Characteristics Of Ship Motion Research Articles

Comprehensive Assessment of Hull Geometry Influence of a Modernized Ship on Maneuvering Performance and Propulsion System Parameters

The necessity to preserve economic efficiency of cruise ships operation stipulates fleet modernization in order to avoid expenses on ordering and construction of new ships. In this paper an approach based on hull length increase in the process of ship modernization is discussed. The method of evaluation of changes in maneuvering characteristics of ship after modernization is developed taking into account the operational parameters of propulsive electric power plants. The calculations are based on the analysis of transient modes of propulsive power plants operation during the corresponding maneuvers. The parameters influencing the characteristics of ship motion during turning circle are revealed; their significance is estimated, comparative analysis of the effect of ship hull length on maneuvering parameters before and after modernization is carried out. It was shown that in some cases the characteristics of the ship’s controllability and operating parameters of the ship power plant after modernization remain within the permissible limits. The comparative results show that the increase in hull length leads to insignificant deterioration of the main maneuverability characteristics while the electric power plant indicators practically do not deteriorate, which confirms the expediency of such modernization.

Autonomous collision avoidance method for MASSs based on precise potential field modelling and COLREGs constraints in complex sailing environments

Autonomous collision avoidance (CA) for maritime autonomous surface ships (MASSs) in complex navigational environments requires accurate environment modelling and efficient CA algorithms. This study proposes a fast construction method for complex environmental potential field models applicable to vector charts. It accurately represents all complex static obstacles, including concave polygons, and dynamically adjusts the range of influence of a potential field according to its danger level. For dynamic ships, a dynamic obstacle modelling method, based on the quaternion ship domain, is designed to highlight the uncertain motion characteristics of ships. Based on the coupled modelling of dynamic and static obstacles, the virtual potential field of target ships, constrained by the International Regulations for Preventing Collisions at Sea (COLREGs), was constructed. By combining the first-order Nomoto model and optimal field prediction strategy, an optimal CA path, satisfying ship dynamics and COLREGs constraints, was realised, and the local optimal problem of the traditional artificial potential field method was solved. Simulation results show that the proposed method accomplishes fast and accurate modelling of complex environments and realises autonomous path planning and real-time multivessel CA tasks for MASSs in complex water considering the COLREGs constraints. Thus, the proposed method can be implemented in actual ships.

Time-domain numerical simulation for multi-ships moving in waves with forward speed

With the development of the shipping industry, the impact of hydrodynamic interaction between two or more ships on navigational safety has received widespread attention. However, limited research has been conducted on multi-ships moving in waves with forward speed due to the increased complexity of hydrodynamic interactions caused by speed. Therefore, this paper establishes a numerical model of multi-ship hydrodynamics under the wave impact based on the time-domain Rankine source panel method. The hydrodynamic performance and motion characteristics of ships advancing in waves are investigated. An artificial damping layer is applied to free surface boundary conditions to absorb reflected waves. The fourth-order Runge-Kutta method is used for time integration to solve the motion of the ship. The hydrodynamic and motion response of the classical Wigley III ship model are calculated at each wavelength, and the simulation results are compared with other calculations to verify the reasonable reliability of the numerical method employed in this study. On this basis, sensitivity analysis of different parameters is conducted to reveal the influence of various parameters such as speed, wave direction, transverse distance, and water depth on the motion response of the Wigley III ship model in waves.

Ship collision avoidance control based on improved velocity obstacle method

The velocity obstacle method has extensive research in collision avoidance, which uses circles to represent robots or ships to find a collision-free velocity. To better describe the motion characteristics of ships, an improved velocity obstacle method based on elliptical ship domain is proposed in this paper. In the previous research on collision avoidance, the ship domains of the own ship and the target ship are seldom considered at the same time. This paper considers the ship domains of the own ship and the target ship at the same time and judges whether the ship domains of the two ships overlap based on the generalized characteristic polynomial. The heading angle is discretized to construct the velocity obstacle (VO) by calculating the collision velocity at different heading angles. Velocities on the boundaries of the velocity obstacle are used to find an optimal heading angle. The algorithm is tested in different encounter situations and successfully realizes collision avoidance.

