Ship Motion Response Research Articles

Numerical Study on the Influence of Interceptor and Stern Flap on Ship Resistance and Motion Response in Regular Waves

Stern flaps and interceptors are prevalent stern appendages on medium- to high-speed ships, designed to modify the sailing posture of ships and diminish resistance. Using the Reynolds-averaged Navier–Stokes (RANS) method combined with overset mesh technology, this study evaluates the performance of a ship in regular waves before and after interceptor and stern flap installation. The findings indicate that the interceptor and stern flap resistance reduction rates initially declined and then rose with wavelength, typically 1–3% higher than in calm water. For a constant wavelength of 1.5 LPP and when wave steepness ak ≥ 0.05, the interceptor and stern flap resistance reduction rates in regular waves decline as wave steepness increases. The stern appendages have a more prominent impact on ship posture owing to heightened ship motion amplitude in wave conditions compared to calm water. Moreover, after fitting the interceptor and stern flap, the heave and pitch transfer functions of the ship lessen after fitting the interceptor and stern flap, particularly when λ/LPP = 1–2; average reduction rates for TF3 and TF5 are 7.2% and 3.9%, respectively, with a stern flap, and 4.4% and 2.1% after fitting the interceptor. This study offers invaluable insights and practical guidance for designing and applying stern appendages.

Numerical study of ship hydrodynamics on ice resistance during ice sheet breaking

For icebreakers to navigate polar routes, the ability to break through ice sheet is extremely important. To quantify this, technology that can estimate the mechanical behaviors of ice and ships is essential. The purpose of this study is to analyze the response of the icebreaker Araon breaking through ice sheet. Drucker-Prager yield function and fracture energy based on continuum damage mechanics were applied to the single prism ice compression simulation. The damage in the single ice initiated and evolved as the yield function and fracture energy were assigned. The icebreaking pattern was analyzed from the cone-ice sheet interaction simulations. Patterns similar to those of previous studies were observed qualitatively. The free decay of Araon was numerically analyzed using the Hydrodynamic plug-in HydroQus that was recently developed by present authors, and very accurate ship motion responses were confirmed. The effect of hydrodynamic forces on ice resistance was analyzed through ice sheet breaking simulations. It was found that radiation forces significantly affect the heave and pitch motions of the icebreaker and increase ice resistance. HydroQus has proven to be able to efficiently and accurately simulate the ship-ice interactions compared to other approaches such as computational fluid dynamics.

Improving Ship Response Estimation using Neural Networks

The feasibility of a data-adaptive multi-fidelity seakeeping model is assessed for use in early stage design in this study. Data adaptive tuning (or correction) of lower-fidelity model predictions are implemented based on training with higher fidelity ship motion response data. Long Short-Term Memory (LSTM) neural networks are incorporated as part of a multi-fidelity approach for prediction of 6 degree of freedom (6-DOF) ship motion responses in waves. LSTM networks are trained and tested with Large Amplitude Motion Program (LAMP)simulations as a target, and SimpleCode simulations and wave time series as inputs. LSTM networks improve the fidelity of SimpleCode seakeeping predictions relative to LAMP, while retaining the computational efficiency of a lower-fidelity simulation tool.

Research on path following control of unmanned ship based on fast wave inversion disturbance compensation and preset performance

In this paper, wave inversion is innovatively applied to the path following control of unmanned ship for the first time. At the same time, the performance constraint problem and input saturation of the control system are considered, and the model uncertainty problem of the system is solved by improving the RBF algorithm. Firstly, the system identification method is used to obtain the wave information in real time and quickly based on the ship motion response under the current sea condition, and the disturbance compensation is carried out in the unmanned ship control system. Secondly, in order to ensure the safety and stability of the unmanned ship during navigation, the performance constraints of the unmanned ship path following control system are carried out. In addition, considering the external disturbance and model uncertainty, the RBF neural network control algorithm based on the predictor estimation error is designed, which greatly improves the transient performance of the controller. Finally, the stability analysis and simulation comparison test verify the correctness and feasibility of the proposed control strategy.

Modeling and simulation analysis of ship 6-dof simulation swing platform based on matlab

In this paper, the kinematics and dynamics model of the ship’s six-degree-of-freedom simulation swing platform were studied. Then, a random wave and ship motion response model was established, and a six-degree-of-freedom motion model of DP ship in four-level sea state was established and studied by using the open source MSS toolbox, which lays a foundation for the subsequent simulation and control strategy research. The ordinary PID controller and fuzzy PID controller were designed and simulated, and the results were compared to verify the effect of fuzzy PID controller.

