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Calibri 83ffff̙̙3f3fff3f3f33333f33333.(TU Delft Repositoryg `uuidrepository linktitleauthorcontributorpublication yearabstract
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departmentresearch group programmeprojectcoordinates)uuid:33950a07dbaf492bbfec8833984afd2fDhttp://resolver.tudelft.nl/uuid:33950a07dbaf492bbfec8833984afd2fdComparison and validation of BEM and free wake unsteady panel model with the Mexico rotor experimentQMicallef, D.; Kloosterman, M.; Simao Ferreira, C.J.; Sant, A.; Van Bussel, G.J.W.&MEXICO experiment; BEM; Free Wake Codeenconference paperEuropean Mechanics SocietyAerospace Engineering,Aerospace Design, Integration and Operations)uuid:d1b1b87de7e04c4183e2f6db067db2c9Dhttp://resolver.tudelft.nl/uuid:d1b1b87de7e04c4183e2f6db067db2c9cApplication of constrained stochastic simulation to determine the extreme response of wind turbines!Bierbooms, W.A.A.M.; Peeringa, J.Up to now just deterministic gust shapes are specified in standards; e.g. the Extreme Operating Gust (IEC) is given by a Mexican hat like shape. In this paper gust shapes will be determined by application of socalled constrained stochastic simulation. This method specifies how to efficiently generate time series around some specific event (e.g. a local maximum) in a normal (Gaussian) process. In this way the generated gusts have the correct stochastic properties of turbulence (like generated wind fields for fatigue analysis). In constrained stochastic simulation a random signal can be generated which satisfies some condition, e.g. a maximum value or jump at some time instant. Usually the condition is applied on the external condition, i.e. the wind or waves (for offshore wind turbines). In this paper the condition of a maximum value, at some time instant, will be applied to the response instead (the blade root flapping moment). Assuming a linearised model of the wind turbine, the accompanying wind input leading to the extreme response, can be derived. By performing load simulations the proposed method is validated. In the future a probabilistic approach of extreme loading may replace the present deterministic procedure in standards.YWind field simulation; Gust models; Constrained stochastic simulation; Extreme conditions&European Wind Energy Association, EWEA)uuid:de06627404b94281b5803a789ad8f218Dhttp://resolver.tudelft.nl/uuid:de06627404b94281b5803a789ad8f2187On actuator disc force fields generating wake vorticity#Van Kuik, G.A.M.; Van Zuijlen, A.H.Actuator disc calculations can be divided in two categories: force models where, for a prescribed force field, the flow is calculated using a CFD method, and kinematic models, where the wake is calculated based on wake boundary conditions and the force field is known when the velocities are known. In both categories, but specifically for the kinematical models, results are reported that differ some 10% from momentum models. Furthermore, most calculations which give details about the flow through the disc do not satisfy the condition derived by Xyros & Xyros (2007) that the axial velocity through the disc is uniform for discs with a uniform surface load. Apart from this, the inconsistency in the momentum models discussed by van Kuik (2003) is still unresolved. These observations raise the questions: what is the relation between force and flow field, what are the requirements for a steady axisymmetric force field to generate vorticity in an Euler flow?+actuator disc; force field; vorticity; wake)uuid:3d535d2655e24d06bce52915592ff9c8Dhttp://resolver.tudelft.nl/uuid:3d535d2655e24d06bce52915592ff9c8Aeroelastic modelling and comparison of advanced active flap control concepts for load reduction on the Upwind 5MW wind turbineBarlas, A.; van Kuik, G.A.M.A newly developed comprehensive aeroelastic model is used to investigate active flap concepts on the Upwind 5MW reference wind turbine. The model is specially designed to facilitate distributed control concepts and advanced controller design. Different conc< epts of centralized and distributed control schemes based on choices of realistic measurement signals are compared. The sensitivity of important parameters to the load reduction capability is investigated and main differences between control approaches are analyzed. Conclusions are drawn regarding optimal integration of active flaps on wind turbines. Research work is performed at Delft University Wind Energy Research Institute (DUWIND), funded by EU s FP6 project UPWIND .)uuid:d7fc9b4871f746d0b8d550e25dab3a88Dhttp://resolver.tudelft.nl/uuid:d7fc9b4871f746d0b8d550e25dab3a883Actuator