6,193 research outputs found
Leiden Exchange
After last year’s extremely successful visit by the lovely Dutch Medical students, we were keen to make the exchange a regular reciprocal visit. Our erstwhile President Paul Mills had been in touch with Monique, his Dutch counter-part for some time and eventually a date was agreed on
Spatial adaption procedures on unstructured meshes for accurate unsteady aerodynamic flow computation
Spatial adaption procedures for the accurate and efficient solution of steady and unsteady inviscid flow problems are described. The adaption procedures were developed and implemented within a two-dimensional unstructured-grid upwind-type Euler code. These procedures involve mesh enrichment and mesh coarsening to either add points in a high gradient region or the flow or remove points where they are not needed, respectively, to produce solutions of high spatial accuracy at minimal computational costs. A detailed description is given of the enrichment and coarsening procedures and comparisons with alternative results and experimental data are presented to provide an assessment of the accuracy and efficiency of the capability. Steady and unsteady transonic results, obtained using spatial adaption for the NACA 0012 airfoil, are shown to be of high spatial accuracy, primarily in that the shock waves are very sharply captured. The results were obtained with a computational savings of a factor of approximately fifty-three for a steady case and as much as twenty-five for the unsteady cases
Three-dimensional time-marching aeroelastic analyses using an unstructured-grid Euler method
Modifications to a three dimensional, implicit, upwind, unstructured-grid Euler code for aeroelastic analysis of complete aircraft configurations are described. The modifications involve the addition of the structural equations of motion for their simultaneous time integration with the governing flow equations. The paper presents a detailed description of the time marching aeroelastic procedure and presents comparisons with experimental data to provide an assessment of the capability. Flutter results are shown for an isolated 45 degree swept-back wing and a supersonic transport configuration with a fuselage, clipped delta wing, and two identical rearward-mounted nacelles. Comparisons between computed and experimental flutter characteristics show good agreement, giving confidence in the accuracy of the aeroelastic capability that was developed
Spatial adaptation procedures on tetrahedral meshes for unsteady aerodynamic flow calculations
Spatial adaptation procedures for the accurate and efficient solution of steady and unsteady inviscid flow problems are described. The adaptation procedures were developed and implemented within a three-dimensional, unstructured-grid, upwind-type Euler code. These procedures involve mesh enrichment and mesh coarsening to either add points in high gradient regions of the flow or remove points where they are not needed, respectively, to produce solutions of high spatial accuracy at minimal computational cost. A detailed description of the enrichment and coarsening procedures are presented and comparisons with experimental data for an ONERA M6 wing and an exact solution for a shock-tube problem are presented to provide an assessment of the accuracy and efficiency of the capability. Steady and unsteady results, obtained using spatial adaptation procedures, are shown to be of high spatial accuracy, primarily in that discontinuities such as shock waves are captured very sharply
Unstructured-grid methods development for unsteady aerodynamic and aeroelastic analyses
The current status of unstructured grid methods development in the Unsteady Aerodynamics Branch at NASA-Langley is described. These methods are being developed for unsteady aerodynamic and aeroelastic analyses. The flow solvers are highlighted which were developed for the solution of the unsteady Euler equations and selected results are given which show various features of the capability. The results demonstrate 2-D and 3-D applications for both steady and unsteady flows. Comparisons are also made with solutions obtained using a structured grid code and with experimental data to determine the accuracy of the unstructured grid methodology. These comparisons show good agreement which thus verifies the accuracy
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Cortisol levels in response to starting school in children at increased risk for social phobia
Background: Research on depression has identified hyperactivity of the HPA axis as a
potential contributory factor to the intergenerational transmission of affective symptoms. However,
this has not yet been examined in the context of social phobia. The current study compared HPA axis
activity in response to a universal social stressor (starting school) in children of 2 groups of women:
one with social phobia and one with no history of anxiety (comparison group). To determine specificity
of effects of maternal social phobia, a third group of children were also examined whose mothers had
generalised anxiety disorder (GAD).
Method: Children provided salivary cortisol samples in the morning, afternoon and at bedtime across 3
time-blocks surrounding the school start: a month before starting school (baseline), the first week at
school (stress response), and the end of the first school term (stress recovery). Child behavioural
inhibition at 14 months was also assessed to explore the influence of early temperament on later stress
responses.
Results: All children displayed an elevation in morning and afternoon cortisol from baseline during the
first week at school, which remained elevated until the end of the first term. Children in the social
phobia group, however, also displayed an equivalent elevation in bedtime cortisol, which was not
observed for comparison children or for children of mothers with GAD. Children in the social phobia
group who were classified as 'inhibited' at 14 months displayed significantly higher afternoon cortisol
levels overall.
Summary: A persistent stress response to school in the morning and afternoon is typical for all
children, but children of mothers with social phobia also display atypical elevations in evening cortisol
levels when at school - signalling long-term disruption of the circadian rhythm in HPA axis activity.
This is the first study to report HPA axis disruption in children at risk of developing social phobia, and
future research should aim to determine whether this represents a pathway for symptom
development, taking early temperament into account
Level statistics and eigenfunctions of pseudointegrable systems: dependence on energy and genus number
We study the level statistics (second half moment and rigidity
) and the eigenfunctions of pseudointegrable systems with rough
boundaries of different genus numbers . We find that the levels form energy
intervals with a characteristic behavior of the level statistics and the
eigenfunctions in each interval. At low enough energies, the boundary roughness
is not resolved and accordingly, the eigenfunctions are quite regular functions
and the level statistics shows Poisson-like behavior. At higher energies, the
level statistics of most systems moves from Poisson-like towards Wigner-like
behavior with increasing . Investigating the wavefunctions, we find many
chaotic functions that can be described as a random superposition of regular
wavefunctions. The amplitude distribution of these chaotic functions
was found to be Gaussian with the typical value of the localization volume
. For systems with periodic boundaries we find
several additional energy regimes, where is relatively close to the
Poisson-limit. In these regimes, the eigenfunctions are either regular or
localized functions, where is close to the distribution of a sine or
cosine function in the first case and strongly peaked in the second case. Also
an interesting intermediate case between chaotic and localized eigenfunctions
appears
Simulation of a finishing operation : milling of a turbine blade and influence of damping
Milling is used to create very complex geometries and thin parts, such as turbine blades. Irreversible geometric defects may appear during finishing operations when a high surface quality is expected. Relative vibrations between the tool and the workpiece must be as small as possible, while tool/workpiece interactions can be highly non-linear. A general virtual machining approach is presented and illustrated. It takes into account the relative motion and vibrations of the tool and the workpiece. Both deformations of the tool and the workpiece are taken into account. This allows predictive simulations in the time domain. As an example the effect of damping on the behavior during machining of one of the 56 blades of a turbine disk is analysed in order to illustrate the approach potential
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