Multi-fidelity data-adaptive autonomous seakeeping

Safe operation of a ship in heavy weather and high sea states requires accounting for the risk of extreme ship motion responses in stochastic ocean waves. Excessive ship motions can lead to hazardous and unsafe conditions such as pure loss of stability, surf-riding and broaching. Mitigation of these risks can be performed through selection of ship speeds and headings for a given seaway, and avoiding conditions likely to lead to severe motions. To address this challenge, a robust, fast, data-adaptive model is a prospective enabling capability for onboard autonomous seakeeping. In this study, data-adaptive Long Short-Term Memory (LSTM) neural networks are investigated as part of a multi-fidelity approach incorporating Large Amplitude Program (LAMP), and a reduced-order model known as SimpleCode. An assessment of this multi-fidelity approach focuses on prediction of ship motion responses in waves. LSTM networks are trained and tested with LAMP simulations as a target, and SimpleCode simulations and wave time-series as inputs. LSTM networks are shown to improve the fidelity of SimpleCode seakeeping predictions relative to LAMP, while retaining the computational efficiency of a reduced-order model. Potential areas of application include unmanned and reduced-crew vessels, operator guidance for manned systems, and weather-informed ship route planning.

Research on the Hydraulic Characteristics of Active Ship Collision Avoidance Devices for Hydrodynamic High-Energy Beam Bridges under Relatively Optimum Deployment Conditions

To address the limitations of existing bridge anti-ship collision devices, which cannot protect both ships and bridges, this study introduced a hydraulic high-energy beam for inland navigation safety. Using a bridge as the technical basis and a typical ship in a navigable river section as the research object, the reasonable deployment angle of the device was investigated and the optimal jet ratio of the device R (the ratio of the high-energy beam jet to the mainstream flow velocity) was clarified through combined numerical simulations and a generalized model test. The ship’s motion response state was subsequently validated when the device was reasonably deployed. The results showed that the reasonable deployment angles of the device were 0°, 15°, and 30°. R = 4 served as the optimal jet ratio. Furthermore, the peak value of turbulence intensity in the Y direction was noticeably smaller than in the other three groups, with a stable change. The coordinate error of the key positions in the numerical simulations and generalized model test of ship motion response was less than 10%, the maximum error of the transverse coordinate of the deflection position was −9.8% and the maximum error of the longitudinal coordinate was −7.0%. The maximum error of the transverse coordinate of the maximum deflection position was −6.8% and the maximum error of the longitudinal coordinate was 3.7%. The numerical simulations and generalized model tests of ship motion response fit well.

Reducing wave impacts on high-speed catamarans through deployment of ride control: Analysis of full-scale measurements

Full-scale trials on a 98 m wave piercer catamaran were conducted in the North Sea and North Atlantic region. In order to examine, amongst other things, the effectiveness of the ride control system, the ship was deliberately operated in sea conditions likely to induce a large number of wave impact events. Primary ship motion and structural response parameters, such as angles, rates and accelerations, and strains at various locations were recorded. Slam and minor wave impact events were identified in the data records and analysed to determine the influence of wave headings, vessel speeds, sea states and ride control system activation on their occurrence rates and severity. The Empirical Mode Decomposition technique was used to remove both noise and the rigid body response from the acceleration signals. This was based on prior work by the authors and found to provide more reliable slam identification than traditional methods. A prediction of extreme slam occurrences was modelled using logistic regression. A key outcome of the study was the finding that the activation of ride control significantly reduces the probability of extreme slams occurring.

Investigation of wave effects on motion of an unmanned surface vehicle at various scales

Motion characteristics of unmanned surface vehicle are mainly affected by sea wave during its operation. This paper shows the numerical results of the unmanned surface ship at various scales in irregular waves based on the boundary element method. The effects of different sea states on each scaled model in a head sea, bow quartering sea, and beam sea are analyzed to predict the safety region of the ship motion. The significant amplitudes of ship motion are obtained from the ship motion responses in regular waves. Steady wave drift forces in the cases of bow oblique sea are calculated to find the impact of second-order waves on the models. It is proved that the motion of model C is remarkable in the narrow frequency domain from 0.2 to 1.4 rad/s but the ship responses of model A are considerable in the range of frequency of 0.2 to 2.5 rad/s. The significant amplitude of surge and pitch motion reaches the peak values in head sea conditions while the peak values of yaw motion are in the oblique sea of 120 degrees. The left motion is maximum in head sea condition.

Ship grounding model tests in a water tank: An experimental study

Ship grounding experiments are important benchmarks used to validate numerical analysis, analytical and empirical formulation. They are key to the understanding of damage mechanism. A set of small-scale ship model grounding tests over a sharp rock are conducted in a water tank considering the influence of surrounding water. Two damage modes are observed in the grounding tests, Mode I for discontinuous fracture/tear and Mode II for continuous fracture/tear. The horizontal grounding resistance forces, damage extents of ship bottom plates, and ship motions are recorded and discussed in detail. Moreover, the energy dissipation process of ship model during grounding process is analyzed based on the test results. The influence of the initial velocity, the initial relative height between the upper surface of the horizontal ship bottom plate and the rock tip, and the rock eccentricity on the ship motion response and structural damage are studied.

