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A numerical hydrodynamic model for a moored interconnected floating large structure under the action of regular waves is presented to analyze the effect of current and wind. The floating structure consists of 20 hinged plates that are linked together and secured with mooring lines along its edges. A brief discussion is provided on the multi-body hydrodynamics equations related to the numerical model definitions in both the frequency and time domains. Conversely, a concise overview of the experiment is given. The numerical model outcomes of vertical displacements and wave quantities are compared against the results obtained from model test data sets and numerical and analytical models in a recent publication. A high degree of accuracy has been noted in reflection and transmission coefficients with a certain value of current velocity. The numerical model simulating interconnected structures of 10 and 16 hinged plates is analyzed, and the resulting vertical displacements under the influence of current are compared to those of a 20-hinged structure. The impact of currents and winds on the hydrodynamic response of the structure is examined by studying various results, using stiffness values for both mooring and hinges. Further, the effect of wavelengths on the wave transmission on every side of the interconnected structure through contour diagrams, hydrodynamic diffraction for different incident angles, and wave quantities on current speed are analyzed. It is observed that as the current speed rises, the structural displacement also escalates; meanwhile, no impact of the wind on the floating interconnected structure is noted. It has been observed that as the wave direction shifts from 0° to 60°, the interconnected floating structure experiences a slight reduction in wave motion throughout the entire system.

A prototype of an autonomous system for the retrieval of oceanographic, wave, and meteorologic data was installed and tested in May 2021 on a Portuguese research vessel navigating on the Atlantic Ocean. The system was designed to be installed in fishing vessels that could operate as a distributed network of ocean data collection. It consists of an automatic weather station, a ferrybox with a water pumping system, an inertial measurement unit, a GNSS unit, an onboard desktop computer, and a wave estimator algorithm for wave spectra estimation. Among several parameters collected by this system’s sensors are the air temperature, barometric pressure, humidity, wind speed and direction, sea water temperature, pH, dissolved oxygen, salinity, chlorophyll-a, roll, pitch, heave, true heading, and geolocation of the ship. This paper’s objectives are the following: (1) describe the autonomous prototype; and (2) present the data obtained during a full-scale trial; (3) discuss the results, advantages, and limitations of the system and future developments. Meteorologic measurements were validated by a second weather station onboard. The estimated wave parameters and wave spectra showed good agreement with forecasted data from the Copernicus database. The results are promising, and the system can be a cost-effective solution for voluntary observing ships.

This study explores the hydrodynamic behaviour of a fish cage in a steady current by employing a fluid–structure interaction model with one-way coupling between a fluid solver and a structural model. The fluid field around the fish cage is predicted using a computational fluid dynamics solver, while the stress and deformation of the netting are calculated using finite element structural algorithm with solid elements reflecting their real geometry. The fluid velocity and hydrodynamic pressure are calculated and mapped to the structural analysis model. The fluid–structure interaction model is validated by comparing drag force results with published experimental data at different current conditions. Instead of modelling the netting of the fish cage as porous media or using lumped mass methods, the complete structural model is built in detail. The analysis of the fluid field around the nets shows that the change in the current condition has a limited impact on the flow behaviour, but the increase in the current velocity significantly enhances the magnitude of the drag force. This study reveals a reduction in flow within and downstream of the net, consistent with prior experimental findings and established research. Mechanical analysis shows that knotted nets have better performance than knotless ones, and although fluid pressure causes some structural deformation, it remains within safe limits, preventing material failure.

This paper explores the cooperative control of unmanned surface vessels (USVs) and unmanned aerial vehicles (UAVs) in maritime rescue and coastal surveillance. The USV-UAV system faces challenges of disturbances and substantial inertia-induced overshooting during path following. A novel position prediction line of sight (LOS) guidance law is proposed to address these issues for USV path following control. Radial basis function-based neural networks (RBF-NNs) are used to estimate disturbances, and a high-order differentiator is used to design a velocity observer for unknown USV velocity. The UAV control system employs proportional–derivative (PD) control with feedforward compensation for quadrotor control design and utilizes a finite-time converging third-order differentiator to differentiate non-continuous functions. The simulation results demonstrate strong robustness in the proposed USV-UAV cooperative control algorithm. It achieves path following control in the presence of wind and wave disturbances and exhibits minimal overshoot.

This paper is dedicated to correcting the WAM/ICON numerical wave model predictions by reducing the residue between the model’s predictions and the actual buoy observations. The two parameters used in this paper are significant wave height and wind speed. The paper proposes two machine learning models to solve this task. Both models are multioutput models and correct the significant wave height and wind speed simultaneously. The first machine learning model is based on gradient boosted trees, which is trained to predict the residue between the model’s forecasts and the actual buoy observations using the other parameters predicted by the numerical model as inputs. This paper demonstrates that this model can significantly reduce errors for all used geographical locations. This paper also uses SHapley Additive exPlanation values to investigate the influence that the numerically predicted wave parameters have when the machine learning model predicts the residue. To design the second model, it is assumed that the residue can be modelled as noise added to the actual values. Therefore, this paper proposes to use the denoising autoencoder to remove this noise from the numerical model’s prediction. The results demonstrate that denoising autoencoders can remove the noise for the wind speed parameter, but their performance is poor for the significant wave height. This paper provides some explanations as to why this may happen.

