Showing papers in "Journal of Naval University of Engineering in 2004"

Evolution and prospect of discrete variable structure control theory

Abstract: The evolution of the discrete variable structure control theory is summarized. Three main design methods are introduced. Finally, some problems encountered in this field and the future research direction are discussed.

Chattering analysis and robustness study of discrete variable rate reaching law

Abstract: The design of variable structure control based on the discrete variable rate reaching law is discussed. The reason for system chattering is analyzed by introducing the inequation form reaching condition, and the robustness property is studied. It is shown that the variable rate reaching law can avoid the chattering, and exhibit good dynamic performance by adjusting parameters. Besides the robust stability of the closed-loop system can be ensured if the uncertainties are bounded. The variable rate reaching law is applied to the controller design for a ship autopilot. Experiment results verify its effectiveness.

Vibration measurement and analysis of gearbox

Abstract: On the basis of the measurement of model, vibration severity and vibration acceleration of a certain kind of gearbox, the measurement results are presented in detail. The result of modal mea-(surement) gets the vibration model and modal parameters of the gearbox, and the result of vibration severity measurement makes it clear that the gearbox is in good condition, and the result of vibration acceleration measurement indicates that the vibration reduction reaches the prospective effect. Some advice for the measurement is given finally.

Experimental determination of roll damping of deep-Vee planing craft

Abstract: The roll decay test in still water and roll tests in regular waves at zero speed on model of a deep-Vee planing craft are conducted, and problems arising from the data processing are discussed The smoothed curves of roll decay tests in still water are obtained from the test data by using the sectional least square method, and the roll damping at different roll angle is calculated by using the peak treatment technique, and the formula of the roll damping of deep-Vee planing craft is obtained by the multiple regression technique

Genetic algorithm of path planning in polygon obstacle environment

Abstract: This paper studies the genetic algorithm of path planning in the planar obstacle environment, and lays emphasis on introducing the model structuring of obstacle environment and the method design of using genetic algorithm to solve the model. The mode of chromosome coding and the design of genetic operator are different from those of existing genetic algorithm, and thus avoiding importing invalid gene into chromosome during the initiating colony, speeding the evolving of chromosome and making the algorithm have good ability of optimization finding. Experiments also indicate the validity of the algorithm.

Point-electrode model of electric field of steady current in sea

Abstract: Based on the fundamental hypothesis of treating an electrode as a point, this paper calculates the distribution of electric potential of the steady current field in the three-layers media (air-sea water-seabed) model by separation of variables and image method, using resemblance between electrostatic field and stable current field in even medium. Thus the paper gives the calculation model of the electric field generated by steady current in the sea based on point-electrode.

Formal description of properties of concurrency system by temporal logic

Abstract: The temporal logic is a formal method for describing sequences of transition between states in a reactive (concurrent) system It is common to use the temporal logic to specify the properties that the design must satisfy The temporal logic is the basic of model checking This paper states the syntax and semantics of CTL~* and its sub-logics: CTL and LTL, and analyzes how to state the properties of concurrent system, and finally the application example is given

Research of data synchronization technology in distributed database

Abstract: Aiming at the requirement of distributed database, this paper analyses and compares the theories, advantages and disadvantages of different data synchronization technology methods based on the research of Oracle and correlative systems. This paper also discusses their applied occasions.

Improved AHP algorithm based on expert weights

Abstract: The index weights of the experts are system cally analyzed according to the method of multi-decision and fuzzy judgment. And the index weight is determined by the AHP. Based on these, a new integrated appraisal method is advanced.

Law and feature of pitting caused by inclusion in carbon steel

Abstract: Five mild steels are selected, and the pitting initiation features of steels in 3% NaCl solution are studied by means of the immersion test, micro-corrosion test, and polarization test. The results indicate that the initial potential of specimens immersed into the solution is higher than their pitting potential (E_(b)), therefore some inclusions becomeactive and initiate pitting firstly. The potential of steels drops rapidly because of the activation of local areas on the surface of specimen. When the potential of steels is lower than the pitting potential, the inclusions which don′t initiate pitting or initiate pitting deficiently are protected and don't initiate pitting anymore. In the polarization test, almost all inclusions can be active and initiate pitting when the potential of steels is equal to or higher than the pitting potential.

