2,173 research outputs found
Wind tunnel tests for a flapping wing model with a changeable camber using macro-fiber composite actuators
No full textIn the present study, a biomimetic flexible flapping wing was developed on a real ornithopter scale by using macro-fiber composite (MFC) actuators. With the actuators, the maximum camber of the wing can be linearly changed from -2.6% to +4.4% of the maximum chord length. Aerodynamic tests were carried out in a low-speed wind tunnel to investigate the aerodynamic characteristics, particularly the camber effect, the chordwise flexibility effect and the unsteady effect. Although the chordwise wing flexibility reduces the effective angle of attack, the maximum lift coefficient can be increased by the MFC actuators up to 24.4% in a static condition. Note also that the mean values of the perpendicular force coefficient rise to a value of considerably more than 3 in an unsteady aerodynamic flow region. Additionally, particle image velocimetry (PIV) tests were performed in static and dynamic test conditions to validate the flexibility and unsteady effects. The static PIV results confirm that the effective angle of attack is reduced by the coupling of the chordwise flexibility and the aerodynamic force, resulting in a delay in the stall phenomena. In contrast to the quasi-steady flow condition of a relatively high advance ratio, the unsteady aerodynamic effect due to a leading edge vortex can be found along the wing span in a low advance ratio region. The overall results show that the chordwise wing flexibility can produce a positive effect on flapping aerodynamic characteristics in quasi-steady and unsteady flow regions; thus, wing flexibility should be considered in the design of efficient flapping wings.KOSEF(R01-2005-000-10848-0), KIDC
Experimental investigation on the aerodynamic characteristics of a bio-mimetic flapping wing with macro-fiber composites
No full textThis study describes the development of a bio-mimetic flapping wing and the aerodynamic characteristics of a flexible flapping wing. First, the flapping wing is designed to produce flapping, twisting, and camber motions by using a bio-mimetic design approach. A structural model for a macro-fiber composite (MFC) actuator is established, and structural analysis of a smart flapping wing with the actuator is performed to determine the wing configuration for maximum camber motion. The analysis model is verified with the experimental data of the smart flapping wing. Second, aerodynamic tests are performed for the smart flapping wing in a subsonic wind tunnel, and the aerodynamic forces are measured for various test conditions. Additionally, the effects of camber and chordwise wing flexibility on unsteady and quasi-steady aerodynamic characteristics are discussed. The experimental results demonstrate that the effect of the camber generated by the MFC produces sufficient aerodynamic benefit. It is further found that chordwise wing flexibility is an important parameter in terms of affecting aerodynamic performance, and that lift produced in a quasi-steady flow condition is mostly affected by the forward speed and effective angle of attack.This work was supported by grant No. R01-2005-000-
10848-0 from the Basic Research Program of the Korea
Science & Engineering Foundation. The first author
would like to thank the Brain Korea 21 Project in 2006
An economic selective assembly procedure for two mating components with equal variance
No full textAn economic procedure of selective assembly is proposed when a product is composed of two mating components. The major quality characteristic of the product is the clearance between the two components. The components are divided into several classes prior to assembly. The component characteristics are assumed to be independently and normally distributed with equal variance. The procedure is designed so that the proportions of both components in their corresponding classes are the same. A cost model is developed based on a quadratic loss function and methods of obtaining the optimal class limits as well as the optimal number of classes are provided. Formulas for obtaining the proportion of rejection and the unavailability of mating components are also provided. The proposed model is compared with the equal width and the equal area partitioning methods using a numerical example. (C) 1999 John Wiley & Sons, Inc.X1115sciescopu
Fabrication of polymer micro/nano-hybrid lens array by microstructured anodic aluminum oxide (AAO) mold
