A three-dimensional method of calculating wave loads of turret moored FPSO (Floating Production Storage and Offloading) tankers is presented. The linearized restoring forces acting on the ship hull by the mooring system are calculated according to the catenary theory, which are expressed as the function of linear stiffness coefficients and the displacements of the upper ends of mooring chains. The hydrodynamic coefficients of the ship are calculated by the three-dimensional potential flow theory of the linear hydrodynamic problem for ships with a low forward speed. The equations of ship motions are established with the effect of the restoring forces from the mooring system included as linear stiffness coefficients. The equations of motions are solved in frequency domain, and the responses of wave-induced motions and loads on the ship can be obtained. A computer program based on this method has been developed, and some calculation examples are illustrated. Analysis results show that the method can give satisfying prediction of wave loads.
The bow structure of FPSO moored by the single mooring system is rather complicated. There are many potential hot spots in connection parts of structures between the mooring support frame and the forecastle. Mooring forces, which are induced by wave excitation and transferred by the YOKE and the mooring support frame, may cause fatigue damage to the bow structure. Different from direct wave-induced-forces, the mooring force consists of wave frequency force (WF) and 2nd draft low frequency force (LF)[3], which are represented by two sets of short-term distribution respectively. Based on two sets of short-term distribution of mooring forces obtained by the model test, the fatigue damage of the bow structure of FPSO is analyzed, with emphasis on two points. One is the procedure and position selection for fatigue check, and the other is the application of new formulae for the calculation of accumulative fatigue damage caused by two sets of short-term distribution of hot spot stress range. From the results distinguished features of fatigue damage to the FPSO’s bow structure can be observed.
The seakeeping performance of a certain ship equipped with semi-submerged bow (SSB) and bow-fins is discussed. The numerical calculations are carried out on a 600t deep-V compound archetypal ship. The results show that the compounded ship form has excellent seakeeping performance and thus it establishes the theoretical foundations for the development of monohull compounded ship form with high seakeeping performance.
Choosing the equipment with good shock-resistant performance and taking shock protection measures while designing the onboard settings, the safety of onboard settings can be assured when warships, especially submarine subjected to non-contact underwater explosion, that is, these means can be used to limit the rattlespace (i. e., the maximum displacement of the equipment relative to the base) and the peak acceleration experienced by the equipment. Using shock-resistant equipments is one of shock protection means. The shock-resistant performance of the shock-resistant equipments should be verified in the design phase of the equipments. The FEA (finite element analysis) software, for example, MSC. NASTRAN®, can be used to verify the shock-resistant performance. MSC. PATRAN® and MSC. NASTRAN are used for modeling and analyzing the floating raft vibration isolating equipment. The model of the floating raft and the floating raft vibration isolating system are theoretically analyzed and calculated, and the analysis results are in agreement with the test results. The transient response analysis of the system model follows the modal analysis of the floating raft vibration isolating system. And it is used to verify the shock-resistant performance. The analysis and calculation method used in this paper can be used to analyze the shock-resistant performance of onboard shock-resistant equipments.
A new marine propulsion system is proposed. A small liquid sodium cooled reactor acts as prime mover; alkali-metal thermal-to-electric conversion (AMTEC) cells are employed to convert the heat energy to electricity; superconducting magneto-hydrodynamic thruster combined with spray-water thruster works as propulsion. The configuration and characteristics of this system are described. Such a nuclear-powered propulsion system is not only free of noise, but also has high reliability and efficiency. It would be a preferable propulsion system for ships in the future.
Water hydraulic systems have provoked major interest because of the human friendly and environmental safety aspects. Piston pump is one of the most frequently used hydraulic units in recent engineering technique. In water hydraulic piston pump, poor lubrication is more likely to happen than in oil hydraulic one because of difference in properties between water and oil. So there are some key problems such as corrosive wear and erosion, which are investigated briefly. Many new materials have been developed, which give longer life expectancies with water without corrosion and erosion. A new type of seawater hydraulic piston pumps with better suction characteristics had been developed at HUST. Much of this research has concentrated on new materials, structure and experiments, which are also specially introduced.
