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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 325 records · Page 18

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NASA NTRS1987

The design and analysis of single flank transmission error tester for loaded gears

To strengthen the understanding of gear transmission error and to verify mathematical models which predict them, a test stand that will measure the transmission error of gear pairs under design loads has been investigated. While most transmission error testers have been used to test gear pairs under unloaded conditions, the goal of this report was to design and perform dynamic analysis of a unique tester with the capability of measuring the transmission error of gears under load. This test stand will have the capability to continuously load a gear pair at torques up to 16,000 in-lb at shaft speeds from 0 to 5 rpm. Error measurement will be accomplished with high resolution optical encoders and the accompanying signal processing unit from an existing unloaded transmission error tester. Input power to the test gear box will be supplied by a dc torque motor while the load will be applied with a similar torque motor. A dual input, dual output control system will regulate the speed and torque of the system. This control system's accuracy and dynamic response were analyzed and it was determined that proportional plus derivative speed control is needed in order to provide the precisely constant torque necessary for error-free measurement.

Bassett, Duane E.↗

NASA NTRS1986

System considerations for a magnetically suspended flywheel

This paper presents the system considerations of a magnetically suspended energy storage system. The key technologies for system success are presented in a technology flowchart. The key areas identified and discussed include: the active bearing control system, the back-up touchdown bearings, and the flywheel dynamic performance and balancing. Two possible hardware designs are described which have been identified as having characteristics suitable for energy storage in low earth orbit spacecraft. Finally, a matrix of the key technologies versus the various prototype designs is presented to show the current progress of inertial energy storage, and to show the direction of future work.

Anand, D. K.↗

NASA NTRS1988

The convertible engine: A dual-mode propulsion system

A variable inlet guide vane (VIGV) convertible engine that could be used to power future high-speed rotorcraft was tested on an outdoor stand. The engine ran stably and smoothly in the turbofan, turboshaft, and dual (combined fan and shaft) power modes. In the turbofan mode with the VIGV open, fuel consumption was comparable to that of a conventional turbofan engine. In the turboshaft mode with the VIGV closed, fuel consumption was higher than that of present turboshaft engines because power was wasted in churning fan-tip air flow. In dynamic performance tests with a specially built digital engine control and using a waterbrake dynamometer for shaft load, the engine responded effectively to large steps in thrust command and shaft torque. Previous mission analyses of a conceptual X-wing rotorcraft capable of 400-knot cruise speed were revised to account for more fan-tip churning power loss that was originally estimated. The calculations confirm that using convertible engines rather than separate life and cruise engines would result in a smaller, lighter craft with lower fuel use and direct operating cost.

Mcardle, Jack G.↗

NASA NTRS1988

Finite-dimensional modeling of network-induced delays for real-time control systems

In integrated control systems (ICS), a feedback loop is closed by the common communication channel, which multiplexes digital data from the sensor to the controller and from the controller to the actuator along with the data traffic from other control loops and management functions. Due to asynchronous time-division multiplexing in the network access protocols, time-varying delays are introduced in the control loop, which degrade the system dynamic performance and are a potential source of instability. The delayed control system is represented by a finite-dimensional, time-varying, discrete-time model which is less complex than the existing continuous-time models for time-varying delays; this approach allows for simpler schemes for analysis and simulation of the ICS.

Ray, Asok↗

NASA NTRS1988

Precise orbit determination for NASA's earth observing system using GPS (Global Positioning System)

An application of a precision orbit determination technique for NASA's Earth Observing System (EOS) using the Global Positioning System (GPS) is described. This technique allows the geometric information from measurements of GPS carrier phase and P-code pseudo-range to be exploited while minimizing requirements for precision dynamical modeling. The method combines geometric and dynamic information to determine the spacecraft trajectory; the weight on the dynamic information is controlled by adjusting fictitious spacecraft accelerations in three dimensions which are treated as first order exponentially time correlated stochastic processes. By varying the time correlation and uncertainty of the stochastic accelerations, the technique can range from purely geometric to purely dynamic. Performance estimates for this technique as applied to the orbit geometry planned for the EOS platforms indicate that decimeter accuracies for EOS orbit position may be obtainable. The sensitivity of the predicted orbit uncertainties to model errors for station locations, nongravitational platform accelerations, and Earth gravity is also presented.

