Ship Roll Research Articles

Interval forecasting of photovoltaic power generation on green ship under Multi-factors coupling

Shipboard photovoltaic power generation is affected by various factors, such as meteorological factors, navigation, and ship rolling. Traditional power prediction methods of the land-based grid do not apply to solar ships. Considering the unavoidable Machine Learning algorithm errors and solar energy fluctuations, an interval prediction framework based on a combination of neural network and kernel density estimation methods is proposed. Its generality is demonstrated by comparing different prediction engines. An improved Extreme Learning Machine approach is used to enhance model robustness, considering the computational speed constraints of online prediction. The improved ELM prediction method is at least 5.26% more accurate than the other forecast engines. Considering the sensitivity of the prediction results to the input data, the K-Means clustering is deployed to cluster the historical data to improve the forecast accuracy. The enhanced prediction framework performs well at different confidence levels (85%-98%). Through experimental verification and comparison with diverse state-of-art benchmarks, the effectiveness and stability of the method are proved. At a confidence level of 98%, the prediction interval average width of the proposed method is at least 26.38% smaller relative to other advanced interval prediction methods. It provides the potential to be applied in a ship’s power system.

Reduction of Effect of Waves Disturbance on Ship Roll Motion by Using Robust Nonlinear Control

Reduction of Effect of Waves Disturbance on Ship Roll Motion by Using Robust Nonlinear Control

Fast Prediction for Damaged Ship Roll Motion in Waves by an Aggregation Model based on GA

Fast Prediction for Damaged Ship Roll Motion in Waves by an Aggregation Model based on GA

Identification of recurring patterns and repetitions in time-series, with application to pseudo-stochastic ship rolling

A scheme for capturing repeating portions in time-series is proposed. Such repetitions may be temporal or permanent. The scheme is applied for investigating repetitions in ship roll time simulation data, incurred by the use of discretized wave spectra. The presence of repetitions in the forcing can slant the ship motion response data collected via Monte Carlo simulations unless certain precautions are applied. The conventional check for repetitions in data series is based on the observation of high peaks in the autocorrelation function. However, as the autocorrelation reflects averaged resemblance between sets of successive data separated by a time interval, these peaks may not imply repetition in exact sense. By the proposed computational scheme can be elicited whether any given portion of the time-series reappears. The basic idea is the construction of low-dimensional vectorial representatives of short-time portions of the series and the check for similarity (to a level of tolerance) through application of a Euclidian distance metric to these vectors. The scheme is also useful for locating the end of the transient part in simulated ship roll motion data deriving from repeating pseudo-stochastic excitation.

Noise Signal Modulation at the Ship Rolling and Pitching due to Fluctuating Interference of Beams

Amplitude modulation of a noise signal of the surface ship is formed both directly at noise emission, when the line of the shaft and the propeller is rotating, and in addition due to the ship rolling and pitching caused by the rough sea. At the same time additional low-frequency (no more than 0,2 Hz) amplitude modulation of the noise emission can be observed as a process of temporary variations of the received signal power. In this regard, it is interesting to find relation of the amplitude-phase modulation spectrum of the ship broadband signal at its rolling and pitching with the spectrum of rolling and pitching process. As a mechanism of formation of the noise signal modulation at the ship rolling and pitching the fluctuating interference of the beams, propagating from vertically dipping underwater point source near the water surface, is considered. The analytical ratios connecting the amplitude-phase modulation spectrum of the ship broadband signal at its rolling and pitching with the spectrum of rolling and pitching process are received.As a result, the parameter describing cumulative conditions by which it is possible to determine spectral properties of modulation is determined. The type of the power variation spectrum can be substantially different depending on values of parameter K = 2kσH sinα 1 where k — the wave number, σH-root mean square value of the vertical component (source shift) due to rolling and pitching, α — the beam grazing angle at the surface. At value 2kσHsinα< 1 results of observation of the signal modulation process can be identified with process of the ship rolling and pitching. At value 2kσHsinα> 1 the signal modulation spectrum will not correspond to the spectrum of rolling and pitching process. With the increase of parameter K value the modulation spectrum extends, goes beyond the spectrum of rolling and pitching process. Significantly lower and high harmonics emerge. Results of computer modeling and natural experiments confirmed dependence of the type of the modulation spectrum on parameter K. Thus, presence of the additional mechanism of noise signal modulation formation at the ship rolling and pitching, caused by the phenomenon of fluctuating interference of the beams propagating from vertically dipping underwater point source near the water surface is found.

