Evaluation of growth potential and growth dynamics of Listeria monocytogenes on ready-to-eat fresh fruit

The consumption of fresh or RTE fruits is increasing every year and Listeria monocytogenes has been identified on raw or minimally processed fruits. A food product can become contaminated with L. monocytogenes anywhere along the pathway of food production during planting, harvesting, packaging, distribution and serving. The aim of this work was to assess the microbiological risks associated with consumption of ready-to-eat fruit such as melon, pineapple, coconut and fruit salad. The presence of Escherichia coli, Salmonella spp. and L. monocytogenes was also evaluated. Microbiological challenge tests were carried out for the evaluation of the L. monocytogenes growth potential in RTE fruit stored at 4 and 8°C. E. coli counts resulted under the detection limit of 10 CFU g-1, Salmonella and L. monocytogenes were not detected (absence in 25g). The growth potential values in coconut and melon (δ>0.5) showed the growth capacity of Listeria at the temperatures considered. A low initial load, also derived from good hygiene practices, and correct storage temperatures are essential to reduce bacterial growth in RTE fruit. The challenge test showed how each type of RTE fruit has a different commercial life based on its specific growth potential and that food should be stored at temperatures not higher than 4°C for a short period

Offshore Wind, Ready to Float? Global and UK Trends in the Floating Offshore Wind Market

Floating wind foundations could unlock offshore wind power generation in deeper and more remote waters. This report examines how quickly floating wind is progressing towards becoming a key contributor to the global electricity supply mix. It contains a special focus on developments in the UK and Scotland, uncovering challenges that could undermine the growth of floating wind, as well as policy recommendations to overcome these. The floating wind market is growing steadily, expanding from almost zero installed capacity in 2008 to 57 MW in 2018. Looking forward, there is an impressive pipeline of projects for future deployment. By 2030, global capacity of floating wind could be as high as 4.3 GW. Deployment of installed capacity has to date been dominated by the UK and Japan, and the vast majority of these foundations have been designed and developed by companies in Norway and Japan. New entrants, most notably the USA and France, are expected to challenge for leadership in both deployment and design. Whilst SMEs have played a central role in driving growth in the sector, multi-national energy firms are investing heavily in floating wind deployment and design. These include: (1) oil and gas majors; (2) energy utilities; and (3) Original Equipment Manufacturers (OEMs). Floating wind rated turbine capacity more than tripled and hub height almost doubled between 2008–13 and 2013–18. However, the majority of projects remain single-turbine demonstration projects, with just one array deployed. During the same period, the projects’ distance from shore has doubled to average 11km but their depth has increased by just 7%. However, at an average depth of 65m, projects are operating in waters deeper than most bottom-fixed foundations are economically capable of. The UK is the world leader in floating wind deployment, with 56% of global capacity. Retaining this future lead will, however, be likely to depend on it retaining an open trading relationship with the EU, a relationship that it has depended on heavily to deliver its two existing floating wind projects. Taking opportunities to grow the UK content of the offshore wind supply chain may help to mitigate some disruption post-Brexit. The removal of the UK’s Renewables Obligation (RO) has created a gap for long-term support of small-scale pre-commercial floating wind projects. Domestic support will become even more important, should the UK lose access to European technology demonstration funding post-Brexit

Adaptations of offshore wind operation and maintenance models for floating wind

This paper presents the key operations & maintenance (O&M) modelling inputs for fixed-bottom wind (FBW) and highlights the adaptations required for floating offshore wind (FOW) uses. The work also highlights major repair strategies such as tow to shore (T2S) and discusses the limitations and constraints which arise in an operational context. The technical and economic feasibility of such O&M strategies requires rethinking of weather risks and constraints, new vessel technologies and operational costs. The work also collates and reviews existing FBW models which have been adapted for FOW uses and analyses O&M inputs for a tow to shore operation. Findings show that there is ambiguity in literature for tug speeds and disconnection/reconnection times of the turbine system. A performed case study investigates the sensitives of both parameters through a weather window analysis of ScotWind sites. Recommendations for future practises, including additional O&M modelling considerations and inputs for FOW uses are given

Limiting wave conditions for the safe maintenance of floating wind turbines

This paper investigates the limiting wave conditions at which a wind turbine technician can complete maintenance activities safely and effectively on a 15MW floating offshore wind turbine. Through linear, frequency-domain statistical analysis of floating turbine motion and applying acceptable motion limits for technician working, significant wave height and peak wave period limits are investigated. It was found that over the range of wave conditions considered, the turbine nacelle motion did not exceed the motion limits for technician working considered in this analysis. Further analysis found that the turbine nacelle motion increased with increasing significant wave height and was also significantly influenced by peak wave period. The impact of differing wave characteristics is also investigated through the use of different wave energy spectra and also found to have an impact on turbine nacelle motion