No full textin the present study, polymer micro/nano-hybrid lens array is fabricated by hot embossing process using a microstructured anodic aluminum oxide (AAO) mold. For a mass replication of functional microoptical elements such as antireflective microlens array, a novel fabrication method of a multiscale mold is proposed and demonstrated. The fabrication method consists of two consecutive steps - an indentation of an electropolished aluminum substrate for microstructures and an electrochemical oxidation process for nanostructures on top of the microstructures. By using the present fabrication method, the microstructured AAO mold is successfully realized and utilized in hot embossing process. In this manner, the PMMA microlens array covered with the close-packed nanolens array is fabricated. (C) 2008 Elsevier B.V. All rights reserved.X1123sciescopu
Replication Data for: Conservation implications of Sabellaria spinulosa reef patches in a dynamic sandy-bottom environment
No full textThis dataset consists of three folders:
Bathymetry_Data (split up into two zip files per campaign year, due to large file sizes)
Endobenthos_Data
Epifauna_Data
Raw video footage is added as separate files per transect, per campaign year. Note that some video files are currently not available due to upload file size limitation; these can be requested by contacting the first author
Hydrogen generation from hydrolysis of NH3BH3 by an electroplated Co-P catalyst
No full textThis paper investigates the effect of an electroplated Co-P catalyst on hydrogen generation kinetics from hydrolysis of NH3BH3. The Co-P catalyst is composed of an amorphous Co-P phase and Co nanoparticles. An increase in NH3BH3 concentration caused the hydrogen generation rate to increase dramatically. The Co-P catalyst shows a large hydrogen generation rate for 2 wt% NH3BH3 solution at 30 degrees C. This is 1.8 times higher than that of the Pt/C catalysts and 6 times higher than that of Ru catalysts. The activation energy for hydrolysis of NH3BH3 by the Co-P catalyst is calculated to be 22 kJ/mol, which is close to that of noble metal-based catalysts. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.This Research was performed for the Hydrogen Energy R&D
Center, one of the 21st Century Frontier R&D Programs funded
by the Ministry of Science and Technology of Korea
Episodic encoding is more than the sum of its parts: An fMRI investigation of multifeatural contextual encoding
No full textEpisodic memories are characterized by their contextual richness, yet little is known about how the various features comprising an episode are brought together in memory. Here we employed fMRI and a multidimensional source memory procedure to investigate processes supporting the mnemonic binding of item and contextual information. Volunteers were scanned while encoding items for which the contextual features (color and location) varied independently, allowing activity elicited at the time of study to be segregated according to whether both, one, or neither feature was successfully retrieved on a later memory test. Activity uniquely associated with successful encoding of both features was identified in the intra-parietal sulcus, a region strongly implicated in the support of attentionally mediated perceptual binding. The findings suggest that the encoding of disparate features of an episode into a common memory representation requires that the features be conjoined in a common perceptual representation when the episode is initially experienced
A procedure to predict subcooled-water-flow-boiling CHF in uniformly heated tubes for high-heat-flux applications
No full textA model to predict critical heat flux (CHF) for high-heat-flux subcooled flow boiling in uniformly heated tubes is proposed. The present CHF model is based on the mechanism of wall-attached bubble coalescence. To take into account the enhanced condensation due to high subcooling and high mass velocity in small-diameter tubes, a mechanistic approach is adopted to evaluate the non-equilibrium flow quality and void fraction in the subcooled water flow boiling. Comparison of the model predictions against similar to 3100 subcooled water CHF data shows relatively good agreement over a wide range of parameters that covers the operating conditions of fusion reactor components. The operating ranges of the present database cover 0.33 less than or equal to D less than or equal to 37.5 mm, 0.002 less than or equal to L less than or equal to 4 m, 0.1 less than or equal to P less than or equal to 20 MPa, 0.37 less than or equal to G less than or equal to 134 Mg/m(2) . s, 49 less than or equal to Delta h(sub, in) less than or equal to 1659 kJ/kg, -1.25 less than or equal to x(em) < 0 and 1.05 less than or equal to q(CHF) less than or equal to 276 MW/m(2)
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