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At least 1,045 records · Page 58

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NASA NTRS1988

The effects of finite rate chemical processes on high enthalpy nozzle performance - A comparison between SPARK and SEAGULL

The generalized chemistry version of the computer code SPARK is extended to include two higher-order numerical schemes, yielding fourth-order spatial accuracy for the inviscid terms. The new and old formulations are used to study the influences of finite rate chemical processes on nozzle performance. A determination is made of the computationally optimum reaction scheme for use in high-enthalpy nozzles. Finite rate calculations are compared with the frozen and equilibrium limits to assess the validity of each formulation. In addition, the finite rate SPARK results are compared with the constant ratio of specific heats (gamma) SEAGULL code, to determine its accuracy in variable gamma flow situations. Finally, the higher-order SPARK code is used to calculate nozzle flows having species stratification. Flame quenching occurs at low nozzle pressures, while for high pressures, significant burning continues in the nozzle.

Carpenter, M. H.↗

NASA NTRS2009

Computing Challenges in Coded Mask Imaging

This slide presaentation reviews the complications and challenges in developing computer systems for Coded Mask Imaging telescopes. The coded mask technique is used when there is no other way to create the telescope, (i.e., when there are wide fields of view, high energies for focusing or low energies for the Compton/Tracker Techniques and very good angular resolution.) The coded mask telescope is described, and the mask is reviewed. The coded Masks for the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) instruments are shown, and a chart showing the types of position sensitive detectors used for the coded mask telescopes is also reviewed. Slides describe the mechanism of recovering an image from the masked pattern. The correlation with the mask pattern is described. The Matrix approach is reviewed, and other approaches to image reconstruction are described. Included in the presentation is a review of the Energetic X-ray Imaging Survey Telescope (EXIST) / High Energy Telescope (HET), with information about the mission, the operation of the telescope, comparison of the EXIST/HET with the SWIFT/BAT and details of the design of the EXIST/HET.

Skinner, Gerald↗

NASA NTRS1979

Calculation of transonic aileron buzz

An implicit finite-difference computer code that uses a two-layer algebraic eddy viscosity model and exact geometric specification of the airfoil has been used to simulate transonic aileron buzz. The calculated results, which were performed on both the Illiac IV parallel computer processor and the Control Data 7600 computer, are in essential agreement with the original expository wind-tunnel data taken in the Ames 16-Foot Wind Tunnel just after World War II. These results and a description of the pertinent numerical techniques are included.

Steger, J. L.↗

NASA NTRS1987

A simplified computer solution for the flexibility matrix of contacting teeth for spiral bevel gears

A computer code, FLEXM, was developed to calculate the flexibility matrices of contacting teeth for spiral bevel gears using a simplified analysis based on the elementary beam theory for the deformation of gear and shaft. The simplified theory requires a computer time at least one order of magnitude less than that needed for the complete finite element method analysis reported earlier by H. Chao, and it is much easier to apply for different gear and shaft geometries. Results were obtained for a set of spiral bevel gears. The teeth deflections due to torsion, bending moment, shearing strain and axial force were found to be in the order 10(-5), 10(-6), 10(-7), and 10(-8) respectively. Thus, the torsional deformation was the most predominant factor. In the analysis of dynamic load, response frequencies were found to be larger when the mass or moment of inertia was smaller or the stiffness was larger. The change in damping coefficient had little influence on the resonance frequency, but has a marked influence on the dynamic load at the resonant frequencies.

Hsu, C. Y.↗

NASA NTRS1990

Simulation Of Three-Dimensional Supersonic Flows

Complicated flows computed with fair accuracy. Report describes simulations of steady, three-dimensional, viscous, supersonic flows by NASA Ames Parabolized Navier-Stokes computer code. Based on assumption flow supersonic in streamwise direction and subsonic flow in viscous sublayer always positive in streamwise direction. Predicts flows in regions of canopies, wings, and canards in addition to simple symmetric configurations used to demonstrate computational techniques. Also simulates interactions between aerodynamic surfaces.

