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At least 469 records · Page 26

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NASA NTRS1992

Rocket engine diagnostics using qualitative modeling techniques

Researchers at NASA Lewis Research Center are presently developing qualitative modeling techniques for automated rocket engine diagnostics. A qualitative model of a turbopump interpropellant seal system was created. The qualitative model describes the effects of seal failures on the system steady state behavior. This model is able to diagnose the failure of particular seals in the system based on anomalous temperature and pressure values. The anomalous values input to the qualitative model are generated using numerical simulations. Diagnostic test cases include both single and multiple seal failures.

Binder, Michael↗

NASA NTRS1992

Analysis and modification of a single-mesh gear fatigue rig for use in diagnostic studies

A single-mesh gear fatigue rig was analyzed and modified for use in gear mesh diagnostic research. The fatigue rig allowed unwanted vibration to mask the test-gear vibration signal, making it difficult to perform diagnostic studies. Several possible sources and factors contributing to the unwanted components of the vibration signal were investigated. Sensor mounting location was found to have a major effect on the content of the vibration signal. In the presence of unwanted vibration sources, modal amplification made unwanted components strong. A sensor location was found that provided a flatter frequency response. This resulted in a more useful vibration signal. A major network was performed on the fatigue rig to reduce the influence of the most probable sources of the noise in the vibration signal. The slave gears were machined to reduce weight and increase tooth loading. The housing and the shafts were modified to reduce imbalance, looseness, and misalignment in the rotating components. These changes resulted in an improved vibration signal, with the test-gear mesh frequency now the dominant component in the signal. Also, with the unwanted sources eliminated, the sensor mounting location giving the most robust representation of the test-gear meshing energy was found to be at a point close to the test gears in the load zone of the bearings.

Zakrajsek, James J.↗

NASA NTRS1991

Diagnostic evaluation of numerical model simulations using the tendency equation

A procedure is proposed to expand the diagnostic capabilities of the pressure tendency equation of a primitive equation NWP model by computing the pressure tendency in physical coordinates. The advantages of isolating the density advection as a diagnostic tool to understand pressure changes is shown. By simple thermodynamic arguments it is demonstrated that in areas of synoptic-scale cyclonic development, the vertically integrated density advection is more than sufficient to explain the depletion of mass over a growing depression. Consequently, the joint contribution of the net divergence and vertical motion opposes the pressure fall. This is illustrated for a case of rapid cyclogenesis in southern South America.

Jusem, Juan C.↗

NASA NTRS1990

Global analyses of water vapor, cloud and precipitation derived from a diagnostic assimilation of SSM/I geophysical retrievals

An analytical approach is described for diagnostically assimilating moisture data from Special Sensor Microwave Imager (SSM/I) into a global analysis of water vapor, cloud content, and precipitation. In this method, 3D fields of wind and temperature values taken from ECMWF gridded analysis are used to drive moisture conservation equations with parameterized microphysical treatment of vapor, liquid, and ice; the evolving field of water vapor is periodically updated or constrained by SSM/I retrievals of precipitable water. Initial results indicate that this diagnostic model can produce realistic large-scale fields of cloud and precipitation. The resulting water vapor analyses agree well with SSM/I and have an additional advantage of being synoptic.

Robertson, Franklin R.↗

NASA NTRS1992

Rocket engine diagnostics using qualitative modeling techniques

Researchers at NASA Lewis Research Center are presently developing qualitative modeling techniques for automated rocket engine diagnostics. A qualitative model of a turbopump interpropellant seal system has been created. The qualitative model describes the effects of seal failures on the system steady-state behavior. This model is able to diagnose the failure of particular seals in the system based on anomalous temperature and pressure values. The anomalous values input to the qualitative model are generated using numerical simulations. Diagnostic test cases include both single and multiple seal failures.

