海洋平台大直径钢管桩打桩过程有限元分析研究

近年来海上工程的规模越来越大,为了满足工程需要,桩基设计常常采用大直径,大长度的钢管桩。打桩过程是个相当复杂的过程,不仅涉及到几何非线性、材料非线性、边界非线性,而且是个动力过程。有限元法在处理打桩分析方面具有很强的优势,采用PLAXIS对不同条件下的打桩问题进行了动力模拟分析。分析显示在打桩过程中,桩端土体会产生较大的水平位移和竖向位移,桩端土体和靠近桩端的部分土塞内会产生较大的超孔隙水压力。在砂土中,停锤较短时间也会使孔压迅速消散,这也是打桩中间的停锤会造成后续打桩困难的主要原因。     

Estimation of colored dissolved organic matter and salinity fields in case 2 waters using SeaWiFS: Examples from Florida Bay and Florida Shelf

Estimates of water quality variables such as chlorophylla concentration (Chl), colored dissolved organic matter (CDOM), or salinity from satellite sensors are of great interest to resource managers monitoring coastal regions such as the Florida Bay and the Florida Shelf. However, accurate estimates of these variables using standard ocean color algorithms have been difficult due to the complex nature of the light field in these environments. In this study, we process SeaWiFS satellite data using two recently developed algorithms; one for atmospheric correction and the other a semianalytic bio-optical algorithm and compare the results with standard SeaWiFS algorithms. Overall, the two algorithms produced more realistic estimates of Chl and CDOM distributions in Florida Shelf and Bay waters. Estimates of surface salinity were obtained from the CDOM absorption field assuming a conservative mixing behavior of these waters. A comparison of SeaWiFS-derived Chl and CDOM absorption with field measurements in the Florida Bay indicated that although well correlated, CDOM was underestimated, while Chl was overestimated. Bottom reflectance appeared to affect these estimates at the shallow central Bay stations during the winter. These results demonstrate the need for new bio-optical algorithms or tuning of the parameters used in the bio-optical algorithm for local conditions encountered in the Bay.     

AOU as indicator of water-flow direction in the central North Pacific

Salinity, preformed phosphate and AOU distribution on the sigma-t surfaces of 26.8 and 27.3 of the central North Pacific Ocean, as well as the topography of these density surfaces, were studied. The direction of water flow suggested by the AOU distribution on these density surfaces was compared to that indicated by the acceleration potential contours on the _t =125 cl/ton and _t =80cl/ton surfaces drawn by Joseph L.Reid, Jr. The disagreements were explained in terms of mixing and possible gradients of primary production at the sea surface. On the 26.8 sigma-t surface a southward flow connecting the westward flow south of the Aleutian chain and the eastward flow farther south, between 175E and 180 is suggested by the AOU distribution but is not implied by the acceleration potential contours. If the circulation pattern at this density surface is similar to that at the sea surface, this southward flow is very likely to be real.     

南海和阿拉伯湾钙质砂工程特性对比研究

钙质砂在我国南海有广泛的分布。随着海上石油工业和海洋资源的开发利用,钙质砂问题日益得到重视。用室内试验的方法,采用相同级配的南海钙质砂和阿拉伯湾钙质砂进行了分析,结果显示,相同级配的南海钙质砂和阿拉伯湾钙质砂的最大最小干密度存在明显差异,南海钙质砂均低于阿拉伯湾钙质砂。同时在级配以及密实度相同的条件下,南海钙质砂的应力-应变关系表现为硬化,而阿拉伯湾钙质砂表现为软化; 两者在Dr=0.3时,内摩擦角接近,均为33°左右,但随着相对密实度的增加,南海钙质砂内摩擦角增长速度更快,在Dr=0.8时达到37.7°,明显高于相同密实度的阿拉伯湾钙质砂的34.9°。电镜分析显示,在微观结构上,南海钙质砂的颗粒多棱角,内孔隙更加发育,这是造成南海钙质砂与阿拉伯湾钙质砂物理力学性质差异的重要原因之一。     

Study on interaction between soil and anchor chain with finite element method

With the development of offshore engineering, deeply embedded anchors are needed to be penetrated to appreciable depth and attached at the pad-eye. The interaction between anchor chain and soil is a very complex process and has not been thoroughly understood yet. In this paper, the finite element method (FEM) was used to study the interaction of soil-chain system. Results of the analysis show that when the attachment point is at a shallow depth, the load-development characteristics of the chain from FEM are in good agreement with that from the model tests and theoretical analysis. But with the depth increment, the results are different obviously in different methods. This phenomenon is resulted from a variety of reasons, and the plastic zone around the chain was studied to try finding the mechanism behind it. It could be seen that the plastic zone extended in different modes at different depths of attachment points. The interaction between the soil and anchor chain makes the load acting on the anchor decrease, but the soil disturbed surrounding the chain increases the anchor failure possibility. When the anchor bearing capacity is evaluated, these two factors should be considered properly at the same time.     

