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Reducing the shipping sector's contribution to climate change requires urgent emission reductions this decade. Both weather routing and wind propulsion offer immediate solutions, where combining sails with efficient routing amplifies the performance of each technology. However, while large emission savings are theoretically available, the impact of stochastic uncertainty from wind forecasts is unknown. Here, we present a novel approach that exploits fuel consumption calculations from over a thousand departures across three routes to characterise stochastic uncertainty. We show that routes with ideal wind conditions and long voyage times are most sensitive to uncertain forecast inputs, reducing savings from Flettner rotors and weather routing by up to 44% when a priori weather routing strategies are used. This paper further shows how an adaptive weather routing strategy can be used as an accurate prediction tool to reduce uncertainty on all routes investigated, reliably amplifying carbon savings from Flettner rotors by between 1.16 and 2.48 times typical great circle route savings. Overall, this paper provides greater assurance around the previously estimated carbon savings that serves to strengthen confidence in a wind-assisted decarbonisation strategy and its potential to provide essential emission reductions this decade.

This paper reviews challenges of relevance to the future development of Arctic sustainable shipping by considering future demands for vessel types, available alternative energy sources, and novel technologies. Results reveal the need to extend existing concept ship design methods to account for the holistic yet sustainable design of Arctic vessels. Accordingly, the paper introduces a decision support framework for holistic and sustainable optimization of the concept design of Arctic ships for different cold regions and purposes of operation. The method presented simultaneously accounts for eco-efficiency, cost-efficiency, and safety. Demonstration for the case of a battery-driven Arctic offshore wind farm service and offshore support vessels shows that optimized designs could outperform their existing environmentally and economically efficient counterparts.

Design and verification of autonomous vessels represent a major interdisciplinary engineering challenge due to the combination of high system complexity and the interaction with dynamic, uncertain, and unstructured environments. This paper investigates the use of contract-based methods to address both design and verification challenges of control systems for autonomous vessels. The paper first presents a formal framework for specification of components and assume-guarantee contracts using the syntax of the Z3 automated theorem prover. Then, the paper proposes a methodology for contract-based verification using the formal framework. The methodology is divided into 4 steps: (1) Hazard identification between the autonomous vessel and the operative environment in order to define the top-level component and contract, (2) stepwise refinement of the top-level component into detailed sub-components and contracts, (3) definition of test setups for simulation-based testing to verify that components meet their contract, and (4) applying a recursive procedure for contracts-based system verification. The framework and methodology are demonstrated the in a case study with an autonomous passenger ferry.

Funding Information: In order to have a holistic perspective and elements for the shipping system, the paper targets a comprehensive and long-term project specifically focusing on holistic safe polar shipping as the analysis basis. The long-term project has coherent focus and involves fundamental elements and holistic views towards safe polar shipping, thus provides a good basis for analysis. The polar project has two stages namely CEARCTIC (Centre of Excellence for Arctic Shipping and Operations) and CEPOLAR (Centre of Excellence for Scenario-based Risk Management in Polar Waters) starting from 2013 to 2022 focusing on different aspects regarding safe shipping in ice-covered waters. It is funded by Lloyd's Register Foundation and combines the research strengths from five universities: Aalto University, Hamburg University of Technology, Memorial University of Newfoundland, Norwegian University of Science and Technology and University of Helsinki. Extensive research work has been carried out in the framework of risk management towards safe shipping and the outcomes are mainly published in scientific journal and conference papers, where various subjects, research directions and methods have been focused and applied.Table 13 shows the toolbox under ecosystem impact topic. The model P3 adopts index-based approach to assess the vulnerability of Arctic biota. The resource and skill level needed are considered as medium and low respectively. The uncertainty is discussed to some extent; therefore, it is considered as a medium level SoE, which gives a M applicability level. The potential limitation is that the model still uses a number of judgements and uniform distribution due to lack of relevant data. In addition, the model does not include the spatial features for both oil spill and Arctic biota, which limits the practical utilization. The model P13 aims to estimate the probability of marine fish cell damages to oil spill. The required resource and skill level are low, and the model considers validation through a general comparison. Therefore, validation level is considered as Medium, and the final applicability level is rated as M as well. The limitation of the model is that the CPT states are limited and the modelling of structure and CPTs lack SoE supports. This project has received funding from the Lloyd's Register Foundation, a charitable foundation, helping to protect life and property by supporting engineering-related education, public engagement and the application of research www.lrfoundation.org.uk. Funding Information: This project has received funding from the Lloyd's Register Foundation , a charitable foundation, helping to protect life and property by supporting engineering-related education, public engagement and the application of research www.lrfoundation.org.uk . Publisher Copyright: © 2022 The Authors With the climate change, polar sea ice is diminishing. This, on one hand, enables the possibility for e.g., Arctic shipping and relevant resource exploitation activities, but on the other hand brings additional risks induced by these activities. Increasing research focuses have been observed on the relevant topics in the complex and harsh polar environment and its fragile ecosystem. However, from risk management perspective, there is still a lack of holistic analysis and understanding towards safe shipping in the ice-covered waters and its available models applicable for managing risks in the system. Therefore, this paper aims to establish a framework and analysis for better understanding of this gap. The paper targets a comprehensive and long-term project specifically focusing on holistic safe shipping in ice-covered waters as the analysis basis. It firstly creates a holistic framework for the shipping system in ice-covered waters and then implements review and analysis of project publications on their overall features. Quantitative prediction models are selected for a structured applicability analysis. Furthermore, an extensive review outside the project following the elements established for the holistic shipping system is conducted so that this paper provides an overview of models for the shipping system in ice-covered waters, addressing the status of the current toolbox. Moreover, it helps to identify the next scientific steps on risk management of shipping in ice-covered waters.