Binder, Michael↗

NASA NTRS1991

Model-based diagnostics for Space Station Freedom

An innovative approach to fault management was recently demonstrated for the NASA LeRC Space Station Freedom (SSF) power system testbed. This project capitalized on research in model-based reasoning, which uses knowledge of a system's behavior to monitor its health. The fault management system (FMS) can isolate failures online, or in a post analysis mode, and requires no knowledge of failure symptoms to perform its diagnostics. An in-house tool called MARPLE was used to develop and run the FMS. MARPLE's capabilities are similar to those available from commercial expert system shells, although MARPLE is designed to build model-based as opposed to rule-based systems. These capabilities include functions for capturing behavioral knowledge, a reasoning engine that implements a model-based technique known as constraint suspension, and a tool for quickly generating new user interfaces. The prototype produced by applying MARPLE to SSF not only demonstrated that model-based reasoning is a valuable diagnostic approach, but it also suggested several new applications of MARPLE, including an integration and testing aid, and a complement to state estimation.

Fesq, Lorraine M.↗

NASA NTRS1992

Scaling and applied field studies of MPD thrusters with laser diagnostics

The topics are presented in viewgraph form and include the following: self-field magnetoplasmadynamics; 1/4-scale applied-field MPD; scaling of arcs and MPD-arcs; magnetic nozzle studies; advanced diagnostic techniques needed for obtaining particle velocity, temperature, and current distributions in plasma thrusters; nonintrusive laser diagnostics for arcs and MPD-arcs; and schematic of multi-beam interferometer for electron density profile determination.

York, Thomas M.↗

NASA NTRS1993

Capabilities and constraints of combustion diagnostics in microgravity

A significant scientific return from both existing and proposed microgravity combustion science experiments is substantially dependent on the availability of diagnostic systems for the collection of the required scientific data. To date, the available diagnostic instrumentation has consisted primarily of conventional photographic media and intrusive temperature and velocity probes, such as thermocouples and hot wire anemometers. This situation has arisen primarily due to the unique and severe operational constraints inherent in reduced gravity experimentation. Each of the various reduced gravity facilities is accompanied by its own peculiar envelope of capabilities and constraints. Drop towers, for example, pose strict limitations on available working volume and power, as well as autonomy of operation. In contrast, hardware developed for space flight applications can be somewhat less constrained in regards to the aforementioned quantities, but is additionally concerned with numerous issues involving safety and reliability.

Greenberg, Paul S.↗

NASA NTRS1992

The Photovoltaic Array Space Power plus Diagnostics (PASP Plus) Flight Experiment

An overview of the Photovoltaic Array Space Power Plus Diagnostics (PASP Plus) flight experiment is presented in outline and graphic form. The goal of the experiment is to test a variety of photovoltaic cell and array technologies under various space environmental conditions. Experiment objectives, flight hardware, experiment control and diagnostic instrumentation, and illuminated thermal vacuum testing are addressed.

Piszczor, Michael F.↗

NASA NTRS1992

Resonance scattering of Fe XVII - A density diagnostic

Resonance scattering of the 15.01 A Fe XVII line, found to be important by Rugge & McKenzie, provides a new density diagnostic for solar active regions that is not subject to the lower density limit of the competing diagnostic. For a 'typical' active region, over 50 percent of the photons for this resonance line could be scattered out of the line of sight. The effect is much stronger for this line than for any other line in the soft X-ray part of the spectrum used routinely to determine active region electron temperatures, emission measures, or densities. Once understood and accounted for in the analysis, the resonance scattering of the 15.01 A Fe XVII line leads to a direct measurement of the density of the active region plasma. In the four active regions studied here, the derived densities range is 1-4 x 10 exp 9/cu cm.

Schmelz, J. T.↗

NASA NTRS1991

An SSME High Pressure Oxidizer Turbopump diagnostic system using G2 real-time expert system

An expert system which diagnoses various seal leakage faults in the High Pressure Oxidizer Turbopump of the SSME was developed using G2 real-time expert system. Three major functions of the software were implemented: model-based data generation, real-time expert system reasoning, and real-time input/output communication. This system is proposed as one module of a complete diagnostic system for the SSME. Diagnosis of a fault is defined as the determination of its type, severity, and likelihood. Since fault diagnosis is often accomplished through the use of heuristic human knowledge, an expert system based approach has been adopted as a paradigm to develop this diagnostic system. To implement this approach, a software shell which can be easily programmed to emulate the human decision process, the G2 Real-Time Expert System, was selected. Lessons learned from this implementation are discussed.