A 3D analytical model is formulated based on linearised small-amplitude wave theory to analyse the behaviour of a horizontal, flexible membrane subject to wave–current interaction. The membrane is connected to spring moorings for stability. Green’s function approach is used to obtain the dispersion relation and is utilised in the solution by applying the velocity decomposition method. On the other hand, a brief description of the experiment is presented. The accuracy level of the analytical results is checked by comparing the results of reflection and the transmission coefficients against experimental data sets. Several numerical results on the displacements of the membrane and the vertical forces are studied thoroughly to examine the impact of current loads, spring stiffness, membrane tension, modes of oscillations, and water depths. It is observed that as the value of the current speed (CS) rises, the deflection also increases, whereas it declines in deeper water. On the other hand, the spring stiffness has minimal effect on the vibrations of the flexible membrane. When vertical force is considered, higher oscillation modes increase the vertical loads on the membrane, and for a mid-range wavelength, the vertical wave loads on the membrane grow as the CS increases. Further, the influence of the phase and group velocities are presented. The influences of CS and comparisons between them in terms of water depth are presented and analysed. This analysis will inform the design of membrane-based wave energy converters and breakwaters by clarifying how current loads affect the dynamics of floating membranes at various water depths.

A set of planar motion mechanism experiments of the Duisburg Test Case Post-Panamax container model executed in a towing tank with shallow depth is applied to train a neural network to analyse the ability of the proposed model to learn the effects of different depth conditions on ship’s manoeuvring capabilities. The motivation of the work presented in this paper is to contribute an alternative and effective approach to model non-linear systems through artificial neural networks that address the manoeuvring simulation of ships in shallow water. The system is developed using the Levenberg–Marquardt backpropagation training algorithm and the resilient backpropagation scheme to demonstrate the correlation between the vessel forces and the respective trajectories and velocities. Sensitivity analyses were performed to identify the number of layers necessary for the proposed model to predict the vessel manoeuvring characteristics in two different depths. The outcomes achieved with the proposed system have shown excellent accuracy and ability in predicting ship manoeuvring with varying depths of shallow water.

The present review focuses on the theoretical model developments made in floating flexible net fish cages and the floating bodies application to offshore aquaculture. A brief discussion of the essential mathematical equations related to various theoretical models of flexible net cages in the frequency domain is presented. The single and array of floating or submerged flexible net cages connected with or without mooring lines are discussed. Further, as the combined effect of the hydroelastic behaviour of floaters and the flexible behaviour of fish cages are necessary to assess their efficiency and survivability from structural damages, the issues and the knowledge gap between the recent and future models are also discussed. In conclusion, the practical suggestions concerning advancements in future research and directions within floating flexible net cages and the hydroelastic response of elastic floaters are highlighted.

The maritime industry faces many pressing challenges due to increasing environmental and safety regulations and crew safety concerns [...]

As the impact of fossil fuels on the planet becomes clear, the world is increasingly focusing on renewable energy sources [...]

The volume of a gravity cage is greatly reduced under a current due to the flexible structure, which affects the growth and health of the fish. Thus, an accurate assessment of cage volume is essential to determine the number of fishes in the cage. In this study, firstly, a numerical model was built to study the cage volume reduction of gravity cages due to the flexible net deformation when subjected to uniform flow. The remaining volume was calculated and compared with earlier experiments. Even though the flow velocity reductions were considered according to the data from previous experiments, the differences between the results from the numerical calculation and the towing tests are still significant. The physical model tests were treated as the reference value to investigate the uncertainty of the model results. Both the velocity-independent model error and velocity-dependent model error were calculated. With the help of the error models, the uncertainty of the remaining volume can be predicted. In addition, the velocity-dependent model error performs better in evaluating the uncertainty of the numerical calculation of the remaining culturing volume. Overall, the results show that the numerical model assisted by the model errors can calculate the cage volume accurately.

This paper proposes a methodology to estimate the probability of basic causes of allision accidents between vessels and offshore platforms that overcomes the problem of data scarcity required for causal analysis. The approach uses information derived from incidental data and expert elicitation, processed by a multiple attribute utility method and hierarchical Bayesian analysis. First, the methodology is detailed, briefly describing the adopted approaches. A dataset of allision incidents provided mainly by the UK Health and Safety Executive and other agencies is prepared. The features of the incidents’ causation in terms of the causal factors and basic causes are presented and discussed. A novel scheme is proposed to evaluate the annual occurrence rates of basic causes of accidents from the relative importance of each basic cause derived by the Deck of Cards method. Then, a hierarchical Bayesian analysis is conducted to predict the posterior distribution of the occurrence rate of each basic cause in the time frame under analysis. The proposed holistic methodology provides transparent estimates of allision causation probabilities from limited and heterogeneous datasets.