Techniques by compound branch and network ripping to find out all spanning trees of an undirected graph

Abstract: The techniques of compoundbranch and network ripping are employed to find out all spanning trees of an undirected graph. The concept, expression and operation rules ofcompound branches are given, and the algorithm to obtain all spanning trees of a graph from those ripped sub-graphs is presented. Because of making use of some parallel algorithms, the computing complexity is reduced.

A rapid algorithm to OCR image slant correction based on primitive recognition

Abstract: This paper proposes a rapid algorithm to OCR image slant correction, which applies the graphic primitive recognition technique and then keeps track of the character center-line. Though (being simple,) the algorithm is so efficient, accurate, and reliable that it can be used in real-ime applications.

Effect of discontinuity of pipe wall on transmission coefficient of pure torsion wave

Abstract: The solution of the pure torsion wave in the pipe wall with discontinuity is obtained by the four-pole parameter method, and based on which the effect of the different materials and their thickness of discontinuous pipe wall on the transmission coefficient of the pure torsion wave is analyzed. The results show that the effect of the material of the discontinuous pipe wall on the transmission wave is very important, whereas the effect of the thickness is not obvious.

Main branches of recent elastic stability theory

Abstract: A brief survey of recent elastic stability theory is represented. Some explanations of different elastic stability theory to the sharp difference between theoretical and experimental results of the buckling problem of axially compressed cylindrical shells are demonstrated. And the basic equations, essential thoughts of three stability theories—non-linear large deflection theory, non-linear prebuckling consistency theory and initial postbuckling theory are presented. The applicability of these theories is discussed.

Optimal Design of hybrid vibration isolation system of marine power machinery

Abstract: The principle of hybrid vibration isolation is analyzed, which reveals that the essential of the hybridvibration isolation is a combined multi-objective optimal problem of the passive and active parts of the vibration system The two-stage vibration isolation system applied widely on ships is designed with the optimal hybrid vibration isolation technology and the numerical simulation is carried out The simulation result demonstrates that the method is feasible and there exists wide application prospect

Algorithm of modified polar adaptive Kalman filter used in bearings-only target tracking

Abstract: A modified polar adaptive extended Kalman filter(MPAEKF)algorithm is presented in order to solve the problem of instability and low accuracy of the passive filter in bearings-only target tracking. This algorithm can be used to estimate the statistics of the state virtual noise on-line, thus it overcomes the bad effect caused by the linearization of nonlinear state model. The simulation result shows that MPAEKF improves the filter convergence rate and accuracy.

Preprocessing of small sampling data

Abstract: The method of mathematical statistic is usually used to process the data, but it is not suitable to process small quantity of data Thus a new method based on the linear mean squares estimation and entropy judging method is used to distinguish the gross errors LMSE is a way by softening the gross errors; the entropy distinguishing is based on the upper limit that is maximum error of the entropy, thus it can he used to distinguish the gross errors of data Many examples prove that the two methods are more effective when they are used to process small sampling data

A kind of grey relational grade problem based on fuzzy membership function

Abstract: With respect to the data of system characteristic sequences and correlative factor sequences being uncertain or existing interval coverage, based on the fuzzy membership function, a new method for determining the relational grade of the grey relational analysis is introduced. And a practical example is given to illustrate the rationality of this method.

Variable structure control and simulation for course-keeping of ships

Abstract: The variable structure control for course-keeping of ships is investigated by using the variable structure control theory and computer simulation technique According to the purpose and requirement of the accurate course and small rudder in navigation, the quadratic optimal control technique is used to design the sliding mode hyperplane, and the exponential approaching law, which satisfies the condition of reaching sliding mode hyperplane, is designed and the corresponding control law is deduced Meanwhile, the PID controller is designed and the correlative parameters are adjusted well for comparing with the variable structure controller By theoretical analysis and numerical simulation, it is shown that the variable structure control is correct and feasible and the control effect is better than PID control for ship course-keeping

Network reconfiguration of large shipboard power system

Abstract: With the appearance of the large shipboard power supply system, the trend of shipboard power supply system is developing from the conventional radial-configuration to the ring-configuration whose network reconfiguration gradually becomes a new study direction. The network topology of the large shipboard power system is given. And the mathematical models of the reconfiguration (consi)-(dering the) capacity of the generators, nodes voltage constraints and load priorities are also given, which can grantee the maximum load power supply. Genetic evolutionary programming is used to solve the model, and an example is given at last to show the feasibilityof the evolutionary programming.