The Motion Response of Trailing Suction Hopper Dredger under the Influence of Swell

With the continuous development of the dredging business to overseas markets, dredging ships are faced with a more and more complex hydrodynamic environment. Swell with long wave periods has a great impact on the adaptability of ship operations. Focused on the Trailing Suction Hopper Dredger (TSHD), this paper studied the motion response characteristics of the TSHD under the influence of swell. The result shows that the motion response of the TSHD is severely affected by swell. The amplitude of the ship motion response increases with the increase of wave height. When subjected to the transverse swell with the 90° wave direction, both the heave and roll response amplitude of TSHD is the most significant. While under the influence of swell with the 0° wave direction, the TSHD only pitches violently. The results can guide the suitability assessment of dredging ships in the swell area.

Sensitivity of Mass Distribution with Respect to Pitch Motions of High-Speed Craft

Beside of environmental conditions, ship characteristics also greatly affect in ship behavior when operating at sea, called seakeeping ability. The shape of the hull, appendages, damping, and the weight distribution of ship are some of the factors that determine how the ship motion response occurred. This paper examines how much the pitch motion is influenced in high-speed craft due to the changing of the gyration radius. By using the strip theory method, and by taking the irregular head sea condition and a wave height of 4 meters, then the ship speed and the wave period are varied to determine the pitch motion amplitude at 3 values ​​of gyration radius: 0.2, 0.25 and 0.3 of the ship's length. The results of the study show that at higher ship speeds, the gyration radii greatly influence the pitch amplitude. As for changes in the wave period, the influence is significant at value of 5 second. From these two results, it is clear that the ship's gyration radii must be determined precisely to be able to predict an accurate pitch motion response on a high-speed craft.

Estimation of sea state parameters from ship motion responses using attention-based neural networks

On-site estimation of sea state parameters is crucial for ship navigation. Extensive research has been conducted on model-based estimation utilizing ship motion responses. Model-free approaches based on machine learning (ML) have recently gained popularity, and estimation from time-series of ship motion responses using deep learning (DL) methods has given promising results. In this study, we apply the novel, attention-based neural network (AT-NN) for estimating wave height, zero-crossing period, and relative wave direction from raw time-series data of ship pitch, heave, and roll. Despite reduced input data, it has been demonstrated that the proposed approaches by modified state-of-the-art techniques (based on convolutional neural networks (CNN) for regression, multivariate long short-term memory CNN, and sliding puzzle neural network) improved estimation MSE, MAE, and NSE by up to 86%, 66%, and 56%, respectively, compared to the best performing original methods for all sea state parameters. Furthermore, the proposed technique based on AT-NN outperformed all tested methods (original and enhanced), improving estimation MSE by 94%, MAE by 74%, and NSE by 80% when considering all sea state parameters. Finally, we proposed a novel approach for interpreting the uncertainty estimation of neural network outputs based on the Monte-Carlo dropout method to enhance the model’s trustworthiness.

Numerical Study on the Green-Water Loads and Structural Responses of Ship Bow Structures Caused by Freak Waves

In recent decades, freak waves, characterized by their unusual high amplitude, sharp crest, and concentrated energy, have attracted researchers’ attention due to their potential threat to marine structures. Green-water loads caused by freak waves can be significant and may lead to local damage to the ship structures. Therefore, this paper focuses on the study of green-water loads and examines the structural responses of ship bow structures under the influence of the green-water loads caused by freak waves. Firstly, a three-dimensional numerical wave tank is established in which the superposition model is used to generate freak waves. Validations on the freak-wave generation, ship motion response and the wave loading are carried out to verify the present solvers. The simulation on the interaction between the freak wave and the ship are conducted to obtain the interaction process and green-water loads. Secondly, a finite element (FEM) model of the ship bow is built, on which the green-water loads are applied to calculate the structural responses. Finally, the displacement and stress of the deck and breakwater structures are analyzed. It is found that green water events caused by freak waves can generate enormous impact forces on the bow deck and breakwater, resulting in severe structural responses and even possible damage to the structures. The local strength of structures under freak waves needs to be considered in practical engineering applications.