Cyber-resilience is an increasing concern in developing autonomous navigation solutions for marine vessels. This paper scrutinizes cyber-resilience properties of marine navigation through a prism with three edges: multiple sensor information fusion, diagnosis of not-normal behaviours, and change detection. It proposes a two-stage estimator for diagnosis and mitigation of sensor signals used for coastal navigation. Developing a Likelihood Field approach, a first stage extracts shoreline features from radar and matches them to the electronic navigation chart. A second stage associates buoy and beacon features from the radar with chart information. Using real data logged at sea tests combined with simulated spoofing, the paper verifies the ability to timely diagnose and isolate an attempt to compromise position measurements. A new approach is suggested for high level processing of received data to evaluate their consistency, that is agnostic to the underlying technology of the individual sensory input. A combined parametric Gaussian modelling and Kernel Density Estimation is suggested and compared with a generalized likelihood ratio change detector that uses sliding windows. The paper shows how deviations from nominal behaviour and isolation of the components is possible when under attack or when defects in sensors occur., Comment: 18 pages, 21 figures

The paper validates novel structural reliability Gaidai-Fu-Xing (GFX) method, particularly suitable for multi-dimensional structural responses, versus well established bivariate statistical method, that is known to accurately predict two-dimensional system extreme response levels. Classic reliability methods, dealing with time series do not have an advantage of dealing easily with system high dimensionality and cross-correlation between different dimensions. An operating Jacket located in the Bohai bay was taken as an example to demonstrate the proposed methodology. Novel state of art bimodal extrapolation technique was applied to predict system reliability with five years return period, which is of practical importance for design of fixed offshore structures. Unlike other reliability methods the new method does not require to re-start simulation each time system fails, in case of numerical simulation. In case of measured structural response, an accurate prediction of system failure probability is also possible as illustrated in this study. Jacket offshore platform subjected to large environmental wave loads, thus structural stresses in different structural critical locations were chosen as an example for this reliability study. The method proposed in this paper opens up the possibility to predict simply and efficiently failure probability for nonlinear multi-dimensional dynamic system as a whole.

The International Maritime Organisation (IMO) requirements for the control of greenhouse gas (GHG) emissions of shipping have raised interest in ship manoeuvrability in adverse weather conditions when compliance is accomplished simply by reducing the main engine power. In response, the IMO has adopted the guidelines for determining minimum propulsion power to maintain the manoeuvrability of ships in adverse conditions. In the present paper, a systematic investigation on the manoeuvrability of a ship with different low advance speeds in adverse weather conditions was conducted by means of an unsteady Reynolds-Averaged Navier-Stokes solver. The numerical results demonstrated the contribution of low advance speeds to the course-keeping and turning circle manoeuvre, providing a practical insight into the manoeuvring performance of a ship with minimum propulsion power in adverse weather conditions. For the course-keeping control, the ship experienced more aggressive steering as the propeller revolution decreased in the oblique waves, while it appeared that the difference in the rudder deflection according to the change in the propeller speed in the head, beam, and following waves is negligible. The difficulty of the low speed turning manoeuvre was clearly noted when the direction of the incident wave was opposite to the direction towards which the ship intended to turn. It is believed that this paper can also be impactful in improving the guidelines of minimum powering of ships for safe navigation in adverse weather conditions.

Digital Twins have much attention in the shipping industry, attempting to support all phases of a vessel’s life cycle. With several tools appearing in Digital Twin software suites, high-quality manoeuvring and performance prediction remain cornerstones. Propulsion efficiency is in focus while in service. Simulator-based training is in focus to ensure safety of manoeuvring in confined waters and harbours. Prediction of ships’ velocity and turn rate are essential for correct look and feel during training, but phenomena like dynamic inflow to propellers, bank and shallow water effects limit simulators’ accuracy, and master mariners often comment that simulations could be in better agreement with actual behaviours of their vessel. This paper focuses on digital twin enhancements to better match reality. Using data logged during in-service operation, we first consider a system identification perspective, employing a first-principles model structure. Showing that a complete firstprinciples model is not identifiable under the excitation met in service, we employ a Recurrent Neural Network to predict deviations between measured velocities and the model output. The outcome is a hybrid of a first-principles model with a machine learning generic approximator add-on. The paper demonstrates significant improvements in prediction accuracy of both in-harbour manoeuvring and shallow water passage conditions.

Current EEDI (Energy Efficiency Design Index) regulations striving to reduce the installed engine power on new ships for a low EEDI may lead to underpowered ships having insufficient power when operating in adverse sea conditions. In this paper, the operational safety of a low-powered ocean-going cargo ship operating in adverse sea conditions has been investigated using an integrated ship propulsion, manoeuvring and sea state model. The ship propulsion and manoeuvring performance, especially the dynamic engine behaviour, when the ship is sailing in heavy weather and turning into head sea, have been studied. According to the results, the dynamic engine behaviour should be considered when assessing the ship operational safety, as the static engine operating envelope is inadequate for the safety assessment. The impact of PTO/PTI (power-take-off/in) operation and changing propeller pitch on the ship thrust availability in adverse sea conditions have also been investigated. To protect the engine from mechanical and thermal overloading, compressor surge and over-speeding during dynamic ship operations and/or in high sea states, the engine and propeller should be carefully controlled. The paper shows that if in (heavy) adverse weather the propeller pitch can be reduced or if the shaft generator can work as a motor (PTI), more thrust can be developed which can significantly improve the operational safety of the ship.

