Effect of sea level rise on tidal circulation in the Hooghly Estuary,Bay of Bengal

The issue of sea level rise is receiving considerable attention all over the world. Although the Indian stations have shown mixed trends, a positive sea level trend has been noticed in the Hooghly Estuary, situated on the east coast of India. The Hooghly River serves as a navigable waterway to Calcutta and Haldia ports. The river is tidal for nearly 250 km. To study the water levels and tidal currents in the lower part of the Hooghly Estuary, from sea face at Sagar to Hooghly Point, a vertically integrated numerical model has been used. The model is fully nonlinear and uses a semiexplicit finite‐difference scheme to solve the basic hydrodynamic equations on a staggered grid. This model is coupled with a one‐dimensional model, which has been used for the upper estuary from Hooghly Point to Swarupganj, where the flow is unidirectional. The computed water levels and currents are found to be in good agreement with the available observations. This model is applied to study the alterations in tidal circulation for a rise and fall in the sea level. The results have shown a substantial increase in the amplitude and velocities of the tidal wave due to the sea level rise.     

一个考虑潮汐、中尺度涡和地形影响的南海底部环流诊断模型

本文构造了一个考虑潮汐、中尺度涡和地形影响下的南海底部环流诊断模型。在该模型中,潮汐混合和涡致混合引起的垂直速率用一个类似的改进参数化方案来表示。该模型结果显示在南海深层吕宋海峡"深水瀑布"和斜压影响最大,潮汐作用和中尺度涡影响次之,风场的影响最小。斜压影响的整体效应与其他因素相反。潮汐混合与涡致混合具有明显的地形依赖性。潮汐混合主要集中在南海北部海盆地形较为陡峭的陆坡区和南海中部海山区,而涡致混合主要集中在海盆西边界区以及中部海山区。在不考虑吕宋海峡"深水瀑布"、潮汐和中尺度涡的情况下(对应吕宋海峡关闭),南海底部环流为反气旋式环流。考虑吕宋海峡"深水瀑布"后,南海底层环流为气旋式环流,而潮汐混合和涡致混合起到加强整个气旋式环流强度的作用。此外,该模型还给出了南海底部环流量级大小与地形坡度之间的密切关系,即地形坡度较大的地方,其流速也大。这对于现场观测有着一定的参考意义。最后,本文用尺度分析的方法从理论上分析了该模型的适用性,证实了该模型具有一定的可靠性。     

Sedimentation and morphological changes at Yuantuojiao Point,estuary of the North Branch,Changjiang River

The North Branch, separated by the Chongming Island, was once the main channel in the estuary of the Changjiang River. Reclamation and a decrease in runoff to the North Branch had led to the narrowing and shallowing of the channel. The Yuantuojiao Point is located at the intersecting point connecting the North Branch of the Changjiang River and the Jiangsu coastline. Erosion cliffs are developed between the typical silty-muddy tidal flat and the salt marsh occupied by Spartina alterniflorea, and this has changed rapidly over the past few years. The sediment grain size analysis results of the surficial and two core samples indicate that the Yuantuojiao Point tidal flat experienced continuous accretional processes. Based upon 137 Cs analysis results of the YT and YY Cores sampled from the tidal flat at the Yuantuojiao Point, the average sedimentation rate of the YT Core was 2.30 cm/a from 1963 to 2007, and 2.38 cm/a from 1954 to 2007 for the YY Core. The sedimentation rates of both core locations have declined since the 1960s corresponding to the seaward reclamation at the Yuantuojiao Point. The average sedimentation rates at the Yuantuojiao Point were similar to that of the silty-muddy tidal flat at the northern Jiangsu coast, but lower than that of the south of the Changjiang River Estuary. According to field morphological investigations from 2006 to 2008 on the salt marsh at the Yuantuojiao Point, cliffs retreated markedly by storm surges and disappeared gradually because of the rapid sedimentation on the silty-muddy tidal flat. The maximum annual retreat reached 10 m. The recent sedimentation and morphological changes of the Yuantuojiao Point tidal flat not only displayed the retreat of the salt marsh and the disappearance of cliffs, but also was accompanied by rapid sedimentation of the silty-muddy tidal flat and the salt marsh, indicating the responses to the tidal currents, storm surges, Spartina alterniflorea trapping sediments and large-scale reclamation. The sediment grain size and their trends, southward coastal flow, and sandspits of the longshore bars suggest that the main sediment source at the Yuantuoijao Point, estuary of the North Branch was possibly from the Changjiang River before 1958, since then, it has been from the south of the submarine radial sand ridges of the southern Huanghai Sea (Yellow Sea).     