Williams, B. G.↗

NASA NTRS1989

Multi-objective/loading optimization for rotating composite flexbeams

With the evolution of advanced composites, the feasibility of designing bearingless rotor systems for high speed, demanding maneuver envelopes, and high aircraft gross weights has become a reality. These systems eliminate the need for hinges and heavily loaded bearings by incorporating a composite flexbeam structure which accommodates flapping, lead-lag, and feathering motions by bending and twisting while reacting full blade centrifugal force. The flight characteristics of a bearingless rotor system are largely dependent on hub design, and the principal element in this type of system is the composite flexbeam. As in any hub design, trade off studies must be performed in order to optimize performance, dynamics (stability), handling qualities, and stresses. However, since the flexbeam structure is the primary component which will determine the balance of these characteristics, its design and fabrication are not straightforward. It was concluded that: pitchcase and snubber damper representations are required in the flexbeam model for proper sizing resulting from dynamic requirements; optimization is necessary for flexbeam design, since it reduces the design iteration time and results in an improved design; and inclusion of multiple flight conditions and their corresponding fatigue allowables is necessary for the optimization procedure.

Hamilton, Brian K.↗

NASA NTRS1989

Aeroelastic modeling for the FIT (Functional Integration Technology) team F/A-18 simulation

As part of Langley Research Center's commitment to developing multidisciplinary integration methods to improve aerospace systems, the Functional Integration Technology (FIT) team was established to perform dynamics integration research using an existing aircraft configuration, the F/A-18. An essential part of this effort has been the development of a comprehensive simulation modeling capability that includes structural, control, and propulsion dynamics as well as steady and unsteady aerodynamics. The structural and unsteady aerodynamics contributions come from an aeroelastic mode. Some details of the aeroelastic modeling done for the Functional Integration Technology (FIT) team research are presented. Particular attention is given to work done in the area of correction factors to unsteady aerodynamics data.

Zeiler, Thomas A.↗

NASA NTRS1989

Pactruss support structure for precision segmented reflectors

The application of the Pactruss deployable structure to the support of large paraboloidal reflectors of very high precision was studied. The Pactruss concept, originally conceived for the Space Station truss, is shown to be suitable for use in a triangular arrangement to support a reflector surface composed of hexagonal reflector panels. A hybrid of Pactruss structural and deployable single-fold beams is shown to accommodate a center body. A minor alteration in the geometry is in order to avoid lockup during deployment. To assess the capability of the hybrid Pactruss structure, an example truss supporting a full-scale (20 meter diameter) infrared telescope was analyzed for static and dynamic performance. A truss structure weighing 800 kilograms gave adequate support to a reflector surface weighing 3,000 kilograms.

Hedgepeth, John M.↗

NASA NTRS1988

The effect of the solenoidal condition on the numerical magnetohydrodynamic simulation of coronal dynamics

Several MHD simulations of coronal dynamics performed more than 10 years ago violated the solenoidality condition for an 'open' magnetic field topology. Using an improved code, consideration is given to the effect on the physical validity of the numerical simulation (for a representative pulse disturbance) for the case when solenoidality is deliberately violated as compared to the case when it is preserved. It is found that the error incurred in this specific case ('open' topology) in the energy density and in the plasma density profiles is rather small and, hence, does not invalidate the earlier conclusions concerning mass and wave motion.

Wu, S. T.↗

NASA NTRS1988

Voyager programmability - Experiences in control system adaptation

The two Voyager spacecraft were designed with reprogrammable attitude and articulation control system flight control processors to permit inflight modification of the software. These software modifications were designed to: (1) correct for hardware failures that occurred during the interstellar journey, and (2) improve spacecraft dynamic performance for better control so that, by minimizing the use of propellant, the life of the mission could be extended. It is suggested that, in the future, spacecraft be launched with additional unused memory to deal with anomalies unforeseen in the decision-making process.

Patel, Keyur↗

NASA NTRS1987

Large-scale Advanced Prop-fan (LAP) static rotor test report

Discussed is Static Rotor Testing of the SR-7L Large Scale Advanced Prop-Fan (LAP). The LAP is an advanced 9 foot diameter, 8 bladed propeller designed and built by Hamilton Standard under contract to the NASA Lewis Research Center. The Prop-Fan employs thin swept blades to provide efficient propulsion at flight speeds up to Mach .85. Static Testing was conducted on a 10,000 HP whirl rig at Wright Patterson Air Force Base. The test objectives were to investigate the Prop-Fan static aerodynamic and structural dynamic performance, determine the blade steady state stressers and deflections and to measure steady and unsteady pressures on the SR-7L blade surface. The measured performance of the LAP correlated well with analytical predictions at blade pitch angles below 30 deg. A stall buffet phenomenon was observed at blade pitch angles above 30 deg. This phenomenon manifested itself by elevated blade vibratory stress levels and lower than expected thrust produced and power absorbed by the Prop-Fan for a given speed and blade angle.

