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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 559 records · Page 31
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NASA NTRS1984

A comparison of the efficiency of numerical methods for integrating chemical kinetic rate equations

The efficiency of several algorithms used for numerical integration of stiff ordinary differential equations was compared. The methods examined included two general purpose codes EPISODE and LSODE and three codes (CHEMEQ, CREK1D and GCKP84) developed specifically to integrate chemical kinetic rate equations. The codes were applied to two test problems drawn from combustion kinetics. The comparisons show that LSODE is the fastest code available for the integration of combustion kinetic rate equations. It is shown that an iterative solution of the algebraic energy conservation equation to compute the temperature can be more efficient then evaluating the temperature by integrating its time-derivative.

Radhakrishnan, K.↗
NASA NTRS1984

A method for computing the kernel of the downwash integral equation for arbitrary complex frequencies

For the design of active controls to stabilize flight vehicles, which requires the use of unsteady aerodynamics that are valid for arbitrary complex frequencies, algorithms are derived for evaluating the nonelementary part of the kernel of the integral equation that relates unsteady pressure to downwash. This part of the kernel is separated into an infinite limit integral that is evaluated using Bessel and Struve functions and into a finite limit integral that is expanded in series and integrated termwise in closed form. The developed series expansions gave reliable answers for all complex reduced frequencies and executed faster than exponential approximations for many pressure stations.

Desmarais, R. N.↗
NASA NTRS1984

Comparison of numerical techniques for integration of stiff ordinary differential equations arising in combustion chemistry

The efficiency and accuracy of several algorithms recently developed for the efficient numerical integration of stiff ordinary differential equations are compared. The methods examined include two general-purpose codes, EPISODE and LSODE, and three codes (CHEMEQ, CREK1D, and GCKP84) developed specifically to integrate chemical kinetic rate equations. The codes are applied to two test problems drawn from combustion kinetics. The comparisons show that LSODE is the fastest code currently available for the integration of combustion kinetic rate equations. An important finding is that an interactive solution of the algebraic energy conservation equation to compute the temperature does not result in significant errors. In addition, this method is more efficient than evaluating the temperature by integrating its time derivative. Significant reductions in computational work are realized by updating the rate constants (k = at(supra N) N exp(-E/RT) only when the temperature change exceeds an amount delta T that is problem dependent. An approximate expression for the automatic evaluation of delta T is derived and is shown to result in increased efficiency.

Radhakrishnan, K.↗
NASA NTRS1985

Assuring structural integrity in Army systems

The object of this study was to recommend possible improvements in the manner in which structural integrity of Army systems is assured. The elements of a structural integrity program are described, and relevant practices used in various industries and government organizations are reviewed. Some case histories of Army weapon systems are examined. The mandatory imposition of a structural integrity program patterned after the Air Force Aircraft Structural Integrity Program is recommended and the benefits of such an action are identified.

Source record↗
NASA NTRS1984

A comparison of the efficiency of numerical methods for integrating chemical kinetic rate equations

A comparison of the efficiency of several algorithms recently developed for the efficient numerical integration of stiff ordinary differential equations is presented. The methods examined include two general-purpose codes EPISODE and LSODE and three codes (CHEMEQ, CREK1D, and GCKP84) developed specifically to integrate chemical kinetic rate equations. The codes are applied to two test problems drawn from combustion kinetics. The comparisons show that LSODE is the fastest code currently available for the integration of combustion kinetic rate equations. An important finding is that an iterative solution of the algebraic energy conservation equation to compute the temperature can be more efficient than evaluating the temperature by integrating its time-derivative.

Radhakrishnan, K.↗
NASA NTRS1985

Application of Modern Aperture Integration (AI) and Geometrical Theory of Diffraction (GTD) Techniques for Analysis of Large Reflector Antennas

The application of aperture integration (AI) and geometrical theory of diffraction (GTO) techniques to analyze large reflector antennas is outlined. The following techniques were used: computer modeling, validation of analysis and computer codes, computer aided design modifications, limitation on the conventional aperture integration (AIC) method, extended aperture integration (AIE) method, the AIE method for feed scattering calculations, near field probing predictions for 15 meter model, limitation on AIC for surface tolerance effects, aperture integration on the surface (AIS) method, and AIC and GTD calculations for compact range reflector.