Guo, Ten-Huei↗

NASA NTRS1993

Polarimetry of the HI Lyman-alpha for coronal magnetic field diagnostics

We discuss and analyze the possible sources of observational and instrumental uncertainty that can be encountered in measuring magnetic fields of the solar corona through polarimetric observations of the Hanle effect of the coronal Ly-alpha line. The Hanle effect is the modification of the linear polarization of a resonantly scattered line, due to the presence of a magnetic field. Simulated observations are used to examine how polarimetric measurements of this effect are affected by the line-of-sight integration, the electron collisions, and the Ly-alpha geocorona. We plan to implement the coronal magnetic field diagnostics via the Ly-alpha Hanle effect using an all-reflecting Ly-alpha coronagraph/polarimeter (Ly-alphaCoPo) which employs reflecting multilayer mirrors, polarizers, and filters. We discuss here the requirements for such an instrument, and analyze the sources of instrumental uncertainty for polarimetric observations of the coronal Ly-alpha Hanle effect. We conclude that the anticipated polarization signal from the corona and the expected performance of the Ly-alphaCoPo instrument are such that the Ly-alpha Hanle effect method for coronal field diagnostics is feasible.

Fineschi, Silvano↗

NASA NTRS1992

Physical processes and diagnostics of gamma-ray burst emission

With improved data from BATSE and other instruments, it is important to develop a range of diagnostic tools to link gamma-ray burst observations with theory. I will review some of the physical processes which may take place to form the spectrum of gamma-ray burst sources, assuming that the bursts originate on strongly magnetized neutron stars. The important diagnostics that these processes provide to probe the emission region and how they might be used to interpret observed spectra will also be discussed.

Harding, Alice K.↗

NASA NTRS1993

Specialized data analysis for the Space Shuttle Main Engine and diagnostic evaluation of advanced propulsion system components

The Marshall Space Flight Center is responsible for the development and management of advanced launch vehicle propulsion systems, including the Space Shuttle Main Engine (SSME), which is presently operational, and the Space Transportation Main Engine (STME) under development. The SSME's provide high performance within stringent constraints on size, weight, and reliability. Based on operational experience, continuous design improvement is in progress to enhance system durability and reliability. Specialized data analysis and interpretation is required in support of SSME and advanced propulsion system diagnostic evaluations. Comprehensive evaluation of the dynamic measurements obtained from test and flight operations is necessary to provide timely assessment of the vibrational characteristics indicating the operational status of turbomachinery and other critical engine components. Efficient performance of this effort is critical due to the significant impact of dynamic evaluation results on ground test and launch schedules, and requires direct familiarity with SSME and derivative systems, test data acquisition, and diagnostic software. Detailed analysis and evaluation of dynamic measurements obtained during SSME and advanced system ground test and flight operations was performed including analytical/statistical assessment of component dynamic behavior, and the development and implementation of analytical/statistical models to efficiently define nominal component dynamic characteristics, detect anomalous behavior, and assess machinery operational condition. In addition, the SSME and J-2 data will be applied to develop vibroacoustic environments for advanced propulsion system components, as required. This study will provide timely assessment of engine component operational status, identify probable causes of malfunction, and indicate feasible engineering solutions. This contract will be performed through accomplishment of negotiated task orders.

Source record↗

NASA NTRS1993

Expert diagnostics system as a part of analysis software for power mission operations

The operation of interplanetary spacecraft at JPL has become an increasingly complex activity. This complexity is due to advanced spacecraft designs and ambitious mission objectives which lead to operations requirements that are more demanding than those of any previous mission. For this reason, several productivity enhancement measures are underway at JPL within mission operations, particularly in the spacecraft analysis area. These measures aimed at spacecraft analysis include: the development of a multi-mission, multi-subsystem operations environment; the introduction of automated tools into this environment; and the development of an expert diagnostics system. This paper discusses an effort to integrate the above mentioned productivity enhancement measures. A prototype was developed that integrates an expert diagnostics system into a multi-mission, multi-subsystem operations environment using the Galileo Power / Pyro Subsystem as a testbed. This prototype will be discussed in addition to background information associated with it.

