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An investigation was made at high subsonic speeds of a complete model having a highly tapered wing and several tail configurations. The aspect-ratio-3.50 wing had a taper ratio of 0.067 and an unswept 0.80 chord line. The complete model was tested with a wing-chord-plane tail, a T-tail, and a biplane tail (combined T-tail and wing-chord-plane tail). The model was tested in the Langley high-speed 7- by 10-foot tunnel at Mach numbers from 0.60 to 0.92 over a range of angle of attack of about +/- 20 deg. and a range of sideslip of -15 deg. to 13 deg. Some data were obtained with the horizontal stabilizer deflected. A few tests were also made with the wing tips clipped to an aspect ratio of 3.00. The data show that shock-interference effects between the tail surfaces (T-tail) can have considerable influence on the directional stability and effective dihedral. For example, the T-tail configuration with horizontal-tail leading-edge overhang showed a considerable loss in directional stability as the angle of attack was reduced to zero or negative values; whereas, the T-tail with zero leading-edge overhang showed the loss to be considerably less. The directional stability of the model with the low tail was essentially constant over a range of angle of attack of +/- 50 deg. All configurations tested showed a large reduction in stability at positive and negative angles of attack larger than about 15 deg., probably because of adverse sidewash associated with wing stall. The data show that a wing-chord-plane horizontal tail (low tail) tends to give a positive pitching-moment increment with increase in sideslip angle; whereas, a high tail (T-tail) tends to give negative increments in pitching moment.
We present a prescription for parametrizing the chemical profile in the core of white dwarfs in light of the recent discovery that pulsation modes may sometimes be deeply confined in some cool pulsating white dwarfs. Such modes may be used as unique probes of the complicated chemical stratification that results from several processes that occurred in previous evolutionary phases of intermediate-mass stars. This effort is part of our ongoing quest for more credible and realistic seismic models of white dwarfs using static, parametrized equilibrium structures. Inspired by successful techniques developed in design optimization fields (such as aerodynamics), we exploit Akima splines for the tracing of the chemical profile of oxygen (carbon) in the core of a white dwarf model. A series of tests are then presented to better seize the precision and significance of the results that can be obtained in an asteroseismological context. We also show that the new parametrization passes an essential basic test, as it successfully reproduces the chemical stratification of a full evolutionary model.
Increasingly, carbon composite structures are being used in aerospace applications. Their highstrength, high-stiffness, and low-weight properties make them good candidates for replacing many aerospace structures currently made of aluminum or steel. Recently, many of the aircraft engine manufacturers have developed new commercial jet engines that will use composite fan cases. Instead of using traditional composite layup techniques, these new fan cases will use a triaxially braided pattern, which improves case performance. The impact characteristics of composite materials for jet engine fan case applications have been an important research topic because Federal regulations require that an engine case be able to contain a blade and blade fragments during an engine blade-out event. Once the impact characteristics of these triaxial braided materials become known, computer models can be developed to simulate a jet engine blade-out event, thus reducing cost and time in the development of these composite jet engine cases. The two main problems that have arisen in this area of research are that the properties for these materials have not been fully determined and computationally efficient computer models, which incorporate much of the microscale deformation and failure mechanisms, are not available. The research reported herein addresses some of the deficiencies present in previous research regarding these triaxial braided composite materials. The current research develops new techniques to accurately quantify the material properties of the triaxial braided composite materials. New test methods are developed for the polymer resin composite constituent and representative composite coupons. These methods expand previous research by using novel specimen designs along with using a noncontact measuring system that is also capable of identifying and quantifying many of the microscale failure mechanisms present in the materials. Finally, using the data gathered, a new hybrid micromacromechanical computer model is created to simulate the behavior of these composite material systems under static and ballistic impact loading using the test data acquired. The model also quantifies the way in which the fiber/matrix interface affects material response under static and impact loading. The results show that the test methods are capable of accurately quantifying the polymer resin under a variety of strain rates and temperature for three loading conditions. The resin strength and stiffness data show a clear rate and temperature dependence. The data also show the hydrostatic stress effects and hysteresis, all of which can be used by researchers developing composite constitutive models for the resins. The results for the composite data reveal noticeable differences in strength, failure strain, and stiffness in the different material systems presented. The investigations into the microscale failure mechanisms provide information about the nature of the different material system behaviors. Finally, the developed computer model predicts composite static strength and stiffness to within 10 percent of the gathered test data and also agrees with composite impact data, where available.
Static indentation-flexure and low-velocity impact tests were performed on quasi-isotropic and cross-ply graphite/epoxy composite laminates. The load-deflection relations in static tests and impact force history in impact tests were recorded. The damage was assessed by using ultrasonic C-scanning and photo-micrographic techniques. Some features of the static behavior were explained by simple analytical models. A good correlation existed between the load-deflection curves for static and impact loading. It was found that results from a few static indentation-flexure tests can be used to predict the impact force history and delamination radius in composite laminates due to low-velocity impact.
