerala coast in southwest India. The tsunami traveled west, south of Sri Lanka, and some of the tsunami energy was diffracted around Sri Lanka and the southern tip of India and moved northward into the Arabian Sea. However, tsunami, being a long gravity wave with a wave length of a few hundred kilometers, has to take a wide turn. In that process, it missed the very southern part of the Kerala coast and did not achieve large amplitudes there. However, further north, the tsunami achieved amplitudes of upto 5 m and caused loss of life and significant damage. Here we identify the physical oceanographic processes that were responsible for selective amplification of the tsunami in certain locations.     

The influence of seaward boundary conditions on swash zone hydrodynamics

The influence of the seaward boundary condition on the internal swash hydrodynamics is investigated. New numerical solutions of the characteristics form of the nonlinear shallow-water equations are presented and applied to describe the swash hydrodynamics forced by breaking wave run-up on a plane beach. The solutions depend on the specification of characteristic variables on the seaward boundary of the swash zone, equivalent to prescribing the flow depth or the flow velocity. It is shown that the analytical solution of Shen and Meyer [Shen, M.C., Meyer, R.E., 1963. Climb of a bore on a beach. Part 3. Runup. J. Fluid Mech. 16, 113–125] is a special case of the many possible solutions that can describe the swash flow, but one that does not appear appropriate for practical application for real waves. The physical significance of the boundary conditions is shown by writing the volume and momentum fluxes in terms of the characteristic variables. Results are presented that illustrate the dependence of internal flow depth and velocity on the boundary condition. This implies that the internal swash hydrodynamics depend on the shape and wavelength of the incident bore, which differs from the hydrodynamic similarity inherent in the analytical solution. A solution appropriate for long bores is compared to laboratory data to illustrate the difference from the analytical solution. The results are important in terms of determining overwash flows, flow forces and sediment dynamics in the run-up zone.     

Analysis of the Tsunami of December 26, 2004, on the Kerala Coast of India—Part II: Arrival Times

The Tsunami of December 26, 2004, in the Indian Ocean arrived on the coast of Kerala in southwest India some three hours after the tsunami was generated. The tsunami activity persisted throughout that day and, in some locations, even into the early morning of the next day. Based on interviews with eye witnesses, arrival times of tsunami waves are presented here followed by some preliminary analysis of the results.     

In-Situ Test and Numerical Analysis of Bore Pressure on Sheet-Pile Groin

1 .Introduction As a conventional hydraulic structure for beach protection and accretion promotion,the groin hasbeen widelyapplied.Thetraditional rock-fill groinis subjectto destructionandthe cost of maintenanceis rather high. As an improvement of traditi…     

Numerical Study of Dam-Break Induced Tsunami-Like Bore with A Hump of Different Slopes

Numerical simulation of dam-break wave, as an imitation of tsunami hydraulic bore, with a hump of different slopes is performed in this paper using an in-house code, named a Constrained Interpolation Profile (CIP)-based model. The model is built on a Cartesian grid system with the Navier Stokes equations using a CIP method for the flow solver, and employs an immersed boundary method (IBM) for the treatment of solid body boundary. A more accurate interface capturing scheme, the Tangent of hyperbola for interface capturing/Slope weighting (THINC/SW) scheme, is adopted as the interface capturing method. Then, the CIP-based model is applied to simulate the dam break flow problem in a bumpy channel. Considerable attention is paid to the spilling type reflected bore, the following spilling type wave breaking, free surface profiles and water level variations over time. Computations are compared with available experimental data and other numerical results quantitatively and qualitatively. Further investigation is conducted to analyze the influence of variable slopes on the flow features of the tsunami-like bore.     

Analysis of the Tsunami of December 26, 2004, on the Kerala Coast of India—Part III: Inundation and Initial Withdrawal

During the Indian Ocean tsunami of December 26, 2004, specific observations were made by our survey team about the arrival times of several tsunami waves, their amplitudes, maximum extent of horizontal inundation on land and initial withdrawal of the ocean. Here the observations on the horizontal inundation and initial withdrawal are presented and briefly discussed.     

