There is an increasing awareness that the exploitation of offshore wind may become the main technology option for decarbonization of the global energy production systems. Various floating wind turbines are therefore being studied at the present time. In this paper we propose to proceed from floating to moving platforms by equipping autonomous sailing ships with hydrokinetic turbines and thereby to open up vast wind rich ocean areas for renewable power generation. The turbine output power is stored either in electric batteries or is fed into electrolysers to produce hydrogen which is compressed and stored in tanks. We provide a summary of our latest technoeconomic optimization studies of this energy ship concept using Multi Pole Systems Analysis and we describe the design, development and testing of a small-scale autonomous hydrofoil boat to serve as a technology demonstrator.

The site-specific load verification for floating offshore wind turbines requires the consideration of the complex interaction of the different system components and their environment. Sensitivity analyses help reducing the simulation amount for both fatigue and ultimate load analysis significantly by highlighting relevant load parameters and increase the understanding for the system behavior in its real environment. Aligned with work in the H2020 project LIFES50+, this study investigates different approaches for global sensitivity analysis using quasi-random sampling for the independent variables. Two different load case groups are analyzed: (1) fatigue loads during power production, (2) ultimate loads during power production and severe sea state. The considered system is the public DTU 10MW turbine’s rotor-nacelle assembly, installed on the public NAUTILUS-10 floating structure. Load simulations are performed by using FAST v8. Simulations are set up based on the LIFES50+ Site B (medium severity). A comparison is made to a similar study with a different platform (Olav Olsen semi-submersible) in order to observe if similar conclusions can be reached for the different floater types.

Structural integrity assessment is the study of the safe design and assessment of components and structures under loads, and has become increasingly important in engineering design. The technology and applications of structural integrity widely range from transportation, oil and gas, power generation to petrochemical, nuclear sectors, etc. In this paper, the character of structural integrity assessment in the maritime field is discussed, the latest approach and techniques are classified in three sub-topics, damage diagnosis, damage prognosis & maintenance strategy and then illustrated using a few practical studies. Finally, the future challenges introduced by new material, new exploitation field and new technology, i.e., IOT, big data, etc., are discussed and the potential development of structural integrity assessment in maritime industry is explored.

About 70% of the earth’s surface area is covered with water. Due to the sea level rise and increasing population in coastal areas we need to use our oceans more for energy production, food production, working and living. In the present paper we discuss the results of a model test for a floating mega island in large waves up to 15.5 m significant wave height. The objective of this study is to investigate the motion response and loads on the island. These results may then be used to support further innovation of these islands. The proposed island comprises 87 large floating triangles that are connected to one another. Together they form a flexible floating island of 1.5 by 2 km in cross-section at scale 1:250. The results are presented for the motion response of the island as well as the forces between the islands triangular modules and the mooring loads. These were measured using forces transducers and motion sensors. The present work is part of a conceptual test carried out at MARIN. The island modules are interconnected with springs and fenders. This method is much similar to what is used in side by side offshore operations in the oil and gas industry. Due to the flexibility in the connections the island will follow the waves in high seas. The forward two rows of the island will move in phase with the sea and therefore the amount of green water is much smaller than for a rigid island.

In this paper a wave energy converter (WEC) based on a segmented floating structure with embedded piezoelectric devices is numerically investigated. To illustrate the idea, a concept design based on assembling existing components is considered. The investigated system is made of three identical box-shaped slender floaters, interconnected by piezoelectric beams, aligned along the wave direction and moored to the seabed. The piezoelectric beams, bent alternatively by the oscillating relative motion of the floaters, constitute the power take-off (PTO) system to generate electricity. The numerical model is divided into two parts: a hydromechanical solver, describing the coupled motion of the floaters and the dynamics of the mooring lines, and a coupled electromechanical solver, which describes the behavior of the piezoelectric benders, including the associated resistive circuit. The coupling between these subsystems is one-way, because the WEC motion deforms the piezoelectric device without any electromechanical feedback on the floating structure. The developed numerical procedure allows for describing the basic features of the WEC response, for estimating the energy that can be generated by the device, and sets the starting point to explore the energy production capability of this kind of device.

