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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 505 records · Page 28

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NASA NTRS1989

Distortion and regulation characterization of a Mapham inverter

Output-voltage total harmonic distortion (THD) of a 20-kHz, 6-kVA Mapham resonant inverter is characterized as a function of its switching-to-resonant frequency ratio, f(s)/f(r), using the EASY5 Engineering Analysis System. EASY5 circuit simulation results are compared with hardware test results to verify the accuracy of the simulations. The effects of load on the THD versus f(s)/f(r) is investigated for resistive, leading, and lagging power factor load impedances. The effect of the series output capacitor on the Mapham inverter output-voltage distortion and inherent load regulation is characterized under loads of various power factors and magnitudes. An optimum series capacitor value which improves the inherent load regulation to better than 3 percent is identified. The optimum series capacitor value is different from the value predicted from a modeled frequency domain analysis. An explanation is proposed which takes into account the conduction overlap in the inductor pairs during steady-state inverter operation, which decreases the effective inductance of a Mapham inverter. A fault protection and current limit method is discussed which allows the Mapham inverter to operate into a short circuit, even when the inverter resonant circuit becomes overdamped.

Sundberg, Richard C.↗

NASA NTRS1990

Data base architecture for instrument characteristics critical to spacecraft conceptual design

Spacecraft designs are driven by the payloads and mission requirements that they support. Many of the payload characteristics, such as mass, power requirements, communication requirements, moving parts, and so forth directly affect the choices for the spacecraft structural configuration and its subsystem design and component selection. The conceptual design process, which translates mission requirements into early spacecraft concepts, must be tolerant of frequent changes in the payload complement and resource requirements. A computer data base was designed and implemented for the purposes of containing the payload characteristics pertinent for spacecraft conceptual design, tracking the evolution of these payloads over time, and enabling the integration of the payload data with engineering analysis programs for improving the efficiency in producing spacecraft designs. In-house tools were used for constructing the data base and for performing the actual integration with an existing program for optimizing payload mass locations on the spacecraft.

Rowell, Lawrence F.↗

NASA NTRS1990

In-flight crew training

The Helmet Mounted Display system and Part Task Trainer are two projects currently underway that are closely related to the in-flight crew training concept. The first project is a training simulator and an engineering analysis tool. The simulator's unique helmet mounted display actually projects the wearer into the simulated environment of 3-D space. Miniature monitors are mounted in front of the wearers eyes. Partial Task Trainer is a kinematic simulator for the Shuttle Remote Manipulator System. The simulator consists of a high end graphics workstation with a high resolution color screen and a number of input peripherals that create a functional equivalent of the RMS control panel in the back of the Orbiter. It is being used in the training cycle for Shuttle crew members. Activities are underway to expand the capability of the Helmet Display System and the Partial Task Trainer.

Gott, Charles↗

NASA NTRS1991

Overview of European and other non-US/USSR/Japan launch vehicle and propulsion technology programs

The following subject areas are covered: majority of propulsion technology development work is directly related to the ESA's Ariane 5 program and heavily involves SEP (Societe Europeenne de Propulsion) in all areas; Hermes; advanced work on magnetic bearings for turbomachinery; electric propulsion using Cs and Xe propellants done by SEP in France, MBB ERNO in West Germany, and by Culham Lab in UK; successfully tested fired H/O composite nozzle exit cone on 3rd stage of Ariane; turbine blades made of composites to allow increase in gas temperature and improvement in efficiency; combined cycle (turboramjet-rocket) engine analysis work done by Hyperspace; and ESA advanced program studies.

Rice, Eric E.↗

NASA NTRS1989

Tethered gravity laboratories study

Variable Gravity Laboratory studies are discussed. The following subject areas are covered: (1) conceptual design and engineering analysis; (2) control strategies (fast crawling maneuvers, main perturbations and their effect upon the acceleration level); and (3) technology requirements.

Lucchetti, F.↗

NASA NTRS1991

User manual for two simple postscript output FORTRAN plotting routines

Graphics is one of the important tools in engineering analysis and design. However, plotting routines that generate output on high quality laser printers normally come in graphics packages, which tend to be expensive and system dependent. These factors become important for small computer systems or desktop computers, especially when only some form of a simple plotting routine is sufficient. With the Postscript language becoming popular, there are more and more Postscript laser printers now available. Simple, versatile, low cost plotting routines that can generate output on high quality laser printers are needed and standard FORTRAN language plotting routines using output in Postscript language seems logical. The purpose here is to explain two simple FORTRAN plotting routines that generate output in Postscript language.

