Vessel Motion Response Research Articles

Towards autonomous inland shipping: a manoeuvring model in confined waterways

ABSTRACT Autonomous inland water vessels are essential for promoting intelligent and sustainable waterborne transport. An accurate ship manoeuvring model ensures reliable control strategies and enhances navigation safety. Although ship manoeuvrability models have existed for decades, few studies address shallow and restricted waters. This study introduces a manoeuvring model for inland water vessels, accounting for confinement effects on ship motion. The Manoeuvring Modelling Group (MMG) model in open water serves as the baseline, incorporating empirical methods for shallow water and bank effects. This approach aims to provide a fast and accurate prediction of vessel motion response. The model was validated with free-running experimental data of a pusher-barge model from turning tests at three water depths. Additional case studies highlight shallow water impact compared to infinite water performance under bank effects. Finally, course-keeping case studies are presented, integrating a Proportional-Derivative controller with combined river current and bank-induced forces..

Analyzing the sensitivity of wave frequency responses of floating vessels to uncertain system variables utilizing Polynomial Chaos Expansion

Abstract From a mathematical viewpoint, the frequency domain analysis of vessel motion responses due to wave actions is based on integration of system dynamics idealized in terms of response amplitude operators (RAOs) for 6 DOF rigid body motions and an input wave spectrum in order to obtain the response spectrum. Various quantities of interest can be deduced from the response spectrum which are then used for deriving response-based operational limits for marine operations, also including extreme value and fatigue analysis. The variation of such quantities, owing to the uncertainties associated with the vessel system parameters, can be quantified by performing uncertainty propagation (UP) and consequent sensitivity analysis (SA). This study emphasizes and proposes a computational-efficient way of assessing the sensitivity of the system model output with respect to the uncertainties residing in the input parameters by operating on a surrogate model representation. In this respect, the global sensitivity analysis was effectively carried out by deploying an efficient non-intrusive polynomial chaos expansion (PCE) surrogate model built using a point collocation strategy. Successively, the Sobol' indices were obtained from the analytical decomposition of the polynomial coefficients. The indices, eventually, are employed to quantitatively measure the effects of input uncertainties on the output 6 DOF vessel Root Mean Square responses.

Response component analysis for sea state estimation using artificial neural networks and vessel response spectral data

The use of the ‘ship as a wave buoy analogy’ (SAWB) provides a novel means to estimate sea states, where relationships are established between causal wave properties and vessel motion response information. This study focuses on a model-free machine learning approach to SAWB-based sea state estimation (SSE), using neural networks (NNs) to map vessel response spectral data to statistical wave properties for a small uninhabited surface vessel. Results showed a strong correlation between heave responses and significant wave height estimates, whilst the accuracy of mean wave period and wave heading predictions were observed to improve considerably when data from multiple vessel degrees of freedom (DOFs) was utilized. Overall, 3-DOF (heave, pitch and roll) NNs for SSE were shown to perform well when compared to existing SSE approaches that use similar simulation setups. One advantage of using small vessels for SAWB was shown as SSE accuracy was reasonable even when motion responses were low (in high-frequency, low wave height sea states). Given the information-dense statistical representation of vessel motion responses in spectral form, as well as the ability of NNs to effectively model complex relationships between variables, the designed SSE method shows promise for future adaptation to mobile SSE systems using the SAWB approach.

Experimental investigation of T-foil hybrid control strategy for ship motion reduction in head seas

A hybrid control strategy is proposed to control the T-foil, which can significantly increase the sea-keeping performance of a high-speed trimaran. The strategy includes a gain, which can adjust the maximum flap angle according to the real-time vessel motion response. To investigate the performance of the hybrid control strategy, experimental tests were conducted in a towing tank. The trimaran model with an active control T-foil was tested in head seas with various wave lengths at two forward speeds. The trimaran's heave, pitch, and local acceleration were measured and compared among four control strategies (passive, linear, step, and hybrid control). It is found that the hybrid control strategy can effectively reduce the motion response of the trimaran in the entire range of the wave lengths, and shows better adaptability than the other control strategies.

Numerical and experimental investigation of the effect of moonpool positioning on the hydrodynamics of floating drilling production storage and offloading vessel

