274 research outputs found
Articulated blade tip devices for load alleviation on wind turbines
This paper investigates the load alleviation capabilities of an articulated tip device, where the outermost portion of the blade can rotate with respect to the rest of the blade. Passive, semi-passive and active solutions are developed for the tip rotation. In the passive and semi-passive configurations tip pitching is mainly driven by aerodynamic loads, while for the active case the rotation is obtained with an actuator commanded by a feedback control law. Each configuration is analyzed and tested using a high-fidelity aeroservoelastic simulation environment, by considering standard operative conditions as well as fault situations. The potential benefits of the proposed blade tip concepts are discussed in terms of performance and robustness
'R&D and export performance: exploring heterogeneity along the export intensity distribution'
This study analyses the relationship between firm-level innovative effort as measured by R&D expenditures and export intensity. We apply quantile regression techniques to a sample of Italian firms to verify whether R&D expendituresâ effect varies along the conditional distribution of export intensity, after controlling for censoring and endogeneity issues. Empirical findings suggest that the effect of R&D expenditures on export intensity is positive and that firms taking most advantage from R&D activity are in the right tail of the export intensity distribution (from the 70th quantile onwards), that is, those exporting 50% of their sales or more. Overall, the results prove robust to several specification checks and suggest not only that firmsâ innovative efforts help explaining heterogeneity in export intensity performance, but also that its positive effect differs across the export to sales ratio distribution. This implies that innovation policy measures might be more effective for firms characterised by a relatively high export intensive margin
Combined preliminaryâdetailed design of wind turbines
This paper is concerned with the holistic optimization of wind turbines. A
multi-disciplinary optimization procedure is presented
that marries the overall sizing of the machine in terms of rotor diameter
and tower height (often termed âpreliminary designâ) with the
detailed sizing of its aerodynamic and structural
components. The proposed combined preliminaryâdetailed approach sizes the
overall machine while taking into full account the subtle and complicated
couplings that arise due to the mutual effects of aerodynamic and
structural choices. Since controls play a central role in
dictating performance and loads, control laws are also updated accordingly
during optimization. As part of the approach, rotor and tower are sized
simultaneously, even in this case capturing the mutual effects of one
component over the other due to the tip clearance constraint. The procedure, here driven by detailed models of the cost of energy, results in a complete aero-structural design of the machine, including its associated control
laws.
The proposed methods are tested on the redesign of two wind turbines, a
2.2âŻMW onshore machine and a large 10âŻMW offshore one. In both cases, the
optimization leads to significant changes with respect to the initial
baseline configurations, with noticeable reductions in the cost of energy.
The novel procedures are also exercised on the design of
low-induction rotors for both considered wind turbines, showing that they
are typically not competitive with conventional high-efficiency rotors
Periodic stability analysis of wind turbines operating in turbulent wind conditions
The formulation is model-independent, in the sense that it does not require
knowledge of the equations of motion of the periodic system being analyzed,
and it is applicable to an arbitrary number of blades and to any
configuration of the machine. In addition, as wind turbulence can be viewed
as a stochastic disturbance, the method is also applicable to real wind
turbines operating in the field.
The characteristics of the new method are verified first with a simplified
analytical model and then using a high-fidelity multi-body model of a
multi-MW wind turbine. Results are compared with those obtained by the well-known operational modal analysis approach
Automatic detection and correction of pitch misalignment in wind turbine rotors
In this work, a new algorithm is presented to correct for pitch misalignment
imbalances of wind turbine rotors. The method uses signals measured in the
fixed frame of the machine, typically in the form of accelerations or loads.
The amplitude of the one per revolution signal harmonic is used to quantify
the imbalance, while its phase is used to locate the unbalanced blade(s). The near
linearity of the unknown relationship between harmonic amplitude and pitch
misalignment is used to derive a simple algorithm that iteratively rebalances
the rotor. This operation is conducted while the machine is in operation,
without the need for shutting it down. The method is not only applicable to
the case of a single misaligned blade, but also to the generic case of
multiple concurrent imbalances. Apart from the availability of acceleration
or load sensors, the method requires the ability of the rotor blades to be
commanded independently from one another, which is typically possible on many
modern machines. The new method is demonstrated in a realistic simulation
environment using an aeroservoelastic wind turbine model in a variety of
wind and operating conditions.</p
Lightweight rotor design by optimal spar cap offset
Bend-twist coupling behavior is induced in a blade by displacing the suction side spar cap towards the leading edge, and the pressure side one in the opposite direction. Additional couplings are introduced by rotating the spar cap fibers. The structural configuration of the blade is optimized using an automated design environment. The resulting blade shows significant benefits in terms of mass and loads when compared to the baseline uncoupled one. Finally, the lightweight design concept is used to increase the rotor size, resulting in a larger energy yield for the same hub loads
Age-related increase in resistance to acute Trypanosoma cruzi infection in rats is associated with an appropriate antibody response
