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At least 1,405 records · Page 78

Evaluation of China’s Environmental Pressures Based on Satellite NO 2 Observation and the Extended STIRPAT Model

China’s rapid urbanization and industrialization have affected the spatiotemporal patterns of nitrogen dioxide (NO 2 ) pollution, which has caused greater environmental pressures. In order to mitigate the environmental pressures because of NO 2 pollution, it is of vital importance to investigate the influencing factors. We first obtained data for NO 2 pollution at the city level using satellite observation techniques and analyzed its spatial distribution. Next, we introduced a theoretical framework, an extended stochastic impacts by regression on population, affluence, and technology (STIRPAT) model, to quantify the relationship between NO 2 pollution and its contributing natural and socio-economic factors. The results are as follows. Cities with high NO 2 pollution are mainly concentrated in the North China Plain. On the contrary, southwestern cities are characterized by low NO 2 pollution. In addition, we find that population, per capita gross domestic product, the share of the secondary industry, ambient air pressures, total nighttime light data, and urban road area have a positive impact on NO 2 pollution. In contrast, increases in the normalized difference vegetation index (NDVI), relative humidity, temperature, and wind speed may reduce NO 2 pollution. These empirical results should help the government to effectively and efficiently implement further emission reductions and energy saving policies in Chinese cities in a bid to mitigate the environmental pressures.

54 ENVIRONMENTAL SCIENCES↗

Mitigation of Galvanic Corrosion in Bolted Joint of AZ31B and Carbon Fiber-Reinforced Composite Using Polymer Insulation

The use of polymer insulation to mitigate galvanic corrosion was examined for bolted joints of AZ31B Mg alloy and carbon fiber-reinforced composite. To assess the corrosion behaviors of bolted joints with and without polymer insulation, solution immersion and salt spray exposure (ASTM B117) tests were conducted, and the corrosion depths and volumes were determined for the joint specimens after the tests. The polymer-insulated bolted joints exhibited much lower corrosion depths and volumes, highlighting the effective mitigation of galvanic corrosion. The reductions of joint strength in the post-corrosion joint specimens were relatively small (up to ~10%) in the polymer-insulated group but greater (up to 90%) in the group with no insulation. Cross-sectional characterization of post-corrosion joints with polymer insulation revealed local pits developed on AZ31B under galvanic influence, indicating that limited galvanic attack (that did not decrease the joining integrity significantly) could still occur during a long salt spray exposure (~1264 h) owing to the permeation of an aqueous corrosive medium.

36 MATERIALS SCIENCE↗

Strain-age cracking in Rene 41 alloy

Weldability test determines the effects of material and process variables on the occurrence of strain-age cracking, and demonstrates effective and practical means for its reduction. Studies consist of tensile, impact, and stress-rupture tests.

Prager, M.↗

Development of improved pyroelectric detectors; Literature survey of pyroelectric materials and their characteristics

The object of this program is to improve the detectivity of the pyroelectric detector with the ultimate goal of operation at or near the temperature-noise limit. Two general areas of investigation are undertaken. The first is to improve responsivity through the use of new materials. The second is directed toward reduction of noise and will be effected with improved field effect transistor characteristics, and improved electroding of the pyroelectric material. The search for new materials has begun with a review of the literature on pyroelectric materials in several languages. The compiled data includes an extensive list of references. From this, several materials have already been selected for investigation. FETs are being obtained from various manufacturers, evaluated, and selected units will be tested with pyroelectric elements as complete detectors.

Weiner, S.↗

Development of improved pyroelectric detectors: Measurements of pyroelectric material characteristics and FET characteristics

The object of this program is to improve the detectivity of the pyroelectric detector with the ultimate goal of operation at or near the temperature noise limit. Two general areas of investigation are undertaken. The first is to improve responsivity through the use of new materials. The second is directed toward reduction of noise and will be effected with improved field effect transistor characteristics, and improved electroding of the pyroelectric material. The review of the literature on pyroelectric materials continues. From this, several materials have already been selected for investigation, and several were tested.