disc momentum theory for low lambda rotors Sorensen, J.N.; Van Kuik, G.A.M.Euromech)uuid:e3e9d472d48f48acaef276f24517d8e4Dhttp://resolver.tudelft.nl/uuid:e3e9d472d48f48acaef276f24517d8e40The VAWT in skew: StereoPIV and vortex modelingUSimao Ferreira, C.J.; Dixon, K.R.; Hofemann, C.; Van Kuik, G.A.M.; Van Bussel, G.J.W.One of the results of the development of wind energy conversion solutions for the built environment is the reappearance of Vertical Axis Wind Turbines (VAWTs). The application of wind turbines in urban environments presents design challenges driven by the complex wind fields experienced in the urban boundary layer. Urban Wind Turbines operate near, on and in the wake of bluff bodies larger than the rotor scale. These flow conditions might result in skewed flow operation. The objective of the current paper is to bring insight into the development of the near wake of a HVAWT in skewed flow, namely understanding: Blade loading asymmetry in spanwise direction. Trajectory of the tip vortices, including inboard movement and radial expansion of the shed and trailing vorticity. Asymmetry of the wake in spanwise direction. Blade vortex interaction of upwind tip vortex with downwind blade passage. Load distribution in downwind blade passage. Effect of skew in the expansion of the midwake. The investigation is composed of experimental wind tunnel research of a two bladed HDarrieus VAWT model with Particle Image Velocimetry, and modeling of the rotor and wake with a 3D unsteady panel method. Simulations of the rotor in skewed flow are validated with the experimental PIV data and with the torque measurements of 1 and 2 . The results of the panel model, validated by experiments, show the impact of skew angle on the near wake s development, both for the upwind blade passage as well as the downwind blade passage.8American Institute of Aeronautics and Astronautics, AIAA)uuid:dff7d6b3b00a4b228daceaf1d963722eDhttp://resolver.tudelft.nl/uuid:dff7d6b3b00a4b228daceaf1d963722esAn overview of NACA 6digit airfoil series characteristics with reference to airfoils for large wind turbine bladesTimmer, W.A.This paper investigates the NACA 63 and 64 6digit series of airfoils tested in the NACA LTPT in view to verify the RFOIL calculated airfoil characteristics for high Reynolds numbers. Some anomalies in the zerolift angles of 15% and 18% thick airfoils from these series are identified, both in the airfoil clean case and in case of wraparound roughness. It is found that RFOIL predicts the maximum lift coefficient at a Reynolds number of 3 million well, but consistently under predicts the Cl,max for Reynolds numbers of 6 and 9 million. It is, however, based on other comparisons at high Reynolds numbers unclear if this is due to an inability of the prediction code or to a deviation in the test results. The drag coefficient is under predicted with about 9% for a wide range of airfoils and Reynolds numbers. Due to wraparound roughness the maximum lift coefficient decreases with 18% to 20%.)uuid:0911faeceee740c7ac5235d951d0c5adDhttp://resolver.tudelft.nl/uuid:0911faeceee740c7ac5235d951d0c5adeA comparison of smart rotor control approaches using trailing edge flaps and individual pitch controlLackner, M.A.; van Kuik, G.A.M.Modern wind turbines have been steadily increasing in size, and have now become very large, with recent models boasting rotor diameters greater than 120 m. Reducing the loads experienced by th< e wind turbine rotor blades is one means of lowering the cost of energy of wind turbines. Wind turbines are subjected to significant and rapid fluctuating loads, which arise from a variety of sources including: turbulence in the wind, tower shadow, wind shear, and yawed flow conditions. "Smart rotor control" concepts have emerged as a major topic of research in the attempt to reduce fatigue loads on wind turbines. In this approach, aerodynamic load control devices are distributed along the span of the wind turbine blade, and through a combination of sensing, control, and actuation, these devices dynamically control the loads on the blades. This research investigates the load reduction potential of smart rotor control devices, namely trailing edge flaps (TEFs), in the operation of a 5 MW wind turbine in the aeroelastic design code "GH Bladed." Specifically in this paper, the fatigue load reductions achieved using trailing edge flaps are evaluated, and the performance is compared to another promising load reduction technique, individual pitch control. A feedback control approach is implemented for load reduction, which utilizes a multiblade coordinate