ABSTRACT The Floating Drilling Production Storage and Offloading (FDPSO) Platform is functionally a non-propelled vessel and belongs to a subset of a wider group of vessels called Floating Production Systems (FPS). The FDPSO, besides its unique attribute of drilling capability, has all the functionalities of FPSOs. Given the remote offshore locations of oil fields, FDPSOs provide viable economic solution for drilling, production, storage and offloading to smaller vessels for transportation of oil. This paper addresses the designer’s concern in the critical role of positioning of the moonpool since it has a direct bearing on the dynamic effects experienced by the platform. The investigation provides valuable quantitative insights into the important effects on drag during towing, sloshing effect within the moonpool and motion dynamics due to the liquid oscillation. The results of this investigation using numerical and experimental tools, is expected to give key inputs for the designer towards the design of better performing FDPSO platform and benefit the industry. This paper investigates the vessel dynamics including the liquid oscillation behaviour inside the moonpool as a function of the moonpool location in the vessel. The results of the study are important inputs to a designer for consideration of new designs. The FDPSO is a dedicated design of a large capacity platform, different from the conventional FPSO which is usually a retrofitted ship for the purpose. The investigation is based on computational simulation using a commercial RANSE solver namely, STAR-CCM+. Comparison with results from towing tank tests serves to initially validate the numerical simulation-based results. The study performs hydrodynamic diffraction analysis using a potential flow-based solver, namely ANSYS – AQWA. A simplified hull form represents the FDPSO, considering that it is a platform predominantly stationary in operation. However, drag and interactive effects with the moonpool as well as a liquid oscillation in the moonpool are important dynamic conditions for investigation in stationary as well as transit conditions during the tow. The focus of the investigation is on moonpool dynamics in calm water and regular sea conditions and ship motion in waves. The moonpool is vertical circular cylindrical shaped and the investigation considers three moonpool locations namely, at the forward, the midship and the aft, respectively. The water column in the moonpool experiences large oscillatory motions in the piston mode or the sloshing mode. The analysis captures the flow physics, amplitude of oscillations, hydrodynamics resistance and the vessel motion response. The results obtained establish that the location of the moonpool contributes to the augmentation of the cavity drag in the FDPSO. For the selected parameters, the study indicates that the moonpool located in the forward region gives better performance as compared to responses in the other locations.

Sea state estimation based on vessel motion responses: Improved smoothness and robustness using Bézier surface and L1 optimization

Floating structures oscillate in waves, where these wave-induced motions may be critical for various marine operations. An important consideration is thereby given to the sea states at the planning and operating stages for an offshore project. The most important information extracted from a sea state is the directional wave spectrum, indicating wave direction, significant wave height, and wave spectrum peak period. Among several available methods of measuring and estimating the directional wave spectrum, the wave buoy analogy technique based on vessel motion responses is an in situ and almost real-time solution without extra costs of devices. If the forms of the wave spectra are not predefined in the estimation, the method is called a nonparametric approach. Its most remarkable advantage is the flexible form, but the smoothness should be regulated. After the discrete Fourier transform has been applied to the measured vessel motions, smoothing is necessary. However, this process results in disturbed vessel cross-spectra and a lowpass characteristic of the windowing function. This paper presents a nonparametric approach for directional wave spectrum estimation based on vessel motion responses. It introduces novel smoothness constraints using Bézier surface and includes a more robust estimate using L1 optimization. Both techniques are applied to the wave buoy analogy for the first time. Numerical simulations are conducted to verify the proposed algorithm.

Vessel hydrodynamic model tuning by Discrete Bayesian updating using simulated onboard sensor data

Vessel and wave hydrodynamics are fundamental for vessel motion prediction. Improving hydrodynamic model accuracy without compromising computational efficiency has always been of high interest for safe and cost-effective marine operations. With continuous development of sensor technology and computational capacity, an improved digital twin concept for vessel motion prediction can be realized based on an onboard online adaptive hydrodynamic model. This article proposes and demonstrates a practical approach for tuning of important vessel hydrodynamic model parameters based on simulated onboard sensor data of vessel motion response. The algorithm relies fundamentally on spectral analysis, probabilistic modelling and the discrete Bayesian updating formula. All case studies show promising and reasonable tuning results. Sensitivities of the approach with respect to its key parameters were also studied. Sensor noise has been considered. The algorithm is found to be computationally efficient, robust and stable when tuning the values of hydrodynamic parameters and updating their uncertainties, within reasonable sensor noise levels.

A shallow water mooring system design methodology combining NSGA-II with the vessel-mooring coupled model

In this paper, a mooring system design methodology combining the Non-dominated Sorting Genetic Algorithm-II (NSGA-II) with the vessel-mooring coupled model is first proposed. In the proposed methodology, the multi-objective optimization problem for mooring system design which involves several design variables, objective functions and constraints is established and solved by the combination of the NSGA-II algorithm and the vessel-mooring coupled model, and the initial feasible range of design variables is narrowed in advance by combining the NSGA-II with the quasi-static mooring system model. A case study is presented to demonstrated the proposed methodology, in which a catenary mooring system is designed from scratch for a semi-submersible very large floating structure (VLFS) module. It can be concluded from the obtained results that, owing to the combination of the NSGA-II algorithm and the vessel-mooring coupled model, the accurate dynamic responses of vessel and mooring systems can be used as the objective functions; thus, the proposed methodology is able to attain an optimal mooring system considering more practical design requirements, such as the vessel motion response, the safety factor of the mooring system, the length of mooring line lay down part and mooring system layout.

