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Tuned Mass Damper (TMD) was applied to an offshore structure to control ocean wave-induced vibration. In the analysis of the dynamic response of the offshore structure, fluid-structure interaction is considered and the errors, which occur in the linearization of the interaction, are investigated. For the investigation of the performance of TMD in controlling the vibration, both regular waves with different periods and irregular waves with different significant wave heights are used. Based on the numerical analysis it is concluded that the fluid-structure interaction should be considered in the evaluation of the capability of TMD in vibration control of offshore structures.
Reflection and transmission of random waves from submerged obstacles under various conditions are investigated in this study by means of the boundary element method. The algorithm is based on the Lagrangian description with finite difference adopted for the approximation of time derivative. The accuracy of the model is confirmed by a previous study of the transmission of irregular waves in a water tank without any obstacle, under which sets of submerged breakwaters are located. To reduce the effect of reflection from the wall, a sponge zone is employed at the other end of the flume as an artificial absorbing beach. The power spectrum of Bretschneider-Mitsuyasu type defined by significant wave height, H_ 1/3 , and period, T_ 1/3 , is employed for the condition of incident waves chosen for the generation of irregular waves. Time histories of water elevations are measured with numerous pseudo wave gages on the free water surface. With reference to the method for the estimation of irregular incident and reflected waves in random sea presented by Goda and Suzuki (1976), the dissipation efficiency of the breakwaters is investigated. Gauges in different positions are tested for their suitability for the estimation of reflection coefficients for irregular waves. The present results demonstrate the effectiveness of the estimation of reflection coefficient for random waves, and indicate the feasibility of the numerical model.
The accumulator is used as a pressure compensation device to realize deep-sea microbe gastight sampling. Four key states of the accumulator are proposed to describe the pressure compensation process and a corresponding mathematical model is established to investigate the relationship between the results of pressure compensation and the parameters of the accumulator. Simulation results show that during the falling process of the sampler, the accumulator's real opening pressure is greater than its precharge pressure; when the sampling depth is 6000 m and the accumulator's precharge pressure is less than 30 MPa, to increase the accumulator's precharge pressure can improve pressure compensation results obviously. Laboratory experiments at 60 MPa show that the accumulator is an effective and reliable pressure compensation device for deep-sea microbe samplers. The success in sea trial at a depth of 2000 m in the South China Sea shows that the mathematical model and laboratory experiment results are reliable.
Adopting the load and resistance factor design format, the design method for steel jacket platform structures is developed. Firstly, the limit state equations and design format for steel jacket platform structures are introduced. Then, the ratio of live load effect to dead load effect is estimated. The target reliabilities for design of offshore structures in China offshore area are calibrated by past practice in API RP2A-WSD code. The load and resistance factors are optimized by minimizing the difference within the target reliability and the resulting reliability over the range of load effect ratios. Considering the concurrence of different loads, load combination factors are obtained through an optimization process, and the relation between the load combination factor and load correlation coefficient is established. Finally, the design formulae for steel jacket structures in China offshore area are recommended.
The total horizontal and vertical forces acting on a partially-perforated caisson breakwater and their phase difference are investigated in this study. The perforated breakwater sits on the rubble filled foundation, and has a rock-filled core. An analytical solution is developed based on the eigenfunction expansion and matching method to solve the wave field around the breakwater. The finite element method is used for simulating the wave-induced flow in the rubble-filled foundation. Experiments are also conducted to study the wave forces on the perforated caissons. Numerical predictions of the present model are compared with experimental results. The phase differences between the total horizontal and vertical forces are particularly analyzed by means of experimental and numerical results. The major factors that affect the wave forces are examined.
Based on mesh regeneration and stress interpolation from an old mesh to a new one, a large deformation finite element model is developed for the study of the behaviour of circular plate anchors subjected to uplift loading. For the deterruination of the distributions of stress components across a clay foundation, the Recovery by Equilibrium in Patches is extended to plastic analyses. ABAQUS, a commercial finite element package, is customized and linked into our program so as to keep automatic and efficient running of large deformation calculation. The quality of stress interpolation is testified by evaluations of Tresca stress and nodal reaction forces. The complete pulling-up processes of plate anchors buried in homogeneous clay arc simulated, and typical pulling force-displacement responses of a deep anchor and a shallow anchor are compared. Different from the results of previous studies, large deformation analysis is of the capability of estimating the breakaway between the anchor bottom and soils. For deep anchors, the variation of mobilized uplift resistance with anchor settlement is composed of three stages, and the initial buried depths of anchors affect the separation embedment slightly. The uplift bearing capacity of deep anchors is usually higher than that of shallow anchors.