Nguyen, T. X.↗

NASA NTRS1990

Launching AI in NASA ground systems

This paper will discuss recent operational successes in implementing expert systems to support the complex functions of NASA mission control systems at the Goddard Space Flight Center, including fault detection and diagnosis for real time and engineering analysis functions in the Cosmic Background Explorer and Gamma Ray Observatory missions and automation of resource planning and scheduling functions for various missions. It will also discuss ongoing developments and prototypes that will lead to increasingly sophisticated applications of artificial intelligence. These include the use of neural networks to perform telemetry monitoring functions, the implementation of generic expert system shells that can be customized to telemetry handling functions specific to NASA control centers, the applications of AI in training and user support, the long-term potential of implementing systems based around distributed, cooperative problem solving, and the use of AI to control and assist system development activities.

Perkins, Dorothy C.↗

NASA NTRS1991

A time-dependent incompressible viscous BEM for moderate Reynolds numbers

The boundary element method is applied to transient viscous incompressible flow. The time-domain formulation allows a boundary-only solution for linear Stokes flow. For higher speed flows in which the nonlinear convective effects cannot be ignored, a volume integral must be retained. However, the introduction of reference velocities often limits the nonlinear region to the vicinity of obstacles or boundary surfaces. Additionally, the volume terms are rewritten to eliminate the need for the calculation of velocity gradients. A general purpose numerical implementation of this new formulation then produces a very attractive tool for engineering analysis. This implementation includes a Newton-Raphson algorithm, permitting accurate solutions up to the moderate Reynolds number range. Several numerical examples are provided to validate the present approach.

Dargush, G. F.↗

NASA NTRS1992

Structural dynamics and vibrations of damped, aircraft-type structures

Engineering preliminary design methods for approximating and predicting the effects of viscous or equivalent viscous-type damping treatments on the free and forced vibration of lightly damped aircraft-type structures are developed. Similar developments are presented for dynamic hysteresis viscoelastic-type damping treatments. It is shown by both engineering analysis and numerical illustrations that the intermodal coupling of the undamped modes arising from the introduction of damping may be neglected in applying these preliminary design methods, except when dissimilar modes of these lightly damped, complex aircraft-type structures have identical or nearly identical natural frequencies. In such cases, it is shown that a relatively simple, additional interaction calculation between pairs of modes exhibiting this 'modal response' phenomenon suffices in the prediction of interacting modal damping fractions. The accuracy of the methods is shown to be very good to excellent, depending on the normal natural frequency separation of the system modes, thereby permitting a relatively simple preliminary design approach. This approach is shown to be a natural precursor to elaborate finite element, digital computer design computations in evaluating the type, quantity, and location of damping treatment.

Young, Maurice I.↗

NASA NTRS1992

Practical quality control tools for curves and surfaces

Curves (geometry) and surfaces created by Computer Aided Geometric Design systems in the engineering environment must satisfy two basic quality criteria: the geometric shape must have the desired engineering properties; and the objects must be parameterized in a way which does not cause computational difficulty for geometric processing and engineering analysis. Interactive techniques are described which are in use at Boeing to evaluate the quality of aircraft geometry prior to Computational Fluid Dynamic analysis, including newly developed methods for examining surface parameterization and its effects.

Small, Scott G.↗

NASA NTRS1992

Generating the complete control environment interface for EASIE

The Environment for Application Software Integration and Execution (EASIE) was designed to meet the needs of conceptual design engineers that face the task of integrating the results of many stand alone engineering analysis programs. EASIE is a set of utility programs which supports rapid integration and execution of programs about a central relational database, and it provides users with two basic modes of executing operations: Application Derived Executive (ADE), a menu-driven execution mode which provides users with sufficient guidance to quickly review data, select menu action items, and execute application programs, and Complete Control Executive (CCE), which provides a full executive interface, allowing users in-depth control of the design process. Users can switch between these modes as needed. This project will consider the CCE mode interface. Two objectives of this project are to redesign the selecting menus by using a windowing system and to reorganize the selecting structures of the selecting menus. The project will be implemented in the C window system, OSF/Motif version.

Tsai, Chia-Lin↗

NASA NTRS1992

Communications support for lunar missions using the TDRS II system

For several years NASA has been performing systems engineering analysis for lunar exploration scenarios with studies focused mainly on lunar communications, data systems and operations. Two basic earth-region communications architectures have been seriously considered, ground terminal architectures such as the deep space network (DSN) and geosynchronous relay satellites such as the tracking and data relay satellite II (TDRS II). An overview of TDRS II is given and lunar coverage, data rate capability, impacts to ground based elements, availability and operational scenarios are discussed. Development of the system is scheduled to begin soon and TDRS II can provide substantial support to early lunar missions without modification. Coverage and data rates are adequate and FLO missions can be supported. With enhancement nearly continuous coverage can be provided. TDRS II is a viable architecture and low cost option and should be considered as an alternative to the currently baselined DSN for precursor and possibly FLO missions.

