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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Performance of correlation receivers in the presence of impulse noise.

An impulse noise model, which assumes that each noise burst contains a randomly weighted version of a basic waveform, is used to derive the performance equations for a correlation receiver. The expected number of bit errors per noise burst is expressed as a function of the average signal energy, signal-set correlation coefficient, bit time, noise-weighting-factor variance and probability density function, and a time range function which depends on the crosscorrelation of the signal-set basis functions and the noise waveform. Unlike the performance results for additive white Gaussian noise, it is shown that the error performance for impulse noise is affected by the choice of signal-set basis function, and that Orthogonal signaling is not equivalent to On-Off signaling with the same average energy. Furthermore, it is demonstrated that the correlation-receiver error performance can be improved by inserting a properly specified nonlinear device prior to the receiver input.

Moore, J. D.↗
NASA NTRS1973

Constrained least-squares analysis of petrologic problems with an application to lunar sample 12040.

Many petrologic problems, which may be expressed as a set of linear equations, have been solved by least-squares analysis. In many cases insufficient attention has been paid to the physical conditions of the model resulting in incorrect application of the method. This paper presents a systematic treatment of the application of least-squares analysis to petrologic problems including the direct utilization of physical constraints and weighting factors in the problem, and the assessment of uncertainties in the solution. As an example, least-squares analysis is used to examine, in detail, the mass balance equations for lunar rock 12040 and to determine the consistency of the available analytical data.

Reid, M. J.↗
NASA NTRS1972

Evaluation of beryllium for space shuttle components

Application of beryllium to specific full-scale space shuttle structural components and assemblies was studied. Material evaluations were conducted to check the mechanical properties of as-received material to gain design information on characteristics needed for the material in the space shuttle environment, and to obtain data needed for evaluating component and panel tests. Four beryllium structural assemblies were analyzed and designed. Selected components of these assemblies, representing areas of critical loading or design/process uncertainty, were designed and tested, and two panel assemblies were fabricated. Trends in cost and weight factors were determined by progressive estimation at key points of preliminary design, final design, and fabrication to aid in a cost/weight evaluation of the use of beryllium.

Trapp, A. E.↗
NASA NTRS1975

A steepest descents method for reentry optimization

A steepest descents optimization program is applied to the problem of a lifting vehicle entering the earth's atmosphere. The program employs penalty functions representing terminal conditions and inflight inequality constraints. During each iteration, it reduces a single performance measure which is the sum of the performance index and the penalty functions. Therefore, only one set of adjoint equations must be integrated per iteration. Values of weight factors, multiplying the penalty functions, are automatically adjusted before each iteration in order that the penalty functions will approach acceptable values. This method is shown to be a form of the classical Lagrange multiplier methods.

Andrus, J. F.↗
NASA NTRS1975

The basic characteristics of hybrid aircraft

The transportation of very heavy or very bulky loads by airships, and the ability to carry out extended duration flights at low speeds and low costs was studied. Structural design and weight factors for airship construction are examined. The densities of various light gases to be used in airships are given, along with their lifting capacities. The aerodynamic characteristics of various airship configurations was studied. Propulsion system requirements for airships are briefly considered.

Nichols, J. B.↗
NASA NTRS1976

Technology outlook for aviation

Growth projections for aviation technology are put forth for a quarter-century ahead. Three main trends envisaged are towards: great efficiency and economy and longer range and endurance for subsonic aircraft; new generations of short-range fixed-wing craft and rotorcraft with versatile applicability; supersonic and hypersonic speeds. Improvements in lift/drag ratio, specific fuel consumption, structural weight factor, aerodynamic improvements (laminar flow control, increased wing aspect ratio, drag reduction for specified lift, propulsion efficiency, higher bypass ratios, composite structures) are discussed along with V/STOL, controllable twist rotors, circulation control rotors, variable-cycle engines, and higher structural efficiencies.