Standards for environmental impact, safety and operational performance of ships are becoming increasingly strict. In order to meet these standards, the performance of new ship designs must be predicted with an increasing level of detail and confidence. As present prediction methods lack realistic, dynamic behaviour of the ship's propulsion plant, there is a need for more advanced methods. In this paper, an open water test with Hardware in the Loop (HIL) functionality is proposed. HIL open water tests combine software and hardware components to emulate realistic behaviour of the ship's propulsion plant in the towing tank. It is known, however, that experiments in the towing tank are subject to viscous scale effects. In addition to this, shaft dynamics are distorted by a number of scale effects occurring inside the scale model propulsion system. In this paper, it is demonstrated with measurements that if corrections for these scale effects are applied, the dynamic interaction between the propeller and simulated engine system can be accurately emulated in the ship model basin.

The objective of this paper is to develop online risk models that can be updated as conditions change, using risk as one metric to control an autonomous ship in operation. This paper extends and integrates the System Theoretic Process Analysis (STPA) and Bayesian Belief Networks (BBN) with control systems for autonomous ships to enable supervisory risk control. The risk metric is used in a Supervisory Risk Controller (SRC) that considers both risk and operational costs when making decisions. This enables the control system to make better and more informed decisions than existing ship control systems. The novel control system is tested in a case study where the SRC can change: (i) which machinery system is active; (ii) which control mode to run the ship in; and (iii) which speed reference to follow. The SRC is able to choose the optimum machinery, control mode, and speed reference to maintain safe control of the ship over a route in changing conditions.

This paper presents an attempts towards creation of generalized models of ships manoeuvring area determination and ship performance created on the base of real simulation results. Those models are needed for better understanding of the safe navigation process in ports areas and its approaches and for risk analysis when no full information about the ships behaviour is available. The data coming from real time ship simulations that are conducted by experienced pilots and captains are applied in the study. In the first step, general regression models are created to determine manoeuvring areas and major correlations between basic parameters affecting the safe area needed for ships to navigate in restricted areas of ports and its approaches. In the second step, the ship performance models are created to describe the behaviour of the ship including human factors. The ship performance for long-term prediction of the navigation risk regarding the possibility of ships exceeding the channel limits, assumed as grounding or collision with a fixed structure are created by the method which consists of two developed models: (1) an ARMAX (Auto Regressive and Moving Average eXogenous) model is adopted to identify the ship steering dynamic system. With the help of this model, the outputs of the system (course, position, etc.) can be estimated based on the system input conditions (rudder, engine, etc.); (2) the stochastic sequences of the inputs for the first model used are generated using a semi-Markov model. In the paper the implementation of the semi-Markov model for rudder actions has been described. The study used input/output measurements from a ship-handling simulator to estimate the model parameters, so the human factor has been included in the models. The method allows us to extend the results obtained from the simulator to predict future conditions of the system outputs. Since the predicted results and using probabilistic approach, possible ship manoeuvring area margins will be identified and long - term assessment of the navigation risk can be realized.

The influence of scour on the lateral response of monopile foundations for offshore wind turbines is investigated in this paper. Application of lateral load-displacement (p-y) curves to predict the lateral pile behaviour is subject to uncertainty as many of the presently used design approaches have been derived for long, slender piles. These piles, with typical length/diameter ratios (L/D) of greater than 10 behave differently compared to rigid monopiles, with L/D typically less than 6. In this paper, centrifuge tests are conducted on a monopile model under various scour scenarios and p-y curves are derived from strain gauges embedded along the model pile wall. Global scour and two different shapes for local scour holes are studied. Using the piecewise polynomial method for extraction of p-y curves from sparsely distributed strain measurements, it is recommended to use a 4th order polynomial for the moment profile to extract soil reaction and a 7th order polynomial for the moment profile to calculate pile deflection. Results indicate that the pile behaviour is significantly influenced by the nature (size, shape) of the scour holes affecting the pile–soil system and suggest that the p-y curves should be appropriately modified to account for this behaviour.

This paper presents the design and dynamic analysis of a multi-column tension leg platform floating offshore wind turbine (TLP FOWT) with broken tendons. The proposed concept is based on a conventional Tri-Floater platform configuration but is especially optimized for an intermediate water depth of 60 m. Tendons are simulated to be broken at a specific time of interest. The hydrodynamic parameters and motion responses of the TLP FOWT have been calculated using the hydrodynamic analysis software WAMIT and ANSYS/AQWA. These parameters are then used in the simulation of coupled responses of the FOWT by the National Renewable Energy Laboratory's analysis suite of tool, FAST. The tendon failure has been investigated to examine the system performance under the accidental limit states (ALS) described in the design code DNV-RP-0286.A series of dynamic analysis under operational and extreme environmental conditions (with 12 different load cases) are carried out with the combination of wind and waves. The results demonstrate that the turbine is able to remain highly stable during the 3-h simulations conducted. The platform's response amplitude operators (RAOs) evaluated show good stability in heave and pitch. The tendon failures affected the FOWT's heave, pitch and roll motions, hence its natural frequencies, and the tension in the non-broken tendons. The average tensile force in the line adjacent to the broken line is found to be doubled, while the safety factors as specified in DNV-OS-E301 are remained within the recommended value. This paper provides further insights into the hydrodynamics of the multi-column TLP FOWT, with the aim to provide new information to the offshore wind research community.

