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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

A theoretical analysis of steady-state photocurrents in simple silicon diodes.

A theoretical analysis solves for the steady-state photocurrents produced by a given photogeneration rate function with negligible recombination in simple silicon diodes, consisting of a uniformly doped quasi-neutral region (called "substrate" below) between a p-n junction depletion region (DR) and an ohmic contact (electrode). Special attention is given to conditions that produce "funneling" (a term used by the single-event-effects community) under steady-state conditions. Funneling occurs when carriers are generated so fast that the DR becomes flooded and partially or completely collapses. Some or nearly all of the applied voltage plus built-in potential normally across the DR is now across the substrate. This substrate voltage drop affects substrate currents. The steady-state problem can provide some qualitative insights into the more difficult transient problem. Chapter 6 discusses some similarities between the steady-state and transient problems...

Edmonds, Larry↗
DOE OSTI2026

FAST-1.2.2: A Computer Code for Thermal-Mechanical Nuclear Fuel Analysis under Steady-state and Transients

Fuel Analysis under Steady-state and Transients (FAST) is the U.S. Nuclear Regulatory Commission (NRC)’s computer code that calculates the steady-state and transient response of nuclear reactor fuel rods during long-term in-reactor burnup, anticipated operational occurrences (AOOs), design basis accidents (DBAs), and dry storage conditions. The code calculates the temperature, pressure, and deformation of a fuel rod as functions of time-dependent fuel rod power and coolant boundary conditions. The phenomena modeled by the code include heat conduction through the fuel and other materials, heat transfer from the cladding-to-coolant, cladding elastic and plastic deformation (including creep), fuel-cladding mechanical interaction, fission gas release from the fuel, rod internal pressure, void volume, and cladding oxidation. The code contains necessary material and coolant properties, as well as clad-to-coolant heat transfer correlations, for normal operation through postulated accidents and AOOs for today’s U.S.-based light water reactor (LWR) fuel designs. FAST-1.2.2 also contains preliminary materials and models for new LWR fuel concepts, such as accident tolerant fuel (ATF), and non-LWR fuel concepts such as metallic fuels for sodium fast reactors (SFRs). FAST has been developed for use on Windows and Linux operating systems. This document describes FAST-1.2.2 and is one of a series of documents on the code; the other documents detail the material properties used by FAST as well as its integral assessment to experiments and commercial data.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS2010

A Data Filter for Identifying Steady-State Operating Points in Engine Flight Data for Condition Monitoring Applications

This paper presents an algorithm that automatically identifies and extracts steady-state engine operating points from engine flight data. It calculates the mean and standard deviation of select parameters contained in the incoming flight data stream. If the standard deviation of the data falls below defined constraints, the engine is assumed to be at a steady-state operating point, and the mean measurement data at that point are archived for subsequent condition monitoring purposes. The fundamental design of the steady-state data filter is completely generic and applicable for any dynamic system. Additional domain-specific logic constraints are applied to reduce data outliers and variance within the collected steady-state data. The filter is designed for on-line real-time processing of streaming data as opposed to post-processing of the data in batch mode. Results of applying the steady-state data filter to recorded helicopter engine flight data are shown, demonstrating its utility for engine condition monitoring applications.

Simon, Donald L.↗
NASA NTRS1978

Effects of grazing flow on the steady-state flow resistance and acoustic impedance of thin porous-faced liners

The effects of grazing flow on the steady state flow resistance and acoustic impedance of seven Feltmetal and three Rigimesh thin porous faced liners were studied. The steady-state flow resistance of the ten specimens was measured using standard fluid mechanical experimental techniques. The acoustic impedance was measured using the two microphone method. The principal findings of the study are that the effects of grazing flow were measured and found to be small; small differences were measured between steady-state and acoustic resistance, and a semi-empirical model was derived that correlated the steady-state resistance data of the seven Feltmetal liners and the face sheet reactance of both the Feltmetal and Rigimesh liners.

Hersh, A. S.↗
NASA NTRS1975

DYNGEN: A program for calculating steady-state and transient performance of turbojet and turbofan engines

The DYNGEN, a digital computer program for analyzing the steady state and transient performance of turbojet and turbofan engines, is described. The DYNGEN is based on earlier computer codes (SMOTE, GENENG, and GENENG 2) which are capable of calculating the steady state performance of turbojet and turbofan engines at design and off-design operating conditions. The DYNGEN has the combined capabilities of GENENG and GENENG 2 for calculating steady state performance; to these the further capability for calculating transient performance was added. The DYNGEN can be used to analyze one- and two-spool turbojet engines or two- and three-spool turbofan engines without modification to the basic program. A modified Euler method is used by DYNGEN to solve the differential equations which model the dynamics of the engine. This new method frees the programmer from having to minimize the number of equations which require iterative solution. As a result, some of the approximations normally used in transient engine simulations can be eliminated. This tends to produce better agreement when answers are compared with those from purely steady state simulations. The modified Euler method also permits the user to specify large time steps (about 0.10 sec) to be used in the solution of the differential equations. This saves computer execution time when long transients are run. Examples of the use of the program are included, and program results are compared with those from an existing hybrid-computer simulation of a two-spool turbofan.