Degeorge, Charles L.↗

NASA NTRS1989

A laser tracking dynamic robot metrology instrument

Research work over several years has resulted in the development of a laser tracking instrument capable of dynamic 3-D measurements of robot end-effector trajectories. The instrument characteristics and experiments to measure the static and dynamic performance of a robot in an industrial manufacturing environment are described. The use of this technology for space applications is examined.

Parker, G. A.↗

NASA NTRS1990

Integrated Communication and Control Systems. III - Nonidentical sensor and controller sampling

Networking in Integrated Communication and Control Systems (ICCS) introduces randomly varying delays which degrade the system dynamic performance and are a source of potential instability. In Part I of this sequence of papers, a discrete-time, finite-dimensional model of the delayed control system for analysis and design of ICCS was developed where the sensor and controller have identical sampling rates. In Part II, two alternate approaches for ICCS design, namely, identical and nonidentical sampling rates for sensor and controller were proposed. This Part III presents extended modeling of ICCS for nonidentical sensor and controller sampling rates. This model is also suitable for analyzing tracking problems, i.e., control systems with time-dependent reference inputs.

Liou, Luen-Woei↗

NASA NTRS1991

Impact processes in the Solar System: New understandings through numerical modeling

A collision of two rocky objects circling the sun in space, each roughly the size and mass of a large mountain range, was modeled. A fragmentation hydrocode was developed to perform dynamical computations of collisional outcomes. Explosive framentation and fluid dynamics were used and drawn together into a single application. To model a solid, certain material parameters, such as density, elasticity, rigidity, and energies of melting and vaporization were input. These parameters are well-known for a variety of important materials, such as ice, iron, granite, and basalt. Another important parameter used is the distribution of initial flaws within the material.

Asphaug, E.↗

NASA NTRS1991

High-pressure promoted combustion chamber

In the preferred embodiment of the promoted combusiton chamber disclosed herein, a thick-walled tubular body that is capable of withstanding extreme pressures is arranged with removable upper and lower end closures to provide access to the chamber for dependently supporting a test sample of a material being evaluated in the chamber. To facilitate the real-time analysis of a test sample, several pressure-tight viewing ports capable of withstanding the simulated environmental conditions are arranged in the walls of the tubular body for observing the test sample during the course of the test. A replaceable heat-resistant tubular member and replaceable flame-resistant internal liners are arranged to be fitted inside of the chamber for protecting the interior wall surfaces of the combustion chamber during the evaluation tests. Inlet and outlet ports are provided for admitting high-pressure gases into the chamber as needed for performing dynamic analyses of the test sample during the course of an evaluation test.

Rucker, Michelle A.↗

NASA NTRS1991

Jovian electrodynamic tether experiment

A case is made for an electrodynamic tether scientific platform to be put into orbit around Jupiter as a follow-on to the present series of earth-based Tethered Satellite System (TSS) experiments. Preliminary system trades are made to bound the amount of power (assuming 100 percent plasma contactor efficiency) that can be obtained from the orbiting Jovian tether. With magnetic field strengths of roughly 4 to 7 Gauss, power levels of the order of 100 kilowatts can be obtained with a thin 500 km long tether. This should suffice to power a Jovian scientific experiment package. The electrodynamic tether also affords a loitering capability as it can be operated as a thruster in addition to a power generator. Further study and research is needed to characterize the Jovian tether as to its electrodynamic and dynamic performance potential. Hollow cathode plasma contactor operation needs to be verified in near earth space.

Hammond, Walter E.↗

NASA NTRS1990

The aerospace plane design challenge - Credible computational fluid dynamics results

In order to establish the credibility of CFD results utilized in aerospace plane design, the following topics are discussed: CFD validation in relation to 'measureable' fluid dynamics (MFD) validation, credibility requirements, responsibility for credibility, and a guide for establishing credibility. What is of paramount concern for fluid dynamic design is not CFD code validation but qualification of CFD unknowns so that their magnitude is greatly reduced and that these uncertainties are employed for designing with margin. The designers must be trained to properly use CFD if they are to produce good designs. In approximately 70 percent of the flight envelopes of SSTO aerospace planes with supersonic combustion, CFD will be necessary to determine dynamics performance and specifications.

Mehta, Unmeel B.↗

NASA NTRS1991

Dynamics of planetary rings

The modeling of the dynamics of particle collisions within planetary rings is discussed. Particles in the rings collide with one another because they have small random motions in addition to their orbital velocity. The orbital speed is roughly 10 km/s, while the random motions have an average speed of about a tenth of a millimeter per second. As a result, the particle collisions are very gentle. Numerical analysis and simulation of the ring dynamics, performed with the aid of a supercomputer, is outlined.

Araki, Suguru↗