Journal of Marine Science and Application 2008 No. 2
LIU Xiang-dong YAO Xiong-liang PANG Fu-zhen
Journal of Marine Science and Application,2008(No. 2): 0
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In this paper,in order to predict the residual deformation of thick spherical structure,a welding program is compiled in APDL language based on Ansys and a numerical welding experiment of a welding example is carried out.The temperature field of welding was simulated firstly, then a thermal-structure coupling analysis was carried out,and at last the residual stress and deformation after welding were got.After that,the numerical experiment result was compared with physical experiment one.The comparative analysis shows that the numerical simulation fits well with physical experiment.On the basis of that,a three-dimensional numerical experiment of a thick spherical shell structure was carried out to get the changing rule of stress and deformation of a thick spherical shell structure during welding. The research is of great value to the prediction of residual deformation and high precision machining.

AI Shang-mao SUN Li-ping
Journal of Marine Science and Application,2008(No. 2): 0
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Underwater cylindrical shell structures have been found a wide of application in many engineering fields,such as the element of marine,oil platforms,etc.The coupled vibration analysis is a hot issue for these underwater structures.The vibration characteristics of underwater structures are influenced not only by hydrodynamic pressure but also by hydrostatic pressure corresponding to different water depths.In this study,an acoustic finite element method was used to evaluate the underwater structures.Taken the hydrostatic pressure into account in terms of initial stress stiffness,an acoustical fluid-structure coupled analysis of underwater cylindrical shells has been made to study the effect of hydrodynamic pressures on natural frequency and sound radiation.By comparing with the frequencies obtained by the acoustic finite element method and by the added mass method based on the Bessel function,the validity of present analysis was checked.Finally,test samples of the sound radiation of stiffened cylindrical shells were acquired by a harmonic acoustic analysis.The results showed that hydrostatic pressure plays an important role in determining a large submerged body motion,and the characteristics of sound radiation change with water depth. Furthermore,the analysis methods and the results are of significant reference value for studies of other complicated submarine structures.

PENG Ying YANG Ping
Journal of Marine Science and Application,2008(No. 2): 0
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Study on the dynamic response,and especially the nonlinear dynamic response of stiffened plates is complicated by their discontinuity and inhomogeneity.The finite element method (FEM) and the finite strip method are usually adopted in their analysis.Although many useful conclusions have been obtained,the computational cost is enormous.Based on some assumptions,the dynamic plastic response of damped stiffened plates with large deflections was theoretically investigated herein by a singly symmetric beam model.Firstly,the deflection conditions that a plastic string must satisfy were obtained by the linearized moment-axial force interaction curve for singly symmetric cross sections and the associated plastic flow rule.Secondly,the possible motion mechanisms of the beam under different load intensity were analysed in detail.For structures with plastic deformations,a simplified method was then given that the arbitrary impact load can be replaced equivalently by a rectangular pulse.Finally,to confirm the validity of the proposed method,the dynamic plastic response of a one-way stiffened plate with four fully clamped edges was calculated.The theoretical results were in good agreement with those of FEM.It indicates that the present calculation model is easy and feasible,and the equivalent substitution of load almost has no influence on the final deflection.

REN Hui-long LIU Wen-xi
Journal of Marine Science and Application,2008(No. 2): 0
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Accurate hydrodynamic calculations for semi-submersibles are critical to support modern rapid exploration and extraction of ocean resources.In order to speed hydrodynamic calculations,lines modeling structures were separated into structural parts and then fitted to Non-uniform Rational B-spline(NURBS).In this way,the bow and stern section lines were generated.Modeling of the intersections of the parts was then done with the universal modeling tool MSC.Patran.Mesh was gererated on the model in order to obtain points of intersection on the joints,and then these points were fitted to NURBS.Next,the patch representation method was adopted to generate the meshes of wetted surfaces and interior free surfaces.Velocity potentials on the surfaces were calculated separately,on basis of which the irregular frequency effect was dealt with in the calculation of hydrodynamic coefficients.Finally,the motion response of the semi-submersible was calculated,and in order to improve calculations of vertical motion,a damping term was affixed in the vertical direction.The results show that the above methods cangenerate fine mesh accurately representing the wetted surface of a semi-submersible and thus improve the accuracy of hydrodynamic calculations.

LI Yun-bo WU Xiao-yu MA Yong WANG Jin-guang
Journal of Marine Science and Application,2008(No. 2): 0
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This research is intended to provide academic reference and design guidance for further studies to determine the most effective means to reduce a ship’s resistance through an air-cavity.On the basis of potential theory and on the assumption of an ideal and irrotational fluid,this paper drives a method for calculating air cavity formation using slender ship theory then points out the parameters directly related to the formation of air cavities and their interrelationships.Simulations showed that the formation of an air cavity is affected by cavitation number,velocity,groove geometry and groove size.When the ship’s velocity and groove structure are given,the cavitation number must be within range to form a steady air cavity.The interface between air and water forms a wave shape and could be adjustedby an air injection system.

