CFD modelling of wind farms in complex terrain

Modelling of entire wind farms in flat and complex terrain using a full 3D Navier–Stokes solver for incompressible flow is presented in this paper. Numerical integration of the governing equations is performed using an implicit pressure correction scheme, where the wind turbines (W/Ts) are modelled as momentum absorbers through their thrust coefficient. The k–ω turbulence model, suitably modified for atmospheric flows, is employed for closure. A correction is introduced to account for the underestimation of the near wake deficit, in which the turbulence time scale is bounded using a general “realizability” constraint for the fluctuating velocities. The second modelling issue that is discussed in this paper is related to the determination of the reference wind speed for the thrust calculation of the machines. Dealing with large wind farms and wind farms in complex terrain, determining the reference wind speed is not obvious when a W/T operates in the wake of another WT and/or in complex terrain. Two alternatives are compared: using the wind speed value at hub height one diameter upstream of the W/T and adopting an induction factor-based concept to overcome the utilization of a wind speed at a certain distance upwind of the rotor. Application is made in two wind farms, a five-machine one located in flat terrain and a 43-machine one located in complex terrain.

Analysis and validation of CFD wind farm models in complex terrain. Effects induced by topography and wind turbines

Wind farms have been extensively simulated through engineering models for the estimation of wind speed and power deficits inside wind farms. These models were designed initially for a few wind turbines located in flat terrain. Other models based on the parabolic approximation of Navier Stokes equations were developed, making more realistic and feasible the operational resolution of big wind farms in flat terrain and offshore sites. These models have demonstrated to be accurate enough when solving wake effects for this type of environments. Nevertheless, few analyses exist on how complex terrain can affect the behaviour of wind farm wake flow. Recent numerical studies have demonstrated that topographical wakes induce a significant effect on wind turbines wakes, compared to that on flat terrain. This circumstance has recommended the development of elliptic CFD models which allow global simulation of wind turbine wakes in complex terrain. An accurate simplification for the analysis of wind turbine wakes is the actuator disk technique. Coupling this technique with CFD wind models enables the estimation of wind farm wakes preserving the extraction of axial momentum present inside wind farms. This paper describes the analysis and validation of the elliptical wake model CFDWake 1.0 against experimental data from an operating wind farm located in complex terrain. The analysis also reports whether it is possible or not to superimpose linearly the effect of terrain and wind turbine wakes. It also represents one of the first attempts to observe the performance of engineering models compares in large complex terrain wind farms.

Proyectar con el delirio. Del Método Crítico Paranoico al gueto de Varsovia a través de Coney Island

RESUMEN. A partir de las diferentes definiciones entre “caer” o “estar” en la paranoia y los conceptos que se le relacionan, esta investigación descubre las diferentes herramientas proyectuales que permiten utilizar la arquitectura como medio para conducir a la sociedad al error, al delirio. Asumiendo que hoy en día el modo en el que se percibe la realidad es consecuencia de un proceso de moldeamiento psíquico, se realiza un proceso retroactivo en Coney Island (1900) y el Gueto de Varsovia (1940) para estudiar, confrontar y poner en duda los distintos formas de aprendizaje con los que actualmente se proyecta. Se pretende, tomando conciencia de lo anterior, plantear las bases de un nuevo método proyectual que sabiendo que es delirante juega con su funcionamiento paranoico. ABSTRACT. From the different definitions between "fall" or "to be" in the paranoia and its related concepts, this research finds out different tools which uses Architecture as a means to lead society to failure, delirium. Assuming that today the way reality is perceived is the result of a mental shaping process,a retrospective process in Coney Island (1900) and the Warsaw Ghetto (1940) is done in order to explore, confront and question various forms of learning with are currently used to design in architecture. It is intended, becoming aware of the above, to lay the groundwork for a new methodological approach in conception that knowing it is delirious, plays with its paranoid functioning.

MAIA: an event-based modular architecture for intelligent agents

Online services are no longer isolated. The release of public APIs and technologies such as web hooks are allowing users and developers to access their information easily. Intelligent agents could use this information to provide a better user experience across services, connecting services with smart automatic. behaviours or actions. However, agent platforms are not prepared to easily add external sources such as web services, which hinders the usage of agents in the so-called Evented or Live Web. As a solution, this paper introduces an event-based architecture for agent systems, in accordance with the new tendencies in web programming. In particular, it is focused on personal agents that interact with several web services. With this architecture, called MAIA, connecting to new web services does not involve any modification in the platform.

Infiltration of a photonic crystal fiber with cholesteric liquid crystal and blue phase

Photonic crystal fibers (PCF) have been selectively filled with a cholesteric liquid crystal (ChLC) with special interest in the blue phase (BP) of the liquid crystal. It has been observed thermal tuning of the guided light in the visible region. A dramatically enhance appears when the phase of the liquid crystal changes from cholesteric to blue phase I (BPI). When a thermal range of the blue phase I is achieved, no changes are observed while increasing temperature from BPI through BPII and to the isotropic phase.

