| 1. |
- Reinke, Beth A, et al.
(author)
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Diverse aging rates in ectothermic tetrapods provide insights for the evolution of aging and longevity
- 2022
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In: Science. - : American Association for the Advancement of Science. - 0036-8075 .- 1095-9203. ; 376:6600, s. 1459-1466
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Journal article (peer-reviewed)abstract
- Comparative studies of mortality in the wild are necessary to understand the evolution of aging; yet, ectothermic tetrapods are underrepresented in this comparative landscape, despite their suitability for testing evolutionary hypotheses. We present a study of aging rates and longevity across wild tetrapod ectotherms, using data from 107 populations (77 species) of nonavian reptiles and amphibians. We test hypotheses of how thermoregulatory mode, environmental temperature, protective phenotypes, and pace of life history contribute to demographic aging. Controlling for phylogeny and body size, ectotherms display a higher diversity of aging rates compared with endotherms and include phylogenetically widespread evidence of negligible aging. Protective phenotypes and life-history strategies further explain macroevolutionary patterns of aging. Analyzing ectothermic tetrapods in a comparative context enhances our understanding of the evolution of aging.
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| 2. |
- Besnard, Francois, 1983, et al.
(author)
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A Model for the Optimization of the Maintenance Support Organization for Offshore Wind Farms
- 2013
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In: IEEE Transactions on Sustainable Energy. - 1949-3029 .- 1949-3037. ; 4:2, s. 443-450
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Journal article (peer-reviewed)abstract
- Maintenance of offshore wind power plants is known to be extensive and costly. This paper presents a model for optimizing the maintenance support organization of an offshore wind farm: the location of maintenance accommodation, the number of technicians, the choice of transfer vessels and the use of a helicopter. The model includes an analysis of a transportation strategy using alternative transportation means, a queuing model of maintenance activities and an economic model of the maintenance support organization. An example based on a generic 100 wind turbine 5MW wind farm is used to present the application of the model. The results show the benefit of the production losses of the different options, which enables the identification of an optimal maintenance support organization based on the reliability, logistic costs and electricity price. The most cost-efficient maintenance support organization in the case study consists of an offshore accommodation with technicians on service 24 hours a day, 7 days a week. The solution suggests transportation by use of a crew transfer vessel equipped with a motion compensated access system.
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| 3. |
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| 4. |
- Besnard, Francois, 1983, et al.
(author)
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A stochastic model for opportunistic maintenance planning of offshore wind farms
- 2011
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In: 2011 IEEE PES Trondheim PowerTech: The Power of Technology for a Sustainable Society, POWERTECH 2011; Trondheim; 19 June 2011 through 23 June 2011. - 9781424484195
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Conference paper (peer-reviewed)abstract
- A sound maintenance planning is of crucial importance for wind power farms, and especially for offshore locations. This paper presents a stochastic optimization model for opportunistic service maintenance of offshore wind farms. The model takes advantage of 7 days wind production ensemble forecast and opportunities at corrective maintenance activities in order to perform the service maintenance tasks at the lowest cost. The model is based on a rolling horizon, i.e. the optimization is performed on a daily basis to update the maintenance planning based on the updated production and weather forecasts. An example based on real wind data is used to demonstrate the value of the proposed approach. In this example, it is shown that 32% of the cost for production losses and transportation could be saved. © 2011 IEEE.
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| 5. |
- Besnard, Francois, et al.
(author)
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An approach for condition-based maintenance optimization applied to wind turbine blades
- 2010
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In: IEEE Transactions on Sustainable Energy. - 1949-3029 .- 1949-3037. ; 1:2, s. 77-83
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Journal article (peer-reviewed)abstract
- A sound maintenance planning is of crucial importance for wind power systems. There is a large potential in cost savings by optimizing maintenance decisions to make the projects more cost-efficient. This paper presents an approach to optimize condition-based maintenance strategies for components which degradation can be classified according to the severity of the damage. The approach is applicable to inspection-based maintenance as well as maintenance based on online condition-monitoring systems. This enables us to compare the maintenance strategies within a unified framework. First decisions associated with the different maintenance strategies are optimized, then the expected life cycle maintenance costs of the strategies are compared. The model is applied to blades of wind turbine in order to compare three maintenance strategies: visual inspection, inspection with a condition-monitoring technique (e.g., ultrasonic or thermography), and online condition monitoring (e.g., fiber optic). It is shown that online condition monitoring is the optimal maintenance strategy for high failure rate and low crack time to failure. In other cases, inspection with condition-based maintenance is slightly more beneficial.
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| 6. |
- Besnard, Francois, et al.
