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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Power electronics for low power arcjets

In anticipation of the needs of future light-weight, low-power spacecraft, arcjet power electronics in the 100 to 400 W operating range were developed. Limited spacecraft power and thermal control capacity of these small spacecraft emphasized the need for high efficiency. Power topologies similar to those in the higher 2 kW and 5 to 30 kW power range were implemented, including a four transistor bridge switching circuit, current mode pulse-width modulated control, and an output current averaging inductor with an integral pulse generation winding. Reduction of switching transients was accomplished using a low inductance power distribution network, and no passive snubber circuits were necessary for power switch protection. Phase shift control of the power bridge was accomplished using an improved pulse width modulation to phase shift converter circuit. These features, along with conservative magnetics designs allowed power conversion efficiencies of greater than 92.5 percent to be achieved into resistive loads over the entire operating range of the converter. Electromagnetic compatibility requirements were not considered in this work, and control power for the converter was derived from AC mains. Addition of input filters and control power converters would result in an efficiency of on the order of 90 percent for a flight unit. Due to the developmental nature of arcjet systems at this power level, the exact nature of the thruster/power processor interface was not quantified. Output regulation and current ripple requirements of 1 and 20 percent respectively, as well as starting techniques, were derived from the characteristics of the 2 kW system but an open circuit voltage in excess of 175 V was specified. Arcjet integration tests were performed, resulting in successful starts and stable arcjet operation at power levels as low as 240 W with simulated hydrazine propellants.

Hamley, John A.↗
NASA NTRS1991

Power electronics for low power arcjets

In anticipation of the needs of future light-weight low-power spacecraft, arcjet power electronics in the 100- to 400-W operating range were developed. Power topologies similar to those in the higher 2-kW and 5- to 30-kW power range were implemented, including a four-transistor bridge-switching circuit, current-mode pulse-width modulated control, and an output current averaging inductor with an integral pulse generation winding. Reduction of switching transients was accomplished using a low inductance power distribution network, and no passive snubber circuits were necessary for power switch protection. Phase shift control of the power bridge was accomplished using an improved pulse width modulation to phase shift converter circuit. These features, along with conservative magnetics designs, allowed power conversion efficiencies of greater than 92.5 percent to be achieved into resistive loads over the entire operating range of the converter.

Hamley, John A.↗
NASA NTRS2004

Part 1 of a Computational Study of a Drop-Laden Mixing Layer

This first of three reports on a computational study of a drop-laden temporal mixing layer presents the results of direct numerical simulations (DNS) of well-resolved flow fields and the derivation of the large-eddy simulation (LES) equations that would govern the larger scales of a turbulent flow field. The mixing layer consisted of two counterflowing gas streams, one of which was initially laden with evaporating liquid drops. The gas phase was composed of two perfect gas species, the carrier gas and the vapor emanating from the drops, and was computed in an Eulerian reference frame, whereas each drop was tracked individually in a Lagrangian manner. The flow perturbations that were initially imposed on the layer caused mixing and eventual transition to turbulence. The DNS database obtained included transitional states for layers with various liquid mass loadings. For the DNS, the gas-phase equations were the compressible Navier-Stokes equations for conservation of momentum and additional conservation equations for total energy and species mass. These equations included source terms representing the effect of the drops on the mass, momentum, and energy of the gas phase. From the DNS equations, the expression for the irreversible entropy production (dissipation) was derived and used to determine the dissipation due to the source terms. The LES equations were derived by spatially filtering the DNS set and the magnitudes of the terms were computed at transitional states, leading to a hierarchy of terms to guide simplification of the LES equations. It was concluded that effort should be devoted to the accurate modeling of both the subgridscale fluxes and the filtered source terms, which were the dominant unclosed terms appearing in the LES equations.