transformation, so that variables in the rotating frame of reference can be mapped into a fixed frame of reference. Single input single output (SISO) control techniques for linear time invariant (LTI) systems are then employed to determine the appropriate response of the TEFs based on the loads on the blades. The use of TEFs and this control approach is shown to eectively reduce the fatigue loads on the blades, relative to a baseline controller. The load reduction potential is also compared to an alternative individual pitch control approach, in the time and frequency domain. The effects on the pitch and power systems are briefly evaluated, and the limitations of the analysis are assessed.2American Institute of Aeronautics and Astronautics)uuid:f1ec3aee09944c45920305c0dcc5bed1Dhttp://resolver.tudelft.nl/uuid:f1ec3aee09944c45920305c0dcc5bed1<Experimental and numerical investigation of the 3D VAWT wake@Simao Ferreira, C.J.; Hofemann, C.; Van Kuik, G.; Van Bussel, G.)uuid:98e819cbdb634aad8780c3dd7b763a93Dhttp://resolver.tudelft.nl/uuid:98e819cbdb634aad8780c3dd7b763a93KEffects of microramps on a shock wave/turbulent boundary layer interaction=Blinde, P.L.; Humble, R.A.; Van Oudheusden, B.W.; Scarano, F.Stereoscopic particle image velocimetry is used to investigate the effects of microramp subboundary layer vortex generators, on an incident shock wave/boundary layer interaction at Mach 1.84. Single and doublerow arrangements of microramps are considered. The microramps have a height of 20% of the unperturbed boundary layer thickness and the measurement planes are located 0.1 and 0.6 boundary layer thicknesses from the wall. The microramps generate packets of individual vortex pairs downstream of their vertices, which produce counterrotating longitudinal streamwise vortex pairs in a timeaveraged view. These structures induce a pronounced spanwise variation of the flow properties, namely the mixing across the boundary layer interface. The probability of reversedflow occurrence is decreased by 20 and 30% for the single and doublerow configurations, respectively. Both configurations of microramps stabilize the shock motion by reducing the length of its motion by about 20% in the lower measurement plane. The results are summarized by a conceptual model describing the boundary layer s and interaction s flow pattern under the effect of the microramps.DShock wave boundary layer interaction; Flow control; Microramps; PIVjournal articleSpringer)uuid:97a12ce0b5664ff3a2916be39f49d9d9Dhttp://resolver.tudelft.nl/uuid:97a12ce0b5664ff3a2916be39f49d9d9vExperiments on the Flow Field and Acoustic Properties of a Mach number 075 Turbulent Air Jet at a Low Reynolds Number0Slot, H.J.; Moore, P.; Delfos, R.; Boersma, B.J._In this paper we present the experimental results of a detailed investigation of the flow and acoustic properties of a turbulent jet with Mach nu< mber 075 and Reynolds number 35 103. We describe the methods and experimental procedures followed during the measurements, and subsequently present the flow field and acoustic field. The experiment presented here is designed to provide accurate and reliable data for validation of Direct Numerical Simulations of the same flow. Mean Mach number surveys provide detailed information on the centreline mean Mach number distribution, radial development of the mean Mach number and the evolution of the jet mixing layer thickness both downstream and in the early stages of jet development. Exit conditions are documented by measuring the mean Mach number profile immediately above the nozzle exit. The fluctuating flow field is characterised by means of a hotwire, which produced radial profiles of axial turbulence at several stations along the jet axis and the development of flow fluctuations through the jet mixing layer. The axial growth rate of the jet instabilities are determined as function of Strouhal number, and the axial development of several spectral components is documented. The directivity of the overall sound pressure level and several spectral components were investigated. The spectral content of the acoustic far field is shown to be compatible with findings of hotwire experiments in the mixing layer of the jet. In addition, the measured acoustic spectra agree with Tam s largescale similarity and finescale similarity spectra (Tam et al., AIAA Pap 96, 1996).EJet noise; Jet flow; Low Reynolds number flow; Validation; Simulation)uuid:c44672818f104f428e077eec363f6469Dhttp://resolver.tudelft.nl/uuid:c44672818f104f428e077eec363f64696Threedimensional vorticity patterns of cylinder wakesScarano, F.; Poelma, C.zThe vortex organization of cylinder wakes is experimentally studied by timeresolved tomographic Particle Image Velocimetry at Reynolds numbers ranging from 180 to 5,540. Time resolved measurements are performed at Re = 180, 360 and 540, whereas the transitional (Re = 1,080) and turbulent regimes (Re = 5,540) are investigated by snapshots separated in phase by more than ?