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At least 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

An analytic model of the neutral cloud evolution in the earth's atmosphere

An analytic model for the expansion of a chemically reacting gas in the upper atmosphere is discussed. The spatial-temporal distribution of released particles in the initial regime is described on the basis of self-similar solutions of Euler's equations. In the case of transition to the diffusion regime an approximate solution of the kinetic equation with the collision integral in the form of BGK is performed. Gravitation and the atmospheric inhomogeneity are taken into account, The diffusion regime is described by an analytic solution of the diffusion equation in an exponential atmosphere taking account of possible losses of the gas due to chemical reactions. Some peculiarities of the expansion of various gases as well as the possibility of applying the model for describing ionospheric 'holes' are discussed.

Bruskin, L. G.↗
NASA NTRS1992

Analytical flow/thermal modeling of combustion gas flows in Redesigned Solid Rocket Motor test joints

A one-dimensional analytical tool, TOPAZ (Transient One-dimensional Pipe flow AnalyZer), was used to model the flow characteristics of hot combustion gases through Redesigned Solid Rocket Motor (RSRM) joints and to compute the resultant material surface temperatures and o-ring seal erosion of the joints. The capabilities of the analytical tool were validated with test data during the Seventy Pound Charge (SPC) motor test program. The predicted RSRM joint thermal response to ignition transients was compared with test data for full-scale motor tests. The one-dimensional analyzer is found to be an effective tool for simulating combustion gas flows in RSRM joints and for predicting flow and thermal properties.

Woods, G. H.↗
NASA NTRS1993

ATTIRE (analytical tools for thermal infrared engineering): A sensor simulation and modeling package

The Advanced Sensor Development Laboratory (ASDL) at the Stennis Space Center develops, maintains and calibrates remote sensing instruments for the National Aeronautics & Space Administration (NASA). To perform system design trade-offs, analysis, and establish system parameters, ASDL has developed a software package for analytical simulation of sensor systems. This package called 'Analytical Tools for Thermal InfraRed Engineering' - ATTIRE, simulates the various components of a sensor system. The software allows each subsystem of the sensor to be analyzed independently for its performance. These performance parameters are then integrated to obtain system level information such as Signal-to-Noise Ratio (SNR), Noise Equivalent Radiance (NER), Noise Equivalent Temperature Difference (NETD) etc. This paper describes the uses of the package and the physics that were used to derive the performance parameters.

Jaggi, S.↗
NASA NTRS1993

An analytical optimization of electric propulsion orbit transfer vehicles

Due to the electric propulsion's inherent propellant mass savings over chemical propulsion, electric propulsion orbit transfer vehicles (EPOTV's) are highly efficient mode of orbit transfer. When selecting an electric propulsion device (ion, MPD, or arcjet) and propellant for a particular mission, it is preferable to use quick, analytical system optimization methods instead of time intensive numerical integration methods. It is also of interest to determine each thruster's optimal operating characteristics for a specific mission. Analytical expressions are derived which determine the optimal specific impulse (Isp) for each type of electric thruster to maximize payload fraction for a desired thrusting time. These expressions take into account the variation of thruster efficiency with specific impulse. Verification of the method is made with representative electric propulsion values on a LEO-to-GEO mission. Application of the method to specific missions is discussed.

Oleson, Steven R.↗
NASA NTRS1993

LOX/hydrocarbon rocket engine analytical design methodology development and validation. Volume 1: Executive summary and technical narrative

During the past three decades, an enormous amount of resources were expended in the design and development of Liquid Oxygen/Hydrocarbon and Hydrogen (LOX/HC and LOX/H2) rocket engines. A significant portion of these resources were used to develop and demonstrate the performance and combustion stability for each new engine. During these efforts, many analytical and empirical models were developed that characterize design parameters and combustion processes that influence performance and stability. Many of these models are suitable as design tools, but they have not been assembled into an industry-wide usable analytical design methodology. The objective of this program was to assemble existing performance and combustion stability models into a usable methodology capable of producing high performing and stable LOX/hydrocarbon and LOX/hydrogen propellant booster engines.

Pieper, Jerry L.↗
NASA NTRS1991

Mechanical and analytical screening of braided composites for transport fuselage applications

The mechanics of materials progress in support of the goal of understanding the application of braided composites in a transport aircraft fuselage are summarized. Composites consisting of both 2-D and 3-D braid patterns are investigated. Both consolidation of commingled graphite/PEEK and resin transfer molding of graphite-epoxy braided composite processes are studied. Mechanical tests were used to examine unnotched tension, open hole tension, compression, compression after impact, in-plane shear, out-of-plane tension, bearing, and crippling. Analytical methods are also developed and applied to predict the stiffness and strengths of test specimens. A preliminary study using the test data and analytical results is performed to assess the applicability of braided composites to a commercial aircraft fuselage.

