Probabilistic model for fracture mechanics service life analysis

The service longevity of complex propulsion systems, such as the Space Shuttle Main Engine (SSME), can be at risk from several competing failure modes. Conventional life assessment practice focuses upon the most severely life-limited feature of a given component, even though there may be other, less severe, potential failure locations. Primary, secondary, tertiary failure modes, as well as their associated probabilities, must also be considered. Futhermore, these probabilities are functions of accumulated service time. Thus a component may not always succumb to the most severe, or even the most probable failure mode. Propulsion system longevity must be assessed by considering simultaneously the actions of, and interactions among, life-limiting influences. These include, but are not limited to, high frequency fatigue (HFF), low cycle fatigue (LCF), and subsequent crack propagation, thermal and acoustic loadings, and the influence of less-than-ideal nondestructive evaluation (NDE). An outline is provided for a probabilistic model for service life analysis, and the progress towards its implementation is reported

Implicit vs Explicit Mood Congruent Memory Bias in Depression.

Mood congruent memory (MCM) in depressed individuals, tends to be biased toward memories consistent with their mood, i.e. negative or unpleasant memories. Although MCM is a robust finding, the large majority of studies have used free-recall paradigms, and that methodology does little to delineate the cognitive mechanisms determining MCM. This study was designed to investigate whether MCM bias is a function of implicit or explicit memory. Implicit memory is taken as a measure of the organization or strength of association of the aspects of a memory representation, whereas explicit memory also taps elaboration that may involve control procedures such as retrieval strategies. Thus a comparison of implicit and explicit MCM bias may provide important information about the involvement of the structure of the memory representation, or the involvement of elaboration processes in MCM. Two groups, a group of clinical depressives and a comparison group, were studied. Each group engaged in an encoding task involving words of varying affective valence. Following this encoding task, all subjects engaged in an explicit memory task (cued recall), and an implicit memory test (word completion). As expected, a MCM bias was found in explicit memory, however, contrary to predictions, no MCM bias was found in implicit memory. This finding was interpreted as supporting the involvement of elaborative mechanisms in MCM. A second finding showed that MCM was found with depression items but not with physical threat words. Thus, the MCM bias in explicit memory is somewhat specific to information that is congruent with depression rather than to all negativistic information

Studies of magnetised and non-local transport in laser-plasma interactions

The application of magnetic fields in inertial fusion experiments has led to renewed interest in fully understanding magnetised transport in laser-plasma regimes. This motivated the development of a new laser magnetohydrodynamic code PARAMAGNET, written to support investigations into classical magnetised transport phenomena and laser propagation in a plasma. This code was used to simulate laser-underdense plasma interactions such as the pre-heat stage of magneto-inertial fusion. Alongside these simulations, this thesis will present analytic focusing and filamentation models derived from magnetohydrodynamics extended with classical magnetised transport coefficients. These results showed the focal length and filamentation growth length shortened with magnetisation, a result of the magnetisation of the thermal conductivity. Further investigation of the transport properties using the diffusion approximation kinetic code IMPACT showed significant deviation of the growth rate at intermediate values of magnetisation and non-locality, inexplicable using fluid models. The kinetic code result motivated exploring the influence of the high-order anisotropies of the distribution function (in terms of spherical harmonics), ignored in conventional approximations. By using a recursive matrix inverse method, corrections to the transport coefficients including all orders of the electron distribution expansion were found. Analysis of the conductivity, resistivity and thermoelectric coefficients showed deviation by up to 50% from the classical form at intermediate magnetisation and nonlocality. The diffusive approximation of the IMPACT simulations was insufficient to capture the transport behaviour present in the theoretical high order calculation. Modern inertial fusion experiments work in regimes that are non-local and susceptible to significant focusing exacerbated by magnetisation. The resulting filamentation has detrimental implications to laser absorption and the modified non-local transport behaviour is a possible source of error in simulations. The complex interplay between non-locality and magnetisation in transport suggests using more terms of the spherical harmonic expansion in closures of plasma equations. Particular consideration is given to the implications to inertial fusion experiments. Together these results suggest the necessity of including non-local magnetised transport in the modelling of high-energy-density laser plasma experiments.Open Acces

