Showing papers by "Wright-Patterson Air Force Base published in 1987"

Numerical Simulation of Supersonic Flow Over a Three-Dimensional Cavity

Abstract: A numerical solution is presented for the unsteady flow over a three-dimensio nal cavity at a freestream Mach number of 1.5 and Reynolds number of 1.09 x 10 6. The self-sustained oscillatory motion within the cavity is generated numerically by integration of the time-dependent compressible three-dimensional Reynolds averaged Navier-Stokes equations. Effects of fine-scale turbulence are simulated via a simple algebraic closure model. Details of the flowfield structure are elucidated, and it is verified that the fundamental behavior of the unsteady phenomena is two dimensional. Comparison with experimental data is made in terms of the mean static pressure and overall acoustic sound pressure levels within the cavity, as well as with the acoustic frequency spectra of the oscillation along the cavity floor and rear bulkhead.

Lift-curve characteristics for an airfoil pitching at constant rate

Abstract: This paper reports the results of wind-tunnel studies of dynamic stall for an NACA 0015 airfoil pitching about the midchord at a constant rate. Time-varying pressure readings from 16 locations on the airfoil were collected and used to determine the lift, pressure-drag, and moment coefficients as functions of angle of attack for 100 test cases, covering 20 dynamic airspeed/pitch rate combinations. The dynamic-stall effects of the change (from steady flow) in the angle of attack at which separation occurs at the quarter chord and the change in the angle of attack at which stall occurs were extracted from these data and found to collapse onto a nondimensional pitch rate given by the chord times the pitch rate divided by two times the freestream velocity. The results showed that relatively slow pitch rates had dramatic effects on both the delay of stall and the magnitude of the maximum lift coefficient. The nondimensional rate is a measure of the speed of the leading edge divided by the speed of the freestream; it was found that nondimensional rates of less than 0.03 more than doubled the maximum coefficient of lift. The reduced data also clearly indicate that quarter-chord separation is systematically linked to dynamic stall.

Structural optimization using optimality criteria

Abstract: First, the historical background leading to the optimality criteria approach is discussed pointing out the role of the traditional design methods on one hand, and Prager’s work based on variational principles on the other hand as the two motivating influences. This is followed by the formal development of the method utilizing the separability properties of discretized structures or models. The importance of the single constraint case is pointed out and the associated particularly simple yet powerful optimality criteria is presented followed by extension to multiple constraints. Examples are used to illustrate the approach for displacement, stress and eigenvalue related constraints.

Electronic properties and optical-absorption spectra of GaAs-Al x Ga 1-x As quantum wells in externally applied electric fields.

Abstract: A study of the electronic and optical properties of GaAs-${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$As quantum wells in external electric fields is presented using a theory which incorporates valence-subband-mixing effects. Electric-field-induced changes in the conduction- and valence-subband structure, exciton binding energies, exciton oscillator strengths of both allowed (\ensuremath{\Delta}n=0) and forbidden (\ensuremath{\Delta}\ensuremath{ e}0) transitions, and the total absorption spectrum are calculated. Optical transitions associated with several conduction and valence subbands are considered. Computed electronic and optical properties are found to be the result of an interplay between the effects of the overlap of electron and hole envelope wave functions and the valence-subband mixing. Valence-subband mixing results in a large splitting of the Kramer's degeneracy in a quantum-well system in the presence of an electric field. The electric-field-induced changes in the computed exciton binding energies and oscillator strengths are caused mainly by the variation of the degree of overlap between the electron and hole wave functions. The foregoing results are compared with those obtained assuming no valence-band-mixing effects and are shown to be both qualitatively and quantitatively different. A brief comparison of our results with available experimental data is presented.

