Hydrodynamic forces on heave plates for offshore systems oscillating close to the seabed or the free surface

La energía eólica marina es uno de los recursos energéticos con mayor proyección pudiendo contribuir a reducir el consumo de combustibles fósiles y a cubrir la demanda de energía en todo el mundo. El concepto de aerogenerador marino está basado en estructuras fijas como jackets o en plataformas flotantes, ya sea una semisumergible o una TLP. Se espera que la energía eólica offshore juegue un papel importante en el perfil de producción energética de los próximos años; por tanto, las turbinas eólicas deben hacerse más fables y rentables para ser competitivas frente a otras fuentes de energía. Las estructuras flotantes pueden experimentar movimientos resonantes en estados de la mar con largos períodos de oleaje. Estos movimientos disminuyen su operatividad y pueden causar daños en los componentes eléctricos de las turbinas y en las palas, también en los risers y moorings. La respuesta de la componente vertical del movimiento puede reducirse mediante diferentes actuaciones: (1) aumentando la amortiguación del sistema, (2) manteniendo el período del movimiento vertical fuera del rango de la energía de la ola, y (3) reduciendo las fuerzas de excitación verticales. Un ejemplo típico para llevar a cabo esta reducción son las "Heave Plates". Las heave plates son placas que se utilizan en la industria offshore debido a sus características hidrodinámicas, ya que aumentan la masa añadida y la amortiguación del sistema. En un análisis hidrodinámico convencional, se considera una estructura sometida a un oleaje con determinadas características y se evalúan las cargas lineales usando la teoría potencial. El amortiguamiento viscoso, que juega un papel crucial en la respuesta en resonancia del sistema, es un dato de entrada para el análisis. La tesis se centra principalmente en la predicción del amortiguamiento viscoso y de la masa añadida de las heave plates usadas en las turbinas eólicas flotantes. En los cálculos, las fuerzas hidrodinámicas se han obtenido con el f n de estudiar cómo los coeficientes hidrodinámicos de masa añadida5 y amortiguamiento varían con el número de KC, que caracteriza la amplitud del movimiento respecto al diámetro del disco. Por otra parte, se ha investigado la influencia de la distancia media de la ‘heave plate’ a la superficie libre o al fondo del mar, sobre los coeficientes hidrodinámicos. En este proceso, un nuevo modelo que describe el trabajo realizado por la amortiguación en función de la enstrofía, es descrito en el presente documento. Este nuevo enfoque es capaz de proporcionar una correlación directa entre el desprendimiento local de vorticidad y la fuerza de amortiguación global. El análisis también incluye el estudio de los efectos de la geometría de la heave plate, y examina la sensibilidad de los coeficientes hidrodinámicos al incluir porosidad en ésta. Un diseño novedoso de una heave plate, basado en la teoría fractal, también fue analizado experimentalmente y comparado con datos experimentales obtenidos por otros autores. Para la resolución de las ecuaciones de Navier Stokes se ha usado un solver basado en el método de volúmenes finitos. El solver usa las librerías de OpenFOAM (Open source Field Operation And Manipulation), para resolver un problema multifásico e incompresible, usando la técnica VOF (volume of fluid) que permite capturar el movimiento de la superficie libre. Los resultados numéricos han sido comparados con resultados experimentales llevados a cabo en el Canal del Ensayos Hidrodinámicos (CEHINAV) de la Universidad Politécnica de Madrid y en el Canal de Experiencias Hidrodinámicas (CEHIPAR) en Madrid, al igual que con otros experimentos realizados en la Escuela de Ingeniería Mecánica de la Universidad de Western Australia. Los principales resultados se presentan a continuación: 1. Para pequeños valores de KC, los coeficientes hidrodinámicos de masa añadida y amortiguamiento incrementan su valor a medida que el disco se aproxima al fondo marino. Para los casos cuando el disco oscila cerca de la superficie libre, la dependencia de los coeficientes hidrodinámicos es más fuerte por la influencia del movimiento de la superficie libre. 2. Los casos analizados muestran la existencia de un valor crítico de KC, donde la tendencia de los coeficientes hidrodinámicos se ve alterada. Dicho valor crítico depende de la distancia al fondo marino o a la superficie libre. 3. El comportamiento físico del flujo, para valores de KC cercanos a su valor crítico ha sido estudiado mediante el análisis del campo de vorticidad. 4. Introducir porosidad al disco, reduce la masa añadida para los valores de KC estudiados, pero se ha encontrado que la porosidad incrementa el valor del coeficiente de amortiguamiento cuando se incrementa la amplitud del movimiento, logrando un máximo de damping para un disco con 10% de porosidad. 5. Los resultados numéricos y experimentales para los discos con faldón, muestran que usar este tipo de geometrías incrementa la masa añadida cuando se compara con el disco sólido, pero reduce considerablemente el coeficiente de amortiguamiento. 