Ship Roll Research Articles

Stochastic dynamic analysis of rolling ship in random wave condition by using finite element method

Nonlinear stochastic rolling is a primary contributor to ship instability. Random wave excitation is described in this study as a combination of harmonic excitation and Gaussian white noise excitation, and the nonlinear rolling of a ship subjected to this composited excitation is investigated using stochastic vibration methodology and a numerical analysis approach. The Fokker-Planck (FP) equation for nonlinear stochastic ship rolling is derived, and the associated transient probability density function (PDF) is numerically solved by applying the finite element method (FEM) and Crank-Nicolson method, and the findings are manifested to be consistent with the Monte Carlo simulation (MCS). This proves the applicability and effectiveness of the FEM in the numerical study of the nonlinear stochastic ship rolling. Then the effects of harmonic excitation amplitude and stochastic excitation intensity in stable and unstable regions on nonlinear ship rolling are investigated, which provide essential references for ship stability and capsizing research.

Ship motion-sloshing interaction with forward speed in oblique waves

Seakeeping properties of large LNG carriers with partially filled tanks are known to be influenced by sloshing inside their tanks, by wave conditions and wave heading, and by their forward speed. An efficient hybrid numerical method was developed to study wave-induced ship response coupled with sloshing-induced compressible fluid response inside the tanks of a 138,000 m3 LNG carrier at zero forward speed and at the constant forward speeds of 12 and 20 kn. Wave conditions considered were oblique regular waves at heading angles of 0, 30, 60, 90, 120, 150, and 180 deg. The numerical approach combined a nonlinear boundary element Rankine source code to solve the weakly nonlinear seakeeping problem with a Reynolds-averaged Navier-Stokes equations solver to compute the compressible sloshing flow inside the tanks. Coupling effects of the six degrees-of-freedom ship motions in beam waves were validated against comparable model test measurements of ship responses and against free surface elevations in tanks. Results demonstrated that sloshing affected the simulated seakeeping behavior of the subject LNG carrier advancing at forward speeds in oblique waves. As sloshing had the greatest influence on the ship's roll motions, a key aspect was the derivation of roll damping from model decay tests.

Ship Roll Analysis Using CFD-Derived Roll Damping: Numerical and Experimental Study

Ship Roll Analysis Using CFD-Derived Roll Damping: Numerical and Experimental Study

Assessment of Excessive Acceleration of the IMO Second Generation Intact Stability Criteria for the Tanker

Recently, the IMO (International Maritime Organization) has reviewed technical issues considering the second generation intact stability criteria in the design stage of ships. In this paper, the evaluation procedure for Lv1 (Level 1) and Lv2 (Level 2) was introduced by focusing on the excessive acceleration mode. Based on real ship data, the calculation process has been explained in detail to make it easy to understand. When the Lv1 criteria considering simple hydrostatic calculations are not satisfied, the computational results of the Lv2 criteria based on mathematical modeling and the hydrodynamics are presented. The relatively low ship roll periods and large changes in the hull shape in the vertical direction make the ships potentially vulnerable to excessive acceleration phenomena. Therefore, the minimum value of height KG that satisfies the stability criteria evaluation in consideration of loading conditions for actually navigating of the ship in the sea should be estimated and operated. In particular, roll damping coefficients using the Ikeda’s method, which are essential for Lv2 vulnerability calculation, were obtained and verified by comparing them with other ship results.

Study of Rolling Motion of Ships in Random Beam Seas with Nonlinear Restoring Moment and Damping Effects Using Neuroevolutionary Technique.

In this paper, a mathematical model for the rolling motion of ships in random beam seas has been investigated. The ships’ steady-state rolling motion with a nonlinear restoring moment and damping effect is modeled by the nonlinear second-order differential equation. Furthermore, an artificial neural network (NN)-based, backpropagated Levenberg-Marquardt (LM) algorithm is utilized to interpret a numerical solution for the roll angle , velocity , and acceleration of the ship in random beam seas. A reference data set based on numerical examples of the mathematical model for a rolling ship for the LM-NN algorithm is generated by the numerical solver Runge–Kutta method of order 4 (RK-4). The LM-NN algorithm further uses the created data set for the validation, testing, and training of approximate solutions. The outcomes of the design paradigm are compared with those of the homotopy perturbation method (HPM), optimal homotopy analysis method (OHAM), and RK-4. Statistical analyses of the mean square error (MSE), regression, error histograms, proportional performance, and computational complexity further validate the worth of the LM-NN algorithm.

