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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Research study on stabilization and control: Modern sampled-data control theory. Design of the large space telescope system

Conditions of self-sustained oscillations in a two-axis model of the nonlinear LST system are studied. The describing function of the CMG frictional nonlinearity of the LST system is used for the analysis, as well as continuous-data and discrete-data models of the simplified LST control system. A numerical-iterative method is described for the analysis of the two-axis system. Approximation methods and the direct plotting of the stability equation are implemented in the study. It is shown that although the dynamics of the two axes are identical, the amplitudes of self-sustained oscillations in the two axes may in principle be different. Analysis shows that the LST systems are of equal amplitudes but with 180-degree phase shift.

Kuo, B. C.↗
NASA NTRS1982

Finite-Element Analysis of Forced Convection and Conduction

TAP2 thermal-analysis program was developed as part of research on finite element methodology for thermal analysis of convectively cooled structures, such as scramjet engines and hypersonic aircraft. Program simplifies computations when both structural and thermal analyses are required and is suited for thermal analysis of nuclear reactors and solar-panel heating systems.

Wieting, A. R.↗
DOE OSTI2020

Calculation of mode lifetimes in weakly anharmonic solids using self-consistent ensemble eigenstates of the Liouvillian

Recent schemes for the efficient calculation of vibrational mode frequencies and lifetimes in weakly anharmonic systems such as solid crystal structures have shown promise, with simple relationships being observed between low order moments of the Liouvillian and the observed lifetime. While only shown empirically, two parameters seemed sufficient to determine the lifetime to high accuracy over a large range of temperatures for a few simple low degree of freedom models and a Lennard–Jones solid. In this paper we analytically reproduce the numerically observed relationship using a few generally applicable assumptions about the density of states. This advance is made by studying the autocorrelation based on an “ensemble eigenstate” of the Liouvillian. We propose the use of this ensemble eigenstate as the basis for autocorrelations to simplify calculations in richer systems. Finally, an analysis is also performed of the relationship between canonical and microcanonical autocorrelation functions and a long standing error in the long time behavior of such functions originally presented by Sen, Sinkovits, and Chakravarti is corrected.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Unconventional nonlinear Hall effects in twisted multilayer 2D materials

We present the first investigation of unusual nonlinear Hall effects in twisted multilayer 2D materials. Contrary to expectations, our study shows that these nonlinear effects are not merely extensions of their monolayer counterparts. Instead, we find that stacking order and pairwise interactions between neighboring layers, mediated by Berry curvatures, play a pivotal role in shaping their collective nonlinear optical response. By combining large-scale Real-Time Time-Dependent Density Functional Theory (RT-TDDFT) simulations with model Hamiltonian analyses, we demonstrate a remarkable second-harmonic transverse response in hexagonal boron nitride four-layers, even in cases where the total Berry curvature cancels out. Furthermore, our symmetry analysis of the layered structures provides a simplified framework for predicting nonlinear responses in multilayer materials in general. Our investigation challenges the prevailing understanding of nonlinear optical responses in layered materials and opens new avenues for the design and development of advanced materials with tailored optical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Direct numerical simulation of supercritical oxy-methane mixing layers with CO 2 substituted counterparts

Direct numerical simulations (DNS) of temporally developing, three dimensional, CH 4 /CO 2 , CH 4 /O 2 and CO 2 /O 2 mixing layers, are conducted at a supercritical pressure of 300 atm. To effectively model the supercritical regime, the employed formulation includes the compressible form of the governing equations, the cubic Peng-Robinson equation of state and a generalized formulation for heat and mass flux vectors derived from non-equilibrium thermodynamics and fluctuation theory. A linear inviscid stability analysis is also performed for each case, to determine its most unstable wavelength. Flow visualizations reveal the presence of high density gradient magnitude regions for all three mixing layers, with conditional averages indicating increased presence of heavier fluid species within these regions. No significant departures are observed from perfect gas behavior, with compressibility factors very close to unity for all three mixing cases. Applicability of presumed probability density function methods (PDF) is examined for the three supercritical mixing layers. An a priori analysis is also conducted to investigate various simplifying assumptions employed in modeling various subgrid scale (SGS) flux models. Two additional terms are identified in the large eddy simulations (LES) equations, the gradient of SGS contribution of pressure in the momentum equation and the gradient of SGS contribution of heat flux in energy equation, whose magnitudes are similar and comparable with their respective resolved terms. The performance of the scale similarity model to represent these additional terms is investigated. Lastly, the performance of Smagorinsky, gradient and scale similarity models are also investigated.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Spring 2020 Dissertation Update [Slides]