Harris, Jennifer A.↗

NASA NTRS1994

The resonance lines of MG2 as diagnostics of the upper solar chromosphere

The resonance lines of singly ionized magnesium, the MgII h&k lines at about 280 nm, are two of the small number of lines in the solar spectrum that are optically thick in the chromospheric part of the solar atmosphere. Potentially these lines contain information on the initial temperature rise that occurs at the top of the photosphere. Unfortunately, few good observations of the lines exist due to their wavelength near 280 nm the ultraviolet. However, a fair number of observations (on the order of 200) are available from the data base of the UltraViolet Polarimeter and Spectrometer (UVSP) instrument that flew on board of NASA's Solar Maximum Mission (SMM) satellite. In addition, this data base contains a number of spectra that include the Mg I resonance line at (lambda)285.2nm, just longward of the h&k lines. The neutral magnesium line is not as strong as its ionic counterparts and samples slightly lower parts of the atmosphere. Its width is a sensitive diagnostic of the ionization balance between neutral and singly ionized magnesium, which determines the opacity scale (and formation height) of other diagnostically important MgI lines like the 457.1 nm intercombination line, the magnesium b lines and the infrared MgI emission lines near 12 microns. Analysis of the observed line profiles shows that it is necessary to include the effects of partial frequency redistribution (PRD) in the formation of the line as in the case of the h&k lines. This implies that the core of the line is very sensitive to the way scattering is treated in the modeling of the line, and in turn this allows us to separate the uncertain effects in the atomic data (viz. the Van der Waals broadening) from the uncertainties in the underlying atmospheric model. The main objective of this research was to compare observed spectra of the magnesium resonance lines against theoretical line profiles calculated from recent models of the solar atmosphere by Fontenla et al., hereafter called FAL. These models extend earlier solar models by Avrett et al. and provide yet a better match between observed and calculated spectra, in particular of the hydrogen Lyman line, by including the effects of ambipolar diffusion of hydrogen and helium in the mass and energy transport equations for the chromosphere-corona transition region. Although the transition region models can be built self-consistently (without additional observational input) once the proper boundary conditions are given at the top of the chromosphere, there are uncertainties in the models precisely because these boundary conditions are not well known. With the analysis of UVSP magnesium observations we strive to constrain these uncertainties.

Avrett, Eugene H.↗

NASA NTRS1994

An enhancement to the NA4 gear vibration diagnostic parameter

A new vibration diagnostic parameter for health monitoring of gears, NA4*, is proposed and tested. A recently developed gear vibration diagnostic parameter NA4 outperformed other fault detection methods at indicating the start and initial progression of damage. However, in some cases, as the damage progressed, the sensitivity of the NA4 and FM4 parameters tended to decrease and no longer indicated damage. A new parameter, NA4* was developed by enhancing NA4 to improve the trending of the parameter. This allows for the indication of damage both at initiation and also as the damage progresses. The NA4* parameter was verified and compared to the NA4 and FM4 parameters using experimental data from single mesh spur and spiral bevel gear fatigue rigs. The primary failure mode for the test cases was naturally occurring tooth surface pitting. The NA4* parameter is shown to be a more robust indicator of damage.

Decker, Harry J.↗

NASA NTRS1994

A Review of Transmission Diagnostics Research at NASA Lewis Research Center

This paper presents a summary of the transmission diagnostics research work conducted at NASA Lewis Research Center over the last four years. In 1990, the Transmission Health and Usage Monitoring Research Team at NASA Lewis conducted a survey to determine the critical needs of the diagnostics community. Survey results indicated that experimental verification of gear and bearing fault detection methods, improved fault detection in planetary systems, and damage magnitude assessment and prognostics research were all critical to a highly reliable health and usage monitoring system. In response to this, a variety of transmission fault detection methods were applied to experimentally obtained fatigue data. Failure modes of the fatigue data include a variety of gear pitting failures, tooth wear, tooth fracture, and bearing spalling failures. Overall results indicate that, of the gear fault detection techniques, no one method can successfully detect all possible failure modes. The more successful methods need to be integrated into a single more reliable detection technique. A recently developed method, NA4, in addition to being one of the more successful gear fault detection methods, was also found to exhibit damage magnitude estimation capabilities.

Zakajsek, James J.↗