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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Opportunities for supersonic performance gains through non-linear aerodynamics

This paper contains a number of examples wherein basic aerodynamic shapes are shown to achieve improved performance when non-linear effects are taken into account. Analytical, numerical, and experimental results have all been used to demonstrate this conclusion. Improvements in both zero lift drag and drag due to lift have been identified. The results show that the exploitation of these non-linear aerodynamic effects may be a key ingredient of future supersonic aircraft.

Mason, W. H.↗
NASA NTRS2013

Performance Gains of Propellant Management Devices for Liquid Hydrogen Depots

This paper presents background, experimental design, and preliminary experimental results for the liquid hydrogen bubble point tests conducted at the Cryogenic Components Cell 7 facility at the NASA Glenn Research Center in Cleveland, Ohio. The purpose of the test series was to investigate the parameters that affect liquid acquisition device (LAD) performance in a liquid hydrogen (LH2) propellant tank, to mitigate risk in the final design of the LAD for the Cryogenic Propellant Storage and Transfer Technology Demonstration Mission, and to provide insight into optimal LAD operation for future LH2 depots. Preliminary test results show an increase in performance and screen retention over the low reference LH2 bubble point value for a 325 2300 screen in three separate ways, thus improving fundamental LH2 LAD performance. By using a finer mesh screen, operating at a colder liquid temperature, and pressurizing with a noncondensible pressurant gas, a significant increase in margin is achieved in bubble point pressure for LH2 screen channel LADs.

Hartwig, Jason W.↗
NASA NTRS1973

Performance gains by using heated natural-gas fuel in an annular turbojet combustor

A full-scale annular turbojet combustor was tested with natural gas fuel heated from ambient temperature to 800 K (980 F). In all tests, heating the fuel improved combustion efficiency. Two sets of gaseous fuel nozzles were tested. Combustion instabilities occurred with one set of nozzles at two conditions: one where the efficiency approached 100 percent with the heated fuel; the other where the efficiency was very poor with the unheated fuel. The second set of nozzles exhibited no combustion instability. Altitude relight tests with the second set showed that relight was improved and was achievable at essentially the same condition as blowout when the fuel temperature was 800 K (980 F).

Marchionna, N. R.↗
DOE OSTI2018

Human performance benefits gained by dynamic instructions compared to smart PDFs

Human performance benefits gained by dynamic instructions compared to smart PDFs In recent years multiple nuclear utilities have deployed an electronic work management solution to replace the traditional paper-based processes. There are many benefits of electronic work management solutions compared to paper processes, such as a more streamlined review and approval process of work packages and a better way to track and resolve any potential bottlenecks causing delays in the review process. These benefits have been recognized where electronic work management solutions have been successfully deployed. However the utilities also hoped the new solution would help the field worker conduct his/her job more efficiently, correctly, and safely. Unfortunately, the industry is now realizing that the deployed solutions did not fully help them reach that goal. The electronic work management solutions present the work instructions as an electronic copy (i.e., a portable document format (PDF)) of the paper instruction. The PDF versions used in these electronic work management solutions have some ability for data input, notes, and mark-ups, but are unable to provide many additional benefits compared to using paper. In fact, conducting work using a PDF on a tablet can be more cumbersome than with a paper instruction. For example, flipping back and forth in a paper instruction can be time consuming, but it is not at all as frustrating as scrolling back and forth on a tablet or continuously having to navigate between tabs. The researchers at Idaho National Laboratory (INL) approached the next step beyond smart PDFs from a human factors perspective. In close collaboration with multiple utilities they investigated how to present instruction content and how to design the interaction with the instruction to improve the workers performance and efficiency. Their solution is a dynamic presentation of the instruction that guides the worker through the correct path as well as ensuring the worker is on the correct component. The solution also automatically validates input and provides guidance if unexpected conditions are identified. A well-designed solution has the opportunity to vastly reduce the risk of human errors in the field, such as preventing actions on incorrect component or unintentionally skipping steps. The human factors researchers at INL leveraged their expertise, existing human performance tools, and a great amount of involvement from field workers in multiple utilities to develop and evaluate design concepts that will provide the human performance and efficiency benefits that the electronic work management solutions fall short to deliver. This paper will describe in detail how these new design concepts improve human performance.

