考虑桩土作用独桩海洋平台横向振动特性研究

采用动Winkler弹性地基梁模型模拟桩土问动力相互作用，并考虑了流体与桩问相互作用，通过组合成层土中、水中桩单元的刚度阵，推得了独桩海洋平台连续系统横向振动的动刚度阵及在波浪力作用下平台甲板处的频率响应函数，进而求得了在确定性波浪力及随机波浪力作用下桩身任意点的位移响应。最后，通过算例研究和分析了在随机波浪力作用下成层土参数、甲板上重量及冲刷淘深等因素对平台振动响应的影响。     

Dynamic Response of Fluid-Single Leg Gravity Platform-Soil Interaction System

- An approximate method is presented to investigate the earthquake response of the fluid-single leg (shortened for S. L.) gravity platform-soil interaction system. By assuming a suitable form of the velocity potential of the radiation waves and by using the motion equation and the boundary conditions, the unknown coefficients can be obtained. Thereafter the function of frequency for the interaction system may also be obtained. In this paper, the difference of the system dynamic response between rigid foundation is analyzed and the influences of the various foundation geometric dimension and the various water-depth on the hydrodynamic loading and dynamic response of the system is illustrated.     

Influence of Energy Directional Spread on Wave Spectral Refraction

Pierson- Moskowitz Spectrum, JONSWAP Spectrum as well as Bretschneider- Mitsuyasu Spectrum are used in this paper for analyzing the influence of wave energy directional spread on refraction of wave spectrum due to both current and topography of sea bed. The author's calculation indicates that such kind influence on the characteristic value of wave height as well as the average direction of wave energy propagation can not be ignored.     

Gravity anomalies and deep structure of the Ninetyeast Ridge north of the equator,eastern Indian Ocean — a hot spot trace model

The Ninetyeast Ridge north of the equator in the eastern Indian Ocean is actively deforming as evidenced by seismicity and its eastward subduction below the Andaman Trench. Basement of the ridge is elevated nearly 2 km with respect to the Bengal Fan; seismic surveys demonstrate continuity of the ridge beneath sediment for 700 km north of 10° N where the ridge plunges below the Fan sediment. The ridge is characterised by a free-air gravity high of 50 mgal amplitude and 350 km wavelength, and along-strike continuity of 1500 km in a north-south direction, closely fringing (locally, even abutting) the Andaman arc-trench bipolar gravity field. Regression analysis between gravity and bathymetry indicates that the ridge gravity field cannot be explained solely by its elevation. The ridge gravity field becomes gradually subdued northwards where overlying Bengal Fan sediments have a smaller density contrast with the ridge material. Our gravity interpretation, partly constrained by seismic data, infers that the ridge overlies significant crustal mass anomalies consistent with the hot spot model for the ridge. The anomalous mass is less dense by about 0.27 g cm^–3 than the surrounding oceanic upper mantle, and acts as a cushion for isostatic compensation of the ridge at the base of the crust. This cushion is up to 8 km thick and 400–600 km wide. Additional complexities are created by partial subduction of the ridge below the Andaman Trench that locally modifies the arc-trench gravity field.     

Hydrodynamic Forces on Inclined Cylinder due to Waves with Crossing Current

Based on Morison's Equation and linear wave theory, hydrodynamic forces acting on inclined cylinders due to waves and crossing current at an angle of a, are analyzed. A method for calculating exciting forces is proposed. Experimental results show that the proposed method in this paper is feasible and can be used in engineering practice.     

上海沿岸天文潮与风暴潮非线性相互作用的数值研究

运用二维非线性风暴潮，天文潮和联合水位模型８次不同路径的热带气旋引起的上海地区天文潮与风暴潮的非线性相互作用进行了数值研究，讨论了天文潮气与风暴潮非线性相互作用引起的增水特征，分析了控制方程中各非线性项对天文潮与风暴晨线性相互作用引起水位变化的贡献，研究表明，考虑天文潮与风暴的非线性相互作用后，使风暴潮和水位的数值模拟结果得到了改善，非线性底摩擦在控制天文潮和风暴潮非线性相互作用中起重要的作用。而     

The free vibration analysis of submerged cantilever plates

Based on empirical added mass formulation, this work presents a simple procedure to determine the vibration frequencies and mode shapes of submerged cantilever plates. Once the added mass formulation is derived, the procedure can be used to analyze free vibration response easily. An analytical and numerical study is also performed for the vibrations of cantilever plates in air and in water, with these results compared with experimental and numerical data from pertinent literature. Besides, the frequency parameters of the submerged plate for various aspect ratios and thickness ratios are given in design data sheet form and are appropriate for engineering design applications.     

Experimental Study on the Interaction Mechanism of Cap—Pile Group—Soil

Static load tests on pile group with prototype size were carried out in order to study the behavior and the working properties of the cap—pile group—soil interaction in the pile group foundation. The soil resistance under the cap, the pile shaft resistance and the tip resistance were measured by installing various measuring gauges. Based on these test results, the cap—pile group—soil interaction characteristics were analyzed. The regulations of the soil reaction on the cap, the shaft resistance and the tip resistance of pile, the mechanism of load transfer have been discussed with comparison to the result of the single pile tests. The bearing capacity of pile group is greater than the sum of the bearing capacity of the single pile obtained from testing in the same site in pile group foundation in the case presented here.     

Air-Sea Interactions under the Existence of Opposing Swell

Data of a comprehensive laboratory study on the coexistent system of wind waves and opposing swell (Mitsuyasu and Yoshida, 1989) have been reanalyzed to clarify the air-sea interaction phenomena under the coexistence of wind waves and swell. It is shown that the magnitude of the decay rate of swell due to an opposing wind is almost the same as that of the growth rate of swell caused by a following wind, as measured by Mitsuyasu and Honda (1982). The decay rate is much smaller than that obtained recently by Peirson et al. (2003), but the reason for the disagreement is not clear at present. The effect of an opposing swell on wind waves is very different from that of a following swell; wind waves are intensified by an opposing swell while they are attenuated by a following one. The phenomenon contradicts the model of Phillips and Banner (1974), but the reason for this is not clear at this time. The high-frequency spectrum of wind waves shows a small increase of the spectral density. Wind shear stress increases a little due to the effect of opposing swell. The intensification of wind waves by opposing swell and the small increase of the spectral density in a high-frequency region can be attributed to the increase of wind shear stress. Such organized phenomena lead to the conclusion that the hypothesis of local equilibrium for pure wind waves (Toba, 1972) can also be satisfied for wind waves that coexist with opposing swell. The recent finding of Hanson and Phillips (1999) can be explained by this mechanism.     

Offshore Structural Control Considering Fluid Structure Interaction

1.IntroductionAmong various control devices,Tuned Mass Damper(TMD)has been mostfrequently usedtothecontrol of structural vibration induced by oscillating loads such as earthquakes,winds,and waves.This is due to the fact that it operates without external e…