Paths of Target Seeking Missiles in Two Dimensions

Parameters that enter into equation of trajectory of a missile are discussed. Investigation is made of normal pursuit, of constant, proportional, and line--of-sight methods of navigation employing target seeker, and of deriving corresponding pursuit paths. Pursuit paths obtained under similar conditions for different methods are compared. Proportional navigation is concluded to be best method for using target seeker installed in missile

Critical Shear Stress Estimates of Sunken Alberta Bitumen

As observed in several recent spills (e.g., DBL-152, TX; Enbridge-Kalamazoo, MI), under certain circumstances, released oil can sink to the bottom of a water body. Once on the bottom, the oil can move or remobilize into the water column. The National Oceanic and Atmospheric Administration’s (NOAA) Office of Response and Restoration (ORR) uses mathematical models to predict the trajectory of spilled oil. The critical shear stress (CSS) for an oil is used to predict the movement of sunken oil along and off the bottom. The CSS has only been measured for one oil (Hibernian crude). The Coastal Response Research Center (CRRC) at the University of New Hampshire (UNH) has an annular flume equipped with a velocity profiler that can be used to estimate CSS by measuring the instantaneous, three-dimensional water current velocities at which sunken oils undergo movement and erosion of visible oil droplets occur. The CSS of sunken Alberta bitumen was determined by progressively increasing current velocities until deformation, movement and erosion of the stranded oil was observed. Tests were conducted in freshwater at water temperatures of 5, 15 and 25°C. At temperatures ≥ 18.5 ± 1.9 °C, mass erosion of visible droplets was observed in current velocities greater than 20 cm/s (0.39 knots.), corresponding to a CSS of 1.9 Pa. No erosion was observed at temperatures \u3c 18.5 ± 1.9 °C in current velocities up to 100 cm/s (2.25 knots). Understanding the transport and fate of sunken oil is an important prerequisite for recovery of non-buoyant oils. Unfortunately, details regarding environmental conditions and physical properties of crude oil are limited. Spill trajectory modelers make a “best guess” of the expected conditions needed to erode and resuspend oil from the bottom. CSS data are needed for a range of oils. This thesis research estimated CSS for an Alberta bitumen, providing modelers information to predict the behavior of sunken Alberta bitumen

Effect of aspect ratio on the air forces and moments of harmonically oscillating thin rectangular wings in supersonic potential flow

This report treats the effect of aspect ratio on the air forces and moments of an oscillating flat rectangular wing in supersonic potential flow. The linearized velocity potential for the wing undergoing sinusoidal torsional oscillations simultaneously with sinusoidal vertical translations is derived in the form of a power series in terms of a frequency parameter. The series development is such that the differential equation for the velocity potential is satisfied to the required power of the frequency parameter considered and the linear boundary conditions are satisfied exactly. The method of solution can be utilized for other plan forms, that is, plan forms for which certain steady-state solutions are known

The Streamline Pattern in the Vicinity of an Oblique Airfoil

A method for determining the streamwise flow pattern of a nonviscous incompressible fluid about an oblique airfoil from the corresponding flow pattern about the airfoil in normal position is presented and illustrated in two examples. The method can be extended to account approximately for compressibility effects by applying the Prandtl-Glauert correction factor to the flow pattern that is normal to the leading edge of the airfoil. The method is expected to be useful in determining the shape of a fuselage or nacelle having a minimum of interference with the flow over a swept-back wing

'My wood isn’t one of those dark and scary ones': children’s experience and knowledge of woodland in the English rural landscape

Recent studies of children have argued that children are suffering from a deficiency in nature experience. Some argue that a lack of experience leads to poor affective relations which for wooded environments may be manifested as fear. This study investigates a geographical knowledge gap in understanding children’s relationships with woodland. This interactive qualitative study included 21 junior age children living in a rural setting in Derbyshire, England, UK. Most were found to visit local woodlands regularly, though unsupervised visits were usually limited to woods adjacent to housing. The children demonstrated good levels of practical knowledge though explicit knowledge, such as tree names, was generally poor. The majority children had positive attitudes towards woodland, especially those with the greatest experience. Adventure, calm and freedom were identified as major themes. Fear was widespread but rarely dominated and was often associated with exhilaration linked to cultural imaginaries such as computer games and films