浅海区域Topex/Poseidon测高卫星数据波形重构方法

根据测高卫星返回波形的特征,给出了由Topex/Poseidon卫星波形数据进行波形重构的方法,并采用函数逼近算法确定波形重构改正量,进而改善测高卫星近海岸海面高观测值的精度.在中国南海区域计算了四圈T/P测高卫星经过波形重构后的海面高数据.近海岸海面高数据与相近时刻验潮站数据相比,精度比波形重构前有了很大提高,证明该方法的有效性.     

南黄海地质及地震

南黄海属于华北地台及扬子准地台的一部分,是一个由隆起、拗陷组成的中、新生代大型复式盆地。海域内新构造运动以断裂、岩浆及差异性升、降活动为主,并且由现代活动断裂控制的地震频繁而活跃。南黄海的地震活动主要集中分布于南部拗陷与勿南沙隆起一带以及与江苏海岸相平行的浜岸断裂带上。今后较长时间内,南黄海的地震活动仍将沿着上述地带往复迁移     

Undrained capacity of surface foundations with zero-tension interface under planar V-H-M loading

Undrained capacity of strip and circular surface foundations with a zero-tension interface on a deposit with varying degrees of strength heterogeneity is investigated by finite element analyses. The method for simulating the zero-tension interface numerically is validated. Failure envelopes for strip and circular surface foundations under undrained planar V-H-M loading are presented and compared with predictions from traditional bearing capacity theory. Similar capacity is predicted with both methods in V-H and V-M loading space while the traditional bearing capacity approach under-estimates the V-H-M capacity derived from the numerical analyses due to superposition of solutions for load inclination and eccentricity not adequately capturing the true soil response. An approximating expression is proposed to describe the shape of normalised V-H-M failure envelopes for strip and circular foundations with a zero-tension interface. The unifying expression enables implementation in an automated calculation tool resulting in essentially instantaneous generation of combined loading failure envelopes and optimisation of a foundation design as a function of foundation size or material factor. In contrast, the traditional bearing capacity theory approach or direct numerical analyses for a given scenario requires ad-hoc analyses covering a range of input variables in order to obtain the ‘best’ design.     

Numerical analysis of suction embedded plate anchors in structured clay

As offshore energy developments move towards deeper water, moored floating production facilities are increasingly preferred to fixed structures. Anchoring systems are therefore of great interest to engineers working on deep water developments. Suction embedded plate anchors (SEPLAs) are rapidly becoming a popular solution, possessing a more accurate and predictable installation process compared to traditional alternatives. In this paper, finite element analysis has been conducted to evaluate the ultimate pullout capacity of SEPLAs in a range of post-keying configurations. Previous numerical studies of anchor pullout capacity have generally treated the soil as an elastic-perfectly plastic medium. However, the mechanical behaviour of natural clays is affected by inter-particle bonding, or structure, which cannot be accounted for using simple elasto-plastic models. Here, an advanced constitutive model formulated within the kinematic hardening framework is used to accurately predict the degradation of structure as an anchor embedded in a natural soft clay deposit is loaded to its pullout capacity. In comparison with an idealised, non-softening clay, the degradation of clay structure due to plastic strains in the soil mass results in a lower pullout capacity factor, a quantity commonly used in design, and a more complex load–displacement relationship. It can be concluded that clay structure has an important effect on the pullout behaviour of plate anchors.     

多跨海底管道横流向涡激振动预报模型

基于欧拉-伯努力梁理论确定了多跨管道结构振动方程,采用非线性Van der pol方程描述旋涡脱落的尾流动力特性,利用弹簧模拟两端和中间的复杂边界约束,构建了多跨海底管道横流向涡激振动预报模型。基于模态正交性展开流-固耦合作用方程,对各阶主坐标响应进行数值求解。对比了本模型预报结果与试验结果、软件分析以及DNV规范推荐值,吻合情况比较理想。本模型可为深海多跨管道涡激振动的研究、防范和治理提供有效的分析方法。     

Effect of Internal Flow on Vortex-Induced Vibration of Submarine Free Spanning Pipelines

At present, most researches on the vortex-induced vibration of submarine free spanning pipelines ignore the effect of internal flowing fluid; furthermore, there are no research reports considering the coupling effect of internal and external fluid with the free span. In this paper, combining Iwan‘s wake oscillator model with the differential equation derived for the dynamic response of submarine free spanning pipelines with inclusion of internal flow, the pipe-fluid coupling equations are developed to investigate the effect of internal flow on the vortex-induced vibration of the free spans. The finite dement approximation is implemented to derive the matrix equations of equilibrium. The Newmark method combined with simple iteration is used to solve the system of equations. The results indicate that the internal fluid flow may cause the shift of resonance band to the lower frequency and a slight decrease in the peak value; the effect will be mare pronounced with the increase of the span length and can be weakened in the presence of the axial tension.     