Weiner, S.↗

Effect of water injection on nitric oxide emissions of a gas turbine combustor burning natural gas fuel

The effect of direct water injection on the exhaust gas emissions of a turbojet combustor burning natural gas fuel was investigated. The results are compared with the results from similar tests using ASTM Jet-A fuel. Increasing water injection decreased the emissions of oxides of nitrogen (NOX) and increased the emissions of carbon monoxide and unburned hydrocarbons. The greatest percentage decrease in NOX with increasing water injection was at the lowest inlet-air temperature tested. The effect of increasing inlet-air temperature was to decrease the effect of the water injection. The reduction in NOX due to water injection was almost identical to the results obtained with Jet-A fuel. However, the emission indices of unburned hydrocarbons, carbon monoxide, and percentage nitric oxide in NOX were not.

Marchionna, N. R.↗

Some effects of tip fins on wing flutter characteristics

A wind tunnel investigation has been conducted over the Mach number range from about 0.6 to 1.2 to determine the effects of large tip fins on the flutter characteristics of a swept wing. The basic wing configuration had an aspect ratio of 0.95, leading-edge sweep of 40 deg 0, and trailing-edge sweep of 21 deg. Two of these configurations were modified with tip fins of 60 deg dihedral and had effective aspect ratios of 1.5 and 2.2. In general, the results indicate that the addition of tip fins reduces the flutter speed, with the larger fin having the greater effect. Comparison of the experimental flutter speeds at Mach numbers between 0.60 and 0.90 with calculated values obtained by using doublet-lattice unsteady aerodynamic theory was good. Analytical results where structural and aerodynamic effects of the tip fins were isolated indicated that the reduction in flutter speed produced by the addition of the fins was caused by both effects, with the structural effect being the more pronounced.

Goetz, R. C.↗

Calculated Hovering Helicopter Flight Dynamics with a Circulation Controlled Rotor

The influence of the rotor blowing coefficient on the calculated roots of the longitudinal and lateral motion was examined for a range of values of the rotor lift and the blade flap frequency. The control characteristics of a helicopter with a circulation controlled rotor are discussed. The principal effect of the blowing is a reduction in the rotor speed stability derivative. Above a critical level of blowing coefficient, which depends on the flap frequency and rotor lift, negative speed stability is produced and the dynamic characteristics of the helicopter are radically altered.

Johnson, W.↗

Calculated hovering helicopter flight dynamics with a circulation-controlled rotor

The flight dynamics of a hovering helicopter with a circulation-controlled rotor are analyzed. The influence of the rotor blowing coefficient on the calculated eigenvalues of the helicopter motion is examined for a range of values of the rotor lift and the blade flap frequency. The control characteristics of a helicopter with a circulation-controlled rotor are discussed. The principal effect of the blowing is a reduction in the rotor speed stability derivative. Above a critical level of blowing coefficient, which depends on the flap frequency and rotor lift, negative speed stability is produced and the dynamic characteristics of the helicopter are radically altered. The handling qualities of a helicopter with negative speed stability are probably unacceptable without a stability augmentation system.

Johnson, W.↗

Theoretical prediction of nonlinear propagation effects on noise signatures generated by subsonic or supersonic propeller or rotor-blade tips

The nonlinear propagation equations for sound generated by a constant speed blade tip are presented. Propagation from a subsonic tip is treated as well as the various cases that can occur at supersonic speeds. Some computed examples indicate that the nonlinear theory correlates with experimental results better than linear theory for large amplitude waves. For swept tips that generate a wave with large amplitude leading expansion, the nonlinear theory predicts a cancellation effect that results in a significant reduction of both amplitude and impulse.

Barger, R. L.↗

Improved methods for fan sound field determination

Several methods for determining acoustic mode structure in aircraft turbofan engines using wall microphone data were studied. A method for reducing data was devised and implemented which makes the definition of discrete coherent sound fields measured in the presence of engine speed fluctuation more accurate. For the analytical methods, algorithms were developed to define the dominant circumferential modes from full and partial circumferential arrays of microphones. Axial arrays were explored to define mode structure as a function of cutoff ratio, and the use of data taken at several constant speeds was also evaluated in an attempt to reduce instrumentation requirements. Sensitivities of the various methods to microphone density, array size and measurement error were evaluated and results of these studies showed these new methods to be impractical. The data reduction method used to reduce the effects of engine speed variation consisted of an electronic circuit which windowed the data so that signal enhancement could occur only when the speed was within a narrow range.