Objectives of this research are: (1) to measure the hysteresis loop, Kerr rotation angle, anisotropy energy profile, Hall voltage, and magnetoresistance of thin-film magneto-optic media using our loop-tracer; (2) measure the wavelength-dependence of the Kerr rotation angle, Theta(sub k), and ellipticity, epsilon(sub k), for thin-film media using our magneto-optic Kerr spectrometer (MOKS); (3) measure the dielectric tensor of thin-film and multilayer samples using our variable-angle magneto-optic ellipsometer (VAMOE); (4) measure the hysteresis loop, coercivity, remanent magnetization, saturation magnetization, and anisotropy energy constant for thin film magnetic media using vibrating sample magnetometry; (5) observe small magnetic domains and investigate their interaction with defects using magnetic force microscopy; (6) perform static read/write/erase experiments on thin-film magneto-optic media using our static test station; (7) integrate the existing models of magnetization, magneto-optic effects, coercivity, and anisotropy in an interactive and user-friendly environment, and analyze the characterization data obtained in the various experiments, using this modeling package; (8) measure focusing- and tracking-error signals on a static testbed, determine the 'feedthrough' for various focusing schemes, investigate the effects of polarization and birefringence, and compare the results with diffraction-based calculations; and (9) measure the birefringence of optical disk substrates using two variable angle ellipsometers.
We report 1.6 ± 1 μm exciton transport in self-assembled supramolecular light-harvesting nanotubes (LHNs) assembled from amphiphillic cyanine dyes. We stabilize LHNs in a sucrose glass matrix, greatly reducing light and oxidative damage and allowing the observation of exciton–exciton annihilation signatures under weak excitation flux. Fitting to a one-dimensional diffusion model, we find an average exciton diffusion constant of 55 ± 20 cm 2 /s, among the highest measured for an organic system. We develop a simple model that uses cryogenic measurements of static and dynamic energetic disorder to estimate a diffusion constant of 32 cm 2 /s, in agreement with experiment. We ascribe large exciton diffusion lengths to low static and dynamic energetic disorder in LHNs. We argue that matrix-stabilized LHNS represent an excellent model system to study coherent excitonic transport.
The influence of ablation on the aerodynamic characteristics of a blunted slender cone was investigated. Plastic models were launched in free flight at ablating conditions. The results were compared with results of similar tests using metal nonablating models. Ablation was found to decrease the dynamic stability and the drag, but had little effect on static stability and lift. The plastic models appeared to experience ablation-induced roll.
The rapid increase in penetration of distributed energy resources on the electric power distribution system has created a need for more comprehensive interconnection modelling and impact analysis. Unlike conventional scenario - based studies , quasi - static time - series (QSTS) simulation s can realistically model time - dependent voltage controllers and the diversity of potential impacts that can occur at different times of year . However, to accurately model a distribution system with all its controllable devices, a yearlong simulation at 1 - second resolution is often required , which could take conventional computers a computational time of 10 to 120 hours when an actual unbalanced distribution feeder is modeled . This computational burden is a clear l imitation to the adoption of QSTS simulation s in interconnection studies and for determining optimal control solutions for utility operations . Our ongoing research to improve the speed of QSTS simulation has revealed many unique aspects of distribution system modelling and sequential power flow analysis that make fast QSTS a very difficult problem to solve. In this report , the most relevant challenges in reducing the computational time of QSTS simulations are presented: number of power flows to solve, circuit complexity, time dependence between time steps, multiple valid power flow solutions, controllable element interactions, and extensive accurate simulation analysis.
Two V/STOL model configurations utilizing lift-cruise-fans for the propulsion system have been tested in the presence of a small landing platform with finite deck edge positions. Results and analysis of these tests are presented. The model was tested at both static (zero velocity) and forward speed conditions with several heights and deck edge positions. Configurations utilizing three fans and four fans were investigated. Incremental forces and moments induced by the various deck edge positions are analyzed as relating to the model height above the ground and the thrust velocity relationships. The test and analysis show the induced forces to be relatively unaffected by deck edge.
A high aspect ratio supercritical wing with oscillating control surfaces is described. The semispan wing model was instrumented with 252 static pressure orifices and 164 in situ dynamic pressure gages for studying the effects of control surface position and sinusoidal motion on steady and unsteady pressures. Results from the present test (the third in a series of tests on this model) were obtained in the Langley Transonic Dynamics Tunnel at Mach numbers of 0.60, 0.78, and 0.86 and are presented in tabular form.