Journal of Marine Science and Application 2009 No. 3
P. MAITI, B. N. Mandal and U. Basu
Journal of Marine Science and Application,2009(No. 3): 183-195
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The problem of wave scattering by undulating bed topography in a two-layer ocean is investigated on the basis of linear theory. In a two-layer fluid with the upper layer having a free surface, there exist two modes of waves propagating at both the free surface of the upper layer and the interface between the two layers. Due to a wave train of a particular mode incident on an obstacle which is bottom-standing on the lower layer, reflected and transmitted waves of both modes are created by the obstacle. For small undulations on the bottom of the lower layer, a perturbation method is employed to obtain first-order reflection and transmission coefficients of both modes for incident wave trains of again both modes in terms of integrals involving the bed-shape function. For sinusoidal undulations, numerical results are presented graphically to illustrate the energy transfer between the waves of different modes by the undulating bed.

YAO Xiong-liang, SUN Shi-li, WANG Shi-Ping and YANG Shu-tao
Journal of Marine Science and Application,2009(No. 3): 196-203
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The traditional calculation method of frequency-domain Green function mainly utilizes series or asymptotic expansion to carry out numerical approximation, however, this method requires very careful zoning, thus the computing process is complex with many cycles, which has greatly affected the computing efficiency. To improve the computing efficiency, this paper introduces Gaussian integral to the numerical calculation of the frequency-domain Green function and its partial derivatives. It then compares the calculation result with that in existing references. The comparison results demonstrate that, on the basis of its sufficient accuracy, the method has greatly simplified the computing process, reduced the zoning and improved the computing efficiency. Keywords: frequency-domain Green function; numerical approximation; Gaussian integral

XU Guo-dong and DUAN Wen-yang
Journal of Marine Science and Application,2009(No. 3): 204-210
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This paper presents the survey and assessment of the estimation techniques on hydrodynamic impact. The description and definition of hydrodynamic impact are presented, and the categorization of prediction techniques and the difficulties are discussed. Analysis theories and numerical simulation techniques are reviewed and the characteristics of those theories and approaches are analyzed. The efforts are made to pinpoint the advantages and disadvantages. Recommendations for further research and development are made.

WANG Yun-long, JI Zhuo-shang and LIN Yan
Journal of Marine Science and Application,2009(No. 3): 211-215
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The present status of self-elevating drilling units was analysed. Based on statistics of the main dimensions of self-elevating drilling units, a mathematical model was established using stepwise return procedures and a back-propagation neural network. Analysis of examples of calculations showed that the mathematical model is applicable and reliable. The model is useful for mastering the essential variations of the main dimensions of self-elevating drilling units and can be used for technical and economic analysis as well as in conceptual designs of drilling units.

ZHANG Li-chuan*, XU De-min, LIU Ming-yong and YAN Wei-sheng
Journal of Marine Science and Application,2009(No. 3): 216-221
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The authors proposed a moving long baseline algorithm based on the extended Kalman filter (EKF) for cooperative navigation and localization of multi-unmanned underwater vehicles (UUVs). Research on cooperative navigation and localization for multi-UUVs is important to solve navigation problems that restrict long and deep excursions. The authors investigated improvements in navigation accuracy. In the moving long base line (MLBL) structure, the master UUV is equipped with a high precision navigation system as a node of the moving long baseline, and the slave UUV is equipped with a low precision navigation system. They are both equipped with acoustic devices to measure relative location. Using traditional triangulation methods to calculate the position of the slave UUV may cause a faulty solution. An EKF was designed to solve this, combining the proprioceptive and exteroceptive sensors. Research results proved that the navigational accuracy is improved significantly with the MLBL method based on EKF.

XIE Xue-shen* and HUANG Sheng
Journal of Marine Science and Application,2009(No. 3): 222-227
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A mathematical model of podded propulsors was established in order to investigate the influence of fins. The hydrodynamic performance of podded propulsors with and without fins was calculated, with interactions between propellers and pods and fins derived by iterative calculation. The differential equation based on velocity potential was adopted and hyperboloidal panels were used to avoid gaps between surface panels. The Newton-Raphson iterative procedure was used on the trailing edge to meet the pressure Kutta condition. The velocity distribution was calculated with the Yanagizawa method to eliminate the singularity caused by use of the numerical differential. Comparisons of the performance of podded propulsors with different fins showed that the thrust of propeller in a podded propulsor with fins is greater. The resistance of the pod is also reduced because of the thrust of the fin. The hydrodynamic performance of a podded propulsor with two fins is found to be best, the performance of a podded propulsor with one fin is not as good as two fins, and the performance of the common type is the worst.