Deformation Front Development at the Northeast Margin of the Tainan Basin, Tainan–Kaohsiung Area, Taiwan

The geological setting south of the Tsengwen River and the Tsochen Fault is the transitional zone between the Tainan foreland basin and Manila accretionary wedge in Southwestern Taiwan. This transitional zone is characterized by the triangle zone geological model associated with back thrusts that is quite unique compared to the other parts of the Western foreland that are dominated by thrust imbrications. The Hsinhua structure, the Tainan anticline, and the offshore H2 anticline are the first group of major culminations in the westernmost part of the Fold-and-Thrust belt that formed during the Penglay Orogeny. Structures in the the Tainan and Kaohsiung areas provide important features of the initial mountain building stage in Western Taiwan. A deeply buried basal detachment with ramp-flat geometry existed in the constructed geological sections. A typical triangle is found by back thrusting, such as where the Hsinhua Fault cuts upsection of the Upper Pliocene and Pleistocene from a lower detachment along the lower Gutingkeng Formation. The Tainan structure is a southward extension of the Hinhua Fault and has an asymmetric geometry of gentle western and steep eastern limbs. Our studies suggest that the Tainan anticline is similar to the structure formed by the Hsinhua Fault. Both are characterized by back thrusts and rooted into a detachment about 5 km deep. The triangle zone structure stops at H2 anticline offshore Tainan and beyond the west of it, All the structures are replaced by rift tectonic settings developed in the passive continental margin. On the basal detachment, a major ramp interpreted as a tectonic discontinuity was found in this study. Above the northeastern end of the major ramp of basal detachment, the Lungchuan Fault is associated with a triangle system development, while at the southwestern end a thrust wedge is present. It could be deduced that a thrust wedge intrudes northwestward. The area below the major ramp, or equivalent to the trailing edge of the basal detachment, mud diapers often occur in relation to the thickest deposits of the Gutingkeng Formation and caused by the mechanism of detachment folding     

涌潮水沙动力过程现场观测研究进展

涌潮是潮波传播过程中产生的一种自然现象,是潮波非线性畸变的结果。涌潮有波状和破碎形态之分,波状涌潮是一系列平行向前传播的涌波构成的波列,破碎涌潮则是前锋陡立向前推进的水滚。基于国内外涌潮水沙动力过程现场观测的主要成果,从形成机理出发,归纳涌潮生成的必要条件,剖析潮波运动非线性和摩擦效应对涌潮生成的影响;针对典型的波状和破碎涌潮,总结潮头的自由表面特征参数、流动结构和传播演化特征;回顾涌潮局部湍流和混合过程、泥沙输运和沉积的研究进展,评述涌潮脉冲过程对河口生态环境的影响。涌潮的周期性传播引起自然系统的大规模混合,对潮汐河口区域的生态环境平衡具有重要意义。涌潮现象的研究推动潮汐学的发展,现场观测是涌潮研究的基础。随着仪器设备和分析手段的进步,涌潮多尺度生成与演化机制、涌潮多物理过程耦合作用机理和涌潮脉冲过程的生态效应定量评价是今后需要深入研究的问题。     

山东半岛冷流暴雪过程的个例分析

2008年12月4~5日,山东半岛出现了1次冷流暴雪过程,渤海上的辐合带对这次暴雪过程起到了重要的作用。本文利用观测资料和数值模式对这次过程进行了研究,探讨渤海辐合带的发展演变机制及对山东半岛冷流暴雪的影响,并分析了太行山脉对渤海辐合带的影响。结果表明,渤海上空生成的西北东南向的中尺度辐合带造成了以烟台-牟平-文登为中心的西北东南向的降雪带。太行山脉的阻挡作用使绕太行山的西北气流在太行山背风侧形成辐合,同时在低层大气存在1个暖脊,所以在渤海形成了1个西北东南向的辐合带。在西北风的水平平流和非地转风的作用下,渤海辐合带向东北移动,当渤海西北岸出现北风后,渤海辐合带西北部在北风的水平平流作用下向南移动,而渤海辐合带东南部在西北风水平平流和非地转风的作用下,继续向东北移动并与山东半岛北部的海岸锋辐合带合并增强,渤海辐合带西北和东南两部分移动方向的不同造成了辐合带的波动。渤海辐合带增强后登陆山东半岛,造成山东半岛西北东南向降雪带。对这次冷流暴雪个例的分析发现,太行山脉通过形成背风低压中尺度系统直接影响渤海上的中尺度辐合带的发展,而渤海辐合带与山东半岛北岸附近海岸锋的耦合使辐合加强,增强了降雪强度。     