Cicon, D. E.↗

Mechanical suppression: Modern technology applied to an old art

Various suppressor configurations were analyzed and evaluated in an effort to reduce combustion instability and improved ballistic reproducibility of the MK 12 motor. A static firing test series of eight field return boosters featured two baseline motor firings with the existing suppressor in each motor, followed by two tests each of two different prototype suppressor designs. Results were analyzed and used to generate the design for the final two firings. Acoustic pressure pulsers were utilized to measure the damping effectiveness of the final design. The reduction in motor vibration and acoustic pressure levels between the baseline tests and the final two improved lightweight tests was significant. The average acceleration level of the motors equipped with flightweight rods was reduced to only 5% of the level in the unmodified motors; the average acoustic pressure level was reduced to 20%; maximum values were reduced to 6% for acceleration and 23% for pressure.

Crockford, W. H.↗

Measuring: The quantifying art

The photograph of a comet or asteroid against background stars contains information in analog form regarding the relative positions of comet and star images. Measuring is the procedure for covnerting this information to digital form for computation of the object's accurate equatorial coordinates at the time of observation. The use of one- and two-coordinate measuring engines to measure the positions of images which may be elongated, comatic, or both, as well as round images is discussed along with the training of novice measurers to cope with such images. The grading of plates for potential accuracy of positions, preparation of plates for measuring, the accuracy of measurement, effects of telescope focal length and reduction technique upon the accuracy of positions, and the procedures and checks which may prevent erroneous positions also are discussed.

Gibson, J.↗

Noise produced by the interaction of a rotor wake with a swept stator blade

An analysis is developed for the noise generated by the interaction of rotor viscous wakes and a single swept stator vane. The stator vane spans a channel with infinite parallel walls which contains a uniform subsonic mean flow. High frequency wakes, for which the noise generation is concentrated at the vane leading edge, are considered. The general wake pattern is expanded in spanwise modes and solutions for each mode are derived using the Wiener-Hopf technique applied to the equations in the nonorthogonal coordinates. Closed form expressions for the acoustic farfield are obtained. The results of the analysis are used in parametric calculations of rotor viscous wake-stator vane interactions in order to study the effectiveness of sweep as a noise reduction mechanism. For the cases studied, moderate stator sweep angles produce sizeable reductions in the level of the farfield noise. The presence of rotor wake circumferential lean actually increases the noise reduction produced by moderate stator sweep angles.

Envia, E.↗

Shuttle payload dynamic environments - Update

This paper represents a brief summary of a report titled, 'Shuttle Payload Bay Dynamic Environments Summary and Conclusion Report' prepared by the Jet Propulsion Laboratory for the NASA Office of Aeronautics and Space Technology (OAST). The report provides a summary of the dynamic environmental data taken during the first five Space Shuttle flights. The present paper is concerned with a brief synopsis of the report's acoustic and high frequency data evaluation, taking into account also an example acoustic prediction method. Attention is given to an acoustic data summary, a vibration data summary, environmental uncertainties, data reduction errors, spatial bias errors, payload effects, spatial variation, flight to flight variation, payload prediction, and an example prediction.

Oconnell, M.↗

Free shear flows - Organized structures and effects of excitation

Recent studies of free shear flows are reviewed. Included are experimental studies of: excited and unexcited circular and elliptic jets, plane wake and mixing layers, and effects of excitation on augmentation and reduction of jet turbulence and jet noise. It is shown that proper excitation can produce both large increases and large decreases in turbulence and Reynolds stress level, mixing and noise generation, suggesting promising technological applications of self-excited jets such as whistler jets. It is also argued that 'ribs' or longitudinal vortices play an important role in production and mixing in free, and perhaps all, turbulent shear flows. The 'cut-and-connect' interaction of vortical structures is proposed as a key mechanism for coherent structure breakdown, mixing, turbulence production, and aerodynamic noise generation. A simple analysis of the viscous vorticity equation using symmetry of configurations of vortical structures before and after the interaction gives realistic predictions.

Hussain, A. K. F.↗

Development of wind tunnel techniques for the solution of problems in planetary Aeolian processes

Kutzbach reports wind profiles over a series of roughness elements on a frozen lake and how the wind profile changed as the surface roughness was varied. The approach of the current study was to duplicate Kutzbach's roughness arrays in the wind tunnel at 1/20 and 1/40 scales, and to compare the wind profiles over these scale models to those derived by Kutzbach at full scale in the field. The effects of scale differences and data reduction techniques are discussed. Although the study suggests that wind tunnel scale models can predict parameters measured in the field, the development of more definitive guidelines requires a field experiment designed specifically for comparison with wind tunnel results.

Sullivan, Robert↗