Based on experimental data from the Marine Renewable Energy Laboratory (MRELab) at the University of Michigan, a data model is developed in order to permit dynamical analysis and controller synthesis for power-plants based on Vortex Induced Vibrations (VIV) for power generation and energy production. For the particular experimental settings used at the MRELab, data series of various kinematic, dynamic and energetic variables were recorded through the use of one to two cylinders as bluff bodies in a cross-flow. In the present research, these data series are analyzed in order to produce a dynamical model in an appropriate phase space. The process of model derivation is entirely data-driven in the sense that the number of degrees of freedom, or state variables, reflects the dimension of the phase space for the process. The outcome is a model which allows the identification of regime-dependent features such as attractors, basins of attraction, separatrices, etc., which can occur in the basic system dynamics.

This paper presents the experimental evaluation results of power production efficiency of model predictive control (MPC) on a wave energy converter (WEC) with a linear generator in regular and irregular waves. A bottom-fixed WEC of point absorber type was subjected to the WEC model in this paper. To compare the power production efficiency, the power production efficiency of the approximate complex-conjugate control with considering the copper loss (ACL) was also evaluated. In regular waves, the MPC performance was comparable to the ACL one in the power-production amount reasonably. In irregular waves which have narrow band spectral distribution, a same trend as the trend in regular waves was obtained. On the other hand, in irregular waves which have broadband spectral distribution, the MPC was more effective than the ACL. Moreover, Experiments in regular and irregular waves were carried out in the MPC under the constraint of the small heave displacement. The constraint of the displacement was approximately satisfied by the MPC. This is useful in practical operation. It is also investigated experimentally how time horizon affects the performance of the MPC. When the time horizon is short, the power production amount of the MPC increases.

Presented herein is the performance of a pontoon-type wave energy converter (WEC) similar to that of the ‘Floater Blanket’ WEC, which consists of a grid of interconnected floating elements. The current WEC design takes into account the elastic deformation of the structure under wave action and investigates its efficiency in generating wave energy as compared to its counterparts that achieve this via rigid body motions. The power take off (PTO) systems are installed at the seabed and attached to the WEC to generate energy via the vertical motions of the WEC’s structural modules. Three types of pontoon-type WEC designs are investigated, i.e. with hinges, with a reduced number of hinges and without hinges. In addition, the influence of the flexibility of the structural modules towards the energy generation is also investigated in order to assess its performance when behaving like an elastic material. The pontoon-type WEC’s structural modules with fewer or without hinge connections are preferable due to their ease in installation, while allowing for flexible deformation in the structural design would yield savings in material cost.

In order to de-risk wave energy technologies and bring confidence to the sector, it is necessary to gain experience and collect data from sea trials. As part of the OPERA H2020 project, the Mutriku Wave Power Plant (MWPP) is being used as a real condition laboratory for the experiment of innovative technologies. The plant is situated in the North shore of Spain and has been operating since 2011. It uses the Oscillating Water Column (OWC) principle, which consists in compressing and expanding the air trapped in a chamber due to the inner free-surface oscillation resulting from the incident waves. The pressure difference between the air chamber and the atmosphere is used to drive an air turbine. In that case, a self-rectifying air turbine is the best candidate for the energy conversion, as it produces a unidirectional torque in presence of a bi-directional flow. The power take-off system installed is composed of a biradial turbine connected to a 30kW off-the-shelf squirrel cage generator. One of the novelties of the turbine is a high-speed stop-valve installed close to the rotor. The valve may be used to control the flow rate through the turbine or for latching control. This paper focuses on the development, the implementation and the numerical simulation of five control strategies including turbine speed and generator torque controllers. The algorithms were designed thanks to a numerical model describing one of the OWC chambers of the Mutriku power plant. Numerical results are presented for a variety of sea states and a comparison between the proposed control laws in terms of energy production and power quality is performed.

Accurate control parameter optimisation and power production assessment is essential to evaluate the performance of a wave energy converter (WEC). However, commonly used numerical models excessively simplify the power take-off (PTO) system of the WEC, which may strongly affect power production predictions. Therefore, the present paper compares a commonly used WEC model that includes nonlinear viscous losses and an ideal PTO system model, referred to as NLideal, with a high-fidelity wave-to-wire model (HFW2W) model. Results show the incapacity of the commonly used NLideal model to accurately optimise control parameters, particularly using reactive control. Likewise, the annual mean power production (AMPP) predicted using the NLideal model is significantly overestimated, with differences of up to 160% with respect to the more realistic HFW2W model. More dramatically, the use of control parameters optimised with the NLideal model in the HFW2W model results in negative AMPP, meaning that the WEC consumes more energy than it produces.