Anti-Roll Characteristics of Marine Gyrostabilizer Based on Adaptive Control and Hydrodynamic Simulation

The gyrostabilizer produces the anti-roll effect through the precession output moment generated by a high-speed rotating flywheel. As a floating-base multi-body system composed of ship and gyrostabilizer, the recent research that has only focused on the control strategies or multi-body dynamics is obviously not comprehensive. This study presents an adaptive controller based on the variable gain control strategy for a marine gyrostabilizer installed on a port salvage tug. The variable gain control strategy controlled the flywheel precession output moment of the gyrostabilizer and thereby of the precession process, to reduce the ship roll motion effectively. Furthermore, a full-system hydrodynamic model of a gyrostabilizer-ship-wave based on three-dimensional numerical wave flume technology was innovatively established to evaluate its anti-roll performance under irregular wave conditions. The simulation results show that, for the sea state considered, the increase of spin rate of gyrostabilizer flywheel improved the anti-roll effect significantly. The average anti-roll rate of the gyrostabilizer decreased with the increase of significant wave height, wave period and wave encounter angle.

Parametric Identification for the Biased Ship Roll Motion Model Using Genocchi Polynomials

Roll motion is one of the key motions related to a vessel’s dynamic stability. It is essential for the dynamic stability of ships in the realistic sea. For this research study, we have investigated the parameters involved in damping of the ship. In general, mathematical modelling of the rolling response of a ship can be formulated by the linear, nonlinear, and fractional differential equations because the amplitude of oscillation is increased. An efficient Genocchi polynomial approximation method (GPAM) is successfully applied for the biased ship roll motion model. The basic idea of the collocation method together with the operational matrices of derivatives used for nonlinear differential equation and convert it into a system of algebraic equations. The convergence and error analysis of the proposed method are also discussed. A few numerical experiments are carried out for some specific and important types of problems including the biased roll motion equations. The results are compared to those produced using the Legendre wavelet method (LWM) and the homotopy perturbation method (HPM). It is observed that the proposed spectral algorithm is robust, accurate, and easy to apply.

Fin-Rudder Joint Control Based on Improved Linear-Quadratic-Regulator Algorithm

Navigation accidents and disasters frequently occur when ships sail at sea due to extreme weather, wind, and wave conditions. The disturbance of wind and waves affects the stability of the ship’s course and makes the ship roll violently. Ships are usually equipped with an autopilot to control the course and a fin stabilizer to reduce rolling during navigation and improve stability and safety. Fin-rudder joint control system considers the coupling effect of the ship’s horizontal plane motion, thereby improving the performance of the rudder and the fin stabilizer. This paper presents an improved linear-quadratic-regulator control algorithm. A rate control law with no static error is proposed based on the traditional linear-quadratic regulator to eliminate the static error of the state vector and achieve a better control effect. Additionally, a closed-loop state observer is used to estimate the system’s state vector, and a dynamic corrector is designed to reduce rolling and heading angle deviation caused by sea wave interference. The simulation results show that the designed fin-rudder joint controller with the improved linear-quadratic regulator algorithm can achieve more than 80% roll reduction effect at level 3 and 5 sea states, and has better course keeping ability compared with the rudder control.