Chaussee, Denny S.↗

NASA NTRS1997

Improving Discrete-Sensitivity-Based Approach for Practical Design Optimization

In developing the automated methodologies for simulation-based optimal shape designs, their accuracy, efficiency and practicality are the defining factors to their success. To that end, four recent improvements to the building blocks of such a methodology, intended for more practical design optimization, have been reported. First, in addition to a polynomial-based parameterization, a partial differential equation (PDE) based parameterization was shown to be a practical tool for a number of reasons. Second, an alternative has been incorporated to one of the tedious phases of developing such a methodology, namely, the automatic differentiation of the computer code for the flow analysis in order to generate the sensitivities. Third, by extending the methodology for the thin-layer Navier-Stokes (TLNS) based flow simulations, the more accurate flow physics was made available. However, the computer storage requirement for a shape optimization of a practical configuration with the -fidelity simulations (TLNS and dense-grid based simulations), required substantial computational resources. Therefore, the final improvement reported herein responded to this point by including the alternating-direct-implicit (ADI) based system solver as an alternative to the preconditioned biconjugate (PbCG) and other direct solvers.

Baysal, Oktay↗

NASA NTRS1978

NASA charging analyzer program: A computer tool that can evaluate electrostatic contamination

A computer code, the NASA Charging Analyzer Program (NASCAP), was developed to study the surface charging of bodies subjected to geomagnetic substorm conditions. This program will treat the material properties of a surface in a self-consistent manner and calculate the electric fields in space due to the surface charge. Trajectories of charged particles in this electric field can be computed to determine if these particles enhance surface contamination. A preliminary model of the Spacecraft Charging At The High Altitudes (SCATHA) satellite was developed in the NASCAP code and subjected to a geomagnetic substorm environment to investigate the possibility of electrostatic contamination. The results indicate that differential voltages will exist between the spacecraft ground surfaces and the insulator surfaces. The electric fields from this differential charging can enhance the contamination of spacecraft surfaces.

Stevens, N. J.↗

NASA NTRS2005

Introduction of the ASP3D Computer Program for Unsteady Aerodynamic and Aeroelastic Analyses

A new computer program has been developed called ASP3D (Advanced Small Perturbation 3D), which solves the small perturbation potential flow equation in an advanced form including mass-consistent surface and trailing wake boundary conditions, and entropy, vorticity, and viscous effects. The purpose of the program is for unsteady aerodynamic and aeroelastic analyses, especially in the nonlinear transonic flight regime. The program exploits the simplicity of stationary Cartesian meshes with the movement or deformation of the configuration under consideration incorporated into the solution algorithm through a planar surface boundary condition. The new ASP3D code is the result of a decade of developmental work on improvements to the small perturbation formulation, performed while the author was employed as a Senior Research Scientist in the Configuration Aerodynamics Branch at the NASA Langley Research Center. The ASP3D code is a significant improvement to the state-of-the-art for transonic aeroelastic analyses over the CAP-TSD code (Computational Aeroelasticity Program Transonic Small Disturbance), which was developed principally by the author in the mid-1980s. The author is in a unique position as the developer of both computer programs to compare, contrast, and ultimately make conclusions regarding the underlying formulations and utility of each code. The paper describes the salient features of the ASP3D code including the rationale for improvements in comparison with CAP-TSD. Numerous results are presented to demonstrate the ASP3D capability. The general conclusion is that the new ASP3D capability is superior to the older CAP-TSD code because of the myriad improvements developed and incorporated.

Batina, John T.↗

NASA NTRS1982

An experience in mesh generation for three-dimensional calculation of potential flow around a rotating propeller

An attempt is made to develop a three-dimensional, finite volume computational code for highly swept, twisted, small aspect ratio propeller blades with supersonic tip speeds, in a way that accounts for cascade effects, hub-induced flow, and nonlinear transonic effects. Attention is presently given to the generation of a computational mesh for such a complex propeller configuration, with the aim of sharing developmental process experience. The problem treated is unique, in that blade chord, blade length, hub length and blade-to-blade distance represent several characteristic length scales among which there is considerable disparity. An ad hoc mesh-generation scheme is accordingly developed.

Jou, W.-H.↗

NASA NTRS1990

PARC Navier-Stokes code upgrade and validation for high speed aeroheating predictions

Applications of the PARC full Navier-Stokes code for hypersonic flowfield and aeroheating predictions around blunt bodies such as the Aeroassist Flight Experiment (AFE) and Aeroassisted Orbital Transfer Vehicle (AOTV) are evaluated. Two-dimensional/axisymmetric and three-dimensional perfect gas versions of the code were upgraded and tested against benchmark wind tunnel cases of hemisphere-cylinder, three-dimensional AFE forebody, and axisymmetric AFE and AOTV aerobrake/wake flowfields. PARC calculations are in good agreement with experimental data and results of similar computer codes. Difficulties encountered in flowfield and heat transfer predictions due to effects of grid density, boundary conditions such as singular stagnation line axis and artificial dissipation terms are presented together with subsequent improvements made to the code. The experience gained with the perfect gas code is being currently utilized in applications of an equilibrium air real gas PARC version developed at REMTECH.