Roberts, L.↗
NASA NTRS1981

Quantification of airport community noise impact in terms of noise levels, population density, and human subjective response

The Fraction Impact Method (FIM), developed by the National Research Council (NRC) for assessing the amount and physiological effect of noise, is described. Here, the number of people exposed to a given level of noise is multiplied by a weighting factor that depends on noise level. It is pointed out that the Aircraft-noise Levels and Annoyance MOdel (ALAMO), recently developed at NASA Langley Research Center, can perform the NRC fractional impact calculations for given modes of operation at any U.S. airport. The sensitivity of these calculations to errors in estimates of population, noise level, and human subjective response is discussed. It is found that a change in source noise causes a substantially smaller change in contour area than would be predicted simply on the basis of inverse square law considerations. Another finding is that the impact calculations are generally less sensitive to source noise errors than to systematic errors in population or subjective response.

Deloach, R.↗
NASA NTRS1982

Sampling errors in the estimation of empirical orthogonal functions

Empirical Orthogonal Functions (EOF's), eigenvectors of the spatial cross-covariance matrix of a meteorological field, are reviewed with special attention given to the necessary weighting factors for gridded data and the sampling errors incurred when too small a sample is available. The geographical shape of an EOF shows large intersample variability when its associated eigenvalue is 'close' to a neighboring one. A rule of thumb indicating when an EOF is likely to be subject to large sampling fluctuations is presented. An explicit example, based on the statistics of the 500 mb geopotential height field, displays large intersample variability in the EOF's for sample sizes of a few hundred independent realizations, a size seldom exceeded by meteorological data sets.

North, G. R.↗
NASA NTRS1981

Components for digitally controlled aircraft engines

Control system components suitable for use in digital electronic control systems are defined. Compressor geometry actuation concepts and fuel handling system concepts suitable for use in large high performance turbofan/turbojet engines are included. Eight conceptual system designs were formulated for the actuation of the compressor geometry. Six conceptual system designs were formulated for the engine fuel handling system. Assessment criteria and weighting factors were established and trade studies performed on their candidate systems to establish the relative merits of the various concepts. Fuel pumping and metering systems for small turboshaft engines were also studied. Seven conceptual designs were formulated, and trade studies performed. A simplified bypassing fuel metering scheme was selected and a preliminary design defined.

Meador, J. D.↗
NASA NTRS1983

Study for analysis of benefit versus cost of low thrust propulsion system

The benefits and costs associated with placing large space systems (LSS) in operational orbits were investigated, and a flexible computer model for analyzing these benefits and costs was developed. A mission model for LSS was identified that included both NASA/Commercial and DOD missions. This model included a total of 68 STS launches for the NASA/Commercial missions and 202 launches for the DOD missions. The mission catalog was of sufficient depth to define the structure type, mass and acceleration limits of each LSS. Conceptual primary propulsion stages (PPS) designs for orbital transfer were developed for three low thrust LO2/LH2 engines baselined for the study. The performance characteristics for each of these PPS was compared to the LSS mission catalog to create a mission capture. The costs involved in placing the LSS in their operational orbits were identified. The two primary costs were that of the PPS and of the STS launch. The cost of the LSS was not included as it is not a function of the PPS performance. The basic relationships and algorithms that could be used to describe the costs were established. The benefit criteria for the mission model were also defined. These included mission capture, reliability, technical risk, development time, and growth potential. Rating guidelines were established for each parameter. For flexibility, each parameter is assigned a weighting factor.

Hamlyn, K. M.↗
NASA NTRS1983

Modeling of transient two-component flow using a four-point implicit method

The four-point, centered implicit scheme that is extensively used in open channel flow simulation is shown to be applicable to rapid and slow pressure transient problems in conduits with nearly single phase and two-phase flows. It is only necessary to choose the proper weighting factor value, theta, of the Courant number. For rapid pressure transients such as waterhammer, the implicit method can yield reasonable results with limited numerical dispersion and attenuation if theta is only slightly greater than the critical value of 0.5. For slower pressure gradients in single and two-phase flows, reasonable numerical solutions may be achieved for Courant number values as high as 20.