6. Un diseño novedoso de heave plate basado en la teoría fractal ha sido experimentalmente estudiado a diferentes calados y comparado con datos experimentales obtenidos por otro autores. Los resultados muestran un comportamiento incierto de los coeficientes y por tanto este diseño debería ser estudiado más a fondo. ABSTRACT Offshore wind energy is one of the promising resources which can reduce the fossil fuel energy consumption and cover worldwide energy demands. Offshore wind turbine concepts are based on either a fixed structure as a jacket or a floating offshore platform like a semisubmersible, spar or tension leg platform. Floating offshore wind turbines have the potential to be an important part of the energy production profile in the coming years. In order to accomplish this wind integration, these wind turbines need to be made more reliable and cost efficient to be competitive with other sources of energy. Floating offshore artifacts, such oil rings and wind turbines, may experience resonant heave motions in sea states with long peak periods. These heave resonances may increase the system downtime and cause damage on the system components and as well as on risers and mooring systems. The heave resonant response may be reduced by different means: (1) increasing the damping of the system, (2) keeping the natural heave period outside the range of the wave energy, and (3) reducing the heave excitation forces. A typical example to accomplish this reduction are “Heave Plates”. Heave plates are used in the offshore industry due to their hydrodynamic characteristics, i.e., increased added mass and damping. Conventional offshore hydrodynamic analysis considers a structure in waves, and evaluates the linear and nonlinear loads using potential theory. Viscous damping, which is expected to play a crucial role in the resonant response, is an empirical input to the analysis, and is not explicitly calculated. The present research has been mainly focused on the prediction of viscous damping and added mass of floating offshore wind turbine heave plates. In the calculations, the hydrodynamic forces have been measured in order to compute how the hydrodynamic coefficients of added mass1 and damping vary with the KC number, which characterises the amplitude of heave motion relative to the diameter of the disc. In addition, the influence on the hydrodynamic coefficients when the heave plate is oscillating close to the free surface or the seabed has been investigated. In this process, a new model describing the work done by damping in terms of the flow enstrophy, is described herein. This new approach is able to provide a direct correlation between the local vortex shedding processes and the global damping force. The analysis also includes the study of different edges geometry, and examines the sensitivity of the damping and added mass coefficients to the porosity of the plate. A novel porous heave plate based on fractal theory has also been proposed, tested experimentally and compared with experimental data obtained by other authors for plates with similar porosity. A numerical solver of Navier Stokes equations, based on the finite volume technique has been applied. It uses the open-source libraries of OpenFOAM (Open source Field Operation And Manipulation), to solve 2 incompressible, isothermal immiscible fluids using a VOF (volume of fluid) phase-fraction based interface capturing approach, with optional mesh motion and mesh topology changes including adaptive re-meshing. Numerical results have been compared with experiments conducted at Technical University of Madrid (CEHINAV) and CEHIPAR model basins in Madrid and with others performed at School of Mechanical Engineering in The University of Western Australia. A brief summary of main results are presented below: 1. At low KC numbers, a systematic increase in added mass and damping, corresponding to an increase in the seabed proximity, is observed. Specifically, for the cases when the heave plate is oscillating closer to the free surface, the dependence of the hydrodynamic coefficients is strongly influenced by the free surface. 2. As seen in experiments, a critical KC, where the linear trend of the hydrodynamic coefficients with KC is disrupted and that depends on the seabed or free surface distance, has been found. 3. The physical behavior of the flow around the critical KC has been explained through an analysis of the flow vorticity field. 4. The porosity of the heave plates reduces the added mass for the studied porosity at all KC numbers, but the porous heave plates are found to increase the damping coefficient with increasing amplitude of oscillation, achieving a maximum damping coefficient for the heave plate with 10% porosity in the entire KC range. 5. Another concept taken into account in this work has been the heave plates with flaps. Numerical and experimental results show that using discs with flaps will increase added mass when compared to the plain plate but may also significantly reduce damping. 6. A novel heave plate design based on fractal theory has tested experimentally for different submergences and compared with experimental data obtained by other authors for porous plates. Results show an unclear behavior in the coefficients and should be studied further. Future work is necessary in order to address a series of open questions focusing on 3D effects, optimization of the heave plates shapes, etc.

