Ship Response Research Articles

A Novel Hull Girder Design Methodology for Prediction of the Longitudinal Structural Strength of Ships

The ship hull girder model has been widely adopted in ship mechanics research such as small-scale and large-scale hydroelastic ship model experiments. Current design methods cannot seriously meet the structural rigidity requirement, and the distinction between the ship structural masses and the cargo masses is rather vague. This research proposes a simple and novel ship hull girder design methodology. The main novelties are that (1) the structural rigidity design requirement for the ship hull girder corresponding to any targeted real ship with arbitrary structural complexity is precisely satisfied by the proposed strategy of adopting a composite hull girder system, and that (2) the mass density per unit length of the proposed hull girder is solely related to the mass density distribution of the targeted ship structures by considering the hull girder system as a complete finite element (FE) model, and thus (3) a better ship hull girder model for prediction of the total structural responses can be consequently established. A real ship is adopted as the design target, and the structural responses of the real ship and the proposed ship hull girder model are compared and analyzed. The proposed model is compared to the currently widely accepted ship hull girder models through numerical experiments. The proposed hull girder design methodology possesses the potential for upgrading the classical structural design approach to match the growing trend of adopting FEM-based approaches for ship structure research.

Seakeeping Performance of Warship Catamaran under Varied Hull Separation and Wave Heading Conditions

Seakeeping criteria significantly impact ship aspects like speed loss, operational optimization, and structural integrity. This study integrated experimental and numerical methods to evaluate the seakeeping performance of an asymmetrical hull with varying hull separations and wave headings. Experimental Fluid Dynamics (EFD) tests were conducted in a towing tank with irregular waves and a Pierson-Moskowitz spectrum. Concurrently, numerical simulations using the Boundary Element Method (BEM) computed Response Amplitude Operators (RAO) for heave, pitch, and roll motions. The numerical mesh demonstrated a high degree of agreement between RAO peak values from BEM simulations and experimental tests, with discrepancies between 1% and 5%, indicating BEM’s precision in predicting ship responses to wave conditions. The analysis demonstrates that wave heading significantly influences the heave, pitch, and roll motions of the catamaran, with beam seas (90°) presenting the most severe conditions for heave and roll, while head seas (180°) lead to the largest pitch motions. Optimal performance is observed at a separation-to-length (S/L) ratio of 0.4, which minimizes excessive motion across various wave headings. The analysis indicates that while both S/L and wave heading influence vessel motions, the impact of wave heading is more pronounced, with optimal S/L values varying based on specific wave angles. Overall, the findings underscore the critical relationship between hull separation and wave direction, indicating that larger S/L ratios contribute to improved seakeeping performance.

An Integrated Framework for Real-Time Sea-State Estimation of Stationary Marine Units Using Wave Buoy Analogy

Understanding the impact of environmental factors, particularly seaway, on marine units is critical for developing efficient control and decision support systems. To this end, the concept of wave buoy analogy (WBA), which utilizes ships as sailing buoys, has captured practitioners’ attention due to its cost-effectiveness and extensive coverage. Despite extensive research, real-time sea-state estimation (SSE) has remained challenging due to the large observation window needed for statistical inferences. The current study builds on previous work, aiming to propose an AI framework to reduce the estimation time lag between exciting waves and respective estimation by transforming temporal/spectral features into a manipulated scalogram. For that, an adaptive ship response predictor and deep learning model were incorporated to classify seaway while minimizing network complexity through feature engineering. The system’s performance was evaluated using data obtained from an experimental test on a semi-submersible platform, and the results demonstrate the promising functionality of the approach for a fully automated SSE system. For further comparison of features of low- and high-fidelity modeling, the deficits with the feature transformation of the existing SSE models are discussed. This study provides a foundation for improving online SSE and promoting the seaway acquisition for stationary marine units.

