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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 1,189 records · Page 66
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Chaotic Dynamics Driven by Particle-Core Interactions

High-intensity beams in modern linacs are frequently encircled by diffuse halos, which drive sustained particle losses and result in gradual degradation of accelerating structures. In large part, the growth of halos is facilitated by internal space-charge forces within the beams, and detailed characterization of this process constitutes an active area of ongoing research. A partial understanding of dynamics that ensue within space-charge dominated beams is presented by the particle-core interaction paradigm – a mathematical model wherein single particle dynamics, subject to the collective potential of the core, are treated as a proxy for the broader behavior of the beam. In this work, we investigate the conditions for the onset of large-scale chaos within the framework of this model, and demonstrate that the propensity towards stochastic evolution is strongly dependent upon the charge distribution of the beam. In particular, we show that while particle motion within a uniformly charged beam is dominantly regular, rapid deterministic chaos readily arises within space-charge dominated Gaussian beams. Importantly, we find that for sufficiently high values of the beam’s space charge and beam pulsation amplitude, enhanced chaotic mixing between the core and the halo can lead to an enhanced radial diffusion of charged particles. We explain our results from analytic grounds by demonstrating that chaotic motion is driven by the intersection of two principal resonances of the system, and derive the relevant overlap conditions. Additionally, our analysis illuminates a close connection between the mathematical formulation of the particle-core interaction model and the Andoyer family of integrable Hamiltonians

43 PARTICLE ACCELERATORS↗
NASA NTRS1974

Stability study of the Large Space Telescope /LST/ system with nonlinear CMG gimbal friction

The purpose of the investigation reported upon is to study the existence and characteristics of self-sustained oscillations in the dynamic behavior of the Large Space Telescope (LST) system due to the presence of nonlinear gimbal friction in the control moment gyroscopes (CMGs). A continuous-data single-axis model of the LST is considered. A solid friction model is used to represent CMG gimbal friction. A rigorous mathematical model is derived for use in a continuous describing function analysis. Conditions for self-sustained oscillations are then determined.

Kuo, B. C.↗
NASA NTRS1975

Limit cycle analysis of large space telescope with CMG nonlinearity

The existence and characteristics of self-sustained oscillations were studied in the Large Space Telescope (LST) system due to the presence of nonlinear gimbal friction in the control moment gyroscopes (CMG's). A continuous data single-axis model of the LST is considered. A solid friction model is used to represent CMG gimbal friction. A rigorous mathematical model is derived for use in a continuous describing function analysis. Conditions for self-sustained oscillations are then determined.

Seltzer, S. M.↗
NASA NTRS1977

Prediction of Skylab attitude motion for space shuttle revisit

Computer simulations were employed to generate results, based on a fairly complicated analytical model. Environmental effects considered include atmospheric drag and gravity gradients. Mathematical models were based on Euler's moment equations and transformations from the body frame to inertial frame. A range of altitudes was considered, from 278 kilometers to 417 kilometers. Skylab is predicted to be in this orbital range during the 1979-1980 period. Results indicated that there will be a cyclic attitude motion due to the combined effect of gravity gradient and atmosphere drag. This motion can be characterized as being a slow tumble.

Alexander, S. G.↗
NASA NTRS1978

Undisturbed heat transfer data analysis on the Space Shuttle External Tank Barrel Section

The paper analyzes the existing continuum undisturbed turbulent heat transfer data on smooth models of the Space Shuttle External Tank and develops a mathematical model for theoretical prediction of heat transfer rates on the External Tank Barrel Section. Experimental data have been obtained from various wind tunnels which simulated the continuum flow regime in the Shuttle flight trajectory. The model data have been compared with theoretical predictions using realistic flow fields and well-known empirical heat transfer relationships. The results show that the predictions are good to within the experimental uncertainties of the measured data.

Praharaj, S. C.↗
NASA NTRS1979

Undisturbed flowfield and turbulent heat-transfer analysis on the Space Shuttle external tank

The paper analyzes the existing undisturbed flowfield and turbulent heat-transfer data on smooth models of the Space Shuttle external tank and extends the mathematical model for theoretical calculation of heat-transfer rates presented in an earlier paper to include both the external tank barrel and ogive sections at zero and nonzero angles of attack. Experimental data have been obtained from various wind tunnels which simulated the continuum flow regime in the Shuttle flight trajectory. The model data have been compared with theoretical predictions using realistic flowfields and well-known empirical heat-transfer relationships. The results show that the predictions are good to within the experimental uncertainties of the measured data.

