126 research outputs found
Aerodynamics, aeroelasticity, and stability of hang gliders. Experimental results
One-fifth-scale models of three basic ultralight glider designs were constructed to simulate the elastic properties of full scale gliders and were tested at Reynolds numbers close to full scale values. Twenty-four minor modifications were made to the basic configurations in order to evaluate the effects of twist, reflex, dihedral, and various stability enhancement devices. Longitudinal and lateral data were obtained at several speeds through an angle of attack range of -30 deg to +45 deg with sideslip angles of up to 20 deg. The importance of vertical center of gravity displacement is discussed. Lateral data indicate that effective dihedral is lost at low angles of attack for nearly all of the configurations tested. Drag data suggest that lift-dependent viscous drag is a large part of the glider's total drag as is expected for thin, cambered sections at these relatively low Reynolds numbers
Role of dynamic Jahn-Teller distortions in Na2C60 and Na2CsC60 studied by NMR
Through 13C NMR spin lattice relaxation (T1) measurements in cubic Na2C60, we
detect a gap in its electronic excitations, similar to that observed in
tetragonal A4C60. This establishes that Jahn-Teller distortions (JTD) and
strong electronic correlations must be considered to understand the behaviour
of even electron systems, regardless of the structure. Furthermore, in metallic
Na2CsC60, a similar contribution to T1 is also detected for 13C and 133Cs NMR,
implying the occurence of excitations typical of JT distorted C60^{2-} (or
equivalently C60^{4-}). This supports the idea that dynamic JTD can induce
attractive electronic interactions in odd electron systems.Comment: 3 figure
Comparison of Two Multidisciplinary Optimization Strategies for Launch-Vehicle Design
The investigation focuses on development of a rapid multidisciplinary analysis and optimization capability for launch-vehicle design. Two multidisciplinary optimization strategies in which the analyses are integrated in different manners are implemented and evaluated for solution of a single-stage-to-orbit launch-vehicle design problem. Weights and sizing, propulsion, and trajectory issues are directly addressed in each optimization process. Additionally, the need to maintain a consistent vehicle model across the disciplines is discussed. Both solution strategies were shown to obtain similar solutions from two different starting points. These solutions suggests that a dual-fuel, single-stage-to-orbit vehicle with a dry weight of approximately 1.927 x 10(exp 5)lb, gross liftoff weight of 2.165 x 10(exp 6)lb, and length of 181 ft is attainable. A comparison of the two approaches demonstrates that treatment or disciplinary coupling has a direct effect on optimization convergence and the required computational effort. In comparison with the first solution strategy, which is of the general form typically used within the launch vehicle design community at present, the second optimization approach is shown to he 3-4 times more computationally efficient
Correlation Time-of-flight Spectrometry of Ultracold Neutrons
The fearures of the correlation method used in time-of-flight spectrometry of
ultracold neutrons are analyzed. The time-of-flight spectrometer for the energy
range of ultracold neutrons is described, and results of its testing by
measuring spectra of neutrons passing through interference filters are
presented.Comment: 16 pages, 5 figure
Comparative study on the uniform energy deposition achievable via optimized plasmonic nanoresonator distributions
Plasmonic nanoresonators of core-shell composition and nanorod shape were
optimized to tune their absorption cross-section maximum to the central
wavelength of a short pulse. Their distribution along a pulse-length scaled
target was optimized to maximize the absorptance with the criterion of minimal
absorption difference in between neighbouring layers. Successive approximation
of layer distributions made it possible to ensure almost uniform deposited
energy distribution up until the maximal overlap of two counter-propagating
pulses. Based on the larger absorptance and smaller uncertainty in absorptance
and energy distribution core-shell nanoresonators override the nanorods.
However, optimization of both nanoresonator distributions has potential
applications, where efficient and uniform energy deposition is crucial,
including phase transitions and even fusion
Multidisciplinary Design Optimization of an Extreme Aspect Ration HALE UAV
Development of High Altitude Long Endurance (HALE) aircraft systems is part of a vision for a low cost communications/surveillance capability. Applications of a multi payload aircraft operating for extended periods at stratospheric altitudes span military and civil genres and support battlefield operations, communications, atmospheric or agricultural monitoring, surveillance, and other disciplines that may currently require satellite-based infrastructure. The central goal of this research was the development of a multidisciplinary tool for analysis, design, and optimization of HALE UAVs, facilitating the study of a novel configuration concept. Applying design ideas stemming from a unique WWII-era project, a pinned wing HALE aircraft would employ self-supporting wing segments assembled into one overall flying wing. When wrapped in an optimization routine, the integrated design environment shows potential for a 17.3% reduction in weight when wing thickness to chord ratio, aspect ratio, wing loading, and power to weight ratio are included as optimizer-controlled design variables. Investigation of applying the sustained day/night mission requirement and improved technology factors to the design shows that there are potential benefits associated with a segmented or pinned wing. As expected, wing structural weight is reduced, but benefits diminish as higher numbers of wing segments are considered. For an aircraft consisting of six wing segments, a maximum of 14.2% reduction in gross weight over an advanced technology optimal baseline is predicted
Optically Induced Modulation of a Laser Beam in Nematic Liquid Crystals Structures
In this paper we report the experimental results obtained when an He-Ne laser beam crosses an MBBA homeotropic sandwich structure and is modulated by the influence of another laser beam, in our case an Ar+ laser, crossing through the same region. We extend some results previously reported by us1 2 concerning the influence of the ratio of the diameters of the laser beams on the modulation characteristics. A theoretical model, based on the one reported in Ref6 , shows good agreement with the
experimental results. If the Ar+ laser is intensity chopped, the resulting He-Ne diffracted image is also intensity modulated. The highest frequency observed has been 500 p. p. s
Crater Formation and Deuterium Production in Laser Irradiation of Polymers with Implanted Nano-antennas
Recent validation experiments on laser irradiation of polymer foils with and
without implanted golden nano-particles are discussed. First we analyze
characteristics of craters, formed in the target after its interaction with
laser beam. Preliminary experimental results show significant production of
deuterons when both the energy of laser pulse and concentration of
nano-particles are high enough. We consider the deuteron production via the
nuclear transmutation reactions where protons are
accelerated by Coulomb field, generated in the target plasma. We argue that
maximal proton energy can be above threshold values for these reactions and the
deuteron yield may noticeably increase due to presence of nano-particles.Comment: 9 pages, 4 figure
Aerodynamic Optimisation of Non-planar Lifting Surfaces
A novel population structured genetic algorithm (sGA) with embedded potential flow
vortex ring panel method (VRM) has been developed to minimise induced and parasitic
drag subject to constraints on lift, root bending moment, and longitudinal static stability.
The optimisation architecture can activate up to four independent wing segments allowing
up to 28 design variables. Minimum drag of wing tip extensions and winglet configurations
are compared using the non-linear stochastic optimisation method. The optimiser identified
joined box wings as offering the greatest induced efficiency followed by C-wings. With span
and root bending moment constraints winglets offered best total drag reduction. C-wings
are further investigated for potential to enhance longitudinal static stability performance
by staggering the horizontal extension of the winglet to balance moments around the wing’s
centre of gravity. Preliminary results suggest that while longitudinal static stability can be
reached it would be very poor. Inclusion of more design constraints and additional analysis
of the structural dynamics of C-wings, especially effecting the torsional mode, is necessary
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