Energy separation in a vortex street

Abstract: When a bluff body is placed in a crossflow, the total temperature in its wake can become substantially less than the incoming one, as manifested by the fact that the recovery factor R on its rearmost surface takes negative values at high subsonic flow: this is the phenomenon referred to here as the Eckert-Weise effect. Although a vortex street has been a suspected cause, the issue of whether this is so, and what the mechanism is, has remained unsettled. In this experimental and theoretical investigation, we first examine the cause of the Eckert-Weise effect by enhancing the vortex shedding through acoustic synchronization: resonance between the vortex shedding and transversely standing acoustic waves in a wind tunnel. At the lowest synchronization, where a ringing sound emanates from the wind tunnel, R at the rearmost section of the cylinder is found to become negative even at a Mach number of 0.2; the base pressure (Cpb) takes dips correspondingly, indicative of the intensification of the vortex street. At this lowest acoustic resonance, the decrease of R and Cpb, uniform along the span, agrees with the expectation based on the spanwise uniformity of the lowest standing wave. At the next acoustic resonance where the standing wave now varies along the span, the corresponding dips in R and Cpb, non-uniform along the span, reveals an interesting ‘strip-theory’-like behaviour of the vortex intensities in the vortex street. These results correlating the change in R with Cpb confirm that the Eckert-Weise effect is indeed caused by the vortex shedding, the mechanism of which is examined theoretically in the latter half of the paper.A simple theoretical argument, bolstered by a full numerical simulation, shows that the time-varying static pressure field due to the vortex movement separates the instantaneous total temperature into hot and cold spots located around vortices; once time-averaged, however, the total temperature distribution conceals the presence of hot spots and takes the guise of a colder wake, the Eckert-Weise effect. Therefore the correct explanation of the Eckert-Weise effect, a time-averaged phenomenon, emerges only out of, and only as a superposition of, instantaneous total temperature separation around vortices. Such a separation is not confined to the outside of vortex cores; every vortex in its entirety becomes thermally separated. Nor is it limited to the far downstream equilibrium configuration of the Karman vortex street but applies to the important near-wake vortices, and to any three-dimensional vortical structure as well. For low subsonic flows in particular, this dynamical explanation also leads to a similar separation of total pressure; these features may thus be potentially exploited as a general marker to identify and quantify vortices.

High-Performance Polymer Fibers

Abstract: Since the pioneering work of Carothers which led to the introduction of strong nylon fibers by DuPont in the 1930s, polymer scientists have pursued the development of high-performance fibers to replace natural or metallic products, both to improve mechanical properties and to reduce weight. That development was relatively slow and evenly paced until DuPont again revolutionized the field with the release of Kevlar™, an aromatic polyamide with unprecedented mechanical properties. Since then, the field has literally boomed with new developments, and now organic fibers are available with properties that compete with the best inorganics and are far superior to metal fibers.Strong motivation for the invention of new organic fibers comes from the aerospace industry, which seeks fibers to use in reinforced composite structural materials. Composites bring new advances in stiffness (airplane wings can't bend too much!) in weight savings (every kilogram saved in the structure of an airplane saves 10,000), and in radically new ideas, such as radar-invisibility (stealth)5 and mission-adaptive wings (in-flight variable-shape wings). Hence, for a variety of specialty applications, otherwise commercially indefensible materials become viable.It may be somewhat counter intuitive to materials scientists unfamiliar with polymers to expect polymer mechanical properties to be greater than in the best metals. The origin of high strength and stiffness in a polymer fiber is the covalent bond, especially when aligned in an ordered array of long chain molecules.

Adjusting Exposure Limits for Long and Short Exposure Periods Using A Physiological Pharmacokinetic Model

Abstract: The rationale for adjusting occupational exposure limits for unusual work schedules is to assure, as much as possible, that persons on these schedules are placed at no greater risk of injury or discomfort than persons who work a standard 8 hr/day, 40 hr/week. For most systemic toxicants, the risk index upon which the adjustments are made will be either peak blood concentration or integrated tissue dose, depending on that chemical's presumed mechanism of toxicity. Over the past ten years, at least four different models have been proposed for adjusting exposure limits for unusually short and long work schedules. This paper advocates use of a physiologically-based pharmacokinetic (PB-PK) model for determining adjustment factors for unusual exposure schedules, an approach that should be more accurate than those proposed previously. The PB-PK model requires data on the blood:air and tissue:blood partition coefficients, the rate of metabolism of the chemical, organ volumes, organ blood flows and ventilation rat...

