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At least 55 records · Page 3

Unification of color postprocessing techniques for 3-dimensional computational mechanics

To facilitate the understanding of complex three-dimensional numerical models, advanced interactive color postprocessing techniques are introduced. These techniques are sufficiently flexible so that postprocessing difficulties arising from model size, geometric complexity, response variation, and analysis type can be adequately overcome. Finite element, finite difference, and boundary element models may be evaluated with the prototype postprocessor. Elements may be removed from parent models to be studied as independent subobjects. Discontinuous responses may be contoured including responses which become singular, and nonlinear color scales may be input by the user for the enhancement of the contouring operation. Hit testing can be performed to extract precise geometric, response, mesh, or material information from the database. In addition, stress intensity factors may be contoured along the crack front of a fracture model. Stepwise analyses can be studied, and the user can recontour responses repeatedly, as if he were paging through the response sets. As a system, these tools allow effective interpretation of complex analysis results.

Bailey, Bruce Charles↗

Interactive color display of 3-D engineering analysis results

A general approach to three-dimensional postprocessing of engineering analyses is presented. The approach is versatile and may handle the results from a wide range of engineering analysis methods which involve the discretization of continua. To facilitate the understanding of complex three-dimensional numerical models, advanced interactive color postprocessing techniques are introduced. Finite element, finite difference, and boundary element models are evaluated with the prototype postprocessor. The existing color graphics program (POSTPRO3D) was ported to a high-resolution device. Interactive graphic tools were implemented to facilitate qualitative mesh evaluation from a single analysis. A postprocessing environment was design for workstation technology.

Abel, John F.↗

Continuous fiber ceramic matrix composites for heat engine components

High strength at elevated temperatures, low density, resistance to wear, and abundance of nonstrategic raw materials make structural ceramics attractive for advanced heat engine applications. Unfortunately, ceramics have a low fracture toughness and fail catastrophically because of overload, impact, and contact stresses. Ceramic matrix composites provide the means to achieve improved fracture toughness while retaining desirable characteristics, such as high strength and low density. Materials scientists and engineers are trying to develop the ideal fibers and matrices to achieve the optimum ceramic matrix composite properties. A need exists for the development of failure models for the design of ceramic matrix composite heat engine components. Phenomenological failure models are currently the most frequently used in industry, but they are deterministic and do not adequately describe ceramic matrix composite behavior. Semi-empirical models were proposed, which relate the failure of notched composite laminates to the stress a characteristic distance away from the notch. Shear lag models describe composite failure modes at the micromechanics level. The enhanced matrix cracking stress occurs at the same applied stress level predicted by the two models of steady state cracking. Finally, statistical models take into consideration the distribution in composite failure strength. The intent is to develop these models into computer algorithms for the failure analysis of ceramic matrix composites under monotonically increasing loads. The algorithms will be included in a postprocessor to general purpose finite element programs.

Tripp, David E.↗

Error analysis of finite element solutions for postbuckled plates

An error analysis of results from finite-element solutions of problems in shell structures is further developed, incorporating the results of an additional numerical analysis by which oscillatory behavior is eliminated. The theory is extended to plates with initial geometric imperfections, and this novel analysis is programmed as a postprocessor for a general-purpose finite-element code. Numerical results are given for the case of a stiffened panel in compression and a plate loaded in shear by a 'picture-frame' test fixture.

Sistla, Rajaram↗

Integration of rocket turbine design and analysis through computer graphics

An interactive approach with engineering computer graphics is used to integrate the design and analysis processes of a rocket engine turbine into a progressive and iterative design procedure. The processes are interconnected through pre- and postprocessors. The graphics are used to generate the blade profiles, their stacking, finite element generation, and analysis presentation through color graphics. Steps of the design process discussed include pitch-line design, axisymmetric hub-to-tip meridional design, and quasi-three-dimensional analysis. The viscous two- and three-dimensional analysis codes are executed after acceptable designs are achieved and estimates of initial losses are confirmed.

Hsu, Wayne↗

Simulating The Gamma-Ray Observatory Spacecraft

Gamma-Ray Observatory (GRO) spacecraft constitutes major advance in gamma-ray astronomy by offering first opportunity for comprehensive observations in range of 0.1 to 30,000 MeV. GRO Attitude Dynamics Simulator (GROSS) computer program designed to simulate mission. Consists of three separate programs: stand-alone profile program; simulator program, containing simulation control input/output (SCIO) subsystem, truth model (TM) subsystem, and on-board computer (OBC) subsystem; and postprocessor program. Written in FORTRAN 77.

