8,127 research outputs found
Numerical analysis of transient combustion response to acoustic oscillations in axisymmetric rocket motors
A numerical analysis of unsteady motions in solid
rocket motors with a nozzle has been conducted. The
formulation treats the complete conservation equations
for the gas phase and the one-dimensional equations in
the radial direction for the condensed phase. A fully
coupled implicit scheme based on a dual time-stepping
integration algorithm has been adopted to solve the governing equations and associated boundary conditions.
After obtaining a steady state solution, periodic pressure
oscillations are imposed at the head end to simulate acoustic oscillations of a traveling-wave motion in
the combustion chamber. The amplitude of the pressure
oscillation is 1.0 % of the mean pressure and the
frequency is 1790 Hz, corresponding to the twice of the
fundamental frequency of the chamber. Magnitude and
phase of pressure and axial velocity fluctuations are influenced by the upstream reflecting wave from the nozzle
wall. Axial velocity near surface region oscillates
in phase advance manner with reference to the acoustic
pressure. Large vorticity fluctuations are observed in
near surface region. The mass-flow-rate at the nozzle
exit periodically oscillates with a time delay compared
to the imposed pressure oscillations at the head end
Applications of Various Methods of Analysis to Combustion Instabilities in Solid Propellant Rockets
Instabilities of motions in a combustion chamber are consequences of the coupled dynamics of
combustion processes and of the flow in the chamber. The extreme complexities of the problem
always require approximations of various sorts to make progress in understanding the
mechanisms and behavior of combustion instabilities. This paper covers recent progress in the
subject, mainly summarizing efforts in two areas: approximate analysis based on a form of
Galerkin's method, particularly useful for understanding the global linear and nonlinear
dynamics of combustion instabilities and numerical simulations intended to accommodate as
fully as possible fundamental chemical processes in both the condensed and gaseous phases.
One purpose of current work is to bring closer together these approaches to produce more
comprehensive and detailed realistic results applicable to the interpretation of observations
and for design of new rockets for both space and military applications. Particularly important
are the goals of determining the connections between chemical composition and instabilities;
and the influences of geometry on nonlinear behavior
Transient combustion responses of homogeneous propellants to acoustic oscillations in axisymmetric rocket motors
A numerical analysis of unsteady motions in solid
rocket motors has been conducted. The formulation
considers a 2-D axisymmetric combustion chamber and
a choke nozzle, and treats the complete conservation
equations accounting for turbulence closure and finiterate
chemical kinetics in the gas phase and subsurface reactions.
A fully coupled implicit scheme based on a dual
time-stepping integration algorithm has been adopted
to solve the governing equations and associated boundary
conditions. Results of the steady-state calculations
indicate that the distributions of pressure in the motor
and Mach number in the nozzle are one-dimensional
along the axial direction. Vorticity contours show similar
pattern to those of Mach number in the combustion
chamber. The nozzle has an influence on the flow and
temperature fields in the combustion chamber. A narrow
pressure pulse is imposed at the head end to simulate
unsteady acoustic oscillations in the combustion
chamber. When the front of the pulse reaches near the
nozzle throat, pressure near the nozzle throat increases
and blocks the hot gas flow from passing through the
nozzle throat. Self-generated oscillations have similar
frequencies to those of standing waves of the combustion
chamber. Large vorticity fluctuations are observed
in near surface region. The luminous flame zone responds
to low-frequency pressure wave rather than highfrequency
one. Temperature fluctuations in the primary
flame zone of the head end oscillates independently of
the imposed pressure oscillations while temperature fluctuations
in downstream region show pressure-dependent
oscillations
Numerical study of acoustic oscillations and combustion instabilities in solid propellant rocket
A numerical analysis of unsteady motions in solid rocket motors has been conducted. A fully coupled
implicit scheme based on a dual time-stepping integration algorithm has been adopted to solve the governing
equations and associated boundary conditions. A narrow pressure pulse is imposed at the head end to
simulate unsteady acoustic oscillations in the combustion chamber. Pressure increases when the front of the
pulse reaches near the nozzle area. Self-generated oscillations with frequency of standing wave propagates
upstream in the combustion chamber. Investigation of transient response of gas-phase dynamics to traveling
pressure wave and its effects on propellant combustion reveals several aspects: Combustion responses have
a strong relationship with vorticity fluctuations in case of high turbulent intensity on the propellant surface.