Okong'o, Nora A.↗
NASA NTRS2007

An Investigation of High-Cycle Fatigue Models for Metallic Structures Exhibiting Snap-Through Response

A study is undertaken to develop a methodology for determining the suitability of various high-cycle fatigue models for metallic structures subjected to combined thermal-acoustic loadings. Two features of this problem differentiate it from the fatigue of structures subject to acoustic loading alone. Potentially large mean stresses associated with the thermally pre- and post-buckled states require models capable of handling those conditions. Snap-through motion between multiple post-buckled equilibrium positions introduces very high alternating stress. The thermal-acoustic time history response of a clamped aluminum beam structure with geometric and material nonlinearities is determined via numerical simulation. A cumulative damage model is employed using a rainflow cycle counting scheme and fatigue estimates are made for 2024-T3 aluminum using various non-zero mean fatigue models, including Walker, Morrow, Morrow with true fracture strength, and MMPDS. A baseline zero-mean model is additionally considered. It is shown that for this material, the Walker model produces the most conservative fatigue estimates when the stress response has a tensile mean introduced by geometric nonlinearity, but remains in the linear elastic range. However, when the loading level is sufficiently high to produce plasticity, the response becomes more fully reversed and the baseline, Morrow, and Morrow with true fracture strength models produce the most conservative fatigue estimates.

Przekop, Adam↗
NASA NTRS1984

Dynamic stress analysis of smooth and notched fiber composite flexural specimens

A detailed analysis of the dynamic stress field in smooth and notched fiber composite (Charpy-type) specimens is reported in this paper. The analysis is performed with the aid of the direct transient response analysis solution sequence of MSC/NASTRAN. Three unidirectional composites were chosen for the study. They are S-Glass/Epoxy, Kevlar/Epoxy and T-300/Epoxy composite systems. The specimens are subjected to an impact load which is modeled as a triangular impulse with a maximum of 2000 lb and a duration of 1 ms. The results are compared with those of static analysis of the specimens subjected to a peak load of 2000 lb. For the geometry and type of materials studied, the static analysis results gave close conservative estimates for the dynamic stresses. Another interesting inference from the study is that the impact induced effects are felt by S-Glass/Epoxy specimens sooner than Kevlar/Epoxy or T-300/Epoxy specimens.

Murthy, P. L. N.↗
NASA NTRS1986

Dynamic stress analysis of smooth and notched fiber composite flexural specimens

A detailed analysis of the dynamic stress field in smooth and notched fiber composite (Charpy-type) specimens is reported in this paper. The analysis is performed with the aid of the direct transient response analysis solution sequence of MSC/NASTRAN. Three unidirectional composites were chosen for the study. They are S-Glass/Epoxy, Kevlar/Epoxy and T-300/Epoxy composite systems. The specimens are subjected to an impact load which is modeled as a triangular impulse with a maximum of 2000 lb and a duration of 1 ms. The results are compared with those of static analysis of the specimens subjected to a peak load of 2000 lb. For the geometry and type of materials studied, the static analysis results gave close conservative estimates for the dynamic stresses. Another interesting inference from the study is that the impact induced effects are felt by S-Glass/Epoxy specimens sooner than Kevlar/Epoxy or T-300/Epoxy specimens.

Murthy, P. L. N.↗
NASA NTRS1986

The effects of task difficulty and workload on training

Four hypotheses regarding the possible effects of workload and task difficulty on training are proposed. These are: (1) increased levels of task difficulty will facilitate learning to the extent that these increases are (a) resource loading and (b) intrinsic to the component task to be learned; (2) decrease of task difficulty will facilitate learning to the extent that these decreases (a) reduce the resource load and (b) are extrinsic of the component task to be learned; (3) the lerner's tendency to conserve resources may bead to the adoption of undesirable, short-term, low resource strategies early in training; and (4) the effect of changes in resource demand on learning will depend upon the similarity of the resource whose demand is changed to the resource involved in learning.