JI Zhen-lin WANG Xue-ren
Journal of Marine Science and Application,2008(No. 2): 0
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In marine engine exhaust silencing systems,the presence of exhaust gas flow influences the sound propagation inside the systems and the acoustic attenuation performance of silencers.In order to investigate the effects of three-dimensional gas flow and acoustic damping on the acoustic attenuation characteristics of marine engine exhaust silencers,a dual reciprocity boundary element method (DRBEM)was developed.The acoustic governing equation in three-dimensional potential flow was derived first,and then the DRBEM numerical procedure is given.Compared to the conventional boundary elementmethod (CBEM),the DRBEM considers the second order terms of flow Mach number in the acoustic governing equation,so it is suitable for the cases with higher Mach number subsonic flow.For complex exhaust silencers,it is difficult to apply the single-domain boundary element method,so a substructure approach based on the dual reciprocity boundary element method is presented.The experiments for measuring transmission loss of silencers are conducted,and the experimental setup and measurements are explained.The transmission loss of a single expansion chamber silencer with extended inlet and outlet were predicted by DRBEM and compared with the measurements.The good agreements between predictions and measurements are observed,which demonstrated that the derived acoustic governing equation and the DRBEM numerical procedure in the present study are correct.

ZHANG Peng-qi ZONG Li-jun WANG Yin-yan
Journal of Marine Science and Application,2008(No. 2): 0
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In order to improve performance of the DA465Q gasoline engine,a substantial amount of research was done to optimize its turbocharging system.The research led to the GT12 turbocharger being selected and its turbocharging parameters being settled.Based on these tests,rational matching was worked out for respective components of the turbocharging system.Results show that this turbocharger allows the engine to easily meet the proposed requirements for power and economic performance,giving insight into further performance improvements for gasoline engines.

HAO Yan-ling CHEN Ming-hui LI Liang-jun XU Bo
Journal of Marine Science and Application,2008(No. 2): 0
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There are many filtering methods that can be used for the initial alignment of an integrated inertial navigation system.This paper discussed the use of GPS,but focused on two kinds of filters for the initial alignment of an integrated strapdown inertial navigation system (SINS).One method is based on the Kalman filter (KF),and the other is based on the robust filter.Simulation results showed that the filter provides a quick transient response and a little more accurate estimate than KF,given substantial process noise or unknown noise statistics.So the robust filter is an effective and useful method for initial alignment of SINS.This research should make the use of SINS more popular,and is also a step for further research.

TAN Ding-zhong WANG Qi-ming SONG Rui-han YAO Xin GU Yi-hua
Journal of Marine Science and Application,2008(No. 2): 0
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In the underwater environment,many visual sensors don’t work,and many sensors which work well for robots working in space or on land can not be used underwater.Therefore,an optical fiber slide tactile sensor was designed based on the inner modulation mechanism of optical fibers.The principles and structure of the sensor are explained in detail.Its static and dynamic characteristics were analyzed theoretically and then simulated.A dynamic characteristic model was built and the simulation made using the GA based neural network.In order to improve sensor response,the recognition model of the sensor was designed based on the’inverse solution’principle of neural networks,increasing the control precision and the sensitivity of the manipulator.

LIANG Yan-hua JIN Hong-zhang LIANG Li-hua
Journal of Marine Science and Application,2008(No. 2): 0
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Conventional PID controllers are widely used in fin stabilizer control systems,but they have time-variations,nonlinearity,and uncertainty influencing their control effects.A lift feedback fuzzy-PID control method was developed to better deal with these problems,and this lift feedback fin stabilizer system was simulated under different sea condition.Test results showed the system has better anti-rolling performance than traditional fin-angle PID control systems.

LIU Yong-wei LI Qi
Journal of Marine Science and Application,2008(No. 2): 0
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China’s coastal waters are turbid and the properties of the seabed are complex.This negatively impacts the performance of underwater detection equipment.The properties of sound absorption in turbid water are not well understood.In this paper,the coefficient of sound absorption in turbid water was measured by the reverberation technique.All work was done in a reverberation barrel made of seamless aluminum.First,pure water was poured into the reverberation barrel and its reverberation time measured.Next,various concentrations of turbid water were poured into the barrel and their reverberation time measured.After all data had been gathered,the coefficient of sound absorption in turbid water of different concentrations was calculated. From this we determined a law of sound absorption in turbid water as summarized in the paper.

LIU He-ping LUO A-ni XIAO Hai-yan
Journal of Marine Science and Application,2008(No. 2): 0
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The control system determines the effectiveness of an underwater hydraulic shock shovel.This paper begins by analyzing the working principles of these shovels and explains the importance of their control systems.A new type of control system’s mathematical model was built and analyzed according to those principles.Since the initial control system’s response time could not fulfill the design requirements,a PID controller was added to the control system.System response time was still slower than required,so a neural network was added to nonlinearly regulate the proportional element,integral element and derivative element coefficients of the PID controller.After these improvements to the control system,system parameters fulfilled the design requirements.The working performance of electrically-controlled parts such as the rapidly moving high speed switch valve is largely determined by the control system. Normal control methods generally can’t satisfy a shovel’s requirements,so advanced and normal control methods were combined to improve the control system,bringing good results.

LIU Chang-hai MA Li-juan TANG Li-qiang
Journal of Marine Science and Application,2008(No. 2): 0
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Low fatigue samples were obtained from the outer edges of rotor steel (30CrlMolV) which had operated under different temperatures conditions.Based on this data,the effects of temperature on fatigue crack growth rates were investigated.This paper presents a derivation of the superposition expression of two natural logarithms governing crack growth rates and also discusses the relationship between a material’s constants and temperature.These results can provide experimental and theoretical references for fatigue life design of root steel in steam turbines.