Temperature fluctuations of the propellant surface in the head end region seem to be very unstable and
independent of the pressure wave. Surface temperature without turbulence effect looks more sensitive to
temperature fluctuations in the primary flame zone. Stability of surface temperature is strongly related to
turbulent intensity on the propellant surface
Numerical Analysis of Solid Rocket Motor Instabilities With AP Composite Propellants
A non-steady model for the combustion of ammonium
perchlorate composite propellants has been developed
in order to be incorporated into a comprehensive gasdynamics
model of solid rocket motor flow fields. The
model including the heterogeneous combustion and turbulence
mechanisms is applied to nonlinear combustion
instability analyses. This paper describes the essential
mechanisms and features of the model and discusses the
methodology of non-steady calculations of the combustion
instabilities of solid rocket motors
Life Cycle Assessment Applied to Green Building Certification in South Korea
AbstractThe purpose of this study is to apply life cycle assessment (LCA) methodology for green building certification in South Korea. The method of environmental assessment in the field of building materials was examined using United States’ LEED, and the United Kingdom's BREEAM building certification systems. Life cycle data and assessment methods were established on major categories of materials thorough theoretical consideration on life cycle assessment.Building materials, assembly methods, and building use considerations were used to develop an assessment model to evaluate the environmental performance of a building. Numeric values for use in the developed model were established for concrete, rebar, gypsum board, steel, cement brick, glass, and insulation materials to potentially reduce greenhouse gas (GHG) emissions by 95% or more. An assessment method and LCA database were established. The model will be used to show that the choice of building materials can affect the GHG emissions during the construction phase of a building
Investment Opportunities Forecasting: Extending the Grammar of a GP-based Tool
In this paper we present a new version of a GP financial forecasting tool, called EDDIE 8. The novelty of this version is that it allows the GP to search in the space of indicators, instead of using pre-specified ones. We compare EDDIE 8 with its predecessor, EDDIE 7, and find that new and improved solutions can be found. Analysis also shows that, on average, EDDIE 8's best tree performs better than the one of EDDIE 7. The above allows us to characterize EDDIE 8 as a valuable forecasting tool
The effects of peripheral and central high insulin on brain insulin signaling and amyloid-β in young and old APP/PS1 mice
Hyperinsulinemia is a risk factor for late-onset Alzheimer's disease (AD). In vitro experiments describe potential connections between insulin, insulin signaling, and amyloid-β (Aβ), but in vivo experiments are needed to validate these relationships under physiological conditions. First, we performed hyperinsulinemic-euglycemic clamps with concurrent hippocampal microdialysis in young, awake, behaving APP(swe)/PS1(dE9) transgenic mice. Both a postprandial and supraphysiological insulin clamp significantly increased interstitial fluid (ISF) and plasma Aβ compared with controls. We could detect no increase in brain, ISF, or CSF insulin or brain insulin signaling in response to peripheral hyperinsulinemia, despite detecting increased signaling in the muscle. Next, we delivered insulin directly into the hippocampus of young APP/PS1 mice via reverse microdialysis. Brain tissue insulin and insulin signaling was dose-dependently increased, but ISF Aβ was unchanged by central insulin administration. Finally, to determine whether peripheral and central high insulin has differential effects in the presence of significant amyloid pathology, we repeated these experiments in older APP/PS1 mice with significant amyloid plaque burden. Postprandial insulin clamps increased ISF and plasma Aβ, whereas direct delivery of insulin to the hippocampus significantly increased tissue insulin and insulin signaling, with no effect on Aβ in old mice. These results suggest that the brain is still responsive to insulin in the presence of amyloid pathology but increased insulin signaling does not acutely modulate Aβ in vivo before or after the onset of amyloid pathology. Peripheral hyperinsulinemia modestly increases ISF and plasma Aβ in young and old mice, independent of neuronal insulin signaling. SIGNIFICANCE STATEMENT The transportation of insulin from blood to brain is a saturable process relevant to understanding the link between hyperinsulinemia and AD. In vitro experiments have found direct connections between high insulin and extracellular Aβ, but these mechanisms presume that peripheral high insulin elevates brain insulin significantly. We found that physiological hyperinsulinemia in awake, behaving mice does not increase CNS insulin to an appreciable level yet modestly increases extracellular Aβ. We also found that the brain of aged APP/PS1 mice was not insulin resistant, contrary to the current state of the literature. These results further elucidate the relationship between insulin, the brain, and AD and its conflicting roles as both a risk factor and potential treatment
Some Spinor-Curvature Identities
We describe a class of spinor-curvature identities which exist for Riemannian
or Riemann-Cartan geometries. Each identity relates an expression quadratic in
the covariant derivative of a spinor field with an expression linear in the
curvature plus an exact differential. Certain special cases in 3 and 4
dimensions which have been or could be used in applications to General
Relativity are noted.Comment: 5 pages Plain TeX, NCU-GR-93-SSC
A Quadratic Spinor Lagrangian for General Relativity
We present a new finite action for Einstein gravity in which the Lagrangian
is quadratic in the covariant derivative of a spinor field. Via a new
spinor-curvature identity, it is related to the standard Einstein-Hilbert
Lagrangian by a total differential term. The corresponding Hamiltonian, like
the one associated with the Witten positive energy proof is fully
four-covariant. It defines quasi-local energy-momentum and can be reduced to
the one in our recent positive energy proof. (Fourth Prize, 1994 Gravity
Research Foundation Essay.)Comment: 5 pages (Plain TeX), NCU-GR-94-QSL
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