This paper explores the impact of sampling rates during sea trials on the estimation of hydrodynamic parameters in a nonlinear manoeuvring model. Sea trials were carried out using an offshore patrol vessel and test data were collected. A nonlinear manoeuvring model is introduced to characterise the ship’s manoeuvring motion, and the truncated least squares support vector machine is employed to estimate nondimensional hydrodynamic coefficients and their corresponding uncertainties using the 25°–25° zigzag test. To assess the influence of the sampling rates, the training set is resampled offline with 14 sampling rates, ranging from 0.2 Hz to 5 Hz, encompassing a rate 10 times the highest frequency component of the signal of interest. The results show that the higher sampling rate can significantly diminish the parameter uncertainty. To obtain a robust estimation of linear and nonlinear hydrodynamic coefficients, the sampling rate should be higher than 10 times the highest frequency component of the signal of interest, and 3–5 Hz is recommended for the case in this paper. The validation is also carried out, which indicates that the proposed truncated least square support vector machine can provide a robust parameter estimation.

A hydroelastic model associated with the interaction between a surface wave and a floating circular structure connected with mooring lines in finite water depth is developed using BIEM. The BIEM solution is achieved using free surface Green’s function and Green’s theorem. Furthermore, the algebraic equations for circular structural displacement are derived from the integro-differential equation. The correctness of the BIEM code is verified with the results of shear force and deflection amplitude existing in the literature, and the hydroelastic response of the circular structure is analyzed. The comparison results show a good level of agreement between the present results and those from other calculations. It is observed that the shear force, bending moment, and deflection decrease for higher values of stiffness of the mooring lines. The current study may be supportive of the visualization of the effect of mooring stiffness and to generalize articulated circular structure models for ocean space utilization.

This study estimates wave energy for the Moroccan Atlantic coast using SWAN, a third-generation wave model, covering a period of 30 years, from 1991 to 2020. The model is forced by the wind from the ERA-5 reanalysis dataset and uses boundary conditions generated by the WAVEWATCH III model. The significant wave height and period are used to obtain wave energy, which is analyzed at a regional scale. The mean wave energy density within the domain is assessed to be about 20 kW/m. Five specific locations are evaluated along the coast in order to determine the most energetic ones. The most energetic area of the Moroccan Atlantic coast is located at the center, between the cities of Agadir and Essaouira. Finally, the performance of six different wave energy converters is assessed through their power matrix for each of the five locations.

In pursuit of more efficient load-bearing solutions for ship deck panels of Very Large Crude Carriers exposed to vertical hull girder bending forces, laser-welded web-core sandwich panels are considered as an alternative to conventional stiffened panels. The primary goal is to identify a lighter steel sandwich structure capable of matching the ultimate strength of conventional counterparts. Utilizing non-linear finite element analysis, the ultimate strength of conventional decks subjected to uniaxial compression is assessed. Attention is then shifted to laser-welded sandwich panels, with a detailed examination of how various design parameters influence their performance. Specifically, four key design aspects of unidirectional vertical webs, including face thickness, web thickness, web height, and web spacing, are optimized to strike a balance between weight and strength through structural optimization techniques combined with the response surface method. Ultimately, a comparison is drawn between the ultimate strength of these innovative steel sandwich panels and their conventional, stiffened counterparts. The findings reveal that web-core sandwich panels, when employed as an alternative, result in a notable reduction in hull weight, thereby showcasing the potential for a more efficient and sustainable approach in the maritime industry.

This paper reviews experimental methods for testing floating wind turbines. The techniques covered include early-stage and up-to-date approaches such as a porous disc method and hybrid model testing. First, the challenges induced by Froude and Reynolds similitudes and the importance of the various aerodynamic phenomena are discussed. The experimental methods are evaluated based on their cost, versatility, requirements, and limitations. The work primarily focuses on representing aerodynamic loads via hybrid and physical rotor testing, and a preliminary classification is proposed to facilitate the selection of the approaches. The work does not aim to identify an optimal method, but it provides insights into each method’s distinctive features, serving as a roadmap for selecting the most appropriate methodology based on the specific testing goals and level of accuracy. Overall, this study offers a comprehensive resource for testing the coupled hydrodynamic and aerodynamic performance of floating wind turbines. The conclusions offer guidance for selecting an appropriate methodology based on the desired testing outcome.

A data-driven method, the truncated LS-SVM, is proposed for estimating the nondimensional hydrodynamic coefficients of a nonlinear manoeuvring model. Experimental data collected in a shallow water towing tank are utilized in this study. To assess the accuracy and robustness of the truncated LS-SVM method, different test data sizes are selected as the training set. The identified nondimensional hydrodynamic coefficients are presented, as well as the corresponding parameter uncertainty and confidence intervals. The validation is carried out using the reference data, and statistical measures, such as the correlation coefficient, centred RMS difference, and standard deviation are employed to quantify the similarity. The results demonstrate that the truncated LS-SVM method effectively models the hydrodynamic force prediction problems with a large training set, reducing parameter uncertainty and yielding more convincing results.