Experimental study on the motion reduction performance of a small suspension catamaran exploiting an active skyhook control strategy

A nine degrees of freedom suspension catamaran has been developed. The ship is so designed that the heave, pitch, and roll motions of the cabin are separable from those of the twin-hull. One brushed DC motor/generator (M/G) is employed at each of the four suspending locations to produce control force. An active skyhook control strategy utilizing proportional-only control is proposed to calculate the desired control input to reduce the cabin’s local vertical velocity and thus improve ride comfort. The mechanical responses of the suspension unit and the performance of the control system are verified through a group of bench tests. The ship motion responses in regular waves are investigated through a series of towing tank experiments. It is found that the proposed control strategy had significant effectiveness on motion reduction of heave and pitch of the cabin in head waves, but a small contribution to the roll motion reduction in beam waves except in the vicinity of the cabin’s natural roll frequency. In head waves, the average motion reduction ratios of the heave and pitch of the cabin both exceeded 50% at zero forward speed, which at 1.5m/s were 39% and 71%, respectively. In beam waves, the average motion reduction ratios of the heave and roll of the cabin were 62% and −57%, respectively.

Model identification of ship turning maneuver and extreme short-term trajectory prediction under the influence of sea currents

To improve the accuracy of extreme short-term prediction of ship motion under environmental disturbances, a method to identify the motion model of ship turning maneuver and predict the ship extreme short-term trajectory with the influence of ocean currents is studied. Under the influence of ocean currents, a ship motion response model is identified based on the least squares method, and a ship extreme short-term trajectory prediction model is established. The velocity distribution extraction algorithm, center point restoration algorithm, and weighted derivation algorithm are proposed to extract the current direction and the velocity of the turning test. By integrating the current information and ship response characteristics in the extreme short-term ship prediction model, the extreme short-term segmented prediction of the ship trajectory is realized, and the current information is corrected online according to the prediction errors. The real test results show that, compared with the prediction method based on the ship dynamic model, inertia derivation and current compensation, the proposed extreme short-term trajectory prediction method has higher accuracy. Specifically, the prediction error of the proposed method is reduced by 80.6%, 89.3%, and 54.7% than abovementioned methods, respectively.

Effects of damping plate on the motion response of transport ships under waves

Starting from a type of offshore wind power transport ship, “Galaxy Dragon·South” (GDS), this paper proposes a damping plate based on the idea of improving the bilge keel and combining it with the heave plate of the floating foundations. The effects of this structure of different sizes on the motion response of the one-step installation scheme of the fan are verified during transportation through a 1:50 model test. ANSYS-AQWA potential flow software is used for numerical simulation, and the numerical and model test results are compared. The numerical calculation considers the influence of the damping plate size, the arrangement scheme of the damping plate relative to the ship, and the draft of the damping plate on the ship motion response. Results showed that with the increase in the size of the damping plate in a certain range, the additional mass of the transport ship in the direction of roll and pitch will also increase. This phenomenon further affects the natural period of the transport ship and reduces the response amplitude of the motion in the four degrees of freedom of roll, pitch, sway, and surge to a certain extent. In addition, in the layout, maintaining the arrangement of the bow and sides of the ship in the wave direction is most conducive to the motion stability of the ship.

Motion Response on The Water Ambulance Ship

In designing a ship, it is necessary to know the response of the ship's motion before sailing. The purpose of this research is to determine the ship's motion response to waves as well as ship speed in ship loading operational conditions. The method used in this study is the B-spiline mathematical equation and the strip theory method, with the help of ship motion software, which varies the ship's load by 100% DWT, 50% DWT, and 25% DWT. While the highest significant amplitude heave value occurs on a ship with 100% DWT conditions with a speed of 18 knots and a wave direction of 900, which is 2.70 meters, the highest significant value of amplitude pitch occurs on a ship with a condition of 25% DWT with a speed of 6 knots and a wave arrival direction of 1800, namely 1.10 degrees, and the highest significant value of roll amplitude occurs in ships with 25% DWT conditions with speeds of 18 knots with a wave arrival direction of 900, which is 3.42 deg. The research results detected at a speed of 18 knots for the significant amplitude heave value, the significant amplitude pitch value, and the maximum RAO value still meet the Nordforsk criteria.

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.

Direct Measurement of Motion on Fast Ferries

This paper describes a new identification method for the fast ferry motions by using the direct measurements on the ship’s board. The inertial sensor type of the Analog Devices (ADIS) 16364 is selected as a as suitable instrument to measure accelerations and velocity of the ship motions namely heave, pitch, and roll in time domain. Furthermore, the ship motion responses are transferred as the energy spectral density in frequency domain which are identified using the Fast Fourier Transform (FFT) method. For the case study, the measurement equipment was placed on the navigation room of MV. Dumai Line 12 recording in 15 minutes within ship voyage from Bengkalis to Batam in September 2021. Finally, the natural frequencies of heave, pitch, and roll motions are identified about 0.568 rad/s, 0.117 rad/s, and 0.227 rad/s, respectively.