An improved exceedance theory for combined random stresses

An extension is presented of Rice's classic solution for the exceedances of a constant level by a single random process to its counterpart for an n-dimensional vector process. An interaction boundary, analogous to the constant level considered by Rice for the one-dimensional case, is assumed in the form of a hypersurface. The theory for the numbers of boundary exceedances is developed by using a joint statistical approach which fully accounts for all cross-correlation effects. An exact expression is derived for the n-dimensional exceedance density function, which is valid for an arbitrary interaction boundary. For application to biaxial states of combined random stress, the general theory is reduced to the two-dimensional case. An elliptical stress interaction boundary is assumed and the exact expression for the density function is presented. The equations are expressed in a format which facilitates calculating the exceedances by numerically evaluating a line integral. The behavior of the density function for the two-dimensional case is briefly discussed

A study of launch-vehicle responses to detailed characteristics of the wind profile

Variations in vertical wind profile to launch vehicle response

A finite difference solution for the propagation of sound in near sonic flows

An explicit time/space finite difference procedure is used to model the propagation of sound in a quasi one-dimensional duct containing high Mach number subsonic flow. Nonlinear acoustic equations are derived by perturbing the time-dependent Euler equations about a steady, compressible mean flow. The governing difference relations are based on a fourth-order, two-step (predictor-corrector) MacCormack scheme. The solution algorithm functions by switching on a time harmonic source and allowing the difference equations to iterate to a steady state. The principal effect of the non-linearities was to shift acoustical energy to higher harmonics. With increased source strengths, wave steepening was observed. This phenomenon suggests that the acoustical response may approach a shock behavior at at higher sound pressure level as the throat Mach number aproaches unity. On a peak level basis, good agreement between the nonlinear finite difference and linear finite element solutions was observed, even through a peak sound pressure level of about 150 dB occurred in the throat region. Nonlinear steady state waveform solutions are shown to be in excellent agreement with a nonlinear asymptotic theory

Duct liner optimization for turbomachinery noise sources

An acoustical field theory for axisymmetric, multisectioned lined ducts with uniform flow profiles was combined with a numerical minimization algorithm to predict optimal liner configurations having one, two, and three sections. Source models studied include a point source located on the axis of the duct and rotor/outlet-stator viscous wake interaction effects for a typical research compressor operating at an axial flow Mach number of about 0.4. For this latter source, optimal liners for equipartition-of energy, zero-phase, and least-attenuated-mode source variations were also calculated and compared with exact results. It is found that the potential benefits of liner segmentation for the attenuation of turbomachinery noise is greater than would be predicted from point source results. Furthermore, effective liner design requires precise knowledge of the circumferential and radial modal distributions

A stability study and moral analysis of a space-station - Centrifuge configuration

Dynamic stability of space station-centrifuge configuratio

Correction to the pathogenic alternative splicing, caused by the common GNB3 c.825C>T allele, using a novel, antisense morpholino

The very common GNB3 c.825C>T polymorphism (rs5443), is present in approximately half of all human chromosomes. Significantly the presence of the GNB3 825T allele has been strongly associated, with predisposition to essential hypertension. Paradoxically the presence of the GNB3 825T allele, in exon 10, introduces a pathogenic alternative RNA splice site into the middle of exon 9. To attempt to correct this pathogenic aberrant splicing, we therefore bioinformatically designed, using a Gene Tools® algorithm, a GNB3 specific, antisense morpholino. It was hoped that this morpholino would behave in vitro as either a potential “ splice blocker and/or exon skipper, to both bind and inhibit/reduce the aberrant splicing of the GNB3, 825T allele. On transfecting a human lymphoblast cell line homozygous for the 825T allele, with this antisense morpholino, we encouragingly observed both a significant reduction (from ~58% to ~5%) in the production of the aberrant smaller GNB3 transcript, and a subsequent increase in the normal GNB3 transcript (from ~42% to ~95%). Our results demonstrate the potential use of a GNB3 specific antisense morpholino, as a pharmacogenetic therapy for essential hypertension

The optimization of force inputs for active structural acoustic control using a neural network

This paper investigates the use of a neural network to determine which force actuators, of a multi-actuator array, are best activated in order to achieve structural-acoustic control. The concept is demonstrated using a cylinder/cavity model on which the control forces, produced by piezoelectric actuators, are applied with the objective of reducing the interior noise. A two-layer neural network is employed and the back propagation solution is compared with the results calculated by a conventional, least-squares optimization analysis. The ability of the neural network to accurately and efficiently control actuator activation for interior noise reduction is demonstrated

A finite element for thermal stress analysis of shells of revolution

A new finite element is described for performing detailed thermal stress analysis of thin orthotropic shells of revolution. The element provides for temperature loadings which may vary over the surface of the shell as well as through the thickness. In a number of sample calculations, results from the present method are compared with analytical solutions as well as with independent numerical analyses. Such calculations are carried out for two cylinders, a conical frustum, a truncated hemisphere, and an annular plate. Generally, the agreement between the present solution and the other solutions is excellent

An evaluation of active noise control in a cylindrical shell

The physical mechanisms governing the use of active noise control in an extended volume of a cylindrical shell are discussed. Measured data was compared with computer results from a previously derived analytical model based on an infinite shell theory. For both the analytical model and experiment, the radiation of the external monopoles is coupled to the internal acoustic field through the radial displacement of the thin, elastic cylindrical shell. An active noise control system was implemented in the cylinder using a fixed array of discrete monopole sources, all of which lie in the plane of the exterior noise sources. Good agreement between measurement and prediction was obtained for both internal pressure response and overall noise reduction. Attenuations in the source plane greater than 15 dB were recorded along with a uniformly quieted noise environment over the entire length of the experimental model. Results indicate that for extended axial forcing distributions or very low shell damping, axial arrays of control sources may be required. Finally, the Nyquist criteria for the number of azimuthal control sources is shown to provide for effective control over the full cylinder cross section

A describing-function analysis of the stability of a launch vehicle with nonlinear thrust vectoring

Describing-function analysis of launch vehicle stability with nonlinear thrust vectorin