A Novel Algorithm for Ship Route Planning Considering Motion Characteristics and ENC Vector Maps

Global route planning is a pivotal function of unmanned surface vehicles (USVs). For ships, the safety of navigation is the priority. This paper presents the VK-RRT* algorithm as a way of designing the planned route automatically. Different from other algorithms or studies, this study employs electronic navigation chart (ENC) vector data instead of grid maps as the basis of the search, which reduces data error when converting the vector map into the grid map. In addition, Delaunay triangulation is employed to organize vector data, in which the depth value is taken as a factor to ensure the safety of the planning route. Furthermore, the initial planned route is not suitable for ship tracking as it does not consider the ship motion characteristics. Therefore, the planned route needs to be further optimized. In the final part, we also conducted experiments to verify the effectiveness and advantages of the proposed algorithm. The results show that the proposed algorithm could reduce the lengths of paths by about 23% on average and save planning time; these are largely dependent on the environment.

Safety range in bridge areas based on the influence of cross flow on ship navigation

The obstructive effect of bridge piers on water flow forms a cross flow, which threatens the navigation of ships. The objective of this study is to contribute to the quantitative study of navigation safety in restricted waters. For this purpose, a hydrodynamic numerical simulation that takes into account ship motion characteristics is combined with navigation safety analysis. Firstly, the cross flow characteristics around tandem double circular piers and their influence on ships are revealed, and the yaw moment is employed to verify the influence. Then, the influence of cross flow on ship navigation is quantified by analyzing the turbulent width under different bridge pier spacings and Reynolds numbers. Finally, the safety range of ship navigation in bridge areas is partitioned. The results demonstrate that when the ship-pier spacing ratio is between 0 and 2.5, there are obvious peak points of the ship's yaw moment near the pier. When the ratio is between 2.5 and 3.0, there is only a negative peak point at the pier body, and the peak value is reduced by 43%, resulting in decreased risk; The qualitative trend of turbulent width is consistent under both single-pier and two-pier conditions. With an increase in Reynolds number, the cross flow velocity in the recirculation region is greater, the stable period of the turbulent width is shorter, and the variation is more noticeable at the downstream pier body; The critical ship-pier spacing ratio for partitioning the high-risk range and the low-risk range is 2.5, and the variation of the ship's yaw moment is consistent with the partition of the safety range by the turbulent width. The research results provide a reference for refined early warning of navigation management.

A three-stage multi-objective heterogeneous integrated model with decomposition-reconstruction mechanism and adaptive segmentation error correction method for ship motion multi-step prediction

Reliable and accurate ship motion prediction is essential for ship navigation at sea and marine operations. Although previous studies have yielded rich results in the field of ship motion prediction, most of them have ignored the importance of the dynamic characteristics of ship motion for constructing forecasting models. Besides, the limitations of the single model and the autocorrelation characteristics of the residual series are also unfavorable factors that hinder the forecasting performance. To fill these gaps, a multi-objective heterogeneous integration model based on decomposition-reconstruction mechanism and adaptive segmentation error correction method is proposed in this paper for ship motion multi-step prediction. Specifically, the proposed model is divided into three stages, which are decomposition-reconstruction mechanism, multi-objective heterogeneous integration model and adaptive segmentation error correction method. The effectiveness of the proposed model is verified using four sets of real ship motion data collected from two sites in the South China Sea. The evaluation results show that the proposed model can effectively improve the prediction performance and outperforms other traditional models and state-of-the-art models in the field of ship motion prediction. Prospectively, the model proposed in this study can be used as an effective aid to ship warning systems and has the potential for practical application in ship marine operations.

