An Experi mental Study on Wave-Induced Dynamic Stresses in Seabed

1 .IntroductionEvery year ,Taiwanis subjectedtotwo or three typhoonintrusions in average which always causedisasters . Most of the disasters which occur around the coastal zone are due to seabed instability andcoastal structure destruction caused bytyphoo…     

Estimation of Land Subsidence Based on Groundwater Flow Model

This article presents an approach for estimating land subsidence due to withdrawal of groundwater. The proposed method calculates the groundwater seepage in 3-D-condition and calculates the land subsidence one-dimensionally. The governing equation on groundwater seepage is based on the three-dimensional mass conservation law and the principle of effective stress. The land subsidence calculation method is derived based on the following assumptions: (1) displacements occur only in the vertical direction, and (2) in vertical direction the total stresses do not change. The governing equation is solved by numerical method, i.e., finite element method (FEM) in spatial discretization and finite difference method (FDM) in time series discretization. In FEM Galerkin method is adopted and in FDM, lumped matrix method is employed. The proposed method is calibrated via analyzing 1-D consolidation problem and the results are compared with those from Terzaghi's one-dimensional consolidation theory and oedometer test. The proposed method is employed to analyze the consolidation of a soft layer due to withdrawal of groundwater from an aquifer under it. Moreover, this method is also applied to a field case of land subsidence due to groundwater pumping in a gas production field in Japan. The analytical results are compared with the field observed data. The results show that this approach simulates the field case well.     

Model simulations of carbon sequestration in the northwest Pacific by patch fertilization

Iron fertilization of nutrient-rich surface waters of the ocean is one possible way to help slow the rising levels of atmospheric CO₂ by sequestering it in the oceans via biological carbon export. Here, I use an ocean general circulation model to simulate a patch of nutrient depletion in the subpolar northwest Pacific under various scenarios. Model results confirm that surface fertilization is an inefficient way to sequester carbon from the atmosphere (Gnanadesikan et al., 2003), since only about 20% of the exported carbon comes initially from the atmosphere. Fertilization reduces future production and thus CO₂ uptake by utilizing nutrients that would otherwise be available later. Effectively, this can be considered as leakage when compared to a control run. This “effective” leakage and the actual leakage of sequestered CO₂ cause a significant, rapid decrease in carbon retention (only 30–45% retained after 10 years and less than 20% after 50 years). This contrasts markedly with the almost 100% retention efficiency for the same duration using the same model, when carbon is disposed directly into the northwest Pacific (Matsumoto and Mignone, 2005). As a consequence, the economic effectiveness of patch fertilization is poor in two limiting cases of the future price path of carbon. Sequestered carbon in patch fertilization is lost to the atmosphere at increasingly remote places as time passes, which would make monitoring exceedingly difficult. If all organic carbon from one-time fertilization reached the ocean bottom and remineralized there, acidification would be about −0.05 pH unit with O₂ depletion about −20 μmol kg⁻¹. These anomalies are probably too small to seriously threaten deep sea biota, but they are underestimated in the model because of its large grid size. The results from this study offer little to advocate purposeful surface fertilization as a serious means to address the anthropogenic carbon problem.     

Modified PIC Method for Sea Ice Dynamics

The sea ice cover displays various dynamical characteristics such as breakup, rafting, and ridging under external forces. To model the ice dynamic process accurately, the effective numerical modeling method should be established. In this paper, a modified particle-in-cell （PIC） method for sea ice dynamics is developed coupling the finite difference （FD） method and smoothed particle hydrodynamics （SPH）. In this method, the ice cover is first discretized into a series of lagrangian ice particles which have their own sizes, thicknesses, concentrations and velocities. The ice thickness and concentration at Eulerian grid positions are obtained by interpolation with the Gaussian function from their surrounding ice particles. The momentum of ice cover is solved with FD approach to obtain the Eulerian cell velocity, which is used to estimate the ice particle velocity with the Gaussian function also. The thickness and concentration of ice particles are adjnsted with particle mass density and smooth length, which are adjusted with the redistribution of ice particles. With the above modified PIC method, numerical simulations for ice motion in an idealized rectangular basin and the ice dynamics in the Bohai Sea are carried out. These simulations show that this modified PIC method is applicable to sea ice dynamics simulation.     

波峰特征量的统计分布

本文在作者另文数值模拟得到的三维海浪基础上 ,进一步分析给出了三维波峰长度、高度及方向角度等特征量的统计分布。发现考虑海浪的方向性质后波峰分布不再是均匀连续的 ;波峰的长度分布受方向函数影响 ,方向分布越宽 ,波峰的平均长度越短 ,波峰的方向角分布越宽 ;波峰高度和长度在波峰高度较小时有很大的相关性 ,而在波峰高度很大时无关     

Effect of Sea Level Variation on Tidal Characteristic Values for the East China Sea

1 .IntroductionTheglobalairtemperatureroseabout 0 .5～ 0 .6°Coverthepast 2 0thcentury ,andtheglobalmeansealevelincreasedbyabout2 0cmduringtheperiod .Theregionalmeansealevelriseswiththerisingglobalmeansealevel.Zuoetal.( 1 997)indicatedthatthemeanrisingrateofabsolutemeansealevelalongtheChinacoastontheassumptionofunifiedisostaticdatumis 2mm a .Woodworth( 1 999)analyzedsealevelspanning 1 76 8tothepresentinLiverpool,andobtainedaseculartrendforheperiodupto 1 880of0 .39± 0 .1 7mm a ,andatrendfort…     

海南东寨港红树林港湾潮汐动力研究

在海南东寨港林市村附近红树林港湾潮汐动力测量的基础上，建立二维可移动边界有限元数值模型，研究红树林港湾浅水湖滩潮流场特征。实测与计算结果表明，潮沟区流速最大，具驻波特征，呈明显时间－速度不对称，东潮沟涨潮优势，百潮沟落潮优势，整个港湾水体呈顺时针循环。白滩与林地周期性淹没，白滩流速较湖沟略小。林地曼宁系数为白滩的１０倍，流速小于１０ｃｍ·ｓ（－１），约为相应潮沟流速的１／１０。林地如去掉林木，流速可增加３倍以上，流向也有变化。