(author)
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An Optimization Framework for Opportunistic Maintenance of Offshore Wind Power System
- 2009
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In: 2009 IEEE BUCHAREST POWERTECH, VOLS 1-5. - NEW YORK : IEEE. - 9781424422340 ; , s. 2970-2976
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Conference paper (peer-reviewed)abstract
- A sound maintenance planning is of crucial importance for wind power farms, and especially for offshore locations. There is a large potential in cost savings by maintenance optimization to make the projects more cost-efficient. This paper presents an opportunistic maintenance optimization model for offshore wind power system. The model takes advantage of wind forecasts and corrective maintenance activities in order to perform preventive maintenance tasks at low costs. The approach is illustrated with an example to demonstrate the value of the optimization. In this example 43% of the cost to perform preventive maintenance could be saved using the proposed method.
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| 7. |
- Besnard, Francois, 1983
(author)
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On maintenance optimization for offshore wind farms
- 2013
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Doctoral thesis (other academic/artistic)abstract
- The maintenance cost is known to be an important part of the levelized cost of energy generated by wind parks. Operational costs can be significantly reduced by optimizing decisions for maintenance strategies, maintenance support organization and maintenance planning. This is especially important for offshore wind power systems to reduce the high economic risks related to the uncertainties in the accessibility and reliability of wind turbines.This thesis proposes decision models for cost efficient maintenance for offshore wind power systems. The economical benefits of condition based maintenance strategies are evaluated for drive train and for blades of wind turbines. A model is presented to optimize the inspection interval for the blades. Models are proposed to perform cost-benefit analysis of the maintenance support organization by evaluating the benefit of logistic and personnel planning on availability. The maintenance planning of service maintenance activities is optimized by taking advantage of opportunities arising at low wind or when corrective maintenance activities are necessary.The models are tested in case studies with real environmental, reliability and cost data when available, and sensitivity analyses are performed for the parameters of interests. The results show that the proposed models can be used to reduce the maintenance costs through optimizing the maintenance strategies, the support organization and the maintenance planning.
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| 8. |
- Besnard, Francois, 1983-
(author)
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On Optimal Maintenance Management for Wind Power Systems
- 2009
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Licentiate thesis (other academic/artistic)abstract
- Sound maintenance strategies and planning are of crucial importance for wind power systems, and especially for offshore locations. In the last decades, an increased awareness of the impact of human living on the environment has emerged in the world. The importance of developing renewable energy is today highly recognized and energy policies have been adopted towards this development. Wind energy has been the strongest growing renewable source of energy this last decade. Wind power is now developing offshore where sites are available and benefits from strong and steady wind. However, the initial investments are larger than onshore, and operation and maintenance costs may be substantially higher due to transportation costs for maintenance and accessibility constrained by the weather. Operational costs can be significantly reduced by optimizing decisions for maintenance strategies and maintenance planning. This is especially important for offshore wind power systems to reduce the high economic risks related to the uncertainties on the accessibility and reliability of wind turbines. This thesis proposes decision models for cost efficient maintenance planning and maintenance strategies for wind power systems. One model is proposed on the maintenance planning of service maintenance activities. Two models investigate the benefits of condition based maintenance strategies for the drive train and for the blades of wind turbines, respectively. Moreover, a model is proposed to optimize the inspection interval for the blade. Maintenance strategies for small components are also presented with simple models for component redundancy and age replacement. The models are tested in case studies and sensitivity analyses are performed for parameters of interests. The results show that maintenance costs can be significantly reduced through optimizing the maintenance strategies and the maintenance planning.
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| 9. |
- Besnard, Francois, et al.
(author)
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On the economic benefits of using condition monitoring systems for maintenance management of wind power systems
- 2010
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In: 2010 IEEE 11th International Conference on Probabilistic Methods Applied to Power Systems, PMAPS 2010. - 9781424457236 ; , s. 160-165
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Conference paper (peer-reviewed)abstract
- The large growth in the wind power industry in the past years mainly focuses on a growing market and the development of large turbines and offshore farms. The high technical availability of wind turbines comes with a high need for frequent maintenance. Current maintenance planning is generally not optimized, and it is possible to make maintenance more efficient. Condition Monitoring Systems (CMS) are commonly used in other industries and can reduce the consequential damage at failure and provides advantages for the planning of the maintenance. It is of interest to determine if the wind industry would benefit of the use of CMS. This paper shows results from Life-Cycle-Cost (LCC) evaluated with probabilistic methods and sensitivity analysis to identify the benefit of using CMS. The results highlight that there is a high economic benefit of using CMS, as well as benefits on the risk. The benefit is highly influenced by the reliability of the gearbox.
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| 10. |
- Besnard, Francois, 1983, et al.