Cell-free activation of neutrophil NADPH oxidase by a phosphatidic acid-regulated protein kinase.

The phosphorylation-dependent mechanisms regulating activation of the human neutrophil respiratory-burst enzyme, NADPH oxidase, have not been elucidated. We have shown that phosphatidic acid (PA) and diacylglycerol (DG), products of phospholipase activation, synergize to activate NADPH oxidase in a cell-free system. We now report that activation by PA plus DG involves protein kinase activity, unlike other cell-free system activators. NADPH oxidase activation by PA plus DG is reduced approximately 70% by several protein kinase inhibitors [1-(5-isoquinolinesulfonyl)piperazine, staurosporine, GF-109203X]. Similarly, depletion of ATP by dialysis reduces PA plus DG-mediated NADPH oxidase activation by approximately 70%. Addition of ATP, but not a nonhydrolyzable ATP analog, to the dialyzed system restores activation levels to normal. In contrast, these treatments have little effect on NADPH oxidase activation by arachidonic acid or SDS plus DG. PA plus DG induces the phosphorylation of a number of endogenous proteins. Phosphorylation is largely mediated by PA, not DG. A predominant substrate is p47-phox, a phosphoprotein component of NADPH oxidase. Phosphorylation of p47-phox precedes activation of NADPH oxidase and is markedly reduced by the protein kinase inhibitors. In contrast, arachidonic acid alone or SDS plus DG is a poor activator of protein phosphorylation in the cell-free system. Thus, PA induces activation of one or more protein kinases that regulate NADPH oxidase activation in a cell-free system. This cell-free system will be useful for identifying a functionally important PA-activated protein kinase(s) and for dissecting the phosphorylation-dependent mechanisms responsible for NADPH oxidase activation.

Does the key to a WMD-free Middle East lie in a nuclear Iran? CEPS Commentary, 10 June 2013

After the presidential elections on June 14th, the Iranian regime will continue its catch-me-if-you-can game with the international community until it has reached the nuclear threshold. Paradoxically, the key to a solution on the nuclear issue might just lie in discussions on a WMD-free Middle East, but only after Iran has obtained nuclear military capability. At that point, and in the context of a new arms race, both regional and international players may be persuaded that the Middle East has more to gain from negotiations on non-proliferation than from prolonged isolation and the prospect of intractable war.

Free movement of workers in the EU. Legal aspects of the transitional arrangements. ZEI Discussion Paper No. 217, 2013

From the Introduction. There are four fundamental freedoms which lay the foundation of the European Union. Those are the free movement of goods, free movement of capital, free movement of services and free movement of persons. They guarantee the existence and effective functioning of an area without internal borders within which goods, capital, services and people move freely. Despite the pivotal importance of these freedoms, there are cases where some freedoms can be partially or fully restricted within the territory of some member states or the Union as a whole. This thesis is going to analyze the restrictions of one of these freedoms: the free movement of persons, resulting from the arrangements applying to new member states. The focus will be the free movement of workers from new to old member states for a transitional period following the date of accession.

Will income inequality cause a middle-income trap in Asia? Bruegel Working Paper 2013/06, 10 October 2013

The Asian economy is expected to realise favourable growth during the first half of this century, but there is no guarantee. There is a discussion about a ‘middle-income trap’, which refers to a country that has realised rapid growth to become a middle-income country but is unable to grow further. A middle-income trap could occur not only if there is a delay in shifting the economy toward a productivity-driven structure, but also if there is a worsening of income distribution.We consider this in line with the theories of development economics and through a quantitative analysis. The relationship between income inequality and the trap can be explained by the Kuznets hypothesis and the basic-needs approach. Our quantitative analysis supports the Kuznets hypothesis, and indicates that,although a low-income country can accelerate its economic growth with the worsening of income distribution as an engine, a middle income country would experience a decreasing growth rate if it fails to narrow the income gap between the top and bottom income groups. The results also show that the basic-needs approach is also applicable in practice, and imply that the improvement of access to secondary education is important. A sensitivity analysis for three Asian upper-middle-income countries(China, Malaysia and Thailand) also shows that the situation related to a middle-income trap is worse than average in China and Malaysia. These two countries, according to the result of the sensitivity analysis, should urgently improve access to secondary education and should implement income redistribution measures to develop high-tech industries, before their demographic dividends expire. Income redistribution includes the narrowing of rural urban income disparities, benefits to low-income individuals, direct income transfers, vouchers or free provision of education and health-care, and so on, but none of these are simple to implement.