An update is provided on the dissertation underway and what has been learned thus far. Work thus far: Developed analytic models for each region in the spent fuel cask – Used to identify and explain physical processes which create features in detailed casks; Developed simplified computational models to identify details not seen in analytic models; SC were calculated in the fuel region; The difference in SC’s between the analytic model and the simplified computational model were identified. Outstanding issues: Analysis of analytic models in stainless steel and carbon steel – These materials are thin and have few features (just the slope); Discrepancies between absorption SC’s in fuel; Create a test problem to show the effects of the high energy resonances in the fuel region. Future Work: Sensitivity analysis needs to be continued through the cask – The detailed model will be added to the remaining materials; Sensitivity analysis paper; and, Addressing outstanding issues.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1970

Man-machine interactive system simplifies computer-aided circuit design

Langley interactive computerized circuit analysis capability /LICCA/ enables designer to draw electronic circuit diagrams on cathode ray tube screen. This information is submitted as input to user-selected circuit analysis program. LICCA accommodates binary logic circuits and circuits with discrete components, and monitors operator's instructions to detect errors.

Bavuso, S. J.↗
NASA NTRS1977

Shuttle's 160 hour ground turnaround - A design driver

Turnaround analysis added a new dimension to the Space Program with the advent of the Space Shuttle. The requirement to turn the flight hardware around in 160 working hours from landing to launch was a significant design driver and a useful tool in forcing the integration of flight and ground systems design to permit an efficient ground operation. Although there was concern that time constraints might increase program costs, the result of the analysis was to minimize facility requirements and simplify operations with resultant cost savings.

Widick, F.↗
NASA NTRS1979

A Simplified Shuttle Payload Thermal Analyzer /SSPTA/ program

A simple thermal analysis program for Space Shuttle payloads has been developed to accommodate the user who requires an easily understood but dependable analytical tool. The thermal analysis program includes several thermal subprograms traditionally employed in spacecraft thermal studies, a data management system for data generated by the subprograms, and a master program to coordinate the data files and thermal subprograms. The language and logic used to run the thermal analysis program are designed for the small user. In addition, analytical and storage techniques which conserve computer time and minimize core requirements are incorporated into the program.

Bartoszek, J. T.↗
NASA NTRS1982

Gas Diffusion in Fluids Containing Bubbles

Mathematical model describes movement of gases in fluid containing many bubbles. Model makes it possible to predict growth and shrink age of bubbles as function of time. New model overcomes complexities involved in analysis of varying conditions by making two simplifying assumptions. It treats bubbles as point sources, and it employs approximate expression for gas concentration gradient at liquid/bubble interface. In particular, it is expected to help in developing processes for production of high-quality optical glasses in space.

Zak, M.↗
NASA NTRS1984

Analytical investigation of synchrophasing as a means of reducing aircraft interior noise

The noise control characteristics of synchrophasing are investigated using a simplified model of an aircraft fuselage. The analysis presented here includes directivity effects of the noise sources and solves in closed form the coupled motion between the interior and exterior acoustic fields and the shell vibrational response. The variation in sound pressure level at various locations inside the shell is studied for various synchrophase angles as well as the shell vibrational response and input power flow in order to uncover the principal mechanisms behind the transmission phenomena.

Fuller, C. R.↗
NASA NTRS1984

Noise control characteristics of synchrophasing - An analytical investigation

In this paper the noise control characteristics of synchrophasing are investigated using a simplified model of an aircraft fuselage. The analysis presented here includes directivity effects of the noise sources and solves in closed form the coupled motion between the interior and exterior acoustic fields and the shell vibrational response. The variation in sound pressure level at various locations inside the shell is studied for various synchrophase angles as well as the shell vibrational response and input power flow in order to uncover the principal mechanisms behind the transmission phenomena.