47 OTHER INSTRUMENTATION↗
NASA NTRS1995

Solar thermal upper stage: Economic advantage and development status

A solar thermal upper stage (STUS) is envisioned as a propulsive concept for the future. The STUS will be used for low Earth orbit (LEO) to geostationary-Earth orbit (GEO) transfer and for planetary exploration missions. The STUS offers significant performance gains over conventional chemical propulsion systems. These performance gains translate into a more economical, more efficient method of placing useful payloads in space and maximizing the benefits derived from space activity. This paper will discuss the economical advantages of an STUS compared to conventional chemical propulsion systems, the potential market for an STUS, and the recent activity in the development of an STUS. The results of this assessment combined with the performance gains, will provide a strong justification for the development of an STUS.

Adams, Alan M.↗
DOE OSTI2011

Discriminating quantum-optical beam-splitter channels with number-diagonal signal states: Applications to quantum reading and target detection

We consider the problem of distinguishing, with minimum probability of error, two optical beam-splitter channels with unequal complex-valued reflectivities using general quantum probe states entangled over M signal and M' idler mode pairs of which the signal modes are bounced off the beam splitter while the idler modes are retained losslessly. We obtain a lower bound on the output state fidelity valid for any pure input state. We define number-diagonal signal (NDS) states to be input states whose density operator in the signal modes is diagonal in the multimode number basis. For such input states, we derive series formulas for the optimal error probability, the output state fidelity, and the Chernoff-type upper bounds on the error probability. For the special cases of quantum reading of a classical digital memory and target detection (for which the reflectivities are real valued), we show that for a given input signal photon probability distribution, the fidelity is minimized by the NDS states with that distribution and that for a given average total signal energy N{sub s}, the fidelity is minimized by any multimode Fock state with N{sub s} total signal photons. For reading of an ideal memory, it is shown that Fock state inputs minimize the Chernoff bound. For target detection under high-loss conditions, a no-go result showing the lack of appreciable quantum advantage over coherent state transmitters is derived. A comparison of the error probability performance for quantum reading of number state and two-mode squeezed vacuum state (or EPR state) transmitters relative to coherent state transmitters is presented for various values of the reflectances. While the nonclassical states in general perform better than the coherent state, the quantitative performance gains differ depending on the values of the reflectances. The experimental outlook for realizing nonclassical gains from number state transmitters with current technology at moderate to high values of the reflectances is argued to be good.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1993

Using Transparent Informed Prefetching (TIP) to reduce file read latency

As processor performance gains continue to outstrip Input/Output gains, I/O performance is becoming critical to overall system performance. File read latency is the most significant bottleneck for high performance I/O. Other aspects of I/O performance benefit from recent advances in disk bandwidth and throughput resulting from disk arrays, and in write performance derived from buffered write behind and the Log-structured File System. The access gap problem limiting improvements in read latency is exacerbated by distributed file systems operating over networks with diverse bandwidth. Focus is on extending the power of caching and prefetching to reduce file read latencies by exploiting hints from high-levels of a system. Such Transparent Informed Prefetching, TIP, and its benefits are described. It is argued that hints that disclose high level knowledge are a means for transferring optimization information across, without violating, module boundaries. How TIP can be used to convert the high throughput of new technologies such as disk arrays and log-structured file systems into low latency for applications is discussed. Our preliminary experiments show reductions in wall - clock execution time of 13 percent and 20 percent for a multiple module compilation tool (make) accessing data on a local disk and remote Coda file server, respectively, and a reduction of 30 percent for a text search (grep) remotely accessing many small files.

Patterson, R. H.↗
NASA NTRS1997

Numerical Assessment of Four-Port Through-Flow Wave Rotor Cycles with Passage Height Variation

The potential for improved performance of wave rotor cycles through the use of passage height variation is examined. A Quasi-one-dimensional CFD code with experimentally validated loss models is used to determine the flowfield in the wave rotor passages. Results indicate that a carefully chosen passage height profile can produce substantial performance gains. Numerical performance data are presented for a specific profile, in a four-port, through-flow cycle design which yielded a computed 4.6% increase in design point pressure ratio over a comparably sized rotor with constant passage height. In a small gas turbine topping cycle application, this increased pressure ratio would reduce specific fuel consumption to 22% below the un-topped engine; a significant improvement over the already impressive 18% reductions predicted for the constant passage height rotor. The simulation code is briefly described. The method used to obtain rotor passage height profiles with enhanced performance is presented. Design and off-design results are shown using two different computational techniques. The paper concludes with some recommendations for further work.

