Ship Sailing Research Articles

The Safety Assessment of Civil Ships against Capsizing Based on the Probability Analysis of Multiple Threshold-crossings of Stochastic Sea Waves

Abstract This paper investigates the impact of threshold-crossing events on ship capsizing through a probabilistic model that predicts random wave heights. Utilizing statistical data from wave height observations, this paper proposes that random waves can be approximated and modeled using the Wiener process, employing autocorrelation function identification and probabilistic statistical verification methods. The threshold-crossing duration of a random wave is just the period of the wave exceeds a given threshold, which can reflect the frequency property of the stochastic sea waves. And the probability distribution of the period can theoretically be determined using the derived probability density function for the time interval between any two adjacent crossings of the Wiener process and a threshold. Based on the above theories, the capsizing probabilities of a civil ship sailing in different wave areas are analyzed under different safety thresholds considering certain ratios of the ship's intrinsic period and wave period. The research results can provide a reference for the anti-overturning design of the ships under the action of random waves.

Effects of propeller cavitation on ship propulsion performance in off-design operating conditions

The propeller cavitation is closely related with its hydrodynamic performance. When the propeller works in the cavitating flow, the propeller hydrodynamic performance, in terms of thrust and torque coefficients, is reduced due to the propeller cavitation. When the high-speed and high-power ship sails in adverse sea, the varying loads on propeller will cause severer cavitation on propeller. The reduction in propulsion performance caused by cavitation will further affect the propulsion system, impacting the ship sailing performance and safety. The VP1304 propeller cavitation CFD simulation are conducted to validate the CFD method. Furthermore, the influence of propeller advance ratio and cavitation numbers on the performance of low-speed high-power series propeller in cavitating flow are studied and illustrated. This influence of cavitation has also been transferred to the propulsion system and this process are calculated by the ship propulsion system numerical model. Additionally, the sailing performance of ship propulsion system under off-design conditions, where the cavitation is more likely to occur, has been investigated in this article. Under severe heavy load conditions, it can even result in a complete loss of propulsion capability, posing significant risks. Therefore, it is necessary to further optimize control strategies for the propulsion system to mitigate the hazards caused by cavitation.

Pitching Stabilization Control for Super Large Ships Based on Double Nonlinear Positive Feedback under Rough Sea Conditions

Due to the rapid development of a global navigation satellite system and the rapid growth of ships, the traditional control algorithms are not suitable; hence, the longitudinal rocking phenomenon generated by external disturbances is more serious when a ship is sailing. This paper takes a mathematical model of the super large oil tanker “KVLCC2”’s longitudinal motion as the controlled plant, establishing a multi-input multi-output instability control system, using the root trajectory shaping method and a weighting matrix to ensure the stability of its transfer function’s mathematical model. An improved closed-loop gain-shaping algorithm is utilized to design a simple robust controller. And a dual nonlinear positive feedback control algorithm is added to the control system to further improve the controller’s pitching stabilization performance and reduce the controller’s output energy. In order to verify that the controller has a consistently strong robustness, simulation experiments are carried out by adding a level 6, 7 and 8 wind wave model and a perturbation link to the control system, respectively. The results show that when the value of the hysteresis constant is taken as 0.25, the output values of the heave displacement and the pitch angle are greatly reduced, and the longitudinal rocking phenomenon is significantly improved. The dual nonlinear positive feedback control algorithm enhances the ship’s pitching stabilization control capability and further reduces the controller’s output energy, which provides technical support for the smooth and efficient sailing of super large ships under changing sea conditions. Combined with a global navigation satellite system, this algorithm provides a new method for pitching stabilization control of super large ships.