A time-varying ensemble model for ship motion prediction based on feature selection and clustering methods

Effective ship motion prediction helps to avoid ship navigation hazards in time. However, there is insufficient attention to potentially valuable information in the multi-factor ship-related data space and the time-varying characteristics of ship motion. In this paper, a time-varying ensemble model based on feature selection and clustering methods is proposed to improve the performance of real-time ship motion prediction. The ensemble model consists of three modules that progressively improve the validity of the model. In Module I, the non-dominated sorting genetic algorithm-II (NSGA-II) algorithm is adopted for feature selection of the original multi-factor data to filter out the feature factors that are useful for ship motion prediction. In Module II, the self-organizing map (SOM) algorithm is applied to cluster the multi-factor data after feature selection to reorganize samples with similar attributes into a limited number of clusters. Then, an ensemble learning model is constructed for each cluster using multiple Elman neural networks and Adaboost techniques. In Module III, a time-varying prediction framework is proposed for real-time prediction of ship motion by combining the ensemble model corresponding to each cluster. An empirical study was conducted using three multifactorial datasets collected from a ship in the South China Sea in December 2020. The results show that the proposed model can be a competitive technique for solving complex multi-factor ship motion predictions and has the potential to be applied to real-time ship motion warning systems.

CFD investigation on the hydrodynamic loads and motions when ship maneuvers in regular and irregular waves

To explore and predict the ship maneuverability in the regular and irregular waves, the zigzag tests, the turning tests, and the course-keeping tests for the model-scale S175 containership under various wave conditions are simulated. The simulations are performed using a structured overset Unsteady Reynolds Averaged Navier-Stokes (URANS) solver with a moving grid. A body force method is adopted to predict the propeller forces. The simulation results are validated by the free-running experiments with satisfactory accuracy, which indicates that the present simulation strategy is effective and reliable. The hydrodynamic loads on the hull and the rudder together with the ship motion characteristics during the maneuvers in waves are obtained. It is concluded that the ship motions and hydrodynamic loads increase with the increase of the wavelength when the wave height is kept constant. The variation trends and magnitudes for low-frequency components of the self-propulsion factors in waves are similar to those in the calm water condition except obvious high-frequency fluctuations due to the wave effect. For the zigzag tests under the long-crested and short-crested irregular waves, the time histories of the yaw and rudder angle are similar. For the turning tests, the amplitude of roll motion in waves is much larger compared with that of the zigzag tests under the same wave condition, and the drift of the trajectory due to the wave is obvious. The current course keeping simulation can be an alternative tool to predict course keeping maneuvers in waves. Furthermore, flow visualizations are presented for providing a better understanding of the wave effect on free-running ship maneuvers.

Ship Motion-Based Prediction of Damage Locations Using Bidirectional Long Short-Term Memory

<i>The initial response to a marine accident can play a key role to minimize the accident. Therefore, various decision support systems have been developed using sensors, simulations, and active response equipment. In this study, we developed an algorithm to predict damage locations using ship motion data with bidirectional long short-term memory (BiLSTM), a type of recurrent neural network. To reflect the low frequency ship motion characteristics, 200 time-series data collected for 100 s were considered as input values. Heave, roll, and pitch were used as features for the prediction model. The F1-score of the BiLSTM model was 0.92; this was an improvement over the F1-score of 0.90 of a prior model. Furthermore, 53 of 75 locations of damage had an F1-score above 0.90. The model predicted the damage location with high accuracy, allowing for a quick initial response even if the ship did not have flood sensors. The model can be used as input data with high accuracy for a real-time progressive flooding simulator on board.</i>

THE DESIGN AND HYDRODYNAMIC ASSESSMENT OF A SUBMARINE CONCEPT WITH OFF-AXIS RESOLVING THE IMPACT OF SHIP’S DESIGN ON DECK AND WELL-DECK LAUNCH AND RECOVERY OPERATIONS BY APPLYING OF QUIESCENT PERIOD PREDICTION (QPP)