Sellers, J. F.↗
NASA NTRS1993

On the accuracy of limiters and convergence to steady state solutions

This paper addresses the practical problem of obtaining convergence to steady state solutions when limiters are used in conjunction with upwind schemes on unstructured grids. The base scheme forms a gradient and limits it by imposing monotonicity conditions in the reconstruction stage. It is shown by analysis in one dimension that such an approach leads to various schemes meeting TVD requirements in one dimension. It is further shown that these formally second order accurate schemes are less than second order accurate in practice because of the action of the limiter function in smooth regions of the solution. Modifications are proposed to the limiter that restore the second order accuracy. In multiple dimensions these schemes produce steady state solutions that are monotone and devoid of oscillations. However, convergence stalls after a few orders of reduction in the residual. With the modified limiter, on the other hand, it is shown that converged steady state solutions can be obtained.

Venkatakrishnan, V.↗
NASA NTRS1995

A theoretical analysis of steady-state photocurrents in simple silicon diodes

A theoretical analysis solves for the steady-state photocurrents produced by a given photo-generation rate function with negligible recombination in simple silicon diodes, consisting of a uniformly doped quasi-neutral region (called 'substrate' below) adjacent to a p-n junction depletion region (DR). Special attention is given to conditions that produce 'funneling' (a term used by the single-eventeffects community) under steady-state conditions. Funneling occurs when carriers are generated so fast that the DR becomes flooded and partially or completely collapses. Some or nearly all of the applied voltage, plus built-in potential normally across the DR, is now across the substrate. This substrate voltage drop affects substrate currents. The steady-state problem can provide some qualitative insights into the more difficult transient problem. First, it was found that funneling can be induced from a distance, i.e., from carriers generated at locations outside of the DR. Secondly, it was found that the substrate can divide into two subregions, with one controlling substrate resistance and the other characterized by ambipolar diffusion. Finally, funneling was found to be more difficult to induce in the p(sup +)/n diode than in the n(sup +)/p diode. The carrier density exceeding the doping density in the substrate and at the DR boundary is not a sufficient condition to collapse a DR.

Edmonds, L.↗
NASA NTRS1974

Steady-state decoupling and design of linear multivariable systems

A constructive criterion for decoupling the steady states of a linear time-invariant multivariable system is presented. This criterion consists of a set of inequalities which, when satisfied, will cause the steady states of a system to be decoupled. Stability analysis and a new design technique for such systems are given. A new and simple connection between single-loop and multivariable cases is found. These results are then applied to the compensation design for NASA STOL C-8A aircraft. Both steady-state decoupling and stability are justified through computer simulations.

Thaler, G. J.↗
NASA NTRS1997

Steady-State Cycle Deck Launcher Developed for Numerical Propulsion System Simulation

One of the objectives of NASA's High Performance Computing and Communications Program's (HPCCP) Numerical Propulsion System Simulation (NPSS) is to reduce the time and cost of generating aerothermal numerical representations of engines, called customer decks. These customer decks, which are delivered to airframe companies by various U.S. engine companies, numerically characterize an engine's performance as defined by the particular U.S. airframe manufacturer. Until recently, all numerical models were provided with a Fortran-compatible interface in compliance with the Society of Automotive Engineers (SAE) document AS681F, and data communication was performed via a standard, labeled common structure in compliance with AS681F. Recently, the SAE committee began to develop a new standard: AS681G. AS681G addresses multiple language requirements for customer decks along with alternative data communication techniques. Along with the SAE committee, the NPSS Steady-State Cycle Deck project team developed a standard Application Program Interface (API) supported by a graphical user interface. This work will result in Aerospace Recommended Practice 4868 (ARP4868). The Steady-State Cycle Deck work was validated against the Energy Efficient Engine customer deck, which is publicly available. The Energy Efficient Engine wrapper was used not only to validate ARP4868 but also to demonstrate how to wrap an existing customer deck. The graphical user interface for the Steady-State Cycle Deck facilitates the use of the new standard and makes it easier to design and analyze a customer deck. This software was developed following I. Jacobson's Object-Oriented Design methodology and is implemented in C++. The AS681G standard will establish a common generic interface for U.S. engine companies and airframe manufacturers. This will lead to more accurate cycle models, quicker model generation, and faster validation leading to specifications. The standard will facilitate cooperative work between industry and NASA. The NPSS Steady-State Cycle Deck team released a batch version of the Steady-State Cycle Deck in March 1996. Version 1.1 was released in June 1996. During fiscal 1997, NPSS accepted enhancements and modifications to the Steady-State Cycle Deck launcher. Consistent with NPSS' commercialization plan, these modifications will be done by a third party that can provide long-term software support.