/4. The vortex structure evolution is visualized by the 3D vorticity field, revealing a regular shedding at the lowest Reynolds, whereas at Re > 500 the BnardKrmn vortex street exhibits counterrotating streamwise vortex pairs (characteristic of Mode B) dominating the 3D motion. The regime at Re = 360 produces a transitional pattern where the counterrotating vortex pairs (Mode B), coexist with profoundly distorted shedding of oblique elements forming a chain of rhombuslike vortex cells. In the turbulent flow regime (Re = 5,540) a large increase in the range of flow scales is directly observed with the appearance of KelvinHelmholtz type vortices in the separated shear layer consistently with what is abundantly reported in literature. The statistical description of the secondary structures is inferred from a 3D autocorrelation analysis yielding two spanwise wavelengths for the counterrotating pairs, an inner length given by (twice) the distance between counterrotating elements and an outer one given by the distance between pairs. The uncertainty analysis of the present tomographic PIV experiments reveals that this approach is suited for the investigation of vortex wakes with a typical error of 2 and 10% on the velocity and vorticity vectors, respectively.)uuid:f3746c292e8944b2a71545ad732501cdDhttp://resolver.tudelft.nl/uuid:f3746c292e8944b2a71545ad732501cd.Stiffnessforce feedback in UAV teleoperation(Lam, T.M.; Mulder, M.; Van Paassen, M.M.Lam, T.M. (contributor)book chapter InTech Education and Publishing)uuid:791fce8ae31b448bab1d495c018d9561Dhttp://resolver.tudelft.nl/uuid:791fce8ae31b448bab1d495c018d9561AA steady solution for Prandtl s selfsimilar vortex sheet spiralsVan Kuik, G.A.M.(Prandtl's [L. Prandtl, ber die Entstehung von Wirbeln in der idealen Flssigkeit, mit Anwendung auf die Tragflgeltheorie und andere Aufgaben, in: von Krmn, LeviCevita (Eds.), Vortrge aus dem Gebiete der Hydro und Aerodynamik, < Springer, Berlin, 1922] selfsimilar, semiinfinite, free vortex sheets are characterized by a twodimensional unsteady flow around an invariable exponential spiral. A similar but steady spiral flow has been published by Schmidt and Sparenberg [G.H. Schmidt, J.A. Sparenberg, On the edge singularity of an actuator disk with large constant normal load, J. Ship Research 21 (1977) 125]. This flow is shown to be, kinematically, the steady solution in Prandtl's class of spirals but with a different dynamic boundary condition since it is not a free vortex sheet but carries a constant load. Due to the kinematic similarity, the analysis of Prandtl's spirals by van Kuik [G.A.M. van Kuik, The flow induced by Prandtl's selfsimilar vortex sheet spirals at infinite distances from the spiral kernel, Eur. J. Mech. B/Fluids 23 (4) (2004) 607 616] is also valid for the spiral with steady flow. As for Prandtl's spirals, the steady spiral flow requires a description on a multibranched Riemann surface, by which an interpretation in the singlebranched twodimensional surface is impossible.Spiral; Vortex sheets; PrandtlElsevier)uuid:6e73e307f4f34b9fb771bc0c02a1cb38Dhttp://resolver.tudelft.nl/uuid:6e73e307f4f34b9fb771bc0c02a1cb38QInfluence of wing kinematics on aerodynamic performance in hovering insect flight6Bos, F.M.; Lentink, D.; Van Oudheusden, B.W.; Bijl, H.hThe influence of different wing kinematic models on the aerodynamic performance of a hovering insect is investigated by means of twodimensional timedependent Navier Stokes simulations. For this, simplified models are compared with averaged representations of the hovering fruit fly wing kinematics. With increasing complexity, a harmonic model, a Robofly model and two morerealistic fruit fly models are considered, all dynamically scaled at Re = 110. To facilitate the comparison, the parameters of the models were selected such that their mean quasisteady lift coefficients were matched. Details of the vortex dynamics, as well as the resulting lift and drag forces, were studied. The simulation results reveal that the fruit fly wing kinematics result in forces that differ significantly from those resulting from the simplified wing kinematic models. In addition, light is shed on the effect of different characteristic features of the insect wing motion. The angle of attack variation used by fruit flies increases aerodynamic performance, whereas the deviation is probably used for levelling the forces over the cycle.Cambridge University Press)uuid:c42fc09d58b74126a2d9bd292c69cd71Dhttp://resolver.tudelft.nl/uuid:c42fc09d58b74126a2d9bd292c69cd71)Laddermill sail: A new concept in sailingPodgaets, A.R.; Ockels, W.J.