Numerical and experimental investigations on coupled motion response of ship and sloshing inside partially flooded compartments

Numerical and experimental investigations on coupled motion response of ship and sloshing inside partially flooded compartments

Predicting a passenger ship's response during evasive maneuvers using Bayesian Learning

Predicting a passenger ship's response during evasive maneuvers using Bayesian Learning

Extreme nonlinear ship response estimations by active learning reliability method and dimensionality reduction for ocean wave

An efficient extreme ship response prediction approach in a given short-term sea state is devised in the paper. The present approach employs an active learning reliability method, named as the active learning Kriging + Markov Chain Monte Carlo (AK-MCMC), to predict the exceedance probability of extreme ship response. Apart from that, the Karhunen-Loève (KL) expansion of stochastic ocean wave is adopted to reduce the number of stochastic variables and to expedite the AK-MCMC computations. Weakly and strongly nonlinear vertical bending moments (VBMs) in a container ship, where the former only accounts for the nonlinearities in the hydrostatic and Froude-Krylov forces, while the latter also accounts for the nonlinearities in the radiation and diffraction forces together with slamming and hydroelastic effects, are studied to demonstrate the efficiency and accuracy of the present approach. The nonlinear strip theory is used for time domain VBM computations. Validation and comparison against the crude Monte Carlo Simulation (MCS) and the First Order Reliability Method (FORM) are made. The present approach demonstrates superior efficiency and accuracy compared to FORM. Moreover, methods for estimating the Mean-out-crossing rate of VBM based on reliability indices derived from the present approach are proposed and are validated against long-time numerical simulations.

Hydroelasticity of a 21000TEU containership under freak waves by fluid-flexible structure interaction simulations

In this paper the CFD-FEM two-way coupled method is used to simulate the motions and wave loads on a 21000TEU containership subjected to freak waves. A numerical wave tank is established for the generation of long-crested freak waves by wave focusing method based on superimposing sinusoidal component waves. The ship hull is modeled with a backbone beam which reproduces the vertical bending vibration modal behaviour of real ship. The simulated freak waves are checked and the evolution of freak waves during propagation is analyzed first. The ship responses in regular waves at different wave heights and ship speeds are compared. The extreme responses of ship motion and sectional loads in freak waves are analyzed and compared with those in regular waves. The influence of ship forward speed and wave height of freak waves on ship motion and load responses are analyzed and discussed.

Data-driven model assessment: A comparative study for ship response determination

Several machine learning approaches to determine ship responses via data-driven models have been applied. Input features and parameters used relied on time-series analyses obtained from computational-fluid-dynamics approach. As inputs into the data-driven model, the heave and pitch motions of a ship advancing in irregular, i.e., natural seaway were considered. By using different models in the framework of machine learning, required computation for the associated ship motions may be avoided, thus reducing the computational effort to forecast ship motions. Comparative predictions with numerical simulations revealed that the deep-neural-network method for training in auto-machine-learning instructions yielded the highest accuracy in heave motion, resulting in a non-normalized mean-absolute-error of 0.74, against the corresponding error of 1.07 from numerical computations, whereas the method trained with the tree-based models (the extreme gradient boosting and the Hist gradient boosting regressor) predicted less accurate motions for the tested ship. The model trained with the random forest regressor exhibited an error of 1.10. Numerical simulation based on a field method proved to be the most suitable choice for pitch motion. Despite the few samples available to train the regressors, results demonstrated that the measured data was sufficient to assess the developed data-driven model for ship response determination.

Modelling Sea-Surface Wave Motion and Ship Response Using Smoothed Particle Hydrodynamics and Finite Element Analysis

The response of a ship or other vessel to surface sea waves, including extreme waves, may compromise crew and vessel safety and long-term operational capability. Herein, a novel high-fidelity numerical time-dependent simulation approach is presented using Smoothed Particle Hydrodynamics (SPH) for modelling sea waves coupled with Finite Element Analysis for modelling vessel structural response under wave loading conditions. The results are compared with physical scale model wave tank test results. Good agreement was obtained for heave and pitch motions and vertical bending moments for various forward (head) speeds in regular head waves, heave and pitch motions, and vertical bending moments. High computational demands can be met by the increasing availability of computation power. Ongoing research is outlined. The implications for the design of vessels such as ships and for through-life assessment are discussed.

