12,577 research outputs found
A simple dynamic engine model for use in a real-time aircraft simulation with thrust vectoring
A simple dynamic engine model was developed at the NASA Ames Research Center, Dryden Flight Research Facility, for use in thrust vectoring control law development and real-time aircraft simulation. The simple dynamic engine model of the F404-GE-400 engine (General Electric, Lynn, Massachusetts) operates within the aircraft simulator. It was developed using tabular data generated from a complete nonlinear dynamic engine model supplied by the manufacturer. Engine dynamics were simulated using a throttle rate limiter and low-pass filter. Included is a description of a method to account for axial thrust loss resulting from thrust vectoring. In addition, the development of the simple dynamic engine model and its incorporation into the F-18 high alpha research vehicle (HARV) thrust vectoring simulation. The simple dynamic engine model was evaluated at Mach 0.2, 35,000 ft altitude and at Mach 0.7, 35,000 ft altitude. The simple dynamic engine model is within 3 percent of the steady state response, and within 25 percent of the transient response of the complete nonlinear dynamic engine model
Development of testing and analysis methodology to assess the long term durability of polymeric composites at high temperatures
A workshop was held to help assess the state-of-the-art in evaluating the long term durability of polymeric matrix composites (PMCs) and to recommend future activities. Design and evaluation of PMCs at elevated temperatures were discussed. The workshop presentations, the findings of the workshop sessions are briefly summarized
Stress-strain analysis of a (0/90)sub 2 symmetric titanium matrix laminate subjected to a generic hypersonic flight profile
Cross ply laminate behavior of Ti-15V-3Cr-3Al-3Sn (Ti-15-3) matrix reinforced with continuous silicon carbide fibers (SCS-6) subjected to a generic hypersonic flight profile was evaluated experimentally and analytically. Thermomechanical fatigue test techniques were developed to conduct a simulation of a generic hypersonic flight profile. A micromechanical analysis was used. The analysis predicts the stress-strain response of the laminate and of the constituents in each ply during thermal and mechanical cycling by using only constituent properties as input. The fiber was modeled using a thermo-viscoplastic constitutive relation. The fiber transverse modulus was reduced in the analysis to simulate the fiber matrix interface failure. Excellent correlation was found between measured and predicted laminate stress-strain response due to generic hypersonic flight profile when fiber debonding was modeled
Efficient Computation of Power, Force, and Torque in BEM Scattering Calculations
We present concise, computationally efficient formulas for several quantities
of interest -- including absorbed and scattered power, optical force (radiation
pressure), and torque -- in scattering calculations performed using the
boundary-element method (BEM) [also known as the method of moments (MOM)]. Our
formulas compute the quantities of interest \textit{directly} from the BEM
surface currents with no need ever to compute the scattered electromagnetic
fields. We derive our new formulas and demonstrate their effectiveness by
computing power, force, and torque in a number of example geometries. Free,
open-source software implementations of our formulas are available for download
online
Ab-initio theory of quantum fluctuations and relaxation oscillations in multimode lasers
We present an \emph{ab-initio} semi-analytical solution for the noise
spectrum of complex-cavity micro-structured lasers, including central
Lorentzian peaks at the multimode lasing frequencies and additional sidepeaks
due to relaxation-oscillation (RO) dynamics. In~Ref.~1, we computed the
central-peak linewidths by solving generalized laser rate equations, which we
derived from the Maxwell--Bloch equations by invoking the
fluctuation--dissipation theorem to relate the noise correlations to the
steady-state lasing properties; Here, we generalize this approach and obtain
the entire laser spectrum, focusing on the RO sidepeaks. Our formulation treats
inhomogeneity, cavity openness, nonlinearity, and multimode effects accurately.
We find a number of new effects, including new multimode RO sidepeaks and three
generalized factors. Last, we apply our formulas to compute the noise
spectrum of single- and multimode photonic-crystal lasers.Comment: 27 pages, 3 figure
Speed-of-light limitations in passive linear media
We prove that well-known speed of light restrictions on electromagnetic
energy velocity can be extended to a new level of generality, encompassing even
nonlocal chiral media in periodic geometries, while at the same time weakening
the underlying assumptions to only passivity and linearity of the medium
(either with a transparency window or with dissipation). As was also shown by
other authors under more limiting assumptions, passivity alone is sufficient to
guarantee causality and positivity of the energy density (with no thermodynamic
assumptions). Our proof is general enough to include a very broad range of
material properties, including anisotropy, bianisotropy (chirality),
nonlocality, dispersion, periodicity, and even delta functions or similar
generalized functions. We also show that the "dynamical energy density" used by
some previous authors in dissipative media reduces to the standard Brillouin
formula for dispersive energy density in a transparency window. The results in
this paper are proved by exploiting deep results from linear-response theory,
harmonic analysis, and functional analysis that had previously not been brought
together in the context of electrodynamics.Comment: 19 pages, 1 figur
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