Ship performance investigation due to deadrise modification: A case study passenger ship

Speed is the main factor that is always considered when designing a ship. Also, a ship designer will try to make a good design regarding the ship's fuel efficiency and seakeeping performance. One example is the operation of passenger ships on the Ketapang - Gilimanuk crossing route in Bali, Indonesia. The Bali strait area has uncertainty waves and ocean currents; the determination of environmental characteristics is needed for an investigation. In this paper, a review is carried out on the primary parameters of ship hydrodynamics performance, i.e., hull changes to reduce ship resistance by modifying the bilge radius from angles of 10°, 15°, and 20°. This modification affects the geometric parameters. Two indicators are used to measure the effect of changes: resistance and seakeeping performance. Numerical methods were used to obtain the results, the calculation of the resistance was approached by the Holtrop process of investigation, and the NORDFORSK criteria validated the feasibility seakeeping assessment. The results of model Z show that when the deadrise angle is large, the ship reduces the resistance by approximately 8.2% at a service speed of 12 knots. Therefore, modification of the hull by raising the radius of the bilge results in a reduction in resistance, which affects the ship's rolling, but with an increase in speed, it can reduce the heave and pitch significantly with the resulting hull with good performance obtained.

Roll dynamic coefficients approach of decay test using the Generalized Reduced Gradient method (GRG)

Sea transportation is the vehicle which dominant and vital in the world. The increasing number of ships, types, and uncertain climate change have caused many ship accidents that have caused loss of life and property. The International Maritime Organization (IMO) issued the latest regulation on the second generation of ship stability criteria based on the dynamic of ship roll motions. The survival of dynamic stability depends on the hydrodynamic coefficients, which numerical and experimental calculations can obtain. The problem is finding the hydrodynamic coefficients of the ship roll quickly and accurately from the experimental roll decay data. This paper uses the Generalized Reduced Gradient (GRG) optimization to find the roll motion coefficient with the objective function of a standard deviation. The results show that the roll decay experiment graph is close optimization for variations of the minimum standard deviation used: all data, maximum-minimum amplitude, maximum amplitude, and minimum amplitude. The most similar chart to the experiment is optimization using a standard deviation of maximum-minimum amplitude with the optimal objective function o = 1.006776 closest o=1; obtained variable x 1 = k4 4 =0.1087688 m; x 2 = B4 4 =3.00306E-05 m-ton-sec. Based on sensitivity tests for various scenarios, optimization with a standard deviation of maximum amplitude has a high sensitivity, so it is necessary to avoid or be careful in its use. Generally, the GRG optimization method has the advantage of finding the hydrodynamic roll coefficient quickly and accurately.

"CONTROL OF SHIP FIN STABILIZERS BY A PID CONTROLLER: A NUMERICAL ANALYSIS "

The reduction of ship roll motion is important in order to prevent damage to cargo, to allow the crew to work efficiently and to provide comfort for the passengers. There are passive devices like bilge keels or anti – roll tanks and active devices like gyrostabilizer and stabilizing fins which are commonly used to generate an opposed moment to the wave and wind excitation roll moments in response to the command of a control system. The paper presents numerical results of using a Proportional - Integral – Derivative (PID) controller for damping the roll motion of a fishing boat equipped with a fin stabilizer system and sailing in regular waves. The nonlinear roll equation, which includes B1 type damping and quantic restoring, besides the wave excitation moment and moment generated by fins, was linearized for relative small roll angles. The role of PID controller was to generate the corrective roll moment through the controlled fins in order to stabilize the roll motion. The thresholds for the controller’s gains were determined using the Laplace transform and Routh – Hurwitz criterion. A simple but precise iterative scheme was used for the rapid integration of the system equations of motion in three cases: only proportional (P) component, proportional and derivative (PD) components and full PID controller. The numerical simulations have showed that all the analysed variants achieved roll reduction satisfactorily.