A Novel Detection Transformer Framework for Ship Detection in Synthetic Aperture Radar Imagery Using Advanced Feature Fusion and Polarimetric Techniques

Ship detection in synthetic aperture radar (SAR) imagery faces significant challenges due to the limitations of traditional methods, such as convolutional neural network (CNN) and anchor-based matching approaches, which struggle with accurately detecting smaller targets as well as adapting to varying environmental conditions. These methods, relying on either intensity values or single-target characteristics, often fail to enhance the signal-to-clutter ratio (SCR) and are prone to false detections due to environmental factors. To address these issues, a novel framework is introduced that leverages the detection transformer (DETR) model along with advanced feature fusion techniques to enhance ship detection. This feature enhancement DETR (FEDETR) module manages clutter and improves feature extraction through preprocessing techniques such as filtering, denoising, and applying maximum and median pooling with various kernel sizes. Furthermore, it combines metrics like the line spread function (LSF), peak signal-to-noise ratio (PSNR), and F1 score to predict optimal pooling configurations and thus enhance edge sharpness, image fidelity, and detection accuracy. Complementing this, the weighted feature fusion (WFF) module integrates polarimetric SAR (PolSAR) methods such as Pauli decomposition, coherence matrix analysis, and feature volume and helix scattering (Fvh) components decomposition, along with FEDETR attention maps, to provide detailed radar scattering insights that enhance ship response characterization. Finally, by integrating wave polarization properties, the ability to distinguish and characterize targets is augmented, thereby improving SCR and facilitating the detection of weakly scattered targets in SAR imagery. Overall, this new framework significantly boosts DETR’s performance, offering a robust solution for maritime surveillance and security.

Accuracy verification of the 2D spectral AIS method by the hull monitoring data

Accuracy validation of the 2D spectral AIS method (AIS method using two-dimensional wave spectrum; 2D-AIS method) using hull monitoring data of a large ore carrier is discussed. The AIS method predicts the response of actual ships using AIS-based ship position data, hindcast wave data, and response characteristics data. The conventional AIS method uses representative parameters(H, T, θ) from wave spectrum modeling. The modeling involves many uncertainties. By using the 2D wave spectrum as it is, the effect of uncertainties associated with wave spectrum modeling is investigated. Compared to the analysis of the monitoring data conducted in this study, it was found that the 2D-AIS method improves the accuracy to about 15 %, while the conventional AIS method shows an error of up to about 35 % compared to the actual measurements in the long-term maximum expected values. This enhancement is attributed to the inability of the modeled wave spectrum to accurately represent the two-peak wave spectrum observed in extreme sea states, leading to a deficiency in reproducing wave frequency components corresponding to peak frequencies of the response. The findings underscore the effectiveness of the 2D-AIS method in refining long-term hull stress estimations, thus offering valuable insights for enhancing the safety and performance of hull structures.

Prediction for Global Whipping Responses of a Large Cruise Ship Under Unprecedented Sea Conditions Using an LSTM-Based Encoder–Decoder Model

Abstract Global whipping responses contribute to a significant increase in vertical bending moments (VBM), making their accurate prediction crucial for ship safety. In this study, a long short-term memory (LSTM)-based encoder–decoder model is established to predict the whipping responses under varying sea states. The model is trained on a comprehensive dataset, which includes motion data and VBM history of a cruise ship under various sea conditions. This dataset is established via numerical simulation, ensuring a wide range of scenarios for the model to learn from. The efficacy of the LSTM encoder–decoder model in capturing global whipping responses is initially verified under a single sea condition case. This step confirms the model's ability to accurately predict vertical bending moments under known conditions. Subsequently, the model's performance under unprecedented sea conditions is examined. Given that the distribution of training data significantly influences the model's performance and the data from diverse sea conditions typically exhibit distinct data distribution, a mixed data training strategy is employed during the training process in this scenario. The results indicate that the LSTM encoder–decoder model effectively captures whipping responses. Furthermore, the mixed data training strategy significantly improves the model's prediction accuracy for global whipping responses under unprecedented sea conditions.