Observing spectral characteristics over a continental shelf and slope in the South China Sea

Using in situ measurement data from May-June, 1998, and data from the Asian seas international acoustics experiment （ASIAEX） from 2001 in the South China Sea （SCS）, the spectral density function and the dissipa- tion spectrum function are estimated. In the inffa-gravity wave （IGW） band, the power spectra of velocity （u, v, w） are universal functions with respect to characteristic frequencies, which correspond to the peak fre- quencies of the dissipation spectrum （PFDS）. This suggests that high-frequency internal waves in the IGW band have similar dynamical characteristics. In addition, the evolution of these characteristic frequencies is explored and its highest value is 8.8 cph （cycles per hour, 1 cph=2.778× 10-3 Hz）.     

海洋中尺度涡的机械能及其源汇研究*

由于观测手段的限制,海洋中尺度涡的能量输送及生成与耗散动力过程一直是世界大洋能量循环中悬而未决的一个问题,而中尺度涡在海洋中又广泛存在,它不仅占据海洋表层动能的绝大部分,而且是能量级串中连接大尺度和小尺度的中间环节,在大洋能量传输中扮演着重要的角色。文章以中尺度涡场机械能的大小、分布、源汇为主线,结合作者在这方面的最新研究成果,综述当前对中尺度涡机械能及其源汇的研究进展。     

长江河口理论最高和最低潮面计算和应用

应用改进的河口海洋数值模式,计算长江河口及其邻近海域水位随时间的变化,利用国际上先进的T_Tide调和常数软件计算得出潮汐的主要调和常数,根据《海道测量规范》(GB12317—1998)理论最低、最高潮面算法,在考虑8个主要分潮M2、S2、N2、K2、K1、O1、P1、Q1的基础上再考虑3个主要浅水分潮M4、M6和MS4,得出长江河口理论最低、最高潮面的空间分布。采用数值模式,设计高分辨的网格,有效解决了潮位站稀少和空间分布不均的不足,提升了理论最低、最高潮面的计算精度。将基于理论最低潮面的2009年长江河口实测地形资料转化为基于85国家高程基面的地形资料,使资料得到了充分应用。     

径流和风对涌潮影响的数值模拟

由于实际江道中地形和江道轮廓等复杂性,难以分析涌潮演变规律。以钱塘江河口为基础,建立了概化河口的水动力数学模型,将复杂问题简单化,通过数学模型计算分析了径流和风况对潮差、涨潮历时、涌潮高度和涌潮传播速度的影响。结果表明,不同河段存在涌潮高度最大值的相应临界流量,越往下游,临界径流量越大;涌潮高度随风向变化规律是"逆风"<"无风"<"顺风";顺风条件下,风速越大,涌潮高度越大。     

“破坏-安全”结构抗震理念及其应用

目前我国房屋建筑抗震采用的以小震弹性计算为基础的设计方法,使工程师忽视了对建筑结构在强烈地震作用下破坏模式的充分考虑与设计,使得建筑结构的大震安全性有时难以得到保证。＂破坏-安全＂抗震理念,以房屋建筑最重要的抗震安全性能为目标,要求设计人员对结构的预期破坏模式有充分的把握和控制,使结构在强烈地震作用下能够形成明确的预期破坏模式并具备一定的耗能能力,从而以经济的代价保证结构其余部分在强烈地震作用下的安全。本文结合我国汶川地震灾后恢复重建与加固改造的实际情况,介绍了＂破坏-安全＂抗震理念及其设计概念,并介绍了国内外研究人员与工程师在实现＂破坏-安全＂抗震理念方面所提出的创新抗震结构体系及其研究成果。希望＂破坏-安全＂这一抗震理念及其相关技术能够在我国广大的经济欠发达地区的抗震设计实践中得到推广,以全面提高我国经济欠发达地区房屋建筑的抗震安全性。     

A new type of damper with friction-variable characteristics

Professor T.T.Soong is one of the early pioneers in fi eld of earthquake response control of structures.A new type of smart damper,which is based on an Energy Dissipating Restraint(EDR),is presented in this paper.The EDR by Nims and Kelly,which has a triangle hysteretic loop,behaves like an active variable stiffness system(AVS) and possesses the basic characteristics of a linear viscous damper but has diffi culty in capturing the output and large stroke simultaneously needed for practical applicataions in e...     

Reaearch on Skempton's coefficient B based on the observation of groundwater of Changping station

Based on isotropic linear poroelastic theory and under the undrained condition, we summarize three equations connecting the Skempton's coefficient B with the groundwater level. After analysis, we propose a method to calculate the Skempton's coefficient B according to the relationship between water level and tidal strain. With this method we can get the value of B without the earthquake occurrence, which can provide the high frequency waves for research. Besides, we can also get the in-suit Skempton's coefficient B without the experiment of rock physics. In addition, we analyze the observed data of Changping station recorded in groundwater monitoring network (abv., GMN) before and after the Wenchuan M_S8.0 with this method, and find out there's a slight change of the value of B after the seismic waves passed by, which implies that the propagation of seismic waves may have brought some variations to the poroelastic medium of the well.