Empirical models based on full-scale or model scale measurements are often preferred over high-fidelity numerical models when real-time predictions for ice actions on ships and floating offshore platforms are needed. This paper presents multiple regression-based empirical models for predicting a Dynamically Position (DP) controlled vessel and managed ice-field interactions developed using a large dataset from ice basin tests of two distinct DP-controlled vessels. The authors carried out a detailed analysis of measurements from two physical modelling programs for developing a unique database. A multiple regression modelling procedure was developed to predict the time-averaged and average peaks of forces and moment of the DP-controlled vessels due to ice actions in multiple configurations of managed ice-field. The models were validated using model scale measurements for the predictions of time-averaged and average peak responses. The models were then used to evaluate the effects of each ice-field parameter on vessel forces and moment and interaction event parameters. The models presented in this paper showed reasonable accuracy in predicting the effects of several ice-field parameters on the forces and moments of two distinct DP-controlled vessels in a range of realistic operating conditions.

Floating breakwaters play an important role in protecting harborage and marine structures from wave impact. Traditional floating breakwaters (FBs) are not applicative for their ineffectiveness in low frequency waves attenuation. Based on the idea of reducing equivalent stiffness, this paper proposes a FB with nonlinear stiffness to improve the wave attenuation performance. The eigenfunction expansion matching method (EEMM) and multi-harmonic balance method (MHBM) are corporately applied to solve the new model involving nonlinear coupling problem of water waves and floating structures. A pile restrained FB with quasi-zero-stiffness (QZS) is taken as an example to verify the feasibility of the hybrid analytical model and to reveal the wave attenuation mechanism of the nonlinear breakwater. The comparison between nonlinear FB and linear FB shows that nonlinear FB can effectively widen the attenuation frequency bandwidth. The conception of nonlinear floating breakwater proposed in this study provides a new technical idea for attenuating low frequency waves and the hybrid solution method adopted in this paper may be extensible to other wave-structure nonlinear coupling problems.

In an offshore environment, offshore wind energy resources are more available and stable, but the investment cost is much higher than that of onshore wind. The installation cost is a crucial factor of the investment. With the increasing number of planned and approved offshore wind farms, offshore wind turbine installation and relevant operations have received tremendous attention. Therefore, expediting the turbine-structure mating operations through a higher level of automation in offshore wind turbine installations may provide important economic benefits. To achieve a higher automation level and reduce the weather waiting time during the installation of offshore wind turbines, a flexible simulation-verification framework with high fidelity is needed. However, state-of-the-art wind turbine numerical analysis code is neither convenient nor open enough for applications concerning the design and verification of control algorithms. MATLAB/Simulink is among the most widely utilized numerical platforms by control engineers and researchers. This paper describes the development of a modularized blade installation simulation toolbox for the purpose of control design in MATLAB/Simulink. The toolbox can be used to simulate several blade installation configurations, both onshore and offshore. The paper presents the key features and equations of the different modules, exemplified by a single blade installation operation. Code-to-code verification results are presented and discussed with both quasi-steady wind and three-dimensional turbulent wind field. This is a submitted manuscript of an article published by Elsevier Ltd in Ocean Engineering , 19 June 2018.

MEPC 70 foresees a greenhouse gas reduction strategy will be in force in 2018. Researchers are striving to investigate different GHG reduction technologies to determine their feasibility in the aspect of both environment and economy. However, the evaluations are not specific or comprehensive so this paper presents a systematic evaluation approach to guide policy makers to evaluate the performances and to help ship owners to select suitable reduction technologies. One carbon reduction method proposed by authors was proved to be cost effective and this paper applies life cycle analysis focusing on all stages of ship life to investigate, determine and compare the feasibility of this methods in the aspect of environmental and cost impact which are two significant standard for the assessment. The results indicate the application of reduction method leads to a lower global warming potential when the carbon reduction target is increased. Oppositely, the economic benefits increased while complying with strict regulation. This paper also indicates to achieve carbon reduction target set up by regulation, a marginal target will be necessary. Evaluation of carbon reduction method using life cycle assessment is also recommended to policy makers and ship owners to provide them comparable results and reasonable decision makings.

This paper provides a general insight into the importance of proper hull maintenance and suggests an optimal maintenance strategy for ship operators from both an economic and environmental point of view. Results of life cycle assessment show that significant cost reductions can be obtained by renewing steels every 10 years within the proposed hull maintenance strategy. The assessment also indicates that annual hull inspections and re-coating can contribute to reducing hull resistance and hence fuel consumption, thereby reducing the overall operating costs and emissions. This paper provides ship owners a direct relationship between effective hull maintenance and the reduction in maintenance cost. It also provides information to inform policy makers of the benefits of following a maintenance optimization strategy. This study shows that life cycle assessment can provide information to shipyards and owners to facilitate reliable long-term maintenance decisions.