Nonlinear similarity characterisation and validation of dynamic response of ship stiffened plate structure under explosion load impacts

The similarity test of ship stiffened plate structures under underwater explosions is a cost-effective and efficient method to evaluate the vitality of ships and guide the design of their shock resistance. This study focuses on the nonlinear impact response model tests of ship stiffened plate structures and their similarity laws with actual ships. The vertical motion of the ship stiffened plate structure is characterized by the Hurst index, and an equivalent relationship between the Hurst index of the model and the prototype is derived from classical similarity law. Based on the Hurst index, a similarity transformation relationship between the strain signals of the model and prototype is established. To verify the conclusions, similarity experiments of underwater explosions were conducted on both the model and the prototype. The original signals were grouped by the natural vibration period to determine the variation of the Hurst index over time. The model experiment strain signals for each natural vibration period were converted and compared with the prototype experiment results to verify the method's effectiveness. Simultaneously, the Hurst index of the stiffened plate structure under explosive shock load and its similarity transformation relationship with the prototype were simulated and analyzed. This provides theoretical and technical support for conducting analogous nonlinear response experiments for ship underwater explosions.

Experimental and numerical investigation on the hydroelastic response of barge and KVLCC2 ship

In this paper, the hydroelasticity of two segmented ship models (Barge and KVLCC2) is investigated by experimental and numerical methods. A two-way Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) coupled method is adopted and further validated its accuracy against experimental results. The current approach emphasizes the overall convergence between two solvers, maintaining a strongly coupled manner to comprehensively address the fluid-structure interaction phenomenon, including the added mass effect. A series of experiments of a segmented Barge and KVLCC2 under various wave conditions were firstly conducted. The motions of the models are measured and the displacement Response Amplitude Operators (RAOs) are calculated. The CFD-FEA coupled method is demonstrated in agreement with experimental results by comparing the numerical prediction with the tank test results in terms of motion, affirming the validity and robustness. Finally, the hydroelastic response is discussed and investigated.

Numerical Simulation of Ship-added Resistance Based on a Numerical Wave Tank

The wave resistance increase of a ship during its actual voyage can affect its speed and safety. To design ships with excellent sailing performance, it is necessary to accurately predict the wave resistance increase of a ship in waves, as well as the motion response and wave resistance prediction of ships in waves, which involves complex hydrodynamic problems. This paper first establishes a physical model of the KCS vessel, then utilizes the numerical wave tank platform independently developed by our university. Based on viscous flow theory, it calculates the resistance of the KCS under calm water conditions. Using three-dimensional potential flow methods and spectral analysis, it computes the wave-induced resistance values for the KCS under six-degree sea states, analyzes the wave-induced resistance performance of the KCS, and ultimately, based on the calculation results of calm water resistance and wave-induced resistance combined with propeller efficiency parameters, calculates the effective power of the engine.

Difference in ship response in waves between strip and 3D methods based on integrated formulation

Numerous benchmark calculations have been performed on ship motions and loads in waves. However, there are usually significant differences between codes, even for programs based on the same theory, and it is often extremely difficult to identify the factors that cause such differences. In this paper, the authors present a formulation of the strip method and 3D method in such a way that the common parts between the two are emphasized, and then develop an integrated program that can handle the two methods (STFM and zero-speed Green's function method) based on this formulation. This approach enables the extraction of the differences in the ship response between the two methods caused by the pure difference in the hydrodynamic force of them, i.e., the 3D effect. A comparison using tank tests under a wide range of conditions is performed to clarify the estimation accuracy of the two methods and the tendency of the 3D effect for ship motion, hull-girder sectional force, and hydrodynamic pressure for a container ship and a VLCC.