颗粒破碎对钙质砂压缩特性影响的试验研究

利用南海钙质砂和阿拉伯湾钙质砂,进行侧限压缩试验,对其压缩特性进行分析,得到了相应的压缩指数;采用相对破碎率为度量指标,评价了钙质砂在压缩试验过程中的颗粒破碎情况。同时根据试验数据得到了不同初始相对密实度的砂样的塑性功,通过建立塑性功与相对破碎率以及塑性功与压缩指数之间的关系,探讨了颗粒破碎对钙质砂压缩特性的影响。研究显示,在本次试验条件下,颗粒破碎是导致钙质砂压缩变形的主要因素,钙质砂的中值粒径以及碳酸钙含量等因素对其颗粒破碎程度有明显影响;钙质砂的相对破碎率与其输入的塑性功有关,并且受到初始相对密实度的影响,采用相对密实度进行归一化后,两者呈现较好的幂函数关系;通过建立钙质砂压缩指数与塑性功之间的关系,进一步建立了钙质砂的压缩指数与相对破碎率之间的关系,经相对密实度归一化后,两者也呈现幂函数规律,此规律可以用于评价颗粒破碎对钙质砂压缩特性的影响。     

Spatial and temporal dynamics of dissolved trace metals, organic carbon, mineral nutrients, and phytoplankton in a coastal lagoon: Great South Bay, New York

Although marine lagoons are ubiquitous features along coastal margins, studies investigating the dynamics of metal, organic matter, and nutrient concentrations in such systems are rare. Here we present a comprehensive examination of the temporal and spatial gradients in dissolved trace metals (Ag, Cd, Cu, Mn, Pb), organic and inorganic nutrients (POC, PON, DOC, N0₃ ⁻, NH₄ ⁺, H₄SiO₄, PO₄ ⁻³, and urea), and algal biomass in a lagoon estuary, Great South Bay (GSB), New York, USA. While this estuary has experienced a series of environmental problems during recent decades (urbanization, loss of fisheries, harmful algal blooms), root causes are largely unknown, in part because levels of bioactive substances, such as trace metals, have never been measured. Sampling was undertaken within multiple estuarine, riverine, and groundwater sites during spring, summer, and fall. Trace metal tracers (e.g., Ag, Mn) and statistical analyses were used to differentiate the influences of natural and anthropogenic processes on the chemical composition of the lagoon. Our analyses revealed three clusters of biogeochemical constituents that behaved similarly in GSB: constituents under strong biological control such as POC, PON, DOC and chlorophyll,a; elements indicative of benthic remobilization processes such as Mn, Cd, and Cu; and constituents strongly influence by anthropogenic processes such as Ag, Pb, PO₄ ⁻³, NO₃ ⁻, and NH₄ ⁺. Although GSB is surrounded by a densely populated watershed (c. 1 million people), it does not appear to be significantly contaminated by trace metals compared to other urban estuaries. Levels of DOC (up to 760 μM) in GSB were well correlated with phytoplankton biomass and exceeded at least 98% of values reported in similar mid Atlantic estuaries at the same salinities. These high levels of DOC are likely to be an important source of carbon export to the coastal ocean and likely promote mixotrophic harmful algal blooms in this system.     

Study of Wave and Tide Influence on Slope Stability of the Navigation Channel of Tianjin Port

The Tianjin Port is the largest man-made port in China.Since the navigation channel of the Tianjin Port is constructed by dredging,a very important problem,as many people concerned,is the submarine slope stability.As the environment on land is different from that in submarine,it is necessary to evaluate the influence of the environmental loading,such as wave and tide,on the stability of navigation channel slope.In the present study,based on the observed results,the characteristics of the navigation channel slope are summarized,and the causes of creating the special slope shape are analyzed.The roles of waves and tides are evaluated,and failure mechanics are discussed to helq us predict what will happen in the future.