Fedro, Mark J.↗
NASA NTRS1992

Analytic description of the electron temperature behavior in the upper ionosphere and plasmasphere

Approximate analytic solutions to the well-known and commonly used time-dependent electron energy balance equation for the upper ionosphere and plasmasphere have been obtained and are discussed. The various potential heating sources for the terrestrial plasmasphere are summarized and the corresponding electron temperatures and related characteristic heating and cooling times are calculated. A comparison between the analytic expressions for the temperature variations and relevant measurements shows excellent agreement.

Khazanov, G. V.↗
NASA NTRS1992

Closed-form analytical solutions of high-temperature heat pipe startup and frozen startup limitation

Previous numerical and experimental studies indicate that the high-temperature heat pipe startup process is characterized by a moving hot zone with relatively sharp fronts. Based on the above observation, a flat-front model for an approximate analytical solution is proposed. A closed-form solution related to the temperature distribution in the hot zone and the hot zone length as a function of time are obtained. The analytical results agree well with the corresponding experimental data, and provide a quick prediction method for the heat pipe startup performance. Finally, a heat pipe limitation related to the frozen startup process is identified, and an explicit criterion for the high-temperature heat pipe startup is derived. The frozen startup limit identified in this paper provides a fundamental guidance for high-temperature heat pipe design.

Cao, Y.↗
NASA NTRS1992

Analytical formulation of optimum rotor interdisciplinary design with a three-dimensional wake

An analytical formulation of optimum rotor interdisciplinary design is presented. A finite-state aeroelastic rotor model, coupling generalized dynamic wake with blade finite elements, is applied to perform the optimum rotor blade design for improved aerodynamic performance and vehicle vibration, while a feasible direction nonlinear optimizer, CONMIN, provides the optimization algorithm. The approach features a systematic rotor aeroelastic model which offers an efficient analytical tool, and retains necessary aerodynamic and blade dynamic building blocks for a sufficient rotor dynamic response analysis. The formulation is well suited for an efficient design sensitivity computation without resorting to finite difference, and thus provides a practical design tool. The results show improved rotor aerodynamic performance and reduced hub vibratory loads for the optimized blade as compared to the advanced rotor of reference design.

He, Chengjian↗
NASA NTRS1992

The analytical control program for the NASA Space Station Freedom Environmental Control and Life Support System (ECLSS) Water Recovery Test

NASA-Marshall has striven to maximize quality assurance and quality control measures in the course of Water Recovery Test (WRT) development for the Space Station Freedom ECLSS. The WRT was subjected to an independent analytical control program that is governed by the Analytical Control Test Plan and the Microbiological Methods for Water Recovery Testing Plan. Attention is given to analysis results for volatiles, sodium, and conductivity.

Tatara, James D.↗
NASA NTRS1993

Bifurcation analysis of a simple analytic model of self-propagating star formation

We investigate the structure and stability of rotationally symmetric nonhomogeneous time-independent solutions derived from a simple analytic model of self-propagating star formation. For this purpose we employ two methodologies: We use bifurcation theoretical methods to prove the existence of nonhomogeneous axisymmetric stationary solutions of an appropriate nonlinear evolution equation for the stellar density. We show that the nonhomogeneous solution branch bifurcates from the homogeneous one at a critical parameter value of the star formation rate. Further, the analytical theory allows us to show that the new solution set is stable in the weakly nonlinear regime near the bifurcation point. To follow the solution branch further, we use numerical methods. The numerical calculation shows the structure and stability of these solutions. We conclude that no periodic time-dependent solutions of this special model exist, and no further bifurcations can be found. The same results have been found in simulations of stochastic self-propagating star formation based on similar models. Therefore, our findings provide a natural explanation, why long-lived large-scale structure have not been found in those simulations.

Neukirch, Thomas↗
NASA NTRS1993

Mechanical properties of triaxially braided composites - Experimental and analytical results

This paper investigates the unnotched tensile properties of two-dimensional (2D) triaxial braid-reinforced composites both experimentally and analytically. The materials are graphite fibers in an epoxy matrix. Three different reinforcing fiber architectures were considered. There were considerable differences in the observed elastic constants from different size strain gage and extensometer readings. Larger strain gages gave more consistent results and correlated better with the extensometer readings. Experimental strains correlated reasonably well with analytical predictions in the longitudinal, 0 deg, fiber direction but not in the transverse direction. Tensile strength results were not always predictable even in reinforcing directions. Minor changes in braid geometry led to disproportionate strength variations. The unit cell structure of the triaxial braid was discussed with the assistance of computer analysis of the microgeometry. Photomicrographs of braid geometry were used to improve upon the computer graphics representations of unit cells. These unit cells were used to predict the elastic moduli with various degrees of sophistication. The simple and the complex analyses were generally in agreement, but none adequately matched the experimental results for all the braids.

