578 research outputs found
An assessment of national risk: General concepts and overall approach
The analysis of risk presented by carbon fiber utilization in commercial aviation is reported. The discussion is presented in three parts: (1) general concepts; (2) overall approach; and (3) risk evaluation and perspective
Assessment of risk due to the use of carbon fiber composites in commercial and general aviation
The development of a national risk profile for the total annual aircraft losses due to carbon fiber composite (CFC) usage through 1993 is discussed. The profile was developed using separate simulation methods for commercial and general aviation aircraft. A Monte Carlo method which was used to assess the risk in commercial aircraft is described. The method projects the potential usage of CFC through 1993, investigates the incidence of commercial aircraft fires, models the potential release and dispersion of carbon fibers from a fire, and estimates potential economic losses due to CFC damaging electronic equipment. The simulation model for the general aviation aircraft is described. The model emphasizes variations in facility locations and release conditions, estimates distribution of CFC released in general aviation aircraft accidents, and tabulates the failure probabilities and aggregate economic losses in the accidents
Statistics of Pressure Fluctuations in Decaying, Isotropic Turbulence
We present results from a systematic direct-numerical simulation study of
pressure fluctuations in an unforced, incompressible, homogeneous, and
isotropic, three-dimensional turbulent fluid. At cascade completion,
isosurfaces of low pressure are found to be organised as slender filaments,
whereas the predominant isostructures appear sheet-like. We exhibit several new
results, including plots of probability distributions of the spatial
pressure-difference, the pressure-gradient norm, and the eigenvalues of the
pressure-hessian tensor. Plots of the temporal evolution of the mean
pressure-gradient norm, and the mean eigenvalues of the pressure-hessian tensor
are also exhibited. We find the statistically preferred orientations between
the eigenvectors of the pressure-hessian tensor, the pressure-gradient, the
eigenvectors of the strain-rate tensor, the vorticity, and the velocity.
Statistical properties of the non-local part of the pressure-hessian tensor are
also exhibited, for the first time. We present numerical tests (in the viscous
case) of some conjectures of Ohkitani [Phys. Fluids A {\bf 5}, 2570 (1993)] and
Ohkitani and Kishiba [Phys. Fluids {\bf 7}, 411 (1995)] concerning the
pressure-hessian and the strain-rate tensors, for the unforced, incompressible,
three-dimensional Euler equations.Comment: 10 pages, 29 figures, Accepted for publication in Physical Review
Structural Studies of Decaying Fluid Turbulence: Effect of Initial Conditions
We present results from a systematic numerical study of structural properties
of an unforced, incompressible, homogeneous, and isotropic three-dimensional
turbulent fluid with an initial energy spectrum that develops a cascade of
kinetic energy to large wavenumbers. The results are compared with those from a
recently studied set of power-law initial energy spectra [C. Kalelkar and R.
Pandit, Phys. Rev. E, {\bf 69}, 046304 (2004)] which do not exhibit such a
cascade. Differences are exhibited in plots of vorticity isosurfaces, the
temporal evolution of the kinetic energy-dissipation rate, and the rates of
production of the mean enstrophy along the principal axes of the strain-rate
tensor. A crossover between non-`cascade-type' and `cascade-type' behaviour is
shown numerically for a specific set of initial energy spectra.Comment: 9 pages, 27 figures, Accepted for publication in Physical Review
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