Aeroelastic simulations of stores in weapon bays using Detached-Eddy simulation

Detached-Eddy Simulations of flows in weapon bays with a generic store at different positions in the cavity and with flexible fins are presented in this paper. Simulations were carried out to better understand the fluid–structure interactions of the unsteady, turbulent flow and the store. Mach and Reynolds numbers (based on the missile diameter) were 0.85 and 326.000 respectively. Spectral analysis showed few differences in the frequency content in the cavity between the store with rigid and flexible fins. However, a large effect of the store position was seen. When the store was placed inside the cavity, the noise reduction reached 7 dB close to the cavity ceiling. The closer the store to the carriage position, the more coherent and quieter was the cavity. To perform a more realistic simulation, a gap of 0.3% of the store diameter was introduced between the fin root and the body of the store. Store loads showed little differences between the rigid and flexible fins when the store was inside and outside the cavity. With the store at the shear layer, the flexible fins were seen to have a reduction in loads with large fluctuations in position about a mean. Fin-tip displacements of the store inside the cavity were of the range of 0.2% of the store diameter, and in the range of 1–2% of store diameter when at the shear layer

Analysis of enhanced diffusion in Taylor dispersion via a model problem

We consider a simple model of the evolution of the concentration of a tracer, subject to a background shear flow by a fluid with viscosity $\nu \ll 1$ in an infinite channel. Taylor observed in the 1950's that, in such a setting, the tracer diffuses at a rate proportional to $1/\nu$, rather than the expected rate proportional to $\nu$. We provide a mathematical explanation for this enhanced diffusion using a combination of Fourier analysis and center manifold theory. More precisely, we show that, while the high modes of the concentration decay exponentially, the low modes decay algebraically, but at an enhanced rate. Moreover, the behavior of the low modes is governed by finite-dimensional dynamics on an appropriate center manifold, which corresponds exactly to diffusion by a fluid with viscosity proportional to $1/\nu$

Store release trajectory variability from weapon bays using scale-adaptive simulations

In this paper, scale-adaptive simulation is used to study store trajectory variability for releases from transonic weapon bays. The scale-adaptive simulation captures the essential physics of the flow in the weapon bay, and its speed of computation allows for several trajectories to be computed within reasonable time. The results of the simulations are treated as a statistical set and a metric is put forward to decide the minimum number of simulations necessary to establish the mean and the standard deviation of the releases. Averaging the results of all trajectories was useful in developing an overall understanding of the bay pressure field role on the store trajectories. Filtering the obtained trajectories provided insight in the flow frequencies affecting the forces acting on the store and the coordinates of its center of gravity during releases. For the store employed in this study, less than one month of CPU time is needed for the complete set of simulations to be obtained, making this method promising as a further test before flight testing

Cavity flow over a transonic weapon bay during door operation

This paper considers a transonic, idealized, weapons bay. The doors are either fixed or opened in a dynamic way. The flow evolves in three stages during door opening, corresponding to closed-cavity flow, transitional flow, and (finally) open-cavity flow. The transition needs to be taken into account to design structures, as the bay wall loads are amplified, as well as the noise. The flow fluctuations are also larger than for the fully established flow. The doors limit the development of the shear layer at the early stage of the door opening

Patterns of distribution and current protection status of the Carnivora, Chiroptera and Insectivora in South Africa

Geographic patterns of species richness and endemism in three mammalian orders (Chiroptera, Insectivora and Carnivora) were studied in relation to the biomes and existing protected areas of greater South Africa (including Lesotho and Swaziland). Locality data for 21500 specimens representing 124 species were analysed with a geographical information system. Species richness of Chiroptera is high in the savanna biome, particularly in the north-east of the country, owing to the marginal intrusion of 14 tropical species. Endemism in Chiroptera is low, however, with only two endemic species in the fynbos and Karoo biomes. The Carnivora display less biome specificity and endemism than the Chiroptera. Whereas the north-eastern savannas have the highest species richness, the transition between the Nama-Karoo and grassland biomes is an important southern African centre of endemism for the Carnivora, particularly the smaller species. In addition to being an important centre for species richness in the Carnivora and Chiroptera, the Kruger National Park is also particularly important for Red Dala Book species in both orders. The Insectivora display both high species richness and endemism. Species richness of the Insectivora is greatest in the mesic south-east of the country, whereas endemism is most pronounced in the forest and grassland biomes. Differences in biome specificity and endemism between these orders reflect not only phylogenetic divergence, but also variation in body size, vagility and life-history strategies. Most of South Africa's endemics are small mammals and many of them are listed in the Red Data Book. Distributions, life-history strategies and trends in man-induced habitat degradation were used to re-evaluale the protection status of the 124 species. We conclude that at least 11 endemic species are not adequately protected by existing publicly owned protected areas and consequently identify several areas which need to be added to the existing protected area system