Location Analysis Of Patrol Boat Fin Stabilizer Based On Numerical Method

The fin stabilizer is located on the hull of the ship, one left and one right, which is connected to the fin stabilizer control room as a tool to respond to excessive ship rolling in both directions. In this study, we will analyze the ship resistance due to the addition of a fin stabilizer type Naca 0013 on patrol boats with variations in angles of 0°, 5°, 10°, 15° with speed variations of 25 - 30 knots. Calculation of ship resistance using Maxsurf modeler software and Numeca fine marine. In the early stages of validating the model that has been tested on a towing tank with a patrol boat design made using the Maxsurf modeler and Numeca fine marine. Validation results with a maximum error of 2.38% maxsurf software and 2% Numeca software. There was an increase in resistance due to the fin being installed at an angle of 0° by 0.56% - 1.22%, at an angle of 5° by 2.26% - 3.75%, at an angle of 10° by 6.48% - 9.49%, at an angle of 15° by 13.92% - 18.79 % of the total drag of the ship.

An Ensemble Multi-Step Forecasting Model for Ship Roll Motion Under Different External Conditions: A Case Study on the South China Sea

An Ensemble Multi-Step Forecasting Model for Ship Roll Motion Under Different External Conditions: A Case Study on the South China Sea

Control of Ship Roll and Yaw Angles During Turning Motion

The aim of this paper is Ships are exposed to assorted hydrodynamic forces originating from internal and external influences. The adverse effect of rolling caused by turning motion should be reduced with anti-rolling systems, to ensure safe navigation. If this effect is not eliminated, it may prevent the ship from keeping its course safely. In this study, fin stabilizer system the computational analysis of the roll motion formed by the turning motion and wave effect is included in fin stabilizer system. The rudder motion that allows the ship to have the desired maneuvering angle; calculations of the fin system, which decreases the excessive roll moment, and the roll motion caused by these two effects are examined using MATLAB software. The analysis period has been determined as 300 seconds, which is the time to reach the desired turning angle of the ship. Linear quadratic tracking (LQT) algorithm has been used to solve partially unknown continuous-time problems such as roll motion in this study.

Analysis and Modelling of Ship Manoeuvring Simulation in Landslide-Generated Waves

The geological conditions of the Three Gorges Reservoir Region are complex and changing, and large- and medium-sized landslides are widely distributed. When a high-speed moving landslide enters the water, the water is significantly disturbed, and a landslide-generated wave will be formed, which will spread along the upstream and downstream of the river, causing significant threats and destruction to the hydraulic structures and the navigation of ships. Based on the typical rock landslide parameters and fracture development, we establish a three-dimensional physics experimental model of the bending section of the landslide-generated wave in the Three Gorges Reservoir Region. This paper primarily studies the variation law of the first wave height of landslide-generated waves with the width, height, and water entry velocity of the landslide body and then provides an empirical formula for the first wave height of landslide-generated waves in the curved section of the Three Gorges Reservoir Region. The ship rolling motion equation in the landslide-generated water area is analysed and established systematically. Additionally, the ship manoeuvring motion model in the landslide-generated water area is built. This paper explains the variation characteristics of ship turning tracks at different sailing speeds and sailing positions and proposes a basis to determine the navigation safety of ships in this area, thus providing new theoretical and technical support for the risk assessment of navigation of ships in the reservoir area.

Nonlinear vibration analysis of the large-amplitude asymmetric response of ship roll motion

Ship roll motion is the single most important factor responsible for ship capsizes. Yet, there is still much to be understood about this subject; especially, how critical parameters influence the asymmetric response during large initial roll amplitudes. Consequently, this paper presents an investigation of the nonlinear vibration of the large-amplitude asymmetric response during ship roll motion. The dynamic model governing the roll motion accounted for quadratic damping and cubic nonlinear restoring moment with softening behaviour. The continuous piecewise linearization method was adopted to solve the governing model. Hence, the effect of four critical parameters (i.e. initial roll amplitude, added mass, quadratic damping and nonlinear restoring moment) on the asymmetric roll response and capsize tendency was investigated. It was observed that capsize tendency was strongly linked to the offset of the equilibrium point and the asymmetric response, which amplified the initial roll amplitude. An increase in the initial roll amplitude or quadratic damping produced a stronger asymmetric response and an increased capsize tendency, while an increase in the added mass or nonlinear restoring moment weakened the asymmetric response and decreased the capsize tendency. Also, an increase in any of the four critical parameters produced a decrease in the frequency of vibration.

