Journal of Marine Science and Application 2009 No. 4
Young Jin KIM1, Hyung Tae KIM1*, Young June CHO1 and Kang Won LEE2
Journal of Marine Science and Application,2009(No. 4): 259-266
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Valuable mineral resources are widely distributed throughout the seabed. autonomous underwater vehicles (AUVs) are preferable to remotely-operated vehicles (ROVs) when probing for such mineral resources as the extensive exploration area makes it difficult to maintain contact with operators. AUVs depend on batteries, so their power consumption should be reduced to extend exploration time. Power for conventional marine instrument systems is incorporated in their waterproof sealing. External intermittent control of this power source until termination of exploration is challenging due to limitations imposed by the underwater environment. Thus, the AUV must have a power control system that can improve performance and maximize use of battery capacity. The authors developed such a power control system with a three-step algorithm. It automatically detects underwater operational states and can limit power, effectively decreasing power consumption by about 15%.

Hassan GHASSEMI
Journal of Marine Science and Application,2009(No. 4): 267-274
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Demand for high-speed marine vehicles (HSMVs) is high among both commercial and naval users. It is the duty of the marine vessel’s designer to provide a hull and propulsion system that diminishes drag, improves propulsive efficiency, increases safety and improves maneuverability. From the propulsor side, surface piercing propellers (SPPs) should improve performance. Unlike immersed propellers, behavior of the SPP is affected by depth of immersion, Weber number and shaft inclination angle. This paper uses a practical numerical method to predict the hydrodynamic characteristics of an SPP. The critical advance velocity ratio is derived using the Weber number and pitch ratio in the transition mode, then the potential based boundary element method (BEM) is used on the engaged surfaces. Two models of three and six-bladed SPPs (SPP-1 and SPP-2) were selected and some results are shown.

CAI Hao-peng*, SU Yu-min, LI Xin and SHEN Hai-long
Journal of Marine Science and Application,2009(No. 4): 275-280
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A new numerical method was developed for predicting the steady hydrodynamic performance of ducted propellers. A potential based surface panel method was applied both to the duct and the propeller, and the interaction between them was solved by an induced velocity potential iterative method. Compared with the induced velocity iterative method, the method presented can save programming and calculating time. Numerical results for a JD simplified ducted propeller series showed that the method presented is effective for predicting the steady hydrodynamic performance of ducted propellers.

Roozbeh PANAHI and Mehdi SHFIEEFAR*
Journal of Marine Science and Application,2009(No. 4): 281-290
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A finite volume algorithm was established in order to investigate two-dimensional hydrodynamic problems. These include viscous free surface flow interaction with free rigid bodies in the case of large and/or relative motions. Two-phase flow with complex deformations at the interface was simulated using a fractional step-volume of fluid algorithm. In addition, body motions were captured by an overlapping mesh system. Here, flow variables are transferred using a simple fully implicit non-conservative interpolation scheme which maintains the second-order accuracy of implemented spatial discretisation. Code was developed and an appropriate set of problems investigated. Results show good potential for development of a virtual hydrodynamics laboratory.

DENG Zhong-chao*, YAO Xiong-liang and ZHANG Da-gang
Journal of Marine Science and Application,2009(No. 4): 291-297
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Isolator systems on ships should ideally be able to simultaneously reduce low frequency vibration response and high frequency shock response. Conventional isolator systems are unable to do so. To solve the problem, a new style isolator system was created. This isolator system consists of a steel coil spring component and a magnetorheological (MR) damper component working in parallel. Experiments on this isolator system were carried out, including tests of vibration reduction and shock resistance. The vibration load frequencies were set from 1-15 Hz, and force amplitudes from 2.94~11.76 kN. The maximum shock input acceleration was 20 g, and impulse width was 10ms. Both the vibration and shock loads were applied using MTS Systems Corporation’s hydraulic actuators. The experimental results indicated that the isolator system performs well on system vibration response, with resonance humps of the vibration response obviously reduced after using the MR damper. For the shock experiment, the attenuation of shock response was much faster with increased MR damping. The MR damper’s effect on shock moments was very different from its performance in vibration mode. The correlation between MR force and control current was not as evident as it was during vibration loads.

WANG Zhi-dong1*, CONG Wen-chao1 and ZHANG Xiao-qing2
Journal of Marine Science and Application,2009(No. 4): 298-304
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The thrust coefficients and propulsive efficiency of a two-dimensional flexible fin with heaving and pitching motion were computed using FLUENT. The effect of different locations of the pitching axis on propulsive performance was examined using three deflexion modes which are respectively, modified Bose mode, cantilever beam with uniformly distributed load and cantilever beam with non-uniformly distributed load. The results show that maximum thrust can be achieved with the pitching axis at the trailing edge, but the highest propulsive efficiency can be achieved with the pitching axis either 1/3 of the chord length from the leading edge in modified Bose mode, or 2/3 of the chord length from the leading edge in cantilever beam mode. At the same time, the effects of the Strouhal number and maximal attack angle on the hydrodynamics performance of the flexible fin were analyzed. Parameter interval of the maximum thrust coefficient and the highest propulsive efficiency were gained. If the Strouhal number is low, high propulsive efficiency can be achieved at low , and vice versa.

WANG Ru-hang*, HUANG Jian-guo and ZHANG Qun-fei
Journal of Marine Science and Application,2009(No. 4): 305-309
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Underwater multi-target tracking logic and decision (UMTLD) has difficulty resolving multi-target tracking problems for underwater vehicles. Present methods assume factors in UMTLD are uncorrelated, when these are actually in a complex, interdependent relationship. To provide this, an index set of multi-target tracking decision characteristics and an analytic network process (ANP) model of the UMTLD method was established. This method brings the index set of multi-target tracking decision into the ANP model, and the optimization multitarket tracking decision is achieved via computation of the resulting supermatrix. The rationality and robustness of decision results increase in simulations by 13% and 47% respectively with analytic hierarchy process (AHP). These results indicate that the ANP method should be the preferred method when UMTLD factors are interdependent.

