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.

This paper explores geometry optimization of an offshore wind turbine’s mooring system considering the minimization of the material cost and the cumulative fatigue damage. A comparison of time domain simulations against frequency domain simulations is made to explore the suitability of these methods to the design process. The efficient design options, the Pareto front, from the frequency domain study are also re-evaluated using time domain simulations and compared against the time domain Pareto front. Both the time and frequency domain results show optimal results utilizing similar design philosophies, however, the frequency domain methods severely under predict the fatigue loads in the mooring system and incorrectly class infeasible solutions as feasible. The frequency domain is therefore not suitable for optimization use without some external means of applying engineering constraints. Furthermore, re-evaluation of the frequency domain solutions provides guidance to the uncertainty and the necessary design fatigue factors required if implementing frequency domain methods in design.

Offshore wind assets have reached multi-GW scale and additional capacity is being installed and developed. To achieve demanding cost of energy targets, awarded by competitive auctions, the operation and maintenance (O&M) of these assets has to become increasingly efficient, whilst ensuring compliance and effectiveness. Existing offshore wind farm assets generate a significant amount of inhomogeneous data related to O&M processes. These data contain rich information about the condition of the assets, which is rarely fully utilized by the operators and service providers. Academic and industrial research and development efforts have led to a suite of tools trying to apply sensor data and build machine learning models to diagnose, trend and predict component failures. This study presents a decision support framework incorporating a range of different supervised and un-supervised learning algorithms. The aim is to provide guidance for asset owners on how to select the most relevant datasets, apply and choose the different machine learning algorithms and how to integrate the data stream with daily maintenance procedures. The presented methodology is tested on a real case example of an offshore wind turbine gearbox replacement at Teesside offshore wind farm. The study uses k-nearest neighbour (kNN) and support vector machine (SVM) algorithms to detect the fault using supervisory control and data acquisition (SCADA) data and an autoregressive model for the vibration data of the condition monitoring system (CMS). The implementation of all the algorithms has resulted in an accuracy higher than 94%. The results of this paper will be of interest to offshore wind farm developers and operators to streamline and optimize their O&M planning activities for their assets and reduce the associated costs.

Large-scale deployment of multiple structures within a Floating Offshore Wind Farm (FOWF) will place many challenges on both the approach to effective integrity management and the demand to reduce through-life operating costs. Additionally, wind farm designers and operators will need to consider the issues related to design robustness in the design of their systems, whereby rational robustness criteria are applied to address possible accidental conditions that are not explicitly addressed in code-specified design basis conditions. This paper will review the significant advances in the approach to integrity management that have been recently made in the mature offshore oil industry and relate them to the nascent offshore wind industry. In particular, the requirement for consideration across the full lifecycle of the potential for threat introduction and the application of controls to prevent or mitigate the evolution of those threats will be described. This includes threats that may be inadvertently introduced during the design, manufacturing and installation phases, in addition to the more traditional rate-based degradation mechanisms such as fatigue, corrosion and wear that occur once the facility is in operation. The challenges that commercial-scale wind farm developments will face relate particularly to integrity issues arising in the design, manufacturing and installation phases, where the focus needs to ensure that degradation threats are not being introduced into the deployment of multiple repeat-copy units. The issues of common cause/common mode degradation threats will have much higher significance for a commercial-scale wind farm, where rectification of a common issue across a large number of floating units could have significant impacts in terms of reliability, operating costs, insurance premiums and power purchase agreements. FOWF mooring system designs are also likely to be more optimized than that for a typical one-off offshore oil facility. This will require the wind farm designer to have a deep understanding of the fundamental dynamic behavior of the overall system and the local dynamic behaviors of the components within the mooring system in order to be able to fully identify the types of threats that may be present. This may also involve robustness considerations where there may be step changes in the dynamic behavior of the system, often termed as cliff-edge effects. The paper will outline issues that wind farm designers will need to consider in building integrity considerations into the design and execution phases of a development, as well as the opportunities that risk-based integrity management processes offer in terms of through-life condition verification and inspection optimization.