Paxson, D. E.↗
DOE OSTI2020

Roles of bandgrading, lifetime, band alignment, and carrier concentration in high-efficiency CdSeTe solar cells

CdSeTe alloying has significantly increased the efficiency of CdTe-based solar technology. Here, computational modeling compares how different CdSeTe bandgrading, carrier lifetimes, band alignment, and carrier concentrations contribute to transport, recombination, and performance. We find that the gain in photocurrent caused by bandgap narrowing alone is insufficient to describe experimental efficiency gains. Performance can be increased by adjusting CdSeTe compositions and bandgrading depths. However, these performance gains are small relative to the contributions of enhanced lifetime by Se alloying, which can explain record cell efficiency gains with minimal open-circuit voltage loss despite significant bandgap narrowing. Similarly, CdSeTe band alignment shifts can significantly increase performance if front interface recombination is prevalent. For a wide range of CdSeTe grading profiles, the hole density is a critical component to achieve efficiencies exceeding 25%.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Strategies for Energy-Efficient Resource Management of Hybrid Programming Models

Many scientific applications are programmed using hybrid programming models that use both message passing and shared memory, due to the increasing prevalence of large-scale systems with multicore, multisocket nodes. Previous work has shown that energy efficiency can be improved using software-controlled execution schemes that consider both the programming model and the power-aware execution capabilities of the system. However, such approaches have focused on identifying optimal resource utilization for one programming model, either shared memory or message passing, in isolation. The potential solution space, thus the challenge, increases substantially when optimizing hybrid models since the possible resource configurations increase exponentially. Nonetheless, with the accelerating adoption of hybrid programming models, we increasingly need improved energy efficiency in hybrid parallel applications on large-scale systems. In this work, we present new software-controlled execution schemes that consider the effects of dynamic concurrency throttling (DCT) and dynamic voltage and frequency scaling (DVFS) in the context of hybrid programming models. Specifically, we present predictive models and novel algorithms based on statistical analysis that anticipate application power and time requirements under different concurrency and frequency configurations. Furthermore, we apply our models and methods to the NPB MZ benchmarks and selected applications from the ASC Sequoia codes. Overall, we achieve substantial energy savings (8.74 percent on average and up to 13.8 percent) with some performance gain (up to 7.5 percent) or negligible performance loss.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2015

Accelerated application development: The ORNL Titan experience

The use of computational accelerators such as NVIDIA GPUs and Intel Xeon Phi processors is now widespread in the high performance computing community, with many applications delivering impressive performance gains. However, programming these systems for high performance, performance portability and software maintainability has been a challenge. In this paper we discuss experiences porting applications to the Titan system. Titan, which began planning in 2009 and was deployed for general use in 2013, was the first multi-petaflop system based on accelerator hardware. To ready applications for accelerated computing, a preparedness effort was undertaken prior to delivery of Titan. In this paper we report experiences and lessons learned from this process and describe how users are currently making use of computational accelerators on Titan.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2024

TunIO: An AI-powered Framework for Optimizing HPC I/O

I/O operations are a known performance bottleneck of HPC applications. To achieve good performance, users often employ an iterative multistage tuning process to find an optimal I/O stack configuration. However, an I/O stack contains multiple layers, such as high-level I/O libraries, I/O middleware, and parallel file systems, and each layer has many parameters. These parameters and layers are entangled and influenced by each other. The tuning process is time-consuming and complex. In this work, we present TunIO, an AI-powered I/O tuning framework that implements several techniques to balance the tuning cost and performance gain, including tuning the high-impact parameters first. Furthermore, TunIO analyzes the application source code to extract its I/O kernel while retaining all statements necessary to perform I/O. It utilizes a smart selection of high-impact configuration parameters of the given tuning objective. Finally, it uses a novel Reinforcement Learning (RL)-driven early stopping mechanism to balance the cost and performance gain. Experimental results show that TunIO leads to a reduction of up to ≈73% in tuning time while achieving the same performance gain when compared to H5Tuner. It achieves a significant performance gain/cost of 208.4 MBps/min (I/O bandwidth for each minute spent in tuning) over existing approaches under our testing.