It has been proved that the thermally insulated ocean pipeline has advantages over the conventional pipe-in-pipe pipeline. The risk of using the thermally insulated pipeline is that the exterior layers covering the steel pipe may be pulled off if the shear stress on the interface induced by the pullout force from the tensioner is greater than the binding force between two neighboring layers during installation. This paper develops a procedure to calculate the shear stress on the interface. The binding force between two neighboring layers can be determined with full scale model tests. The safety of the thermally insulated pipe under installation can then be checked by comparison of the interface shear stress with the binding force.
In the present study a numerical model developed by Lynett and Liu (2002) is modified to include density difference in a stratified two-layer fluid in a three-dimensional internal wave domain. The internal solitary wave (ISW) in the model is assumed to be weakly nonlinear and weakly dispersive, and the viscosity effects at all boundaries are ignored. The governing equations based on the Navier-Stokes and Euler equations are solved for internal solitary wave propagation over variable seabed topography. Theoretical formulations are established, from which analytical solutions are obtained, in addition to numerical results. Wave profiles from previous experimental studies are compared with the numerical results from the present analytical solutions. Numerical models developed on the basis of the present analytical solutions are better than those developed by Lynett and Liu (2002). The results of numerical modeling agree well with the experimental data.
In recent years, attention has been focused on the spar platform for gas and oil exploitation in deep water. With the development of offshore technology, many new spar concepts have been put forward and fully studied. This paper presents the results of an experimental investigation on the hydrodynamic behavior of a new spar concept from Novellent Offshore LLC, USA, which is called Geometric Spar (G-spar). A new type of buoyancy can concept from the same company, viz. Integrated Buoyancy Can (IBC), is researched in the meantime. The G-spar and IBC models with a 1:70 scale are tested in the State Key Laboratory of Ocean Engineering at Shanghai Jiao Tong University for the global performance of the spar hull, in which the second-order wave drift force is involved, as well as the effect of heave plates on the motion characteristics and mooring force of the G-spar platform.
Underwater acoustic modem technology has attained a level of maturity to support underwater acoustic sensor networks (UASNs) which are generally formed by acoustically connected sensor nodes and a surface station providing a link to an on-shore control center. While many applications require long-term monitoring of the deployment area, the battery-powered network nodes limit the lifetime of UASNs. Therefore, designing a UASN that minimizes the power consumption while maximizing lifetime becomes a very difficult task. In this paper, a method is proposed to determine the optimum number of clusters through combining an application-specific protocol architecture and underwater acoustic communication model so as to reduce the energy dissipation of UASNs. Deploying more sensor nodes which work alternately is another way to prolong the lifetime of UASNs. An algorithm is presented for selecting sensor nodes and putting them into operation in each round, ensuring the monitoring to the whole given area. The present results show that the algorithm can help prolong system lifetime remarkably when it is applied to other conventional approaches for sensor networks under the condition that the sensor node density is high.
The mean wavelength of ocean waves is an important environmental parameter in ocean engineering. Owing to the difficulty in its measurement, it is usually estimated from the mean wave period according to the theoretical relationship between the two wave parameters. However, the relationships that have been proposed are not very satisfactory. In this paper, some suggestions are made for improvement of the data analysis method by which the mean wavelength is estimated from surface elevation records. Laboratory experiments are conducted in a wind-wave flume, and a new relationship between the mean wavelength and mean wave period is obtained by the application of the improved data analysis method. The new relationship deviates from that of Xu et al. (1999) while it is very close to the one proposed by Kinsman (1965), although the last one is theoretically deficient.
ScholarOne Manuscripts Log In
- Volume 33
- Issue 6
- December 2019
- Superintended by:
CHINA ASSOCIATION FOR SCIENCE AND TECHNOLOGY
- Sponsored by:
Chinese Ocean Engineering Society （COES）
- Edited by:
Nanjing Hydraulic Research Institute
Adaptive Predictive Inverse Control of Offshore Jacket Platform Based on Rough Neural Network
Numerical Simulation of Water Exchange Characteristics of the Jiaozhou Bay Based on A Three-Dimensional Lagrangian Model
A Global Reliability Assessment Method on Aging Offshore Platforms with Corrosion and Cracks