VanDrei, Donald E.↗
NASA NTRS1992

Numerical computation of steady-state acoustic disturbances in flow

Two time domain methods for computing two dimensional steady-state acoustic disturbances propagating through internal subsonic viscous flow fields in the presence of variable area are investigated. The first method solves the Navier-Stokes equations for the combined steady and acoustic field together and subtracts the steady flow to obtain the acoustic field. The second method solves a system of perturbation equations to obtain the acoustic disturbances, making use of a separate steady flow computation as input to the system. In each case the periodic steady-state acoustic fluctuations are obtained numerically on a supercomputer using a second order unsplit explicit MacCormack predictor-corrector method. Results show that the first method is not very effective for computing acoustic disturbances of even moderate amplitude. It appears that more accurate steady flow algorithms are required for this method to succeed. On the other hand, linear and nonlinear acoustic disturbances extracted from the perturbation approach are shown to exhibit expected behavior for the problems considered. It is also found that inflow boundary conditions for an equivalent uniform duct can be successfully applied to a nonuniform duct to obtain steady-state acoustic disturbances.

Watson, W. R.↗
NASA NTRS1972

Unipolar interaction of Mercury with the solar wind - The steady state bow shock problem.

The steady state electromagnetic interaction of the solar wind with the planet Mercury is computed for a spectrum of electrical conductivity functions using the assumption that no atmosphere or planetary magnetic field prohibits the direct interaction. The form of the induction is described by the unipolar effect and corresponds to the zero frequency limit of a transverse magnetic (TM) mode. Calculations are included to determine the effective surface temperature of the planet. These calculations include the apparent motion of the sun in the Hermean sky. It is shown that a significant interaction, detectable by a space probe, is plausible for reasonable conductivity functions. The strength of the interaction is considered in terms of the subsurface thermal gradient, and computations are given relating the strength of the solar wind interaction with the conductivity parameters.

Colburn, D. S.↗
NASA NTRS1992

Role of irregular otolith afferents in the steady-state nystagmus during off-vertical axis rotation

1. During constant velocity off-vertical axis rotations (OVAR) in the dark a compensatory ocular nystagmus is present throughout rotation despite the lack of a maintained signal from the semicircular canals. Lesion experiments and canal plugging have attributed the steady-state ocular nystagmus during OVAR to inputs from the otolith organs and have demonstrated that it depends on an intact velocity storage mechanism. 2. To test whether irregularly discharging otolith afferents play a crucial role in the generation of the steady-state eye nystagmus during OVAR, we have used anodal (inhibitory) currents bilaterally to selectively and reversibly block irregular vestibular afferent discharge. During delivery of DC anodal currents (100 microA) bilaterally to both ears, the slow phase eye velocity of the steady-state nystagmus during OVAR was reduced or completely abolished. The disruption of the steady-state nystagmus was transient and lasted only during the period of galvanic stimulation. 3. To distinguish a possible effect of ablation of the background discharge rates of irregular vestibular afferents on the velocity storage mechanism from specific contributions of the dynamic responses from irregular otolith afferents to the circuit responsible for the generation of the steady-state nystagmus, bilateral DC anodal galvanic stimulation was applied during optokinetic nystagmus (OKN) and optokinetic afternystagmus (OKAN). No change in OKN and OKAN was observed.(ABSTRACT TRUNCATED AT 250 WORDS).

NASA Discipline Neuroscience↗
NASA NTRS1995

A steady-state Kalman filter for assimilating data from a single polar orbiting satellite

A steady-state scheme for data assimilation in the context of a single, short period (relative to a day), sun-synchronous, polar-orbiting satellite is examined. If the satellite takes observations continuously, the gains, which are the weights for blending observations and predictions together, are steady in time. For a linear system forced by random noise, the optimal steady-state gains (Wiener gains) are equivalent to those of a Kalman filter. Computing the Kalman gains increases the computational cost of the model by a large factor, but computing the Wiener gains does not. The latter are computed by iteration using prior estimates of the gains to assimilate simulated observations of one run of the model, termed 'truth' into another run termed 'prediction'. At each stage, the prediction errors form the basis for the next estimate of the gains. Steady state is achieved after three or four iterations. Further simplification is achieved by making the gains depend on longitudinal distance from the observation point, not on absolute longitude. For a single-layer primitive equation model, the scheme works well even if only the mass field is observed but not the velocity field. Although the scheme was developed for Mars Observer, it should be applicable to data retrieved from Earth atmosphere satellites, for example, UARS.

