Characteristics Of Ship Motion Research Articles

Pseudorange Measurement Method Based on AIS Signals.

In order to use the existing automatic identification system (AIS) to provide additional navigation and positioning services, a complete pseudorange measurements solution is presented in this paper. Through the mathematical analysis of the AIS signal, the bit-0-phases in the digital sequences were determined as the timestamps. Monte Carlo simulation was carried out to compare the accuracy of the zero-crossing and differential peak, which are two timestamp detection methods in the additive white Gaussian noise (AWGN) channel. Considering the low-speed and low-dynamic motion characteristics of ships, an optimal estimation method based on the minimum mean square error is proposed to improve detection accuracy. Furthermore, the α difference filter algorithm was used to achieve the fusion of the optimal estimation results of the two detection methods. The results show that the algorithm can greatly improve the accuracy of pseudorange estimation under low signal-to-noise ratio (SNR) conditions. In order to verify the effectiveness of the scheme, prototypes containing the measurement scheme were developed and field tests in Xinghai Bay of Dalian (China) were performed. The test results show that the pseudorange measurement accuracy was better than 28 m (σ) without any modification of the existing AIS system.

Innovative Fast Time Simulation Tools for Briefing / Debriefing in Advanced Ship Handling Simulator Training and Ship Operation

The innovative “Simulation-Augmented Manoeuvring Design, Monitoring & Control” system (SAMMON) based on Fast Time Simulation (FTS) technology was developed at the Institute for Innovative Ship Simulation and Maritime Systems (ISSIMS) of the Maritime Simulation Centre Warnemuende MSCW. The system consists of software modules for (a) Manoeuvring Design & Planning, (b) Monitoring & Control based on Multiple Dynamic Prediction and (c) Trial & Training. It is based on complex ship dynamic models for rudder, thruster or engine manoeuvre simulation under different environmental conditions. It is an effective tool for lecturing and demonstrating ship's motion characteristics, as well as for ship handling simulator training. It allows the trainee to immediately see the results of the actual rudder, engine or thruster commands, without having to wait for the real-time response of the vessel. The Maritime Simulation Centre of AIDA Cruises at Rostock/Germany and the CSMART Center for Simulator Maritime Training of Carnival Corporation at Almere/NL have some experience with the use of this new technology to improve simulator training in Advanced Ship Handling Training courses. Examples of its application in briefing/debriefing and introductory lectures for simulator exercises specifically for typical cruise ships with Twin-Screw and Rudder systems will be presented in the paper and at the conference.

Ship motion estimation from polarized Doppler spectra from ship wakes on two-dimensional sea surfaces

The main purpose of this paper is to investigate the Doppler spectra from ship wakes on two-dimensional sea surfaces and further estimate the ship motion characteristics. The analysis of the ship wakes is helpful to detect the existence of ships on sea surface. And it will be an alternative method when the radar cross-section values are not competent to identify the ship target. In the study, Doppler spectra for different polarizations are compared with and without ship’s wakes based on the second-order small slope approximation method. As expected, there appears the second spectral peak when ship’s wake is considered. Moreover, the ship velocities, wind speed, and direction are also analyzed. As the results shown, there is a good linearity relation between the position of the second Doppler spectral peak and the ship velocity. Therefore, it is feasible to detect ship according the Doppler spectra.

Dynamic Modelling, Investigation of Manoeuvring Capability and Navigation Control of a Cargo Ship by using Matlab Simulation

Abstract: In this paper a simplified dynamic analysis of a cargo ship using simulation and modelling are presented. Provided with mathematical equations dynamics of ship motion characteristics with several maneuvering capabilities are demonstrated with MATLAB & SIMULINK as simulation tool. The equations extended with acting thrust, resistance, steering and ruder forces are demonstrated for several maneuvers like on straight track coasting from full ahead to stop, turning actions A numerical application of fast time simulations on a freighter ship is given with graphical representations. Furthermore a simplified model for rolling motion of ship is introduced and some examples are simulated to explain the general effects of stability and wave parameters. The relation of these results to the more practical use for decision making to avoid resonance effects of ship in waves by loading operations or speed/course changes is demonstrated by means of simulation tool.

Energy optimization of the fin/rudder roll stabilization system based on the multi-objective genetic algorithm (MOGA)

Energy optimization is one of the key problems for ship roll reduction systems in the last decade. According to the nonlinear characteristics of ship motion, the four degrees of freedom nonlinear model of Fin/Rudder roll stabilization can be established. This paper analyzes energy consumption caused by overcoming the resistance and the yaw, which is added to the fin/rudder roll stabilization system as new performance index. In order to achieve the purpose of the roll reduction, ship course keeping and energy optimization, the self-tuning PID controller based on the multi-objective genetic algorithm (MOGA) method is used to optimize performance index. In addition, random weight coefficient is adopted to build a multi-objective genetic algorithm optimization model. The objective function is improved so that the objective function can be normalized to a constant level. Simulation results showed that the control method based on MOGA, compared with the traditional control method, not only improves the efficiency of roll stabilization and yaw control precision, but also optimizes the energy of the system. The proposed methodology can get a better performance at different sea states.