One of the most challenging tasks in the deployment of ship-based manned and unmanned VTOL aviation is the launch and recovery and deck handling operational performance on smaller ship platforms. The same may be said of ship Well-deck-based surface boats, like Rhib and LCACs. Awareness and prediction of the ship’s position and movement in the ocean is key to ship-based air operations by targeting the right time to deploy and recover. The ships above waterline design coupled by the propulsion systems, affects ship’s motion and ship motion induced air wake behaviour. MoD/University of Exeter’s Quiescent Period Prediction (QPP) Program Aims to deliver technologies which support launch and recovery from Naval assets, particularly in higher sea states. The Quiescent Period Prediction (QPP) system achieves this by using a wave sensor system to measure the sea surface several hundred meters in advance of the ship. From the measured sea surface, a short-term deterministic wave model can be constructed allowing the wave system to be propagated to the ship's location. The ship's response to the wave spectrum is calculated to determine the level of quiescence at the time of encounter. The results are mapped dynamically on speed-polar visual graphics providing the ship’s best course to steer to ensure encountering the quiescent zone in a timely manner. The ability to fully define a ship’s motion as a function of a recovery device, greatly enhances the overall system operational capability whilst fundamentally reducing the inherent risks associated with platform manipulation in high sea conditions. The use of simulation, routinely considered in the UK, as an alternative to traditional approaches such as scale model testing and fullscale sea trials, to predict the safety and performance envelopes of platforms and systems, is discussed. Operating over deck whilst the ship is experiencing a quiescent period normally has the secondary effect of reduced air wake confusion. This is owing to fewer ship structure excursions into and out of the air flow. To better define off deck airflow around the ship a future QPP improvement will be the development and installation of a Doppler LiDAR federate. The objective of this work is to define ship-helicopter operational deck limits (SHOL), and then to safely expand ship operating deck limits. This article discusses the background to aircraft/ship operations in relation to QPP and goes on to consider both short term implementations (the Landing Period Designator System) and longer horizon deterministically predictive forms of QPP. This article describes the development of the QPP System concentrating on test procedures, timely seaway mapping and ship motion characteristics to complete specific motion sensitive task. An overview of the theory and application is provided concerning dynamic interface analysis with the focus on encountered forces and vehicle to platform response stability.

Nonparametric modeling of ship maneuvering motion based on self-designed fully connected neural network

A self-designed fully connected neural network is proposed for nonparametric modeling of ship maneuvering motion by extracting the dynamic characteristics of ship motion from observed input-output data. The automatic design is conducted by Bayesian optimization, which aims at minimizing the validation error with respect to different hyperparameter settings of the neural network, including learning rate, activation function, as well as network depth and widths. Gaussian process is adopted as the surrogate model to estimate the unobserved validation errors, and lower confidence bound is adopted for trading off exploration and exploitation in the process of optimization. Taking the KVLCC2 ship as the study object, the experimental data provided by Hamburg Ship Model Basin is utilized for modeling and validation of prediction, and the detailed procedures to prepare and preprocess the input-output data are discussed. After well designed and trained, the selected neural network model is evaluated by the prediction results of ship maneuvers in comparison with the experimental data. It shows the high prediction accuracy and strong generalization ability of the established neural network model, indicating the effectiveness of the proposed modeling method.

Maritime traffic flow clustering analysis by density based trajectory clustering with noise

Most of the existing ship trajectory clustering algorithms focus on the properties of single AIS point or sub-trajectories: the trajectory point clustering does not consider the spatio-temporal correlation between neigh-boring points on the same ship trajectory, and is incapable to portray the overall characteristics of ship motion; the ship sub-trajectories clustering needs to discard some points in the ship trajectories, which may lose the vital part of trajectories for clustering purpose. In order to solve the mentioned problems, this paper proposes a DBTCAN (Density based Trajectory Clustering of Applications with Noise) algorithm. This algorithm is suitable for clustering complete trajectories or sub-trajectories of different lengths by using Hausdorff distance as a similarity measure, and can recognize noise trajectories. In addition, DBTCAN algorithm can adaptively determine its optimal input parameters by using adaptive parameter algorithm. We test this method by real AIS data from Bohai Sea, and the experimental results show that DBTCAN algorithm can cluster ship trajectories and extract the main routes of Bohai Sea. Furthermore, the results can provide guidance for the VTS and other agents for carrying out route planning, vessel traffic separation and regulating traffic flows.

