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Results for “Mathematical Model”

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 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

A Combined Model of Charging of the Surface and Bulk of a Dielectric Target by Electrons with the Energies 10–30 keV

A physico-mathematical model of the processes of radiation-induced charging of dielectric materials with open surfaces, irradiated with monoenergetic electrons in the energy range 10–30 keV, is described. The model takes into account the relationship between the processes of surface and bulk charging for the given conditions of the experimental design, which accounts for the effect of anomalously long charging of dielectrics after the incident energy of primary electrons during charging is reduced to below the second critical energy for the secondary electronic emission coefficient. The initial fast phase of charging a high-resistivity dielectric material (Al{sub 2}O{sub 3}) is investigated. It is shown that as the incident electron energy is approaching the second critical energy during charging, the secondary electronic emission is partially suppressed due to negative charging of the open surface of the dielectric and formation of a near-surface inversion electrical field retarding the electronic emission yield.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1966

Photoviscoelasticity

Stress analysis method of photoelasticity extended to viscoelastic materials by manufacturing mathematical model from transparent birefringent material properties

MATHEMATICAL MODEL↗
DOE OSTI2019

Solid Rocket Motor Design using a Low-Dimensional Fluid Model

This document is a summary of the mathematical models that are used in the DARPA TRADES project for the solid rocket motor design challenge. It is hoped that this brief description of these models will be of use to those that are working on the project.

42 ENGINEERING↗
DOE OSTI2017

Modeling of wave processes in blocky media with porous and fluid-saturated interlayers

The wave processes in blocky media are analyzed by applying different mathematical models, wherein the elastic blocks interact with each other via pliant interlayers with the complex mechanical properties. Four versions of constitutive equations are considered. In the first version, an elastic interaction between the blocks is simulated within the framework of linear elasticity theory, and the model of elastic–plastic interlayers is constructed to take into account the appearance of irreversible deformation of interlayers at short time intervals. In the second one, the effects of viscoelastic shear in the interblock interlayers are taken into the consideration using the Poynting–Thomson rheological scheme. In the third option, the model of an elastic porous material is used in the interlayers, where the pores collapse if an abrupt compressive stress is applied. In the fourth case, the model of a fluid-saturated material with open pores is examined based on Biot's equations. The collapse of pores is modeled by the generalized rheological approach, wherein the mechanical properties of a material are simulated using four rheological elements. Three of them are the traditional elastic, viscous and plastic elements, the fourth element is the so-called rigid contact, which is used to describe the behavior of materials with the different resistance to tension and compression. It was shown that the thermodynamically consistent model is provided, which means that the energy balance equation is fulfilled for an entire blocky structure, where the kinetic and potential energy of the system is the sum of the kinetic and potential energies of the blocks and interlayers. Under numerical implementation of the interlayers models, the dissipationless finite difference Ivanov's method was used. The splitting method by spatial variables in the combination with the Godunov gap decay scheme was applied in the blocks. As a result, robust and stable computational algorithms are built and tested. Using MPI technology, the parallel software was designed for the modeling of wave processes in 2D setting. The numerical results are presented, discussed and future studies are outlined. - Highlights: • We model the propagation of waves in a blocky medium with compliant interlayers. • Models of porous and fluid saturated interlayers are proposed using Biot's approach. • A parallel computational algorithm is developed for supercomputers of cluster type. • Problems of instant rotation of central and boundary blocks are solved numerically. • Wave motions are compared in the cases of elastic and fluid-saturated interlayers.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Modeling the Operation of Bulk-Action Hybrid Piston Power Systems

The operation of a bulk-action hybrid piston power unit is described by a mathematical model based on the laws of energy, mass, and momentum conservation and the equation of state. The influence of the pressure in the pump and compressor sections, the gap in the compressor section, and the eccentricity on the relation between the opposing liquid flow rates through the piston seal and on the thickness of the liquid layer above the piston is analyzed.

42 ENGINEERING↗
DOE OSTI2017

Modeling of Coupled Thermo-Hydro-Mechanical-Chemical Processes for High-Level Radioactive Waste Repositories - 17361

To ensure that multi-barrier systems in high-level radioactive waste (HLW) repositories can efficiently perform their functions and isolate the waste from the biosphere, coupled thermo-hydro-mechanical-chemical (THMC) processes used for the performance assessment of HLW disposal facilities should be modeled. To evaluate coupled THMC processes, the DECOVALEX project, a unique international research collaboration project initiated in 1992, developed mathematical models and field experiments involving THMC processes in engineered barrier systems and host rocks for HLW disposal. The DECOVALEX project and the current status of coupled THMC model development can provide further insights into the performance assessment of HLW disposal facilities. This study provides information regarding the DECOVALEX project and reviews the development of coupled THMC models. The study results furnish knowledge of coupled THMC processes and techniques for the performance assessment and safety analysis of the final HLW disposal. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS1971

A cardiovascular system model for lower-body negative pressure response

Mathematical models used to study complex physiological control systems are discussed. Efforts were made to modify a model of the cardiovascular system for use in studying lower body negative pressure. A computer program was written which allows orderly, straightforward expansion to include exercise, metabolism (thermal stress), respiration, and other body functions.

Mitchell, B. A., Jr.↗
NASA NTRS1972

A new model for dual-spin satellites.

A new mathematical model for the analysis of dissipative dual-spin satellites has been developed. This model makes explicit use of the fact that the high speed rotor is symmetric by modeling the rotor energy dissipation with symmetrically placed dampers. This permits the use of a quasi-holonomic transformation for the reduction of the periodic system of variational equations to an autonomous system in accordance with the Floquet Theory and the Liapunov Reducibility Theorem.-

Guha, A. K.↗
NASA NTRS1971

Reliability model of a monopropellant auxiliary propulsion system

A mathematical model and associated computer code has been developed which computes the reliability of a monopropellant blowdown hydrazine spacecraft auxiliary propulsion system as a function of time. The propulsion system is used to adjust or modify the spacecraft orbit over an extended period of time. The multiple orbit corrections are the multiple objectives which the auxiliary propulsion system is designed to achieve. Thus the reliability model computes the probability of successfully accomplishing each of the desired orbit corrections. To accomplish this, the reliability model interfaces with a computer code that models the performance of a blowdown (unregulated) monopropellant auxiliary propulsion system. The computer code acts as a performance model and as such gives an accurate time history of the system operating parameters. The basic timing and status information is passed on to and utilized by the reliability model which establishes the probability of successfully accomplishing the orbit corrections.

Greenberg, J. S.↗