Freedom Ship Research Articles

A Method for Forcing a Number of Motions or Rotations in 6 Degrees of Freedom Ship Simulators

In this paper, a method is introduced which enables the forcing of any degrees of freedom in 6 DoFs ship simulator. It is based on the introduction of an extra force in the equation of motion of the ship and on the forcing of the second derivatives of the forced degrees of freedom rather than the forced degrees of freedom themselves. The method is explicit which makes it easy to implement in existing software. Examples of its application to oblique towing tests and forced heading in wind and waves are presented.

Strong fixed-time dynamic inverse adaptive LQR integrated control strategy for dynamic positioning of ship

To ensure compositive capacities for dynamic positioning ship, a dynamic inverse adaptive linear quadratic regulator (DI-ALQR) control strategy is proposed for dynamic positioning ship based on strong fixed-time prescribed performance function (SFPPF) and cascaded fixed-time extended state observer (CFESO). Firstly, a high-fidelity four degree of freedom ship motion model including roll motion is constructed, and an inverse system of the ship is proposed to realize decoupling of variables and pseudo linearization of control systems. Next, the SFPPF is employed to ensure prescribed performance with predefined convergence. The DI-ALQR control strategy is presented to achieve integrated control of position, roll and heading of ship considering the balance between energy consumption and control accuracy. Simulation results and analysis prove that the proposed control strategy makes the position, roll and heading of ship reach in predefined-time and maintain the desired values, which ensures prescribed performance.

Prediction of Resistance and Self-Propulsion Characteristics of a Full-Scale Naval Ship by CFD-Based GEOSIM Method

Resistance and self-propulsion characteristics of a naval ship at full scale have been investigated by using Telfer’s GEOmetrically SIMilar (GEOSIM) method based on the computational fluid dynamics (CFD) approach. For this purpose, first, the resistance forces of the Office of Naval Research Tumblehome (ONRT) hull have been computed at different three model scales by using the overset mesh technique. The full-scale resistance and nominal wake fraction of the ONRT hull have been estimated by using Telfer’s GEOSIM method. Resistance and nominal wake fraction have then been compared with those of CFD at full scale. Later, the self-propulsion characteristics of the ONRT hull have been examined using Telfer’s GEOSIM method based on the CFD approach. Self-propulsion factors at the full-scale hull have been predicted by using the SST k–x turbulence model to involve 2-degrees of freedom ship motions (heave and pitch). Rotational motion of the propeller has also been simulated by using the rigid body motion technique. The results calculated by Telfer’s GEOSIM method and the 1978 International Towing Tank Conference (ITTC) extrapolation technique have been compared with each other and discussed with those of the CFD approach at full scale. It was found that the full-scale results (both resistance and self-propulsion factors) predicted by Telfer’s GEOSIM method are closer to those of the CFD approach than those of the 1978 ITTC technique. It can be noted that Telfer’s GEOSIM method is fast, robust, and reliable and can be used as an alternative to the 1978 ITTC method for predicting the self-propulsion performance of a full-scale ship. Introduction Resistance and self-propulsion characteristics of a surface ship should be known properly in the design stages. For this purpose, model tests and numerical methods are used together to determine the resistance and self-propulsion performance of a ship. However, model tests are expensive and time-consuming, and the accuracy of the International Towing Tank Conference (ITTC) extrapolation technique from model scale to full scale may not have in a satisfactory level. On the other hand, Telfer’s GEOmetrically SIMilar (GEOSIM) method based on computational fluid dynamics (CFD) can overcome these difficulties.

Ship energy performance study of three wind-assisted ship propulsion technologies including a parametric study of the Flettner rotor technology

ABSTRACTA 4 degrees of freedom ship performance prediction model is used to compare wind-assisted ship propulsion technologies: the Flettner rotor, a wingsail and the DynaRig concept. An Aframax Oil Tanker on a route between Gabon and Canada is used in a case study to compare the three technologies using actual information for the voyage. The fuel savings for were calculated and they varied between 5.6% and 8.9%; the Flettner rotor showed the largest fuel savings. A parametric study of the Flettner rotor technology was carried out to research how its dimensions and operation conditions for two ship types on two voyages influence the fuel savings. The results show that fuel savings were achieved by several percentages. It is shown that it is necessary to select and operate the Flettner rotor according to its ship type, speed, voyage routes and corresponding weather conditions to achieve as large fuel savings as possible.

Design of Classical Washout Algorithm for Six Degree of Freedom Ship Motion Simulator

The motion washout aims to bring the actual movement of the ship back to the six degree of freedom motion simulator, and to provide as real motion as possible in the limited space of the simulator. The emphasis of the classic washout algorithm lies in the choice of parameters. This paper analyzes the time domain response of the filter and combines the platform motion range with the human sensory system threshold to impose performance requirements on the system. To optimize the parameter selection according to the system performance, and get a good result of motion washout.

Numerical investigation of a two - degrees - of - freedom ship model for pitch - roll motion

This paper numerically investigates a two degrees of freedom harmonically excited pendulum system, known in the literature to be a good model for the coupling between the roll and the pitch ship motions. We concentrate mainly on the dangerous situation for the ship where the pitch frequency is almost twice the roll frequency and the excitation period is near the pitch period. In this case, although only the pitch excitation is taken into consideration, part of the energy in the pitch mode is transferred to the roll mode through the non - linear coupling leading to excessive resonant rolling amplitudes and, as a consequence, to ship capsizing. The stability of the system is studied using both frequency response curves and bifurcation diagrams. It was proven that for small external forcing often co-exist two periodic attractors and that the jump phenomena accomplish the transition from one attractor to the other. Periodic oscillations take place with the external frequency for pitch mode and half of the external frequency for roll mode. Mostly, the transient towards the steady state is slowly, stage in which the model behaves chaotically. For moderate and high forcing the system evolves quasiperiodically or chaotically, especially in the neighbourhood of the jump points and for resonant frequencies. The effects of damping on dynamics are also illustrated.