Measurement, data transfer, modelling, controller systems are the main subjects of interdisciplinary area during prototyping of marine automatic control systems. Experimental parameter identification is an essential step for modelling and control system design are in question for various marine applications. The selection of variables to be measured, type of measurement sensors, type of control algorithms and controller systems, communication, signal conditioning are all important topics for parameter identification and real-time control applications in maritime engineering. The objective of this paper is to present a brief review of these important topics based on our case studies, such as ship roll motion reduction control, optimal trim control of a high speed craft, and dynamic position control of underwater vehicles. These projects involved extensive dynamic modelling, simulation, control algorithm design, real-time implementation and full-scale sea trials. In this paper, the presented methods, and the required characteristics of the marine control systems are demonstrated with the results obtained by the simulation studies and full-scale sea trials. Also, insight into the selection of hardware and software components for mechatronic applications in marine engineering is provided.

This paper presents two novel globally exponentially stable position estimators using hydroacoustic measurements from a single transponder to several transceivers on the vehicle. A comparison study of these and several existing filters is conducted with both experimental and simulated data. Two classes of filters for position estimation are compared: filters expressing the position of an underwater vehicle in the body-fixed and north-east-down coordinate frames. The comparison study showed that the latter formulation yields lower estimation errors. Furthermore, one of the novel filters developed in this paper using the north-east-down formulation is found to serve well as a compromise between performance, theoretical stability, and computational complexity relative to the near-optimal linearization-based filters with which it is compared. © 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/).

The level of automation around the world has grown significantly over the past few decades, and continues to do so. There are many reasons behind this trend, such as safety and potential economic benefits. However, when automation fails or behaves unexpectedly, the impact on the human operator can be severe. In a safety critical operation, such as on the bridge of a ship, the consequences could be catastrophic. The research presented in this paper aims to improve understanding in this important area of study for the maritime industry. An experiment was conducted to assess the awareness of deck officer cadets in the recognition of a developing emergency situation due to failure of the autopilot. Using the results from this experiment and experiences from the aviation industry, the paper provides a potential strategy to improve automation monitoring and accuracy of situation awareness. This has led to the identification of opportunities to improve human-machine interaction.

The continuous increase in marine traffic and the construction of several offshore installations has led to a serious concern regarding the risks to offshore platforms from ship collisions. The main aim of this study was to carry out a probabilistic collision-risk analysis for offshore platforms exposed to powered collisions with passing vessels using an automatic identification system (AIS) database. The paper first describes the statistical distribution of the ship traffic under study and then considers how this information can be effectively used to estimate collision frequencies and impact energies for various categories of vessel, based on a simple probabilistic method. The effects of various collision mitigation measures, such as the use of enhanced collision alarming devices and the ability of platforms to rotate using thrusters, are considered in the frequency calculations. The risk method presented in this paper can be applied in the design and development phase of both new and existing platforms.

Fault-tolerance is crucial to maintain safety in offshore operations. The objective of this paper is to show how systematic analysis and design of fault-tolerance is conducted for a complex automation system, exemplified by thruster assisted Position-mooring. Using redundancy as required by classification societies' class notations for offshore position controlled vessels, the paper shows how violations of normal behaviour of main components can be detected and isolated. Using a functional service philosophy, diagnosis procedures are auto-generated based on provable correct graph analysis methods. Functional faults that are only detectable, are rendered isolable through an active isolation approach. Once functional faults are isolated, they are handled by fault accommodation techniques to meet overall control objectives specified by class requirements. The paper illustrates the generic methodology by a system to handle faults in mooring lines, sensors or thrusters. Simulations and model basin experiments are carried out to validate the concept for scenarios with single or multiple faults. The results demonstrate that enhanced availability and safety are obtainable with this design approach. While methods are introduced at a tutorial level, the paper is original by providing a total Position-mooring system design that ensures resilience to any single fault and to selected multiple faults.

Undesired wave reflections, which occur at domain boundaries in flow simulations with free-surface waves, can be minimized by applying source terms in the vicinity of the boundary to damp the waves. Examples of such approaches are absorbing layers, damping zones, forcing zones, relaxation zones and sponge layers. A problem with these approaches is that the effectivity of the wave damping depends on the parameters in the source term functions, which are case-dependent and must be adjusted to the wave. The present paper presents a theory which analytically predicts the reflection coefficients and which can be used to optimally select the source term parameters before running the simulation. The theory is given in a general form so that it is applicable to many existing implementations. It is validated against results from finite-volume-based flow simulations of regular free-surface waves and found to be of satisfactory accuracy for practical purposes., Comment: Please cite the journal publication: http://www.sciencedirect.com/science/article/pii/S0029801817306066 A computer code to evaluate the theory given in the paper is available as free software: https://github.com/wave-absorbing-layers/absorbing-layer-for-free-surface-waves arXiv admin note: text overlap with arXiv:1705.06937

The paper is concerned with the use of the open source computational fluid dynamics software package, OpenFOAM® for predicting and analysing the behaviour of a semi-immersed horizontal cylinder subject to different types of wave conditions. This study involves two separate cases of wave-structure interaction involving a semi-immersed horizontal cylinder, which may represent the simplified form of a cylindrical component of a wave energy converter. First, the flow around a fixed semi-immersed horizontal cylinder subject to regular waves is studied, in which the horizontal and vertical forces are computed and compared to linear wave theory and available experimental data. Further, a semi-immersed horizontal cylinder with a prescribed oscillatory vertical motion is considered to determine the surface wave elevations generated by the motion of the cylinder. The measured numerical surface elevations are also compared with theoretical predictions and experimental data. Both cases considered in this paper are simulated in a numerical wave tank where wave relaxation zones are utilised to avoid wave reflections. It is concluded that the numerical data produced by OpenFOAM® provide good overall agreement within the limitations of the relevant theory and experimental data.

