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At least 1,333 records · Page 74
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

On Characterization of Flow Disturbances in Arc-Jet Testing

This paper reports computational simulations and analysis of flow characterization tests in high enthalpy arc-jet facilities at NASA Ames Research Center. Flow disturbances and their characterization are presented through case studies, and their implications for testing are discussed. The case studies include free-jet test configurations from three different arc heaters and nozzles: the 60-MW IHF 30-inch conical nozzle, the 10-MW TP3 15-inch conical nozzle, and the 20-MW AHF 12-inch conical nozzle. For all cases, test articles are placed in the jet exiting the conical nozzle, and the existence of a flow disturbance is confirmed through flow survey data using pitot pressure and heat flux probes and accompanying analysis. The paper focuses on cases where the effects of the disturbances on test article surface quantities are important. The present analysis comprises computational fluid dynamics simulations of the nonequilibrium flowfield in the facility nozzles and test box, including the models tested. Comparisons of computations with the experimental measurements are presented. The computations that reproduce the probe sweep data approximately are essential to interpret the arc-jet test data accurately, while providing insights into several observed calorimeter anomalies caused by flow disturbances.

Arc-jet testing↗
DOE OSTI2016

Simulation of electron beam formation and transport in a gas-filled electron-optical system with a plasma emitter

The results of computer simulations of the electron-optical system of an electron gun with a plasma emitter are presented. The simulations are performed using the KOBRA3-INP, XOOPIC, and ANSYS codes. The results describe the electron beam formation and transport. The electron trajectories are analyzed. The mechanisms of gas influence on the energy inhomogeneity of the beam and its current in the regions of beam primary formation, acceleration, and transport are described. Recommendations for optimizing the electron-optical system with a plasma emitter are presented.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2026

Interpolation of computed gamma-ray detector response functions

Gamma-ray spectra measured by traditional detectors contain features that result from a combination of the effects of detector materials/geometry, the incident gamma-ray energy, and the angle of entry. The features, such as the full-energy photopeak, Compton continuum, annihilation peak, and escape peaks, are governed by simple relationships depending on incident energy and have been known for a long time. Monte Carlo computer simulations of gamma rays interacting with a detector will show these features, and with a resolution function applied, the results should look similar to real measurements. The traditional approach to creating a detector response function requires many separate simulations of monoenergetic gamma rays striking the detector. This paper presents a new approach to developing computed detector response functions. The new approach involves a much smaller number of monoenergetic gamma-ray simulations and uses interpolation to quickly generate the responses of gamma rays that were not simulated. During the interpolation process, the underlying physics equations are used to accurately compute the response of a given energy gamma ray from the small set of simulations. Such work enables accelerated generation of synthetic radiation detector data.

Detector response↗
NASA NTRS2016

Flow Characterization Studies of the 10-MW TP3 Arc-Jet Facility: Probe Sweeps

This paper reports computational simulations and analysis in support of calibration and flow characterization tests in a high enthalpy arc-jet facility at NASA Ames Research Center. These tests were conducted in the NASA Ames 10-MW TP3 facility using flat-faced stagnation calorimeters at six conditions corresponding to the steps of a simulated flight heating profile. Data were obtained using a conical nozzle test configuration in which the models were placed in a free jet downstream of the nozzle. Experimental surveys of arc-jet test flow with pitot pressure and heat flux probes were also performed at these arc-heater conditions, providing assessment of the flow uniformity and valuable data for the flow characterization. Two different sets of pitot pressure and heat probes were used: 9.1-mm sphere-cone probes (nose radius of 4.57 mm or 0.18 in) with null-point heat flux gages, and 15.9-mm (0.625 in) diameter hemisphere probes with Gardon gages. The probe survey data clearly show that the test flow in the TP3 facility is not uniform at most conditions (not even axisymmetric at some conditions), and the extent of non-uniformity is highly dependent on various arc-jet parameters such as arc current, mass flow rate, and the amount of cold-gas injection at the arc-heater plenum. The present analysis comprises computational fluid dynamics simulations of the nonequilibrium flowfield in the facility nozzle and test box, including the models tested. Comparisons of computations with the experimental measurements show reasonably good agreement except at the extreme low pressure conditions of the facility envelope.