Interaction of jet in hypersonic cross stream

Abstract: A jet stream issuing normally from both sharp- and blunt-nose ogive-cylinder configurations into a hypersonic flow was investigated by a side-by-side experimental and numerical simulation. At a hypersonic Mach number of 12, strong interaction between jet-induced and bow shock wave systems, the jet plume trajectory, and the separated-flow surface shear pattern were highlighted for basic understanding. After the numerical solution was verified with the experimental data, the flowfield topology was reconstructed. Several unique features of this inviscid-viscous interaction phenomenon of shock-wave formation, vortical flow structure, and jet plume were delineated.

An infrared spectroscopic investigation of the curing reactions of the EPON 828/meta-phenylenediamine system

Abstract: Mid- and near-infrared (IR) spectroscopy has been used to study the curing of a bisphenol-A based epoxy resin (EPON-828) with a tetrafunctional curing agent, viz., meta-phenylenediamine (MPDA). Three different cure cycles were used in the study. Primary amine functionality was observed to react relatively rapidly; none remained after curing for 2 h at 75°C. Secondary amine functionality was exhausted in epoxy rich samples subjected to the standard cure cycle (2 h at 75°C followed by 2 h at 125°C). In samples with stoichiometric amount or higher MPDA, complete reaction of secondary amine or epoxy groups was not observed. In amine-rich samples subjected to post curing (6 h at 175°C), evidence was seen for the reaction of hydroxyl and epoxy groups, resulting in a considerable increase in the crosslink density of these samples.

Notched Strength Prediction and Design of Laminated Composites Under In-Plane Loadings:

Abstract: Two models based on the first-ply-failure stresses of notched and unnotched laminates are developed for the strength prediction of composite laminates containing an opening under in-plane loadings. Comparisons show that these models provide good agreement with experimental data for quasi-isotropic and orthotropic laminates containing a circular hole or a center crack. In conjunction with these models, a ranking method is applied for the laminate designs that is found reliable and very useful.

The Effect of Luteal Phase Estrogen Antagonism on Endometrial Development and Luteal Function in Women

Abstract: Previous studies of the role of estrogen in primate luteolysis, designed to investigate the effects of estrogen antagonism or selective inhibition of luteal phase estrogen production on luteal function, have ignored the impact of such treatments on secretory endometrial development. We examined the effect of luteal phase estrogen antagonism on endometrial maturation and luteal function in six women. In each of two menstrual cycles in each woman, blood samples were obtained on alternate days from cycle days 3–9, daily until 1 day after the urinary LH surge (day 0), and again on alternate days until the onset of menses. In the second of each pair of cycles, clomiphene citrate (100 mg) was administered daily from 2 days after the LH surge until menses. Endometrial biopsy was performed 13 days after the LH surge in each cycle. Serum FSH, LH, estradiol, and progesterone (P) were measured by RIA. The endometrial histological date and concentration of cytosolic (C) and nuclear (N) estrogen (ER) and P (PR) recept...