Local and non-local approaches to fatigue crack initiation and propogation

Copyright @ 2003 Kulwer Academic Publishers.A functional form of local strength conditions under fatigue loading is introduced and employed to formulation and analysis of fatigue crack initiation and propagation. For the strength conditions associated with the Palmgren-Miner linear damage accumulation rule and the power-type S-N diagram, the problem is reduced to a non-linear integral Volterra equation, which can be transformed to a linear one for the case of a single crack. An analytical solution of some simple problems are presented for the latter case and shortcomings of the local approach are pointed out. A non-local approach free from the shortcomings is presented along with an example of its implementation.This work was completed under the research grant GR/M24592 "Non-local approach to high cyclic fatigue: Theoretical basis" of the Engineering and Physical Sciences Research Council, UK

Search for High Spin Particle-Hole States in 20-Ne

This research was sponsored by the National Science Foundation Grant NSF PHY 87-1440

Time Lumps in Nonlocal Stringy Models and Cosmological Applications

We study lump solutions in nonlocal toy models and their cosmological applications. These models are motivated by a description of D-brane decay within string field theory framework. In order to find cosmological solutions we use the simplest local approximation keeping only second derivative terms in nonlocal dynamics. We study a validity of this approximation in flat background where time lump solutions can be written explicitly. We work out the validity of this approximation. We show that our models at large time exhibit the phantom behaviour similar to the case of the string kink.Comment: Latex, 24 pages, 13 figures, Typos corrected, references adde

Gastric cancer and Helicobacter pylori: a combined analysis of 12 case control studies nested within prospective cohorts

BACKGROUND: The magnitude of the association between Helicobacter pylori and incidence of gastric cancer is unclear. H pylori infection and the circulating antibody response can be lost with development of cancer; thus retrospective studies are subject to bias resulting from classifi- cation of cases as H pylori negative when they were infected in the past. AIMS: To combine data from all case control studies nested within prospective cohorts to assess more reliably the relative risk of gastric cancer associated with H pylori infection.To investigate variation in relative risk by age, sex, cancer type and subsite, and interval between blood sampling and cancer diagnosis. METHODS: Studies were eligible if blood samples for H pylori serology were collected before diagnosis of gastric cancer in cases. Identified published studies and two unpublished studies were included. Individual subject data were obtained for each. Matched odds ratios (ORs) and 95% confidence intervals (95% CI) were calculated for the association between H pylori and gastric cancer. RESULTS: Twelve studies with 1228 gastric cancer cases were considered. The association with H pylori was restricted to noncardia cancers (OR 3.0; 95% CI 2.3–3.8) and was stronger when blood samples for H pylori serology were collected 10+ years before cancer diagnosis (5.9; 3.4–10.3). H pylori infection was not associated with an altered overall risk of cardia cancer (1.0; 0.7–1.4). CONCLUSIONS: These results suggest that 5.9 is the best estimate of the relative risk of non-cardia cancer associated with H pylori infection and that H pylori does not increase the risk of cardia cancer. They also support the idea that when H pylori status is assessed close to cancer diagnosis, the magnitude of the non-cardia association may be underestimated

A Generalized Fluctuation-Dissipation Theorem for Nonlinear Response Functions

A nonlinear generalization of the Fluctuation-Dissipation Theorem (FDT) for the n-point Green functions and the amputated 1PI vertex functions at finite temperature is derived in the framework of the Closed Time Path formalism. We verify that this generalized FDT coincides with known results for n=2 and 3. New explicit relations among the 4-point nonlinear response and correlation (fluctuation) functions are presented.Comment: 34 pages, Revte