Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

Pulse detonation propulsion : challenges, current status, and future perspective

Flame acceleration and transition to detonation in ducts

Bubbles in liquids, soft and squeezy objects made of gas and vapour, yet so strong as to destroy any material and so mysterious as at times turning into tiny light bulbs, are the topic of the present report. Bubbles respond to pressure forces and reveal their full potential when periodically driven by sound waves. The basic equations for nonlinear bubble oscillation in sound fields are given, together with a survey of typical solutions. A bubble in a liquid can be considered as a representative example from nonlinear dynamical systems theory with its resonances, multiple attractors with their basins, bifurcations to chaos and not yet fully describable behaviour due to infinite complexity. Three stability conditions are treated for stable trapping of bubbles in standing sound fields: positional, spherical and diffusional stability. Chemical reactions may become important in that respect, when reacting gases fill the bubble, but the chemistry of bubbles is just touched upon and is beyond the scope of the present report. Bubble collapse, the runaway shrinking of a bubble, is presented in its current state of knowledge. Pressures and temperatures that are reached at this occasion are discussed, as well as the light emission in the form of short flashes. Aspherical bubble collapse, as for instance enforced by boundaries nearby, mitigates most of the phenomena encountered in spherical collapse, but introduces a new effect: jet formation, the self-piercing of a bubble with a high velocity liquid jet. Examples of this phenomenon are given from light induced bubbles. Two oscillating bubbles attract or repel each other, depending on their oscillations and their distance. Upon approaching, attraction may change to repulsion and vice versa. When being close, they also shoot self-piercing jets at each other. Systems of bubbles are treated as they appear after shock wave passage through a liquid and with their branched filaments that they attain in standing sound fields. The N-bubble problem is formulated in the spirit of the n-body problem of astrophysics, but with more complicated interaction forces. Simulations are compared with three-dimensional bubble dynamics obtained by stereoscopic high speed digital videography.

Physics of bubble oscillations

A flux splitting scheme is proposed for the general nonequilibrium flow equations with an aim at removing numerical dissipation of Van-Leer-type flux-vector splittings on a contact discontinuity. The scheme obtained is also recognized as an improved Advection Upwind Splitting Method (AUSM) where a slight numerical overshoot immediately behind the shock is eliminated. The proposed scheme has favorable properties: high-resolution for contact discontinuities; conservation of enthalpy for steady flows; numerical efficiency; applicability to chemically reacting flows. In fact, for a single contact discontinuity, even if it is moving, this scheme gives the numerical flux of the exact solution of the Riemann problem. Various numerical experiments including that of a thermo-chemical nonequilibrium flow were performed, which indicate no oscillation and robustness of the scheme for shock/expansion waves. A cure for carbuncle phenomenon is discussed as well.

A Flux Splitting Scheme with High-Resolution and Robustness for Discontinuities(Proceedings of the 12th NAL Symposium on Aircraft Computational Aerodynamics)

An analytical model for the impulse of a single-cycle pulse detonation tube has been developed and validated against experimental data. The model is based on the pressure history at the thrust surface of the detonation tube. The pressure history is modeled by a constant pressure portion, followed by a decay due to gas expansion out of the tube. The duration and amplitude of the constant pressure portion is determined by analyzing the gasdynamics of the self-similar flow behind a steadily moving detonation wave within the tube. The gas expansion process is modeled using dimensional analysis and empirical observations. The model predictions are validated against direct experimental measurements in terms of impulse per unit volume, specific impulse, and thrust. Comparisons are given with estimates of the specific impulse based on numerical simulations. Impulse per unit volume and specific impulse calculations are carried out for a wide range of fuel–oxygen–nitrogen mixtures (including aviation fuels) of varying initial pressure, equivalence ratio, and nitrogen dilution. The effect of the initial temperature is also investigated. The trends observed are explained using a simple scaling analysis showing the dependency of the impulse on initial conditions and energy release in the mixture.

/pdf/analytical-model-for-the-impulse-of-single-cycle-pulse-2ol2i7xxaq.pdf

Analytical Model for the Impulse of Single-Cycle Pulse Detonation Tube

Direct impulse measurements were carried out by using a ballistic pendulum arrangement for detonations
and deflagrations in a tube closed at one end. Three tubes of different lengths and inner diameters were tested
with stoichiometric propane– and ethylene–oxygen–nitrogen mixtures. Results were obtained as a function of
initial pressure and percent diluent. The experimental results were compared to predictions from an analytical
model and generally agreed to within 15% (Wintenberger, E., Austin, J., Cooper, M., Jackson, S., and Shepherd,
J. E., “Analytical Model for the Impulse of a Single-Cycle Pulse Detonation Engine, AIAA Paper 2001–3811,
July 2001). The effect of internal obstacles on the transition from deflagration to detonation was studied. Three
different extensions were tested to investigate the effect of exit conditions on the ballistic impulse for stoichiometric
ethylene–oxygen–nitrogen mixtures as a function of initial pressure and percent diluent.

/pdf/direct-experimental-impulse-measurements-for-detonations-and-x20q8v3h9o.pdf

Direct Experimental Impulse Measurements for Detonations and Deflagrations

https://apps.dtic.mil/dtic/tr/fulltext/u2/a539314.pdf

Direct observations of reaction zone structure in propagating detonations

Detonations in hydrocarbon fuel blends

Experimental images of detonation fronts are made for several fuel-oxidizer mixtures, including hydrocarbon–air systems. Schlieren and planar laser induced fluorescence techniques are used to image both the shock configurations and the OH reaction front structure in a single experiment. The experiments are carried out in a narrow rectangular channel. The degree of instability of detonation fronts in different mixtures is evaluated by comparing calculated mixture parameters with the longitudinal neutral stability curve. The images reveal that the structure of the front increases dramatically in complexity as the mixture parameters move away from the neutral stability curve into the unstable region. Of the mixtures studied, nitrogen-diluted hydrocarbon mixtures are predicted to be the most unstable, and these show the greatest degree of wrinkling in the shock and OH fronts, with distortion occurring over a wide range of spatial scales. In the most unstable cases, separation of the shock and OH front occurs, and localized explosions in these regions are observed in a high-speed schlieren movie. This is in dramatic contrast to the weakly unstable waves that have smooth reaction fronts and quasi-steady reaction zones with no evidence of localized explosions. A key feature of highly unstable waves is very fine scale wrinkling of the OH and shock fronts, which is absent in the low-activation energy cases. This may be due to the superposition of cellular structures with a wide range of cell sizes. In contrast to soot foils, images of the OH front have a more stochastic appearance, and organized cellular structure is not as apparent.

Joanna Austin

Papers

Analytical Model for the Impulse of Single-Cycle Pulse Detonation Tube

Direct Experimental Impulse Measurements for Detonations and Deflagrations

Direct observations of reaction zone structure in propagating detonations

Detonations in hydrocarbon fuel blends

Reaction zones in highly unstable detonations