Interdecadal Variation of the Transition Zone Chlorophyll Front: A Physical-Biological Model Simulation between 1960 and 1990

The interdecadal climate variability affects marine ecosystems in both the subtropical and subarctic gyres, consequently the position of the Transition Zone Chlorophyll Front (TZCF). A three-dimensional physical-biological model has been used to study interdecadal variation of the TZCF using a retrospective analysis of a 30-year (1960–1990) model simulation. The physical-biological model is forced with the monthly mean heat flux and surface wind stress from the COADS. The modeled winter mixed layer depth (MLD) shows the largest increase between 30°N and 40°N in the central North Pacific, with a value of 40–60% higher during 1979–90 relative to 1964–75 values. The winter Ekman pumping velocity difference between 1979–90 and 1964–75 shows the largest increase located between 30°N and 45°N in the central and eastern North Pacific. The modeled winter surface nitrate difference between 1979–90 and 1964–75 shows increase in the latitudinal band between 30°N and 45°N from the west to the east (135°E–135°W), the modeled nitrate concentration is about 10 to 50% higher during the period of 1979–90 relative to 1964–75 values depending upon locations. The increase in the winter surface nitrate concentration during 1979-90 is caused by a combination of the winter MLD increase and the winter Ekman pumping enhancement. The modeled nitrate concentration increase after 1976–77 enhances primary productivity in the central North Pacific. Enhanced primary productivity after the 1976–77 climatic shift contributes higher phytoplankton biomass and therefore elevates chlorophyll level in the central North Pacific. Increase in the modeled chlorophyll expand the chlorophyll transitional zone and push the TZCF equatorward. This revised version was published online in August 2006 with corrections to the Cover Date.     

赤道东太平洋温度锋附近的混沌输运与混合

运用 Mc Creary和 Yu(1992 )的非线性 2 12 层模式的积分流场 ,研究了混沌混合与输运对海水及要素浓度的输运和混合问题。模式结果显示混沌混合区主要分布于赤道东太平洋不稳定区及东、西边界附近 ,中西太平洋的大部分区域为非混沌区。释放在混沌区内的示踪团随时间的弥散过程要较非混沌区内的示踪团复杂的多。因多模态不稳定波动的共同作用 ,尤其是在赤道上经向运动最强的 Yanai波的加入 ,使得赤道不稳定区的流体以混沌混合的方式均匀地弥散开 ,趋向于粗粒 (coarse- grained)意义下的均匀化。并有大量释放于赤道东太平洋不稳定区的示踪质点越过赤道进入对面半球。背景辐散流的加入能将部分示踪点输送出混合区使其不加入均匀化过程 ,故最后混入另一半球的质点数少于半数。过赤道交换速率则主要由混沌混合的强度有关。     

河口海岸泥沙输移的分组数学模型研究

根据河口海岸水沙输移的特点,建立了一个新的二维分组数学模型,用来预测该区域的水沙输移过程。该模型耦合了水动力模块、泥沙输移模块和床面演变模块。其中水动力模块基于浅水方程组,综合考虑了柯氏力、床面切应力以及表面风应力的影响,引入干湿判断法处理动边界。泥沙输移模块首先将泥沙按照粒径分组,针对不同泥砂性质,对各组泥沙分别进行建模求解。床面演变模块基于质量守恒方程,实时更新床面高程以及床沙级配变化,并传递给水动力模块,更新底部边界。该模型被应用在了英国塞汶(Severn)河口,其预测的泥沙浓度和实测数据以及不分组的模型的预测结果进行了比较,结果显示,文中建立的分组模型预测的结果要明显好于不分组模型。