Optimization of Controllable-Pitch Propeller Operations for Yangtze River Sailing Ships

The Yangtze River’s substantial variation in water depth and current speeds means that inland ships face diverse operational conditions within a single voyage. This paper discusses the adoption of controllable-pitch propellers, which adjust their pitch to adapt to varying navigational environments, thereby optimizing energy efficiency. We developed an optimization framework to determine the ideal pitch angle and rotation speed (RPM) under different sailing conditions. The energy performance model for inland ships was enhanced to account for the open-water efficiency of CPPs across various pitch angles and RPMs, considering the impacts of current and shallow water, among other factors. The optimization approach was refined by incorporating an improved genetic algorithm with an annealing algorithm to enhance the initial population, applying the K-means clustering algorithm for population segmentation, and using multi-parent crossover from diverse clusters. The efficacy of the optimization method for CPP operations was validated by analyzing three operational scenarios of a Yangtze sailing ship. Additionally, key components of the ship performance model were calibrated through experimental tests, demonstrating an anticipated fuel consumption reduction of approximately 5% compared to conventional fixed-pitch propellers.

Positive Youth Development at Sea: A Case Study of the Shenandoah Model

Background: Tall ship sail training, a form of outdoor adventure education, has historically been used with youth to build competency in seamanship and social and emotional skills. However, there is a void in the literature documenting precise program models connected to specific goals. Purpose: This paper presents a case study of the Shenandoah Model of sail training. It details its Positive Youth Development (PYD) framework and mean changes in PYD assets reported by participants. Methodology/Approach: Participants were surveyed using a one-group retrospective pretest-posttest pre-experimental design to assess the impact of participation. Findings/Conclusions: The participants reported significant mean increases across all PYD assets (Caring, Connection, Contribution, Competence, Character, Confidence, and Happiness), including moderate effect sizes for all measures except Happiness. In addition, over 70% of the participants would recommend the program and/or do it again, suggesting program satisfaction. Implications: Connecting different PYD assets to various program activities allows future program designs to intentionally develop sail training voyages to build competencies. Future follow-up research is needed, including qualitative methods to capture the impact of these programs from the participants’ viewpoint.

Real-time prediction of ship motions based on the reservoir computing model

Real-time prediction of ship motions is crucial for ensuring the safety of offshore activities. In this study, we investigate the performance of the reservoir computing (RC) model in predicting the motions of a ship sailing in irregular waves, comparing it with the long short-term memory (LSTM), bidirectional LSTM (BiLSTM), and gated recurrent unit (GRU) networks. The model tests are carried out in a towing tank to generate the datasets for training and testing the machine learning models. First, we explore the performance of machine learning models trained solely on motion data. It is found that the RC model outperforms the LSTM, BiLSTM, and GRU networks in both accuracy and efficiency for predicting ship motions. Besides, we investigate the performance of the RC model trained using the historical motion and wave elevation data. It is shown that, compared with the RC model trained solely on motion data, the RC model trained on the motion and wave elevation data can significantly improve the motion prediction accuracy. This study validates the effectiveness and efficiency of the RC model in ship motion prediction during sailing and highlights the utility of wave elevation data in enhancing the RC model’s prediction accuracy.

Design, analysis, and operation optimisation of a shipborne absorption refrigeration–ice thermal storage system based on waste-heat utilization

The integration of waste-driven absorption refrigeration technology into marine applications is recognized as a promising low-carbon solution. Nonetheless, its practical application does not inherently outperform electric compression technology, primarily due to the absorption system’s inherent thermal inertia and limited adjustability. This characteristic renders the system less responsive to the dynamic refrigeration requirements typically encountered on board vessels. In this study, a shipborne ammonia absorption refrigeration–ice storage system is proposed to balance the cooling load between supply and demand. To evaluate the efficiency of the integrated system for ice storage and cooling during ship sailing, key operational variables including refrigeration temperature, cooling water temperature, and generation temperature are analyzed to assess the thermal cycle performance of the system. A typical shipping route is considered for cooling operation optimisation of the absorption refrigeration–ice storage system. This paper explores four typical cooling-supply strategies and determines the operation modes for the ice storage period and the cooling period based on considerations of energy consumption, energy utilization, and economic factors. The final optimisation results indicate that the combined system has significant advantages based on energy consumption and operation cost. In comparison to compression and absorption refrigeration systems, the proposed system exhibits 52.4% and 8.31% reductions in energy consumption, respectively. Additionally, the operation costs are decreased by 12.27% and 27.41%, respectively, and the life cycle costs are lowered by 11.51% and 32.35%, respectively. The findings of this combined system can provide a technical reference for the design and operation of a ship waste-heat refrigeration system.