PAN Xin-ying1* and ZHANG Zhao-de2
Journal of Marine Science and Application,2009(No. 4): 311-315
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An inevitable consequence of the development of the offshore petroleum industry is the eventual obsolescence of large offshore structures. Proper methods for removal of decommissioned offshore platforms are becoming an important topic that the oil and gas industry must pay increasing attention to. While removing sections from a decommissioned jacket platform, the stability of the remaining parts is critical. The jacket danger indices Dσ and Ds defined in this paper are very useful for analyzing the safety of any procedure planned for disassembling a jacket platform. The safest piles cutting sequence can be determined easily by comparing every column of Dσ and Ds or simply analyzing the figures of every row of Dσ and Ds.

XU Shan-shan*, LIU Shi-ming, GUO Shao-jing and ZHANG A-man
Journal of Marine Science and Application,2009(No. 4): 316-322
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A submodel method was proposed that works from computational models of marine gear cases to verify that the proposed bolts will give it sufficient structural integrity. Calculations for marine equipment using this system accorded well with conventional results. As an example, an anti-shock computation was processed for a gear case, and the submodel was then employed to check the strength of individual components. The results showed that the gear case connecting structure can satisfy relative anti-shock requirements, and the dynamic response characteristics seen in the bolt structures had a close relationship with the method used for attaching the bolt. This provides a new means for checking the strength of connecting structures on large-scale equipment and thus has significant reference value.

ZHANG Bo*, ZHANG Yu-wen and YUAN Xu-long
Journal of Marine Science and Application,2009(No. 4): 323-327
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The authors designed three different front profiles for supercavitating vehicles based on cavity theory and the Granville streamlined equation are designed. Experiments were done using these front profiles in the Northwestern Polytechnical University high-speed water tunnel. The experiments indicated that the critical volume of gas required for supercavitation is affected by the axial distribution of the front-end’s slope. The experimental data showed critical gas flow rates required for the three designs were less than mod-1, with the greatest decrease 24%. The experimental results also showed the supercavitation generation speeds of the models were faster than mod-1 by up to 32.4%. This verifies that the front profile of a supercaviting vehicle effects supercavity generation speed and critical gas flow rates. The smaller the changes in axial distribution of pressure, the higher the supercavity generation speed. The smaller the changes in curvature distribution of axial, the smaller the critical gas flow rates.

CHEN Sheng and LIN Guan-cheng
Journal of Marine Science and Application,2009(No. 4): 328-332
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Cymbal hydrophones have small volume and high sensitivity, but their reception is not stable enough, and their reception is in too narrow a frequency band. In order to overcome these inadequacies, the structure of the cymbal hydrophone was improved. The single ceramic piezoelectric element was replaced with a double one, the radius of the ceramic piezoelectric element was reduced, and a parallel circuit was added. A static analysis of this new structure was developed, and then simulations were made of both the traditional and new hydrophone structure using finite element software. Tests were then conducted in a tank. The results showed that the improved hydrophone has reception in a wider frequency band, reception performance is stable within this frequency band, and sensitivity is still high.

SONG Bao-wei*, LIU Zhan-yi, Xu Ting, HU Hai-bao and HUANG Ming-ming
Journal of Marine Science and Application,2009(No. 4): 333-337
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This paper presents a method based on the Spalding formula for testing drag-reduction on riblet surfaces. Its advantage lies in that it is more convenient and yields more precise data compared with testing methods using instruments such as a scale. With this method, data is obtained from the velocity distribution within the inner layer, nearest the riblet surface. Precision of measurement of the velocity distribution is the key factor affecting the precision of the testing.

GAO Zhu1*, LI Xing2, TANG Hong-wu3, GU Zheng-hua4
Journal of Marine Science and Application,2009(No. 4): 338-342
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Revetments of concrete frame tetrahedrons are being used more and more in river engineering in China. Due to their complex geometry, it is difficult to measure the velocity fields inside them using traditional measurement methods. This limits understanding of their mechanics, potentially leading to suboptimal solutions. A 3-D hydrodynamic model based on the commercial computational fluid dynamics (CFD) code, Fluent, was developed to predict velocity fields and drags. The realizable k-ε model was adopted for turbulent closure of the Reynolds averaged Navier Stokes (RANS) equations. The study demonstrates that the numerical model can effectively supplement experimental studies in understanding the complex flow fields and mechanics of concrete frame tetrahedron revetments. Graphs showing the drag coefficient CD versus Reynolds number Re and lift coefficient CL versus Reynolds number Re were produced.

YAN Guang-hong*, CHEN Zhi-fei and SUN Jin-cai
Journal of Marine Science and Application,2009(No. 4): 343-349
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A new method uses a linear array that takes advantage of underwater physical sound fields to estimate the velocity of an underwater moving target. The mathematical model was established by considering the geometric relationship between the moving target installed with only two transducers to radiate sound of different frequencies and the linear array. In addition, deterministic maximum likelihood and signal phase matching algorithms were introduced to effectively find the directions of arrival (DOAs) of the sound sources of the two transducers installed on the target. Factors causing velocity measurement errors were considered. To track the target, a linear array with a compass, a pressure transducer, a signal conditioner and a digital recorder was configured. Relevant requirements for the array parameters were derived. The simulation showed that a 16-element array with an aperture of less than 1m can measure velocity with relative error of no more than 4% when including typical system errors. Anechoic pool and reservoir experiments confirmed these results.