Inoculation at weaning with Trypanosoma cruzi in inbred 'l' rats resulted in a self-resolving acute infection characterized by marked parasitaemias, whereas challenge to adult rats revealed a mild disease with extremely low parasitaemias. To explore the mechanisms underlying such age-associated differences in disease outcome, we analysed the in vitro replication of T. cruzi, nitric oxide and tumour necrosis factor-α (TNF-α) production in peritoneal macrophages (PMs), the serum concentrations of the specific immunoglobulins (Igs) IgM and IgG, antibodies exhibiting lytic activity against bloodstream forms of T. cruzi and circulating levels of nitrate, TNF-α and interferon-Îł (IFN-Îł). Macrophages from young rats were as effective as their adult counterparts for restraining intracellular parasite replication. When stimulated with IFN-Îł, culture supernatants from young PMs contained higher amounts of nitrite and TNF-α. Serum samples from 4 and 7 days post infection revealed easily detectable amounts of nitrate, with values being further augmented by day 7 post infection and significantly higher in the young group. TNF-α levels were only detected in the young group by day 7 post infection. Both groups had increased amounts of IFN-Îł in their sera, although in adult rats, this trend was followed by a significant drop at day 7, with young rats showing values still higher by the same time point evaluation. In contrast, young rats presented significantly lower levels of IgM and IgG antibodies during the first week of infection. Increased resistance in adult rats seems to be the result of a more appropriate antibody production.Fil: Pascutti, MarĂa Fernanda. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Rosario. Instituto de InmunologĂa Clinica y Experimental de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias MĂ©dicas. Instituto de InmunologĂa Clinica y Experimental de Rosario; ArgentinaFil: Bottasso, Oscar Adelmo. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Rosario. Instituto de InmunologĂa Clinica y Experimental de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias MĂ©dicas. Instituto de InmunologĂa Clinica y Experimental de Rosario; ArgentinaFil: Hourquescos, M. C.. Universidad Nacional de Rosario; ArgentinaFil: Wietzerbin, Jeanne. Institute Curie; FranciaFil: Revelli, Silvia Susana. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Rosario. Instituto de InmunologĂa Clinica y Experimental de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias MĂ©dicas. Instituto de InmunologĂa Clinica y Experimental de Rosario; Argentin
Brief communication: Wind inflow observation from load harmonics â wind tunnel validation of the rotationally symmetric formulation
The present paper further develops and experimentally validates the
previously published idea of estimating the wind inflow at a turbine rotor
disk from the machine response. A linear model is formulated that relates one
per revolution (1P) harmonics of the in- and out-of-plane blade root bending
moments to four wind parameters, representing vertical and horizontal shears
and misalignment angles. Improving on this concept, the present work exploits
the rotationally symmetric behavior of the rotor in the formulation of the
load-wind model. In a nutshell, this means that the effects on the loads of
the vertical shear and misalignment are the same as those of the horizontal
quantities, simply shifted by Ïâ2. This results in a simpler
identification of the model, which needs a reduced set of observations. The
performance of the proposed method is first tested in a simulation
environment and then validated with an experimental data set obtained with an
aeroelastically scaled turbine model in a boundary layer wind tunnel.</p
Wake behavior and control: comparison of LES simulations and wind tunnel measurements
This paper applies a large-eddy actuator line approach to the simulation of
wind turbine wakes. In addition to normal operating conditions, a specific
focus of the paper is on wake manipulation, which is performed here by
derating, yaw misalignment and cyclic pitching of the blades. With the
purpose of clarifying the ability of LES methods to represent conditions that
are relevant for wind farm control, numerical simulations are compared to
experimental observations obtained in a boundary layer wind tunnel with
scaled wind turbine models. Results indicate a good overall matching of
simulations with experiments. Low-turbulence test cases appear to be more
challenging than moderate- and high-turbulence ones due to the need for
denser grids to limit numerical diffusion and accurately resolve tip-shed
vortices in the near-wake region.</p
Clinical and serological studies of tuberculosis patients in Argentina receiving immunotherapy with Mycobacterium vaccae (SRL 172)
AbstractTwo small, placebo-controlled studies of immunotherapy with heat killed Mycobacterium vaccae added to routine chemotherapy for pulmonary tuberculosis, together involving 40 HIV seronegative patients, were carried out in Argentina. The immunotherapy was associated with reduced sputum smear positivity of AFB at 1 month and a greater reduction in ESR at 2 months. In the first study radiological improvement was better (P < 0·05) among immunotherapy recipients. In the second study, weight regain and time to become apyrexial were measured and were found to be improved amongst immunotherapy recipients (P < 0·05).In the first month of treatment the levels of IgG to the 65 kDa and 70 kDa heat-shock proteins showed greater falls following immunotherapy (P < 0·05 and P < 0·001, respectively). On admission serum cytokine levels of interleukins 4 and 10 (IL-4, IL-10), interferon gamma (IFN-γ) and tumour necrosis factor alpha (TNF-α) were grossly raised in comparison with a matched control group (P < 0·001). After 1 month. Levels of IL-4, IL-10 and TNF-α fell (P < 0·001, P < 0·01 and P < 0·01, respectively) and levels of IFN-γ rose more (P = 0·005) in immunotherapy recipients than in those receiving chemotherapy alone. The results are in accord with a switch towards a TH1 immunological status and clinical benefit for immunotherapy recipients
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