Perception And Control Of Self-Motion: Implications For Visual Simulation Of Vehicular Locomotion

Abstract: Few pedestrians have ever died by running into another pedestrian or a tree. Vehicles travel faster than people can run and people do die. Curiously, the perceived speed of self-motion may be alarmingly slow such as experienced in a high flying jet. Further, the same physical speed may be experienced differently, for example, when traveling in a car versus a truck. Still further, the same speed in the same vehicle may appear quite different after traveling several hours on a high-speed road. Because the discrepancy between physical and perceived speeds presumably does lead to fatal accidents, human factors researchers are actively trying to achieve a fundamental understanding of the problem of the perception and control of self-motion. This includes the control of altitude and heading as well as speed. The researchers are also studying ways to prevent accidents during real self-motion by better use of vehicle simulators. Better simulator use refers to their design, to the information they provide, and to the training programs. The general review in this chapter indicates that we do not yet have a sufficient knowledge of the principles of the perception and control of self-motion to satisfactorily deal with the problems at hand. However, several studies are presented in detail from an aviation psychology program which is achieving a union of basic and applied research.

Thermal Conductivity/Diffusivity of Silicon Carbide Whisker Reinforced Mullite

Abstract: The thermal conductivity and diffusivity of silicon carbide whisker reinforced mullite was shown to increase with whisker content. This effect was much greater for vapor-liquid-solid (VLS) whiskers than for rice-hull (RH) whiskers. This suggests that the thermal conductivity for the VLS whiskers was significantly higher than for the RH whiskers. Due to preferred orientation of the whiskers, thermal conductivity and diffusivity of the composite samples exhibited significant anisotropy.

Effect of Adhesive Ductility on Cyclic Debond Mechanism in Composite-to-Composite Bonded Joints

Abstract: An investigation of an adhesively bonded composite joint with a brittle adhesive was conducted to characterize both the static and fatigue debond growth mechanism under mode I and mixed mode I-II loadings. The bonded system consisted of graphite/epoxy adherends bonded with FM-400 adhesive. Two specimen types were tested: (1) a double-cantilever-beam specimen for mode I loading and (2) a cracked-lap-shear specimen for mixed mode I-II loading. In all specimens tested, failure occurred in the form of debond growth either in a cohesive or adhesive manner. The total strain-energy-release rate is not the criterion for cohesive debond growth under static and fatigue loading in the birttle adhesive as observed in previous studies with the ductile adhesives. Furthermore, the relative fatigue resistance and threshold value of cyclic debond growth in terms of its static fracture strength is higher in the brittle adhesive than its counterpart in the ductile adhesive.

High Temperature Decomposition of Military Specification L-23699 Synthetic Aircraft Lubricants:

Abstract: Previous investigations reported the formation of a neurotoxicant, tri methylolpropane phosphate (TMP-P) during pyrolysis of synthetic, aircraft engine lubricating oils. Employing both sealed-tube and open-to-air methods of pyrolysis, we confirmed the formation of TMP-P during lubricant pyrolysis. Rodent bioassay and GC/MS analysis were performed for detection and quanti tation of neurotoxicant production. Maximal production of TMP-P for sealed- tube pyrolysis occured after 20 min at 500°C. A comparable amount of TMP-P was formed after 5 min at 650°C in open-to-air pyrolysis of lubricants. Our examination of TMP-P production was limited to L-23699 lubricants composed primarily of a trimethylolpropane (TMP) ester base stock. The formation of TMP-P was only dependent upon the presence of an organic phosphorous addi tive and TMP. Pyrolysed lubricants composed of a pentaerythritol base did not cause neurotoxicity in mice or rats following intraperitoneal (i.p.) injection. Other toxic bicyclophosphorous ester ...

Vibration of symmetrically laminated rectangular plates considering deformation and rotatory inertia

Abstract: An analytical study was conducted using the Galerkin technique to determine the natural frequencies and mode shapes for symmetrically laminated rectangular plates, considering the effects of shear deformation and rotatory inertia. Two different graphite-epoxy symmetric plates were used in the analysis and three different boundary conditions for each plate, simply supported, clamped, and two opposite sides clamped/two opposite sides simply supported, were considered. Convergence characteristics, comparison to classical results, and the effects of length to thickness ratios were investigated. The finding indicated that as the length to thickness ratios were reduced («//*, b/h<3Q for the first mode), shear deformation effects significantly lowered the natural frequencies. Analysis also showed that rotatory inertia effects were very small. Convergence characteristics for all three boundary conditions were very good, and excellent agreement with the classical solutions was achieved.