Study on Effect of Shipborne Missile Launch Position Based on Fast Fourier Transform

In allusion to the problem of launching precision, it carried on the research of the effect of shipborne missile launch position based on the spectrum analysis technology. A rigid-flexible coupling integrative model of ship movement and missile launch was built by use of virtual prototype technology. Simulation analyses on a variety of conditions were automatic conducted by launch time parameterized scripting language, and missile muzzle attitude parameters of different launch position were gained. By using of spectrum analysis which is based on FFT, the missile dynamic responsive was analyzed, and the relationship between launch position and accuracy was established. Then the position of the weapon system can be designed according to the specific motion characteristics of ship. The research result is also constructive to the selecting of suitable launch position.

Adaptive robust sliding mode control for ship straight-line tracking in random waves

Since complex controllers do not suit for application, we design a simple controller with robustness in changeable sea state. The characteristics of ship motion are large inertia, strong nonlinearity and large time delay. This paper employs adaptive sliding mode technique. We focus on a class of underactuated ship systems with parametric uncertainties and wave effects. Random wave effects are seldom considered in former studies. Various simulations validate the adaptive characteristics and robustness of the proposed controller. The closed-loop system is stable and tracking error can be arbitrarily small by Lyapunov approach.

소형 트롤 어선의 예망중 동요특성

This paper deals with an experimental study on the dynamical characteristics of ship motion during trawling job on the real sea. The experiments were carried out on the small stern trawler, and roll and pitch motion of the ship according to the wave directions were simultaneously recorded by P/C in the same sea conditions. From these data, the statistical properties and power spectra were obtained, and then the analysis of ship motion in trwal job was made. As a result, it was found that the pitch motions in trwal job were displayed low amplitudes on the whole, but the rolling motions were displayed high amplitudes relatively, and very high value on the beam and quartering sea especially. Also, the trial ship has a high extinction coefficient in the roll motion, compared with the rule of stability, but when wave height takes 2.5m over, it can induce the safety of ship to scare occasionally. Therefore, a usefull countermeasure for the safety of ship has to be made adequately.

Estimation of Response Amplitude Operators for Ships via the Circular-Hyperbolic Decomposition

The frequency-domain analysis is commonly used to determine ship-motion characteristics, such as transfer functions and Response Amplitude Operators (RAOs). The Discrete Fourier Transform (DFT) has been the most widely used technique to conduct such an analysis. Nevertheless, application of the DFT is not always desirable because of leak-age. This problem cannot be eliminated unless the frequency content of a signal is known and all frequency components are rational multiples of each other. In this paper, we apply a recently developed closed-form decomposition technique, called the circular-hyperbolic decomposition (CHD), to estimate the RAOs of coupled heave and pitch motions using evenly sampled discrete ship-motion data. We show the advantages of the new technique over the DFT when leakage is present. We also introduce enhancements to the CHD in terms of a decimation parameter and a generalization for multiple signals. The results show that it is a promising technique.

Application of Hybrid Anti-Rolling System to Actual Ship

An actively controlled anti-rolling system has been developed with a view of reducing the rolling motion of ship. It is a new type of anti-rolling systems to replace the conventional systems, such as anti-rolling tank and fin stabilizer, and is of hybrid type combining the pendulum-base passive type with active type driven by relatively small electric motors. This system is composed of a moving weight oscillating on rail shaped in circular arc, carrying the driving motors and reduction gears, and the passive, compact mechanism is realized. The driving force to control the movement of the moving weight is imparted from the electric motors through reduction gears connected to a lack and pinion mechanism. The actual system of a moving weight of 100 tons has been applied to oceanographic research vessel “MIRAI” (8672 GT.) for practical use. Prior to service at open sea areas, the control system has been designed based on the identified parameters of ship motion characteristics obtained by results of forced rolling oscillation test using anti-rolling system in the calm sea. Control performance and dynamic behavior have been analyzed by recorded data of ship motion and displacement of moving weight at open sea areas. It has been revealed that the system operated following the control law and provided performance to be aimed in design.

港内操船における曳船の支援効果について-II : 風潮流等外乱の影響

In the previous paper, we discussed the characteristics of turning motion of ship under tugboat's assistance without disturbance. But the characteristics of ship motion in harbour is rather complex due to wind and tidal current effect. In this paper, we have investigated and cleared these characteristics of turning and lateral motion of ship in harbour. The summary results are as follows. (1) The area required in turning motion depends on the wind direction and speed. (2) It is possible to decrease the area required in turning motion by control of the ship longitudinal motion under wind effect. (3) In case of approaching berth, the usage of performance curve of transeverse speed enables to know the timing to brake of motion. (4) In case of lateral motion under wind effect, it is most important to cancel initial wind force by tugboats.

On the Course Stability of Ship under the Manual Steering

Manual steering is assumed to be written analytically in the following Laplace transform, δ* (s) =-K*p (1+T*Ds+T*I/s) θ (s).δ* (s) is the angle of rudder given by a quartermaster, θ (s) is the angle between ships head and the desired course, and K*p, T*D, T*I are proportional constants.In the practical point of view it is advantageous to adopt the approximated form of equation of ship motionTdθ/dt+θ=Kδ, which has been proposed by K. Nomoto. This simplified equation can give directly the characteristics of ship motion under manual steering.According to the above two equations, the author has pointed out the possibility of finding the optimum value of ship maneuverability.