Masters, John E.↗
NASA NTRS1989

Current analytical gaps: Future needs for large space systems

Viewgraphs on current analytical gaps for future needs for large space systems are presented. Topics covered include: future spacecraft; common control objectives; accuracy requirements; increasing complexity; promising approaches; and analytical gaps.

Taylor, Larry↗
NASA NTRS1948

An Analytical Method of Estimating Turbine Performance

A method is developed by which the performance of a turbine over a range of operating conditions can be analytically estimated from the blade angles and flow areas. In order to use the method, certain coefficients that determine the weight flow and friction losses must be approximated. The method is used to calculate the performance of the single-stage turbine of a commercial aircraft gas-turbine engine and the calculated performance is compared with the performance indicated by experimental data. For the turbine of the typical example, the assumed pressure losses and turning angles give a calculated performance that represents the trends of the experimental performance with reasonable accuracy. The exact agreement between analytical performance and experimental performance is contingent upon the proper selection of the blading-loss parameter. A variation of blading-loss parameter from 0.3 to 0.5 includes most of the experimental data from the turbine investigated.

Kochendorfer, Fred D↗
NASA NTRS1954

Analytical Study of Losses at Off-design Conditions for a Fixed Geometry Turbine

An analytical investigation was made to determine the off-design loss characteristics of a fixed-geometry turbine of which the experimental performance was known. The method of analysis utilized an effective loss parameter and assumed that the velocity normal to the blade entrance angle was lost as a total-pressure loss. The method also assumed constant tangential component of velocity between the station just upstream and just downstream of the stator and rotor trailing edge. Good correlation between the analytically and experimentally obtained performance was found over the entire map until limiting loading was approached. The large decrease in efficiency at low-speed high pressure ratios and at high-speed low pressure ratios was found in the analysis to be almost entirely due to the rotor incidence and turbine exit whirl losses. From the results of the investigation it was concluded that for turbines designed to operate efficiently at more than one point, the design must compromise rotor incidence angle and exit whirl losses.

Stewart, Warner L↗
NASA NTRS1949

An analytical method of estimating turbine performance

A method is developed by which the performance of a turbine over a range of operating conditions can be analytically estimated from the blade angles and flow areas. In order to use the method, certain coefficients that determine the weight flow and the friction losses must be approximated. The method is used to calculate the performance of the single-stage turbine of a commercial aircraft gas-turbine engine and the calculated performance is compared with the performance indicated by experimental data. For the turbine of the typical example, the assumed pressure losses and the tuning angles give a calculated performance that represents the trends of the experimental performance with reasonable accuracy. The exact agreement between analytical performance and experimental performance is contingent upon the proper selection of a blading-loss parameter.

Kochendorfer, Fred D↗
NASA NTRS1993

On the Gibbs phenomenon 3: Recovering exponential accuracy in a sub-interval from a spectral partial sum of a piecewise analytic function

The investigation of overcoming Gibbs phenomenon was continued, i.e., obtaining exponential accuracy at all points including at the discontinuities themselves, from the knowledge of a spectral partial sum of a discontinuous but piecewise analytic function. It was shown that if we are given the first N expansion coefficients of an L(sub 2) function f(x) in terms of either the trigonometrical polynomials or the Chebyshev or Legendre polynomials, an exponentially convergent approximation to the point values of f(x) in any sub-interval in which it is analytic can be constructed.

Gottlieb, David↗
NASA NTRS1994

Analytical Design Package (ADP2): A computer aided engineering tool for aircraft transparency design

The Analytical Design Package (ADP2) is being developed as a part of the Air Force Frameless Transparency Program (FTP). ADP2 is an integrated design tool consisting of existing analysis codes and Computer Aided Engineering (CAE) software. The objective of the ADP2 is to develop and confirm an integrated design methodology for frameless transparencies, related aircraft interfaces, and their corresponding tooling. The application of this methodology will generate high confidence for achieving a qualified part prior to mold fabrication. ADP2 is a customized integration of analysis codes, CAE software, and material databases. The primary CAE integration tool for the ADP2 is P3/PATRAN, a commercial-off-the-shelf (COTS) software tool. The open architecture of P3/PATRAN allows customized installations with different applications modules for specific site requirements. Integration of material databases allows the engineer to select a material, and those material properties are automatically called into the relevant analysis code. The ADP2 materials database will be composed of four independent schemas: CAE Design, Processing, Testing, and Logistics Support. The design of ADP2 places major emphasis on the seamless integration of CAE and analysis modules with a single intuitive graphical interface. This tool is being designed to serve and be used by an entire project team, i.e., analysts, designers, materials experts, and managers. The final version of the software will be delivered to the Air Force in Jan. 1994. The Analytical Design Package (ADP2) will then be ready for transfer to industry. The package will be capable of a wide range of design and manufacturing applications.

Wuerer, J. E.↗