88 research outputs found
Vertical-axis wind turbines in oblique flow: sensitivity to rotor geometry
No full textIncreasing interest is being shown worldwide in the application of vertical-axis wind turbines for decentralised electricity generation within cities. The distortion of the onset air flow by buildings within the urban environment might however, under certain conditions of wind speed or direction, cause vertical-axis wind turbines to operate in oblique flow – in other words in conditions in which the wind vector is non-perpendicular to the axis of rotation of the turbine. Little is known about the effect on the operation of a vertical-axis wind turbine when the wind is perturbed from supposedly optimal conditions. In the present study, the Vorticity Transport Model has been used to simulate the aerodynamic performance and wake dynamics, both in normal and in oblique flow, of three different vertical-axis wind turbines: one with a straight-bladed configuration, another with a curved-bladed configuration and another with a helically twisted configuration. The results partly confirm previous experimental measurements that suggest that a straight-bladed vertical-axis wind turbine that operates in oblique flow might produce a higher power coefficient compared to when it is operated in normal flow. The simulations suggest, however, that significantly higher power coefficients in oblique flow are obtained only at higher tip speed ratios, and indeed only if the height of the turbine is not large compared to its radius. Furthermore, it is shown that a vertical-axis wind turbine with blades that are helically twisted around its rotational axis produces a relatively steady power coefficient in both normal and oblique flow when compared to that produced by turbines with either a straight- or a curved-bladed configuration
Modelling the aerodynamics of vertical-axis wind turbines in unsteady wind conditions
No full textMost numerical and experimental studies of the performance of vertical-axis wind turbines have been conducted with the rotors in steady, and thus somewhat artificial, wind conditions - with the result that turbine aerodynamics, under varying wind conditions, are still poorly understood. The Vorticity Transport Model has been used to investigate the aerodynamic performance and wake dynamics, both in steady and unsteady wind conditions, of three different vertical-axis wind turbines: one with a straight-bladed configuration, another with a curved-bladed configuration and another with a helically twisted configuration. The turbines with non-twisted blades are shown to be somewhat less efficient than the turbine with helically twisted blades when the rotors are operated at constant rotational speed in unsteady wind conditions. In steady wind conditions, the power coefficients that are produced by both the straight- and the curved-bladed turbines vary considerably within one rotor revolution because of the continuously varying angle of attack on the blades and, thus, the inherent unsteadiness in the blade aerodynamic loading. These variations are much larger, and thus far more significant, than those that are induced by the unsteadiness in the wind conditions
Cyclopropyl Building Blocks for Organic Synthesis. Part 138. Diels—Alder Reactions of Novel (1′‐Arylallylidene)cyclopropanes with Heterodienophiles.
No full textDiels-Alder reactions of novel (1 '-arylallylidene)cyclopropanes with heterodienophiles
No full textPalladium-catalyzed cross-coupling of various aryl iodides with bicyclopropylidene provided isolable (1'arylallylidene)cyclopropanes, which reacted with a number of carbonyl compounds in the presence of Eu(fod)(3) under high pressure to furnish oxaspiro[2.5]octene derivatives in moderate to good yields (22-69%). The reactions of the allylidenecyclopropanes with two azo compounds as dienophiles afforded diazaspiro[2.5]octenes in high yields (82 and 99%) even at ambient pressure. When treated with nitrosobenzene, two of the allylidenecyclopro-panes gave the Diels-Alder adducts in up to 83 and 40% yield. 2,5-Diiodo-pxylene coupled twice with bicyclopropylidene, and the product underwent a twofold Diels-Alder reaction with nitrosobenzene to produce the bis(spirocyclopropaneoxazine) derivative in 88% yield. This overall transformation can be brought about in a one-pot, two-step operation by addition of the nitrosoarene to the reaction mixture immediately after formation of the allylidenecyclopropanes to furnish various 5-oxa-4-azaspiro[2.5]oct-7-ene derivatives in 22-77% yield. The coupling of methyl bicyclopropylidenecarboxylate with 2,6-dimethylphenyl iodide produced a mixture of very stable regioisomeric allylidenecyclopropane derivatives in 90% yield. The reaction of this mixture with N-phenyl-triazolinedione gave a corresponding mixture of the spirocyclopropanated heterobicycles in 61% yield