Praharaj, S. C.↗
NASA NTRS1979

The magnetic field of Mercury

The paper examines the magnetic field observations and their analyses relating to the determination of the Mercury magnetic field. Methods of analyzing data included: (1) comparison of bow shock and magnetopause relative positions at Mercury to the earth, (2) direct spherical harmonic analysis, (3) magnetosphere modeling by an image dipole, and (4) scaling of a mathematical model for the terrestrial magnetosphere. Dipole moments were determined using partial quadrupole and octupole terms to improve the least-square fit of models to observations; analyses by method (2) yield a convergent series of dipole moments values considered to best represent the intrinsic planetary field. Finally, it is suggested that the origin of the magnetic field of Mercury cannot be uniquely determined, but the sources of convective energy may be radiogenic decay and heat release, gravitational settling, and differentiation of processional torques.

Ness, N. F.↗
NASA NTRS1982

Glass shell manufacturing in space

Highly-uniform, hollow glass spheres, which are used for inertial-confinement fusion targets, are formed from metal-organic gel powder feedstock in a drop-tower furnace. The modelling of this gel-to-sphere transformation has consisted of three phases: gel thermochemistry, furnance-to-gel heat transfer, and gravity-driven degradation of the concentricity of the molten shell. The heat transfer from the furnace to the free-falling gel particle was modelled with forced convection. The gel mass, dimensions, and specific heat as well as furnace temperature profile and furnace gas conductivity, were controlled variables. This model has been experimentally verified. In the third phase, a mathematical model was developed to describe the gravity-driven degradation of concentricity in molten glass shells.

Nolen, R. L.↗
NASA NTRS2001

Experimental and Numerical Investigation of Two Dimensional CO2 Adsorption/Desorption in Packed Sorption Beds under Non-Ideal Flows

The experimental results of CO2 adsorption and desorption in a packed column indicated that the concentration wave front at the center of the packed column differs from those which are close to the wall of column filled with adsorbent material even though the ratio of column diameter to the particle size is greater than 20. The comparison of the experimental results with one dimensional model of packed column shows that in order to simulate the average breakthrough in a packed column a two dimensional (radial and axial) model of packed column is needed. In this paper the mathematical model of a non-slip flow through a packed column with 2 inches in diameter and 18 inches in length filled with 5A zeolite pellets is presented. The comparison of experimental results of CO2 absorption and desorption for the mixed and central breakthrough of the packed column with numerical results is also presented.

Mohamadinejad, H.↗
NASA NTRS1997

Meta-Modeling: A Knowledge-Based Approach to Facilitating Model Construction and Reuse

In this paper, we introduce a new modeling approach called meta-modeling and illustrate its practical applicability to the construction of physically-based ecosystem process models. As a critical adjunct to modeling codes meta-modeling requires explicit specification of certain background information related to the construction and conceptual underpinnings of a model. This information formalizes the heretofore tacit relationship between the mathematical modeling code and the underlying real-world phenomena being investigated, and gives insight into the process by which the model was constructed. We show how the explicit availability of such information can make models more understandable and reusable and less subject to misinterpretation. In particular, background information enables potential users to better interpret an implemented ecosystem model without direct assistance from the model author. Additionally, we show how the discipline involved in specifying background information leads to improved management of model complexity and fewer implementation errors. We illustrate the meta-modeling approach in the context of the Scientists' Intelligent Graphical Modeling Assistant (SIGMA) a new model construction environment. As the user constructs a model using SIGMA the system adds appropriate background information that ties the executable model to the underlying physical phenomena under investigation. Not only does this information improve the understandability of the final model it also serves to reduce the overall time and programming expertise necessary to initially build and subsequently modify models. Furthermore, SIGMA's use of background knowledge helps eliminate coding errors resulting from scientific and dimensional inconsistencies that are otherwise difficult to avoid when building complex models. As a. demonstration of SIGMA's utility, the system was used to reimplement and extend a well-known forest ecosystem dynamics model: Forest-BGC.

Keller, Richard M.↗
NASA NTRS1994

A comprehensive Guyton model analysis of physiologic responses to preadapting the blood volume as a countermeasure to fluid shifts

The Guyton model of fluid, electrolyte, and circulatory regulation is an extensive mathematical model capable of simulating a variety of experimental conditions. It has been modified for use at NASA to simulate head-down tilt, a frequently used analog of weightlessness. Weightlessness causes a headward shift of body fluids that is believed to expand central blood volume, triggering a series of physiologic responses resulting in large losses of body fluids. We used the modified Guyton model to test the hypothesis that preadaptation of the blood volume before weightless exposure could counteract the central volume expansion caused by fluid shifts, and thereby attenuate the circulatory and renal responses that result in body fluid losses. Simulation results show that circulatory preadaptation, by a procedure resembling blood donation immediately before head-down bedrest, is effective in damping the physiologic responses to fluid shifts and reducing body fluid losses. After 10 hours of head-down tilt, preadaptation also produces higher blood volume, extracellular volume, and total body water for 20 to 30 days of bedrest, compared with non-preadapted control. These results indicate that circulatory preadaptation before current Space Shuttle missions may be beneficial for the maintenance of reentry and postflight orthostatic tolerance in astronauts. This paper presents a comprehensive examination of the simulation results pertaining to changes in relevant physiologic variables produced by blood volume reduction before a prolonged head-down tilt. The objectives were to study and develop the countermeasure theoretically, to aid in planning experimental studies of the countermeasure, and to identify potentially disadvantageous physiologic responses that may be caused by the countermeasure.

