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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 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

A microscopic study of crack initiation mechanisms in 7075 aluminum alloy sheets.

A study of the opening mode of crack initiation in 7075-T6 aluminum alloy sheets has been conducted with the aid of a scanning electron microscope. Observations were made from several orientations, including the top view of the specimen which showed the notch profile and the edge view of the specimen which showed the entire notch front along the specimen thickness. It was found that the edge view exhibited the first signs of permanent deformation at about 55% of the breaking strength. These changes took the form of deformation bands which were aligned in the direction of the tensile axis and apparently defined limiting regions of homogeneous slip. It is felt that the appearance of microcracks at loads approaching the breaking strength was of fundamental importance in the formation of the final fracture surface. Many of these microcraks were initiated at intermetallic particles and other metallurgically weak regions on the notch surface. It was also possible to correlate the strain in the notch with the stress intensity factor for the various loads. Very large plastic strains were observed on the notch tip as compared to published values of elongation at fracture for unnotched specimens.

Jones, D. L.↗
NASA NTRS1974

Stress analysis of the compact specimen including the effects of pin loading

An improved method of boundary collocation was applied to the two-dimensional stress analysis of the compact specimen. The effects of the pin-loaded holes on stress-intensity factors and crack-opening displacements were investigated for various crack-length-to-specimen-width ratios, hole locations, and internal loadings. The stress-intensity factors for the 'standard' compact specimen under plane-stress or plane-strain conditions were found to be within 1 percent of the stress-intensity factors reported in the ASTM Test for Plane-Strain Fracture Toughness of Metallic Materials (E 399-72) over a range of crack-length-to-specimen-width ratios of 0.4 to 0.7. However, for crack-length-to-specimen-width ratios less than 0.4, the pin-load holes (which were not previously accounted for) had a significant effect on stress intensity and crack-opening displacements.

Newman, J. C., Jr.↗
NASA NTRSDate not supplied

Analysis and Evaluation of NASA's MK40B Six-Component TASK Balance

The paper discusses the physical characteristics NASA's MK40B TASK balance. It is NASA's newest TASK balance that was optimized for the testing of wind tunnel models in the NASA Ames 11-ft Transonic Wind Tunnel. The calibration data of the MK40B balance was obtained in Calspan's Automatic Balance Calibration System. A machine load schedule design was used for the calibration that was developed at the NASA Ames Balance Calibration Laboratory. The calibration data was analyzed using both the Non-Iterative Method and the Iterative Method. Then, the chosen regression models of the calibration data were assessed and compared using the percent contribution, the variance inflation factor, and the calibration load residuals. Interactions of single-component loads were also quantified. In addition, the bi-directional characteristics of the six gage outputs of the balance were assessed by applying a semi-empirical test that was developed at the Ames Balance Calibration Laboratory. It was concluded that four of the six gages of the balance have bi-directional characteristics. Finally, the accuracy of the load prediction equations of the balance was tested by applying the equations to independent check load data that was obtained at the NASA Ames Balance Calibration Laboratory. The standard deviation of the check load residuals met expectations. The check load data also confirmed that the interactions of the forward and aft normal forces on the axial force gage output are very small. - This paper is to be presented in the invited special session titled: "65 Years of TASK Wind Tunnel Balances - Past, Present, and Future".

wind tunnel balance↗
NASA NTRS1999

Fracture Mechanics of Thin, Cracked Plates Under Tension, Bending and Out-of-Plane Shear Loading