Liver, Peter A.↗

NASA NTRS1991

Rotorcraft airframe structural optimization for combined vibration and fatigue constraints

This paper addresses the application of a formal optimization technique in rotorcraft airframe structural design studies to reduce the structural weight, to lower airframe vibrations, and to enhance fatigue life of the structure. Vibration and fatigue considerations in airframe design are described. An optimization methodology based on the use of a nonlinear programming technique to size airframe structural members subjected to constraints on weight, vibration response and fatigue stresses under dynamic loads, are described. The paper focuses on the development of necessary computational tools for airframe structural optimization and describes the sensitivity analysis procedure for these types of design constraints. Further, the paper describes the optimization procedure as implemented in a computer code called DYNOPT which is a unique operational combination of several newly developed Fortran codes as well as modification of existing codes consisting of the direct matrix abstraction modules of the MSC/NASTRAN Program and CONMIN optimizer. The application of the optimization procedure is demonstrated using an elastic-line model of the Bell AH-1G helicopter airframe structure and computational results are discussed.

Sareen, Ashish K.↗

NASA NTRS1994

Thermal/Structural Tailoring of Engine Blades (T/STAEBL) User's manual

The Thermal/Structural Tailoring of Engine Blades (T/STAEBL) system is a computer code that is able to perform numerical optimizations of cooled jet engine turbine blades and vanes. These optimizations seek an airfoil design of minimum operating cost that satisfies realistic design constraints. This report documents the organization of the T/STAEBL computer program, its design and analysis procedure, its optimization procedure, and provides an overview of the input required to run the program, as well as the computer resources required for its effective use. Additionally, usage of the program is demonstrated through a validation test case.

Brown, K. W.↗

NASA NTRS1994

An optimization program based on the method of feasible directions: Theory and users guide

The theory and user instructions for an optimization code based on the method of feasible directions are presented. The code was written for wide distribution and ease of attachment to other simulation software. Although the theory of the method of feasible direction was developed in the 1960's, many considerations are involved in its actual implementation as a computer code. Included in the code are a number of features to improve robustness in optimization. The search direction is obtained by solving a quadratic program using an interior method based on Karmarkar's algorithm. The theory is discussed, focusing on the important and often overlooked role played by the various parameters guiding the iterations within the program. Also discussed is a robust approach for handling infeasible starting points. The code was validated by solving a variety of structural optimization test problems that have known solutions obtained by other optimization codes. It has been observed that this code is accurate and robust: it has solved a variety of problems from different starting points. However, the code is inefficient in that it takes considerable CPU time as compared with certain other available codes. Further work is required to improve its efficiency while retaining its robustness.

Ashok D. Belegundu↗

NASA NTRS1980

Nonreflecting far-field boundary conditions for unsteady transonic flow computation

The approximate nonreflecting far-field boundary condition, as proposed by Engquist and Majda, is implemented in the computer code LTRAN2. This code solves the implicit finite-difference representation of the small disturbance equations for unsteady transonic flows about airfoils. The nonreflecting boundary condition and the description of the algorithm for implementing these conditions in LTRAN2 are discussed. Various cases are computed and compared with results from the older, more conventional procedures. One concludes that the nonreflecting far-field boundary approximation allows the far-field boundary to be located closer to the airfoil; this permits a decrease in the computer time required to obtain the solution through the use of fewer mesh points.

Kwak, D.↗

NASA NTRS1984

Calculation of the 3-D viscous flow at the endwall leading edge region of an axial annular turbine cascade

A three-dimensional viscous computer code (VANS/MD) was employed to calculate the turbulent flow field at the end wall leading edge region of a 20 inch axial annular turbine cascade. The initial boundary layer roll-up and formation of the end wall vortices were computed at the vane leading edge. The calculated flow field was found to be periodic with a frequency of approximately 1600 Hz. The calculated size of the separation region for the hub endwall vortex compared favorably with measured endwall oil traces. In an effort to determine the effects of the turbulence model on the calculated unsteadiness, a laminar calculation was made. The periodic nature of the calculated flow field persisted with the frequency essentially unchanged.

