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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 955 records · Page 53

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NASA NTRS1991

Component technology for stirling power converters

NASA Lewis Research Center has organized a component technology program as part of the efforts to develop Stirling converter technology for space power applications. The Stirling Space Power Program is part of the NASA High Capacity Power Project of the Civil Space Technology Initiative (CSTI). NASA Lewis is also providing technical management for the DOE/Sandia program to develop Stirling converters for solar terrestrial power producing electricity for the utility grid. The primary contractors for the space power and solar terrestrial programs develop component technologies directly related to their goals. This Lewis component technology effort, while coordinated with the main programs, aims at longer term issues, advanced technologies, and independent assessments. An overview of work on linear alternators, engine/alternator/load interactions and controls, heat exchangers, materials, life and reliability, and bearings is presented.

Thieme, Lanny G.↗

NASA NTRS1991

Computer-aided design of flight control systems

A computer program is presented for facilitating the development and assessment of flight control systems, and application to a control design is discussed. The program is a computer-aided control-system design program based on direct digital synthesis of a proportional-integral-filter controller with scheduled linear-quadratic-Gaussian gains and command generator tracking of pilot inputs. The FlightCAD system concentrates on aircraft dynamics, flight-control systems, stability and performance, and has practical engineering applications.

Stengel, Robert F.↗

NASA NTRS1991

Vibration suppression using a proofmass actuator operating in stroke/force saturation

The design of the control-loop structure for a feedback control system which contains a proofmass actuator for suppressing vibration is discussed. The loop structure is composed of inner control loops, which determine the frequency of the actuator and which are directly related to the actuator and the outer loops which add damping to the structure. When the frequency response of the actuator is matched to the stroke/force saturation curve, the actuator is most effective in the vibration suppression loops, and, since the stroke/force saturation curve is characterized by the stroke length, the mass of the proofmass, and the maximum current delivered by the motor electronics, the size of the actuator can be easily determined. The results of the loop-structure model calculations are verified by examining linear DC motors as proofmass actuators for the Mast in NASA's Control of Flexible Structures program.

Lindner, D. K.↗

NASA NTRS1991

Component technology for Stirling power converters

Thieme, Lanny G.↗

NASA NTRS1992

Active structural control for the mini-MAST and ACES structures

Two experiments based on the maximum entropy/optimal projection design approach are discussed which were conducted by Harris Corporation as part of the NASA Controls Structures Interaction Guest Investigator program. The design equations consist of four coupled matrix equations which specialize to the standard linear-quadratic Guassian Riccati equations, when the plant is known perfectly and a full order controller is desired. These experiments demonstrate successful control system design and implementation for flexible structures.

Collins, E. G., Jr.↗

NASA NTRS1993

Dust in the Small Magellanic Cloud

Observations of reddened stars in the Small Magellanic Cloud (SMC) indicate that the interstellar grains in that galaxy may show distinct optical properties from those in the Galaxy. In a careful study of three SMC objects, Prevot showed that the UV extinction law in the SMC is almost linear with inverse wavelength and the 2200A feature is generally absent. The first results of a program to determine the wavelength dependence of the interstellar optical polarization in the SMC indicate that highly polarized objects are scarce. Our study has uncovered, however, several objects with optical polarization greater than around 1 percent: AZV 126, AZV 211, AZV 221, AZV 398, and AZV 456. The latter two have already had their UV extinction law determined. Our aim was to obtain International Ultraviolet Explorer (IUE) data and determine the UV extinction law also for AZV 126, AZV 211, and AZV 221. AZV 456, which presents a 'galactic' extinction law, has a 'normal' value for its wavelength of maximum polarization, lmax, while AZV 398, which shows a 'typical' SMC extinction curve, shows a somewhat smaller value for such wavelength. AZV 126, AZV 211, and AZV 221 all present extreme small values of lmax but had not had its extinction curve in the W determined yet. We therefore aimed at ultimately determining the extinction law in the direction of these three objects. Such results, in combination with the optical polarization data, have an important bearing on constraining the composition and size distribution of the interstellar dust in the SMC. In the last report, the images gathered with IUE, their processing, and the extinction curves derived from them were described. Such extinction curves and the theoretical models developed to interpret the SMC extinction and polarization data are discussed. Details are presented in an enclosed preprint. The activities in our ongoing polarimetric program of determining the magnetic field structure of the SMC and the images collected at Cerro Tololo Interamerican Observatory during the period are also briefly described. Other activities are also described.