Cracks in the skin of aircraft fuselages or other shell structures can be subjected to very complex stress states, resulting in mixed-mode fracture conditions. For example, a crack running along a stringer in a pressurized fuselage will be subject to the usual in-plane tension stresses (Mode-I) along with out-of-plane tearing stresses (Mode-III like). Crack growth and initiation in this case is correlated not only with the tensile or Mode-I stress intensity factor, K(sub I), but depends on a combination of parameters and on the history of crack growth. The stresses at the tip of a crack in a plate or shell are typically described in terms of either the small deflection Kirchhoff plate theory. However, real applications involve large deflections. We show, using the von-Karman theory, that the crack tip stress field derived on the basis of the small deflection theory is still valid for large deflections. We then give examples demonstrating the exact calculation of energy release rates and stress intensity factors for cracked plates loaded to large deflections. The crack tip fields calculated using the plate theories are an approximation to the actual three dimensional fields. Using three dimensional finite element analyses we have explored the relationship between the three dimensional elasticity theory and two dimensional plate theory results. The results show that for out-of-plane shear loading the three dimensional and Kirchhoff theory results coincide at distance greater than h/2 from the crack tip, where h/2 is the plate thickness. Inside this region, the distribution of stresses through the thickness can be very different from the plate theory predictions. We have also explored how the energy release rate varies as a function of crack length to plate thickness using the different theories. This is important in the implementation of fracture prediction methods using finite element analysis. Our experiments show that under certain conditions, during fatigue crack growth, the presence of out-of-plane shear loads induces a great deal of contact and friction on the crack surfaces, dramatically reducing crack growth rate. A series of experiments and a proposed computational approach for accounting for the friction is discussed.

Zehnder, Alan T.↗
NASA NTRS1979

Wind Loads on Flat Plate Photovoltaic Array Fields

The aerodynamic forces resulting from winds acting on flat plate photovoltaic arrays were investigated. Local pressure distributions and total aerodynamic forces on the arrays are shown. Design loads are presented to cover the conditions of array angles relative to the ground from 20 deg to 60 deg, variable array spacings, a ground clearance gap up to 1.2 m (4 ft) and array slant heights of 2.4 m (8 ft) and 4.8 m (16 ft). Several means of alleviating the wind loads on the arrays are detailed. The expected reduction of the steady state wind velocity with the use of fences as a load alleviation device are indicated to be in excess of a factor of three for some conditions. This yields steady state wind load reductions as much as a factor of ten compared to the load incurred if no fence is used to protect the arrays. This steady state wind load reduction is offset by the increase in turbulence due to the fence but still an overall load reduction of 2.5 can be realized. Other load alleviation devices suggested are the installation of air gaps in the arrays, blocking the flow under the arrays and rounding the edges of the array. A wind tunnel test plan to supplement the theoretical study and to evaluate the load alleviation devices is outlined.

Miller, R.↗
NASA NTRS2004

Linear and Nonlinear Analyses of a Wind-Tunnel Balance

The NASA Langley Research Center (LaRC) has been designing strain-gauge balances for utilization in wind tunnels since its inception. The utilization of balances span a wide variety of aerodynamic tests. A force balance is an inherently critically stressed component due to the requirements of measurement sensitivity. Force balance stress analysis and acceptance criteria are under review due to LaRC wind tunnel operational safety requirements. This paper presents some of the analyses done at NASA LaRC. Research and analyses were performed in order to investigate the structural integrity of the balances and better understand their performance. The analyses presented in this paper are helpful in understanding the overall behavior of an existing balance and can also be used in design of new balances to enhance their performance. As a first step, maximum load combination is used for linear structural analysis. When nonlinear effects are encountered, the analysis is extended to include the nonlinearities. Balance 1621 is typical for LaRC designed balances and was chosen for this study due to its traditional high load capacity, Figure 1. Maximum loading occurs when all 6 components are applied simultaneously with their maximum value allowed (limit load). This circumstance normally will not occur in the wind tunnel. However, if it occurs, is the balance capable of handling the loads with an acceptable factor of safety? Preliminary analysis using Pro/Mechanica indicated that this balance might experience nonlinearity. It was decided to analyze this balance by using NASTRAN so that a nonlinear analysis could be conducted. Balance 1621 was modeled and meshed in PATRAN for analysis in NASTRAN. The model from PATRAN/NASTRAN is compared to the one from Pro/Mechanica. For a complete analysis, it is necessary to consider all the load cases as well as use a dense mesh near all the edges. Because of computer limitations, it is not feasible to analyze model with the dense mesh near all edges. In the present study, the dense mesh is limited to the surface on the end of the axial sections.