A BiLSTM hybrid model for ship roll multi-step forecasting based on decomposition and hyperparameter optimization

The forecasting of ship's roll motion is the key to ensuring the safety of ship surface operations and improving operations efficiency. A new hybrid multi-step forecasting model is proposed in this paper. The proposed model combines three methodologies, including adaptive empirical wavelet transform (EWT), multi-step forecasting under the multi-input multi-output (MIMO) strategy of bidirectional long short-term memory (BiLSTM) model, and hybrid particle swarm optimization and gravitational search algorithm (PSOGSA) hyperparameter optimization. The three sets of ship roll datasets in the South China Sea are selected to verify the performance of the hybrid multi-step prediction model. In the end, the results of the research indicate that: (a) The proposed model has a superior prediction accuracy in multi-step prediction, taking dataset #1 as an example, the root mean square error (RMSE) of the prediction result is 0.0934°, the mean average error (MAE) is 0.0742°, and the mean absolute percentage error (MAPE) is 2.9878%; (b) The proposed hybrid multi-step forecasting model is suitable for different datasets and has strong robustness. Taking the 3-step prediction of dataset #1 to #3 as examples, the RMSEs of the proposed model are 0.0879°, 0.0742°, and 0.0991°, respectively.

Nonlinear dynamics of marine rotor-bearing system coupled with vibration isolation structure subject to ship rolling motion

This study focuses on the nonlinear dynamic behavior of a marine rotor-bearing system coupled with vibration isolation structure under ship rolling motion. After considering the effect of the nonlinear oil film force and the ship rolling motion, a mathematical model is established based on Lagrange's equation. By employing a numerical method, the dynamic steady-state response of the system is analyzed, such as the orbits of the rotor and its Poincaré maps, spectrum waterfall diagram, and the displacements and frequency spectrum diagram of the raft frame. We also studied the effects of the rotor speed, the amplitude and frequency of ship rolling on the marine rotor-bearing system coupled with isolation structure under ship rolling motion. The results indicates that response of the rotor shows obvious nonlinear dynamic behaviors such as amplitude jumping, bifurcation and chaos due to the influence of the nonlinear oil film force and the ship rolling motion. As the rotor speed increases, the motion of the rotor experiences the process of quasi-periodic and chaos vibration. Both the amplitude and frequency of ship rolling have effects on the amplitude of the rotor and the raft frame. Moreover, the rotation angle of the raft frame is greatly influenced by the amplitude and frequency of ship rolling, and it is necessary to control the vibration attitude of the raft frame.

Short-term ship motion attitude prediction based on LSTM and GPR

The random motions of a ship due to the sea waves directly affects the safety and efficiency of marine operations. Accurate short-term ship attitude prediction plays a vital role in operational decision-making in future seconds. In this paper, a new hybrid prediction model of ship motion attitude is proposed based on Long Short-Term Memory (LSTM) neural network and Gaussian Process Regression (GPR). When dealing with nonlinear regression problems, LSTM model can get high-accuracy point prediction results, while GPR model with lower prediction accuracy can obtain interval prediction results with probability distribution significance. The LSTM-GPR model successfully combines the advantages of LSTM and GPR, and can obtain high-accuracy point prediction results and reliable interval prediction results at the same time. The prediction experiments of ship rolling angle and pitch angle are carried out under both motion and static conditions. The results show that the LSTM-GPR hybrid model can obtain reliable interval prediction results without reducing the forecasting accuracy of LSTM model, which verifies the effectiveness and advancement of the hybrid model.