Concrete platforms have proven to be a viable offshore solution for deep-water projects according to the documented performance of over 40 years [1]. Since concrete has resistance to seawater corrosion, reduced maintenance costs and motions, concrete structures have become attractive to the offshore oil and gas industry [2, 3]. There are many floating concrete structures such as barge, ship, platform and LNG/LPG terminals. While most concrete offshore platforms are the fixed structures, floating concrete platforms have been used for drilling, extraction /storage and production units for oil and gas including heavy lifter. There are two representative floating concrete facilities on the Norwegian shelf, Troll B and Heidrun A [4, 5]. Troll B is the first concrete semi-submersible product unit and Heidrun A is the floating concrete tension leg platform. The concrete FPSO (Floating Production Storage and Offloading), however, was assessed to be inferior to the steel FPSO in respect of feasibility. In this study, an optimization design of the cross-section for cylinder shaped concrete platform is presented in order to promote the feasibility of a concrete hull for an FPSO. Optimal aspect ratio (depth to diameter) with economic analysis is examined and tangerine-shaped section which can utilize the excellent material properties of the concrete in compressive strength is developed. Exterior wall having a small curvature are applied to transmit the load to interior bulkhead. A parametric sensitivity study was conducted to find the optimal curvature of the exterior wall. Subsequently, an arch-shaped wall is applied to center wall in order to improve the upper and lower tension force caused by bending moment. The tendon was placed in the center of any cross-section, taking into account the tensile force that can be caused by additional asymmetric loads. The effect of tangerine shaped cross-section can be clearly identified by comparing the results with the circular shaped cross-section.

This paper presents details of the numerical modelling of a novel vertical axis tidal turbine that incorporates localised flow acceleration and variable-pitch blades. The focus of this research is to develop a computational fluid dynamics model of a 1:20 scale model of the device using ANSYS ® Fluent ® . A nested sliding mesh technique has been developed, with an outer sliding mesh being used to model the turbine and additional inner sliding meshes being used for each of the six blades. The turbine sliding mesh is embedded in an outer static domain which includes the flow accelerating bluff body. The variable pitch of the blades is specified in the model using a user-defined function (UDF) which faithfully reproduces the blade pitch during operation of the 1:20 scale model. Modelled power performance and velocity data are compared with experimental results obtained from scale model tests in a recirculating flume. The modelled power curves show good agreement with the measured data; the difference in maximum C P , for example, is just 5.7 %. The model also accurately reproduces measured flows downstream of the turbine. The high model accuracy means that it can now be used for design optimisation studies.

The management of a heterogeneous mix of underwater vehicles needs a robust and reliable communication network, able to connect the remote command and control station (typically ashore or on board of a support ship) with nodes and vehicles in the deep sea. On the basis of this scenario, the infrastructure shall satisfy requirements such as: medium to extremely long distances between the control room and the area of operation; management of a variable number and type of nodes and vehicles (mobile, fixed, underwater, surfaced); a guaranteed bandwidth to send commands and receive platform status and tasks execution information with minimum latency; a high bitrate to transfer sensor data, pictures and videos in “near real time”; etc. Compared to the available solutions used nowadays for radio communication systems, the underwater environment imposes several constraints on the maximum achievable bandwidth and distance, drastically reducing data transfer rates. This means that the full communication network is a trade-off between different requirements and performances. The SWARMs project approach to this problem is to select, combine and integrate different and heterogeneous communication technologies, components and solutions, in order to obtain the best performances for the management and control of underwater vehicles during the execution of different missions and tasks. The network is mainly based on commercial components, but specific adaptations were made in order to fulfil the requirements of ad hoc underwater and overwater sub networks in maritime specific scenarios. Several experiments and sea trials have allowed the verification of the performance of the full network and the optimization of its configuration according to the mission needs.