<A new innovative approach to sailing has been proposed by TU Delft. It allows sailing in any desired direction, including straight into the wind. The concept consists of generating energy with a sky sail and then using it in an electric motor of the ship. The paper describes a mathematical model of laddermill sail. Laddermill; sailing; wind energy)uuid:25c716ffb3e242cd8e301fa5ad92ceeeDhttp://resolver.tudelft.nl/uuid:25c716ffb3e242cd8e301fa5ad92ceee/Robust Control of Laddermill Wind Energy SystemLaddermill flight control problem with closed loop is considered in this paper. Laddermill is an alternative concept for energy production using high altitude kites. The kites have been simulated as rigid bodies and the cable as a thin elastic line. Euler angles and cable speed are controls. Flight control is written as a fusion of two approaches: design of experiments and stochastic optimization. Such combination ensures finding global optimum for any reasonable number of parameters and objectives in a reasonable time while also collecting some information about sensitivities these two features are much harder to achieve by other means. Robustness has been formulated as an additional objective. We found the system very steady despite big variations of wind velocity. The resulting optimal trajectories can be also used as a first iteration for open loop control algo< rithms. The methods used can be also employed in wide range of wind energy applications.Laddermill; wind energy system)uuid:aee7a88f72cc4d2db3de164c7448c5dcDhttp://resolver.tudelft.nl/uuid:aee7a88f72cc4d2db3de164c7448c5dcqInvestigation of a turbulent spot and a tripped turbulent boundary layer flow using timeresolved tomographic PIVFSchrder, A.; Geisler, R.; Elsinga, G.E.; Scarano, F.; Dierksheide, U.zIn this feasibility study the tomographic PIV technique has been applied to time resolved PIV recordings for the study of the growth of a turbulent spot in a laminar flat plate boundary layer and to visualize the topology of coherent flow structures within a tripped turbulent flat plate boundary layer flow. The experiments are performed around (Re x )1/2 ? 450 in a low speed windtunnel using four high speed CMOS cameras operating up to 5 kHz. The volume illumination required a multiplereflection system able to intensify light intensity within the measurement volume. This aspect is deemed essential when a highspeed tomographic PIV system is applied in air flows. The particle image recordings are used for a three dimensional tomographic reconstruction of the light intensity distribution within the illuminated volume. Each pair of reconstructed threedimensional light distributions is analyzed by 3D spatial crosscorrelation using iterative multigrid schemes with volumedeformation, yielding a correlated time sequence of threedimensional instantaneous velocity vector volumes. The coherent structures organization is analyzed by 3Dvorticity and swirlingstrength isosurfaces visualization. In both flow types streaks and hairpinlike or arch vortical structures are most prominent. The data gives insight into the role of these structures for the spatiotemporal arrangement of the wall normal flow exchange mechanisms, especially of the instantaneous Reynolds stress events Q2 and Q4. A description of different selfsustainable flow organizations based on modifications of the hairpinvortex and streakmodels is given. Two preliminary results are essential: Selfsustainability of a coherent vortical structure depends on the ability to entrain high momentum fluid, initially Q4. And, streamwise swirl at the nearwall region of arch or hairpinlike vortices has been observed to be rare.)uuid:9e8e2dae639b4fd6b4bd1318b37e60c2Dhttp://resolver.tudelft.nl/uuid:9e8e2dae639b4fd6b4bd1318b37e60c2=A multibody dynamics approach to a cable simulator for kitesBreukels, J.; Ockels, W.J. For the purpose of ultimately building a fully dynamic simulation of kites, an investigation is launched into a viable model of the cable with which the kite is attached to the ground. In the model proposed in this paper, only the slow modes of motion are taken into account due to the fact that only the slow motions have a real effect on the flight characteristics of the kite. Fast vibrations have a low amplitude