Immigration and free movement in an unusual electoral race: what implications for the next political cycle? EPC Policy Brief, 20 May 2014

Immigration and freedom of movement of EU citizens are among the main issues debated throughout the European Parliament election campaign and have some potential in determining who tomorrow’s EU leaders will be. This Policy Brief looks at how the two policies are debated at national level – in France, Germany and the UK – and at EU level between the ‘top candidates’ for European Commission Presidency – Jean-Claude Juncker (EPP), Ska Keller (Greens), Martin Schulz (PES) and Guy Verhofstadt (ALDE) – who have participated in several public debates. Two different campaigns have been unfolding in front of EU citizens’ eyes. The tense debate that can be identified at national level on these issues, is not transferred to the EU level, where immigration and free movement are less controversial topics. Furthermore, although participating in European elections, national parties present agendas responding exclusively to the economic and social challenges of their Member State, while the candidates for the Commission Presidency bring forward ‘more European’ programmes. Hence, several aspects need to be reflected upon: What will the consequences of this discontinuity be? How will this impact the future European agenda in terms of immigration and free movement? What institutional consequences will there be? Answering these questions is not a simple task, however, this paper aims to identify the parameters that need to be taken into account and the political landscape which will determine the future EU agenda in terms of immigration and free movement.

Making the impossible possible: the prospects for visa-free movement between the EU and its eastern partners. OSW Point of View Number 27, May 2012

To make the abolition of visas in relations between the EU and the Eastern European countries possible, the ”spell cast” must be broken on this issue. With the present levels of mobility and people-to-people, business and political contacts the introduction of a visa-free regime will be a natural consequence of the liberalisation processes which have been at work for years.Moreover, the decision to lift the visa requirement is unlikely to significantly stimulate an increase in migration pressure from Eastern European countries but could reduce the operating costs of expanded Schengen consular network. Lifting the visa requirement for Eastern European citizens can be temporary and conditional and allow for actual implementation of an increased conditionality rule. In political terms, making visa liberalisation a key issue would fundamentally change the partners’ approach to the Eastern Partnership and would provide a link to the Partnership for Modernisation targeted at Russia.

The prospects for the EU-Ukraine free trade agreement. OSW Commentary No. 94, 2012-10-15

The European Union and Ukraine initialled the Deep and Comprehensive Free Trade Area Agreement (DCFTA) on 19 July 2012. The scope of the agreement which the EU and Ukraine reached following their negotiations is much more extensive than that of a typical free trade agreement. It envisages not only the lifting of tariff and extra-tariff barriers but also, more importantly, Kyiv adopting EU legal solutions and standards in this area. Whether the agreement will be signed and implemented is still an open question and depends on the existing political conditions. On the one hand, the repression imposed by the government in Kyiv on its political opponents (including the detention of the former prime minister, Yulia Tymoshenko) has provoked criticism from the EU, which refuses to sign the agreement if the government in Kyiv continues to violate democratic principles. The manner in which Ukraine’s parliamentary elections are conducted this October will be the key test. On the other hand, Russia is increasingly active in its efforts to involve Ukraine in the integration projects it has initiated (the Customs Union and the Eurasian Economic Community). It should be noted that Moscow has effective instruments to exert its will, such as the dependence of the Ukrainian economy on supplies of Russian oil and gas and on exports to the Russian market. Besides, Moscow also has political instruments at its disposal. It is impossible to participate in integration projects both with the EU and with Russia. Therefore, Kyiv will have to make a strategic decision and choose the direction of its economic integration. Unless Ukraine takes concrete action to implement its agreements with the EU, primarily including the free trade agreement, its economic dependence on Russia will grow, and it will be more likely to join the Russian integration projects.