This paper investigates the use of the permeable surface integral formulation based on the Ffowcs Williams–Hawkings Equation to predict the noise field generated by marine propellers. After derivation of the integral formulation, first, in the framework of potential flows, its main features are discussed for case-studies that allow a straightforward interpretation of the results achieved. Then, issues related to the use of pseudo-compressible, performance-oriented CFD solvers to detect the sources of sound over the permeable surface of integration are carefully examined. Among them, the occurrence of undesired boundary reflection effects and the strategies for their mitigation are discussed. The end-cap problem, open v s closed surface strategies, placement/sizing of the permeable surface and CFD grid topology suitability for hydroacoustic purposes are further topics considered in the paper. In order to provide guidelines and best practices for FWH permeable-surface hydroacoustics, the strategic choices made in determining the numerical predictions are discussed in detail. As one of the most interesting outcomes of the numerical investigation, it has been proven that accurate noise predictions are achievable through tailored CFD grid stretching capable of avoiding boundary reflections, an issue affecting hydroacoustics more than hydrodynamics.

Multi-purpose offshore structures are very complex systems to be designed as many different requirements have to be taken into account simultaneously. Experimental tests on scaled models can be very useful to verify structural behavior and to validate numerical models. The definition of the scale can play a key role in performing tests as high scales, closer to full-scale, are generally related to more reliable results. The present paper concerns the design of a wind turbine model for a large-scale model of a Multi-purpose offshore Platform developed within the EU project H2020 Blue Growth Farm. This project aims at developing an offshore farm, based on a modular floating structure that integrates wave energy converters and a wind turbine with aquaculture. The scale model of the complete structure will be deployed at the Natural Ocean Engineering Laboratory (NOEL). The paper will focus on the strategies adopted to scale 1:15 the DTU 10 MW wind turbine in order to represent both the main aeroelastic features and all the functionalities of a real machine. The complete design of the machine and its control will be also provided.

This paper examines the hydroelastic response of a monopile structure, supporting an offshore wind turbine. A new numerical simulation tool is presented, coupling a nonlinear potential flow solver to a structural model based on modal superposition. The hydrodynamic solver is based on the Weak-Scatterer (WS) approach and assumes small perturbations of the incident flow. A finite element method (FEM) solver is used to compute the modal parameters, which are then superposed to compute the dynamics of the system in time domain. Small deformations are assumed in the coupling. The two theories are tightly coupled in time domain. The theory of the coupling is fully described in the paper. The new coupled solver WS_CN-FEM is then applied to the case of a large diameter monopile. Results are compared to simulations using the Morison equation to compute the hydrodynamic loads and a beam element FEM model to compute the response of the structure and to experimental measurements made on a monopile-based offshore wind turbine model. The physical model has Froude-scaled geometry and natural frequencies, which allows an accurate validation of the hydroelastic numerical models including realistic flexible modes of the structure and wave–structure interaction. The results of WS_CN-FEM show a good agreement with the experimental measurements, and in particular on the first and second mudline bending moments’ harmonics in a series of regular waves of various wave steepness.

This article presents preliminary design formulas developed using a database of container ships built since 2015. Artificial neural networks and multiple nonlinear regressions with randomly searched functions were used to develop these formulas. The use of random search for nonlinear functions in a Multiple Nonlinear Regression model gave estimates which were just as precise as estimates created by the artificial neural network. All equations presented in this paper could have practical application for the estimation of dimensions, such as: length between perpendiculars, breadth, draught moulded and side depth. The equations were developed in relation to deadweight, TEU capacity and ship speed. These kinds of relationships have not been demonstrated before in ship theory. A statistical analysis showed that the main dimensions of the container ships can be estimated highly accurately by using the equations presented in the paper. The study showed that taking into account deadweight, TEU capacity and ship speed as three input parameters can improve the accuracy of an estimation by up to 44 percent, than when compared to the estimate accuracy of the design equations which are based on one input parameter.

This paper focuses on recent innovations in the methods used for external remote subsea pipeline inspection. An unmanned method is revealed, in which an Autonomous Underwater Vehicle (AUV), paired with an Unmanned Surface Vessel (USV) was utilised to complete inspections. Results are presented from a recent project, in which existing hardware and software were integrated and combined with automated workflows to form a solution, involving an AUV operated from a USV, with operations remotely controlled from shore. As inspection data was acquired, self-actuating workflows ran onboard the AUV, enabling data processing tasks to commence and QC messages/alerts to be transmitted to the control centre, this allowed execution of in-water mission adjustments. The primary focus of this paper is on the development and implementation of an automated, fully unmanned system for subsea inspection operations. Initially, a brief review is presented of recent developments in this field. Links are drawn between these wider developments and progress made within the project, and areas are highlighted where further work is required for realisation of a comprehensive unmanned pipeline inspection solution.

This paper presents a dynamic positioning control scheme for concrete caissons in an attempt to automate part of the manoeuvres which usually require a complex deploy of personnel and equipment for port infrastructures development. The aim of this paper is to propose a control scheme, which is able to provide a reduction in costs and an improvement in security for the dynamic positioning manoeuvres . To do so, a dual loop controller is developed and the unscented Kalman filter is applied for states and perturbances estimation. Furthermore, a control allocation algorithm is proposed based on anchoring lines and winches. Finally, some simulations are performed to verify the effectiveness of the proposed approach. The Spanish FEDER/Ministry of Science, Innovation and Universities — State Research Agency (Fig. 14) is greatly acknowledged for funding our research through SAFE Project (Desarrollo de un Sistema Autónomo para el Fondeo de Estructuras para Obras Marítimas), Grant Agreement: RTC-2017-6603-4. The authors would like to thank FCC CO as a collaborator in the development of the SAFE Project. R. Guanche also acknowledges financial support from the Ramon y Cajal Program (RYC-2017-23260) of the Spanish Ministry of Science, Innovation and Universities.