Methylation of DNA guanine during the course of induction of liver cancer in hamsters by hydrazine or dimethylnitrosamine

Abstract: Hydrazine is carcinogenic to the mouse and rat, but three earlier studies have reported no carcinogenicity of hydrazine in the hamster. Administration of hydrazine to mice, rats and hamsters results in rapid methylation of liver DNA guanine for which endogenous formaldehyde appears to be the source of the methyl moiety. Hamsters were given hydrazine sulfate at 170, 340 and 510 mg/l in the drinking water for 2 years [average dose of 4.6, 8.3 and 10.3 mg hydrazine (free base)/kg body wt over the 2-year period], during which levels of methylation of DNA guanine in liver, kidney and lung, and histopathologic examinations of these tissues were carried out; dimethylnitrosamine, as a positive control, was administered at 10 mg/l in the drinking water (average dose of 1.1 mg/kg body wt over the 4-month measurement period). Both 7-methylguanine and O6-methylguanine were readily detectable at 6 months exposure in hamsters given hydrazine or dimethylnitrosamine; in hydrazine-treated animals only trace amounts of these bases could be detected after 12 months exposure; these bases were again detected in liver DNA at exposure times of 18 and 24 months. Hepatocellular carcinomas were observed in hamsters treated at the highest dose of hydrazine sulfate after 78 weeks of exposure; the incidence of liver cancer was dose-related over the course of the experiment: 32% for hamsters exposed to 510 mg hydrazine sulfate/l, 12% for 340 mg/l and none at 170 mg/l. Hamsters given dimethylnitrosamine developed high levels of 7-methylguanine and even higher levels of O6-methylguanine and both liver cholangiocellular carcinomas (73% incidence), as reported before, and hepatocellular carcinomas (27% incidence), a new finding. These results demonstrate for the first time that hydrazine is a liver carcinogen in the hamster and provide new information regarding the accumulation of DNA damage during the entire induction period for the carcinomas.

Resources, Confusions, and Compatibility in Dual Axis Tracking: Displays, Controls, and Dynamics

Abstract: Dual axis compensatory tracking was investigated as a function of whether error displays were integrated or separated, whether axis controls were integrated into one stick or remained separate, and whether the control dynamics on the two axes were the same or different. Tracking error increased and control activity decreased as a function of the summed difficulty of the two control dynamics. Integrated displays and integrated controls both led to increased confusions between tracking axes although error was unaffected. Importantly, performance was also affected by whether the integrality of displays matched that of controls. These results suggest that dual axis tracking is subject to independent effects of resource competition, confusions, and Wickens' (1986b) compatibility of proximity principle.

Immunohistochemical localization of substance P and enkephalin in the nucleus tractus solitarii of the rhesus monkey, Macaca mulatta

Abstract: The nucleus tractus solitarii in the monkey Macaca mulatta was found to have several subdivisions based upon cytoarchitectonics and immunohistochemistry. Subdivisions that could be identified included commissural, medial, parvicellular, dorsolateral, ventrolateral, intermediate, and interstitial. Substance P and enkephalin immunoreactivity was localized within discrete regions of the nucleus tractus solitarii, by means of the peroxidase-antiperoxidase technique. Substance P immunoreactivity occurred most frequently in the interstitial subdivision of the nucleus tractus solitarii. Moderate accumulations of substance P immunoreactivity were present in the commissural, medial, parvicellular, dorsolateral, and intermediate subdivisions, but very little was present in the ventrolateral subdivision. Enkephalin immunoreactivity followed the staining patterns of substance P; however, the amounts of enkephalin immunoreactivity were less than amounts for substance P. Following colchicine treatment, large numbers of enkephalin-immunoreactive neurons were distributed throughout all subdivisions, many being located in the parvicellular and medial subdivisions. The few substance P-immunoreactive neurons found were restricted to the parvicellular subdivision. The distribution of substance P and enkephalin immunoreactivity in M. mulatta is very similar to that described in the cat and rat. In addition, the extensive overlap of the distribution of these two putative neurotransmitters provides morphological evidence for their possible participation in the autonomic regulation within the nucleus tractus solitarii.