The paper explores Kriging-based surrogate model combined with Weighted Expected Improvement approach and for the ship hull form optimization. The training dataset of the Kriging-based surrogate model is obtained by sampling the design space (Design of Experiments, DOE) and performing expensive high-fidelity computations on the selected points. Expected Improvement (EI) is used as a criterion to select one additional sample point in each iteration. The Weighted Expected Improvement (WEI) is derived from EI by adding a tunable parameter which can adjust the weights on exploration and exploitation in the Efficient Global Optimization (EGO). The proposed method selects more than one new sample point by changing the weight parameter for each optimization iteration, thus it can be performed by parallel computation or multi-computer runs which improves the computational efficiency distinctly. This makes it possible not only to improve the accuracy of the surrogate model, but also to explore the global optimum much more quickly. The present method is applied to mathematical test function and a ship hull form optimization design in order to find the optimal hull form with best resistance performance in calm water in different speeds. The result shows that the criterion of WEI can be applied in EGO for optimization design and can be easily extended to other hull form optimization design problems based on computational fluid dynamics.

This paper focuses on getting optimised ship trajectories in narrow waterways under wind disturbances considering time as an objective function, i.e. the ship tends to sail by taking the optimised rudder output for minimum time manoeuvre. Non-linear programming (NLP) has been proposed to use with weighted sigmoid function as non-equality constraints to follow up the reference line if it is necessary. Problems with different boundary conditions and disturbance values have been investigated to justify the effectiveness of the proposed method. The problem regarding the initial value for the start-up of the optimisation process has also been resolved by applying a systematic technique for this method.

Semi-submersible is designed with low heave motions compared with conventional ships by utilizing the cancelation effects between pontoons and columns. During the past years, continuous efforts have been devoted to reducing the heave amplitudes considering utilizing dry-tree system. Different concepts of semi-submersible have been proposed with favorable heave response. Deep draft semi-submersibles have been proved to be efficient in reducing the heave motions, and the damper structures under the pontoon may also reduce the heave responses significantly. Those concepts are beyond the conventional semi-submersible design, which may bring high costs for fabrication and installations. During computer-aided design and analysis, optimization algorithms are used to search for the optimal hull configuration. However, due to the restrictions of computer capacities, the global optimization algorithm, in some cases, have difficulties in finding out the optimal solutions without the aid from engineering experience. In this paper, the geometry of a ring-pontoon four-column semi-submersible is generated by parametric modelling. The heave transfer functions at center of gravity are calculated using WADAM. Genetic algorithm is used to find the most favorable heave responses. In the end, the parameters that influence the heave motions are summarized and discussed.

The offshore oil fields exploitation, especially giant fields in the Santos basin, brings with it demands for systems capable of operating at ultra-deep waters, with high capacity production wells and high gas/oil ratio (GOR) with large amount of contaminants. In this scenario, steel catenary risers (SCRs) offer the simplest, most robust and lowest cost solution. However, due to its rigidity compared to flexible risers, this solution is affected by the high dynamic forces imposed on the top of the riser, in consequence of the FPSOs large vertical movement in waves, making difficulties on their application in conventional FPSO hull units. This dynamic problem is caused by environmental conditions of the region, which are harsher than those observed in the Campos Basin. The reservoir characteristics described above demands high-capacity oil & gas process plants, larger than those used today in the Brazilian offshore. Initial estimates show that these plants require a much larger deck area than conventional platforms and, more than that, a greatest breadth of the vessel. This paper presents the ULFPSO (Ultra Large Floating Production, Storage and Offloading) concept, developed to satisfy such conflicting requirements. The design process, including the preliminary sizing, physical scale model test and the hull form optimization are discussed and presented in this paper based on a high-capacity process plant case study.

In this paper, we are comparing fuel consumption on a case study hybrid marine power plant with diesel gensets and batteries. Optimization methods are used to find an optimal operating point for the gensets, under different power demands, with regards to fuel consumption and NO x emissions. Three different power system example configurations for an offshore construction vessel are explored in this study, and the simulations are carried out to compare the resulting fuel consumption and NO x emissions for these power system configurations.

