Applicability of offshore mooring and foundation technologies for marine renewable energy (MRE) device arrays

Published onlineThe marine renewable energy (MRE) sector is progressing from single device units to device arrays. Currently, the mooring/foundation technologies used in MRE are based on offshore oil/gas industry practices. For MRE arrays to reach commercialization, several issues need to be addressed including the hy-drodynamic array layout, electrical infrastructure, operations, maintenance, control, moorings, foundations, installation and logistics. The DTOcean (The Optimal Design Tools for Ocean Energy Arrays) project is aimed at accelerating the industrial development of ocean energy power generation knowledge, and providing design tools for deploying the first generation of wave and tidal energy converter arrays. In this paper, the ap-plicability of offshore mooring/foundation technologies for marine renewable energy (MRE) device arrays are assessed. The paper introduces the criteria which can be used to appraise technologies and approaches rele-vant to MRE devices. Existing mooring/foundation technologies used in the offshore industry are summarized with examples given of MRE device deployments. The guidance from certification agencies which is used for the design and analysis of mooring/foundation systems is summarized. If not addressed, the failure to opti-mize the design of ocean energy arrays and failure to properly understand economic, environmental, or relia-bility impacts of individual components could have significant consequences for the overall project and sec-tor. The function and type of mooring and/or foundation system are determined by a number of factors including the cost, site characteristics, expected environmental loading and environmental or legislative con-straints and these factors are discussed

All-optical generation and photoassociative probing of sodium Bose-Einstein condensates

We demonsatrate an all optical technique to evaporatively produce sodium Bose-Einstein condensates (BEC). We use a crossed-dipole trap formed from light near 1060 nm, and a simple ramp of the intensity to force evaporation. In addition, we introduce photoassociation as diagnostic of the trap loading process, and show that it can be used to detect the onset of Bose-Einstein condensation. Finally, we demonstrate the straightforward production of multiple traps with condensates using this technique, and that some control over the spinor state of the BEC is achieved by positioning the trap as well.Comment: 8 pages, 10 figure

Sub-Natural-Linewidth Quantum Interference Features Observed in Photoassociation of a Thermal Gas

By driving photoassociation transitions we form electronically excited molecules (Na$_2^*$) from ultra-cold (50-300 $\mu$K) Na atoms. Using a second laser to drive transitions from the excited state to a level in the molecular ground state, we are able to split the photoassociation line and observe features with a width smaller than the natural linewidth of the excited molecular state. The quantum interference which gives rise to this effect is analogous to that which leads to electromagnetically induced transparency in three level atomic $\Lambda$ systems, but here one of the ground states is a pair of free atoms while the other is a bound molecule. The linewidth is limited primarily by the finite temperature of the atoms.Comment: 4 pages, 5 figure

Travelling to exotic places with cavity QED systems

Recent theoretical schemes for utilizing cavity QED models as quantum simulators are reviewed. By considering a quadrature representation for the fields, it is shown how Jahn-Teller models, effective Abelian or non-Abelian gauge potentials, transverse Hall currents, and relativistic effects naturally arise in these systems. Some of the analytical predictions are verified numerically using realistic experimental parameters taking into account for system losses. Thereby demonstrating their feasibility with current experimental setups.Comment: 5 pages, 3 figure

Modelling the propagation of underwater acoustic emissions for condition monitoring of marine renewable energy

Marine Renewable Energy (MRE) has progressed towards commercialisation over the recent years but significant barriers still exist. This includes the currently high cost of energy, leaving MRE uncompetitive with respect to other more established renewable energy technologies. A significant proportion of this cost comes from Operation and Maintenance (O&M) activities. O&M activity can be reduced through the use of condition-based maintenance scheduling. In offshore environments, the submerged location of most devices enables the use of underwater Acoustic Emission (AE), a new condition -monitoring technique. It combines acoustics (used for environmental monitoring of MRE influence on noise levels) with AE condition monitoring as used in air. This paper assesses the practicality of such an approach in complex ocean environments through detailed sound propagation modelling using the propagation model Bellhop in the Matlab toolbox AcTUP. Results show that acoustic propagation is very sensitive to variations in the shallow water environments considered. When concerning sensor placement, multiple-path interferences mean that the location of the measuring sensor(s) needs to be carefully considered, but might not cover all environmental variations over the several months necessary for accurate long-term monitoring. Associated to the shallow depths, these environmental variations also mean that some frequencies cannot be back-propagated easily, generally limiting access to the monitoring of Received Levels. The results presented here are the first steps toward optimizing AE sensor positions and AE measuring strategies for arrays of devices.JW is funded by the Natural Environment Research Council (NERC grant NE/L002434/1) as part of the GW4+ Doctoral Training Partnership (http://www.nercgw4plus.ac.uk/). IB is funded through the SuperGen UK Centre for Marine Energy Research (EPSRC grant EP/M014738/1

Modelling the propagation of underwater acoustic emissions for condition monitoring of marine renewable energy