Experimental Observation of Cavitating Squeeze-Film Dampers

Abstract: This paper presents the results of an experimental investigation intended to observe cavitation in squeeze-film bearing dampers representative of those commonly found in aircraft gas turbine engines. Two different squeeze-film damper geometries were tested with both high-speed motion pictures and stroboscopic video recordings acquired at speeds up to 20,000 r/min. The results presented are limited to 8000 r/min due to the increased clarity of the photos acquired at the lower speeds and the similarity of trends at the higher speeds. Comparisons are also made with analysis formulated to handle the dynamics of the film rupture for the “short” damper case. The test results confirmed several of the commonly held “short” bearing assumptions (i.e., predominant axial flow and the effect of supply pressure and eccentricity on the cavitation zone). However, the test results demonstrated that significant flow reversals and film rupture were experienced in the feed/drain grooves in contradiction to the assumed boundary conditions. While agreement between analysis and test is of the right order of magnitude in predicting the cavitation zone shape and circumferential extent, current analyses do not adequately account for the observed variations in the boundaries and change in shape of the cavitation zone.

Three-Dimensional Auditory Cue Simulation for Crew Station Design/Evaluation:

Abstract: A three-dimensional (3-D) auditory display can increase the pilot's situational awareness without requiring visual fixation. When visual acquisition is required, the directional sound can give the ...

Robot Vision by Encoded Light Beams

Abstract: A robot eye is more than a camera and less than a complete vision understanding system. It is a device which can scan or sense objects in the three-dimensional environment and extract useful numerical information about those objects. The information obtained by the robot eye should be of a form that can be interrogated by a vision understanding system. This article describes the development of a dependable, robust, and versatile robot eye which can rapidly mensurate a surface in three dimensions. Using an active/passive camera pair, surface mensuration is achieved with fast electro-optic implementation of well-known stereophotogrammetric principles. We discuss the calibration of the robot eye and the application of the robot eye to exploring and mensurating 3-D objects.

Organotin-induced hemolysis, shape transformation and intramembranous aggregates in human erythrocytes.

Abstract: Organotin compounds examined in this study exhibited a relative order of potency for induction of in vitro hemolysis in human erythrocytes as follows: tri-n-butyltin > tri-n propyltin > tetra-n-butyltin > triphenyltin chloride > tri-n-ethyltin bromide > dibutyltin dichloride > stannous chloride > tri-n-methyltin chloride = butyltin chloride dihydroxide. All of the organotin compounds induced erythrocyte shape transformation from the normal discocyte to an echinocyte and, in addition, triphenyltin chloride, tetra-n-butyltin and tri-n-ethyltin bromide also elicited stomatocyte formation at higher concentrations. Select organotin compounds also formed tin-containing aggregates within the plasma membrane. The relative order of effectiveness for organotin induction of intramembranous aggregates was tri-n-butyltin > tri-npropyltin > tetra-n-butyltin > tri-n-ethyltin bromide, which was based upon the lowest concentration at which they were observed. These results support the previously suggested theory that organotins are membrane effectors because of their comparatively high hydrophobic, lipid partitioning properties. The relatively lipophilic compound, triphenyltin chloride, appeared to be anomalous because it did not readily promote hemolysis or induce the formation of intramembranous aggregates in human erythrocytes. A log-linear statistical model demonstrated an association of hemolysis with both tri-n-butyltin aggregate formation and shape transformation. Select organotin compounds should be useful probes in membrane studies because of their numerous effects.