Journal of Marine Science and Application 2008 No. 4
XU Gang DUAN Wen-yang
Journal of Marine Science and Application,2008(No. 4): 0
+Show Abstract -Hide Abstract

Direct time-domain simulation of floating structures has advantages: it can calculate wave pressure fields and forces directly;and it is useful for coupled analysis of floating structures with a mooring system. A time-domain boundary integral equation method is presented to simulate three-dimensional water wave radiation problems. A stable form of the integration free-surface boundary condition (IFBC) is used to update velocity potentials on the free surface. A multi-transmitting formula (MTF) method with an artificial speed is introduced to the artificial radiation boundary (ARB). The method was applied to simulate a semi-spherical liquefied natural gas (LNG) carrier and a semi-submersible undergoing specified harmonic motion. Numerical parameters such as the form of the ARB,and the time and space discretization related to this method are discussed. It was found that a good agreement can be obtained when artificial speed is between 0.6 and 1.6 times the phase velocity of water waves in the MTF method. A simulation can be done for a long period of time by this method without problems of instability,and the method is also accurate and computationally efficient.

ZHANG Lei PANG Yong-jie SU Yu-min ZHAO Fu-long QIN Zai-bai
Journal of Marine Science and Application,2008(No. 4): 0
+Show Abstract -Hide Abstract

S-surface control has proven to be an effective means for motion control of underwater autonomous vehicles (AUV). However there are still problems maintaining steady precision of course due to the constant need to adjust parameters,especially where there are disturbing currents. Thus an intelligent integral was introduced to improve precision. An expert S-surface control was developed to tune the parameters on-line,based on the expert system,it provides S-surface control according to practical experience and control knowledge. To prevent control output over-compensation,a fuzzy neural network was included to adjust the production rules to the knowledge base. Experiments were conducted on an AUV simulation platform,and the results show that the expert S-surface controller performs better than an S-surface controller in environments with currents,producing good steady precision of course in a robust way.

YAO Xiong-liang TIAN Zheng-dong SHEN Zhi-hua GUO Shao-jing
Journal of Marine Science and Application,2008(No. 4): 0
+Show Abstract -Hide Abstract

A new isolator composed of a steel rope spring and a magneto-rheological (MR) damper was designed and a study on low-frequency mechanical characteristics of MR dampers in isolators was carried out. It used the characteristics of the MR damper,such as fast response,controllable damping,small energy consumption,wide dynamic scope,and great adaptation. The relationships between MR damping forces and influencing factors were analyzed based on experimental data. The results show that damping force is not only related to structural dimensions,but also closely related to controllable current and vibration frequency. Finally,the empirical formula for damping forces was corrected,and the relationship between correction coefficients and factors analyzed.

JIN Hong-zhang QI Zhi-gang ZHOU Ting Li Dong-song
Journal of Marine Science and Application,2008(No. 4): 0
+Show Abstract -Hide Abstract

With the increasing importance of ocean exploitation,providing anti-rolling stability for ships at anchor has become more and more important. The lift-generation theory of traditional fin stabilizers is based on incoming flow velocity,which is not suitable for explaining lift generated at anchor. We analyzed non-steady flows,with forces on fin stabilizers generated by non-incoming flow velocity conditions,and gave a new lift-generation model. The correctness of the model was proven by comparing experimental results of fin stabilizer motion under non-incoming velocity conditions from the fluid computation software with that from the emulator of the lift-generation model. Finally,the model was used in an anti-rolling system on a ship and the reduction of roll was much better than what could be achieved by passive anti-rolling tanks.

QIU Zhong-liang
Journal of Marine Science and Application,2008(No. 4): 0
+Show Abstract -Hide Abstract

Variable ballast systems are necessary for manned submersibles to adjust their buoyancy. In this paper,the design of a variable ballast system for a manned submersible is described. The variable ballast system uses a super high pressure hydraulic seawater system. A super high pressure seawater pump and a deep-sea brushless DC motor are used to pump seawater into or from the variable ballast tank,increasing or decreasing the weight of the manned submersible. A magnetostrictive linear displacement transducer can detect the seawater level in the variable ballast tank. Some seawater valves are used to control pumping direction and control on-off states. The design and testing procedure for the valves is described. Finally,the future development of variable ballast systems and seawater hydraulic systems is projected.

FAN Li-yun ZHU Yuan-xian LONG Wu-qiang MA Xiu-zhen XUE Ying-ying
Journal of Marine Science and Application,2008(No. 4): 0
+Show Abstract -Hide Abstract

WIT Electronic Fuel System Co.,Ltd. has developed a new fuel injector,the Electronic In-line Pump (EIP) system,designed to meet China’s diesel engine emission and fuel economy regulations. It can be used on marine diesel engines and commercial vehicle engines through different EIP systems. A numerical model of the EIP system was built in the AMESim environment for the purpose of creating a design tool for engine application and system optimization. The model was used to predict key injection characteristics under different operating conditions,such as injection pressure,injection rate,and injection duration. To validate these predictions,experimental tests were conducted under the conditions that were modeled. The results were quite encouraging and in agreement with model predictions. Additional experiments were conducted to study the injection characteristics of the EIP system. These results show that injection pressure and injection quantity are insensitive to injection timing variations,this is due to the design of the constant velocity cam profile. Finally,injection quantity and pressure vs. pulse width at different cam speeds are presented,an important injection characteristic for EIP system calibration.