Design and control studies of six-phase interleaved boost converter for integrated energy efficiency improvement of green ship

The operation of offshore vessels is characterized by stable loads during normal voyages and significant load variations when leaving port or docking. Conventional ships emit large amounts of greenhouse gases during navigation. In the development of the modern shipbuilding industry, how to effectively reduce gas emissions during ship sailing is a challenging task that still remains under-explored. Green ships equipped with new energy power systems have a greater potential for application. They are equipped with fuel cells and lithium batteries as energy sources, and such a hybrid system requires a comprehensive energy management system to achieve the power distribution between the two energy sources. In this paper, a powerful 10kW six-phase interleaved boost converter (IBC) for the hybrid power generation system of ships is designed to manage the output power of the fuel cell. Firstly, the new circuit topology design principle and construction process are introduced. Later, a step-by-step current adjustment controller is designed for the converter to progressively enforce output current and a maximum limitation of the fuel cell. Afterwards, LTspice simulation is performed to verify the ripple suppression effect and stable anti-interference performance. Finally, the designed IBC has been experimentally constructed, including the input/output current and voltage sampling, temperature control and sampling, and other functions, significantly benefiting real-world marine high-power fuel cells. The stability, reasonableness and effectiveness of the designed IBC are further evaluated through the extensive experimental analyses.

Cyber risk assessment of cyber-enabled autonomous cargo vessel

The increasing interest in autonomous ships within the maritime industry is driven by the pursuit of revenue optimization, operational efficiency, safety improvement and going greener. However, the industry’s increasing reliance on emerging technologies for the development of autonomous ships extends the attack surface, leaving the underlying ship systems vulnerable to potential exploitation by malicious actors. In response to these emerging challenges, this research extends an existing cyber risk assessment approach called FMECA-ATT&CK based on failure modes, effects and criticality analysis (FMECA), and the MITRE ATT&CK framework. As a part of our work, we have expanded the FMECA-ATT&CK approach to assessing cyber risks related to systems with artificial intelligence components in cyber-enabled autonomous ships (e.g. autonomous engine monitoring and control). This new capability was developed using the information and semantics encoded in the MITRE ATLAS framework. FMECA-ATT&CK has been adopted due to its comprehensive and adaptable nature and its promising venue for supporting continuous cyber risk assessment. It helps evaluate the cyber risks associated with the complex and state-of-the-art operational technologies on board autonomous ships. The cyber risk assessment approach assists cybersecurity experts in aligning mitigation strategies for the cyber defence of autonomous ships. It also contributes towards advancing overall cybersecurity in the maritime industry and ensures the safe and secure sailing of autonomous ships. Our key findings after applying the proposed approach against a model of an autonomous cargo ship is the identification of the Navigation Situation Awareness System (NSAS) of the ship as being at the highest risk followed by the Autonomous Engine Monitoring and Control (AEMC) system. Additionally, we identified 3 high, 48 medium, and 5776 low risks across 29 components.

Ship pitch prediction method based on LSTMC and multi-head attention

When ships sail in the sea, ship motion is unstable and stochasticity due to the ever-changing weather and marine conditions. Aiming to address the issue of low prediction accuracy in traditional prediction methods, short term predictions of ship pitch at 1 step, 3 steps, 6 steps, and 12 steps in advance are conducted, and the impact of input-output ratios on the prediction model is studied. The seven types of data of the marine environment and ship motion are taken as model inputs, with pitch as the model output. When predicting 1 step in advance, a prediction model based on LSTM and multi-head attention (LMA) is proposed. This model firstly uses LSTM layer to extract the temporal feature of the input sequence, and then uses the multi-head attention layer to assign larger weights to the key information to enhance prediction accuracy. When predicting 3 steps, 6 steps, and 12 steps in advance, as the input-output ratio increases, the length of the input sequence keeps growing. The model needs to sufficiently capture the local spatial characteristic and long-range dependency between multi-variable inputs, a deep prediction model based on Conv2d and LMA model is proposed. The model firstly uses two-dimensional convolution layer to extract local spatial feature of long sequences, and then through the attention layer, assign larger weights to temporal information and spatial information that are conducive to continuous prediction in order to enhance prediction accuracy. Research on the input-output ratio indicates that, as the number of predicted steps increases, the appropriate ratio continuously decreases, but the length of the input sequence keeps increasing. Finally, four evaluation metrics are used to evaluate the proposed algorithms on real ship data, and the prediction stability and accuracy of the LMA model and the LCMA model are also verified.