Numerical prediction of ship motion and slamming load characteristics in cross wave

When waves from two weather systems converge at a certain sea area, cross waves can be produced. It is important to have a better understanding of the motion characteristics of ship in cross sea to ensure its navigation safety. In this paper, the motion responses of a S175 container ship hull in cross sea is first analyzed based on CFD technique using RANS method. VOF method is used to model and capture the free surface and overset grid technique is adopted to simulate ship motions in waves. Verifications on ship motion by the numerical method have been conducted for time step- and grid-independent studies. According to the motion results by numerical simulation, typical conditions are chosen for further investigation of slamming pressure on bow area and green water on deck. It is found that vertical motion responses of ship induced by cross waves can be quite large and the ship experienced obvious roll–pitch-coupled motion. Severe bow slamming and green water under cross sea state are also observed. The bow flare slamming pressure on the baseline can be quite large in symmetric cross wave. Asymmetrical slamming impacts occurred when the ship sails in an asymmetric cross wave field.

Моделирование траектории судна на волнах на базе STAR-CCM+

The reliable ship motion trajectory signal provides a basis for six-degree-of-freedom test bench to simulate ship motion in waves. The characteristics of ship motion in waves were analyzed. Aiming at the problem of complex hull shape and large displacement at sea, the dynamic overlapping grid technique was used. Based on STAR-CCM+, the free surface was solved by CFD (Computational Fluid Dynamics) numerical simulation method. The numerical model of ship motion in waves was established, and the DFBI (Dynamic Fluid Body Interaction) method was used to simulate the ship motion in the waves. The ship’s motion trajectory was obtained in the regular and irregular heading waves, which provides important support for the six-degree-of-freedom test bench wave simulation system.

Scale effects in AR model real-time ship motion prediction

Real-time prediction of ship motion is essential for decision making in shipborne maritime operations. Differences in ship hulls render different ship motion characteristics, which consequently affects the performance of real-time prediction models. In this study, the ship hull scale effects in real-time motion prediction are investigated using the AR model. The ship datasets are generated by applying the strip theory. These ship motions datasets with various spectral characteristics are used in real-time prediction simulations. This study explores how the spectrum bandwidth, peak frequency, and ship hull scale influence prediction performance, and conclusions are drawn based on numerical simulation results. Prediction accuracy shows a negative relation to spectrum bandwidth and peak frequency. The AR model performance is better for ships with larger principal dimensions where ship hulls are the same. A preliminary empirical formulation for evaluating the maximum predictable time duration is developed based on the above regularities.

Calculation of ship roll hydrodynamic coefficients in regular beam waves

Simulation of a ship's roll motion through equation-based approaches requires restoring moment, added mass moment of inertia and damping coefficients. Accurate estimation of these coefficients enhances the prediction of ship roll response at a resonance condition. However, the magnitude of these coefficients in regular beam seas and close to a resonance condition is unknown. The present study adopts numerical and experimental simulations to investigate the effects of different wave heights and wave frequencies on ship motion characteristics. The motion characteristics results from numerical simulations are compared against experimental measurements, and a good correlation is achieved. The restoring moment in dynamic conditions is calculated and compared to the hydrostatic restoring moment. The dynamic restoring moment is greater than the hydrostatic restoring moment for some wave frequencies and smaller for other wave frequencies. The magnitudes of roll damping and added mass moment of inertia coefficients are calculated at different wave heights and frequencies, and the results yield that there is quite a nonlinear relationship between the roll hydrodynamic coefficients and roll motion characteristics.