This paper presents the performance of a new, floating, mono-hull wind turbine installation vessel (Nordic Wind) in the installation process. The vessel can transport pre-assembled wind turbines from the marshalling port to the offshore installation site. Each assembled turbine will be positioned over the pre-installed floating spar structure. The primary difficulty lies in examining the multibody system’s reactions when subjected to combined wind, current, and wave forces. Time-domain simulations are utilized to model the interconnected system, incorporating mechanical coupling between components, the mooring system for the spar, and the installation vessel. The primary objective is to focus on the monitoring and connection stages preceding the mating operations between the turbine and the floating spar. Additionally, it involves examining the impacts of wind, current, and wave conditions on the motion responses of the installation vessel and the spar, as well as the relative motions at the mating point, gripper forces, and mooring forces. The simulations show that the resulting gripper forces are reasonable to compensate. The relative motion at the mating point is not significantly affected by the orientations of the turbine blades, but it is influenced by the prevailing wave conditions. In addition, vessel heading optimization can minimize the relative motions at the mating point and gripper forces. Given the examined environmental conditions, the presented installation concept exhibits a commendable performance.

A subsea pipeline (also known as an offshore pipeline or submarine pipeline) is a pipeline that is laid on the seabed or inside a specially constructed trench [...]

A new uncertainty quantifier is presented for linear transfer functions of wave-induced ship motions and loads obtained by various seakeeping codes. The numerical simulations are conducted for the high-speed Flokstra container ship in regular waves at various heading angles, and the results are compared with existing experimental data. The study employs five numerical codes that are based on three different seakeeping theories, namely strip theory, 3D frequency-domain method, and 3D time-domain method. Multiple measures are applied to quantify the uncertainty in the calculated transfer functions, such as frequency-independent model error, coefficient of determination, and the total difference. In addition, a new measure of uncertainty, termed modified total difference, is proposed for determining the uncertainty of individual seakeeping codes based on experimental data rather than the mean of results obtained by numerical codes. Results show that the uncertainty measures can identify differences between the codes. The predicted wave-induced loads have higher uncertainties compared to motions. The uncertainty assessment shows that none of the applied codes can produce accurate estimates for all wave-induced motions and loads at all heading angles at the same time.

The effects of hull and propeller roughness are presented over ten years of operation on ship performance. The developed model used in this study is a combination of NavCad and Matlab to perform the resistance and propulsion computations of the selected ship as well as the processing of input and output data. By considering the ship hull, the engine installed and an optimized propeller, the ship performance is computed for a different combination of hull and propeller roughness according to the ITTC recommendations and the opinion of experts in the marine field. Twelve cases are simulated over the selected years of operations and compared to the new ship performance. The hull roughness has the dominant effect on the performance of the ship due to its large area. However, by adding the effect of propeller roughness, an increment is noticed in the loading ratio and fuel consumption by 1–4% and 2–4%, respectively, in addition to the hull roughness. From this study, it is concluded that the roughness of both the hull and propeller is important consider to achieve more accurate results than just considering the hull roughness.

This paper presents a review of the different methods and techniques used to optimize ship hulls over the last six years (2017–2022). This review shows the different percentages of reduction in ship resistance, and thus in the fuel consumption, to improve ships’ energy efficiency, towards achieving the goal of maritime decarbonization. Operational research and machine learning are the common decision support methods and techniques used to find the optimal solution. This paper covers four research areas to improve ship hulls, including hull form, hull structure, hull cleaning and hull lubrication. In each area of research, several computer programs are used, depending on the study’s complexity and objective. It has been found that no specific method is considered the optimum, while the combination of several methods can achieve more accurate results. Most of the research work is focused on the concept stage of ship design, while research on operational conditions has recently taken place, achieving an improvement in energy efficiency. The finding of this study contributes to mapping the scientific knowledge of each technology used in ship hulls, identifying relevant topic areas, and recognizing research gaps and opportunities. It also helps to present holistic approaches in future research, supporting more realistic solutions towards sustainability.

Ship hydrodynamics and dynamics is a rather old, traditional branch of applied mechanics and also of naval architecture [...]

An assessment is made of the stress distribution and the hydrodynamic response of the preliminary structural design of the tension leg platform of a 10 MW wind turbine. The platform supporting a 10 MW turbine is modelled and analysed by the finite element method. The stress distribution of the platform is determined in still water with the turbine at above-rated conditions, and the response of the tension leg platform is estimated in the time domain. The results of the time domain analysis show reasonable agreement between the present results and the available data. To check the design stiffener dimensions, span, and spacing against stress distribution, classification societies’ recommendations are used. The results of the stress distribution analysis indicate that the critical locations of the platform are the interaction of the lower columns with the upper columns and the connection of the tower of the turbine.