Garrick, J.↗

Development and validation of an advanced low-order panel method

A low-order potential-flow panel code, PMARC, for modeling complex three-dimensional geometries, is currently being developed at NASA Ames Research Center. The PMARC code was derived from a code named VSAERO that was developed for Ames Research Center by Analytical Methods, Inc. In addition to modeling potential flow over three-dimensional geometries, the present version of PMARC includes several advanced features such as an internal flow model, a simple jet wake model, and a time-stepping wake model. Data management within the code was optimized by the use of adjustable size arrays for rapidly changing the size capability of the code, reorganization of the output file and adopting a new plot file format. Preliminary versions of a geometry preprocessor and a geometry/aerodynamic data postprocessor are also available for use with PMARC. Several test cases are discussed to highlight the capabilities of the internal flow model, the jet wake model, and the time-stepping wake model.

Ashby, Dale L.↗

Reanalysis, compatibility and correlation in analysis of modified antenna structures

A simple computational procedure is synthesized to process changes in the microwave-antenna pathlength-error measure when there are changes in the antenna structure model. The procedure employs structural modification reanalysis methods combined with new extensions of correlation analysis to provide the revised rms pathlength error. Mainframe finite-element-method processing of the structure model is required only for the initial unmodified structure, and elementary postprocessor computations develop and deal with the effects of the changes. Several illustrative computational examples are included. The procedure adapts readily to processing spectra of changes for parameter studies or sensitivity analyses.

Levy, R.↗

Processes responsible for the compositional structure of the thermosphere

The relative importances of the various physical and chemical mechanisms that force changes in neutral thermospheric composition for a given geophysical situation were quantified using a diagnostic postprocessor analysis package in conjunction with runs of the NCAR thermospheric general circulation model (TGCM) that was extended to include the terms of the neutral composition equation. New information was obtained on the causal mechanisms responsible for changes in the concentrations of the three neutral species, O2, O, and N2, whose time-dependent mass mixing ratios were calculated within the TGCM. Principal results calculated for F-region altitudes are described, and thermospheric compositions calculated using the NCAR-TGCM model are compared with the predictions of the empirical thermospheric model of Hedin (1987).

Burns, A. G.↗

Performance effects of tie-truss modifications for a 70-meter centerline beam waveguide antenna

The elevation-axis tie truss of the 70-m antennas would have to be modified to accommodate a centerline beam waveguide. To accomplish this, the center section of the tie truss has to be altered, causing a change in the tie-truss compliance and affecting structural performance. Even with the center section completely removed, the worst-case rms pathlength error due to gravity load is increased from 0.025 to only 0.030 inches. Using a simple postprocessor technique, the effects of modifying the compliance can be predicted without resorting to multiple and costly re-analyses of large finite-element models on a mainframe computer.

Cucchissi, J. J.↗

COMGEN: A computer program for generating finite element models of composite materials at the micro level

COMGEN (Composite Model Generator) is an interactive FORTRAN program which can be used to create a wide variety of finite element models of continuous fiber composite materials at the micro level. It quickly generates batch or session files to be submitted to the finite element pre- and postprocessor PATRAN based on a few simple user inputs such as fiber diameter and percent fiber volume fraction of the composite to be analyzed. In addition, various mesh densities, boundary conditions, and loads can be assigned easily to the models within COMGEN. PATRAN uses a session file to generate finite element models and their associated loads which can then be translated to virtually any finite element analysis code such as NASTRAN or MARC.

Melis, Matthew E.↗

Gamma Ray Observatory (GRO) dynamics simulator requirements and mathematical specifications, revision 1

The requirements and mathematical specifications for the Gamma Ray Observatory (GRO) Dynamics Simulator are presented. The complete simulator system, which consists of the profie subsystem, simulation control and input/output subsystem, truth model subsystem, onboard computer model subsystem, and postprocessor, is described. The simulator will be used to evaluate and test the attitude determination and control models to be used on board GRO under conditions that simulate the expected in-flight environment.