DEFINING PARAMETERS OF EQUILIBRIUM STRANDING OF A SHIP USING SIMULATION MODELLING

Equilibrium stranding of a ship is a necessary preliminary step for application of other decision support system algorithms, such as identification of a flooded compartment, predicting an emergency vessel capsize probability, and others. The equilibrium stranding using a real ship as an example based on the heel angle sensors readings for rolling and pitching, and the water column pressure sensors readings for the vertical roll, is calculated. In the linear case, the mean value of an individual value coincides with the equilibrium position on the corresponding coordinate axis. However, a ship rolling in a sea is, as a rule, non-linear process, and hence the mathematical average correction is required. The use of the Nechaev’s method for determining the equilibrium position of a floating vessel in a heavy sea is illustrated in the paper. An algorithm based on simulation modeling in the Virtual Testbed software package is proposed. It has been proved that complication of wave model used for coefficients obtaining in Y. I. Nechaev’s algorithm changes obtained equilibrium parameter value insignificantly, but in this case time spent for generation of one simulation is increased significantly enough. When using linear waves or Stokes waves, the generation of two minutes of simulation is faster than two minutes of real time; when using Gerstner waves, the simulation time approaching three minutes of real time, which already exceeds the simulation time. In this case, when using the Stokes waves model, it is possible to achieve the results closer to the Gerstner model than when using the linear waves model without consuming additional time. This fact allows us to conclude about the optimal use of the algorithm.

Investigation on time-domain simulation and experiment of harmonic rolling of ultra-large container ship in waves

When an accident due to harmonic rolling occurs, loss will be huge, especially for ultra-large container ships (ULCS). In the paper, the time-domain method is adopted to study and analyze the occurrence of non-linear harmonic rolling phenomenon of ULCS and subsequent motion behaviors. Under the weakly scattering hypothesis, six-degree-of freedom(6-DOF) time-domain ship motion equation is established by employing impulse response function. The incidental wave force and the restoring force are obtained by pressure integrating on instantaneous wet surface, while the roll damping coefficient is obtained by experiment. An ULCS navigating in regular waves of various frequencies is numerically simulated and investigated by model tests. The characteristics and mechanism of harmonic rolling of the ship with different metacenter-heights, which sails in head and following waves of different periods, are studied and analyzed. The result comparison shows that the time-domain method used in the paper can predict the occurrence and motion amplitude of the harmonic rolling very well. Although the seaworthiness of ULCS is generally better than smaller ships, there is still the possibility of triggering the problem of harmonic rolling in real sea navigation. Thus, it is necessary to study and analyze during ship design.

Deterministic ship roll forecasting model based on multi-objective data fusion and multi-layer error correction

With the increasing frequency of international shipping and marine resources development activities, ship motion prediction plays an increasingly important role in ensuring the safety of offshore operations. However, in the field of ship motion prediction, the deep feature information of raw high-resolution ship motion data, as well as the predictable components in the initial prediction residuals is usually neglected. In this paper, a deterministic ship roll forecasting model based on multi-objective data fusion and multi-layer error correction is proposed. The proposed model consists of three stages, which are data pre-processing stage, multi-objective data fusion forecasting stage, and multi-layer error correction stage. To verify the stability and validity of the proposed model, an experimental study was conducted using three sets of measured ship roll motion data collected in the South China Sea from 2018 to 2020. Taking the 1-step, 5-step, and 10-step predictions of dataset #1 as an example, the RMSE values of the proposed model are 0.0130°, 0.0612°, and 0.0791°, respectively. Through three analytical experiments and four comparison experiments, it is proved that the proposed model is able to obtain accurate deterministic point forecasts, which can better assist the sailor in decision making.

Efficient computation of temporal exceeding probability of ship responses in a random wave field

In this work, we develop a computational framework to efficiently quantify the temporal exceeding probability of ship responses in a random wave field generated by a narrow-band spectrum, i.e., the fraction of time that ship responses exceed a given threshold. In particular, we consider large thresholds so that the response exceedance needs to be treated as rare events. Our computational framework builds on the parameterization of wave field into wave groups and efficient sampling in the group parameter space through Bayesian experimental design (BED). Previous works following this framework exclusively studied extreme statistics of group-maximum response, i.e., the maximum response within a wave group, which is however not straightforward to interpret in practice (e.g., its value depends on the subjective definition of the wave group). In order to adapt the framework to the more robust measure by the temporal exceeding probability, novel developments need to be introduced to the two components of BED (on surrogate model and acquisition function), which are detailed in the paper. We validate our framework for a case of ship roll motion (without capsizing) calculated by a nonlinear roll equation, in terms of the agreement of our results to the true solution and the independence of our results to the criterion of defining groups. Finally, we demonstrate the coupling of the framework with CFD models to handle more realistic and general ship response problems.