with little effect. Also, by taking out all the fast modes of motion, the time step for integration can remain fairly large, speeding up the calculation process. Of special interest in the model is the damping which consists of aerodynamic damping and materialbased damping. The relation between these two forms of damping is investigated. Verification of the model is done through comparison with analytical and reallife measured data. The resulting model is simulated in MSC ADAMS. It is shown that the aerodynamic damping is of prime interest because it dampens the slower motions. Material damping dampens mostly the fast vibrations.ikites; cable; simulation; dynamic modelling; model development; applications of simulation in engineering)uuid:a6e0f41cfb924638b9a89b2df345cd48Dhttp://resolver.tudelft.nl/uuid:a6e0f41cfb924638b9a89b2df345cd48PComparison of two mathematical models of the kite for Laddermill sail simulationLaddermill sail is an innovative approach to propel the ship with the power generated by kites. The first Laddermill system is currently being designed however existing mathematical models of the system produce differ< ent optimal recommendations. Thus a decision has been made to step back and to take a closer look at the mathematical models of Laddermill sail. Each kite is considered a single rigid body as is the ship. It s been found that the differences between results might come from the fact that the two models possess features of the kite that cannot be combined in the rigid wing approach. More adequate modelling of controlling mechanisms will allow adequate modelling of Laddermill sail as a whole./Laddermill; Laddermill sail; kiteboat; kitesail,IAENG International Association of Engineers)uuid:f9aab449cafc447c9979a7999b2c713aDhttp://resolver.tudelft.nl/uuid:f9aab449cafc447c9979a7999b2c713azIs Time a creation of Life in response to Gravity?: This hypothesis suggests new ways for looking at extraterrestrial lifeOckels, W.J.
From his personal experience during a space flight (Challenger 1985) onward, the author has been struck repeatedly by the remarkable influence of Earth's environment on life, in particular by its most inevitable elements: time and gravity. Our life might be peculiar to the local Earth conditions, and not cosmic per se. In this article the hypothesis is postulated that our speed of life, in relation to the speed of information (in this case the speed of light), is specific to humankind. Life is the process that makes time. In this approach the constancy of the speed of light is not so much a property of the external world, but rather a consequence of our getting older at a fixed timespeed . We are sitting in a time train and all the information that we observe from the outside world is travelling relative to us at the same speed as our train. The train speed is, in a sense, the speed of light. If that is the case, then the expanding universe is an illusion. The remnants of the big bang are standing still while we move away and see all distances increasing. It is also shown in this article that there is a relationship between this timespeed and gravity, and that it can be the result of a process in the brain. By interpreting gravity as the result of a rotating motion, rather than a linear upward acceleration, time is introduced. In today s science we consider all universal processes in respect to our present (= now). In fact, we believe that the universe started 13.6 billion years ago. This approach to science is set against the history of centralism: from the geocentrism of Ptolemy to the heliocentrism of Galilei, extrapolated to the chronocentrism of today. An intriguing consequence of this theory is that extraterrestrial life would have a different speed of light. To couch this in a metaphor: we are living in a green world and see only green, while the others live in a red world and see only red. Each of these worlds can be part of one system, but we cannot see each other. Ideas are presented on how one might be able to communicate with these extraterrestrial living systems. Based on the assumption that different time propagations are still made up from the same time quanta, but with different lengths of empty time in between, one can imagine that those time speeds could be transferred by a replay at our speed, like the frames in a film. Following the same assumption, a Lorentz transformation could connect both worlds, implying that the signals from another world would, for us, be split into two signals, each with a different time speed and distance speed not corresponding to our speed of light. Detecting those two signals simultaneously could lead to an intriguing experiment.)uuid:e1c9e380517045dca10c664e1b388576Dhttp://resolver.tudelft.nl/uuid:e1c9e380517045dca10c664e1b388576BOptimal CrossWind Towing and Power Generation with Tethered Kites&Williams, P.; Lansdorp, B.; Ockels, W.