Mane, Amir↗
NASA NTRS1980

Design and Analysis of a Stiffened Composite Fuselage Panel

A stiffened composite panel has been designed that is representative of the fuselage structure of existing wide bodied aircraft. The panel is a minimum weight design, based on the current level of technology and realistic loads and criteria. Several different stiffener configurations were investigated in the optimization process. The final configuration is an all graphite epoxy J-stiffened design in which the skin between adjacent stiffeners is permitted to buckle under design loads. Fail-safe concepts typically employed in metallic fuselage structure have been incorporated in the design. A conservative approach has been used with regard to structural details such as skin frame and stringer frame attachments and other areas where sufficient design data was not available.

Dickson, J. N.↗
NASA NTRS2005

Space Shuttle Partial Stack Rollout Test Analytical Correlation In Support Of Fatigue Load Development

A rollout test with only the Solid Rocket Boosters was conducted in November 2003 to gather structural dynamic response data of the transportation environment from the Vehicle Assembly Building to the Launch Pad. The data was acquired to develop and validate analytical methods used to predict rollout Orbiter fatigue load spectra. Earlier predictions computed by a base drive approach with only 5 input drive degrees-of-freedom raised questions that commissioned the partial stack test. Not only was there a concern because of the input degree-of-freedom omission due to measurement limitations, but there was also a concern with the implementation of the "large mass" itself. Three methods were evaluated with the partial stack test data. The analytical correlations to measured strain derived SRB base loads and acceleration5 showed the earlier 5 degree-of-freedom base drive approach to yield the most conservative results for all quantities monitored except the SRB base moment about the axis in which the input drive was missing. This non-conservative shortcoming led to a recommendation to use either the 6 degree-of-freedom base drive or the 12 degree-of-freedom Craig-Bampton boundary drive methods whose results did not substantially differ.

DelBasso, Steve↗
NASA NTRS2010

Comparison of Methods to Predict Lower Bound Buckling Loads of Cylinders Under Axial Compression

Results from a numerical study of the buckling response of two different orthogrid stiffened circular cylindrical shells with initial imperfections and subjected to axial compression are used to compare three different lower bound buckling load prediction techniques. These lower bound prediction techniques assume different imperfection types and include an imperfection based on a mode shape from an eigenvalue analysis, an imperfection caused by a lateral perturbation load, and an imperfection in the shape of a single stress-free dimple. The STAGS finite element code is used for the analyses. Responses of the cylinders for ranges of imperfection amplitudes are considered, and the effect of each imperfection is compared to the response of a geometrically perfect cylinder. Similar behavior was observed for shells that include a lateral perturbation load and a single dimple imperfection, and the results indicate that the predicted lower bounds are much less conservative than the corresponding results for the cylinders with the mode shape imperfection considered herein. In addition, the lateral perturbation technique and the single dimple imperfection produce response characteristics that are physically meaningful and can be validated via testing.

Haynie, Waddy T.↗
NASA NTRS2009

Silicon Wafer-Scale Substrate for Microshutters and Detector Arrays

The silicon substrate carrier was created so that a large-area array (in this case 62,000+ elements of a microshutter array) and a variety of discrete passive and active devices could be mounted on a single board, similar to a printed circuit board. However, the density and number of interconnects far exceeds the capabilities of printed circuit board technology. To overcome this hurdle, a method was developed to fabricate this carrier out of silicon and implement silicon integrated circuit (IC) technology. This method achieves a large number of high-density metal interconnects; a 100-percent yield over a 6-in. (approximately equal to 15-cm) diameter wafer (one unit per wafer); a rigid, thermally compatible structure (all components and operating conditions) to cryogenic temperatures; re-workability and component replaceability, if required; and the ability to precisely cut large-area holes through the substrate. A method that would employ indium bump technology along with wafer-scale integration onto a silicon carrier was also developed. By establishing a silicon-based version of a printed circuit board, the objectives could be met with one solution. The silicon substrate would be 2 mm thick to survive the environmental loads of a launch. More than 2,300 metal traces and over 1,500 individual wire bonds are required. To mate the microshutter array to the silicon substrate, more than 10,000 indium bumps are required. A window was cut in the substrate to allow the light signal to pass through the substrate and reach the microshutter array. The substrate was also the receptacle for multiple unpackaged IC die wire-bonded directly to the substrate (thus conserving space over conventionally packaged die). Unique features of this technology include the implementation of a 2-mmthick silicon wafer to withstand extreme mechanical loads (from a rocket launch); integrated polysilicon resistor heaters directly on the substrate; the precise formation of an open aperture (approximately equal to 3x3cm) without any crack propagation; implementation of IR transmission blocking techniques; and compatibility with indium bump bonding. Although designed for the microshutter arrays for the NIRSpec instrument on the James Webb Space Telescope, these substrates can be linked to microshutter applications in the photomask generation and stepper equipment used to make ICs and microelectromechanical system (MEMS) devices.