Redefining fatigue predictions : a multi-sea state HPC framework for FOWTs

Offshore wind is essential in the global transition to Net Zero carbon emission goals. As the industry pushes into deeper waters, fixed offshore wind solutions are no longer viable, increasing the reliance on floating alternatives. During their operational lifespan of at least 25 years, floating wind turbines are exposed to stochastic winds, waves, currents and the non-linear coupled loads, making fatigue assessment critical in their design and maintenance planning. The industry standard approach is to group similar conditions together into bins, each with a corresponding probability of occurrence based on historical data. However, by assuming all bin members are equivalent, this binning approach results in a loss of information, leading to inaccuracies. Here we propose a more detailed approach, called Numerical Prototype approach, where every individual sea state is considered, produces in turn fatigue estimates expected to be closer to reality since less information is lost due to binning. This paper studies the UMaine VolturnUS-S semi-submersible platform with the IEA 15 MW turbine for with a modified tower for an Atlantic site on the west of France. For the turbine tower, the Numerical Prototype results indicate lower cumulative fatigue estimations by 24 % for the principal direction of fatigue than those calculated using the classical binning method, while for the mooring line fairleads fatigue estimations are up to 14 % lower. These findings suggest that a more discretised calculation and more detailed representation of met-ocean loads lead to lower fatigue predictions, revealing the conservative nature of existing industrial methods. The binning methods currently used in industry result in conservative designs with increased material use and increased costs of floating wind turbines. The present results indicate for the first time a detailed methodology for fatigue estimation that allows optimised designs to reduce structural weight with consequent savings in both installation and material costs. Although the proposed methodology is computationally expensive, the potential savings offer significant benefits for project developers

A review of operations and maintenance modelling with considerations for novel wind turbine concepts

New wind turbine technologies and designs are being explored in order to reduce the cost of energy from offshore wind farms. Two potential routes to a lower cost of energy are the XRotor Concept (XRC) and Multi-Rotor System (MRS) turbines. A key cost saving for both Novel concepts included in this paper is operation and maintenance (O&M) costs savings. The major component replacement cost for conventional horizontal axis, XRC and MRS turbines are examined and the benefits of the concepts are provided in this paper. A review on existing decision support systems for offshore wind farm O&M planning is presented with a focus on how applicable these previous models are to novel turbine concepts, along with analysis of how the influential factors can be modified to effectively model XRC and MRS

Operation and maintenance modelling for multi rotor systems : bottlenecks in operations

Abstract: As the installed capacity of individual turbines increases, so do costs associated with manufacture and maintenance. One proposed solution to this problem is the Multi-Rotor System (MRS) which utilises many small rotors to yield the same energy capture as a single large turbine. The operational advantage of the MRS is the built in redundancy between rotors on the same structure. However, despite this advantage, an increase in number of components is likely to result in an increase in transfers. This work examines the balance between additional crew and vessel requirements for such a structure against the expected savings in downtime due to redundancy and small rotor power rating. Three scenarios are analysed to determine the distribution of the failures which contribute to downtime. The study aims to find the optimal vessel fleet which limits downtime without drastically increasing direct operational expenditure (OpEx). As site size increases, the impact of global failures, which shut down the whole asset, is lessened. However, there is a significant increase in the number of vessels required to reduce downtime t

The Impact of LIDAR‐Assisted Pitch Control on Floating Offshore Wind Operational Expenditure

Floating offshore wind (FOW) is a renewable energy source that is set to play an essential role in addressing climate change and the need for sustainable development. However, due to the increasing threat of climate emergency, more wind turbines are required to be deployed in deep water locations, further offshore. This presents heightened challenges for accessing the turbines and performing maintenance, leading to increased costs. Naturally, methods to reduce operational expenditure (OpEx) are highly desirable. One method that shows potential for reducing OpEx of FOW is LIDAR‐assisted pitch control. This approach uses wind velocity measurements from a nacelle‐mounted LIDAR to enable feedforward control of floating offshore wind turbines (FOWTs) and can result in reductions to the variations of structural loads. Results obtained from a previous study of combined feedforward collective and individual pitch control (FFCPC + FFIPC) are translated to OpEx reductions via reduced component failure rates for future FOW developments, namely, in locations awarded in the recent ScotWind leasing round. The results indicate that LIDAR‐assisted pitch control may allow for an up to 5% reduction in OpEx, increasing to up to 11% with workability constraints included. The results varied across the three ScotWind sites considered, with sites furthest from shore reaping the greatest benefit from LIDAR‐assisted control. This work highlights the potential savings and reduction in the overall levelised cost of energy for future offshore wind turbine projects deliverable through the implementation of LIDAR‐assisted pitch control