Harman, R.↗

Elevated temperature crack growth

A study was performed to examine the applicability of path-independent (P-I) integrals to crack growth problems in hot section components of gas turbine aircraft engines. Alloy 718 was used and the experimental parameters included combined temperature and strain cycling, thermal gradients, elastic-plastic strain levels, and mean strains. A literature review was conducted of proposed P-I integrals, and those capable of analyzing hot section component problems were selected and programmed into the postprocessor of a finite element code. Detailed elastic-plastic finite element analyses were conducted to simulate crack growth and crack closure of the test specimen, and to evaluate the P-I integrals. It was shown that the selected P-I integrals are very effective for predicting crack growth for isothermal conditions.

Kim, K. S.↗

Program Analyzes Errors In STAGS

EAC computer program designed for analysis of errors in results of STAGS computer program (COSMIC Program HQN-10967). Requires input data for geometry of plate, properties of material, and set of boundary conditions. These input data come from STAGS code. (The specific link between input and output data from STAGS and input data for EAC is POSTP, postprocessor program in STAGS processors.) EAC computes continuous solution from discrete results of STAGS in order to estimate error of results of STAGS. Written in FORTRAN 77.

Thurston, Gaylen A.↗

Finite element analysis of thermal distortion effects on optical performance of solar dynamic concentrator for Space Station Freedom

An analysis was performed to predict the thermal distortion of the solar dynamic concentrator for Space Station Freedom in low earth orbit and to evaluate the effects of that thermal distortion on concentrator on-orbit performance. The analysis required substructural finite element modeling of critical concentrator structural subsystems, structural finite element modeling of the concentrator, mapping of thermal loading onto the structural finite element model, and the creation of specialized postprocessors to assist in interpreting results. Concentrator temperature distributions and thermally induced displacements and slope errors and the resulting receiver flux distribution profiles are discussed. Results determined for a typical orbit indicate that concentrator facet rotations are less than 0.2 mrad and that the change in facet radius due to thermal flattening is less than 5 percent. The predicted power loss due to thermal distortion effects is less than 0.3 percent. As a consequence the thermal distortions of the solar dynamic concentrator in low earth orbit will have a negligible effect on the flux distribution profiles within the receiver.

Doherty, Michael P.↗

Validation of the space shuttle main engine steady state performance model

The primary objective was to present methods for validating predictions of Rocketdyne's most current version of the Space Shuttle Main Engine (SSME) Power Balance Model (PBM) with respect to physical relations governing flow systems. This required the development and implementation of postprocessors to check results of PBM computations for satisfaction of conservation relations. A cursory uncertainty analysis of PBM predictions with respect to mass and energy balances was performed. In addition, an effort to identify the empirical relations and physical assumptions within PBM which impact the ability of the model to attain rigorous balance was begun.

Santi, L. Michael↗

Overview of the fatigue/fracture/life working group program at the Lewis Research Center

Constitutive and life prediction models are developed and verified for materials typically used in hot gas path components of reusable space propulsion systems over the range of relevant operating environments. The efforts were centered on the development of crack initiation life prediction methods, while the efforts of a counterpart group were centered on the development of cyclic crack propagation life prediction methods. The complexion of the active tasks are presented. A significant new task started this year will incorporate the various material constitutive and life prediction models developed in this program into a comprehensive creep-fatigue damage analysis and life assessment computer code. The program will function as a postprocessor to general structural analysis programs (such as finite element or boundary element codes) using the output of such analyses (stress, strain, and temperature fields as functions of time) as the input to the damage analysis and life assessment code. The code will be designed to execute on engineering/scientific workstations and will feature a windowing, mouse-driven user interface. Current plans call for the code to be finished and made available for use in mid 1991.

Mcgaw, Michael A.↗

Optimum mirror shapes and supports for light weight mirrors subjected to self-weight

A parametric design study of light weight mirror shapes with various support conditions was performed utilizing the finite element program NASTRAN. Improvements in the mirror performance were made based on the following design criteria: (1) minimization of the optical surface wavefront variations, (2) minimization of the self-weight directly related to cost of manufacturing, and (3) optimal location of support points. A preprocessor to automatically generate a finite element model for each mirror geometry was developed in order to obtain the structural deformations systematically. Additionally, a postprocessor, which prepares an input data file for FRINGE (an optical computer code) was developed for generating the optical deflections that lead to the surface wavefront variations. Procedures and modeling techniques to achieve the optimum (the lightest and stiffest mirror shape due to self-weight) are addressed.

Cho, Myung K.↗