Accessing offshore wind turbines for maintenance : calculating access probabilities, expected delays and the associated costs using a probabilistic approach

There are ambitious plans in place for the expansion of offshore wind-power capacity in the EU and elsewhere. However, the cost of energy from offshore wind is much higher than that from land-based generation and anything between 15% and 30% of this cost is attributable to the cost of operation and maintenance (O&M). For exposed UK round three sites these costs could be higher still. The stochastic nature of the occurrence of faults, down-times due to adverse weather and sea-state and the associated losses in energy production, as well as vessel and personnel costs, all add to the potential risk to the finance of an offshore wind farm project. There is a clear need to estimate these effects and the risks associated with them when planning and financing a wind-farm. Key to all such calculations are the restrictions on safe access for maintenance associated with vessels and access methods and the consequent delays caused by adverse sea-state and weather. A computational approach has been developed at University of Strathclyde, based on an event tree and closed-form probabilistic calculations, enabling very fast estimates to be made of offshore access probabilities and expected delays using a simple spreadsheet. Examples are presented for calculations of accessibility. Turbine availability and loss of energy production are calculated based on given turbine component reliability data together with an agreed maintenance scheme. Direct maintenance cost and revenue lost due to down-time can also be calculated with suitable data on the costs of personnel, components, and vessel hire as well as electricity unit and ROC prices, and examples are given. Sensitivities to some of the key parameters are also presented

Estimating the cost of offshore maintenance and the benefit from condition monitoring

The EU generally, and the UK, Belgium, Netherlands and Germany specifically, have ambitious plans for the large scale installation of offshore wind-power capacity. However, the cost of energy from offshore wind is much higher than that from land-based generation and a substantial portion of that cost, anything between 15% and 30%, may be due to the cost of O&M alone, largely driven by delays in access and repair caused by adverse weather and sea-state, high vessel costs, higher wage costs, and lost revenue from extended down-time. As part of a condition monitoring project commissioned and funded by the ETI (Energy Technologies Institute), the authors have developed a simple tool to estimate the cost of O&M and associated lost revenue, and also to estimate the potential for condition monitoring to allow operators to reduce those costs and the loss in revenue through better maintenance scheduling. The tool builds on earlier work conducted at Strathclyde and presented at EOW 2009 on estimating offshore access delays and turbine availability using a closed form probabilistic method based on an event tree, but without extensive time-domain or Monte Carlo simulation. It currently uses wind and wave data, reliability data and component cost data mainly available in the public domain. Repairs and replacements of subsystems have been classified into a small range of different repair severities, each having their specific requirements for vessels, plant, personnel and time. Expected delays can be calculated directly for each type of repair and the overall effects are summed. Condition monitoring and other maintenance strategies are assumed to change the allocation of a particular subsystem's faults between repair categories and thereby affect its overall impact on down-time and other costs.Calculations are carried out in a spreadsheet that updates instantly when any parameter is changed. The advantage of the approach developed is that it is possible to explore the impact of changing access thresholds, reliabilities or site parameters quickly and easily without having to run a long series of simulations for each new situation

Comparison against theory, context without concept

Comment on van der Veer, Peter. 2016. The value of comparison. Durham, NC: Duke University Press

Welcoming dangerous benefactors: incense, gods and hospitality in north-eastern Taiwan

Chinese festival ritual offers an extreme case of hospitality to outsider benefactors, to gods. They are invited outsiders. Their host is a territorial community of households represented by their divinely selected master of the god’s incense burner. Mediation to communicate with and separate from powerful guests is a courting of great power and avoiding its danger. Their welcome poses the danger of offence. To these points I add other sides and counterparts to rites of hospitality, such as rites of charitable feeding. I begin by arguing that the dangers of hospitality suggested by others in this volume are applicable in this case. Finally, I suggest how the terms in which I analyse these Chinese rites are applicable to other orders of hospitality

Replacing Leads by Self-Energies Using Nonequilibrium Green's Functions

An open quantum system consists of leads connected to a device of interest. Within the nonequilibrium Green's function technique, we examine the replacement of leads by self-energies in continuum calculations. Our starting point is a formulation of the problem for continuum systems by T.E. Feuchtwang. In this approach there is considerable flexibility in the choice of unperturbed Green's functions. We examine the consequences of this freedom on the treatment of leads. For any choice the leads can be replaced by coupling self-energies which are simple functions of energy. We find that the retarded self-energy depends on the details of the choice of unperturbed Green's function, and can take any value. However, the nonequilibrum self-energy or scattering function can be taken to be independent of this choice. Expressed in terms of these self-energies, nonequilibrium transport calculations take a particularly simple form.Comment: 14 pages, 0 figure

Implicit comparisons, or why it is inevitable to study China in comparative perspective