D[formula omitted]-Net: Integrated multi-task convolutional neural network for water surface deblurring, dehazing and object detection

Visual perception is one of the key technologies for smart ships to achieve intelligent navigation in various complex water scenes, which adopts the object detection algorithm based on visible image to detect obstacles. Affected by the rolling and high-speed motion of ships and bad weather, motion blur and haze appear in the images of vision sensor, which seriously interfere with the obstacle detection. To ensure the navigation safety of smart ships, we propose the integrated multi-task deblurring, dehazing and object detection convolutional neural network (D3-Net). Firstly, the proposed method is able to complete deblurring, dehazing and object detection within a single network, which is more suitable to be applied in intelligent navigation. Secondly, different from traditional methods that reconstruct enhanced images first and then perform object detection, D3-Net combines image reconstruction and detection feature extraction to realize the integration of image enhancement and detection procedure. Finally, to improve the deblurring and dehazing performance of the network, we propose classification attention-based detection feature loss (CADF-Loss), which uses the image classification features to guide the network perform the detection feature enhancement more specifically. The experimental results in real navigation scenes show that D3-Net not only improves the detection accuracy of blurred and hazy images by 42%, but also has excellent detection efficiency, which is helpful to improve the navigation safety performance of smart ships.

A New Theoretical Dynamic Analysis of Ship Rolling Motion Considering Navigational Parameters, Loading Conditions and Sea State Conditions

Despite the IMO’s efforts and the large quantity of research carried out over the years concerning the sudden loss of stability in fishing vessels, and even the damage done to merchant fleets due to cargo shifting, accidents with very relevant consequences continue to occur. This paper can be considered as a continuation of the recent research of authors which was carried out with ships in static conditions, with pure beam seas and without resistance. The aim of the present research is to provide a reference for ships’ operators to improve the ship’s behavior and seakeeping, to alter the ship’s loading conditions or the navigational parameters (heading and speed), and even be aware of the time available to carry out these modifications before reaching dangerous situations. For this, all sea state conditions were mathematically modelled for, including the ship’s rolling motion both in static and in realistic and dynamic conditions, with the waves influencing the vessel by coming from any direction. Relevant results of easy comprehension for ships’ operators are shown in each of the models, which were validated with a representative real case study.

A scheme for capturing the kinetic energy of the flow liquid in a ship's cabin

The study proposes a solution for the energy capture of a sailing liquid cargo ship, which is essentially an organic combination of an Savonius turbine and a ship's rolling cabin. A model of the cabin turbine was simulated in ANSYS FLUENT from the perspective of the ship's roll and the rotor's rotational motion. Specifically, three cabin with opening lengths of 0.5, 1.0 and 1.5m were simulated to illustrate the sinusoidal trend of the axial velocity curves of the liquid at the cabin's opening position where the turbine is installed; When the burden of ship increases, the velocity at the opening decreases; when the burden is 90% and the ship's rolling angle is 20°, the peak axial velocity can reach 2.2 m/s, the average kinetic energy reaches 2.2 kJ and the flow rate reaches 1.38 m3/s. Then, the maximum values of the turbine's power coefficients are 0.21, 0.25 and 0.33 respectively, and their corresponding tip-speed rates are 1.0, 1.4 and 1.0. The torque coefficients decrease as the tip-speed rate increases. The velocity and pressure in the vicinity of the turbine present the non-stationary gradient images. Finally, the prediction of the power of turbine is discussed.

Stochastic bifurcation and chaos analysis for a class of ships rolling motion under non-smooth perturbation and random excitation

The actions of wind and wave have a great influence on the ship rolling motion, which may cause chaotic situation even capsizing. Stochastic bifurcation and chaos for a class of ships rolling motion in longitudinal waves under non-smooth perturbation and random excitation, i.e., the effects of wind and wave, is studied by analytical and numerical methods. The stationary probability density function (SPDF) for rolling motion is obtained through the stochastic averaging method as well as stochastic phenomenological (P) bifurcation is analysed by the qualitative change of it. The parameter conditions for chaos are strictly derived through Melnikov method and random Melnikov method, respectively. Chaotic regions and characteristics of systems parameters are illustrated and discussed in detail. In addition, taking the maritime patrol ship as an example, the analytical results as well as the effects of parameter excitation and noise on chaos are verified and analysed by relevant numerical simulations. These results demonstrate that changing parameter excitation amplitude or noise intensity can induce or suppress chaos.

