Regression Formulations for the Stress at Hot Spot of Multiplanar Tubular DT Joints

- Stress concentration analysis of multiplanar tubular DT joints plays an important role in the fatigue design of offshore platforms. A semi-analytic method for stress analysis under the condition of any loads is briefly introduced in the paper. Nineteen multiplanar tubular DT joints with one of two braces of the same dimension subjected to axial loads and out- of- plane bending moments are computed for parametric stress analysis by using the present method. The influence of geometrical parameters on the stresses of multiplanar tubular DT joints is discussed and compared with corresponding uniplanar T joints. The regression formulae for the stress at hot spot of multiplanar DT joints are found by modification of SCF of corresponding uniplanar T joints. The parametric formulae for the maximum stress by superposition. Finally, the influences of stiffening effect and load-interaction effect on the maximum stress of DT joints are discussed.     

A Linear Programming Model for Seabed Oil-Gas Pipe Network

This paper analyzes the pipe network system of oil-gas collection and transportation foroffshore oilfield development.A"0-1"integer linear programming model is constructed to optimize theinvestment of seabed pipe network.The mathematical model is solved by the spanning tree method ofgraph theory and network analysis.All spanning trees of a network graph compose all the feasible solu-tions of the mathematical model.The optimal solution of the model is the spanning tree with the minimumcost among all spanning trees.This method can be used to optimize the seabed pipe network system andgive a minimum cost plan for the development of offshore marginal oilfield groups.     

Numerical Simulation of Water Level Under Interaction Between Runoff and Estuarine Dynamics in Tidal Reach of the Yangtze River

The Yangtze Estuary, the largest estuary in China, is under an obvious interaction between runoff and astronomical tide. The research on the interaction is very important for the exploitation and utilization of water resources in this area. A horizontal 2D hydrodynamic numerical model is established and verified in the present study with the modeling range from Datong to the Yangtze Estuary. Based on the comparison of high water levels under the interaction between different runoff and estuarine dynamics, s...     

Model Test Study on Ice-Induced Vibrations of Compliant Multi-Cone Structures

For the study on the ice-induced vibration of a compliant mono-cone structure,a series of model tests were performed from 2004 to 2006.In these tests,the ice sheet before the compliant conical structure was found to be failed in two-time breaking.Based on this important finding,model tests study of the ice force on a compliant multi-cone structure were performed from 2006 to 2007.in these tests,the ice sheet broke before each single cone non-simultaneously.The exciting energy of the total ice force was found to be in a wide range of frequencies,and the structure can be easily excited with nonlinear resonance.     

Effect of Fly Ash on Frost-Resistance and Chloride Ions Diffusion Properties of Marine Concrete

It is necessary to pay more attention to the durability of concrete undergoing freeze-thaw cycles and seawater attack simultaneously.Investigated are the effects of water-binder ratio,fly ash (FA) contents and air-entraining agent on resistance to frost and chloride diffusion of marine concrete blended with FA in natural seawater.The results show that fly ash does not improve the frost resistance of concrete but can improve its resistance to chloride diffusion by addition of less than 30%.The resistance to frost and chloride diffusion of FA concrete can be improved with the decrease of water-binder ratio,and FA may improve both of them simultaneously only being mixed with air-entraining agent.A ratio (named as R) of the frost-resisting durability factor to chloride diffusion coefficient can be used to evaluate the durability of marine concrete.Scanning electron microscope (SEM) analyses are consistent with the evaluations by the value of R.     

The Optimal Design of TMD for Offshore Structures

This paper presents the optimal design procedure of Tuned Mass Damper(TMD)for re-ducing vibration of an actual steel jacket offshore platform excited by random wave loading.In this study,a frequency domain is taken.The force on the structure is determined by use of the linearized Morisonequation for an input Power Spectral Density(PSD)of wave elevation.The sensitivity of optimum valuesof TMD to characteristic parameters of random wave spectrum is analyzed.An optimized TMD designfor the modeled platform is given based on design conditions and the findings of the study.     

Application of Line Boundary Technique to 2D Tidal Current Simulation

To deal with the problems concerning the shore boundary,moving boundary and engineeringboundary which are encountered frequently in 2D tidal current simulation by the finite difference method,theconcept of line boundary is introduced and studied here,and then the line boundary technique in common useis proposed in this paper.Analysis of some calculation cases shows that this technique is practical,effective,and simple in 2D tidal current simulation involving different boundaries.     

基本结构有限元算法及大地电磁测深一维连续介质正演

提出了一种新的数值方法——基本结构有限元法. 从经典的伽辽金法（Galerkin method）出发,首先定义了基本结构插值基函数,在此基础上建立了基本结构方程,然后用有限元法进行进一步的具体实现. 该算法被成功应用到大地电磁测深一维连续介质正演计算中. 采用了6种不同的单元插值基函数进行计算,并对计算结果进行了比较和分析.     

2.5-D DC Resistivity Modeling Considering Flexibility and Accuracy

We highlighted the flexibility of using unstructured mesh together with the local refinement by a resistivity model with complicated topography. The effect of topography is emphasized. Based on this, we calculated a specific class of layered models and found that the accuracy is not always satisfactory by utilizing the standard approach. As an improvement, we employed the layered earth as the reference model to calculate the wavenumbers. The comparison demonstrates that the accuracy is considerably improved...     

岩层离距图法研究沉积岩断裂发育史——以松辽盆地敖古拉断裂为例

利用断裂活动过程中留下的各种地质标记研究断裂发育史是比较困难的 ,已有的研究方法主要可归纳出七种 ,都存在局限性。岩层离距图法是以地震剖面为基础 ,将穿过断裂的各剖面上的标志层投影到沿断裂走向的铅垂面上 ,得到多组标志层的垂向断距数据 ,然后用下部各标志层的断距减去最上部标志层的断距 ,并作多轮次计算 ,直到最后的断距差近似为零或仅剩一个非零标志层。每一轮次计算代表一个活动期次 ,如果出现负值 ,则表示有构造反转。对松辽盆地敖古拉断裂作了实例计算 ,结果为该断裂发育经历了三个正断活动期和一个逆断活动期 ,与盆地区域性活动有些差别。岩层离距图法比起其他已有方法 ,可靠程度大大提高