Effects of whole body vibration on strength and jumping performance in volleyball and beach volleyball players

The primary aim of this study was to examine the effects of 6-week strength training with whole body vibration (WBV) on leg strength and jumping performance in volleyball and beach volleyball players. Twenty-three sub-elite male volleyball (VB; n=12) and beach volleyball players (BVB; n=11) aged 21.2±3.0 years were divided into two groups and subjected to 6 weeks of strength training (three one-hour sessions per week): (I) 12 players (6 VB and 6 BVB players) underwent training with WBV (30-40 Hz, 1.7-2.5 mm, 3.0-5.7 g), and (II) 11 players (6 VB and 5 BVB players) underwent traditional strength training. Squat jump (SJ) and countermovement squat jump (CMJ) measurements by the Ergo Tester contact platform and maximum leg press test (1RM) were conducted. Three-factor (2 time x 2 WBV use x 2 discipline) analysis of variance for SJ, CMJ and 1RM revealed a significant time main effect (p<0.001), a WBV use effect (p<0.001) and a discipline effect (p<0.001). Significantly greater improvements in the SJ (p<0.001) and CMJ (p<0.001) and in 1RM (p<0.001) were found in the WBV training groups than in traditional training groups. Significant 3-way interaction effects (training, WBV use, discipline kind) were also found for SJ, CMJ and 1RM (p=0.001, p<0.001, p=0.001, respectively). It can be concluded that implementation of 6-week WBV training in routine practice in volleyball and beach volleyball players increases leg strength more and leads to greater improvement in jump performance than traditional strength training, but greater improvements can be expected in beach volleyball players than in volleyball players.

Detection and mapping of burnt areas from time series of MODIS-derived NDVI data in a Mediterranean region

Moderate resolution remote sensing data, as provided by MODIS, can be used to detect and map active or past wildfires from daily records of suitable combinations of reflectance bands. The objective of the present work was to develop and test simple algorithms and variations for automatic or semiautomatic detection of burnt areas from time series data of MODIS biweekly vegetation indices for a Mediterranean region. MODIS-derived NDVI 250m time series data for the Valencia region, East Spain, were subjected to a two-step process for the detection of candidate burnt areas, and the results compared with available fire event records from the Valencia Regional Government. For each pixel and date in the data series, a model was fitted to both the previous and posterior time series data. Combining drops between two consecutive points and 1-year average drops, we used discrepancies or jumps between the pre and post models to identify seed pixels, and then delimitated fire scars for each potential wildfire using an extension algorithm from the seed pixels. The resulting maps of the detected burnt areas showed a very good agreement with the perimeters registered in the database of fire records used as reference. Overall accuracies and indices of agreement were very high, and omission and commission errors were similar or lower than in previous studies that used automatic or semiautomatic fire scar detection based on remote sensing. This supports the effectiveness of the method for detecting and mapping burnt areas in the Mediterranean region.

National Visions of EU Defence Policy - Common Denominators and Misunderstandings. CEPS Paperbacks. December 2013

The premise of this study is simple: before discussing what defence strategy the EU should adopt at Brussels-level, member states should clarify what they expect individually from the EU Common Security and Defence Policy (CSDP). Inspired by the confusion about EU defence policy in most European capitals, this authoritative study inverts the usual analytical approach applied to the debate on European strategy. Rather than initiating the enquiry from the perspective of common interests guiding CSDP, it analyses how seven prominent member states see CSDP as a tool to pursue their strictly national interests. Five researchers immersed themselves in the foreign policy worlds of Paris, London, Berlin, Rome, Warsaw, Stockholm and Madrid, looking at CSDP through national lenses and away from the potentially distorting influence of ‘Brussels’ rhetoric.

The US-China Joint Announcement on Climate Change: Can the G2 make a difference? CEPS Commentary, 26 November 2014

This Commentary finds that the US-China joint declaration on climate change, issued following the Asia-Pacific Economic Cooperation (APEC) Summit in Beijing on November 12th, is undoubtedly an important announcement by the two global economic giants responsible for emitting over 30% of the world’s GHG emissions. As such, it needs to be seen as important and relevant – a very positive development towards a new global climate change agreement in Paris. It is a challenge to those that have announced their pledges and are seen as capable of doing more, as well as to those that have not yet announced their intentions. It shows the importance and success of the UN climate change conference in Warsaw last year, when the decision was made that all Parties should announce their commitments by the first quarter of 2015. It also represents a total breakdown of the Kyoto Protocol-style separation in climate change negotiations between countries into Annex 1 and non-Annex 1, with China signalling that it is taking on the leadership role that comes with being a great economic power. In broader terms, it shows that there is scope for cooperation between the two main economic actors, even in the face of competition in other spheres. It is also a challenge to the EU, which was a leader and needs to show that there is a benefit in maintaining its leadership. Finally, agreements are deemed historic only by history. This one is important, and a potential game-changer, on the face of it. But it needs to live up to its promise. There is sufficient uncertainty for us to withhold final judgement and see if its promise materialises through implementation. But, as sober a judgement as we must make on such important matters, this announcement certainly gives us great hope that it is possible to do what needs to be done, and we must wholeheartedly welcome and applaud it.