Development of spatio-temporal neutron kinetics simulation software for marine nuclear reactor core

Abstract: According to the structural characters and operating mode of the marine nuclear power (equipments,) the mesh-cell structure neutron kinetics models of two neutron energy groups and 3D are built. The spatio-temporal neutron kinetics simulation software for the marine nuclear reactor core is developed, by which some core neutron kinetics problems are solved after calculation. It is concluded from the simulation results that the models in the software system are accurate, and the soft packages can be used to the development and design of marine nuclear equipment simulator.

Analysis of conflict between security and real-time requirements in MLS/RTDBMS

Abstract: A multilevel real-time database system must have security constrains in addition to timing constrains. Covert channel and priority inversion problems can not be avoided because of the conflict between security and timeliness requirements. This paper analyzes the conflict between these two requirements in multilevel real-time database system, and then based on HP-2PL gives an algorithm combining with the secure factor for the conflict.

Numerical computation of cavitating flow around axisymmetric bodies

Abstract: Axisymmetric cavitating flows around the cone-capped cylinder are numerically simulated with the boundary element method under potential flow assumption. The relationship between the cavity number, cavity length, cavity thickness and cone angle is analyzed. Computing results agree with experimental ones.

Short-circuit current calculation for naval alternating current loop power network

Abstract: According to the characteristics of naval alterrating current loop power network, a simple and effective short-circuit current calculation method is put forward. It regards each power station as a unit, using "equivalent generators" and "equivalent motc rs" to describe the power station, then simplifies looped power network in the form that electrical source and fault connect directly by impedance and calculates short-circuit currents in an improved way. The result of simulation indicates that the method is accurate enough for engineering. It breaks a new path for short-circuit current calculation of isolated power system with complex construction.

On remote maintenance supporting system of warship equipment

Abstract: Based on the open complex giant system and its methodology: metasynthesis, an approach from qualitative description to quantitative description, which is proposed by Chinese scientists in the early 1990s, this paper argues that the warship equipment remote maintenance supporting system is an open complex giant system, and then proposes a general frame about the system based on multi-agent and discusses the way to solve the remote diagnosis problem, and finally gives the future research items.

Realization of Chinese menu interface based on graphic dot matrix LCD

Abstract: The problem of how to realize the man-machine interface of Chinese menu based on the graphic dot matrix LCD (DEM12864P) is studied. The characteristics of LCD model (DEM12864P) are first analyzed. The relation of the DD RAM addressing and LCD dot matrix is explained, so are the display rules of Chinese characters and Chinese menu on the LCD model. Then the design of the cursor realization method and menu data structure based on the multi-task background is introduced; meanwhile the realization method of the design of the correlative software is also proposed.

Simulation of fuzzy controller of fin stabilizer with Matlab

Abstract: The ship model is built based on the Conolly theory. The fuzzy controller of fin stabilizer is designed by using the fuzzy logic control, which uses the roll angle and angular velocity of roll angel as the input and the fin angel as the output. The controller is simulated with the fuzzy logic toolbox of Matlab. Results show that compared with the conventional PID controller, the fuzzy controller has better effect.

Correction of algorithm for thermodynamic performance of superheater of certain turbocharged boiler

Abstract: Combining the heat transfer algorithm of tubes in the superheater with the structural specialty of the superheater of certain turbocharged boiler,the mathematical model of heat transfer is constructed In addition, a correction of algorithm for thermodynamic performance of the superheater is made At last, the temperature distribution of smoke behind the superheater is obtained by calculation

Propagation properties of electromagnetic wave in sea water

Abstract: Using Maxwell equations which are the basic requirement of the electromagnetic wave pro-(pagation,) the authors calculate and analyze some special propagation properties of the electromagnetic wave in the conducting medium. An example of the sea water selected as the conducting medium is given. And some useful results are derived, which will be the theoretic base of the research in such aspects as the communication in sea water, signal detection and fusee of mine.

Research of improvement of Stein estimators of coefficients in linear regression models

Abstract: In the light of the essence of the ill condition in the linear regression model, this paper first proposes the c-k class of estimators of the coefficients, which combines the ridge regression estimators and the Stein shrinkage estimators into a bigger class of estimators The c-k class of estimators is studies, and it is proved that under the mean square error criterion the Stein estimators can be improved via the ridge regression technique Then the optimal value of the parameters is examined and each of its upper bounds and lower bounds is given respectively, which provides a technical way to the improvement of the biased estimators of the coefficients in the linear regression models