Vortex-lattice-based nonlinear aeroservoelastic modelling and analysis of large floating wind turbines

Wind turbine blades have significantly increased in length over the last few decades and are being operated in increasingly complex inflows such as the wake of other wind turbines or on floating platforms. This is increasing the unsteady and three-dimensional aerodynamic effects and the nonlinear structural dynamics that are neglected by the industry-standard Blade-Element Momentum and linear structural theories, respectively. In this dissertation, we employ Unsteady Vortex-Lattice Method for the aerodynamics and nonlinear Geometrically-Exact Beam Theory for the structural dynamics computations to describe these phenomena and their role on wind turbine aeroelasticity. We show that, Unsteady Vortex-Lattice Method fails to provide accurate drag estimation that we overcome with a semiempirical correction to include drag from steady-state tabulated data. We also show that, in cases of yaw, Blade-Element Momentum theory predicts accurate root-bending moments and rotor coefficients up to about ten degrees of yaw, for larger yaw angles, it over estimates the loads decay with the yaw angle. Furthermore, the interaction between radial sections of the blade under turbulent inflow is significant but not accounted for by Blade-Element Momentum theory so we study this phenomenon with Unsteady Vortex-Lattice Method and propose a correction to include the interaction between blade sections in Blade-Element Momentum theory that improves the prediction of loads along the span. We also reduce the computational cost of the Unsteady Vortex-Lattice Method by proposing a new wake discretisation scheme of the wake convection equation. We study the change in aerodynamic surface orientation in long flexible blades and conclude that capturing the twist degree of freedom is important for loads and power estimation. Moreover, we describe the influence of the platform pitch and roll motions in the unsteady character of the aerodynamic loads. Finally, we redesign the controller of the blade pitch to account for nonlinear structural dynamics and unsteady aerodynamics showing a reduction in the fluctuations of the main platform motions and energy production around the equilibrium position.Open Acces

Recubrimientos de hidroxiapatita (HA) depositados porproyecci ́on t ́ermica por combusti ́on (PTC)

The thermal spray combustion (PTC) is a technique that is exploring the possibility of depositing biomate-rials as the case of HA, as a new procedure works that are being done are exploratory, so this is a field opento investigation. The HA used in this work was synthesized in specialized laboratories of the University ofAntioquia. The substrate used is Ti-6Al-4V is the most widely used in these applications in biomedicine.La proyección térmica por combustión (PTC) es una técnica en la que se está explorando la posibilidad de depositar biomateriales como el caso de la HA, por ser un procedimiento nuevo los trabajos que se están haciendo son exploratorios, por lo que este es un campo abierto a la investigacióon. La HA utilizada en el presente trabajo fue sintetizada en los laboratorios especializados de la Universidad de Antioquia. El sustrato utilizado es el Ti-6Al-4V que es la aleación más utilizada en este tipo de aplicaciones enbiomedicina.Fil: Muñoz Medina, Guillermo Arturo. Universidad de Antioquia; Colombia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentin

Remarks on multisymplectic reduction

The problem of reduction of multisymplectic manifolds by the action of Lie groups is stated and discussed, as a previous step to give a fully covariant scheme of reduction for classical field theories with symmetries.Comment: 9 pages. Some comments added in the section "Discussion and outlook" and in the Acknowledgments. New references are added. Minor mistakes are correcte

Backlash Against International Courts in West, East and Southern Africa: Causes and Consequences

This paper discusses three credible attempts by African governments to restrict the jurisdiction of three similarly-situated sub-regional courts in response to politically controversial rulings. In West Africa, when the ECOWAS Court upheld allegations of torture by opposition journalists in the Gambia, that country’s political leaders sought to restrict the Court’s power to review human rights complaints. The other member states ultimately defeated the Gambia’s proposal. In East Africa, Kenya failed in its efforts to eliminate the EACJ and to remove some of its judges after a decision challenging an election to a sub-regional legislature. However, the member states agreed to restructure the EACJ in ways that have significantly affected the court’s subsequent trajectory. In Southern Africa, after the SADC Tribunal ruled in favor of white farmers in disputes over land seizure, Zimbabwe prevailed upon SADC member states to suspend the Tribunal and strip its power to review complaints from private litigants. Variations in the mobilization efforts of Community secretariats, civil society groups and sub-regional Parliaments explain why efforts to eliminate the three courts or narrow their jurisdiction were defeated in ECOWAS, scaled back in the EAC, and largely succeeded in SADC