Walitt, L.↗

NASA NTRS2015

On Hilbert-Huang Transform Based Synthesis of a Signal Contaminated by Radio Frequency Interference or Fringes

Norden E. Huang et al. had proposed and published the Hilbert-Huang Transform (HHT) concept correspondently in 1996, 1998. The HHT is a novel method for adaptive spectral analysis of non-linear and non-stationary signals. The HHT comprises two components: - the Huang Empirical Mode Decomposition (EMD), resulting in an adaptive data-derived basis of Intrinsic Mode functions (IMFs), and the Hilbert Spectral Analysis (HSA1) based on the Hilbert Transform for 1-dimension (1D) applied to the EMD IMF's outcome. Although paper describes the HHT concept in great depth, it does not contain all needed methodology to implement the HHT computer code. In 2004, Semion Kizhner and Karin Blank implemented the reference digital HHT real-time data processing system for 1D (HHT-DPS Version 1.4). The case for 2-Dimension (2D) (HHT2) proved to be difficult due to the computational complexity of EMD for 2D (EMD2) and absence of a suitable Hilbert Transform for 2D spectral analysis (HSA2). The real-time EMD2 and HSA2 comprise the real-time HHT2. Kizhner completed the real-time EMD2 and the HSA2 reference digital implementations respectively in 2013 & 2014. Still, the HHT2 outcome synthesis remains an active research area. This paper presents the initial concepts and preliminary results of HHT2-based synthesis and its application to processing of signals contaminated by Radio-Frequency Interference (RFI), as well as optical systems' fringe detection and mitigation at design stage. The Soil Moisture Active Passive (SMAP mission (SMAP) carries a radiometer instrument that measures Earth soil moisture at L1 frequency (1.4 GHz polarimetric - H, V, 3rd and 4th Stokes parameters). There is abundant RFI at L1 and because soil moisture is a strategic parameter, it is important to be able to recover the RFI-contaminated measurement samples (15% of telemetry). State-of-the-art only allows RFI detection and removes RFI-contaminated measurements. The HHT-based analysis and synthesis facilitates recovery of measurements contaminated by all kinds of RFI, including jamming [7-8]. The fringes are inherent in optical systems and multi-layer complex contour expensive coatings are employed to remove the unwanted fringes. HHT2-based analysis allows test image decomposition to analyze and detect fringes, and HHT2-based synthesis of useful image.

Spacecraft Electronics Equipment↗

NASA NTRS2023

Simulations of Zero Boiloff, Densification, and Solidification in a Large-Scale Liquid Hydrogen Tank

The current research utilizes an Energy of Fluid (EOF) approach to develop a finite volume-based Computation Fluid Dynamic (CFD) model to create a benchmark simulation of the densification of liquid hydrogen (LH2) in an experimental Integrated Refrigeration and Storage (IRAS) tank at the Kennedy Space Center (KSC). The computational code will incorporate the FLUENT pressure-based model with User Defined Functions (UDF) to implement the EOF model. The enhanced model will solve the energy equation in terms of internal energy and provide temperature and pressure calculations for a given tank geometry. Specifically, a convection term will be added to an already existing code for a more accurate simulation of LH2 densification. However, currently the research focuses on utilizing User Defined Scalars (UDS) with FLUENT to show the built-in solvers are as accurate as the written UDS. This will reduce the computational time down significantly by utilizing an already built in solver for the momentum equation. A custom UDF has been written to solve transient and steady state conduction, and results obtained using the UDF agree with results obtained using the built-in FLUENT solver. Currently, a convection UDF is being added and will be verified using known solutions for solidification and validated with the experimental results from the Cryogenics Test Laboratory (CTL) at KSC for the IRAS densification process.

Colin Philip Mahony↗

NASA NTRS2004

Benchmark Solutions for Computational Aeroacoustics (CAA) Code Validation

NASA has conducted a series of Computational Aeroacoustics (CAA) Workshops on Benchmark Problems to develop a set of realistic CAA problems that can be used for code validation. In the Third (1999) and Fourth (2003) Workshops, the single airfoil gust response problem, with real geometry effects, was included as one of the benchmark problems. Respondents were asked to calculate the airfoil RMS pressure and far-field acoustic intensity for different airfoil geometries and a wide range of gust frequencies. This paper presents the validated that have been obtained to the benchmark problem, and in addition, compares them with classical flat plate results. It is seen that airfoil geometry has a strong effect on the airfoil unsteady pressure, and a significant effect on the far-field acoustic intensity. Those parts of the benchmark problem that have not yet been adequately solved are identified and presented as a challenge to the CAA research community.

Scott, James R.↗