南海北部海区无柄蔓足类的分布

于1986－1991年在南海北部对16个海洋结构物上的无柄蔓足类水平分布、垂直分布和个体大小进行调查。研究表明，所采集到的标本隶属于无柄蔓足类的3科7属19种，其中藤壶科5属16种，笠藤壶科1属2种和小藤壶科1属1种。共有17种无柄蔓足类分布在珠江口东南海区；而琼东海区仅发现2种；琼东南海区有8种；莺歌海海区11种和北部湾海区10种。纵肋巨藤壶、美丽藤壶和珠江藤壶为珠江口东南海区特有种。研究无柄蔓足类在南海北部近海海区的分布及其与海流的关系，不仅有助于深入了解该类生物的生活习性和生态特点，也为海洋石油平台的设计及污损生物的防除提供参数。     

Buckling Propagation in Marine Pipelines

The buckling propagation in marine pipelines is studied by means of the cylindrical shell model in this paper. Several parameters including geometrical parameter D/ T, L/ D, physical parameter E and σy are discussed. The computed results are compared with the available experimental data and other computed results, it is found that the present results are closer to the experimental results than other computed results.     

The Bremen ocean bottom tiltmeter (OBT) – a technical article on a new instrument to monitor deep sea floor deformation and seismicity level

The Bremen ocean bottom tiltmeter is a new 6000 m-depth deep sea instrument for autonomous observation of sea floor tilt with signal periods longer than 7.5 s. The instrument also records vertical acceleration in the frequency range from DC to 1 Hz. The tiltmeter has an Applied Geomechanics Inc. 756 wide angle biaxial bubble tilt sensor with a resolution of 1.0μ rad (0.2 arc second). A Kistler Corp. MEMS accelerometer of type Servo K-Beam 8330A2.5 with about 10⁻⁵m/s² resolution is used for the acceleration measurements. An Oceanographic Embedded Systems AD24 24 bit Sigma-Delta converter, which is controlled by a low-power Persistor Inc. embedded computer system of type CF 2, samples the data. The duration of tiltmeter operation is more than one year, which is controlled by the battery life. In our design the tiltmeter does not need active leveling devices, i.e., servo motors or other moving components to adjust sensors or frame. We designed the instrument for deployments by means of a remote operated vehicle. Since May 2005 the Bremen ocean bottom tiltmeter has recorded sea floor deformation and seismicity level in the Logatchev hydrothermal vent field, Mid-Atlantic Ridge. The tiltmeter is a part of the monitoring system of project ‘Logatchev Long-Term Environmental Monitoring,’ called LOLEM, of the German research program with the name ‘Schwerpunktprogramm 1144: Vom Mantel zum Ozean.’     

Stability analysis of TLP tethers

Compliant offshore TLPs are essentially meant for deep oil/gas exploration and are usually constructed on the seashore and then towed down to the particular location for anchorage. They are connected to the sea bed by means of pretension cables. The increased use of TLPs in deep waters and necessity of reduction of usually high value of pretension make the effect of variable tension in the tether dynamics more significant. This work presents the dynamic analysis of tethers and TLPs considering the linearly varying tension along the tether length. The modal analysis considers a linear cable equation for tether modeling subjected to tension which varies along its length. A Mathieu stability analysis is then performed for TLPs of different shapes and different water depth vis-à-vis of 527.8, 872, and 1200 m respectively to obtain the amplitudes of tether vibrations. The unstable modes of vibration are also verified. The resultant modal forms for the tether's dynamic model are then obtained in form of Bessel's function. From the numerical studies conducted it is seen that increased tether tension not only leads to a stable platform but also improves the stability due to increased hydrodynamic loading contributing to added mass. From the studies conducted it is also seen that the triangular configuration TLPs with increased initial pretension are more stable compared to four leg TLP in the first mode of vibration.