Optimization And Implementation of Waste Management Planning on Indonesian Flag Non-Convention Ships Sailing in Indonesian Waters

Abstract Waste is one of the objects of concern on ships, especially in terms of its storage and disposal, where more attention must be given to all ships with a gross tonnage of one hundred or more. Every ship certified to carry fifteen people or more, and every fixed or floating platform must have a waste management planning on ship, which includes written procedures for minimizing, collecting, storing, processing and disposing of waste including the use of equipment on the ship. In discussing this material, the researchers analyze the procedures and handling of waste disposal on Indonesian-flagged non-conventional ships. The method used in this research was the case research method. Data collection techniques included observation, interviews and library research methods. The research results show that on Indonesian-flagged non-conventional ships entering the Port of Makassar, there was still waste thrown into the sea, especially by crew members who did not comply with the waste management procedures regulated in The International Convention for the Prevention of Pollution from Ships Annex V. Ships - Non-conventional ships had not handled waste in accordance with The International Convention for the Prevention of Pollution from Ships 73/78 regulations due to various factors, one of which is that there is no equipment for handling waste in the ship and the lack of understanding of ship crew members in protecting the maritime environment. It is recommended that the company supervise the handling of waste in the ship and on the other hand, the port management must prepare waste storage facilities.

Proposal of a New Control System Making Use of AI Tools to Predict a Ship’s Behaviour When Approaching the Synchronism Phenomenon

In spite of the IMO’s efforts to improve the safety of intact stability on ships, synchronous rolling still causes large rolling angles, resulting in a very dangerous situation on board. The implementation of automatic tools to predict this undesirable situation has not been widely implemented. Furthermore, the safety of ship stability is not the only responsibility of people involved in the design process, so ship operators must have enough knowledge to predict and avoid these dangerous situations well in advance. Therefore, from a theoretical point of view, in the first part, this paper aims to present a valuable guiding tool for ship operators in order to predict synchronous rolling and avoid undesirable situations on board by making use of only empirical observations of the wave profile and moments. With this purpose, mathematical models are first proposed, with the ship sailing in the worst condition, i.e., with and without considering the damping factor, at zero speed and considering the influence of any pure beam and trochoidal waves. Relevant results shown provide the exact time and wave profile at which the maximum rolling angles are reached. In the second part of the paper, a new control system making use of AI tools is proposed in order to be used by ship operators on board, avoiding dangerous situations. Finally, the results are validated using a set of ship rolling simulations for the most common and representative ship loading conditions and wave periods.

Quay-to-quay mission with autonomous docking: a model-scale experimental validation

Transport of cargo by short-sea shipping is at the forefront of the European Union's transportation policy. It has the promise to alleviate congested land transport and decrease pollution [European Commission. 2021. Putting European transport on track for the future]. However, the shortage of qualified personnel might impede this solution. Autonomous sailing of ships could help, especially if the whole trip is automated. In this study a control system is designed that is capable of sailing a round-trip with a model-scale feeder vessel in Marin's Seakeeping and Manoeuvring Basin. The Guidance-Navigation-Control framework is used to sail this journey with attention given to smooth switching between the operational modes. A set of experiments is conducted to validate the controller and identify crucial parts in the operation. The experiments showed that the controlled vessel can sail a round-trip with different levels of waves and wind disturbances coming from different directions. Furthermore, the round-trip can be modified such that the approach angle to the quay changes and the ship still successfully docks at the quay. It was found that the approach to the quay is most difficult during transition from high to low speed, when the bow thrusters have yet to become effective, and a large change in course is needed. This can be circumvented by changing the trajectory to the quay to have a longer straight approach, or it can be corrected when the bow thrusters become active.

