Showing papers in "CTIT technical reports series in 1990"

Stabilization and projection methods for multibody dynamics

Abstract: In recent years, there has been growing interest in stabilized index reduction techniques for differential-algebraic equations (DAE) of multibody dynamics. A number of the proposals which incorporate the idea of a projection onto the constraint manifold are discussed. The methods are divided into classes based on whether the projection is performed on the residuals of the discretized DAE or on the numerical solution itself, and demonstrate relationships between the methods of each class

Shake-and-bake algorithms for generating uniform points on the boundary of bounded polyhedra

Abstract: We present a class of shake-and-bake algorithms for generating (asymptotically) uniform points on the boundary of full-dimensional bounded polyhedra. We also report chi-square goodness-of-fit tests, and the results of simulations for some elementary testproblems.

Resistance to 3-trifluoromethyl-4-nitrophenol (TFM) in sea lamprey

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Air Force Procedure for Predicting Aircraft Noise Around Airbases: Airbase Operations Program (BASEOPS) Description

Abstract: : This report is a users manual for the BASEOPS 300 program developed by AAMRL/BBE It describes the installation, use and limitations of this program BASEOPS is the menu driven computerized airbase operations input program used in doing airbase noise assessments under the USAF Air Installation Compatible Use Zone (AICUZ) program BASEOPS will create a file that can be directly interfaced to the NOISEMAP 60 program, used to calculate the total noise exposure from these input operations BASEOPS contains default performance profiles (takeoff and landing) for Military Transient and Civil aircraft The program also allows the user to create a NOISEMAP input file for any subset of the input data through a Global Editing Menu This can be used for quickly creating multiple noise analyses for different operational input scenarios Keywords: Acoustics; Aircraft noise; Engine noise; Community noise exposure; Environmental impact

Measurements of surface shear stresses under a three-dimensional turbulent boundary layer using oil-film laser interferometry

Abstract: : Measurements of surface shear stress magnitude and direction are reported for a three-dimensional, pressure driven, turbulent boundary layer around a wing body junction. Measurements were made using a dual-beam oil film laser interferometer at 56 locations. An iterative procedure was developed which increased the precision of the data extracted from the data records. Skin friction directions computed using a least square error fit were compared to angles obtained from surface oil flows, hot wire anemometry, and LDV measurements. Also, the magnitude of the skin friction coefficients were compared to independently obtained skin friction coefficients. The data agreed to within experimental error outside the effects from the vortex legs present along the side of the wing-body. No accurate data was available for quantitative comparison under the effects of the vortex, but the magnitudes followed the qualitative trends expected. This method failed badly in the region of large three-dimensional effects and requires further study in this area of application. (SDW)

An Overview of Modern Permanent Magnet Design

Abstract: : The high-energy product magnet materials have made possible many (compact, light weight) high-field magnetic flux sources that were not practicable before their advent. Near-revolutionary device consequences are unfolding as a result. This report discusses the approaches to the design of such devices and gives various examples that apply to electron-beam devices, nuclear magnetic resonance, electric motors, and others.

Physical Property Measurements on Analog Granites Related to the Joint Verification Experiment

Abstract: : A key element in JVE conducted jointly between the United States and the USSR is the analysis of the geology and physical properties of the rocks in the respective test sites. A study was initiated to examine unclassified crystalline rock specimens obtained from areas near the Soviet site, Semipalatinsk and appropriate analog samples selected from Mt. Katadin, Maine. These rocks were also compared to Sierra White and Westerly Granite which have been studied in great detail. Measurements performed to characterize these rocks were: (1) Uniaxial strain with simultaneous compressional and shear wave velocities; (2) Hydrostatic compression to 150 MPa with simultaneous compressional and shear wave velocities; (3) Attenuation measurements as a function of frequency and strain amplitude for both dry and water saturated conditions. Elastic moduli determined from the hydrostatic compression and uniaxial strain test show that the rock matrix/mineral properties were comparable in magnitudes which vary within 25% from sample to sample. These properties appear to be approximately isotropic, especially at high pressures. However, anistropy evident for certain samples at pressures below 35 MPa is attributed to dominant pre-existing microcrack populations and their alignments. Dependence of extensional attenuation and Young's modulus on strain amplitude were experimentally determined for intact Sierra White granite using the hysteresis loop technique.

Study of three-dimensional pressure-driven turbulent boundary layer

Abstract: : A three dimensional, pressure driven turbulent boundary layer created by an idealized wing-body junction flow is experimentally studied. The body used is a 3 : 2 elliptical nosed NACA 0020 tailed symmetric profile which has a chord length of 30.5 cm (12 inches), maximum thickness of 7.17 cm (2.824 inches), height of 22.9 cm (9.016 inches). The body was sitting on a flat plate. The nominal reference velocity of the flow is 27 m/sec and the Reynolds number based on the momentum thickness at 0.75 chord upstream of the body on the centerline of the tunnel is approx. 5936. The data presented include time-mean static pressure, skin friction magnitude and direction on the wall, as well as the mean velocity and all Reynolds stresses at several stations on a line determined with the mean velocity vector component parallel to the wall in the layer where the normal stress is maximum. The mean velocity and stress data were obtained both with hot-wire (HW) and laser-Doppler-velocimeter (LDV) techniques. The LDV measurement were taken twice due to the differences observed between the HW and LDV data, which is also shown with the present study. This gave a chance to study the uncertainties on the mean velocity and the stresses extensively. Pressure on the bottom plate were obtained with a Scanivalve and an inclined manometer. (SDW)