Goekcen, Tahir↗
NASA NTRS2016

Flow Characterization Studies of the 10-MW TP3 Arc-Jet Facility: Probe Sweeps

This paper reports computational simulations and analysis in support of calibration and flow characterization tests in a high enthalpy arc-jet facility at NASA Ames Research Center. These tests were conducted in the NASA Ames 10-MW TP3 facility using flat-faced stagnation calorimeters at six conditions corresponding to the steps of a simulated flight heating profile. Data were obtained using a conical nozzle test configuration in which the models were placed in a free jet downstream of the nozzle. Experimental surveys of arc-jet test flow with pitot pressure and heat flux probes were also performed at these arc-heater conditions, providing assessment of the flow uniformity and valuable data for the flow characterization. Two different sets of pitot pressure and heat probes were used: 9.1-mm sphere-cone probes (nose radius of 4.57 mm or 0.18 in) with null-point heat flux gages, and 15.9-mm (0.625 in) diameter hemisphere probes with Gardon gages. The probe survey data clearly show that the test flow in the TP3 facility is not uniform at most conditions (not even axisymmetric at some conditions), and the extent of non-uniformity is highly dependent on various arc-jet parameters such as arc current, mass flow rate, and the amount of cold-gas injection at the arc-heater plenum. The present analysis comprises computational fluid dynamics simulations of the nonequilibrium flowfield in the facility nozzle and test box, including the models tested. Comparisons of computations with the experimental measurements show reasonably good agreement except at the extreme low pressure conditions of the facility envelope.

CFD↗
NASA NTRS1992

An experiment on the use of disposable plastics as a reinforcement in concrete beams

Illustrated here is the concept of reinforced concrete structures by the use of computer simulation and an inexpensive hands-on design experiment. The students in our construction management program use disposable plastic as a reinforcement to demonstrate their understanding of reinforced concrete and prestressed concrete beams. The plastics used for such an experiment vary from plastic bottles to steel reinforced auto tires. This experiment will show the extent to which plastic reinforcement increases the strength of a concrete beam. The procedure of using such throw-away plastics in an experiment to explain the interaction between the reinforcement material and concrete, and a comparison of the test results for using different types of waste plastics are discussed. A computer analysis to simulate the structural response is used to compare the test results and to understand the analytical background of reinforced concrete design. This interaction of using computers to analyze structures and to relate the output results with real experimentation is found to be a very useful method for teaching a math-based analytical subject to our non-engineering students.

Chowdhury, Mostafiz R.↗
NASA NTRS1999

Taxiing, Take-Off, and Landing Simulation of the High Speed Civil Transport Aircraft

The aircraft industry jointly with NASA is studying enabling technologies for higher speed, longer range aircraft configurations. Higher speeds, higher temperatures, and aerodynamics are driving these newer aircraft configurations towards long, slender, flexible fuselages. Aircraft response during ground operations, although often overlooked, is a concern due to the increased fuselage flexibility. This paper discusses modeling and simulation of the High Speed Civil Transport aircraft during taxiing, take-off, and landing. Finite element models of the airframe for various configurations are used and combined with nonlinear landing gear models to provide a simulation tool to study responses to different ground input conditions. A commercial computer simulation program is used to numerically integrate the equations of motion and to compute estimates of the responses using an existing runway profile. Results show aircraft responses exceeding safe acceptable human response levels.