Methodological nationalism and the Sino-centrism of Chinese studies stand in the way of sustained comparisons in the study of China. But the supposed singularity of China either relies on implicit comparisons, or on the rejection of comparability. Comparison is a necessity, if only because there are so many contradictory claims to define ‘China’ and what should be part of it. Concepts such as society, empire, and civilization, as well as their substantialization (as in ‘Chinese society’), always rely on implicit comparisons that are accepted as shared fictions. We point to the effects of concealing comparative structures, with examples of Chinese social scientists defining native Chinese concepts; and we discuss the argumentative and political effects of revealing underlying comparisons. On this basis, we argue, it is inevitable to study China in comparative perspective

Tales of Territoriality

AbstractTerritorial place is the most open and inclusive of places. At the same scale the terrifying abstractions of deterritorialisation can be seen to be a negotiated stand-off between different territorialisations. In other words, the deterritorialisation thesis of Deleuze and Guattari, the state project thesis of James Scott, and the dislocation thesis of postmodernists need severe modification. That modification is carried out by ethnography and local history, here by a case study of a Chinese village that is in the process of being urbanised. What is revealed when this is done is that so-called deterritorialisation is a pair of territorialisations, of state projects and of capitalist ribbon development and the nodes of its economic institutions and functions. At this scale they are brought into negotiation with reappropriations of territorial place by local actors.RésuméLe territoire est le plus ouvert et le plus inclusif de tous les lieux. À cette échelle les redoutables abstractions que représente la déterritorialisation peuvent être vues comme un compromis entre différentes formes de territorialisation. En d’autres termes, les thèses de Deleuze et Guattari, de James Scott et des postmodernes, qui mettent l’accent sur la dislocation, doivent être révisées. Cette tâche incombe à l’ethnographie et à l’histoire locale. Dans cet article, une étude de cas sur un village chinois en voie d’urbanisation fait ressortir que la soi-disant déterritorialisation est en fait le résultat de deux territorialisations : celle qui relève du programme de l’État et celle qui s’appuie sur une frange capitaliste de développement dont les points nodaux constituent les institutions économiques et leurs fonctions. À ce niveau, la négociation s’impose avec la réappropriation par les acteurs locaux du territoire

The Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction across a tunneling junction out of equilibrium

The Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between two magnetic $s$-$d$ spin impurities across a tunneling junction is studied when the system is driven out of equilibrium through biasing the junction. The nonequilibrium situation is handled with the Keldysh time-loop perturbation formalism in conjunction with appropriate coupling methods for tunneling systems due to Caroli and Feuchtwang. We find that the presence of a nonequilibrium bias across the junction leads to an interference of several fundamental oscillations, such that in this tunneling geometry, it is possible to tune the interaction between ferromagnetic and antiferromagnetic coupling at a fixed impurity configuration, simply by changing the bias across the junction. Furthermore, it is shown that the range of the RKKY interaction is altered out of equilibrium, such that in particular the interaction energy between two slabs of spins scales extensively with the thickness of the slabs in the presence of an applied bias.Comment: 38 pages revtex preprint; 5 postscript figures; submitted to Phys. Rev.

The State and the Rural Economy in the People's Republic of China

SUMMARY Chinese rural policy, assisted by Mao Zedong's critique of Stalinism, has moved away from the policy of ‘squeeze’, from uncritical assumptions about economies of scale in farming, and from insistence on the necessity of the collectivisation of farm labour as opposed to agricultural infrastructure and agricultural planning. The emphasis is now on increasing peasant purchasing power, on family?scale farming, and on relationships of contract between farming families and state planners as represented by local authorities and parastatal cooperatives. RESUMEN El estado y la economía rural en la República Popular China La política rural China, apoyada en la crítica maoísta al estalinismo, ha abandonado la política de austeridad, así como las hipótesis acríticas sobre las economías de escala en las granjas y la insistencia en la necesidad de colectivizar el trabajo rural en oposición a la infraestructura y planificación agrícolas. Ahora se enfatiza el aumento del poder de compra campesino, la granja a escala familiar y las relaciones contractuales entre las familias de las granjas y los planificadores estatales, representados por las autoridades locales y las cooperativas paraestatales. RESUMES L'état et l'économie rurale dans la République Populaire de Chine La politique rurale chinoise, avec l'aide de la critique du Stalinisme de Mao Zeding, s'est éloignée de la politique de compression, des hypothèses dépourvues de sens critique sur les économies d'échelles de l'exploitation agricole, et de l'insistance de la nécessité de la collectivisation de la main d'oeuvre fermière par opposition à l'infrastructure agricole et à la planification agricole. Le point principal, maintenant, est l'augmentation du pouvoir d'achat des paysans, au niveau de l'exploitation agricole familiale, et les rapports contractuels entre les familles fermières et les planificateurs de l'état representés par les autorités locales et les co?opératives paraétatiques