YIN Peng*, CHEN Yuan-ming, CUI Tong-kai, WANG Zi-shen, GONG Li-jiang and YU Xiang-fen
Journal of Marine Science and Application,2009(No. 3): 228-232
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The plant design management system (PDMS) is an integrated application which includes a database and is useful when designing complex 3-D industrial projects. It could be used to simplify the most difficult part of a subsea oil extraction project—detailed pipeline design. It could also be used to integrate the design of equipment, structures, HVAC, E-ways as well as the detailed designs of other specialists. This article mainly examines the applicability of the Vantage PDMS database to pipeline projects involving jack-up drilling ships. It discusses the catalogue (CATA) of the pipeline, the spec-world (SPWL) of the pipeline, the bolt tables (BLTA) and so on. This article explains the main methods for CATA construction as well as problem in the process of construction. In this article, the authors point out matters needing attention when using the Vantage PDMS database in the design process and discuss partial solutions to these questions.

FENG Heng*, SUN Chun-mei, CHEN Zheng-wei and HONG Xue-fu
Journal of Marine Science and Application,2009(No. 3): 233-236
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This paper analyzes the motion performance and mooring system of deepwater semi-submersible drilling unit in the district of the South China Sea using the MOSES procedure system. After the 3-D panel model of the unit was built, the 3-D diffraction-radiation theory was used to obtain the hydrodynamic loads on the wet surfaces and the response amplitude operators (RAO) of the unit. According to the environmental data, the short-term motion response to motion performance of the unit is predicted by the spectral method. Then a time-domain calculation was done to analyze the motion of the unit with its mooring system. The research results can be a reference for the model test of unit.

XU Jun-ling and ZHU Ren-qing*
Journal of Marine Science and Application,2009(No. 3): 237-245
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With the development of the offshore deep water oil industry many researchers are focusing on the vortex-induced vibrations (VIV) of deep risers. In the present work, Reynolds–averaged Navier–Stokes (RANS) equations were combined with the SST turbulent model to simulate the stream-wise and transverse motion of an elastically mounted cylinder with a low mass-ratio, a natural frequency ratio of and an Re number between 5 300 and 32 000. The four-order Runge–Kutta method was applied to solve the oscillating equation of the cylinder. The relationship between reduced velocity and parameters of the cylinder, including the lift coefficient, the drag coefficient, displacement and the vortex structure were then compared with recent experimental results and discussed in detail. The present numerical simulation reproduced effects have been observed in experiments, such as the lock-in phenomenon, the hysteretic phenomenon and beating behavior.

GUO Yong-feng*, JI Shao-jun and TANG Chang-quan
Journal of Marine Science and Application,2009(No. 3): 246-251
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This paper introduces the recent highly significant activity of China Oilfield Services Ltd. (COSL) in the South China Sea, where COSL conducted pretrial drilling in June of 2008. The paper discusses some key research and new practices which led to the fabrication of related equipment which was evaluated in the trial. The market for deepwater drilling in the world has grown over the past 10 years but there are few drilling vessels or platforms suitable for drilling in deepwater or super deepwater. China needs equipment capable of deepwater drilling operations. COSL has some semisubmersible platforms, but they are only considered suitable for operations in water depths less than 475 m. An enabling technology, referred to as an artificial seabed, has been under development by COSL since 2004, and it applies the research results and experiences of many experts in deepwater drilling. COSL hopes this technology will allow drilling to depths of approximately 1 000~1 500 m with its current platforms. The paper presents research progress and improvements in fabrication and necessary upgrades to equipment for extending deepwater drilling. The pretrial well was executed at a water depth of nearly 500 m. COSL will drill the trial well around 2009 at the same location in the South China Sea.

MA Wen-jun1* and TANG Li-qiang2
Journal of Marine Science and Application,2009(No. 3): 252-258
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A mechanical model of the quasi-static interface of a mode I crack between a rigid and a pressure-sensitive viscoelastic material was established to investigate the mechanical characteristic of ship-building engineering bi-materials. In the stable growth stage, stress and strain have the same singularity, ie . The variable-separable asymptotic solutions of stress and strain at the crack tip were obtained by adopting Airy’s stress function and the numerical results of stress and strain in the crack-tip field were obtained by the shooting method. The results showed that the near-tip fields are mainly governed by the power-hardening exponent n and the Poisson ratio of the pressure-sensitive material. The fracture criterion of mode I quasi-static crack growth in pressure-sensitive materials, according to the asymptotic analyses of the crack-tip field, can be viewed from the perspective of strain.