Sensitivity analysis of the hydrodynamic coefficients in 4 degrees of freedom ship manoeuvring mathematical model

The S-type test is simulated based on a ship manoeuvring mathematical model of 4 degrees of freedom (4-DOF); simultaneously, sensitivity analysis of the hydrodynamic coefficients in the mathematical model is implemented by using an indirect method. The mathematical model is simplified by omitting the coefficients of smaller sensitivity according to the results of sensitivity analysis. The 10° /10° zigzag test and 35° turning circle manoeuvre are simulated with the original and the simplified mathematical models. The comparison of the simulation results shows the effectiveness of the sensitivity analysis and the validity of the simplified model.

The Next Rising Tax Haven

The Next Rising Tax Haven

Research on Network Communication Model of Intelligent Ship Handling Simulator

Due to the target ship in the traditional ship handling simulator have not the ability to give way to other ships automatically to avoid collision, this paper put forward a new idea that bringing the hydraulic servo platform, six degrees of freedom ship mathematical model, the actual traffic flow, researching achievement of automatic anti-collision in research of the new pattern ship handling simulator, and successfully develop the Intelligent Ship Handling Simulator(ISHS for short). The paper focuse on the research on the network communication model of ISHS. We took the entire simulator system as three relatively independent networks, proposed a framework of communication network that combined IOCP model based on TCP with blocking model based on UDP, and gave the communication process and protocols of system. Test results indicate that this is an effective way to improve the ownship capacity of ship handling simulator and meet the need of multi-ownship configuration of desktop system of ship handling simulator.

A Six Degrees of Freedom Ship Simulation System for Maritime Education

The title of this paper was changed from 'A Ship Simulation System for Maritime Education' to 'A Six Degrees of Freedom Ship Simulation System for Maritime Education' on 21/09/2012.The authors N Kodikara, C Keppitiyagama and R Rosa were added to the paper on 21/09/2012.This paper presents Six-degrees-of-freedom ship simulation system which allows simulated ship handling under complicated environmental conditions and threat scenarios. This system simulates real-time six degrees of freedom ship motions (pitch, heave, roll, surge, sway, and yaw) under user interactions, and environmental conditions. The simulation system consists of a ship motion prediction system and a perception enhanced immersive virtual environment with greater ecological validity. This ship motion prediction system uses a few model parameters which can be evaluated by using standard ship maneuvering test or determined easily from databases such as Lloyd’s register. This virtual environment supports multiple-display viewing that can greatly enhance user perception. Ecological environment for strong sensation of immersion is also developed. The virtual environment facilitates the incorporation of real world ships, geographical sceneries, different environmental conditions and wide range of visibility and illumination effects. This simulation system can be used to demonstrate ship motions, maneuvering tactics and assign focused missions to trainees and evaluate their performance. Trainees can use the simulation system to study at their own pace. Implementation and operational cost of this ship simulation system is only a fraction of the conventional training involving real ships. DOI: http://dx.doi.org/10.4038/icter.v3i2.2847 The International Journal on Advances in ICT for Emerging Regions 2010 03 (02) :34 - 47

Freedom Stone (review)

Freedom Stone (review)

Appraisal for the Freeboard of ILLC 1966 Based on Estimating the Time Lasting Period of Deck Wetness

This study deals with the influences of probability density distribution of exceeding lasting-time on deck wetness for ocean-going ships. Using the envelope theory for the random functions, a general formula for approximation calculation of density function between zero level is induced and expanded to the problems above a given non-zero level. A supplementary algorithm of estimating the time lasting period for deck wetness is also induced in this paper. Comparing results in the distribution range between the 1st quarter number and 3rd quarter number of probability density, the reliability of the proposed method to estimating the deck wetness for ocean-going ships is also confirmed. Based on wave statistics data, GWS, the deck wetness related to freeboard sea zones of ILLC 1966 is appraised by discussing exceeding lasting-time during which the amplitude of relative motion between deck and wave surface remains above a level of freeboard. A series of numerical calculations are executed for an ocean-going container ship based on the 5 freedom ship motions theory (the Ordinary Strip Method, OSM), and it is certified that the lasting time affects the trend of deck wetness.

Statistical Prediction of Deck Wetness on an Ocean-going Ship

This study presents a new statistical prediction method for deck wetness on ocean-going ships. The deck wetness is one of the most important performance factor of seaworthiness. When the characteristics of deck wetness are investigated in relation to loads on deck due to shipping of water, seakeeping quality etc, the deck wetness generally means the situation in which the relative motion amplitude between deck and wave surface exceeds the freeboard. The excess has two physical natives, that is, the magnitude of the amplitude and the time during which the amplitude remain above a level of freeboard. Until now, many studies have been proposed in relation to the former, but few studies have been done for the later. Therefore, this paper proposes a practical method for estimating statistically the time period (lasting time) related to deck wetness in sea waves. The method is constructed with the basic statistics and the 5 freedom ship motions theory (the Ordinary Strip Method, OSM). A series of numerical calculations are executed for an ocean-going container ship by using the method, and it is certified that the lasting time affects the trend of deck wetness.