Theoretical manual of ‘YTU DEEP’ SHIP motion program

The theoretical background for an in-house seakeeping code ‘YTU DEEP’ that calculates heave, roll and pitch motions of displacement ships is established in this paper. The code consists of two main parts: frequency and time-domain calculations. Two-dimensional added mass and damping coefficients are calculated by using Ursell's multipole expansion theory. Lewis conformal mapping technique is used together with Tasai's method to compute the sectional hydrodynamic coefficients. The strip theory of Salvesen et al. is used to obtain the global hydrodynamic coefficients. The damping values for the roll motion are calculated by using Ikeda's method. Excitation terms for pitch and heave motions are computed by using head seas approximation. The excitation term for roll motion is predicted by using low steepness waves approximation. For frequency domain code validation, Response Amplitude Operators for the AME CRC hulls motions are plotted at different forward speeds and in head waves. The results are compared with the experimental results and a good agreement is observed. For time-domain calculations, Cummins' method is utilized which used the sectional hydrodynamic coefficients in the frequency domain. The coupled pitch & heave and uncoupled roll motion equations are solved via the 4th order Runge Kutta Method. The solution of Cummins equations is tested for a container and passenger ship form simulation in bow quartering waves. A user-friendly interface is created for performing both frequency and time-domain simulations. Pre-processing, solution, and post-processing are applied with a MATLAB code. The proposed seakeeping code aims to create a quick and efficient ship motion program.

An alternative methodology for the simplified operational guidance in the framework of second generation intact stability criteria

Within the framework of the second-generation intact stability criteria (SGISc), a procedure to provide simplified operational guidance (OG) has been proposed. In particular, the phenomenon of parametric rolling has been investigated. The proposed methodology is meant to be an intermediate level between the suggested simplified OG and the deterministic OG, as defined in the MSC.1/Circ.1627. The proposed guidance relies on a simplified numerical tool able to assess ship roll motion due to non-linear irregular wave effects in the time domain. Outcomes are elaborated in the post-process phase, taking the maximum roll angle as leading criterion. Once defined the structure of this tool, an application has been carried out to a representative model of post-panamax container vessel. As benchmark study, the results have been compared to those obtained by the application of MSC.1/Circ.1228 and MSC.1/Circ.1627 (simplified OG) by means of polar diagram representation. Outcomes have been discussed and a general agreement can be found between the simplified OG and the proposed one. Although, it appears that the latter can detect dangerous roll motion for a more comprehensive set of sailing condition.

A wavelet approximation method for solving nonlinear ship roll damping equations: An operational matrix of derivative approach

The effect of roll damping on ship dynamics is more significant. Here, an efficient Lucas wavelet method is applied to estimate the parameters of ship roll motion models. For the first time, a learning model was approached for forecasting over ship roll angle with damping and restoring moments where the results are obtained from Lucas wavelet method. A barge-like vessel fitted with two spherical tank models and FPSO tank model equations with different damping and restoring coefficients are investigated to estimate the validity and applicability of the proposed LWM for different loading conditions. With the help of operational matrices of derivatives, the nonlinear differential equations are converted into a system of algebraic equations using an appropriate collocation point. The proposed wavelet approximation results are compared with experimental data, frozen cargo, Runge-Kutta method of 4th order (RKM) and Homotopy Perturbation Method (HPM) results. Moreover, numerical experiments are provided to show that the proposed wavelet method is an effective and convenient method for solving nonlinear differential equations in ship dynamics.

Study of the Influence of Nonlinear Moments upon Intensity of Parametric Roll

Hydrodynamical analysis of the conditions for the occurrence of chaotic ship roll, leading in some cases to the capsizing of the vessel, showed that such conditions are most likely to occur in the zone of the main parametric resonance of the roll when its period is sequentially doubled, and subharmonic oscillations turn into chaotic ones. This circumstance necessitates special attention to the regime of parametric roll resonance, issues of its occurrence, development, and establishment as well as to the methods of calculation of its amplitudes. In the present paper, the study of the parametric ship roll is conducted on the basis of the Lugovsky formula. An account is taken of the additional nonlinear moments M¯X23 and M¯X24, obtained through the application of the small parameter method. Presented are the calculation results for the parametric roll of five different ships performing motions at various course angles both with and without account of the aforementioned nonlinear moments. Demonstrated therewith is a significant influence of the nonlinear moments upon the maximum amplitudes of the parametric roll, especially in the case of beam waves.