An analytical model describing the motion of vortex rings in an incompressible fluid is constructed. The model is valid both for homogeneous and inhomogeneous vortices buoyant in the gravity field, as well as for combined vortices. The expansion angle of a buoyant vortex is found from the characteristic parameters that define the flow rather than specified on the basis of experiments. Significant differences in the expansion angles of homogeneous and buoyant vortex rings are explained. The calculation results for the proposed model are compared with the results of laboratory experiments and data on the rise of the cloud produced by an atomic explosion.

Analytical model of motion of turbulent vortex rings in an incompressible fluid

During bomb scene investigation the collection of trace explosive residue is a principal forensic task which allows the cause of the explosion to be determined. However the optimum locations around a detonation from where these undetonated trace residues should be sampled has not been determined scientifically. Crime scene investigation guides describe several methods for collecting and analysing explosive residues, but literature regarding the most efficacious areas to sample from is relatively scarce. In this thesis, analysis of the spatial distribution patterns of post-blast explosive residues from detonation and simulation experiments with 0.5 kg, 1 kg and 2 kg aluminised ammonium nitrate and RDX composition charges are the primary original contributions to the literature. Residue samples were collected by swabbing sample sites positioned around the explosive charges and condensed phase particles were collected onto smaller sample sites in order to ascertain the physical morphology of the residues. Both organic and inorganic residues ultimately decreased in concentration nonlinearly with increasing distance from the charge centre. However, the distribution trends between different explosive analytes varied, suggesting the dispersal mechanisms or factors which affected the distribution for each were different. The post-blast particles had varying morphologies at different distances from the detonation and also exhibited different features based on the explosive type. Computational simulations of residue distributions compared well to the experimental results; substantiating the capability of numerical methods to be used as a forensic investigation aid. The key findings from this thesis have provided empirical evidence which validates the current forensic practice of concentrating trace evidence collection near the central region of a detonation area during bomb scene investigation. The findings also imply that surfaces which are downwind of the detonation should be focused on for residue sampling and that microscopic examination of items in the vicinity of a detonation may allow identification of the explosive used based on particle morphology, prior to any chemical analyses. Furthermore, having demonstrated the reliability and capability of simulation techniques to model explosive residue distribution, these can now be developed and validated through further tests which also assess the detonations of further explosives under different conditions.

The Spatial Distribution of Post-blast Condensed Phase Explosive Residues

Приводятся первые результаты по экспериментальной диагностике аэроакустических свойств фундаментального объекта механики жидкости и газа – турбулентного вихревого кольца, которые были получены с помощью современных методов многоканальных акустических измерений и постпроцессинга. Шум вихревого кольца удается различить на фоне помех только в специальных акустически заглушенных камерах. В данной работе регистрация шума свободно летящего вихревого турбулентного кольца проводилась в заглушенной камере размерами 10×6,7×4,1 м, недавно построенной и введенной в эксплуатацию в лаборатории механизмов генерации шума и модального анализа Пермского национального исследовательского политехнического университета. В результате проведенных экспериментов удалось выделить шум кольца и получить усредненные по ансамблю реализаций узкополосные спектры звукового давления, что говорит о хорошем акустическом качестве разработанного и изготовленного генератора вихрей и введенной в эксплуатацию в ПНИПУ акустической заглушенной камеры в целом. Эти эксперименты, в свою очередь, дают возможность проведения на их основе тонких аэроакустических исследований. Ключевые слова: турбулентное вихревое кольцо, аэроакустика, заглушенная камера, поршневой генератор вихрей.

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Experimental investigation of turbulent vortex ring noise in anechoic chamber

Ascent of a large-scale thermal in a standard atmosphere is calculated with the use of the Reynolds equations and the k model of turbulence, which takes into account temperature inhomogeneity and vorticity of the flow, and the Euler equations. Results of numerical calculations of a flow examined experimentally are presented. Gas-dynamic and turbulent flow parameters obtained in calculations and experiments are compared.

Numerical Simulation of a Turbulent Thermal

This study presents a model for the dispersion of radioactive smoke clouds from a nuclear weapon explosion. A model based on a modified Settlement model is chosen to simulate the dispersion of radioactive contaminants from a nuclear explosion in the atmosphere. The arrival time and dose rate of radioactive fallout at various distances in the downwind direction are given for different equivalents of the surface explosion and typical meteorological conditions. Thus, the prediction of the dispersion of radioactive contaminants from a nuclear explosion can be achieved under the conditions of known nuclear explosion equivalence and local meteorological parameters. This provides a theoretical basis for the estimation of the affected environment and the input of rescue forces after the explosion.

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A. T. Onufriev

Papers

Theory of the motion of a vortex ring under gravity. Rise of the cloud from a nuclear explosion