A time-domain method for analyzing the ship roll stabilization based on active fin control

The phenomenon of indirectly exciting the roll motion of a vessel due to nonlinear couplings of the heave, pitch and roll modes is investigated theoretically and analytically. Two nonlinear mechanisms that cause large-amplitude rolling motions in a head or following sea are investigated. The first mechanism is internal or autoparametric resonance and the second is parametric resonance. The energy put into the pitch and heave modes by the wave excitations may be transferred into the roll mode by means of nonlinear coupling among these modes; thus, the roll can be indirectly excited. As a result, a ship in a head or following sea can spontaneously develop severe rolling motion. In the analytical approach, the method of multiple scales is used to determine a system of nonlinear first-order equations governing the modulation of the amplitudes and phases of the system. The fixed-point solutions of these equations are determined and their bifurcations are investigated. Hopf bifurcations are found in the case of two-to-one internal resonance. Numerical simulations are used to investigate the bifurcations of the ensuing limit cycles and how they produce chaos. Experiments are conducted with tanker and destroyer models. They demonstrate some of the nonlinear effects, such as the jump phenomenon, the subcritical instability, and the coexistence of multiple solutions. The experimental results are in good qualitative agreement with the results predicted theoretically.

Contemporary Ideas on Ship Stability and Capsizing in Waves

Parametric roll is a phenomenon in which there is a large rolling motion of a ship even when the ship is moving into head seas with no direct excitation. It is a nonlinear dynamic phenomenon of a ship rolling system with nonlinearities in the stiffness as well as the damping terms. Parametric roll of container ships in head seas is a relatively new problem, which has gained lot of importance after the catastrophic incidence of APL China in 1998. Analysis of parametric roll of container ships in regular head waves has been studied extensively. However, the ships do not encounter regular waves in the ocean. So, it is necessary to study how important parametric roll is in irregular seas. To study this, it is first important to model the variation of metacentric height in irregular waves, which is nonlinear as a result of the influence of underwater geometry and the motions of the ship in a seaway. In this work, the change of metacentric height (GM) in irregular waves has been modeled using a Volterra series approach. This transfer function for metacentric height (GM) is used to study parametric rolling of ships in irregular waves. Based on this study, roll motion sensitivity to the spectral peak period and significant wave height has been carried out.

Parametric roll is a phenomenon in which there is a large rolling motion of a ship even when the ship is moving into head seas with no direct excitation. It is a nonlinear dynamic phenomenon of a ship rolling system with nonlinearities in the stiffness as well as the damping terms. Parametric roll of container ships in head seas is a relatively new problem, which has gained lot of importance after the catastrophic incidence of APL China in 1998. Analysis of parametric roll of container ships in regular head waves has been studied extensively. However, the ships do not encounter regular waves in the ocean. So, it is necessary to study how important parametric roll is in irregular seas. To study this, it is first important to model the variation of metacentric height in irregular waves, which is nonlinear as a result of the influence of underwater geometry and the motions of the ship in a seaway. In this work, the change of metacentric height (GM) in irregular waves has been modeled using a Volterra series approach. This transfer function for metacentric height (GM) is used to study parametric rolling of ships in irregular waves. Based on this study, roll motion sensitivity to the spectral peak period and significant wave height has been carried out.

This paper presents an intelligent control of a ship's roll motion damping system consisting of a pair of active fins driven by a hydraulic system. The suggested intelligent controller updates coefficients of the proportional-derivative-second derivative controller (PDD <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) using particle swarm optimization (PSO). The memory-based and the triggered-memory-based PSO algorithms are studied to improve the performance of PSO-PDD <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> algorithm for various sea conditions using simulations. The resulting triggered-memory-based PSO-PDD <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> controller shows a superior total roll motion damping performance. Damping of small roll motions has also been achieved. The PSO-PDD <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> active fin system controller has been implemented for the sample ship, Marti, in a full-scale sea trial in real time. Results of both simulations and real-time trials are presented. Application of PSO has yielded very promising results not only for PDD <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> roll damping controller but also for other possible marine control application.

Prediction of a ship roll added mass moment of inertia using numerical simulation

Real-time control of ship's roll motion with gyrostabilisers

This paper shows a study on anti-rolling tank and its effects on ship roll motion. A flexible passive anti-rolling tank that consists of two fixed reservoirs, a set of three connected ducts and a set of five connected air pipes is designed for carrying out experiments. Experiments were conducted in regular sinusoidal waves of small amplitude and in irregular waves. First step, experiments are conducted in regular waves. Second step, experiments are conducted in irregular waves. For regular wave, experiments were conducted in constant wave heights and constant wave slopes. For irregular wave, experiments were conducted in two idealized wave spectrum. Those spectrum are ITTC (International Towing Tank Conference) idealized spectrum and JONSWAP (Joint North Sea Wave Project) idealized spectrum. After carrying out experiments and analysis, a view of the effects of the designed anti-rolling tank on roll motion of the model ship is shown in this paper. Both theoretical and experimental results show that when the model ship using the anti-rolling tank, the roll stability of the model ship is increased. It is recognized that the highest effects of anti-rolling tank on roll motion of the model ship in experiments with both regular waves and irregular waves are obtained when the model ship is experimented with a wave frequency nearby its natural roll frequency. At this level of the water, the natural frequency of the anti-rolling tank is also nearby the natural roll frequency of the model ship.