Aligned with work performed in deliverable D7.7 of the H2020 project LIFES50+, this study supports the definition of the numerical setup in the design of floating offshore wind turbines. The results of extensive simulation studies are presented, which focus particularly on determining the requirements for the load simulations in the design process. The analysis focusses on the cases of: (1) fatigue during power production and (2) ultimate loads during power production and severe sea state. For the fatigue load case, sensitivity study is performed in order to determine relevant load conditions and the expected impact of a variation in the environmental loading. Additionally, focus is put on the requirements regarding the run-in time, number of seeds and the simulation length for both fatigue and ultimate limit state (FLS, ULS) analysis. Another topic addressed is the benefit of using an increased number of seeds rather than extending the simulation time of single seeds, when a given total simulation time is required as described in the guidelines. The run-in time may be shortened when using predetermined steady states as initial conditions. Requirements for the steady state simulations are also determined and presented.

Economic factors together with protection laws and policies pertaining to marine pollution drive research for improved power generation. Fuel cells, being fuel efficient and environmentally friendly, could provide a desirable option and suitable alternative to conventional propulsion systems based on fossil fuels or even nuclear fission. Fuel cells are becoming fast a mature technology and employed in many various other areas. Flexibility of special purpose watercraft, power autonomy and modularity can all benefit from the use of fuel cells. Specifically, proton exchange membrane fuel cells are considered among the most promising options for marine propulsion applications. Switching converters are the common interface intermitted between fuel cells and the load in order to provide a stable regulated voltage. DC-DC converters have been widely used since the advent of semiconductors. These devices are typically adopted to accomplish voltage regulation tasks for a multitude of applications: from renewable energy power-plants to military, medical and transportation systems. Nonetheless voltage regulators exhibit the need for consistent closed- and open-loop control. Most common approaches are PID controllers, sliding mode controllers and artificial neural networks that are considered in this work. An artificial neural network (ANN) is an adaptive, often nonlinear system that learns to perform a functional mapping from data. In our approach, a typical example of a fuel cell, a power converter outfitted with an ANN controller, and a resistive load configuration is investigated. Simulation studies are crucial in power electronics to essentially predict the behavior of the device before any hardware implementation. General requirements, design specification together with control strategies can be iteratively tested using computer simulations. This paper shows the simulation results of the full system behavior, as described above, under dynamic conditions. Initially, an open-loop simulation of the system is performed. Next, an appropriately trained ANN is incorporated to the switching model of the DC-DC converter to perform simulations for validation. Conversely, during design and calibration of the ANN controller, instead of the switching model of the DC-DC converter, a trained ANN equivalent is employed.

Tidal current power generation is one of marine renewable energies whose merit is stable and predictable power generation. In the present study, a potential map of tidal current energy in Seto Inland Sea is developed on GIS from the datasets of hydraulic model experiments. Fisheries value maps are also developed from the database of fish catch for typical species in the target area. The developed maps are integrated through GIS, to investigate suitable locations for tidal current power plants in Seto Inland Sea. From the combined map considering both the economic value of tidal current power generation and the fishery, it is found that the areas with positive total value significantly decrease as damage rate on fishery becomes larger, though the areas with high energy potential of tidal current have larger total economic values even when the damage rate increases. On the other hand, some areas where the fishery value is small will become candidate site when the damage rate on fishery gets larger.