Effect of dynamic stall on the aerodynamics of vertical-axis wind turbines
No full textAccurate simulations of the aerodynamic performance of vertical-axis wind turbines pose a significant challenge for computational fluid dynamics methods. The aerodynamic interaction between the blades of the rotor and the wake that is produced by the blades requires a high-fidelity representation of the convection of vorticity within the wake. In addition, the cyclic motion of the blades induces large variations in the angle of attack on the blades that can manifest as dynamic stall. The present paper describes the application of a numerical model that is based on the vorticity transport formulation of the Navier–Stokes equations, to the prediction of the aerodynamics of a verticalaxis wind turbine that consists of three curved rotor blades that are twisted helically around the rotational axis of the rotor. The predicted variation of the power coefficient with tip speed ratio compares very favorably with experimental measurements. It is demonstrated that helical blade twist reduces the oscillation of the power coefficient that is an inherent feature of turbines with non-twisted blade configurations
Reflections on relationship-building between tangata whenua and local government: Notes from research and practice
No full textIn this paper, the author takes a reflective look at two areas: the preliminary discussions and fieldwork they undertook to set up a collaborative doctoral research project exploring relationship-building between
tangata whenua and local government (regional and district councils); and their
practice as a community psychologist within local government, advising on social
research and community participation in a number of environmental management
projects
Non-apoptotic signalling by TRAIL and anti-APO-1
No full textDie Liganden FasL und TRAIL, zwei Mitglieder der TNF-Familie, wurden bisher vor allem auf ihre apoptotischen Eigenschaften hin untersucht. Ziel dieser Arbeit war es, die nicht-apoptotischen Eigenschaften dieser Liganden näher zu untersuchen.
Es konnte gezeigt werden, dass TRAIL wie auch anti-APO-1 in der Lage waren die JNK zu aktivieren (anti-APO-1 ist ein agonistischer Antikörper, der anstatt FasL zur Stimulation des Fas-Moleküls verwendet wurde). Im Vergleich zur transienten und schnellen TNF-induzierten JNK-Aktivierung waren die Aktivierungskinetiken der TRAIL- und anti-APO-1-induzierten JNK-Aktivierung langsam und lang anhaltend. Die TRAIL-induzierte JNK-Aktivierung erwies sich, je nach Zelltyp, als Caspase-abhängig oder -unabhängig. Dies zeigt, dass TRAIL zwei Signalwege zur Aktivierung der JNK induzieren kann. Da die untersuchten Zellen alle vier TRAIL-Rezeptoren exprimierten, ist es unwahrscheinlich, dass die beobachteten Unterschiede auf die Stimulierung unterschiedlicher TRAIL-Rezeptoren zurückzuführen ist.
So zeigten Studien mit TRAIL-R1- und -2-spezifischen Seren, dass für die Aktivierung der JNK nur der TRAIL-R2 verantwortlich ist, die NFkB-Aktivierung jedoch durch beide TRAIL-Rezeptoren vermittelt werden kann.
In HeLa-Zellen induzieren TRAIL und anti-APO-1 in der Anwesenheit des Proteinsyntheseinhibitors CHX Apoptose. Wurden HeLa-Zellen mit CHX und dem Caspase-Inhibitor z-VAD-fmk behandelt, konnte in diesen Zellen sowohl mit TRAIL, als auch mit anti-APO-1 NFkB aktiviert werden. Dieser Befund läßt den Schluß zu, dass die Aktivierung von NFkB kein Epiphenomen der Apoptose ist, da diese durch z-VAD-fmk verhindert wird. Da die NFkB-Aktivierung nur bei gleichzeitiger Behandlung mit CHX zu beobachten war, liegt der Schluß nahe, dass die Konzentration eines intrazellulären Inhibitors der TRAIL- und anti-APO-1-induzierten NFkB-Aktivierung durch den Proteinsyntheseinhibitor verringert wird.The ligands FaslL and TRAIL, two members of the TNF-family, were predominantly described as apoptotic ligands. Purpose of this thesis was to investigate the non-apoptotic propperties of these ligands, like JNK-activation and activation of the transcriptionsfactor NFkB.
It could be shown that TRAIL and anti-APO-1 were able to activate the JNK (anti-APO-1 is an agonistic antibody which was used instead of FasL to stimulate Fas). In constrast to the fast activation of the JNK by TNF, the TRAIL and anti-APO-1 induced JNK activation was slow but sustained. The TRAIL-induced JNK activation occured caspase-dependent and independent, depending on the celltype. This shows that TRAIL can engage two pathways leading to JNK activation. This effect is most likely not due to the different expression of TRAIL-receptors as all investigated cell-lines expressed all four TRAIL-receptors.