3rd PRIMaRE conference, 5-6 July 2016, University of Bath, Bath, UKMarine Renewable Energy (MRE) has progressed towards commercialisation over the recent years but significant barriers still exist. This includes the currently high cost of energy, leaving MRE uncompetitive with respect to other more established renewable energy technologies. A significant proportion of this cost comes from Operation and Maintenance (O&M) activities. O&M activity can be reduced through the use of condition-based maintenance scheduling. In offshore environments, the submerged location of most devices enables the use of underwater Acoustic Emission (AE), a new condition-monitoring technique. It combines acoustics (used for environmental monitoring of MRE influence on noise levels) with AE condition monitoring as used in air. This paper assesses the practicality of such an approach in complex ocean environments through detailed sound propagation modelling using the propagation model Bellhop in the Matlab toolbox AcTUP. Results show that acoustic propagation is very sensitive to variations in the shallow water environments considered. When concerning sensor placement, multiple-path interferences mean that the location of the measuring sensor(s) needs to be carefully considered, but might not cover all environmental variations over the several months necessary for accurate long-term monitoring. Associated to the shallow depths, these environmental variations also mean that some frequencies cannot be back-propagated easily, generally limiting access to the monitoring of Received Levels. The results presented here are the first steps toward optimizing AE sensor positions and AE measuring strategies for arrays of devices.JW is funded by the Natural Environment Research Council (NERC grant NE/L002434/1) as part of the GW4+ Doctoral Training Partnership (http://www.nercgw4plus.ac.uk/). IB is funded through the SuperGen UK Centre for Marine Energy Research (EPSRC grant EP/M014738/1)

Modelling the propagation of underwater acoustic emissions for condition monitoring of marine renewable energy

This is the author accepted manuscript. The final version is available from CRC PressMarine Renewable Energy (MRE) has progressed towards commercialisation over the recent years but signifi-cant barriers still exist including the currently high cost of energy. A significant proportion of this cost comes from Operation and Maintenance activities which can be reduced through the use of condition-based mainte-nance scheduling. In offshore environments, the submerged location of most devices enables the use of un-derwater Acoustic Emission (AE), a new condition-monitoring technique. It combines underwater acoustics with AE condition monitoring as used in air. This paper assesses the practicality of such an approach in com-plex ocean environments through detailed sound propagation modelling using the propagation model Bellhop in the Matlab toolbox AcTUP. Results show that acoustic propagation is very sensitive to variations in the shallow water environments considered. Associated to the shallow depths, environmental variations mean that some frequencies cannot be back-propagated easily, generally limiting access to the monitoring of Received Levels. The results presented here are the first steps toward optimizing AE sensor positions and AE measuring strategies for arrays of devices.JW is funded by the Natural Environment Research Council (NERC grant NE/L002434/1) as part of the GW4+ Doctoral Training Partnership (http://www.nercgw4plus.ac.uk/). IB is funded through the SuperGen UK Centre for Marine Energy Research (EPSRC grant EP/M014738/1)

Offshore Wind Farm Electrical Cable Layout Optimization

This is the author accepted manuscript. The final version is available from Taylor & Francis via the DOI in this record.This article explores an automated approach for the efficient placement of substations and the design of an inter-array electrical collection network for an offshore wind farm through the minimization of the cost. To accomplish this, the problem is represented as a number of sub-problems that are solved in series using a combination of heuristic algorithms. The overall problem is first solved by clustering the turbines to generate valid substation positions. From this, a navigational mesh pathfinding algorithm based on Delaunay triangulation is applied to identify valid cable paths, which are then used in a mixed-integer linear programming problem to solve for a constrained capacitated minimum spanning tree considering all realistic constraints. The final tree that is produced represents the solution to the inter-array cable problem. This method is applied to a planned wind farm to illustrate the suitability of the approach and the resulting layout that is generated

Specific requirements for MRE foundation analysis

PublishedMarine Renewable Energy (MRE) systems involve single or arrays of devices that are secured to the seafloor via foundations and/or anchors. These MRE devices will transmit long-term cyclic loads to the seafloor sediment or rock, which may affect seafloor material properties and hence the overall physical performance of the MRE system. The response of seafloor sediments or rock formations is uncertain for the novel MRE systems and especially large arrays of 10s to >1000s of devices. This report summarizes critical inputs and tools for the design and analysis of foundations, anchors, and the response of the seafloor materials. Followed by an introduction in Section 1, Section 2 reviews the offshore structure and MRE literature to highlight current approaches and needed inputs for assessing interactions between foundations or anchors and seafloor materials, including potential environmental impacts. Section 3 addresses relevant marine geological settings that control key geotechnical engineering properties. Data collection activities are described, including in-situ site surveys and laboratory testing. Section 4 considers the unique interactions between MRE systems and seafloor materials, particularly cyclic loading and sediment response. Section 5 describes analytical and numerical tools and associated inputs for the design process of MRE foundations and anchors. Constitutive models are key to simulating sediment response and thus are discussed in detail. Important summary tables relate key variables of geology, geotechnical parameters, foundation or anchor type, and quantitative assessment tools including numerical analysis. Section 5 also addresses the incorporation of the geotechnical analysis into system-level tools to support decision making for MRE arrays. Section 6 presents conclusions and recommendations for future work.European Commission’s 7th Framework; Grant agreement number: 60859