Magalhaes, A. M.↗

NASA NTRS1994

Development of long-life, low-noise linear bearings for atmospheric interferometry

This paper describes the development of dry-lubricated linear bearings for use on the Michelson interferometer for passive atmospheric sounding (MIPAS). Two candidate bearing systems were developed and tested. In the first, use was made of linear roller (needle) bearings equipped with a pulley-and-cable arrangement to prevent cage drift and to minimize roller slip. The second design was of a roller-guided bearing system in which guidance was provided by all bearings rolling along guide rods. The paper focuses on the development of these linear bearings systems and describes the approach taken in terms of bearing design, lubrication methods, screening programs, and thermal-vacuum testing. Development difficulties are highlighted and the solutions ultimately adopted are described.

Roberts, E. W.↗

NASA NTRS1993

A SIMULINK environment for flight dynamics and control analysis: Application to the DHC-2 Beaver. Part 1: Implementation of a model library in SIMULINK. Part 2: Nonlinear analysis of the Beaver autopilot

The design of advanced Automatic Aircraft Control Systems (AACS's) can be improved upon considerably if the designer can access all models and tools required for control system design and analysis through a graphical user-interface, from within one software environment. This MSc-thesis presents the first step in the development of such an environment, which is currently being done at the Section for Stability and Control of Delft University of Technology, Faculty of Aerospace Engineering. The environment is implemented within the commercially available software package MATLAB/SIMULINK. The report consists of two parts. Part I gives a detailed description of the AACS design environment. The heart of this environment is formed by the SIMULINK implementation of a nonlinear aircraft model in block-diagram format. The model has been worked out for the old laboratory aircraft of the Faculty, the De Havilland DHC-2 'Beaver', but due to its modular structure, it can easily be adapted for other aircraft. Part I also describes MATLAB programs which can be applied for finding steady-state trimmed-flight conditions and for linearization of the aircraft model, and it shows how the built-in simulation routines of SIMULINK have been used for open-loop analysis of the aircraft dynamics. Apart from the implementation of the models and tools, a thorough treatment of the theoretical backgrounds is presented. Part II of this report presents a part of an autopilot design process for the 'Beaver' aircraft, which clearly demonstrates the power and flexibility of the AACS design environment from part I. Evaluations of all longitudinal and lateral control laws by means of nonlinear simulations are treated in detail. The AACS design environment from part I proved to be a very useful tool for designing the control laws of the 'Beaver' autopilot within a very tight time-schedule. The autopilot design process itself will be used as a guideline for future AACS research at the Faculty of Aerospace Engineering. Flight tests of the 'Beaver' autopilot, done after evaluating the control laws in the SIMULINK package, proved to be quite successful. In the future, the AACS design package will evolve into a standardized, integrated design environment which can be applied to virtually any type of aircraft. The AACS design cycle will be shortened further by developing tools for automatically porting control laws from the MATLAB/SIMULINK environment to a piloted real-time flight simulator and the Flight Control Computers of the aircraft.

Flight Control System Design↗

NASA NTRS1996

An Assessment of IMPAC - Integrated Methodology for Propulsion and Airframe Controls

This report documents the work done under a NASA sponsored contract to transition to industry technologies developed under the NASA Lewis Research Center IMPAC (Integrated Methodology for Propulsion and Airframe Control) program. The critical steps in IMPAC are exercised on an example integrated flight/propulsion control design for linear airframe/engine models of a conceptual STOVL (Short Take-Off and Vertical Landing) aircraft, and MATRIXX (TM) executive files to implement each step are developed. The results from the example study are analyzed and lessons learned are listed along with recommendations that will improve the application of each design step. The end product of this research is a set of software requirements for developing a user-friendly control design tool which will automate the steps in the IMPAC methodology. Prototypes for a graphical user interface (GUI) are sketched to specify how the tool will interact with the user, and it is recommended to build the tool around existing computer aided control design software packages.

Walker, G. P.↗

NASA NTRS1996

Age Life Evaluation of Space Shuttle Crew Escape System Pyrotechnic Components Loaded with Hexanitrostilbene (HNS)