This paper focusses on the hydrodynamic performance of an unmanned vehicle system, consisting of a remotely operated underwater vehicle (ROV) that has to be launched and recovered autonomously from an Autonomous Surface Vehicles (ASV). The hydrodynamic model of the ASV/ROV coupled system is described in detail and solved numerically. The paper seeks to assess the overall performance of the ASV/ROV system, including the stability of the ASV, the ROV tidal current capacity and the required power of the launch and recovery winch system. The results demonstrate that this ASV/ROV system can complete the launch, holding and recovery tasks meeting stability for the given winch power requirements. The tidal current capacity of the ROV decreases with a larger target water depth. The maximum ROV umbilical tension is observed during steep wave instances when the ROV is in proximity to the ASV. A down-control force is demonstrated to be a suitable solution to limit the maximum tension within the umbilical rated force limits. This paper presents the methods and considerations for working towards a fully autonomous ASV/ROV system capable of autonomous inspection and maintenance missions. The work will be useful for practitioners and researcher working on autonomous offshore systems.

The future of wave energy converters lies in the design and realization of farms comprising of several devices, given the level of actual power flow for the individual devices and because of several operational issues. Therefore, not only the hydrodynamics of individual and isolated devices should be analysed, but interactions among devices within an array must also be carefully evaluated. In this paper, the authors attempt to parameterize the behaviour of small-, medium- and large-arrays of wave energy converters, in a particular staggered configuration, at four different locations characterized by realistic wave climates. The arrays studied in the present paper consist of heaving cylinders of different slenderness ratios. It turns out that for arrays of very short inter-device distances, regardless of the cylinder and array size, interactions are strong and lead to not negligible effects of destructive interference (total power reduction compared to the sum of isolated devices). Under these conditions, the bigger the array, the stronger the interactions and the higher the loss of power. However, a range of inter-device distances, referred to as intermediate region, where the power absorption is consistent and the interaction effect appears to be positive, has been found. This intermediate region is easily detectable for small arrays, but loses its ideal characteristics with the increase of the size of the array. This project was possible thanks to a collaboration between the University of ENSTA Bretagne in Brest (France) and the area of Marine Renewable Energy at TECNALIA. Tecnalia's authors gratefully acknowledge the support of Basque Government ELKARTEK 2015 program -grant KK-2015/00097- that made this work possible.

The understanding, modelling and analysis of the behaviour of a non-linear ship propulsion plant are of great importance for conceptual system design, component selection, selection of control strategy and for propulsion control system tuning. Conceptual propulsion system design activities, such as deciding the combinator curve, require a relatively simple steady state simulation model, while propulsion controller design and tuning requires a non-linear time domain simulation model which captures the intricacies of the propulsion plant. In this paper a linearised model of the uncontrolled ship propulsion system is derived which can be used for analysis of propulsion system behaviour in waves and for initial controller design and tuning. Furthermore a thorough analysis is made of the conditions under which local instability of the system can occur. In a follow up paper the linearised model is extended and verified by means of comparison with a non-linear model. There it is furthermore used to investigate the effect of engine governor settings on a propulsion plant when sailing in waves at different encounter frequencies. The authors believe that, due to its transparency and clear link to well known parameters and variables, the linearised core propulsion system model as derived in this paper should appeal to marine system engineers, control engineers and hydrodynamicists alike. The linearised model should however not be seen as the replacement for a non-linear model, but rather as an additional tool that can be used.

The effect of shaft inclination can induce important unsteady hydrodynamic phenomenon usually associated with small and high-speed craft. This paper presents systematic cavitation tunnel tests with a 214 mm diameter model propeller of a catamaran research vessel. The propeller is subjected to uniform and inclined flow conditions, to investigate its efficiency, cavitation and underwater radiated noise characteristics. The experiments were conducted in the Emerson Cavitation Tunnel of Newcastle University based on the starboard 5 -bladed right-hand propeller of the University׳s research vessel, The Princess Royal . In the paper the details of the tests and significant findings for the effect of the shaft inclination on the propeller efficiency, cavitation and underwater radiated noise characteristics are presented. A better understanding is sought in relation to the noise signatures of different types of cavitation. The systematic tests presented in the paper also have a long-term objective, being the first of an organised round robin test campaign that is being currently undertaken by the members of the Underwater Noise Community of Practice (CoP) of Hydro-Testing Forum (HTF). This long-term objective is to repeat similar tests in the different facilities of all CoP members to reveal the relative merits of their testing facilities for underwater noise investigations.