Karkehabadi, R.↗
NASA NTRS2012

CRYogenic Orbital TEstbed Ground Test Article Thermal Analysis

The purpose of this study was to anchor thermal and fluid system models to CRYOTE ground test data. The CRYOTE ground test artide was jointly developed by Innovative Engineering Solutions, United Launch Alliance and NASA KSC. The test article was constructed out of a titanium alloy tank, Sapphire 77 composite skin (similar to G10), an external secondary payload adapter ring, thermal vent system, multi layer insulation and various data acquisition instrumentation. In efforts to understand heat loads throughout this system, the GTA (filled with liquid nitrogen for safety purposes) was subjected to a series of tests in a vacuum chamber at Marshall Space Flight Center. By anchoring analytical models against test data, higher fidelity thermal environment predictions can be made for future flight articles which would eventually demonstrate critical cryogenic fluid management technologies such as system chilldown, transfer, pressure control and long term storage. Significant factors that influenced heat loads included radiative environments, multi-layer insulation performance, tank fill levels and pressures and even contact conductance coefficients. This report demonstrates how analytical thermal/fluid networks were established and includes supporting rationale for specific thermal responses.

Piryk, David↗
DOE OSTI2020

An Improved Transmission Switching Algorithm for Managing Post-(N-1) Contingencies in Electricity Networks

In this presentation, we detail the shortcomings of existing transmission switching (TS) methodologies for preventing post-contingency loss of load in wide area electric power networks. Following that, we present a bi-level algorithm as an improvement to the state of the art. We show proof-of-concept level results that indicate computational viability, fast solutions, and the ability to pick the same best candidate as non computationally viable methods. Further, our method also minimizes load shedding after the contingency, thus enhancing the reliability and security of electricity supply. We also include a futuristic scenario of increased renewables and decreased natural gas sourced generators to show promising results. We grant permission for our presentation to be recorded and uploaded by the conference organizers.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2023

Multi-atom Pt and PtRu catalysts for high performance AEMFCs with ultra-low PGM content

To reduce the platinum group metal (PGM) loading in anion exchange membrane fuel cells (AEMFCs), it is important to transition to catalysts with very low PGM content, and eventually to catalysts that are completely PGM-free. Here, in this work, four supported low-PGM Pt and PtRu catalysts were prepared using a new, simple, scalable technique: Controlled Surface Tension (CST) method. CST allows for a high density of very small multi-atom clusters. Catalysts were physically characterized using a wide array of techniques and tested for their ORR and HOR activity both ex-situ and integrated into operating AEMFCs. The PGM loading was reduced by a factor of 14 while achieving comparable performance to commercial catalysts. AEMFCs were also assembled with ultralow PGM loading (0.05 mgPGM cm -2 ), where PtRu anodes were paired with Fe–N–C cathodes to achieve a specific power of 25 W/mg PGM (40 W/mg Pt ).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1996

Mechanical load induces sarcoplasmic wounding and FGF release in differentiated human skeletal muscle cultures

The transduction mechanism (or mechanisms) responsible for converting a mechanical load into a skeletal muscle growth response are unclear. In this study we have used a mechanically active tissue culture model of differentiated human skeletal muscle cells to investigate the relationship between mechanical load, sarcolemma wounding, fibroblast growth factor release, and skeletal muscle cell growth. Using the Flexcell Strain Unit we demonstrate that as mechanical load increases, so too does the amount of sarcolemma wounding. A similar relationship was also observed between the level of mechanical load inflicted on the cells and the amount of bFGF (FGF2) released into the surrounding medium. In addition, we demonstrate that the muscle cell growth response induced by chronic mechanical loading in culture can be inhibited by the presence of an antibody capable of neutralizing the biological activity of FGF. This study provides direct evidence that mechanically induced, sarcolemma wound-mediated FGF release is an important autocrine mechanism for transducing the stimulus of mechanical load into a skeletal muscle growth response.