A multiparameter simulation-driven analysis of ship response when turning concerning a required number of irregular wave realizations

The growing implementation of Decision Support Systems on modern ships, digital-twin technology, and the introduction of autonomous vessels cause the marine industry to seek accurate modeling of vessel response. Despite the contemporary 6DOF models can be used to predict ship motions in irregular waves, the impact of their stochastic realization is usually neglected and remains under-investigated. Especially in the case of turning, differences arising from the stochastic representation of the waves may result in excessive ship motions or even stability failure during maneuver execution. Therefore, in this study, statistical distributions of maximum amplitudes of roll, pitch, and lateral acceleration calculated in two representative locations on board a passenger vessel were analyzed concerning stochastic wave realization and existing extremes. The research utilized 6DOF simulation data and numerous realizations of the irregular wave with random phases of its components. Furthermore, the required number of wave realizations allowing for capturing the actual ranges of ship response at an assumed confidence level has been determined and analyzed. Ultimately, the results were compared in the safety-critical cases concerning various wave and operational conditions. The outcome of this study may be found useful by all parties involved in developing maritime autonomous systems and modeling ship motions.

Ship grounding simulation with different rock shapes and its verification

ABSTRACT Ship grounding often results in damage to the hull, which poses a threat to structural integrity, ship stability, and human life. To reduce the consequences from ship grounding accidents, it is necessary to investigate the damage mechanism and motion responses of ship grounding. The research’s objective is to carry out experimental validation and perform a series of numerical investigations on the ship dynamic responses in grounding. A simulation based on the Coupled Eulerian–Lagrangian(CEL) method was carried out to reproduce a grounding test case conducted in a water tank. It was demonstrated that the numerical results are in good agreement with the experimental results. Then, based on the verified simulation technology, the influences of rock shapes and friction on the grounding damage and motion responses of ships were investigated and discussed. The dynamic response analysis of ships in different grounding scenarios can provide a reference for grounding damage prediction.

Numerical Study on Hydrodynamic Characteristics of Two Ships Advancing in Parallel for Underway Replenishment of Luxury Cruise Ships

For a long time, seakeeping data has been the basis for judging ship amenities and seaworthiness. Luxury cruise ships, as large passenger ships, put forward higher requirements for seakeeping. To analyze the seakeeping response of luxury cruise ships, AQWA is used to build a model and conduct numerical simulations. The hydrodynamic characteristics of cruise ships and replenishment tankers with different typical sea conditions, various ship spacing and wave directions are studied. According to the results, when two ships are advancing in parallel, the cruise ship should pay attention to the movement of the replenishment tanker while considering its seakeeping to avoid collision danger. The conclusions can avoid dangerous situations in the replenishment and improve the safety of the replenishment operation.

Numerical Investigation of Motion Response of the Tanker at Varying Vertical Center of Gravities

<i>The vertical center of gravity (VCG) has a significant impact on the roll motion response of a surface ship, particularly oil tankers based on the oil level in the tanker after discharging oil at several stations or positional changes, such as changes in the superstructure and deck structure. This study examined the motion response of the Korea very large crude carrier 2 (KVLCC2) at various VCGs, especially roll motion when the VCG changed. The potential theory in the Ansys AQWA program was used as a numerical simulation method to calculate the motion response. On the other hand, the calculations obtained through potential theory overestimated the roll amplitudes during resonance and lacked precision. Therefore, roll damping is a necessary parameter that accounts for the viscosity effect by performing an experimental roll decay. The roll decay test estimated the roll damping coefficients for various VCGs using Froude’s method. The motion response of the ship in regular waves was evaluated for various VCGs using the estimated roll-damping coefficients. In addition, the reliability of the numerical simulation in motion response was verified with those of the experiment method reported elsewhere. The simulation results showed that the responses of the surge, sway, heave, pitch, and yaw motion were not affected by changing the VCG, but the natural frequency and magnitude of the peak value of the roll motion response varied with the VCG.</i>