Determining deterioration characteristics of the Space Shuttle crew escape system pyrotechnic components loaded with hexanitrostilbene would enable us to establish a hardware life-limit for these items, so we could better plan our equipment use and, possibly, extend the useful life of the hardware. We subjected components to accelerated-age environments to determine degradation characteristics and established a hardware life-limit based upon observed and calculated trends. We extracted samples using manufacturing lots currently installed in the Space Shuttle crew escape system and from other NASA programs. Hardware included in the study consisted of various forms and ages of mild detonating fuse, linear shaped charge, and flexible confined detonating cord. The hardware types were segregated into 5 groups. One was subjected to detonation velocity testing for a baseline. Two were first subjected to prolonged 155 F heat exposure, and the other two were first subjected to 255 F, before undergoing detonation velocity testing and/or chromatography analysis. Test results showed no measurable changes in performance to allow a prediction of an end of life given the storage and elevated temperature environments the hardware experiences. Given the lack of a definitive performance trend, coupled with previous tests on post-flight Space Shuttle hardware showing no significant changes in chemical purity or detonation velocity, we recommend a safe increase in the useful life of the hardware to 20 years, from the current maximum limits of 10 and 15 years, depending on the hardware.

Hoffman, William C., III↗

NASA NTRS2002

Thermophysical ESEM Characterization of Carbon Fibers

Coefficients of thermal expansion (CTE) of carbon fibers create residual stresses in aggressive manufacturing and service environments. In this effort, environmental scanning electron microscope (ESEM) is used for in situ observations of a carbon fiber cross-section up to 1000 C in order to evaluate the much neglected transverse CTE. The perimeter of fiber cross-section is calculated with the Scion image processing program from images that were taken at every 100 C increments. CTE values are calculated by linear regression of the strain data based on the perimeter changes. Furthermore, through SEM, WDS and TEM observations, we are in the process of bringing an interactive rationale between CTE, crystallinity and surface roughness of carbon fibers.

Sue, Jiwoong↗

NASA NTRS1991

A nuclear fragmentation energy deposition model

A formalism for target fragment transport is presented with application to energy loss spectra in thin silicon devices. A nuclear data base is recommended that agrees well with the measurements of McNulty et al. using surface barrier detectors. High-energy events observed by McNulty et al., which are not predicted by intranuclear cascade models, are well represented by the present work.

NASA Discipline Number 04-10↗

NASA NTRS1998

XV-15 Tiltrotor Low Noise Terminal Area Operations

Acoustic data have been acquired for the XV-15 tiltrotor aircraft performing a variety of terminal area operating procedures. This joint NASA/Bell/Army test program was conducted in two phases. During Phase 1 the XV-15 was flown over a linear array of microphones, deployed perpendicular to the flight path, at a number of fixed operating conditions. This documented the relative noise differences between the various conditions. During Phase 2 the microphone array was deployed over a large area to directly measure the noise footprint produced during realistic approach and departure procedures. The XV-15 flew approach profiles that culminated in IGE hover over a landing pad, then takeoffs from the hover condition back out over the microphone array. Results from Phase 1 identify noise differences between selected operating conditions, while those from Phase 2 identify differences in noise footprints between takeoff and approach conditions and changes in noise footprint due to variation in approach procedures.

Conner, David A.↗

NASA NTRS1996

Effects of track structure and cell inactivation on the calculation of heavy ion mutation rates in mammalian cells

It has long been suggested that inactivation severely effects the probability of mutation by heavy ions in mammalian cells. Heavy ions have observed cross sections of inactivation that approach and sometimes exceed the geometric size of the cell nucleus in mammalian cells. In the track structure model of Katz the inactivation cross section is found by summing an inactivation probability over all impact parameters from the ion to the sensitive sites within the cell nucleus. The inactivation probability is evaluated using the dose-response of the system to gamma-rays and the radial dose of the ions and may be equal to unity at small impact parameters for some ions. We show how the effects of inactivation may be taken into account in the evaluation of the mutation cross sections from heavy ions in the track structure model through correlation of sites for gene mutation and cell inactivation. The model is fit to available data for HPRT mutations in Chinese hamster cells and good agreement is found. The resulting calculations qualitatively show that mutation cross sections for heavy ions display minima at velocities where inactivation cross sections display maxima. Also, calculations show the high probability of mutation by relativistic heavy ions due to the radial extension of ions track from delta-rays in agreement with the microlesion concept. The effects of inactivation on mutations rates make it very unlikely that a single parameter such as LET or Z*2/beta(2) can be used to specify radiation quality for heavy ion bombardment.