Sea state identification based on vessel motion response learning via multi-layer classifiers

In order to extend the operational weather window for marine vessels under Dynamic Positioning (DP) control, a novel sea state identification method with multi-layer classifiers is proposed in this paper. Due to the distinction of system responses for various sea states, four motion signals including surge, sway, roll and yaw are adopted for classification purpose. Firstly, preprocessing techniques, like filtration and k-means clustering are performed to the raw data to filter out the “corrupted” low frequency (LF) information and generate the band-pass filter bank. Then, the processed data is decomposed into 20 categories via Hilbert-Huang transform (HHT), filter bank method and wavelet transform and 11 statistical features are extracted for each category. Subsequently, Max-relevance Min-redundancy (mRMR) method helps to select salient features with best trade-off between relevance and redundancy. With these selected features, a newly developed three-layer classification structure with Adaptive Neuro-Fuzzy Inference System (ANFIS), Random Forest (RF) and Particle Swarm Optimization (PSO) based combination classifiers is proposed to derive the current sea state. The simulation results demonstrate that the proposed identification system can achieve satisfactory classification accuracy. Moreover, the multi-layer classifier outperforms single layer classifier and can rapidly classify the sea state in real-time implementation.

Modelling and Simulation of Vessel Alongside Replenishment Motion Response Based on Sea Conditions Analysis

Offshore accurate replenishment technology is a vital basement of conducting ocean research and deep ocean exploitation for every advanced country. However, It’s necessary to compensate waving for ensuring the security and accuracy of offshore project due to the fact that wave makes vessel generate 6-DOF motions. This paper set offshore accurate supplying for vessels as the background, basing on Froude-Krylov assumption, to do research on 6-DOF motion responses of different sea conditions. This paper builds the vessel motion response formulas on the basis of the 3-dimensional potential theory and then resolve it by AQWA. The simulation results indicate the regularity of vessel motions, which can be considered as requirement indicators during designing AHC (Active Heaving Compensation) system.

Full-scale unsteady RANS simulations of vertical ship motions in shallow water

The seakeeping behaviour of a vessel in shallow water differs significantly from its behaviour in deep water. In shallow water, a vessel's motion responses to incident waves will be affected by hydrodynamic effects caused by the presence of a finite depth. Given that a vessel will sail in shallow water at various times during its service life, such as when entering harbours, it is important to have an understanding of the influence of shallow water on ship motions. In this study, using a commercial unsteady Reynolds–Averaged Navier–Stokes solver, a numerical study of ship motions in shallow water was carried out. Firstly, the characteristics of shallow water waves were investigated by conducting a series of simulations. Then, a full-scale large tanker model was used as a case study to predict its heave and pitch responses to head waves at various water depths, covering a range of wave frequencies at zero speed. The motion results obtained were validated against related experimental studies available in the literature, and were also compared to those from 3-D potential theory. The results were found to be in good agreement with the experimental data. Finally, it was shown that vertical motions were significantly affected by shallow water.

Active Motion Control of High-Speed Hydrofoil Vessels by State-Space Methods

Hydrofoil ships cruising at high speeds often operate in rough weather conditions and hence experience uncomfortable or even unsafe motions without the use of some form of motion control. The research described here concerns an active motion control mechanism for high-speed hydrofoil vessels, aiming at the significant reduction of the vessel motions in regular and random waves. The seakeeping equations of motion are cast into a linear state-space form leading to a linear-quadratic optimal controller shown to attenuate the vessel motion responses significantly. The deterministic control laws designed in the present study are found to perform satisfactorily both in monochromatic and random waves for high-speed vessels supported by hydrofoils and buoyancy.

4P-1180 Prognostic impact of aortic calcification index in patients under hemodialysis

The seakeeping behaviour of a vessel in shallow water differs significantly from its behaviour in deep water. In shallow water, a vessel's motion responses to incident waves will be affected by hydrodynamic effects caused by the presence of a finite depth. Given that a vessel will sail in shallow water at various times during its service life, such as when entering harbours, it is important to have an understanding of the influence of shallow water on ship motions. In this study, using a commercial unsteady Reynolds–Averaged Navier–Stokes solver, a numerical study of ship motions in shallow water was carried out. Firstly, the characteristics of shallow water waves were investigated by conducting a series of simulations. Then, a full-scale large tanker model was used as a case study to predict its heave and pitch responses to head waves at various water depths, covering a range of wave frequencies at zero speed. The motion results obtained were validated against related experimental studies available in the literature, and were also compared to those from 3-D potential theory. The results were found to be in good agreement with the experimental data. Finally, it was shown that vertical motions were significantly affected by shallow water.

Use of springs to simulate the wind induced moments on turret moored vessels

This paper presents the results of an experimental study investigating the behaviour of a system of springs used to simulate wind-induced loading effects on turret moored vessels. These vessel types are extensively used offshore for hydrocarbon storage and production with model testing commonly performed at the design stage to gauge the influence of the environment on the vessel motion responses. The performance of the spring system is evaluated using a model vessel in a square complex wave basin over a range of long crested sea states represented by JONSWAP wave spectra and for two turret positions along the vessel longitudinal centre line. The measurements are compared with results from tests using conventional wind fans. It is shown that the spring design may be used as a mechanism during preliminary model testing to simulate the influence of wind on the yawing.