This paper presents a LNG Liquefaction cycle configuration using two stages of methane expansion and a single stage of nitrogen expansion (Dual Refrigerant) to improve the efficiency of the conventional methane and nitrogen refrigerant expansion cycle (Niche Cycle). The chosen configuration further optimizes the composite cooling and heating curve of the liquefaction cycle, resulting in a higher thermodynamic efficiency. The production efficiency of the liquefaction cycle can be improved by reducing the interval between the cooling curve of the natural gas and the warming curve of the refrigerant: the closer both curves are, the better the efficiency of the cycle. This optimization is achieved by adjusting the refrigerant operating temperatures and pressures. The advanced dual refrigerant expansion cycle includes three levels of expansion, each having different temperature and pressure levels. In the methane expansion loop there are two stages, which are classified warm and cold. The warm loop is applied in the pre-cooling zone and the cold loop is responsible for the main liquefaction. The nitrogen loop is a single stage and is used for sub-cooling. This configuration allows the methane and nitrogen warming curve to closely match the cooling curve of the natural gas cooling curve by changing the methane and nitrogen warming curve from two straight lines into multiple intersecting straight lines of different gradient. That is to say, the additional new methane expander generates an added inflection point within the cold composite curve. As a result, thermodynamic inefficiencies are minimized and the power requirements are reduced when compared to Niche Cycle. In comparison with other previous expansion cycles, the cycle efficiency has increased approximately from 13.13 to 12.08 kW/ton/day (8% efficiency increase) assuming similar feed gas (methane: 80%, MW: 21.38). The composition of this feed gas is representative for associated gas or pipe line gas which is preliminary treated to remove bulk water and hydrocarbon condensate. A case study is presented for an open sea associated gas FLNG concept, comparing three kinds of liquefaction processes (Double Nitrogen Expansion Cycle, Methane & Nitrogen Expansion Cycle and Developed Dual Refrigerant Expansion Cycle). A Life Cycle Cost (LCC) analysis based on Net Positive Value (NPV) also shows an improvement in terms of project NPV, against a minor increment of the CAPEX of these cycles.

This paper presents a cost driven, high-level optimization of Offshore Supply Vessel (OSV) operations in the Flemish Pass sector. This is an area located in the offshore waters of Newfoundland where significant oil discoveries were made in recent years, but where oil extraction will pose logistical challenges due to the increased distance from shore bases. In the first part of this paper, a simple non-linear programming model is used to minimize the monthly costs to supply a hypothetical offshore oil installation located in the Flemish Pass and to assess whether hypothetical fast supply vessels make economic sense. The second part of this paper explores the application of Pareto frontiers to the non-linear system, to evaluate the impact of schedule slack on costs, but also to look at winter operations in the Flemish Pass area.

Steel Catenary Riser (SCR) design is a complex issue for the petroleum industry. The fact that it is strongly influenced by safety and cost saving factors has motivated the use of optimization techniques mostly based on metaheuristic algorithms such as Genetic Algorithms, Artificial Immune Systems and Particle Swarm Optimization. However, this particular offshore engineering problem requires high computational costs, associated to the time-domain nonlinear dynamic analyses with Finite Element (FE) models that are needed for a large number of loading cases for each candidate solution of the optimization process. This fact motivates studies the use of meta-models (or surrogate models) to replace the expensive FE analyses, leading to results with adequate accuracy and remarkably lower computational costs. In this context, this work applies as meta-models Artificial Neural Networks (ANN) and Multivariate Adaptive Regression Splines (MARS) to estimate the response of SCR risers in a lazy-wave configuration. Case studies are presented to assess the results comparing to a FE analysis.