Transverse Variability of the Flow and Density in Inlets of Southern Chile

Measurements of velocity and density profiles were made to describe the flow transverse structure in three inlets of southern Chile. The inlets show marked differences in their transverse dynamics in response to external forcing. In Aysen Fjord (45.2°S) the mean flow showed a three layer structure that was consistent with up-fjord wind-induced exchange, while in Chacao Channel (41.8°S), the mean flow exhibited predominantly a lateral structure that featured sharp velocity shears. In both cases, a bank in the center of the sections seemed to play an important role in shaping the mean flows. In Ventisquero Sound (44.4°S), the presence of a sill/contraction combination determined differences in the residual circulation on both sides of the contraction. The subtidal transverse momentum balance in Aysen alternates from quasigeostrophic during calm winds to a frictional layer and quasigeostrophic interior during periods of wind forcing. In Chacao, both advective accelerations and friction seem to play a major role in the transverse dynamics. In Ventisquero Sound, advective accelerations were dominant to the north of the contraction and over the sill. Typical nondimensional groups such as Rossby number, Ekman number, Reynolds number and Richardson number revealed dynamic similarities and differences among the different systems

Business cycle asymmentries: An investment cost approach

In this paper, investment cost asymmetry is introduced in order to test wheter this kind of asymmetry can account for asymmetries in business cycles. By using a smooth transition function, asymmetric investment cost is modeled and introduced in a canonical RBC model. Simulations of the model with Perturbations Method (PM) are very close to simulations through Parameterized Expectations Algorithm (PEA), which allows the use of the former for the sake of time reduction and computational costs. Both symmetric and asymmetric models were simulated and compared. Deterministic and stochastic impulse-response excersices revealed that it is possible to adequately reproduce asymmetric business cycles by modeling asymmetric investment costs. Simulations also showed that higher order moments are insu_cient to detect asymmetries. Instead, methods such as Generalized Impulse Response Analysis (GIRA) and Nonlinear Econometrics prove to be more e_cient diagnostic tools

A DSGE model with loss aversion in consumption and leisure : an explanation for business cycles asymmetries

ABSTRACT: In this chapter, an asymmetric DSGE model is built in order to account for asymmetries in business cycles. One of the most important contributions of this work is the construction of a general utility function which nests loss aversion, risk aversion and habits formation by means of a smooth transition function. The main idea behind this asymmetric utility function is that under recession the agents over-smooth consumption and leisure choices in order to prevent a huge deviation of them from the reference level of the utility; while under boom, the agents simply smooth consumption and leisure, but trying to be as far as possible from the reference level of utility. The simulations of this model by means of Perturbations Method show that it is possible to reproduce asymmetrical business cycles where recession (on shock) are stronger than booms and booms are more long-lasting than recession. One additional and unexpected result is a downward stickiness displayed by real wages. As a consequence of this, there is a more persistent fall in employment in recession than in boom. Thus, the model reproduces notonly asymmetrical business cycles but also real stickiness and hysteresis

El poder de decisión o el último grito del ápeiron

The present work analyzes the issue of freedom or free will rethinking the classic concepts from atomistic Materialism and Medieval philosophy, and contrasting them with recent emergent phenomena studies in the neurosciences. The forms and explanations about freedom from Aristotelian and Galilean traditions are compared from a phenomenological viewpoint. It is proposed that the transformations and the emerging nervous properties, viewed as the modern concept of plasticity, may be determinant for the possibility of freedom