Wiggert, D. C.↗
NASA NTRS1985

Optimal design application on the advanced aeroelastic rotor blade

The vibration and performance optimization procedure using regression analysis was successfully applied to an advanced aeroelastic blade design study. The major advantage of this regression technique is that multiple optimizations can be performed to evaluate the effects of various objective functions and constraint functions. The data bases obtained from the rotorcraft flight simulation program C81 and Myklestad mode shape program are analytically determined as a function of each design variable. This approach has been verified for various blade radial ballast weight locations and blade planforms. This method can also be utilized to ascertain the effect of a particular cost function which is composed of several objective functions with different weighting factors for various mission requirements without any additional effort.

Wei, F. S.↗
NASA NTRS1986

Supersonic airfoil optimization

A procedure for the optimization of supersonic airfoils is presented. A nonlinear, full-potential solver (NCOREL) is coupled with a numerical optimizer (CONMIN). The NCOREL code is a three-dimensional supersonic marching method, however, only two-dimensional (conical) results are used for the airfoil problem. Each airfoil evaluated in the NCOREL aerodynamic code is composed of a linear combination of user-specified basis airfoils. The weighting factors of the basis airfoils plus the angle of attack form the design variable vector. The inviscid drag coefficient is minimized subject to lift and crossflow Mach number gradient constraints. The optimization strategy is found to be extremely important for the efficient determination of an optimum airfoil.

Pittman, J. L.↗
NASA NTRS1987

Separating Peaks in X-Ray Spectra

Deconvolution algorithm assists in analysis of x-ray spectra from scanning electron microscopes, electron microprobe analyzers, x-ray fluorescence spectrometers, and like. New algorithm automatically deconvolves x-ray spectrum, identifies locations of spectral peaks, and selects chemical elements most likely producing peaks. Technique based on similarities between zero- and second-order terms of Taylor-series expansions of Gaussian distribution and of damped sinusoid. Principal advantage of algorithm: no requirement to adjust weighting factors or other parameters when analyzing general x-ray spectra.

Nicolas, David↗
NASA NTRS1987

Effects of Control Parameters on a Robot Welder

Gains and weighting factors in vision-based controller evaluated. Report describes study of trajectory control in vision-based robotic welder. Covers evaluation of user-programmable parameters that dictate control response to perceived error in tracking weld seam.

Gangl, K. J.↗
NASA NTRS1987

Preliminary design and cost of a 1-megawatt solar-pumped iodide laser space-to-space transmission station

A preliminary conceptual design of a space-based solar pumped iodide laser emitting 1 megawatt of laser power for space-to-space power transmission is described. A near parabolic solar collector focuses sunlight onto the t-C4F9I (perfluoro-t butyl iodide) lasant within a transverse flow optical cavity. Using waste heat, a thermal system was designed to supply compressor and auxiliary power. System components were designed with weight and cost estimates assigned. Although cost is very approximate, the cost comparison of individual system components leads to valuable insights for future research. In particular, it was found that laser efficiency was not a dominant cost or weight factor, the dominant factor being the laser cavity and laser transmission optics. The manufacturing cost was approx. two thirds of the total cost with transportation to orbit the remainder. The flowing nonrenewable lasant comprised 20% of the total life cycle cost of the system and thus was not a major cost factor. The station mass was 92,000 kg without lasant, requiring approx. four shuttle flights to low Earth orbit where an orbital transfer vehicle will transport it to the final altitude of 6378 km.

Deyoung, R. J.↗
NASA NTRS1988

Joints in fiber-reinforced aluminum alloys

Problems of joining involving structural components made of aluminum alloys with boron-fiber reinforcements are discussed, giving attention to a diffusion-welding process. The tension characteristics and weight factors in the case of various types of welded joints are considered. Diffusion-welding equipment used in the experimental investigation is described. The strength characteristics obtained in various cases of weld and component design are examined, taking into account static and dynamic stresses.

Gerber, K.↗