NASA Discipline Number 45-10↗

NASA NTRS2017

Automation of POST Cases via External Optimizer and "Artificial p2" Calculation

During early conceptual design of complex systems, speed and accuracy are often at odds with one another. While many characteristics of the design are fluctuating rapidly during this phase there is nonetheless a need to acquire accurate data from which to down-select designs as these decisions will have a large impact upon program life-cycle cost. Therefore enabling the conceptual designer to produce accurate data in a timely manner is tantamount to program viability. For conceptual design of launch vehicles, trajectory analysis and optimization is a large hurdle. Tools such as the industry standard Program to Optimize Simulated Trajectories (POST) have traditionally required an expert in the loop for setting up inputs, running the program, and analyzing the output. The solution space for trajectory analysis is in general non-linear and multi-modal requiring an experienced analyst to weed out sub-optimal designs in pursuit of the global optimum. While an experienced analyst presented with a vehicle similar to one which they have already worked on can likely produce optimal performance figures in a timely manner, as soon as the "experienced" or "similar" adjectives are invalid the process can become lengthy. In addition, an experienced analyst working on a similar vehicle may go into the analysis with preconceived ideas about what the vehicle's trajectory should look like which can result in sub-optimal performance being recorded. Thus, in any case but the ideal either time or accuracy can be sacrificed. In the authors' previous work a tool called multiPOST was created which captures the heuristics of a human analyst over the process of executing trajectory analysis with POST. However without the instincts of a human in the loop, this method relied upon Monte Carlo simulation to find successful trajectories. Overall the method has mixed results, and in the context of optimizing multiple vehicles it is inefficient in comparison to the method presented POST's internal optimizer functions like any other gradient-based optimizer. It has a specified variable to optimize whose value is represented as optval, a set of dependent constraints to meet with associated forms and tolerances whose value is represented as p2, and a set of independent variables known as the u-vector to modify in pursuit of optimality. Each of these quantities are calculated or manipulated at a certain phase within the trajectory. The optimizer is further constrained by the requirement that the input u-vector must result in a trajectory which proceeds through each of the prescribed events in the input file. For example, if the input u-vector causes the vehicle to crash before it can achieve the orbital parameters required for a parking orbit, then the run will fail without engaging the optimizer, and a p2 value of exactly zero is returned. This poses a problem, as this "non-connecting" region of the u-vector space is far larger than the "connecting" region which returns a non-zero value of p2 and can be worked on by the internal optimizer. Finding this connecting region and more specifically the global optimum within this region has traditionally required the use of an expert analyst.

Dees, Patrick D.↗

NASA NTRS1976

Phase modulating with odd and even finite power series of a modulating signal

Method and apparatus is presented for producing a phase-modulated waveform having a high degree of linearity between the modulating signal and the phase of the modulated carrier signal. Two signals representing finite odd and even power series transformations of the modulating signal are produced and multiplied with two quadrature components of the input carrier signal, respectively. One of the multiplied signals is subtracted from the other and the resulting signal is hard-limited to produce a phase-modulated output signal. The means for producing the two signals representing the odd and even power series of the modulating signal includes means for varying the coefficients of the two power series. By means of an existing computer program, the coefficients of the two power series are selected such that there is an extremely high degree of linearity between the modulating signal and the phase of the modulated carrier signal.

Hearn, C. P.↗

NASA NTRS1989

Parallel processors and nonlinear structural dynamics algorithms and software

A nonlinear structural dynamics finite element program was developed to run on a shared memory multiprocessor with pipeline processors. The program, WHAMS, was used as a framework for this work. The program employs explicit time integration and has the capability to handle both the nonlinear material behavior and large displacement response of 3-D structures. The elasto-plastic material model uses an isotropic strain hardening law which is input as a piecewise linear function. Geometric nonlinearities are handled by a corotational formulation in which a coordinate system is embedded at the integration point of each element. Currently, the program has an element library consisting of a beam element based on Euler-Bernoulli theory and trianglar and quadrilateral plate element based on Mindlin theory.

Belytschko, Ted↗

NASA NTRS1992

Intensive optical monitoring of the BL Lacertae object PKS 2155-304

Ground-based optical polarimetry and photometry of the BL Lac object PKS 2155-304 conducted just before and during the IUE monitoring program from November 1 to 19, 1991 are presented. The optical observations reveal strong daily variability in both flux and linear polarization. Broadband UBVRI photometry shows that the slope of the optical continuum remained relatively constant even though the object brightened by nearly a magnitude. PKS 2155-304 was near its historical photometric maximum during the last two weeks of November. The degree of polarization varied between 2 and 8 percent, and fluctuations of 2-3 percent were observed in a day. Daily variations in the position angle of the polarization were observed to be as high as 25 percent, though the position angle was observed to lie between 105 and 140 deg throughout the monitoring program. Some of the implications that these optical data have on models of the source of the continuum emission in PKS 2155-304 are discussed.

Smith, Paul S.↗