Banfield, Don↗
NASA NTRS1977

Effects of grazing flow on the steady-state flow resistance and acoustic impedance of thin porous-faced liners

The results of an investigation of the effects of grazing flow on the steady-state flow resistance and acoustic impedance of seven Feltmetal and three Rigimesh thin porous-faced liners are presented. The acoustic impedance was measured using the two-microphone method. The principal findings of the study are (1) the effects of grazing flow were measured and found to be negligible, (2) negligible differences were measured between steady-state and acoustic resistance, (3) a semi-empirical model was derived that correlated both the steady-state resistance data and the acoustic impedance data of the seven Feltmetal liners. These findings suggest that nongrazing flow steady-state flow resistance tests could provide considerable insight into the acoustic behavior of porous liners in a grazing flow environment.

Hersh, A. D.↗
DOE OSTI2025

Initial steady-state core simulation capability or thermal and pool-type molten salt reactors, coupling reactor physics, thermal-hydraulics, and evolving chemistry

This report presents the development and validation of an initial steady-state multiphysics capability for molten salt reactors (MSRs) under the Nuclear Energy Advanced Modeling and Simulation (NEAMS) program in Fiscal Year 2025. The framework integrates neutronics, thermal-hydraulics, species transport, and thermochemistry to capture the coupled dynamics of liquid-fueled systems. Implementation and testing were performed on two representative designs: the Molten Salt Reactor Experiment (MSRE), a thermal-spectrum, channeled-flow reactor, and the Lotus Molten Salt Reactor (L-MSR), a fast-spectrum, pool-type reactor. The modeling suite employs Griffin for reactor physics and depletion, Pronghorn and SAM for thermal-hydraulics, Thermochimica for chemistry, and Saline for thermophysical properties, with benchmarking and validation carried out against historical MSRE data, experimental flow-loop measurements, and reference depletion calculations from Monte Carlo codes. The framework demonstrated the ability to reproduce key reactor behaviors including temperature feedback, reactivity losses, delayed neutron precursor transport, xenon poisoning, and redox potential evolution. The results confirm the feasibility and accuracy of the coupled models in predicting steady-state and selected transient MSR behaviors. This latter ones are used in this report as a proxy indicating that the steady-state models from which the transient starts are accurate. For MSRE, validation showed good agreement with pump start-up and natural circulation tests, while for the L-MSR, benchmarking confirmed hydraulic calibration and consistency of neutronics–thermal coupling. The tools also provided new insights into species transport, noble metal deposition, and salt solidification dynamics. On the Xenon transport front, the code is validated against the steady state Xenon poisoining measurement and showed good agreement with the experimental value. Identified areas for future work include advanced void transport modeling, three-dimensional simulations, improved alloy corrosion models, and tighter integration with high-fidelity Monte Carlo codes. These developments provide a foundation for high-fidelity MSR simulations that can support reactor design optimization, safety assessments, and long-term operational strategies.

42 - ENGINEERING↗
NASA NTRS2014

Current Pressure Transducer Application of Model-based Prognostics Using Steady State Conditions

Prognostics is the process of predicting a system's future states, health degradation/wear, and remaining useful life (RUL). This information plays an important role in preventing failure, reducing downtime, scheduling maintenance, and improving system utility. Prognostics relies heavily on wear estimation. In some components, the sensors used to estimate wear may not be fast enough to capture brief transient states that are indicative of wear. For this reason it is beneficial to be capable of detecting and estimating the extent of component wear using steady-state measurements. This paper details a method for estimating component wear using steady-state measurements, describes how this is used to predict future states, and presents a case study of a current/pressure (I/P) Transducer. I/P Transducer nominal and off-nominal behaviors are characterized using a physics-based model, and validated against expected and observed component behavior. This model is used to map observed steady-state responses to corresponding fault parameter values in the form of a lookup table. This method was chosen because of its fast, efficient nature, and its ability to be applied to both linear and non-linear systems. Using measurements of the steady state output, and the lookup table, wear is estimated. A regression is used to estimate the wear propagation parameter and characterize the damage progression function, which are used to predict future states and the remaining useful life of the system.

Fault Estimation↗