Investigation into the Mechanism of Polymer Thread Drag Reduction

Abstract: : This study investigated the mechanism of drag reduction that occurs when a long chain, high molecular weight polymer is injected along the centerline of a pipe with a concentration high enough to form a coherent unbroken thread. The objective of this study was to test the hypothesis that drag reduction is caused by the diffusion of polymer molecules from the thread into the near-wall region of the pipe. The objective was realized through the measurement of the polymer concentration in the near-wall region, the drag reduction and the radial location of the thread. The concentration was measured using a laser induced fluorescence technique where the polymer was marked with fluorescein dye. The experiments were conducted in a 3.18 cm diameter, clear acrylic pipe at Re = 40,000 using a 5000 ppm concentration solution of Separan AP 273 as the injectant. The drag reduction increased from zero at the point of injection to a maximum value about 200 diameters downstream of the injector.

Radar Detection during Scintillation

Abstract: : Electromagnetic signals that propagate through a disturbed region of the ionosphere can experience scattering which can cause fluctuations in the received amplitude, phase, and angle-of-arrival. This report considers the performance of a radar that must operate through a disturbed propagation environment such as might occur during strong equatorial scintillation, during a barium release experiment or after a high altitude nuclear detonation. The severity of the channel disturbance is taken to range from weak scattering where the signal quadrature components are uncorrelated Gaussian variates. The detection performance of noncoherent combining is compared to that of double threshold (M out of N) combining under various levels of scintillation disturbance. Results are given for detection sensitivity as a function of the scintillation index and the ratio of the radar hopping bandwidth to the channel bandwidth. It is shown that both types of combining can provide mitigation of fading, and that noncoherent combining generally enjoys an advantage in detection sensitivity of about 2 dB. This work serves as a quantitative guideline to the advantages and disadvantages of certain types of detection strategies during scintillation and is, therefore, useful in the radar design process. However, a detailed simulation of the radar detection algorithms is necessary to evaluate a radar design strategy to predict performance under scintillation conditions.

Temperature and Coupling Behavior of Resonators and Transducers of Lithium Tetraborate Driven by Lateral and Thickness Fields

Abstract: : Lithium tetraborate is a tetragonal material of considerable promise for signal processing, transducer, and frequency control applications. It exhibits piezoelectric coupling values that fall between those of lithium niobate and quartz, but possesses orientations for which the temperature coefficient of frequency or delay time is zero for both bulk and surface acoustic waves. Calculations have previously been made for rotated y-cut, bulk wave plates, including the regions where the quasi-extensional and quasi-shear thickness modes have zero temperature coefficients of frequency. In this report we extend the calculations to doubly rotated bulk wave resonators, and compute the coupling factors for the three simple thickness modes driven by (TE) and lateral (LE) quasistatic electric fields as a function of the orientation angles phi and theta, and the direction of the applied lateral field psi. Because of the temperature coefficients of the piezoelectric coupling factors, the temperature coefficient of a resonator will depend not only upon orientation, but also upon harmonic number and location of the resonator operating point on the immittance circle. It is found that two unique orientations exist in lithium tetraborate for which plate resonators have zero temperature coefficients of frequency of both first- and second-order with high values of piezo coupling factor. One cut has this favorable behavior in its thickness-stretch mode, while the other possesses it for its slow thickness-shear mode.

Correlation of electron-transfer rates with the surface density of states of native and anodically grown oxide films on titanium

Abstract: The authors report tunneling spectroscopy (TS) and surface density of states (SDOS) plots ((dI/dV)/(I/V) vs V) for native and anodically grown titanium dioxide (TiO{sub 2}) films on polycrystalline Ti. The results are compared to data obtained by using single-crystal TiO{sub 2} ((001) and (110) surface orientations). SDOS plots for anodically grown TiO{sub 2} films (160 {Angstrom} thick) and single-crystals TiO{sub 2} show a large bandgap region ({approximately}2 eV) with a low state density separating the conduction and valence band edges. The similarity in the distribution of SDOS for anodically grown TiO{sub 2} films and single-crystal TiO{sub 2} indicates that the anodically grown film has a well-ordered rutile structure. In contrast, SDOS plots obtained on native TiO{sub 2} films show a nearly constant density of states over a 5-eV range and {approximately}20-50-fold increase in state density at energies corresponding to the bandgap region of anodically grown films and single-crystal TiO{sub 2}. Electron-transfer rates for the oxidation of ferrocene in acetonitrile at native and anodically grown TiO{sub 2} films are reported and correlated with the measured SDOS of these materials.

Quantum coherence of a narrow band interacting with phonons and static disorder

Abstract: : This work deals with the quantum dynamics of a narrow band particle interacting with phonons and static disorder. The present theory is exact in the limit of small band width compared with the Debye energy, and covers various regimes in the parameter space of temperature and disorder strength. Therefore, the theory provides a unified framework for studying when and how the particle motion changes from coherent band like behavior to incoherent hopping, as the temperature and/or disorder strength are increased. The theory also includes the double well problem as a special case, where rather complete description of the particle motion is obtained.