NASA Center JSC↗
NASA NTRS1977

Save power in AC induction motors

Relatively simple and inexpensive circuitry improves power factor and reduces power dissipation in induction motors operating below full load. Electronic control loop conserves energy by reducing voltage applied to lightly loaded motor. Circuit forces motor to run at constant predetermined optimum power factor, regardless of load or line voltage variations. Solid-state switch varies voltage.

Nola, F. J.↗
DOE OSTI2023

Air Source Heat Pumps in Very Cold Climates

Air source heat pumps (ASHPs) in heating mode use a refrigeration cycle to remove heat from the outside air and transfer it into a building. Therefore, ASHPs have the potential to save energy compared to conventional heat sources that create the heat as opposed to transferring it from outside. Many cold climate ASHPs available on the market today can operate at outside temperatures of -25 degrees C (-13 degrees F) or even lower. As a result of technological advances and other factors, there is growing interest in ASHPs in cold climates, including very cold regions such as Alaska. However, guidance on the selection, installation, and operation of ASHPs in these very cold climates is limited, as significant data gaps exist regarding the performance of ASHPs in very cold environments. To address these data gaps and guide future innovations, our research team has studied the field performance of several ASHP installations in Alaska and done lab evaluations of several ASHP models using a cold chamber. While a cold chamber cannot fully reflect field conditions, it allowed for changing one variable at a time and gaining additional understanding of the behavior of ASHPs that would be difficult to gain from field studies only. This study focused on two main variables: the temperature in the chamber (representing the outdoor temperature) and the level of thermal loading of the ASHP. The results from the field as well as the lab show that ASHPs can operate with relatively high efficiency even in very cold climates if used in appropriate situations and in an appropriate way. It was found that not only the outside temperature, but also the level of thermal loading is a significant factor affecting the ASHP efficiency and needs to be carefully considered when sizing and operating ASHPs in very cold climates.

air source heat pump↗
DOE OSTI2025

Characterization of wind conditions and impact on wind loading at an operational parabolic trough concentrating solar power plant using LiDAR observations

Wind loading is a major factor influencing the structural design costs of Concentrating Solar Power (CSP) collector systems, including heliostats and parabolic troughs. Traditionally, these designs have been based on wind-tunnel data, which often fail to accurately represent the dynamic effects experienced at full scale. This study presents a first-of-its-kind experimental characterization of wind conditions within an operational parabolic-trough CSP power plant focusing specifically on using lidar observations. The lidar observations give a unique opportunity to provide insights into wind flow conditions deep within the trough arrays. Our results suggest that (1) after being blocked by the first few rows, the wind speed above the troughs recovers to 73% of its inflow magnitude as it flows further over the trough field due to enhanced turbulent mixing and (2) due to the wind speed recovery, troughs in the interior field will likely experience higher shear-induced turning moments compared those at the front. The conclusions from this work stress the importance of better understanding the wind patterns and interior wind loads when designing solar collectors and highlights the need for more interior load measurements in the future field campaigns.

17 WIND ENERGY↗
NASA NTRS1977

Mode I analysis of a cracked circular disk subject to a couple and a force

Mode 1 stress intensity coefficients were obtained for an edge-cracked disk (round compact specimen). Results for this plane elastostatic problem, obtained by a boundary collocation analysis are presented for ratios 0.35 less than A/D less than 1, where A is the crack length and D is the disk diameter. The results presented are for two complementary types of loading. By superposition of these results the stress intensity factor K sub I for any practical load line location of a pin-loaded round compact specimen can be obtained.