Considering the special resistance characteristics of fluids flowing through ducts with small gaps, experiments are performed to investigate the resistance characteristics of single-phase water, which is forced to flow through vertical annuli. The gap sizes are 0.9, 1.4 and 2.4mm, respectively. The experiments are conducted under condition of 1 atm. The water in the annuli is heated by high temperature water reversely flowing through the inner tube and the outer annulus. The results show that the flow pattern begin to change from laminar to turbulent before Reynolds number approaches 2000, the flow resistance in annulus has little relations with the temperature difference and ways of being heated, but mainly depends on the ratio of mass flux to the width of annulus.
The structure, function and recognition method of an axis orbit auto-recognizing system are presented in this paper. In order to make the best use of information of format and dynamic characteristics of marine steam turbine axis orbit, the structure and functions or neural network are applied to this system, which can be used to auto-recognize axis orbit of the system turbine rotor using BP neural network.
A new gray-spatial histogram is proposed, which incorporates spatial information with gray compositions without sacrificing the robustness of traditional gray histograms. The purpose is to consider the representation role of gray compositions and spatial information simultaneously. Each entry in the gray-spatial histogram is the gray frequency and corresponding position information of images. In the experiments of sonar image recognition, the results show that the gray-spatial histogram is effective in practical use.
By the sketch of structure of MVWG, the working laws of this kind of gyroscope were explained. To the aid of Euler’s Dynamics Equation, a mathematical model of the gyroscope was constructed, and then by the basic working laws of MVWG the model was simplified. Under the conditions of the three axial direction rotations and general rotation, the mathematical model was resolved. And finally by the solutions, the working laws of the gyroscope, the working disparity among all sorts of gyrations and the influences from the gyrations in the axial directions were analysed.
A new algorithm is proposed for underwater vehicles multi-path planning. This algorithm is based on fitness sharing genetic algorithm, clustering and evolution of multiple populations, which can keep the diversity of the solution path, and decrease the operating time because of the independent evolution of each subpopulation. The multi-path planning algorithm is demonstrated by a number of two-dimensional path planning problems. The results show that the multi-path planning algorithm has the following characteristics: high searching capability, rapid convergence and high reliability.
The selecting and preparing method of the basic material of magnetic fluid was introduced. By using a chemical method, the magnetic micropowder Fe3O4 was successfully yielded, and an oil-base as a working carrier and dispersing agent was determined. The preparation process of the magnetic fluid and prescription of the oil-base magnetic fluid were discussed. The simulation experimental rig of magnetic fluid sealing for propeller shaft was designed. The sealing ability experiment was conducted and results were analyzed. The pressure of sealing is up to 2 MPa.
A simple rate equation model for 2µm Tm,Ho:YLF laser is given to study laser dynamics. Under low pump power, the explicit formulae for the threshold pump power and the relation between output power and incident power are obtained. The present model provides a straightforward procedure to design the laser resonator and the optical coupling system for optimization. At the same time, the experimental results are reported. At room temperature the slope efficiency is 22.4% and the typical lasing threshold is about 328mW. The theory is in good agreement with experiment.
Adopting an elastic-viscoplastic, the asymptotic problem of mode I propagating crack-tip field is investigated. Various asymptotic solutions resulting from the analysis of crack growing programs are presented. The analysis results show that the quasistatically growing crack solutions are the special case of the dynamic propagating solutions. Therefore these two asymptotic solutions can be unified.
The backdoor or information leak of Web servers can be detected by using Web Mining techniques on some abnormal Web log and Web application log data. The security of Web servers can be enhanced and the damage of illegal access can be avoided. Firstly, the system for discovering the patterns of information leakages in CGI scripts from Web log data was proposed. Secondly, those patterns for system administrators to modify their codes and enhance their Web site security were provided. The following aspects were described: one is to combine web application log with web log to extract more information, so web data mining could be used to mine web log for discovering the information that firewall and Information Detection System cannot find. Another approach is to propose an operation module of web site to enhance Web site security. In cluster server session, Density-Based Clustering technique is used to reduce resource cost and obtain better efficiency.