A fracture mechanics-based fatigue reliability analysis of a submarine pipeline is investigated using the Bayesian approach. The proposed framework enables the estimation of the reliability level of submarine pipelines based on limited experimental data. Bayesian updating method and Markov Chain Monte Carlo simulation are used to estimate the posterior distribution of the parameters of a fracture mechanics-based fatigue model regarding different sources of uncertainties. Failure load cycle distribution and the reliability-based performance assessment of API 5L X56 submarine pipelines as a case study are estimated for three different cases. In addition, the impact of different parameters, including the stress ratio, maximum load, uncertainties of stress range and initial crack size, corrosion-enhanced factor, and also the correlation between material parameters on the reliability of the investigated submarine pipeline has been indicated through a sensitivity study. The applied approach in this study may be used for uncertainty modelling and fatigue reliability-based performance assessment of different types of submarine pipelines for maintenance and periodic inspection planning.

This paper focuses on the buckle propagation pressure of a pipe-in-pipe system under uniform external pressure. After the validation of the finite element model used in this research, several effects were studied. At first, the effects of the initial imperfection of the inner pipe, including the ovality and eccentricity, were checked out. Second, the influence of the scantling of the inner and outer pipes was tested. It was found that the dominant factor which affects the buckle propagation mode is changeable. Then, the boundary value of the above factor was investigated by varying the ratio of the outer and inner diameters. Finally, after a summary of the calculation results, an empirical formula was proposed to illustrate the relationship between the buckle propagation pressure and the geometrical parameters of the pipe-in-pipe system. Utilizing this formula, the buckle propagation pressure of the pipe-in-pipe system can be estimated rapidly with good accuracy.

Mixed-integer linear programming is adopted to translate the routing of service operation vessels that support the logistic aspects of the maintenance of offshore floating wind farms into mathematical language. The models attempt to help the decision-makers by providing quantified tools to screen out the optimal planning for preventive maintenance. The models search for the optimal offshore base location, vessel’s routing per day, vessel’s capacity, and vessel fleet composition that minimize the total fixed and variable infrastructure cost. The integration of the vehicle fleet size and mix problem, facility location–allocation problem, and vehicle-routing problem with time window advances the state of the art. A realistic case study is shown, and the results and discussions demonstrated that the practical insights of the solutions, as well as the identification of the route patterns through a navigation route table, may improve the decision planning of preventive maintenance.

With the expansion of the Arctic route, the safety of ship crossing the area in light of the low temperature and ice has become of focus, especially with regards to the ship’s structure. The mechanical properties of the material making up the ship’s structure may not be suitable for the Arctic environment. A series of quasi-static and dynamic tests were performed to investigate the behaviour of EH36 steel, which is used to build Arctic ships, at temperatures ranging from 20 °C to −60 °C. The yield and ultimate tensile stress increased more than 10% as the temperature decreased from 20 °C to −60 °C, whereas the toughness decreased as the temperature decreased. A formula was derived to illustrate the relationship between the temperature reduction and the yield strength by fitting the experimental data. Four common constitutive rigid-perfectly plastic, elastic-perfectly plastic, bilinear elastic-plastic, and multi-linear elastic plastic models were fitted to simulate the hull structure under static loading and low temperature. Additionally, the strain rate effect of EH36 steel at low temperatures was illustrated by quasi-static and high-speed impact tests. A constitutive model including the low temperature and strain rate was introduced based on a modified Cowper-Symonds model, in which the coefficients of the constitutive model are fitted by the test results. It is improved by an iterative numerical method used to obtain more accurate coefficients using a series of numerical analyses. Detailed finite element simulations of the experiment conditions revealed that the constitutive model accurately predicts the dynamic response at low temperatures.

Sensitivity analysis is applied to ship manoeuvring mathematical models as a means of dealing with model uncertainties, and often leads to model simplifications. A rather standard 3DOF manoeuvring model was tuned with the available results of full-scale trials of a naval combatant and was further used as the reference model for sensitivity analysis. The present research was based on multiple perturbed simulations of the turning, zigzag and spiral manoeuvres. A salient feature of the present study is that the perturbations were applied to the total hydrodynamic forces and moments as well as separately to their characteristic parts, i.e., to the linear and nonlinear single-variable and coupled components. Another special feature is that the deviations of the perturbated responses were estimated not only considering the standard manoeuvring performance indices, but also through application of the Euclidean metric directly to the time histories and to the spiral curve. The performed analysis permitted the sensitivity of the model to be traced to various parameters and groups thereof. It was established that the highest sensitivity of the model was to linear and some nonlinear multivariable parameters, and the Euclidean metric permitted a more detailed analysis than that based only on standard discrete manoeuvring indices. The obtained results are expected to be useful in the application of system identification methods to typical inherently stable fast surface-displacement ships.

Recent years have seen the rapid development of autonomous ships [...]