SUN Jian-hua WANG Wei YU Hai-yan
Journal of Marine Science and Application,2008(No. 4): 0
+Show Abstract -Hide Abstract

The flexibility demand of marine nuclear power plant is very high,the multiple parameters of the marine nuclear power plant with the once-through steam generator are strongly coupled,and the normal PID control of the turbine speed can’t meet the control demand. This paper introduces a turbine speed Fuzzy-PID controller to coordinately control the steam pressure and thus realize the demand for quick tracking and steady state control over the turbine speed by using the Fuzzy control’s quick dynamic response and PID control’s steady state performance. The simulation shows the improvement of the response time and steady state performance of the control system.

FENG Xiao-ning WANG Shuo WANG Zhuo LIU Qun
Journal of Marine Science and Application,2008(No. 4): 0
+Show Abstract -Hide Abstract

This paper informally introduces colored object-oriented Petri Nets(COOPN) with the application of the AUV system. According to the characteristic of the AUV system’s running environment,the object-oriented method is used in this paper not only to dispart system modules but also construct the refined running model of AUV system,then the colored Petri Net method is used to establish hierarchically detailed model in order to get the performance analyzing information of the system. After analyzing the model implementation,the errors of architecture designing and function realization can be found. If the errors can be modified on time,the experiment time in the pool can be reduced and the cost can be saved.

ZHANG Wei-ying LIN Yan JI Zhuo-shang ZHANG Guang-fa
Journal of Marine Science and Application,2008(No. 4): 0
+Show Abstract -Hide Abstract

Containership stowage plans are a pivotal teaches in the system of container transportation. With the increasing containers shipping,planning containership stowage has become more and more complicated. So intelligent stowage planning for containerships is of great significance. An effective stowage plan may improve efficiency of transportation system. First,the progress of containership stowage plan at home and abroad is reviewed,including the latest developments,such as the application of various optimization methods and computer techniques to the problem. Then,the complexities of the problem are discussed and areas where investigations are still needed are pointed out. This will provide a reference for further research on the subject.

QIN Ting-rong CHEN Wei-jiong ZENG Xiang-kun
Journal of Marine Science and Application,2008(No. 4): 0
+Show Abstract -Hide Abstract

Quantified risk assessment (QRA) needs mathematicization of risk theory. However,attention has been paid almost exclusively to applications of assessment methods,which has led to neglect of research into fundamental theories,such as the relationships among risk,safety,danger,and so on. In order to solve this problem,as a first step,fundamental theoretical relationships about risk and risk management were analyzed for this paper in the light of mathematics,and then illustrated with some charts. Second,man-machine-environment-management (MMEM) theory was introduced into risk theory to analyze some properties of risk. On the basis of this,a three-dimensional model of risk management was established that includes: a goal dimension;a management dimension;an operation dimension. This goal management operation (GMO) model was explained and then emphasis was laid on the discussion of the risk flowchart (operation dimension),which lays the groundwork for further study of risk management and qualitative and quantitative assessment. Next,the relationship between Formal Safety Assessment (FSA) and Risk Management was researched. This revealed that the FSA method,which the international maritime organization (IMO) is actively spreading,comes from Risk Management theory. Finally,conclusion were made about how to apply this risk management method to concrete fields efficiently and conveniently,as well as areas where further research is required.

SONG Tian-shu LI Dong REN Zheng-yi
Journal of Marine Science and Application,2008(No. 4): 0
+Show Abstract -Hide Abstract

Wave propagation in an infinite elastic piezoelectric medium with a circular cavity and an impermeable crack subjected to steady-state anti-plane shearing was studied based on Green’s function and the crack-division technique. Theoretical solutions were derived for the whole elastic displacement and electric potential field in the interaction between the circular cavity and the impermeable crack. Expressions were obtained on the dynamic stress concentration factor (DSCF) at the cavity’s edge,the dynamic stress intensity factor (DSIF) and the dynamic electric displacement intensity factor (DEDIF) at the crack tip. Numerical solutions were performed and plotted with different incident wave numbers,parameters of piezoelectric materials and geometries of the structure. Finally,some of the calculation results were compared with the case of dynamic anti-plane interaction of a permeable crack and a circular cavity in an infinite piezoelectric medium. This paper can provide a valuable reference for the design of piezoelectric actuators and sensors widely used in marine structures.

SUN Li-hong, SHEN Ji-hong
Journal of Marine Science and Application,2008(No. 4): 292-296
+Show Abstract -Hide Abstract

Ship motion, with six degrees of freedom, is a complex stochastic process. Sea wind and waves are the primary influencing factors. Prediction of ship motion is significant for ship navigation. To eliminate errors, a path prediction model incorporating ship pitching was developed using the Gray topological method, after analyzing ship pitching motions. With the help of simple introduction to Gray system theory, we selected a group of threshold values. Based on an analysis of ship pitch angle sequences over 40 second intervals, a Grey metabolism GM(1,1) model was established according to the time-series which every threshold corresponded to. Forecasting future ship motion with the GM (1,1) model allowed drawing of the forecast curve with effective forecasting points. The precision of the test results show that the model is accurate, and the forecast results are reliable.