Fuller, C. R.↗
NASA NTRS1988

Aerodynamic maneuvering hypersonic flight mechanics

The emergence of current high-interest mission involving aeromaneuvering hypersonic flight has given rise to the corresponding need for preliminary design and performance analyses of such vehicles. This need in turn has motivated efforts to develop simplified analytical and computational methods for parametric analysis of maneuvering hypersonic flight under conditions appropriate to the mission involved. The effort included a review of different formulations of the general equations of motion, their associated coordinate frames, various simplifications of the equations, and previously achieved analytical solutions. This study sought to both extend previous solution methods and to develop new ones. In addition, evaluation of the literature and developing a systematic perspective on the knowledge it represents proved to be a major portion of the effort.

Desautel, Dick↗
NASA NTRS1992

Stability of fully developed rotating stall

In McCaughan (1989b) it was observed that the slopes of both the axisymmetric and rotating stall characteristics play a major role in determining the mode of instability of the engine and the recovery point. That analysis was carried out for the grossly simplified model where the stall cell was considered as a traveling sine wave. That work has been extended to the more reasonable situation where the stall cell is represented by forty Fourier modes. The results from the simple model of three ordinary differential equations are discussed in the light of the more realistic calculations. In particular we discuss the effects of two parameters: the steepness of the axisymmetric characteristic and the shutoff head.

Mccaughan, F. E.↗
NASA NTRS1999

Land-Ocean Differences in LIS and OTD Tropical Lightning Observations

Significant differences are known to exist on a global scale between continental and oceanic total lightning regional flash rates, suggesting differences in the properties of convective storms in these regimes. Lightning properties observed by the Optical Transient Detector (OTD) and Lightning Imaging Sensor (LIS) over land and ocean are compared, limited to analysis over the tropics in order to simplify physical interpretation. We find that the mean flash rates of individual storms over tropical land only exceed those over ocean by a factor of 2 (far less than the observed differences in regional flash rates). However, the average nearest neighbor distance of continental thunderstorms in half that over oceans. Cloud-top lightning optical radiance in oceanic storms is also twice as large as over land, suggesting either more energetic flashes over the oceans or less intervening cloud particles.

Boccippio, Dennis J.↗
NASA NTRS1999

Land-Ocean Differences in LIS and OTD Tropical Lightning Observations

Significant differences are known to exist on a global scale between continental and oceanic total lightning regional flash rates, suggesting differences in the properties of convective storms in these regimes. Lightning properties observed by the Optical Transient Detector (OTD) and Lightning Imaging Sensor (LIS) over land and ocean are compared, limited to analysis over the tropics in order to simplify physical interpretation. We find that the mean flash rates of individual storms over tropical land only exceed those over ocean by a factor of 2 (far less than the observed differences in regional flash rates). However, the average nearest neighbor distance of continental thunderstorms is half that over oceans. Cloud-top lightning optical radiance in oceanic storms is also twice as large as over land, suggesting either more energetic flashes over the oceans or less intervening cloud particles.

Boccippio, D. J.↗
NASA NTRS1958

The Interaction of a Reflected Shock Wave with the Boundary Layer in a Shock Tube

Ideally, the reflection of a shock from the closed end of a shock tube provides, for laboratory study, a quantity of stationary gas at extremely high temperature. Because of the action of viscosity, however, the flow in the real case is not one-dimensional, and a boundary layer grows in the fluid following the initial shock wave. In this paper simplifying assumptions are made to allow an analysis of the interaction of the shock reflected from the closed end with the boundary layer of the initial shock afterflow. The analysis predicts that interactions of several different types will exist in different ranges of initial shock Mach number. It is shown that the cooling effect of the wall on the afterflow boundary layer accounts for the change in interaction type. An experiment is carried out which verifies the existence of the several interaction regions and shows that they are satisfactorily predicted by the theory. Along with these results, sufficient information is obtained from the experiments to make possible a model for the interaction in the most complicated case. This model is further verified by measurements made during the experiment. The case of interaction with a turbulent boundary layer is also considered. Identifying the type of interaction with the state of turbulence of the interacting boundary layer allows for an estimate of the state of turbulence of the boundary layer based on an experimental investigation of the type of interaction. A method is proposed whereby the effect of the boundary-layer interaction on the strength of the reflected shock may be calculated. The calculation indicates that the reflected shock is rapidly attenuated for a short distance after reflection, and this result compares favorably with available experimental results.

Mark, Herman↗