Multi-dimensional prediction method based on Bi-LSTMC for ship roll

When ships sail in the sea, they will move irregularly due to the influence of strong wind, waves and other complex marine environment. Among them, the ship roll is very important to the safety of ship navigation. In order to ensure navigation safety, it is necessary to predict the ship roll effectively and accurately in advance to provide a basis for ship advance control. Aiming at the problem that traditional methods and machine learning methods are not accurate for ship roll prediction, a single input single output (SISO) and multiple input single output (MISO) ship roll prediction methods based on deep learning are proposed, and the influence of input variables on the ship roll prediction model is studied. Firstly, a single input Bi-LSTMC ship roll prediction method is proposed. The network takes the advantage of LSTM time series prediction and combines convolution kernel to extract cross time features. Then the analysis and test results of six different single input prediction models are given based on real ship data. Secondly, a deep bidirectional feature network with multiple inputs of ship roll angle, roll angular velocity, relative wind speed, relative wind direction, turning angle and rudder angle is proposed for ship roll prediction. The network uses Bi-LSTM to extract forward and reverse information respectively, and introduces two Bi-LSTMC branch structures to explore the deep features between multiple input data to improve the accuracy of ship roll prediction. Finally, four error indexes were used to evaluate the proposed single input and multiple input ship roll prediction algorithms on real ship data. The applicable conditions of the single input and multiple input ship roll prediction algorithms are obtained, and the effectiveness of the proposed algorithms are also verified.

Modeling and Simulation of Ship-Borne Weapon Stabilization System Based On Double Position Loop Control

In order to solve the problem of increasing system cost and low control accuracy by adding gyroscope or inertial navigation system, a dual position loop control ship-borne stabilization system is proposed in the paper. The mathematical model is established to analyze the influence of ship rolling factors on the space pointing of single position loop weapon system. On this basis, the control strategy of double position loop is proposed, and the simulation structure and control method of inner position loop and double position loop are described respectively. The simulation results show that the method can isolate the factors of ship rolling, realize the closed-loop stabilization control of weapon system in geodetic coordinate without adding system hardware cost, and have good control effect as well.

Determination of ship roll damping coefficients by a differential evolution algorithm

The execution of the so-called extinction tests represents the classical experimental method used to estimate the damping of an oscillatory system. For the specific case of ship roll motion, the roll decay tests are carried out at model-scale in a hydrodynamic basin. During these tests, the vessel is posed in an imbalance condition by an external moment and, after the release, the motion decays to the equilibrium condition. When the damping is far below the critical one, the transient decay is oscillatory. Here a new methodology is presented to determine the damping coefficients by fitting the roll decay curves directly, using a least-square fitting through a differential evolution algorithm of global optimisation. The results obtained with this methodology are compared with the predictions from standard methods. This kind of approach seems to be very promising when the motion model of the system under investigation is established with any level of non-linearities included. The usage of the fitting procedure on the approximate analytic solution of the differential equation of motion demonstrates the flexibility of the method. As a benchmark example, two experimentally measured roll extinction curves have been considered and suitably fitted. The newly predicted results, compared with the ones obtained from standard roll decay analysis, show that the algorithm is capable to perform a good regression on the experimental data.

Nonlinear vibration suppression control of underactuated shipboard rotary cranes with spherical pendulum and persistent ship roll disturbances

Shipboard rotary cranes are widespread used in industrial fields to carry out large-scale cargoes under marine environment, which are a class of representative nonlinear systems. For crane systems, there exist unactuated state variables (e.g., payload swing angles), which hence make them typically underactuated systems, whose degrees of freedom (DOFs) are more than the number of control inputs. Besides, due to the complexity disturbances of the marine environment, there are always inaccuracies in the three-dimensional (3D) dynamics model of shipboard rotary cranes, such as ocean waves, wind waves, ocean currents and so on, which make the control methods hard to achieve the perfect control effect. Most of the existing methods are built on the basis of simplified linear model, which often require precise model parameters or velocity signals. In order to solve the control problems caused by the above uncertainties, this paper proposes two nonlinear anti-swing control methods. First, considering the uncertain parameters, an adaptive controller is designed, which can achieve the control effect of suppressing swing when the model has unknown parameters. Second, considering the unmeasurable velocity signals, an output feedback controller is designed, which can achieve the control effect to suppress the swing angle with no need of velocity signals. On the basis of the above two control methods, we design corresponding different energy storage functions including kinetic energy and potential energy, respectively. Specifically, this paper has achieved an excellent effect of restraining swing without any linear approximation of the dynamic model. Lyapunov theorem and LaSalle invariance principle are utilized to further prove the asymptotic stability of the closed-loop system. Finally, experiments are implemented to further demonstrate the effectiveness of the proposed control methods.