Rajesh, Neeraj↗
NASA NTRS1987

Trellis coding with asymmetric modulations

Through the asymmetric design of signal constellations, it often becomes possible to obtain a performance gain over conventional symmetric constellations combined with trellis coding. Attention is given to the joint design of n/(n+1) trellis codes and asymmetric 2 exp (n+1)-point signal constellations having no bandwidth expansion relative to an uncoded 2 exp n-point symmetric signal set. The asymptotic performance gains due to coding and asymmetry are explained in terms of the minimum free Euclidean distance of the trellis; examples are given which show the performance gain due to the asymmetry of the signal set. Since asymmetry does not affect bandwidth or power requirements, these improvements come at little or no cost.

Divsalar, Dariush↗
DOE OSTI2016

Magnet system optimization for segmented adaptive-gap in-vacuum undulator

Segmented Adaptive Gap in-vacuum Undulator (SAGU), in which different segments have different gaps and periods, promises a considerable spectral performance gain over a conventional undulator with uniform gap and period. According to calculations, this gain can be comparable to the gain achievable with a superior undulator technology (e.g. a room-temperature in-vacuum hybrid SAGU would perform as a cryo-cooled hybrid in-vacuum undulator with uniform gap and period). However, for reaching the high spectral performance, SAGU magnetic design has to include compensation of kicks experienced by the electron beam at segment junctions because of different deflection parameter values in the segments. Here we show that such compensation to large extent can be accomplished by using a passive correction, however, simple correction coils are nevertheless required as well to reach perfect compensation over a whole SAGU tuning range. Magnetic optimizations performed with Radia code, and the resulting undulator radiation spectra calculated using SRW code, demonstrating a possibility of nearly perfect correction, are presented.

47 OTHER INSTRUMENTATION↗
NASA NTRS1997

Concatenated Coding Using Trellis-Coded Modulation

In the late seventies and early eighties a technique known as Trellis Coded Modulation (TCM) was developed for providing spectrally efficient error correction coding. Instead of adding redundant information in the form of parity bits, redundancy is added at the modulation stage thereby increasing bandwidth efficiency. A digital communications system can be designed to use bandwidth-efficient multilevel/phase modulation such as Amplitude Shift Keying (ASK), Phase Shift Keying (PSK), Differential Phase Shift Keying (DPSK) or Quadrature Amplitude Modulation (QAM). Performance gain can be achieved by increasing the number of signals over the corresponding uncoded system to compensate for the redundancy introduced by the code. A considerable amount of research and development has been devoted toward developing good TCM codes for severely bandlimited applications. More recently, the use of TCM for satellite and deep space communications applications has received increased attention. This report describes the general approach of using a concatenated coding scheme that features TCM and RS coding. Results have indicated that substantial (6-10 dB) performance gains can be achieved with this approach with comparatively little bandwidth expansion. Since all of the bandwidth expansion is due to the RS code we see that TCM based concatenated coding results in roughly 10-50% bandwidth expansion compared to 70-150% expansion for similar concatenated scheme which use convolution code. We stress that combined coding and modulation optimization is important for achieving performance gains while maintaining spectral efficiency.

Thompson, Michael W.↗
DOE OSTI2023

A parallel p ‐adaptive discontinuous Galerkin method for the Euler equations with dynamic load‐balancing on tetrahedral grids

Abstract A novel p ‐adaptive discontinuous Galerkin (DG) method has been developed to solve the Euler equations on three‐dimensional tetrahedral grids. Hierarchical orthogonal basis functions are adopted for the DG spatial discretization while a third order TVD Runge‐Kutta method is used for the time integration. A vertex‐based limiter is applied to the numerical solution in order to eliminate oscillations in the high order method. An error indicator constructed from the solution of order and is used to adapt degrees of freedom in each computational element, which remarkably reduces the computational cost while still maintaining an accurate solution. The developed method is implemented with under the Charm++ parallel computing framework. Charm++ is a parallel computing framework that includes various load‐balancing strategies. Implementing the numerical solver under Charm++ system provides us with access to a suite of dynamic load balancing strategies. This can be efficiently used to alleviate the load imbalances created by p ‐adaptation. A number of numerical experiments are performed to demonstrate both the numerical accuracy and parallel performance of the developed p ‐adaptive DG method. It is observed that the unbalanced load distribution caused by the parallel p ‐adaptive DG method can be alleviated by the dynamic load balancing from Charm++ system. Due to this, high performance gain can be achieved. For the testcases studied in the current work, the parallel performance gain ranged from 1.5× to 3.7×. Therefore, the developed p ‐adaptive DG method can significantly reduce the total simulation time in comparison to the standard DG method without p ‐adaptation.

97 MATHEMATICS AND COMPUTING↗