Will Cameron get what he wants? Anticipating reactions to Britain’s EU reform proposals. CEPS Commentary, 29 October 2015

After months of speculation about the British Prime Minister’s specific demands in terms of the “renegotiation” of the UK’s relationship with the EU, David Cameron has bowed to pressure from the heads of state or government of the other EU member states and committed himself to setting out the UK’s specific “concerns” in writing by early November. While we cannot be certain of the contents of David Cameron’s missive to the EU, his recent pronouncements before Parliament set out an agenda whose contours have become quite clear. In this Commentary the authors consider how far the other EU member states might be willing to accommodate Cameron’s demands and provide him with the political capital he seeks to lead the ‘in’ campaign. They distinguish four different attitudes among EU countries, and advocate a constructive approach that sets the scene for a Convention after 2017 – one that opens the treaty for a revision that could accommodate both the British demands for an ‘opt-out’ from ever closer union and gives leeway to those who wish to integrate further. Putting emphasis on strengthening the single market in the more immediate term would allow the Prime Minister to show his home audience that he is a leading reformer and that the EU gives oxygen to the British economy.This is an obvious area where he might be able to seal deals during the UK’s Presidency of the Council of the EU in the second half of 2017. The authors also consider what the European Council Conclusions on the UK’s wish list for EU reform might look like, given that any treaty revision before the time set for the UK referendum is unattainable. They present the results of a two-day simulation exercise involving a cross-section of national experts and present mock European Council Conclusions on the areas of ever closer union; the role of national parliaments; competitiveness; economic and monetary integration; and the free movement of labour.

Who Benefits from a Transatlantic Free Trade Agreement? Policy Brief #2013/04

From a purely economic standpoint, the US and the entire EU will profit from a dismantling of tariffs and non-tariff trade barriers between both regions. The real gross domestic product per capita would increase in the US and in all 27 EU member countries. Also when one looks at labor markets, the positive effects on employment predominate: Two million additional jobs could be created in the Organization for Economic Co-operation and Development (OECD) zone over the long run. The public welfare gains of these economies admittedly do stand in contrast with real losses in income and employment in the rest of the world. On balance, however, the beneficial effects on economic welfare prevail.

Tomorrow's silk road: Assessing an EU-China Free Trade Agreement.

Foreword. The Foreign Trade Association, which represents the European and international distribution and retail sector, commissioned this study in light of the importance of China as a sourcing country and its attractiveness as a rapidly growing consumer market. We believe that open borders and free trade can contribute to a broader choice and lower costs for consumers and create growth and employment in both Europe and China. This independent study aims to provide an in-depth contribution on the status of bilateral economic exchanges and persistent trade barriers that exist between the European Union and China. The second objective of the report is to encourage a frank and open dialogue, based on a scientific evaluation and without prejudice, on the possibility of a preferential trade agreement between the two sides. This study should be read by anyone who is interested in economic relations between the EU and China and in trade policy in general. The report provides many interesting findings and raises a number of surprising points. Overall, this study is one of the most significant contributions to the discourse on EU-China relations in recent years. We hope that this study will stimulate fresh thoughts on the benefits of closer future cooperation between two regions that have been interlinked since the times of antiquity and the first Silk Road.

The oldest abolition society : being a short story of the labors of the Pennsylvania Society for Promoting the Abolition of Slavery, the Relief of Free Negroes Unlawfully Held in Bondage, and for Improving the Condition of the African Race.

Cover title.

Free, and other stories /

"Fifth printing."

The Examiner, and journal of political economy : devoted to the advancement of the cause of state rights and free trade.

Goldsmiths'-Kress serials no. 3652.

Measurement of free drug and clinical end-point by high-performance liquid chromatography-mass spectrometry: Applications and implications for pharmacokinetic and pharmacodynamic studies

Free drug measurement and pharmacodymanic markers provide the opportunity for a better understanding of drug efficacy and toxicity. High-performance liquid chromatography (HPLC)-mass spectrometry (MS) is a powerful analytical technique that could facilitate the measurement of free drug and these markers. Currently, there are very few published methods for the determination of free drug concentrations by HPLC-MS. The development of atmospheric pressure ionisation sources, together with on-line microdialysis or on-line equilibrium dialysis and column switching techniques have reduced sample run times and increased assay efficiency. The availability of such methods will aid in drug development and the clinical use of certain drugs, including anti-convulsants, anti-arrhythmics, immunosuppressants, local anaesthetics, anti-fungals and protease inhibitors. The history of free drug measurement and an overview of the current HPLC-MS applications for these drugs are discussed. Immunosuppressant drugs are used as an example for the application of HPLC-MS in the measurement of drug pharmacodynamics. Potential biomarkers of immunosuppression that could be measured by HPLC-MS include purine nucleoside/nucleotides, drug-protein complexes and phosphorylated peptides. At the proteomic level, two-dimensional gel electrophoresis combined with matrix-assisted laser desorption/ionisation time-of-flight (TOF) MS is a powerful tool for identifying proteins involved in the response to inflammatory mediators. (C) 2003 Elsevier Science B.V. All rights reserved.