Wind power generation has been paid much attention over the years as a countermeasure against global warming. Especially in recent years, researches and developments have also been made on Floating Offshore Wind Turbine (FOWT) in relatively deep offshore. Unlike Bottom-mounted Offshore Wind Turbine (BOWT), the motion characteristics of FOWT is complicated owing to coupled response of wind turbine and floating platform motions since the FOWT system is not fixed to the seabed. Due to these complexities, negative damping is one of the major problems reported for SPAR type FOWT moored by catenary chains. Negative Damping, in which the natural periodic motion is excited by blade pitch control employed for keeping the power generation constant, has to be addressed. In this paper, we discuss the negative damping of TLP type FOWT with a series of dedicated experiments. We manufactured a 1/100th-scale model TLP type FOWT model with a primary control system of the blade pitch angle for a geometrically scaled model of the 5MW wind turbine based on the NREL. At first, we formulated the mechanism for occurrence of Negative Damping and derived the conditions under which unstable fluctuations of the floating platform occurs using the motion equation. After that, we conducted scale model tank tests in wind alone and confirmed the phenomenon wherein the fluctuation of the floating platform does not converge. Finally, how dangerous such coupled motion of wind turbine and floating platform would be for real-scale FOWT is discussed.

In the present paper, the effects of misaligned wave and wind action on the dynamic response of the WindWEC combined concept are evaluated and presented. WindWEC is a recently proposed combined wind and wave energy system; a hybrid offshore energy system that consists of: (a) a 5MW floating wind turbine supported by a spar-type substructure (e.g. Hywind), a Wave Energy Converter (WEC) that is of heaving buoy type (e.g. Wavestar), (c) a structural arm that connects the spar with the WEC and (d) a common mooring system. Hybrid offshore platforms are combining wave and wind energy systems and are designed in order to gain the possible synergy effects and reduce the cost of generated electrical power while increasing the quality of delivered power to grids. During the lifetime of a combined concept, wave and wind can be misaligned which may affect the dynamic response and as a result the functionality of it. In particular, for asymmetric configurations, the misalignment of the wave and wind may result in unexpected behaviour and significant effects that may reduce the produced power. For the case of the WindWEC concept, the relative motion of the spar platform and WEC buoy results to the produced power. In this paper, the dynamic response and power production of the buoy type WEC and wind turbine are examined for different loading conditions where the wave and wind are misaligned. Integrated/coupled aero-hydro-servo-elastic time-domain dynamic simulations considering multi-body analyses are applied. The motion, structural and tension responses as well as power production are examined. The misalignment of wave and wind results to higher loads that affect the mooring line system and motion responses of the spar. It is found that the produced power of wind turbine is not significantly affected.

A vertical axis wind turbine (VAWT) typically has a low position of the center of gravity and a large allowable tilt angle, which could allow for a relatively small floating support structure. Normally however, the drawback of large loads on the VAWT rotor during parked survival conditions limits the extent to which the floater size can be reduced. If active blade pitch control is applied to the VAWT, this drawback can be mitigated and the benefits can be fully utilized. The coupled dynamics of a 6 MW VAWT with active blade pitch control supported by a GustoMSC Tri-Floater semi-submersible floater have been simulated using coupled aero-hydro-servo-elastic software. The applied blade pitch control during power production results in a steady-state thrust curve which is more comparable to a HAWT, with the maximum thrust occurring at rated wind velocity. During power production, floater motions occur predominantly at low frequencies. These low frequency motions are caused by variations in the wind velocity and consequently the rotor thrust and torque. For the parked survival condition, it is illustrated that active blade pitch control can be used to effectively reduce dynamic load variations on the rotor and minimize floater motions and mooring line tensions.

Installing devices of marine renewable energy is planned off Kamaishi city, Iwate prefecture, Japan. A device of wave power generation was settled at this site as a test case. It is important to coexist the power generation device and local fishermen. Since Kamaishi is known as a good fishing area, acceptance of fishermen is required to run the wave power generation at the test site. Especially, local fishermen in Kamaishi have a concern about how wave power generation moves along with ocean waves and currents. To acquire an acceptance from local fishermen in terms of setting wave power generation, a model test was conducted to understand the device of wave power generation. It consists of float, spar, middle float, gimbal mechanism and anchor. Middle float, gimbal mechanism and anchor are mooring. The submerged weights of the model almost satisfy the targeted values calculated by the scale ratio and actual submerged weights. The experiment was conducted for 1/125 scale model at a water tank in marine environmental and ecosystem laboratory, the university of Tokyo. We monitored the motion of the model under several conditions of regular waves and currents. The motions of the model were recorded by a video camera and were analyzed. The model was moved with respect to the surface waves and currents. We assessed the motions of the float based on the experiment. The experimental results will be used to explain local fishermen.