Mooring of offshore structures is a well-known concept in the naval and offshore Oil & Gas sectors, but has been proven to cause complications and be infeasible in the newer wave and wind energy sectors when applying the traditional solutions and experience. Early-stage wave energy concepts are often planned for deployment in shallow to intermediate water depths, where the traditional catenary systems are insufficient, and have experienced several failures due to large line loads. As a result, considerable amount of line and anchor material is often required and causes undesirably high mooring cost. A need for applying more novel systems and materials is present in order to increase durability and decrease the cost. This study focusses on three different mooring systems, which have been considered in earlier studies and makes direct comparison between the lifetime cost using existing cost databases and design procedures stated in design standards from certification companies. All systems are primarily composed of synthetic lines, and are designed using validated numerical models together with a surrogate based optimization routine. Furthermore, the study investigates the sensitivity on line tensions from varying environmental loads in order to quantify the sensibility and the importance of pre-assessment of the conditions at the expected deployment site.

A lot of effort is put to achieve bolt preload uniformity during the assembly process of offshore bolted joint connections resulting in potentially high economic costs and project delays. The complexity of this operation is due to the effect of the elastic interaction between the different joint elements which causes load variations of adjacent bolts whenever a bolt is tightened. As a consequence, it is difficult to achieve a uniform target load in the bolts. In order to avoid this phenomenon, tightening sequences of a large number of passes are usually carried out until a uniform target load is achieved. This solution is neither practical nor efficient when treating hundreds or even thousands of bolted joints due to the large assembly time needed. Several methods were developed to study the effect of the elastic interaction and minimize the assembly time. These methods usually predict the loss of load of every bolt during the tightening sequence, and thus calculate the tightening loads that will provide a uniform final load at the end of the sequence. As a result, an optimized tightening sequence is achieved, which provides a uniform final load distribution in only one or two tightening passes. However, several complex and costly analyses are previously necessary for such purpose. Based on these traditional methods, this paper presents a new and more efficient optimization methodology to achieve assembly bolt load uniformity. The method is based on the use of superelement technique and is capable of producing similar results with computational costs reduced by 30 times as compared to the more conventional Finite Element (FE) modeling. The results were satisfactorily validated with the latter as well as with tests conducted on a NPS 4 class 900 bolted joint.

This paper proposes several schemes for optimal online configuration and load sharing for a shipboard power system of a typical offshore vessel, having a number of varying capacity gensets. Different methods are presented for optimal online scheduling and minimization of specific fuel oil consumption using mixed integer linear programming. The simulations for optimization of specific fuel oil consumption for three different scheduling methods demonstrate their properties.

Kinetic turbines harnessing tidal and ocean currents make use, in some designs, of nozzles and/or diffusers. Nozzles come at a cost, but they can help from the structural, hydrodynamic or positioning points of view. In those cases, they might make sense as long as they drive the LCoE (Levelized Cost of Energy) down, which is the ultimate objective of energy-harnessing devices. The design must then optimize the combined performance of both blades and nozzle. However, the interaction between turbine blades and nozzle is not always fully clear, and even less its optimization. A relevant amount of efficiency can be lost if the design spiral is not appropriate. The authors have suggested in [1] an approach for the optimization of turbines within nozzles. This approach was followed in [2] and validated with model tests. In the approach, the turbine is initially substituted by an actuator disc that applies a radially constant pressure drop. But in these references, the optimum pressure drop in the actuator disc was the same as if there was no nozzle at all, i.e., 4/9 ρv 2 . This is equivalent to considering the nozzle coefficient does not depend on the pressure drop, and thus, on the induced velocity field. Hence it is a somewhat arbitrary assumption. This paper describes, using actuator disc theory, how nozzles affect the disc optimum pressure drop in uniform flow conditions. The effect of a hub is also analyzed. Then, using a viscous FVM CFD code, the variation of the pressure drop is quantified for two different acceleration nozzles, one suffering flow separation and the other one not. As the pressure drop increases, so does the flow expansion downstream. This rises the average radial component of velocity at the nozzle, increasing the thrust and nozzle coefficient. Therefore the optimum pressure drop goes up compared to that without nozzle. The increment in efficiency that can be obtained with this approach is quantified for the studied nozzles. Finally, the integration of this effect into the blade design is discussed.

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.