Counter-reforms in times of prosperity. OSW Point of View, September 2006

In 2000, Vladimir Putin came to power after nearly a decade of the rule of the first Russian president, Boris Yeltsin. As prime minister, and later as a candidate for president, Putin announced that he would reform the state. The main assumptions of this reform were presented during a congress of the pro-Kremlin Unity movement, in Putin's address entitled 'Russia at the turn of the millennium' which was delivered on 29 December 1999, and later in a open letter to voters published on 25 February 2000. Both declarations were rather general, but they gave a clear picture of the principal directions of and priority areas for the future president's efforts: they outlined Russia's development path as pro-market and democratic. Nearly seven years have passed since Vladimir Putin came to power, a time for a summary of his achievements. In a way, Vladimir Putin has partially delivered on his initial declarations; indeed, Russia has undergone a deep transformation. However, when seen in the light of the president’s initial promises, the changes appear to be no more than 'counter-reforms', because instead of putting into practice the policy he outlined seven years ago, they have largely followed a different, if not entirely opposite direction.

Chechnya: Between a Caucasian Jihad and ‘hidden’ separatism. OSW Point of View, January 2007

1. Even though Chechnya remains the most unstable republic in the Russian North Caucasus, the open armed conflict known as the Second Chechen War, which broke out in the autumn of 1999, is gradually dying down. 2. Several years ago, the conflict in Chechnya could have been characterised as a war between Chechen separatists and the government of the Russian Federation. However, the nature of the conflict has changed significantly over the last four or five years. 3. Even though the intensity of fighting in Chechnya has abated in recent years, the conflict has spilt over to the other Caucasus republics such as Ingushetia, Dagestan and Kabardino-Balkaria. As a result, this is presently not so much a Chechen conflict as a regional clash between the authorities and the Caucasian (including Chechen) Islamists. 4. The Chechen militants are weaker now, and the conflict has changed from a struggle for national liberation into a fight for the Islamic cause; but this does not mean that Russia has ultimately solved the problem of Chechen separatism.

The invisible hand... of the Kremlin. Capitalism 'a la russe'. OSW Point of View, February 2007

This study describes the two main economic processes observed in Russia during President Vladimir Putin's second term; renationalisation, and the concentration of economic assets. As a result of these processes, the share of state-owned property has increased and the position of the state in the economy has strengthened. According to the authorities, the wide-range renationalisation of the assets and the construction of superholdings based on the state enterprises are intended to boost Russia's potential and stimulate the development of the whole economy. However, in practice the current ruling elite are using these superholdings to strengthen Russia's position on the international arena and to promote their vested interests.

Reintegration or Reconquest? Georgia's policy towards Abkhazia and South Ossetia in the context of the internal and international situation. OSW Point of View, May 2008

The conflicts in Abkhazia and South Ossetia have been Georgia's main security problem since the beginning of the 1990s, and, along with the Armenian-Azeri conflict over Nagorno-Karabakh, have made up the main security problems in the South Caucasus.

The Great Game around Turkmenistan. OSW Point of View, August 2008

The rise of a new leader of the state of Turkmenistan – President Gurbanguly Berdymukhammedov, who became ruler of the central Asian state after the 21-year rule of Saparmurad Niyazov, the self-proclaimed Turkmenbashi, who died on December 21, 2006 – has initiated changes in Turkmenistan’s political life. The new president has broken with the previous policy of self-isolation, and has directed the country towards openness to the outside world. Opportunities have thereby arisen for competitors in the ‘Great Game’, to gain political influence in Turkmenistan and access to hitherto unexploited Turkmen deposits of gas and oil. A new stage in the Great Game, which has been played for influence in Central Asia and control of access to its energy resources for many years, can thus be said to have been launched, and Turkmenistan has become the main setting for it. The major actors involved are Russia, the United States, China and the European Union.

The Paradoxes of Moldovan Sports. An insight into the nature of the Transnistrian conflict. OSW Point of View, November 2011

Mutual relations in the area of sports, which in contemporary international contacts often not only reflect the true nature of political relations but sometimes even affect them, can be a valuable contribution to the analysis of this conflict’s nature. Why did the Transnistrian government, despite the use of anti-Moldovan rhetoric, agree to Transnistrian athletes representing Moldova during the Olympics and in other international competitions? Why does it accept the presence of sports teams from both banks of the Dniester playing in the same leagues? Why does Transnistria, despite being much smaller, predominate in many sports? How is it that Sheriff Tiraspol, the flagship football club of the business and political circles controlling Transnistria, managed to win the Moldovan championship ten times in a row and is the main source of players for Moldova’s national team? Does sport really ‘know no borders’ or perhaps the border on the Dniester is different than seems at first sight?