Rudduck, R. C.↗
NASA NTRS1985

Qualification needs for advanced integrated aircraft

In an effort to achieve maximum aircraft performance, designers are integrating aircraft systems. The characteristics of aerodynamics, vehicle structure, and propulsion systems are being integrated and controlled through embedded, often flight critical, electronic systems. The qualification needs for such highly integrated aircraft systems are addressed. Based on flight experience with research aircraft, a set of test capabilities is described which allows for complete and efficient qualification of advanced integrated aircraft.

Mackall, D. A.↗
NASA NTRS1984

Impact of flight systems integration on future aircraft design

Integrations trends in aircraft are discussed with an eye to manifestations in future aircraft designs through interdisciplinary technology integration. Current practices use software changes or small hardware fixes to solve problems late in the design process, e.g., low static stability to upgrade fuel efficiency. A total energy control system has been devised to integrate autopilot and autothrottle functions, thereby eliminating hardware, reducing the software, pilot workload, and cost, and improving flight efficiency and performance. Integrated active controls offer reduced weight and larger payloads for transport aircraft. The introduction of vectored thrust may eliminate horizontal and vertical stabilizers, and location of the thrust at the vehicle center of gravity can provide vertical takeoff and landing capabilities. It is suggested that further efforts will open a new discipline, aeroservoelasticity, and tests will become multidisciplinary, involving controls, aerodynamics, propulsion and structures.

Hood, R. V.↗
NASA NTRS1984

Air Revitalization System integration

This paper presents a status review of Spacecraft Air Revitalization System (ARS) integration using regenerable techniques. The paper addresses concepts of integration of individual subsystems into an Air Revitalization System, as well as integration of components within subsystems. An ARS design is presented based on the Electrochemical Depolarized Carbon Dioxide Concentrator Subsystem, the Sabatier Carbon Dioxide Reduction Subsystem, the Static Feed Water Electrolysis Subsystem, a condensing Humidity Control Subsystem, and a Water Handling Subsystem to perform the functions of CO2 removal, CO2 reduction, O2 generation, humidity control and by-product water distribution, respectively. The paper also highlights the numerous advantages of this integration. Trace contaminant control and the nitrogen supply are not included in the ARS described in this paper.

Quattrone, P. D.↗
NASA NTRS1985

Qualification needs for advanced integrated aircraft

In an effort to achieve maximum aircraft performance, designers are integrating aircraft systems. The characteristics of aerodynamics, vehicle structure, and propulsion systems are being integrated and controlled through embedded, often flight-critical, electronic systems. This paper addresses the qualification needs for such highly integrated aircraft systems. Based on flight experience with research aircraft, a set of test capabilities is described which allows for complete and efficient qualification of advanced integrated aircraft.

Mackall, D. A.↗
NASA NTRS1985

Monolithic optical integrated control circuitry for GaAs MMIC-based phased arrays

Gallium arsenide (GaAs) monolithic microwave integrated circuits (MMIC's) show promise in phased-array antenna applications for future space communications systems. Their efficient usage will depend on the control of amplitude and phase signals for each MMIC element in the phased array and in the low-loss radiofrequency feed. For a phased array contining several MMIC elements a complex system is required to control and feed each element. The characteristics of GaAs MMIC's for 20/30-GHz phased-array systems are discussed. The optical/MMIC interface and the desired characteristics of optical integrated circuits (OIC's) for such an interface are described. Anticipated fabrication considerations for eventual full monolithic integration of optical integrated circuits with MMIC's on a GaAs substrate are presented.

Bhasin, K. B.↗
NASA NTRS1985

On the solution of integral equations with strong ly singular kernels

In this paper some useful formulas are developed to evaluate integrals having a singularity of the form (t-x) sup-m, m or = 1. Interpreting the integrals with strong singularities in Hadamard sense, the results are used to obtain approximate solutions of singular integral equations. A mixed boundary value problem from the theory of elasticity is considered as an example. Particularly for integral equations where the kernel contains, in addition to the dominant term (t,x) sup-m, terms which become unbounded at the end points, the present technique appears to be extremely effective to obtain rapidly converging numerical results.