Judicial Review of the Obligation to Have an Approval Letter for Sailing in the Crime of Sailing in Indonesia

Shipping is controlled by the state and carried out by the Government. Sailing approval letter can be given by a Harbor Master to the ship user or owner if the ship has fulfilled several important requirements. The aim of research is to find out how the obligation a sailing approval letter is regulated and what the legal consequences of not having a sailing approval letter are. Research methods used a normative juridical method with analytical descriptive specifications. The results of the research found that ship sailing is required to have a Sailing Approval Letter issued by the Harbormaster as stated in article 219 paragraph (1) of Law Number 17 of 2008 concerning Shipping. Meanwhile, the legal consequences if you do not have a letter of approval from the harbormaster will be threatened with imprisonment and find as regulated in Article 323 Paragraph (1) of Law Number 17 of 2008 concerning Shipping and Law Number 8 of 1981 concerning Criminal Procedure Law, as well as statutory regulations.

Numerical investigations of the restriction effects on a ship navigating in pack-ice channel

This paper adopts Computational Fluid Dynamics (CFD) method and Discrete Element Method (DEM) to simulate a ship navigating in pack-ice channel considering the effects of channel restriction. First, from the simulations of the ship sailing in open-water channel by CFD, it is found that the effects of channel width on water resistance is more pronounced than the impacts by level-ice thickness. Then, based on the stable and converged flow field obtained by CFD simulations, the CFD-DEM coupling method is applied to reveal the effects of channel width and level ice thickness on ship-ice-water interactions and ice resistances at different ship speeds. The results indicate that as the channel width decreases, the accumulation of pack ice in the areas of bow and midship intensifies. The ice resistances on the bow and midship increase notably, and the lateral ice forces exhibit pronounced asymmetric and random characteristics. In extremely narrow pack-ice channels, lower ship speed results in lager ice resistance and lateral ice force on the ship. In addition, as the level ice thickness decreases, the pack ice is more easily squeezed below the level ice, resulting in the decreases of ice resistance and lateral ice force.

Asymmetric water entry of a wedged grillage structure investigated by CFD-FEM co-simulation

When a ship sails in ocean waves the relative movement between ship and wave is very complex. Slamming of bow or stern structures usually occurs in a manner of asymmetric oblique water entry. This implies that both the deflection angle θ and velocity angle α will likely grow to a large value at the same time. In this study, the hydrodynamics problem associated with the asymmetric and oblique water impact of a three-dimensional wedge is investigated using a partitioned CFD-FEM two-way coupled numerical tool by coupling the commercial software STAR-CCM+ and Abaqus within the framework of SIMULIA co-simulation engine. The hydrodynamic problem is solved by the CFD software using overset grid technique while the structural dynamic response is solved by the FEM software. Validation of the numerical results is conducted by using existing test results of symmetric water entry of the wedge first. Then the behaviours of movements, slamming pressure and structural response of the wedge structure during asymmetric water entry by varying the deflection angle θ or the velocity angle α or both are systematically and comparatively investigated. This research shows that the present numerical simulation well predicts both the fluid and structural dynamic characteristics such as fluid cavity and structural stress concentration of asymmetric impact problems, which has potential engineering application value in the field of ship design and slamming loads evaluation.

Analysis of Hybrid Ship Machinery System with Proton Exchange Membrane Fuel Cells and Battery Pack

As marine traffic is contributing to pollution, and most vessels have predictable routes with repetitive load profiles, to reduce their impact on environment, hybrid systems with proton exchange membrane fuel cells (PEMFC-s) and battery pack are a promising replacement. For this purpose, the new approach takes into consideration an alternative to diesel propulsion with the additional benefit of carbon neutrality and increase of system efficiency. Additionally, in the developed numerical model, control of the PEMFC–battery hybrid energy system with balance of plant is incorporated with repowering existing vessels that have two diesel engines with 300 kWe. The goal of this paper is to develop a numerical model that analyzes and determines an equivalent hybrid ship propulsion system for a known traveling route. The developed numerical model consists of an interconnected system with the PEMFC stack and a battery pack as power sources. The numerical model was developed and optimized to meet the minimal required power demand for a successful route, which has variable loads and sees ships sail daily six times along the same route—in total 54 nautical miles. The results showed that the equivalent hybrid power system consists of a 300 kWe PEMFC stack and battery pack with 424 kWh battery and state of charge varying between 20 and 87%. To power this new hybrid power system, a hydrogen tank of 7200 L holding 284.7 kg at pressure of 700 bar is required, compared to previous system that consumed 1524 kg of diesel and generated 4886 kg of CO2.