<Nonpowered flight vehicles such as kites can provide a means of transmitting wind energy from higher altitudes to the ground via tethers. Although there have been many proposals for systems to extract wind energy from higher altitudes, this paper focuses on the use of a light lifting body at the end of a te< ther to generate useful power. Two major configurations are studied: 1) the kite is used to tow a ground vehicle in the crosswind direction, 2) the kite is flown to generate power using a ground generator. In both cases, the useful work done by the kite is transmitted to the ground through the tether. Both applications require automatic control of the kite. A simplified system model is used to study the nature of the optimal trajectories of the system for different wind speeds. Numerical results illustrate that optimal power generation requires complex threedimensional kite trajectories, whereas crosswind towing requires much simpler trajectories. A feedback tracking controller is demonstrated for tracking the kite trajectories in the presence of unsteady winds.)uuid:94bbe5b5891e425da6cf81362ed2a7caDhttp://resolver.tudelft.nl/uuid:94bbe5b5891e425da6cf81362ed2a7caVThe role of continuity in residualbased variational multiscale modeling of turbulenceDAkkerman, I.; Bazilevs, Y.; Calo, V.M.; Hughes, T.J.R.; Hulshoff, S.This paper examines the role of continuity of the basis in the computation of turbulent flows. We compare standard finite elements and nonuniform rational Bsplines (NURBS) discretizations that are employed in Isogeometric Analysis (Hughes et al. in Comput Methods Appl Mech Eng, 194:4135 4195, 2005). We make use of quadratic discretizations that are C 0continuous across element boundaries in standard finite elements, and C 1continuous in the case of NURBS. The variational multiscale residualbased method (Bazilevs in Isogeometric analysis of turbulence and fluidstructure interaction, PhD thesis, ICES, UT Austin, 2006; Bazilevs et al. in Comput Methods Appl Mech Eng, submitted, 2007; Calo in Residualbased multiscale turbulence modeling: finite volume simulation of bypass transition. PhD thesis, Department of Civil and Environmental Engineering, Stanford University, 2004; Hughes et al. in proceedings of the XXI international congress of theoretical and applied mechanics (IUTAM), Kluwer, 2004; Scovazzi in Multiscale methods in science and engineering, PhD thesis, Department of Mechanical Engineering, Stanford Universty, 2004) is employed as a turbulence modeling technique. We find that C 1continuous discretizations outperform their C 0continuous counterparts on a perdegreeoffreedom basis. We also find that the effect of continuity is greater for higher Reynolds number flows.Incompressible flows; Finite elements; NURBS; NavierStokes equations; Boundary layers; Turbulent channel flows; Residualbased turbulence modeling; Isogeometric Analysis; Continuity of discretization; Variational multiscale formulation)uuid:50d74dc755634207a5af5970b160f2c2Dhttp://resolver.tudelft.nl/uuid:50d74dc755634207a5af5970b160f2c25Flight Control of the High Altitude Wind Power System]Closed loop Laddermill flight control problem is considered in this paper. Laddermill is a high altitude kites system for energy production. The kites have been simulated as rigid bodies and the cable as a thin elastic line. Euler angles and cable speed are controls. Flight control is written as a fusion of two approaches: design of experiments and stochastic optimization. Such combination ensures finding global optimum for any reasonable number of parameters and objectives in a reasonable time while also collecting some information about sensitivities these two features are much harder to achieve by other means. Robustness has been formulated as an additional objective. We found the system very steady despite big variations of wind velocity. The resulting optimal trajectories can be also used as a first iteration for open loop control algorithms.)uuid:c2187fd651854ea4b76a3b480a69dfeaDhttp://resolver.tudelft.nl/uuid:c2187fd651854ea4b76a3b480a69dfea[Assessment of Innovative Transport Concepts Using Cost Benefits Analyses: The Superbus caseMelkert, J.; Van Wee, B.Since the year 2000 the Netherlands are using a new guideline for assessing the costs and benefits of transport systems. This guideline has been used several