Analysis of seismo-acoustic emission from ice fracturing events during SIMI’94

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 1999In this thesis the analysis of natural ice events is carried out based on direct measurements of ice-borne seismo-acoustic waves generated by ice fracturing processes. A major reason for studying this phenomenon is that this acoustic emission is a significant contributor to Arctic ocean ambient noise. Also the Arctic contains rich mineral and oil resources and in order to design mining facilities able to withstand the harsh environmental conditions, we need to have a better understanding of the processes of sea ice mechanics. The data analyzed in this thesis were collected during the Sea Ice Mechanics Initiative SIMI’94 experiment which was carried out in the spring of 1994 in the Central Arctic. One of the contributions of this thesis was the determination of the polarization characteristics of elastic waves using multicomponent geophone data. Polarization methods are well known in seismology, but they have never been used for ice event data processing. In this work one of the polarization methods so called Motion Product Detector method has been successfully applied for localization of ice events and determination of polarization characteristics of elastic waves generated by fracturing events. This application demonstrates the feasibility of the polarization method for ice event data processing because it allows one to identify areas of high stress concentration and "hot spots" in ridge building process. The identification of source mechanisms is based on the radiation patterns of the events. This identification was carried out through the analysis of the seismo-acoustic emission of natural ice events in the ice sheet. Previous work on natural ice event identification was done indirectly by analyzing the acoustic energy radiated into the water through coupling from elastic energy in the ice sheet. After identification of the events, the estimation of the parameters of fault processes in Arctic ice is carried out. Stress drop, seismic moment and the type of ice fracture are determined using direct near-field measurements of seismo-acoustic signals generated by ice events. Estimated values of fracture parameters were in good agreement with previous work for marginal ice zone. During data processing the new phenomenon was discovered: "edge waves", which are waves propagating back and forth along a newly opened ice lead. These waves exhibit a quasi-periodic behavior suggesting some kind of stick-slip generation mechanism somewhere along the length of the lead. The propagation characteristics of these waves were determined using seismic wavenumber estimation techniques. In the low frequency limit the dispersion can be modeled approximately by an interaction at the lead edges of the lowest order, antisymmetric modes of the infinite plate.Support for this thesis was provided by Office of Naval Research

Study of Decarbonization Processes During Siderite Ore Roasting

The dissociation process of powdered and lumpy siderite ore in the helium, carbon dioxide and air atmospheres is studied with the use of OD-102 derivatograph. The dependences of dissociation degrees and rates from the temperature are received through thermograms processing. The kinetic equations of powders dissociation from the siderite ore are obtained with the help of complex method. It is determined that found regularities also remain unchanged for the lumpy materials. However, the temperature intervals of decomposition will be different. The received results may be used for optimization of thermal conditions of siderite ore burning in the shaft furnaces which heating causes the decomposition of carbonates within iron-bearing minerals, as well as further endothermic effects. They are necessary to compare the material and heat balances of roasting process, which provide an opportunity to properly determine the fuel-consumption rate and work out recommendationsfor its lowering. Moreover, they are necessary to optimize the design and operating parameters of thermal treatment of siderite ore in the shaft furnaces, which ensure the obtaining of roasted siderite ore in accordance with the requirements applicable to the quality of raw materials during the blast-furnace production. Furthermore, they may be used when working out the methods of reducing roasting and further receiving of metalized iron product rich in iron. Keywords: derivatograph, dissociation process, siderite ore, shaft furnace, roasting, kinetic equations, carbonates, temperature, dissociation degree and rate, heating rate, gas phase, helium, air, carbon dioxid

Study of Heat Exchange Processes During Roasting of Iron-ore Pellets

The method for approximate calculation of heat exchange in a layer of iron-ore pellets is developed, based on the regularities of heat transfer in the stationary layer. It is noted that the duration of oxidizing roasting of iron-ore pellets on a belt of the conveyor-type machine is influenced by the conditions of heat exchange, distribution of temperatures of gas and material along the height of the layer; the physical and chemical processes occurring in the layer of pellets during its heating (magnetite oxidation, decomposition of carbonates, etc.) have a great influence. Most of them flow with the release or absorption of heat. As a result, the calculation of heat exchange in the roasting layer of pellets is a complex problem. It is shown that it is not possible to obtain a solution of the system of equations describing the heat exchange in a layer of pellets in the general case, but only approximately using stepwise approximation of the boundary conditions and parameters of the problem,or by a numerical method with the help of a computer, which is considered in this article. With the help of the drawn-up program, the calculation of heat exchange in the layer of pellets has been carried out with respect to the mode of their roasting on a conveyor-type machine. The considered method has a great practical application, since it allows determining the optimal duration of the pellet roasting process, taking into account the effect on heat exchange of various factors, and consequently, the specified degree of completeness of all physicochemical transformations in the treated layer to obtain a high-quality product. Keywords: heat exchange, calculation method, iron-ore pellets, physical and chemical processes, layer, conveyor-type machine, roasting, temperature, solution, approximation, parameters, problem, numerical methods, duration, boundary condition

Mathematical Model of Heat Exchange and Approximate Methods of Solution of Radiation Transfer Equation in the Melting Furnace Tank

Mathematical model of heat exchange in melting furnace tank is considered. Equations of impulse balance for infinitesimal volume as well and continuity equation are simplified. Dimensionless parameters for compilation of discrete analogue are introduced. The system of equations of melt movement is made, solution of which issupposed to be performed using finite-difference methods. The approximate methods of solution of radiation transfer equation for optically thin and optically thick layers are considered. For optical thin layer expressions of spectral function of the source in the assumption of isotropic radiation and axial symmetry, intensity of radiation on the boundary areas and density of the monochromatic flux for the resulting radiation are simplified. Expression for the density of the monochromatic flux in the approximation of the optically dense layer is developed. Keywords: melting furnace, approximate methods, heat exchange by radiation, radiation transfer equation, mathematical mode

Tetra­aqua­bis[(1-ammonio-1-phosphono­ethyl)phospho­nato]zinc(II) tetra­hydrate

The title compound, [Zn(C2H8NO6P2)2(H2O)4]·4H2O, was synthesized by the reaction of ZnCl2 with 1-amino­ethane-1,1-diyldiphospho­nic acid in aqueous solution. The asymmetric unit contains one-half of the complex and two water mol­ecules of solvation. The Zn atom occupies a special position on an inversion centre. This results in a slightly distorted octa­hedral coordination environment, which consists of the O atoms from two phospho­nic acids and four water mol­ecules. The crystal structure displays N—H⋯O and O—H⋯O hydrogen bonding, which creates a three-dimensional network

Ductile-brittle transition in martensitic 12%Cr steel

Mechanical behavior of a 12Cr–0.6Mo–2.2W–4Co–0.8Cu-VNb steel was studied by tension and the Charpy impact tests in the temperature range of 133–473 K. The yield stress and uniform elongation increase concurrently with decrease of temperature because of the work-hardening rate tends to increase with decrease of temperatur