Discrete Distribution Model of Ship Noise Source in Shipping Channel

Ship noise plays an important role in low-frequency ocean ambient noise. With the increasingly busy sea traffic, the randomness of the spatiotemporal distribution characteristics of ship noise is also increasing. However, most ships sail in a relatively fixed range in different sea areas. Most of the previous studies assumed that the ship noise sources in shipping channel satisfy a uniformly distribution, actually all kinds of large ships are not uniformly distributed in the shipping channel, and there are also many small boats distributed on the channel that contribute significantly to low-frequency ocean ambient noise. The channel within a certain sea area will be divided into different regions, and ship information (AIS) in different regions will be analyzed statistically in this paper. It is assumed that the ship noise sources in different channel regions are discrete point noise sources that obey a certain spatiotemporal statistical distribution, combined with the noise source level models of different types of ships to form a discrete source model of ship noise in shipping channel. Using the ray propagation theory considering the horizontal refraction of sound energy, the vertical distribution of the ship noise level in this sea area is calculated, and compared with the vertical noise level distribution of ship noise source uniform distribution model, the variation range of noise level vertical distribution of two models is close calculated noise level (such as maximum and minimum values) is consistent with the measured data. The discrete source model of ship noise established in this paper may provide a technical support for predicting low-frequency ambient noise characteristics near the channel.

Numerical Study of a Model and Full-Scale Container Ship Sailing in Regular Head Waves

In the present study, the added resistance, heave, and pitch of the KRISO Container Ship (KCS) in waves, at both model scale and full scale, are predicted numerically in regular head waves, for four wavelengths and three wave heights. The ISIS-CFD viscous flow solver, implemented in the Fidelity Fine Marine software provided by CADENCE, was employed for the numerical simulations. The spatial discretization was based on the finite volume method using an unstructured grid. The unsteady Reynolds-averaged Navier–Stokes (RANS) equations were solved numerically, with the turbulence modeled by shear stress transport (k-ω) (SST). The free-surface capturing was based on the volume-of-fluid method. The computed solutions were validated through comparisons with towing test data available in the public domain. To predict the uncertainties in the numerical solution, a systematic grid convergence study based on the Richardson extrapolation method was performed for a single wave case on three different grid resolutions. Specific attention was given to the free-surface and wake flow in the propeller plane. The purpose was to compare the numerical results from the model- and full-scale tests to examine the scale’s effect on the ship’s performance in regular head waves. The comparison between the model scale and full scale showed obvious differences, less accentuated for the free-surface topology and clearly observed in terms of boundary layer formation in the propeller’s vicinity.

“The Stepping Stones of Empire”: Conrad, Coal, and Oceanic Infrastructure

The political geography of empire transformed with the Victorian rise of steam power and its infrastructure, especially with the emerging dominance of steam as the primary means of transoceanic travel and shipping. Oceanic infrastructure was a new feature of the British Empire especially in the period after 1860, when steamships were increasingly replacing sailing ships and when the material exigencies of fueling and refueling required the installation of coaling stations to support long-haul transport for steam-powered ships. In this essay we explore how these changes registered in literature and discourse, with Joseph Conrad as our prime example. We analyze two of Conrad's works that feature coaling stations and steam-carrying, Victory (1915) and The Mirror of the Sea (1906). Drawing on infrastructure studies, critical ocean studies, and the energy humanities, we make a case for more attention to oceangoing coal as part of a broader reconsideration of empire in the Anthropocene. We also make a case for Conrad as one of the great observers of environmental-infrastructural change in the early fossil-fuel era, worth revisiting now as both witness and interpreter.