NASA Center JSC↗
NASA NTRS1978

Stable boundary layer wind shear model for aircraft flight hazard definition

It is pointed out that wind shear, particularly at the lower altitudes in the terminal area, has been identified as being hazardous to aircraft operations. Accurate and reliable wind profiles are required for use in fast time and manned flight simulation studies aimed at fully defining and understanding the wind shear hazard. A description is presented of wind speed profiles for neutral and stable atmospheric conditions developed for the simulation studies to improve the safety and reliability of operations in the terminal area. The wind shear is mathematically modeled and the mathematical scenarios are presented in a format for direct application to wind shear hazard/flight simulation studies.

Frost, W.↗
DOE OSTI2020

Generating Massive Scale-free Networks: Novel Parallel Algorithms using the Preferential Attachment Model

Recently, there has been substantial interest in the study of various random networks as mathematical models of complex systems. As real-life complex systems grow larger, the ability to generate progressively large random networks becomes all the more important. This motivates the need for efficient parallel algorithms for generating such networks. Naïve parallelization of sequential algorithms for generating random networks is inefficient due to inherent dependencies among the edges and the possibility of creating duplicate (parallel) edges. In this article, we present message passing interface-based distributed memory parallel algorithms for generating random scale-free networks using the preferential-attachment model. Our algorithms are experimentally verified to scale very well to a large number of processing elements (PEs), providing near-linear speedups. The algorithms have been exercised with regard to scale and speed to generate scale-free networks with one trillion edges in 6 minutes using 1,000 PEs.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1985

Modelling Equilibrium and Fractional Crystallization in the System MgO-FeO-CaO-Al2O3-SiO2

A mathematical modelling technique for use in petrogenesis calculations in the system MgO-FeO-CaO-Al2O3-SiO2 is reported. Semiempirical phase boundary and elemental distribution information was combined with mass balance to compute approximate equilibrium crystallization paths for arbitrary system compositions. The calculation is applicable to a range of system compositions and fractionation calculations are possible. The goal of the calculation is the computation of the composition and quantity of each phase present as a function of the degree of solidification. The degree of solidification is parameterized by the heat released by the solidifying phases. The mathematical requirement for the solution of this problem is: (1) An equation constraining the composition of the magma for each solid phase in equilibrium with the liquidus phase, and (2) an equation for each solid phase and each component giving the distribution of that element between that phase and the magma.

Herbert, F.↗
NASA NTRS2004

A "Kane's Dynamics" Model for the Active Rack Isolation System Part Two: Nonlinear Model Development, Verification, and Simplification

Many microgravity space-science experiments require vibratory acceleration levels that are unachievable without active isolation. The Boeing Corporation's active rack isolation system (ARIS) employs a novel combination of magnetic actuation and mechanical linkages to address these isolation requirements on the International Space Station. Effective model-based vibration isolation requires: (1) An isolation device, (2) an adequate dynamic; i.e., mathematical, model of that isolator, and (3) a suitable, corresponding controller. This Technical Memorandum documents the validation of that high-fidelity dynamic model of ARIS. The verification of this dynamics model was achieved by utilizing two commercial off-the-shelf (COTS) software tools: Deneb's ENVISION(registered trademark), and Online Dynamics Autolev(trademark). ENVISION is a robotics software package developed for the automotive industry that employs three-dimensional computer-aided design models to facilitate both forward and inverse kinematics analyses. Autolev is a DOS-based interpreter designed, in general, to solve vector-based mathematical problems and specifically to solve dynamics problems using Kane's method. The simplification of this model was achieved using the small-angle theorem for the joint angle of the ARIS actuators. This simplification has a profound effect on the overall complexity of the closed-form solution while yielding a closed-form solution easily employed using COTS control hardware.

Beech, G. S.↗
NASA NTRS1972

Evaluation of massless-spring modeling of suspension-line elasticity during the parachute unfurling process

A general theory on mathematical modeling of elastic parachute suspension lines during the unfurling process was developed. Massless-spring modeling of suspension-line elasticity was evaluated in detail. For this simple model, equations which govern the motion were developed and numerically integrated. The results were compared with flight test data. In most regions, agreement was satisfactory. However, poor agreement was obtained during periods of rapid fluctuations in line tension.

Poole, L. R.↗