Reaves, Mercedes C.↗
NASA NTRS1994

Design of a composite filter realizable on practical spatial light modulators

Hybrid optical correlator systems use two spatial light modulators (SLM's), one at the input plane and the other at the filter plane. Currently available SLM's such as the deformable mirror device (DMD) and liquid crystal television (LCTV) SLM's exhibit arbitrarily constrained operating characteristics. The pattern recognition filters designed with the assumption that the SLM's have ideal operating characteristic may not behave as expected when implemented on the DMD or LCTV SLM's. Therefore it is necessary to incorporate the SLM constraints in the design of the filters. In this report, an iterative method is developed for the design of an unconstrained minimum average correlation energy (MACE) filter. Then using this algorithm a new approach for the design of a SLM constrained distortion invariant filter in the presence of input SLM is developed. Two different optimization algorithms are used to maximize the objective function during filter synthesis, one based on the simplex method and the other based on the Hooke and Jeeves method. Also, the simulated annealing based filter design algorithm proposed by Khan and Rajan is refined and improved. The performance of the filter is evaluated in terms of its recognition/discrimination capabilities using computer simulations and the results are compared with a simulated annealing optimization based MACE filter. The filters are designed for different LCTV SLM's operating characteristics and the correlation responses are compared. The distortion tolerance and the false class image discrimination qualities of the filter are comparable to those of the simulated annealing based filter but the new filter design takes about 1/6 of the computer time taken by the simulated annealing filter design.

Rajan, P. K.↗
DOE OSTI2022

Dataset of Simulated Intracardiac Transmembrane Voltage Recordings and ECG Signals

The dataset consists of pairs of computationally simulated intracardiac transmembrane voltage recordings and ECG signals. In total, 16140 organ-level simulations were conducted to create this dataset, using a range of cardiac geometries and physiological parameters. Simulations were performed at LLNL's Lassen supercomputer, concurrently utilizing 4 GPUs and 40 CPU cores. Each simulation produced pairs of 500ms-by-10 ECG signals and 500ms-by-75 transmembrane voltage signals. For convenience, the signals are concatenated and saved as matrices. Each of these matrices is then stored as a numpy array. See the documentation for further details.

Landajuela, Mikel↗
NASA NTRS1984

Simulation of the earth's monthly average regional radiation balance derived from satellite measurements

Computer simulations of satellite-derived earth radiation parameters are used to determine the source and size of errors arising from measuring parameters over 1 month on a 2.5 deg x 2.5 deg longitude-latitude grid. November 1979 GOES data are used as a source of radiation parameter fields within each region. A mathematical model is given for the data-processing algorithms that are used to produce daily, monthly, and monthly hourly estimates of shortwave, longwave and net radiant exitance. Resulting retrieval errors are found to be due to insufficient knowledge of the temporal distribution of measurements. These errors, in combination with similar sampling errors produce biases in monthly net radiant exitance which are complex, regionally-dependent functions of the local time of the measurements. The 40 region standard errors of estimate for three satellites ranged from 2 to 3 W per sq. m., while single satellite errors ranged from 5 to 19 W per sq. m. A three-satellite system is therefore recommended to reduce biases.

Brooks, D. R.↗
NASA NTRS1995

Simulation Results for PCM/PM/NRZ Receivers in Non-Ideal Channels

This paper studies, by computer simulations, the performance of deep space telemetry signals that employ PCM/PM/NRZ modulation technique under the separate and combined effects of an unbalanced data stream, data asymmetry, and band-limited channel. The study is based on measuring the Symbol Error Rate (SER) performance and comparing the results to the theoretical results presented in previous reports [1,2]. Only the effects of imperfect carrier tracking due to an imperfect data stream are considered.

PCM/PM/NRS Receivers↗
NASA NTRS1994

Comdisco Simulation Results for PCM/PM Receivers in Non-Ideal Channels

This paper studies, by computer simulations, the performance of a PCM/PM/NRZ receiver in the presence of two separate effects: unbalanced data stream and band-limited channel. The results obtained are then compared to the theoretical results presented in a previous report.