times < now to assess transport systems using existing transport modes like trains. This paper reports on the first time this guideline was used to assess an innovative transport concept, the Superbus, a possible option to connect the North of the Netherlands to the Western urbanized part, the Randstad. The innovative character of the Superbus concept and the fact that it is under development made it difficult to assess this concept. In the assessment the costs of infrastructure, the demand driven logistics and the environmental aspects played an important role. The assessment caused major challenges with respect to the costs of infrastructure, the demand driven logistics and the environmental aspects. From the Cost and Benefit Analysis (CBA) performed it showed that in comparison with the other transport alternatives the Superbus has the lowest costs and the highest benefits. It is concluded that that is has been possible to assess the innovative Superbus concept by using the Dutch guideline for CBA assessments. The most important lessons learnt were the following:  It has been possible to assess the cost of infrastructure based on a combination of a toolbox of infrastructure elements, possible trajectories and adding costs for uncertainties.  Modelling the demand driven logistics has also been possible within the framework of the National Modelling System.  Environmental assessment of the concept has shown to be possible in this early stage of the development as well.  The assessment of the indirect benefits due to the innovative nature of the Superbus has not been possible  A CBA assumes a fully developed system. In case of an innovative system the end of the road towards maturity has not yet been reached. A CBA should be able to take this into account. An approach for this is presented. The authors conclude that in a future assessment of such an innovative concept, the assessment of the potential benefits of innovation, including factors determining success and failure, requires more research since they now have not been taken into account.)uuid:5a24676eef1643c6b8cfa72bba08d269Dhttp://resolver.tudelft.nl/uuid:5a24676eef1643c6b8cfa72bba08d269&Design of a large inflatable kiteplaneThis paper presents the various structural considerations in designing a large inflatable kiteplane. Material issues are addressed and a departure from conventional inflatable kites is suggested by using a single material instead of a structural foil and an internal gas barrier. Furthermore, rigging the kite using bridle lines is given attention. It is shown that the required internal pressure for a beam to keep it stiff is greatly influenced by the location of the bridle line. An optimum placement of the bridle line is found through analysis of the bending behavior of the beam in combination with a stressbased wrinkling criterion.)uuid:306785d0f75b4378a14575905c83efa7Dhttp://resolver.tudelft.nl/uuid:306785d0f75b4378a14575905c83efa74An inflatable wing using the principle of Tensairity(Breuer, J.; Ockels, W.; Luchsinger, R.H.The paper describes the new concept Tensairity which can be used to significantly improve the load bearing capacity of inflatable wings. The basic principle of Tensairity is to use an inflatable structure to stabilize conventional compression and tension elements. So far, Tensairity has been mainly used in civil engineering application like roof structures and bridges. In this work, considerations to apply Tensairity to wing structures are given and the construction of two winglike Tensairity kite prototypes is described. Test results on the Tensairity structure used in these kites are presented and compared to purely air inflated structures. Finally, the advantages of Tensairity wings are discussed and some application areas of these wings are suggested.)uuid:74d0307d416d4a90a06ffe0f1a268906Dhttp://resolver.tudelft.nl/uuid:74d0307d416d4a90a06ffe0f1a268906@Flight control and stability of a multiple kites tethered systemOne of novel concepts to use the energy of high altitude winds is by launching a series <of kite on a long rope and let them pull the rope thus driving the generator. A mathematical model of tethered kites system has been developed consisting of models of kites and of the cable that links them together and to the generator on the ground energy station. The model described is then investigated for stability in various wind conditions including random wind gusts which require stochastic stability problem statement.DLaddermill; wind energy; kites; cable dynamics; stochastic stability
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