This paper assesses the uncertainty of the partial safety factors for the design of corroded pipelines against burst failure due to the variability associated with the strength model selection. First, 10 calibrated burst pressure prediction models for corroded pipelines are adopted and duly categorised under low-, medium- and high-grade steel classes. The probabilistic characteristics of the pipe burst strength are studied using Monte Carlo simulation for the selected models. Model uncertainty factors are used to correct the burst pressure predictions by the design equations. Model strength factors are derived for models in each category that will provide coherent reliability. The first-order reliability method is employed to estimate the partial safety factors and their uncertainty as a function of operational time. Finally, the influence of the corrosion growth model on the evaluation of partial safety factors is assessed. The results obtained in this study can provide vital guidance regarding the design and maintenance of different steel-grade pipelines.

This paper presents the effect of hull roughness over 10 years of operation on ship performance. The numerical model is developed by coupling NavCad and Matlab to perform the computation and the data processing. On the basis of a given hull, an engine, and an optimized propeller, the performance of the ship is computed for eight cases of hull roughness according to the ITTC recommendations in both calm waters and different weather conditions along the ship route. The effect of both wind and waves is considered for computing the added ship resistance along the route, thus requiring more power than just only the added resistance in waves. This provides a more accurate estimation of the ship’s performance along the different sea states. Lastly, a weighted average of the main ship parameters is estimated to evaluate better the ship’s performance. According to this study, the fuel consumption in calm water can be increased by around 20% after 10 years of ship operation based on the level of hull roughness. However, in the same weather conditions along the ship route, the ship’s fuel consumption can be increased by 10% compared to the same trip with a clean hull.

This work evaluates the experimental test results regarding the operational performance of a free-float capable tension leg platform with a 10 MW wind turbine. It covers the platform dynamics in the selected installation area: Ribadeo, Spain. The model and the facility are initially presented, along with the experimental setup and the load cases. The testing campaign includes a software-in-the-loop method to emulate the rotor thrust and the aerodynamic and gyroscopic moments in pitch and yaw. The result sets are structured to start from basic information from system identification cases and continue with responses against regular and irregular waves accompanied by steady and stochastic wind scenarios. The performance in operational and extreme conditions is assessed as well as fault scenarios. The experiments demonstrate auspicious motion dynamics and mooring line behavior when examined against class society rules.

A detailed analysis is performed on a dataset of failure and maintenance records from various onshore wind farms located in different geographical areas for the safety, risk, reliability, availability, and maintainability characterization of wind turbines. Specifically, characteristics related to failures, including the criticality of failure modes, failure frequencies, failure rates, and lifetime distributions of components, are analyzed to support the failure identification and failure prevention of wind turbines. Additionally, characteristics of maintenance, including typical maintenance measures of failures, policies for spare components, delayed maintenance, as well as related times such as reaction time, travelling time, and mean time to repair, are provided to support the maintenance management of wind farms. Based on the operational data analysis results, a reliability influence factor-based failure data correction approach is presented to transfer the onshore data to floating offshore turbines by modeling the differences in failure occurrences based on experts’ judgment. A comprehensive comparison with existing studies validates the performance of the proposed approach.

Artificial neural networks are applied to model the manoeuvrability characteristics of a ship based on empirical information acquired from experiments with a scaled model. This work aims to evaluate the performance of the proposed method of training the artificial neural network model even with a very small quantity of noisy data. The data used for the training consisted of zig-zag and circle manoeuvres carried out in agreement with the IMO standards. The wind effect is evident in some of the recorded experiments, creating additional disturbance to the fitting scheme. The method used for the training of the network is the Levenberg–Marquardt algorithm, and the results are compared with the scaled conjugate gradient method and the Bayesian regularization. The results obtained with the different methodologies show very suitable accuracy in the prediction of the referred manoeuvres.

An approach is developed for floating wind farm installation by creating a model that allows the planning of the main logistics and installation aspects of a floating wind farm. The method aims to preserve the coherency between logistic methods and project performance, as floating wind farm installation is a complex problem, due to the number of components that impose specific constraints in areas such as transportation and manufacturing. The planning tool is developed based on the knowledge about how to use the various approaches and on the analysis of different logistical solutions. A techno-economic view of the logistics and installation involved in the floating wind farm design is the main objective of this study. A case study for the CENTEC TLP concept implemented in Spanish and Irish waters is performed. Case study findings reveal the major aspects that affect the design and logistics factors. The tool is developed for the main types of floating wind platforms and is applicable for the preliminary design of wind farms worldwide. The tool suggests a strategy of design and logistic aspects dependent on a few inputs such as the number of components for installation, distances and the maximum number of turbines. These findings are especially important for the new floating wind farms being positioned further offshore.