Optimizasyon Sürecinde Alternatif Tekne Formlarının Denizcilik Performanslarının Değerlendirilmesi İçin Yeni Bir Yaklaşım

Designing hull forms with superior seakeeping performance demands basic information about the correlation between hull form parameters and ship motions. Classical model testing is still seen to be the most accurate way to get information about wave-induced ship motion characteristics for a hull design. Besides, in the last decades, there is an increased interest in CFD simulations in hydrodynamic optimization studies. Generally, due to the sea environment is generally not definite at the preliminary design phase, hydrodynamic optimization of a ship in terms of seakeeping is realized by comparing response amplitude operator (RAO) graphs in head seas. However, in a systematic optimization study, it becomes impossible to compare these graphs because of the large number of variants. In this study, a new approach will be presented which enables numerical interpretation of a large number of RAOs for systematic optimization studies. A script is developed in order to convert graphical data into numerical and to enable automatic use in an optimization process. As a case study, a systematic planing hull series is developed with 120 variants and RAOs are obtained as a result of viscous CFD analysis. Finally, RAOs of all variants are compared by means of the suggested approach.

The Optimal Design of Modulation Angular Rate for MEMS-Based Rotary Semi-SINS.

In previous studies, the semi-strapdown inertial navigation system (SSINS), based on microelectromechanical system (MEMS) sensors, had realized cross-range measurement of attitude information of high-spinning projectiles through construction of a “spin reduction” platform of the roll axis. However, further improvement of its measurement accuracy has been difficult, due to the inertial sensor error. In order to enhance the navigational accuracy, a periodically rotating method is utilized to compensate for sensor error, which is called rotation modulation. At present, the rotation scheme, as one of the core technologies, has been studied by a lot of researchers. It is known that the modulation angular rate is the main factor affecting the effectiveness of error modulation. Different from the long-endurance and low-dynamic motion characteristics of ships, however, the short-endurance and high-dynamic characteristics of the high-spinning projectile not only require the modulation angular rate to be as fast as possible but, also, the influence of the rotation speed error caused by rotating mechanism errors cannot be ignored. Combined with the rotation speed error of the rotating mechanism, this paper explored the relationship between modulation angular rate, device error, and the navigation error, and then proposed a design method for optimal modulation angular rate. Experiments were carried out to validate the performance of the method. In addition, the proposed method is applicable for rotation modulation systems with different types of motors as the rotating mechanism.

A Hybrid Model of Flooding of the Ro-Ro Ships in Damaged Conditions

The paper presents some results on investigations concerning development of a hybrid model for assessment of performance of the ro‐ro ships in damaged conditions. The model is devoted towards assessing the performance of the damaged ro‐ro ships at the preliminary stage of design. The key problems associated with preparing of such the model are associated with working out a method of assessment of the damaged roro ships performance, investigating all the phenomena which associated with the flooding process of the damaged ro‐ro ships and preparing the model itself. Introducing the method of assessment of the damaged roro ships performance it has been assumed that there is a dependence between the arrangement of internal spaces of a ro‐ro ship and flooding process. The major phenomena which have been decided to take into account when considering flooding of the ro‐ro ships are the flooding understood as the flow of external water into the data damaged compartment, impact of the flooding water on the ship structure and damaged ro‐ro ship motion. Knowing the damaged ro‐ro ship motion characteristics in time domain it is relatively easy to assess the damaged ro‐ro ship performance according to the heeling angle and assess the ro‐ro ship design according to the data arrangement of internal spaces. The last research issue is to investigate if the proposed model may be appropriate tool for assessing the performance of the ro‐ro ships in damaged conditions at the preliminary stage of design. The aim of this paper is to show how to incorporate the dynamics of the damaged ro‐ro ships when assessing the ship performance and safety at the preliminary stage of design. The basic information on the model for estimation of the damaged ro‐ro ship behavior during the flooding process is presented. The complexity of this model is shown depending on the approach applied to consider the flooding process itself. The model is devoted towards assessment of performance of the damaged ro‐ro ships and it is still under the development according to a Ph.D. research at the Faculty of Mechanical Engineering Gdansk University of Technology.