Experiments with TRAIL-R-1 and –2 specific seras showed that only the TRAIL-R2 is activating the JNK, whereas both, TRAIL-R-1 and –2 are able to activate NFkB.
In presence of the protein synthesis inhibitor CHX, TRAIL and anti-APO-1 induce apoptosis in HeLa cells. If HeLa cells where treated with CHX and the caspase-inhibitor z-VAD-fmk, TRAIL and anti-APO-1 were also able to induce the activation of the transcriptionfactor NFkB. This shows that the activation of NFkB is not an epiphenomen of apoptosis, as apoptosis is blocked by z-VAD-fmk. But as NFkB-activation could only be observed in the presence of the protein synthesis inhibitor CHX, one can postulate that the concentration of an intracellular inhibitor is reduced by CHX so that the NFkB activation can take place
Modelling the aerodynamics of vertical-axis wind turbines
No full textThe current generation of wind turbines that are being deployed around the world features, almost exclusively, a three-bladed rotor with a horizontal-axis configuration. In recent years, however, a resurgence of interest in the vertical-axis wind turbine configuration has been prompted by some of its inherent advantages over horizontal-axis rotors, particularly in flow conditions that are typical of the urban environment.
The accurate modelling of the aerodynamics of vertical-axis wind turbines poses a significant challenge. The cyclic motion of the turbine induces large variations in the angle of attack on the blades during each rotor revolution that result in significant unsteadiness in their aerodynamic loading. In addition, aerodynamic interactions occur between the blades of the turbine and the wake that is generated by the rotor. Interactions between the blades of the turbine and, in particular, tip vortices that were trailed in previous revolutions produce impulsive variations in the blade aerodynamic loading, but these interactions are notoriously difficult to simulate accurately.
This dissertation describes the application of a simulation tool, the Vorticity Transport Model (VTM), to the prediction of the aerodynamic performance of three different vertical-axis wind turbines - one with straight blades, another with curved blades and a third with a helically twisted blade configuration - when their rotors are operated in three different conditions. These operating conditions were chosen to be representative of the flow conditions that a vertical-axis wind turbine is likely to encounter in the urban environment. Results of simulations are shown for each of the three different turbine configurations when the rotor is operated in oblique flow, in other words when the wind vector is non-perpendicular to the axis of rotation of the rotor, and also when subjected to unsteady wind. The performance of the straight-bladed turbine when it is influenced by the wake of another rotor is also discussed. The capability of the VTM to simulate the flow surrounding vertical-axis wind turbines has been enhanced by a dynamic stall model that was implemented in the course of this research in order to account for the effects of large, transient variations of the angle of attack on the aerodynamic loading on the turbine blades.
It is demonstrated that helical blade twist reduces the oscillation of the power coefficient that is an inherent feature of turbines with non-twisted blades. It is also found that the variation in the blade aerodynamic loading that is caused by the continuous variation of the angle of attack on the blades during each revolution is much larger, and thus far more significant, than that which is induced by an unsteady wind or by an interaction with the wake that is produced by another rotor. Furthermore, it is shown that a vertical-axis turbine that is operated in oblique flow can, potentially, produce a higher power coefficient compared to the operation in conditions in which the wind vector is perpendicular to the axis of rotation, when the ratio between the height of the turbine and the radius of the rotor is sufficiently low
Erstellung eines Prozessmodells zur Integration der Fehlermöglichkeits- und Einflussanalyse (FMEA) in den Entwicklungsprozess
No full textIm Rahmen dieser Diplomarbeit wird ein Modell entwickelt, wie die Fehlermöglichkeits- und Einflussanalyse in bestehende Prozesse der Entwicklung von mechatronischen Systemen eingebunden werden kann. Dazu werden anfangs die Grundlagen für die Modellierung und ein adäquates Vorgehensmodell gewählt. Nach diesem vorgehend, werden Anforderungen an die Prozesse gesetzt und der Bereich der zu betrachtenden Prozesse definiert. Im Anschluss wird der vorhandene IST-Zustand in entsprechende Modelle überführt. Aufbauend auf eine Analyse der Prozesse mit Benennung vorhandener Schwächen und ihrer Ursachen folgen Vorschläge zur Optimierung und weiterhin die Modellierung eines SOLL-Zustandes mit Integration der erreichten Erkenntnisse. Erläuterungen zur betrieblichen Umsetzung des modellierten SOLL-Zustandes schließen die Diplomarbeit ab
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