Kaya, A. C.↗
NASA NTRS1986

Development and validation of the crew-station system-integration research facility

The various issues associated with the use of integrated flight management systems in aircraft were discussed. To address these issues a fixed base integrated flight research (IFR) simulation of a helicopter was developed to support experiments that contribute to the understanding of design criteria for rotorcraft cockpits incorporating advanced integrated flight management systems. A validation experiment was conducted that demonstrates the main features of the facility and the capability to conduct crew/system integration research.

Nedell, B.↗
NASA NTRS1986

On the solution of integral equations with strongly singular kernels

Some useful formulas are developed to evaluate integrals having a singularity of the form (t-x) sup-m ,m greater than or equal 1. Interpreting the integrals with strong singularities in Hadamard sense, the results are used to obtain approximate solutions of singular integral equations. A mixed boundary value problem from the theory of elasticity is considered as an example. Particularly for integral equations where the kernel contains, in addition to the dominant term (t-x) sup -m , terms which become unbounded at the end points, the present technique appears to be extremely effective to obtain rapidly converging numerical results.

Kaya, A. C.↗
NASA NTRS1986

Integrated analysis system for box truss antenna mesh performance

An integrated analysis system has been developed to more efficiently design and analyze the mesh reflective surface and the mesh tie system of the box truss antenna. Six integrated computer programs using nonlinear finite-element, surface topography and interpolation, and RF aperture integration techniques, analyze the effects of manufacturing errors, mesh pillowing, and operating environment on antenna performance. The level of rigor of analysis can be varied, providing the possibility of a lower cost preliminary study on various designs using a minimum number of reduced box section models. By including the random and systematic errors with the aperture integration of minimum rms reflector surface roughness, the RF Performance Solver determines the far-field pattern, including the beam efficiency, and thus the antenna performance of the mesh reflector antenna.

Bachtell, E. E.↗
NASA NTRS1986

Finite-volume and integral-equation techniques for transonic and supersonic vortex-dominated flows

Two computational techniques are developed to calculate the compressible vortex-dominated flows. The first technique is a finite-volume Euler Solver which uses four-Stage Runge-Kutta time stepping with second- and fourth-order dissipation terms. The technique is applied to supersonic conical and three-dimensional flows about sharp- and round-edged delta wings. Attached and separated-flow solutions have been obtained depending on the values of damping coefficients. The second technique is an integral-equation solver of the full potential equation which uses a volume-integral term in addition to the classical surface-integral terms. The technique is applied to transonic three-dimensional flows about sharp-edged delta wings. A hybrid technique which combines the finite-volume and the integral-equation solvers is also presented.

Kandil, O. A.↗
NASA NTRS1987

Integrated restructurable flight control system demonstration results

The purpose of this study was to examine the complementary capabilities of several restructurable flight control system (RFCS) concepts through the integration of these technologies into a complete system. Performance issues were addressed through a re-examination of RFCS functional requirements, and through a qualitative analysis of the design issues that, if properly addressed during integration, will lead to the highest possible degree of fault-tolerant performance. Software developed under previous phases of this contract and under NAS1-18004 was modified and integrated into a complete RFCS subroutine for NASA's B-737 simulation. The integration of these modules involved the development of methods for dealing with the mismatch between the outputs of the failure detection module and the input requirements of the automatic control system redesign module. The performance of this demonstration system was examined through extensive simulation trials.

Weiss, Jerold L.↗
NASA NTRS1987

Highly integrated digital electronic control: Digital flight control, aircraft model identification, and adaptive engine control

The highly integrated digital electronic control (HIDEC) program at NASA Ames Research Center, Dryden Flight Research Facility is a multiphase flight research program to quantify the benefits of promising integrated control systems. McDonnell Aircraft Company is the prime contractor, with United Technologies Pratt and Whitney Aircraft, and Lear Siegler Incorporated as major subcontractors. The NASA F-15A testbed aircraft was modified by the HIDEC program by installing a digital electronic flight control system (DEFCS) and replacing the standard F100 (Arab 3) engines with F100 engine model derivative (EMD) engines equipped with digital electronic engine controls (DEEC), and integrating the DEEC's and DEFCS. The modified aircraft provides the capability for testing many integrated control modes involving the flight controls, engine controls, and inlet controls. This paper focuses on the first two phases of the HIDEC program, which are the digital flight control system/aircraft model identification (DEFCS/AMI) phase and the adaptive engine control system (ADECS) phase.

Baer-Riedhart, Jennifer L.↗