(author)
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Reliability-Centred Asset Maintenance – A step towards enhanced reliability, availability, and profitability of wind power plants
- 2010
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In: In Proceedings of the IEEE PES Conference on Innovative Smart Grid Technologies Europe, 11-13 October 2010, Gothenburg, Sweden. - 9781424485109
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Conference paper (peer-reviewed)abstract
- Reliability and availability are key issues for theimplementation of future sustainable power systems. This paper discusses the need, methods and challenges for maintenance optimization to improve the reliability, availability, and profitability of wind power plants being a major source of renewable energy today and in future “smart grids”. The present maintenance of wind power plants is extensive and costly, especially at offshore sites. The paper discusses approaches to maintenance strategy optimization aiming at reaching cost efficient maintenance and thus enhanced profitability of wind power plants. It presents results from practical case studies utilising the method of Reliability-Centred Asset Maintenance and highlights the factors that impact the benefit of the maintenance strategies. The results show that new solutions for condition monitoring of the drive train and blades in wind turbines can be cost-efficient with respect to the reliability and availability of wind turbines today.
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| 11. |
- Clement, Yves, et al.
(author)
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Evolutionary forces affecting synonymous variations in plant genomes
- 2017
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In: PLOS Genetics. - : PUBLIC LIBRARY SCIENCE. - 1553-7390 .- 1553-7404. ; 13:5
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Journal article (peer-reviewed)abstract
- Base composition is highly variable among and within plant genomes, especially at third codon positions, ranging from GC-poor and homogeneous species to GC-rich and highly heterogeneous ones (particularly Monocots). Consequently, synonymous codon usage is biased in most species, even when base composition is relatively homogeneous. The causes of these variations are still under debate, with three main forces being possibly involved: mutational bias, selection and GC-biased gene conversion (gBGC). So far, both selection and gBGC have been detected in some species but how their relative strength varies among and within species remains unclear. Population genetics approaches allow to jointly estimating the intensity of selection, gBGC and mutational bias. We extended a recently developed method and applied it to a large population genomic dataset based on transcriptome sequencing of 11 angiosperm species spread across the phylogeny. We found that at synonymous positions, base composition is far from mutation-drift equilibrium in most genomes and that gBGC is a widespread and stronger process than selection. gBGC could strongly contribute to base composition variation among plant species, implying that it should be taken into account in plant genome analyses, especially for GC-rich ones.
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| 12. |
- Fischer, Katharina, 1979, et al.
(author)
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A Limited-Scope Reliability-Centred Maintenance Analysis of Wind Turbines
- 2011
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In: Scientific Proceedings of the European Wind Energy Conference & Exhibition EWEA 2011, 14-17 March 2011, Brussels, Belgium. ; , s. 89-93
-
Conference paper (peer-reviewed)abstract
- This paper presents results from a limited-scope Reliability-Centred Maintenance (RCM) analysis of the wind turbines Vestas V44-600kW and V90-2MW. The RCM analysis has been carried out within a workgroup involving a wind turbine owner and operator, a maintenance service provider, a provider of condition-monitoring services and wind turbine component supplier as well as researchers at academia. The study forms the basis for the development of quantitative models for maintenance strategy selection and optimization.Taking into account both the results of failure statistics and expert opinion, the analysis focuses on the most critical subsystems with respect to failure frequency and consequences. The analysis provides the most relevant functional failures and their failure causes as well as suitable measures to prevent either the failure itself or to avoid critical secondary damage. In this paper, results for the subsystems gearbox, generator and rotor current control / converter are presented.Challenges identified by the RCM workgroup which are considered to impede the achievement of cost-effective operation and maintenance of wind turbines are discussed together with proposed solutions. Standardized and automated collection of in-depth failure and maintenance data, enhanced training of maintenance personnel, and the utilisation of quantitative methods for decision support in wind turbine maintenance are identified as important steps to improve the reliability, availability and profitability of wind turbines.
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| 13. |
- Fischer, Katharina, 1979, et al.
(author)
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Reliability-Centred Maintenance for Wind Turbines Based on Statistical Analysis and Practical Experience
- 2012
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In: IEEE Transactions on Energy Conversion. - 1558-0059 .- 0885-8969. ; 27:1, s. 184 - 195
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Journal article (peer-reviewed)abstract
- The concept of Reliability-Centred Maintenance (RCM) is applied to the two wind turbine models Vestas V44-600kW and V90-2MW. The executing RCM workgroup includes an owner and operator of the analyzed wind turbines, a maintenance service provider, a provider of condition-monitoring services and wind-turbine component supplier as well asresearchers at academia. Combining the results of failurestatistics and assessment of expert judgement, the analysis is focused on the most critical subsystems with respect to failure frequencies and consequences: the gearbox, the generator, the electrical system and the hydraulic system. The study provides the most relevant functional failures, reveals their causes and underlying mechanisms and identifies remedial measures to prevent either the failure itself or critical secondary damage. Thestudy forms the basis for development of quantitative models for maintenance strategy selection and optimization, but may also provide a feedback of field experience for further improvement of wind-turbine design.
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