There are increasing concerns and regulations regarding the emission of pollutants from shipping. Therefore, regulations such as the Ship Energy Efficiency Management Plan (SEEMP) and Energy Efficiency Design Index (EEDI) have been made mandatory to cope with climate change concerns. To put these efforts into practice, the Energy Efficiency Operational Indicator (EEOI) was introduced in 2009 to account for the fuel consumption, distance travelled by the vessel and cargo mass. However, it is stated that these do not apply to ships that are not engaged in transport work such as research vessels and tugboats. These short sea shipping vessels have been neglected under current indexes and it is not possible for their properties to be quantified since current indices are for vessels carrying loads. The numbers of these specialised vessels are increasing in local waters, and are closer to coastal communities where concerns and impact from these pollutants would be more direct. In the IMO greenhouse gas study, options for improving energy efficiency in terms of design includes the concept, design speed and capability, hull and superstructure, power and propulsion whilst the principle of energy efficiency in terms of operation includes fleet management, logistics and incentives, voyage optimisation and energy management. A reliable energy flow breakdown architecture and diagnostics for these smaller vessels is important and will contribute to an understanding of the energy production, distribution and consumption on-board. This feeds into the IMO plan to encourage energy management. A systematic approach consisting of five distinct stages is recommended to accomplish a holistic approach for energy efficiency management. This includes understanding of energy flow breakdown architecture, vessel survey to understand operation and conduct, review existing sensors and new sensor installation, sensor communication and data processing, and finally data analysis. These stages are addressed in this paper to provide an overall understanding of a robust energy efficiency audit procedure and sensor matrix. This includes unifying the existing on-board sensors with the proposed new sensors for additional data collection where primary parameters are not readily available. Inferred secondary parameter calculations are also applied where direct data collection is not possible. This will allow information from the vessel to be transmitted to a common platform to enable detailed data analysis. The aim of this work is to improve energy management and monitoring, which leads to understanding and managing consumption of energy. A case study of this methodology has been carried out on the Princess Royal, a Newcastle University research vessel. Recommendations for further testing and optimisation of this methodology will be applied to tugboats and Offshore Supply Vessels (OSV).

On-board Energy systems in vessels have to use fuel efficiently to maintain ship speed at lowest possible costs. This paper describes how to use ship operational data to improve and maintain efficiency of the vessel’s power production with respect to the condition and performance of equipment. The paper describes an overview of an automated Technical Operations Performance (TOP) Monitoring service. TOP monitors the performance of marine main and auxiliary diesel engines by use of the information collected onboard vessels at regular intervals. Performance data are stored in xml-reports sent as email attachments from ship to shore. This communication is reliable and cost efficient for merchant ships that are on-line only for shorter periods. Load, ISO and environmental corrections make results valid for benchmarking and trending. The service aggregates the hierarchical information obtained from different sources by transferring measurement readings into unified indicators, the Technical Condition Index (TCI) [1]. Experts manually check the automatically generated performance reports and add additional guidance on options to improve power production and machinery conditions analyzing the available data with respect to different targets, such as low engine degradation and high fuel efficiency. The performance reports then influence business processes indicating possible causes for loss of performance in equipment and possible erroneous instrumentation, and the need for maintenance actions. The obtained TCI values show the performance of individual units, or for a fleet/class of equipment and vessels.

In the field of wave energy converter control, high fidelity numerical models have become the predominant tool for the development of accurate and comprehensive control strategies. In this study, a numerical model of a novel wave energy converter, employing a pneumatic power take-off, is created to provide a low-cost method for the development of a power-maximizing control strategy. Device components and associated architectures are developed in the time domain solvers Proteus DS and MATLAB/Simulink. These two codes are dynamically coupled at run time to produce a complete six degree of freedom, time domain simulation of the converter. Utilizing this numerical framework, a genetic algorithm optimization procedure is implemented to optimally select eight independent parameters governing the PTO geometry. Optimality is measured in terms of estimated annual energy production at a specific deployment location off the West Coast of Canada. The optimization exercise is one layer of PTO force control — the parameters selected are seen to provide significant improvements in the annual power output, while also smoothing the WEC power output on both a sea-state by sea-state and wave-by-wave basis.