During the emergency evacuation on passenger vessels, an individual's walking speed will be affected by the ship's rolling motions. It is necessary and beneficial to evaluate the effect of such motions on individuals' walking speeds in order to facilitate the evacuation and reduce the consequence of a maritime accident. In this study, we collected primary data from a series of walking experiments on-board a real ship to quantitatively evaluate the effect of different ship roll angular magnitudes on an individual's walking speed in two scenarios of flat terrains and staircases, respectively. It was found that on flat terrains, the ship's rolling motion results in the reduction of an individual's walking speed at a rate of 7%–16%. On a staircase, an individual's speed of walking up the staircases was reduced by approximately 5% due to the ship's rolling motion. The findings will contribute to the development of optimal evacuation routes on passenger ships. The used method can also be tailored to model the effect of the other dynamic environments on walking speeds at sea (e.g., on offshore platforms) and onshore (e.g., during earthquakes) to improve evacuation efficiency for disaster prevention.

Numerical study on damaged ship rolling and capsizing in irregular beam waves during quasi-steady flooding

Ship roll motion control is important for vessels engaged in oceanographic research activities and this paper focuses on the design of a controller for fin based roll motion stabilization of a Coastal Research Vessel (CRV). Based on the geometry of a pair of actuator fins installed at the midship of the vessel, the hydrodynamic coefficients are calculated for the vessel including the fin lift capacity. The wave disturbances are simulated as a sine time series. The objective is to design a Linear Quadratic Regulator (LQR), a state feedback controller and obtain the performance of the system. The larger objective is to implement the system eventually in laboratory scale physical simulations in wave environment. This paper primarily presents the design of the control system and evaluation through Simulink in Matlab environment. The global cost function of the system is minimized by precision tuning of the two control parameters (or weighting matrices), Q and R. The system analysis is done using frequency domain and state space approach. The simulation results show that the natural frequency and roll response closely match with the response of the physical model (CRV) in laboratory environment, as observed during the experimental study. The proposed control system is compared with a conventional PID controller. The simulation results demonstrate the effectiveness of the designed roll motion stabilization system with significant roll reduction over the operational range of the vessel.

This paper proposes a predictive control system for balancing an inverted wheeled robot on a ship using both the autoregressive model and a Kalman filter. In general, the control system of inverted wheeled robots is designed on the assumption that the ground does not move. However, a ship has six degrees of freedom. Therefore, a method of predicting the ship's motion was required in order to control the balancing inverted wheeled robot on the ship. This study was focused on the ship's rolling motion. On the ship, the rolling motion was predicted by the autoregressive model and a Kalman filter. Then, the inverted wheeled robot was controlled by adding accelerations to the inverted wheeled robot for canceling out the inertia forces of the predicted rolling motion. The effectiveness of the proposed control system was indicated with experimental results.

In this study, a short-term prediction method for ship roll motion in waves based on convolutional neural network (CNN) is presented. Firstly, based on the ship roll motion equation, the data for free roll attenuation motion in still water, roll motion in regular waves, and roll motion excited by irregular waves are simulated, respectively. Secondly, the simulation data is normalized and preprocessed, and then the time-sliding window technique is applied to construct the training and testing sample sets. Thirdly, the CNN model is trained by learning from the constructed training sample sets, and the well-trained CNN model is applied to predict the roll motion. To validate the CNN model’s prediction accuracy and effectiveness, a comparison between the forecasted results and the simulation data is conducted. Meanwhile, the predicted results are also compared with that of the long-short-term memory (LSTM) neural network. The research results demonstrate that CNN can effectively achieve accurate prediction of ship roll motion in waves, and its prediction accuracy is the same as that of the LSTM neural network.

Controlled passive tank is able to achieve a more perfect stabilizing effect by extending the natural period of water tank with opening/closing the air-valves in accordance with the variation tendency of ship's rolling. Two controlling parameters, which are most important, are the closing-time and closing time span. The determination of closing time span has a direct relation with the ship's real-time rolling period. By adopting wavelet neural network to predict the ship's rolling motion and real-time updating the closing time span of closing valves with the predicted values, meanwhile, real-time analysing the rolling power spectrum is applied before and after anti rolling according to the known input-output relation of anti-rolling tank model coupled with rolling. The paper shows this predictive control method which is more perfect than traditional anti rolling control effect and possess favourably practical value in engineering.

In maritime engineering, ensuring vessel stability remains a paramount concern. This study investigates the hydrodynamic response of Magnus anti-rolling devices, modeled as swinging or slewing rotating cylinders, under a ship's rolling motion. Through numerical simulations using the overset mesh technique and large eddy simulation, we analyze various parameters, including rolling angles, rotating speeds, and swinging amplitudes. Our findings highlight the importance of considering the ship's degree of freedom as substantial ship rolling significantly affects hydrodynamic coefficients on the rotating cylinder. We observe interesting dynamics during slewing motion, with the cylinder forming a spiral tip vortex. Optimizing the cylinder's rotating speed enhances the lift-to-drag ratio, particularly for small rolling angles. Furthermore, the effective lift generated during swinging motion is lower than during slewing motion, emphasizing the need to optimize the swinging amplitude, which is recommended to be no less than 170°. These insights advance our understanding of Magnus anti-rolling devices and offer practical guidance for improving vessel stability in complex maritime environments.