This paper focuses on the study of cavitation and underwater noise performance of a biomimetically improved horizontal axis tidal turbine (HATT) with a leading edge design inspired by the tubercles on the pectoral fins of humpback whales. Systematic model tests were recently conducted and details of this test campaign together with the findings are summarised in the paper. Several full-scale tidal turbine application cases were studied to understand the full-scale operating conditions considering the characteristics of varied kinds of tidal energy devices, the varying wave height and the flood/ebb tide. A systematic test regime was then designed and conducted. A set of tidal turbines with different leading-edge profiles was manufactured and tested under different loading and hence cavitation conditions. During the tests, cavitation was observed and underwater noise level was measured in comparison with the cavitation and noise performance of a counterpart HATT without tubercles. The tested turbines displayed two main types of cavitation patterns independent of the tubercles. These were steady tip vortex cavitation and relatively intermittent cloud cavitation with a misty appearance. The leading-edge tubercles triggered the cavitation onset earlier for the tidal turbine but constrained the cavitation region to the trough between tubercles with a lesser extent on the blades. The noise performance was strongly related to the blade cavitation hence it was influenced by the leading-edge tubercles. While the turbine was working under the non-cavitating conditions the total noise level was similar to the background noise level. With the increase of the tip speed ratio the noise level was increased, while increasing blade pitch angle reduced the noise level due to lower blade loading. Cavitation inception and noise diagrams are provided as a database for future studies.

The aim of this paper is to critically assess the methods used for the evaluation of wave-induced loads on ships examining analytical, numerical and experimental approaches. The paper will focus on conventional ocean going vessels and loads originating from steady state and transient excitations, namely slamming, sloshing and green water, for the latter, and including extreme or rogue waves, as well as the more occasional loads following damage. The advantages and disadvantages of the relatively simpler potential flow ap-proaches against the more time consuming CFD methods will be discussed with reference to accuracy, modelling nonlinear effects, ease of modelling and coupling, suitability for long term response evaluation and suitability for incorporation within design and operational decision making. The paper will also asses the uncertainties involved in predicting wave-induced loads and the probabilistic approaches used for the evaluation of long term response and fatigue analysis. The current design practice will be reviewed and the role of numerical prediction methods within the classification framework and goal based design approach will be discussed. Finally the suitability of current developments in prediction methods to meet the needs of the industry and future challenges will be discussed focusing on hybrid approaches, systems approach and data fusion.

This paper deals with the reproduction of unidirectional extreme events in a numerical wave basin. From a rogue wave measurement at a given location, experiments or numerical simulations are conducted with the same wave profiles using reproduction procedures. Although it is recognized that many different physical mechanisms may be at play in freak wave formation, reproduction procedures generally use frequency focusing to generate these high waves. This paper intends to assess the validity of this approach. In particular, it will focus on the relationship between an accurate reproduction of the free surface elevation and the accuracy of the corresponding wave kinematics inside the fluid domain. A highly nonlinear model is used to compute the occurrence of unidirectional freak waves in large periodic domain, which are reproduced in a 2-D numerical wave tank and compared. The study presents an advanced reproduction procedure that deals with rogue waves embedded in an irregular sea state. It shows that, using the appropriate reproduction procedure, it is possible to accurately reproduce free surface elevation as well as kinematics induced by this extreme event.

Breakwater concrete armour units have been continuously evolving since the 1950s. Lower concrete consumption, increased hydraulic stability, reduced wave run-up, and easier placement techniques are the main drivers of this development. A recent innovative solution for breakwater armour, based on one of the oldest type of units available, consists of a configuration adopting a single-layer of concrete cubes placed in a regular pattern and a porosity of 0.25–0.30. This paper presents a summary of the laboratory test results available from literature in terms of hydraulic stability and wave overtopping. Studies indicate that this is a feasible solution with several advantages over other armour configurations related to the simplicity of the cube unit and placement pattern. However, there is still some degree of uncertainty in both hydraulic stability and wave overtopping estimates for a structure with this configuration where few laboratory tests have been conducted in comparison to other armour units. Furthermore, the available methods for quantification of damage are not considered adequate for use in single-layer cube armour with a regular placement pattern. This paper discusses current knowledge gaps and provides guidelines for future research.

In the present paper the dynamic response of tall offshore monopile steel wind turbine towers under wind, wave and current during the erection stage is studied. In particular, in the present paper the effect of current-wave-wind interaction as dynamic loading on the dynamic response of offshore wind turbine towers is for first time studied experimentally. Various loading states involving wind-wave, wind-current, wave-current, wind-wave-current to measure the displacement, velocity and acceleration of the tower model at three points on the tower wall respectively. A statistical analysis of the dynamic displacements of the model is conducted to study the effect of various loading states on the respective dynamic response. As outcome of the present study it was confirmed that the current field strongly affects the dynamic response of offshore monopoles and in particular, more significantly than the wave field. In the final part, an advanced finite element model is proposed for the efficient study of the structural response of the tower model during erection under current, wave and wind interaction.

For a human reliability assessment in the maritime domain, the main question is how we correctly understand the human factors in the maritime situation in a practical manner. This paper introduces a new approach based on Cognitive Reliability and Error Analysis Method (CREAM). The key to the method is to provide a framework for evaluating specific scenarios associated with maritime human errors and for conducting an assessment of the context, in which human actions take place. The output of the context assessment is, then, to be applied for the procedure assessment as model inputs for reflection of the context effect. The proposed approach can be divided into two parts: processing context assessment and modelling human error quantification. Fuzzy multiple attributive group decision-making method, Bayesian networks and evidential reasoning are employed for enhancing the reliability of human error quantification. Fuzzy conclusion of the context assessment is utilised by the model input in CREAM basic method and weighting factors in CREAM extended method respectively for considering human failure probability which varies depending on external conditions. This paper is expected to contribute to the improvement of safety by identifying frequently occurred human errors during the maritime operating for minimising of human failures.