Gross, B.↗
DOE OSTI2020

Validation of high-fidelity ion cyclotron range of frequencies antenna coupling simulations in full 3D geometry against experiments in the ASDEX Upgrade tokamak

We address the validation of finite elements ion cyclotron range of frequencies (ICRF) antenna coupling simulation against experiments performed in the ASDEX Upgrade tokamak. Measurements of the loading resistance in ICRF-heated, magnetically-perturbed 3D plasma discharges are compared against numerical predictions of the RAPLICASOL code. To this end, the 3D induction field and the 3D density profile are modeled by concatenating the PARVMEC, BMW and EMC3-EIRENE codes. The 3D density is input to RAPLICASOL, where full-wave simulations are performed on a finite element mesh retaining full 3D geometry in the ICRF antenna model and the plasma description. The results are further compared with RAPLICASOL simulations using a 1D density profile as measured at the outboard midplane in the same experiments. We find that simulations using a 1D density profile overestimate the change in loading resistance by a factor of ~197 -248%, while simulations using the full 3D density profile are in agreement with experiments within a factor ~16%.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Overview of the results from divertor experiments with attached and detached plasmas at Wendelstein 7-X and their implications for steady-state operation

Abstract Wendelstein 7-X (W7-X), the largest advanced stellarator, is built to demonstrate high power, high performance quasi-continuous operation. Therefore, in the recent campaign, experiments were performed to prepare for long pulse operation, addressing three critical issues: the development of stable detachment, control of the heat and particle exhaust, and the impact of leading edges on plasma performance. The heat and particle exhaust in W7-X is realized with the help of an island divertor, which utilizes large magnetic islands at the plasma boundary. This concept shows very efficient heat flux spreading and favourable scaling with input power. Experiments performed to overload leading edges showed that the island divertor yields good impurity screening. A highlight of the recent campaign was a robust detachment scenario, which allowed reducing power loads even by a factor of ten. At the same time, neutral pressures at the pumping gap entrance yielded the particle removal rate close to the values required for stable density control in steady-state operation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

The three-way junction structure of the HIV-1 PBS-segment binds host enzyme important for viral infectivity

HIV-1 reverse transcription initiates at the primer binding site (PBS) in the viral genomic RNA (gRNA). Although the structure of the PBS-segment undergoes substantial rearrangement upon tRNALys3 annealing, the proper folding of the PBS-segment during gRNA packaging is important as it ensures loading of beneficial host factors. DHX9/RNA helicase A (RHA) is recruited to gRNA to enhance the processivity of reverse transcriptase. Because the molecular details of the interactions have yet to be defined, we solved the solution structure of the PBS-segment preferentially bound by RHA. Evidence is provided that PBS-segment adopts a previously undefined adenosine-rich three-way junction structure encompassing the primer activation stem (PAS), tRNA-like element (TLE) and tRNA annealing arm. Disruption of the PBS-segment three-way junction structure diminished reverse transcription products and led to reduced viral infectivity. Because of the existence of the tRNA annealing arm, the TLE and PAS form a bent helical structure that undergoes shape-dependent recognition by RHA double-stranded RNA binding domain 1 (dsRBD1). Mutagenesis and phylogenetic analyses provide evidence for conservation of the PBS-segment three-way junction structure that is preferentially bound by RHA in support of efficient reverse transcription, the hallmark step of HIV-1 replication.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

A Novel Three-Phase Oak Ridge AC / AC Converter for Wireless Mobility Energy Storage System (WMESS) Connectivity

In this study, a novel three-phase Oak Ridge ac to ac converter is introduced for wireless mobility energy storage system (WMESS) applications for grid support or ancillary service applications. The proposed topology can be used in bidirectional operation between ac grid and ac terminals of energy storage (output of the ESS inverter) by accomplishing unity power factor. Inherent merit of the technology is that it can directly merge ac input 60 Hz grid frequency with the high frequency by superimposing them with the Oak Ridge Converter (ORC) and through the wireless coils. Theoretical and simulation results are provided for 10 kW output power. The functionality of the proposed three-phase system is demonstrated with the coupling coils separated by 6 inches of air gap with the input / output of 277 V AC,RMS . The system overall design is presented, and simulation results demonstrate achieving 3% current total harmonic distortion (THD) and 0.99 power factor (PF) at full load of 10 kW wireless power transfer.

Asa, Erdem↗