Jhabvala, Murzy↗
NASA NTRS1977

The 100 kW space station

Solar array power systems for the space construction base are discussed. Nickel cadmium and nickel hydrogen batteries are equally attractive relative to regenerative fuel cell systems at 5 years life. Further evaluation of energy storage system life (low orbit conditions) is required. Shuttle and solid polymer electrolyte fuel cell technology appears adequate; large units (approximately four times shuttle) are most appropriate and should be studied for a 100 KWe SCB system. A conservative NiH2 battery DOD (18.6%) was elected due to lack of test data and offers considerable improvement potential. Multiorbit load averaging and reserve capacity requirements limit nominal DOD to 30% to 50% maximum, independent of life considerations.

Mckhann, G.↗
NASA NTRS1981

Computerized energy analysis for the Mars operations support building

A detailed computerized building load simulation of the Operations Support Building at the Mars Deep Space Station, Goldstone, California is described. Five energy conservation suggestions were investigated prior to implementation. The results showed that cost savings of about 16 percent of present energy costs are possible.

Yung, C. S.↗
NASA NTRS1991

In-phase and out-of-phase axial-torsional fatigue behavior of Haynes 188 at 760 C

Isothermal, in-phase and out-of-phase axial-torsional fatigue experiments have been conducted at 760 C on uniform gage section, thin-walled tubular specimens of a wrought cobalt-base superalloy, Haynes 188. Test-control and data acquisition were accomplished with a minicomputer. Fatigue lives of the in- and out-of-phase axial-torsional fatigue tests have been estimated with four different multiaxial fatigue life prediction models that were developed primarly for predicting axial-torsional fatigue lives at room temperature. The models investigated were: (1) the von Mises equivalent strain range; (2) the Modified Multiaxiality Factor Approach; (3) the Modified Smith-Watson-Topper Parameter; and (4) the critical shear plane method of Fatemi, Socie, and Kurath. In general, life predictions by the von Mises equivalent strain range model were within a factor of 2 for a majority of the tests and the predictions by the Modified Multiaxiality Factor Approach were within a factor of 2, while predictions of the Modified Smith-Watson-Topper Parameter and of the critical shear plane method of Fatemi, Socie, and Kurath were unconservative and conservative, respectively, by up to factors of 4. In some of the specimens tested under combined axial-torsional loading conditions, fatigue cracks initiated near extensometer indentations. Two design modifications have been proposed to the thin-walled tubular specimen to overcome this problem.

Kalluri, Sreeramesh↗
NASA NTRS2012

High Resolution Visualization Applied to Future Heavy Airlift Concept Development and Evaluation

This paper explores the use of high resolution 3D visualization tools for exploring the feasibility and advantages of future military cargo airlift concepts and evaluating compatibility with existing and future payload requirements. Realistic 3D graphic representations of future airlifters are immersed in rich, supporting environments to demonstrate concepts of operations to key personnel for evaluation, feedback, and development of critical joint support. Accurate concept visualizations are reviewed by commanders, platform developers, loadmasters, soldiers, scientists, engineers, and key principal decision makers at various stages of development. The insight gained through the review of these physically and operationally realistic visualizations is essential to refining design concepts to meet competing requirements in a fiscally conservative defense finance environment. In addition, highly accurate 3D geometric models of existing and evolving large military vehicles are loaded into existing and proposed aircraft cargo bays. In this virtual aircraft test-loading environment, materiel developers, engineers, managers, and soldiers can realistically evaluate the compatibility of current and next-generation airlifters with proposed cargo.