InterSymobol Interference (ISI)↗
DOE OSTI2016

Enabling Technologies for High-Throughput Screening of Nano-Porous Materials: Collaboration with the Nanoporous Materials Genome Center

The overarching goal of this research was to develop new methodologies to enable the accurate and efficient modeling of complex materials using computer simulations. Using inter-molecular interaction energies calculated via an accurate but computationally expensive approach (symmetry-adapted perturbation theory), we parameterized efficient next-generation “force fields” to utilize in subsequent simulations. Since the resulting force fields incorporate much of the relevant physics of inter-molecular interactions, they consequently exhibit high transferability from one material to another. This transferability enables the modeling of a wide range of novel materials without additional computational cost. While this approach is quite general, a particular emphasis of this research involved applications to so-called “metal-organic framework”(MOF) materials relevant to energy-intensive gas separations. We focused specifically on CO 2 /N 2 selectivity, which is a key metric for post combustion CO 2 capture efforts at coal-fired power plants. The gas adsorption capacities and selectivity of the MOFs can be tailored via careful functionalization. We have demonstrated that our force fields exhibit predictive accuracy for a wide variety of functionalized MOFs, thus opening the door for the computational design of “tailored” materials for particular separations. Finally, we have also demonstrated the importance of accounting for the presence of reactive contaminant species when evaluating the performance of MOFs in practical applications.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Simulating strongly correlated molecules with a superconducting quantum processor

Many of the biggest challenges in expanding the nation’s access to clean and low-cost energy resources are fundamentally chemistry or materials challenges. An important case is the development of new catalysts for the up-conversion of cheap and readily available materials such as methane or water into materials suitable for use as a fuel such as methanol or oxygen. To understand and exploit such processes, computer simulations of chemical reactions provide a natural complement to experimental studies. Unfortunately, most catalytic reactions involve so-called “strongly correlated” molecules which are notoriously difficult to study with simulation algorithms that can be executed on existing (classical) computers. The recent growth in quantum information science offers an alternative potential route for simulating these difficult systems. As a result, an increasing number of computational chemists are becoming interested in quantum computing. At the same time, quantum information scientists have identified chemistry simulation as a possible first demonstration of a quantum computer providing an improvement over a classical computer. The objective of this project is to accurately simulate strongly correlated molecules on a quantum processor. To meet the high challenges of this objective, new hybrid quantum/classical algorithms will be co-designed with advanced quantum gate developments and computed on customized quantum hardware. Some of the developed techniques will be transferable to study other molecular systems, while the project as a whole will help define better strategies for advancing the quantum simulation of matter more generally.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Superhigh-Speed Electric Motor with Unipolar Magnetic Bearing

New unipolar magnetic bearings of high-speed and superhigh-speed electric motors for different branches of industry are described. A new design is proposed and investigated by computer simulation. On the basis of the results, a mockup is created, and the computer models are verified.

42 ENGINEERING↗
NASA NTRS1994

Direct numerical simulation of sheared turbulent flow

The summer assignment to study sheared turbulent flow was divided into three phases which were: (1) literature survey, (2) computational familiarization, and (3) pilot computational studies. The governing equations of fluid dynamics or Navier-Stokes equations describe the velocity, pressure, and density as functions of position and time. In principle, when combined with conservation equations for mass, energy, and thermodynamic state of the fluid a determinate system could be obtained. In practice the Navier-Stokes equations have not been solved due to the nonlinear nature and complexity of these equations. Consequently, the importance of experiments in gaining insight for understanding the physics of the problem has been an ongoing process. Reasonable computer simulations of the problem have occured as the computational speed and storage of computers has evolved. The importance of the microstructure of the turbulence dictates the need for high resolution grids in extracting solutions which contain the physical mechanisms which are essential to a successful simulation. The recognized breakthrough occurred as a result of the pioneering work of Orzag and Patterson in which the Navier-Stokes equations were solved numerically utilizing a time saving toggling technique between physical and wave space, known as a spectral method. An equally analytically unsolvable problem, containing the same quasi-chaotic nature as turbulence, is known as the three body problem which was studied computationally as a first step this summer. This study was followed by computations of a two dimensional (2D) free shear layer.

Harris, Vascar G.↗