Todd, Jacqueline↗

NASA NTRS1992

An approach for increasing aeroelastic divergence dynamic pressure of wind-tunnel models

An approach for increasing the aeroelastic divergence dynamic pressure of wind-tunnel model support systems is presented. A study has been conducted to investigate the effect of increased flexibility of the forward portion of balances on the divergence pressure of wind-tunnel models. The study utilized prior divergence analyses completed for various models to be tested in NASA Langley Research Center's National Transonic Facility, the Engineering Analysis Language finite-element analysis code, and an in-house computer program which solves for divergence dynamic pressure utilizing a transfer-matrix method based on fourth-order Runge-Kutta integration. Analytical results for balance flexibility changes versus changes in divergence pressure were obtained and demonstrate that a significant increase in divergence pressure can be obtained from the increased flexibility of the balance's forward portion for many models and their support systems.

Edwards, R. W.↗

NASA NTRS1993

PATSTAGS: PATRAN-To-STAGSC-1 Translator

PATSTAGS computer program translates data from PATRAN finite-element mathematical model into STAGS input records used for engineering analysis. Reads data from PATRAN neutral file and writes STAGS input records into STAGS input file and UPRESS data file. Supports translations of nodal constraints, and of nodal, element, force, and pressure data. Written in FORTRAN 77.

Otte, Neil↗

NASA NTRS1993

Modeling Thermodynamics Of Charring Of A Polymer

Improved method of predicting and of nondestructively analyzing pyrolytic effects in, and thermomechanical properties of, polymers combines theories and techniques from several engineering and scientific disciplines. Evolved in effort to understand charring and erosion of carbon phenolic ablative material in nozzle of rocket engine. Also applicable to other polymers and particularly to nondestructive engineering analysis of specimens heated, charred, or burned.

Funaro, Gregory V.↗

NASA NTRS1992

CFD modeling of turbulent flows around the SSME main injector assembly using porosity formulation

Hot gas turbulent flow distribution around the main injector assembly of the Space Shuttle Main Engine (SSME) and LOX flow distribution through the LOX posts have a great effect on the combustion phenomena inside the main combustion chamber. In order to design a CFD model to be an effective engineering analysis tool with good computational turn-around time (especially for 3-D flow problems) and still maintain good accuracy in describing the flow features, the concept of porosity was employed to describe the effects of blockage and drag force due to the presence of the LOX posts in the turbulent flow field around the main injector assembly of the SSME. Two-dimensional numerical studies were conducted to identify the drag coefficients of the flows, both through tube banks and round the shielded posts, over a wide range of Reynolds numbers. Empirical, analytical expressions of the drag coefficients as a function of local flow Reynolds number were then deduced. The porosity model was applied to the turbulent flow around the main injector assembly of the SSME, and analyses were performed. The 3-D CFD analysis was divided into three parts: LOX dome, hot gas injector assembly, and hydrogen cavity. The numerical results indicate that the mixture ratio at the downstream of injector face was close to stoichiometric around baffle elements.

Cheng, Gary C.↗

NASA NTRS1992

Reliability evaluation methodology for NASA applications

Liquid rocket engine technology has been characterized by the development of complex systems containing large number of subsystems, components, and parts. The trend to even larger and more complex system is continuing. The liquid rocket engineers have been focusing mainly on performance driven designs to increase payload delivery of a launch vehicle for a given mission. In otherwords, although the failure of a single inexpensive part or component may cause the failure of the system, reliability in general has not been considered as one of the system parameters like cost or performance. Up till now, quantification of reliability has not been a consideration during system design and development in the liquid rocket industry. Engineers and managers have long been aware of the fact that the reliability of the system increases during development, but no serious attempts have been made to quantify reliability. As a result, a method to quantify reliability during design and development is needed. This includes application of probabilistic models which utilize both engineering analysis and test data. Classical methods require the use of operating data for reliability demonstration. In contrast, the method described in this paper is based on similarity, analysis, and testing combined with Bayesian statistical analysis.

Taneja, Vidya S.↗

NASA NTRS1991

Design and fabrication of an autonomous rendezvous and docking sensor using off-the-shelf hardware

NASA Marshall Space Flight Center (MSFC) has developed and tested an engineering model of an automated rendezvous and docking sensor system composed of a video camera ringed with laser diodes at two wavelengths and a standard remote manipulator system target that has been modified with retro-reflective tape and 830 and 780 mm optical filters. TRW has provided additional engineering analysis, design, and manufacturing support, resulting in a robust, low cost, automated rendezvous and docking sensor design. We have addressed the issue of space qualification using off-the-shelf hardware components. We have also addressed the performance problems of increased signal to noise ratio, increased range, increased frame rate, graceful degradation through component redundancy, and improved range calibration. Next year, we will build a breadboard of this sensor. The phenomenology of the background scene of a target vehicle as viewed against earth and space backgrounds under various lighting conditions will be simulated using the TRW Dynamic Scene Generator Facility (DSGF). Solar illumination angles of the target vehicle and candidate docking target ranging from eclipse to full sun will be explored. The sensor will be transportable for testing at the MSFC Flight Robotics Laboratory (EB24) using the Dynamic Overhead Telerobotic Simulator (DOTS).

Grimm, Gary E.↗