FordCook, A. B.↗
NASA NTRS2009

Investigating Response from Attached and Separated Flow Excitations on a Real Launch Vehicle using SEA

Statistical Energy Analysis (SEA) response has been fairly well anchored to test observations for Diffuse Acoustic Field (DAF) loading by others. Meanwhile, not many examples can be found in the literature anchoring the SEA vehicle panel response results to Turbulent Boundary Layer (TBL) fluctuating pressure excitations. This deficiency is especially true for supersonic trajectories such as those required by this nation s launch vehicles. Response and excitation data from vehicle flight measurements gathered during the development flight era of the Space Shuttle have been used in a trial to assess the sensitivity of response analysis to certain known and unknown parameters of the flight. This assessment compares vibration response predictions for TBL excitations produced by the SEA tool to flight measurements. A secondary, but perhaps more important objective, is to provide more clarity concerning the accuracy and conservatism that can be expected from response estimates to TBL-excited vehicle models in SEA. What range of parameters must be included in such an analysis in order to land on the conservative side in response predictions? What is the variability produced in the results with changes in these parameters? The TBL fluid structure loading model used for this study is provided from the SEA module of the commercial code VA One.

Harrison, Phil↗
NASA NTRS2009

Investigating Response from Turbulent Boundary Layer Excitations on a Real Launch Vehicle using SEA

Statistical Energy Analysis (SEA) response has been fairly well anchored to test observations for Diffuse Acoustic Field (DAF) loading by others. Meanwhile, not many examples can be found in the literature anchoring the SEA vehicle panel response results to Turbulent Boundary Layer (TBL) fluctuating pressure excitations. This deficiency is especially true for supersonic trajectories such as those required by this nation s launch vehicles. Space Shuttle response and excitation data recorded from vehicle flight measurements during the development flights were used in a trial to assess the capability of the SEA tool to predict similar responses. Various known/measured inputs were used. These were supplemented with a range of assumed values in order to cover unknown parameters of the flight. This comparison is presented as "Part A" of the study. A secondary, but perhaps more important, objective is to provide more clarity concerning the accuracy and conservatism that can be expected from response estimates of TBL-excited vehicle models in SEA (Part B). What range of parameters must be included in such an analysis in order to land on the conservative side in response predictions? What is the sensitivity of changes in these input parameters on the results? The TBL fluid structure loading model used for this study is provided by the SEA module of the commercial code VA One.

Harrison, Phillip↗
NASA NTRSDate not supplied

Solar Cruiser TRAC Boom Development

The TRAC boom studied is a 30 meter, high-aspect ratio and highly nonlinear structural element planned for the NASA Solar Cruiser spacecraft where it would serve as the solar sail’s skeletal system designed to deploy the packaged reflective sail membrane as well as support operational sail tension loads for flight. Key design drivers for this boom are understanding and characterizing load-deformation behavior and quantifying buckling performance–under flight conditions (zero gravity). Knowing that the full-scale solar sail system cannot be feasibly tested for flight conditions under Earth’s gravity, a building block approach is methodically followed to verify finite element analysis (FEA) predictions and to evolve the finite element model (FEM) accordingly, beginning with the lowest level complexity to match global elastic behavior to the highest level complexity to bound theoretical responses under conservative expected flight conditions. Although the testing campaign for the TRAC boom has not developed yet to produce a full-scale test data point that loads the boom to failure, the fidelity of simulations have evolved with success and warrant further interest and work on this high-aspect ratio, but highly stable, deployable structural boom.

Lee Nguyen↗