This paper presents the Nenuphar concept, an innovative wave energy converter designed to use the kinetic and the potential energy of sea waves, based on the motions of seven modules. First, the main characteristics of the Nenuphar and its work principle are presented. Afterwards, the mathematical formulation of its dynamics is introduced and its validation with a simplified device. A specific MATLAB code was developed to determine the dynamics of hinged, multi-directional bodies. Then, the system’s behaviour was analysed under different wave conditions. The system performance was not strongly dependent on the wave characteristics or the device inclination angle. This initial study confirms the Nenuphar as a potential technology to extract energy from waves.

This paper proposes an improved failure mode and effect analysis method for a comprehensive failure analysis that provides a holistic perspective of actions on the potential failures of floating offshore wind turbines. A new way of constructing risk priority numbers was developed by considering the background knowledge of the specialists involved in the failure analysis. The failure analysis was conducted based on an extensive dataset from multiple specialists that covers five floating offshore wind turbine systems, 15 main components, 42 failure modes, and 104 failure causes. Consequently, 21 recommendations are suggested for designers and operators to prevent and mitigate the risk of unexpected failures of floating offshore wind turbines. Furthermore, a comparison analysis was conducted to illustrate the similarities and differences between the proposed failure mode and effect analysis and the conventional method.

This paper presents the effect of selecting a contra-rotating propeller (CRP) for a bulk carrier at the engine operating point with minimum fuel consumption, as well as ensuring the safety of the propeller in terms of cavitation and noise. Using a developed optimization model, the geometry of a CRP was selected for different propeller diameters, the same propeller diameter as that of a fixed pitch propeller (FPP) installed on the bulk carrier, and at 90% of the FPP diameter. Additionally, each case was optimized with both no-cup and heavy-cup configurations. In general, the CRP showed better performance than the FPP in terms of efficiency, cavitation, and fuel economy. At the same time, the level of performance was increased when considering the CRP cupping percentage. It was concluded that the CRP can achieve a gain in fuel economy of up to 6.2% in a no-cup configuration when compared to an FPP, and up to 11.7% with a cupped configuration.

The WIND-bos spar Floating Offshore Wind Turbine is studied both experimentally and numerically. The experimental model of the moored WIND-bos platform is presented, and the different numerical models that have been developed to analyze the hydrodynamics of the platform are described. The results provide a detailed comparison of numerical and experimental motion responses of the floating structure in regular and irregular waves. The numerical study includes frequency domain results from spectral analysis, weakly nonlinear time-domain results from a validated in-house code, and coupled time-domain results from commercial software. The importance of damping calibration is put in evidence, whereas damping ratios are calculated iteratively in the coupled time-domain simulations, and nonlinear damping force is considered within the developed numerical scheme. The results compare well and also show that the novel concept has a good motion performance in general.

A Multi-Scale Convolutional Neural Network with Self Attention-based Auto Encoder–Decoder (MSCSA-AED), is a novel high-performance framework, presented here for the quantification of damage on a multibody floating offshore wind turbine (FOWT) structure. The model is equipped with similarity measurement to enhance its capability to accurately quantify damage effects from different scales of coded features using raw platform responses and without human intervention. Case studies using different damage magnitudes on tendons of a 10 MW multibody FOWT were used to examine the accuracy and reliability of the proposed model. The results showed that addition of Square Euclidean (SE) distance enhanced the MSCSA-AED model’s capability to suitably estimate the damage in structures operating in complex environments using only raw responses. Comparison of the model’s performance with other variants (DCN-AED and MSCNN-AED) used in the industry to extract the coded features from FOWT responses further demonstrated the superiority of MSCSA-AED in complex operating conditions, especially in low magnitude damage quantification, which is the hardest to quantify.

A feasibility analysis was conducted on a crude oil tanker. Differences in power generation and fuel consumption of the diesel generators based on the noon report of the specified marine vessel were analyzed for similar periods before and after the scrubber application. Accordingly, the changes in releasing amounts of emissions were calculated. Then, a financial evaluation was realized with three economic indicators. As a result of the analysis performed, it is found that the power generation and fuel consumption realized by each diesel generator are increased after scrubber application. Nevertheless, its implementation on board may be considered acceptable in light of the economic findings. However, it has been determined that scrubber implementation causes an increase in all pollutants’ amounts except SOX. Therefore, it contradicts the zero-emission ship target and decarbonization strategy stated by IMO.

This paper presents an approach for probabilistic design and safety assessment of sandwich pipelines under external pressure. The methodology consists of the categorisation of sandwich pipeline collapse strength models based on interlayer adhesion conditions. The models are validated by comparing their predictions against collapse test data of sandwich pipelines. The accuracy of the strength models and their prediction uncertainty are used to select the best model in each category. Regarding interlayer adhesion categories, uncertainty propagation of models’ predictions over a wide range is assessed by the Monte Carlo simulation method. The proposed methodology is demonstrated using a case study of a sandwich pipeline with adequate probabilistic modelling of the basic random variables. Different limit states are defined for three categories of sandwich pipelines, based on which structural reliability indices are estimated. In employing the First Order Reliability Method for sensitivity analysis, the importance of basic variables of the limit states is evaluated. Later, a parametric analysis is conducted, presenting reliability variations for several design and operational scenarios of sandwich pipelines. Finally, to achieve a uniform level of structural reliability of sandwich pipelines, a few suggestions are provided, and practical partial safety factors are calculated. The results of the present analysis can provide guidance on the probabilistic design and operational safety assessment of sandwich pipelines.

A two-stage ship path planning method is proposed, based on the Rapid-exploring Random Tree (RRT) algorithm, which is composed of global path planning and local path planning, addressing the important problem of finding an economical and safe path from start to destination for ships under dynamic environment, especially in waters with multiple obstacles and multiple target ships. The global path planning takes into consideration the ship draft and Under Keel Clearance to find navigable water using RRT, and reduces the path length and waypoints based on elliptic sampling and smoothing. In the local path planning, a dynamic collision risk detection model is constructed by introducing the Quaternion Ship Domain under a dynamic environment, and the restrictions of ship manoeuvrability and COLREGs are also involved. The simulation results show that the proposed model can find a satisfactory path within a few iterations, and keep clear of both static obstacles and dynamic ships. The research can be used to make and verify planned ship routes before sailing and to guide officers to make decisions regarding collision avoidance.

Introduction Multiple sclerosis (MS) is a chronic inflammatory, demyelinating, and neurodegenerative disease of the central nervous system. This condition is enhanced by stress. In turn, stress symptoms are a risk factor for the onset and progression of MS. However, knowledge about predictors of stress in patients with MS is scarce. Objectives This preliminary study aimed to verify whether the number of relapses, fatigue, physical disability (MS characteristics), experiential avoidance and self-judgment (emotion regulation processes) predict stress symptoms in patients diagnosed with MS. Methods A convenience sample of 101 patients diagnosed with MS and without other neurological diseases participated in this study. Participants completed the Depression Scale of the Depression, Anxiety and Stress Scales-21, Analog Fatigue Scale, World Health Organization Disability Assessment Schedule-12, Acceptance and Action Questionnaire-II, and Self-Judgment Subscale of the Self-Compassion Scale. Results All predictors initially hypothesized and years of education have significant correlations with stress symptoms. Simple linear regression analyses showed that the variables significantly predicted stress symptoms and were, therefore, included in the multiple linear regression model. This model explained 51.8% of the variance of the stress symptoms and showed that years of education, the number of relapses, fatigue, and experiential avoidance significantly predicted those symptoms. Conclusions The promotion of mental health mental in patients with MS must develop functional skills to deal with stress induced by years of education (possibly responsible for the degree of awareness about MS and its consequences), recurrence of relapses and fatigue, and should minimize emotion regulation strategies focused on experiential avoidance.

This paper addresses subsea electric cable routing using the application of decision support systems combined with the experts’ knowledge. The methodology is successfully applied to a case study on the Spanish coast. The ranking method calculates the multiple criteria weights, and the weighted product method determines the most suitable space. The environmental criteria, with a weight of 61.4%, exceed the significance of other essential criteria in the study based on experts’ considerations. These rankings are input into the model to extract the suitable spaces to deploy the underwater cable. The final result accurately highlights an optimal route in alignment with the experts’ preferences.

A mathematical model of solitary wave interaction with a pontoon-type rigid floating structure over a flat bottom is formulated based on Boussinesq-type equations under weakly nonlinear dispersive waves. Based on the higher-order Boussinesq equations, the solitary wave equation is derived, and a semi-analytical solution is obtained using the perturbation technique. On the other hand, brief descriptions of the application of wave2Foam and OceanWave3D on the aforementioned problem are presented. The analytical solitary wave profiles in the outer region are compared with Computational Fluid Dynamics (CFD) and OceanWave 3D model simulations in different cases. The comparison shows a good level of agreement between analytical, wave2Foam, and OceanWave3D. In addition, based on the wave2Foam and coupled OceanWave3D model, the horizontal, vertical wave forces, and the pressure distributions around the pontoon are analysed. Further, the effect of the Ursell number, pontoon length, and water depth on the solitary wave profiles are analysed based on the analytical solution. The paper validates each of the three models and performs intercomparison among them to assess their fidelity and computational burden.

This paper defines a methodology for the economic feasibility analysis of a floating offshore wind farm composed of tensioned leg platforms, which are part of the EU ARCWIND research project. In this context, the phases and subphases of its life-cycle process are considered to deal with aspects such as bathymetry, characteristics of the platforms, distance from the farm to shore, distance from the farm to port and offshore wind speed. All the costs and other external parameters such as capital cost, electric tariff, interest rate, percentage of financing and corporate tax have been analysed to calculate the internal rate of return, net present value, discounted pay-back period and levelized cost of energy of the farm. This work studies a farm composed of TLP offshore wind platforms designed by CENTEC and located at Ribadeo in Spain. Results indicate the costs and the economic feasibility of this platform for deep waters. They indicate that the platform is economically feasible for the location selected.