AMIRKABIR
Year:2006 | Volume:16 | Issue:63-C|Papers Count:12

In this research, the effect of mechanical activation on phase transformation of monoclinic zirconia was investigated. It was revealed that the transformation of monoclinic to tetragonal at a temperature as high as 1250° C is very slow. Milling of pure zirconia with monoclinic structure facilitates this phase transformation. The XRD patterns of the milled samples show that after 4 hrs tetragonal peaks are appeared and after 48 hrs phase transformation is completed. The kinetics of this transformation was also studied and the corresponding correlation was proposed. Cubic structure could also been obtained after 150 hrs milling. The sharp increase of the pressure and temperature at the collision points of the balls are the main reasons for this phase transformation at the ambient overall temperature.

In the present research the influences of manufacturing parameters e. g. laser scan rate and working atmosphere on densification and microstructure of M2 high-speed steel powder via direct metal laser sintering (DMLS) were studied. Density and micro-hardness measurement experiments were performed on, produced specimens and microstructural evaluation was done with both optical and scanning electron microscopy (SEM). The result of experiments showed that the density of laser sintered specimens decreased linearly with increasing the laser scan rate. Furthermore, sintering under the argon atmosphere yields higher densification than the nitrogen atmosphere. It was found that laser sintered specimens have cellular and/or dendrite microstructure due to rapid solidification during the DMLS process. Also, the size of pores is independent to laser scan rate, sintering atmosphere and chemical composition.

The feasibility of using electrokinetic's to clean up contaminants from soils has been established and addressed by several authors. However, the effects of soil composition on the efficiency of the method not yet fully studied. Many of soils especially in semi-arid regions of the world have carbonates. The most common of the carbonate minerals found in soils is calcite (CaCO3). Carbonates are the most predominant mechanism of retention of heavy metals in soil solids in comparison with exchangeable phases, organics and amorphous materials. In order to investigate the effect of calcite on the removal efficiency, electrokinetic experiments in bench scale were conducted on two soils: kaolinite and natural soil of a landfill in Hamedan. Kaolinite specimens with different percentages of calcite were mixed with zinc nitrate as a source of heavy metal contamination. Batch tests were also performed to define Zn (II) adsorption onto these samples. Series of electrokinetics experiments were performed on these artificially prepared samples. The study showed that soils which have higher carbonate percentages and natural soil with 28% carbonate prevent the development of an acid front which results in alkaline conditions throughout the soil during electrokinetic remediation and significantly lower the efficiency of method.

Using collocated grid is very popular because of its flexibility and easiness in programming, to solve fluid flow equations specially in complex geometry. Momentum interpolation is used for this type of grid to prevent pressure oscillation. In the present paper, two methods of momentum interpolation are studied to solve steady state problems using unsteady equations in shallow water flows. Results of numerical model for a complex flow pattern showed that both of these methods give almost the same results. Therefore, the simpler model which needs less calculations can be employed to achieve the same accurate results. However, shorter time step should be used in the simpler method because of stability constrains.

Results obtained from different numerical methods applying to intensive hydraulic gradients are associated with fluctuations. In current study, attempts have been made to eliminate non-physical oscillations by the use of slope limiters in both steady and unsteady flow conditions. A 2D, depth integrated, free surface flow solver is developed on the cell centered unstructured triangular grids. The governing differential equations were descretized using Finite Volume Method. Shallow water equations were solved principally by Reimann problem and Godunov-type wave propagation formulation. The model has second order accuracy spatially and temporally. For the time derivatives, the two-step Runge- Kutta method was deployed. Results obtained from the developed model were verified against analytical approaches found in the literature for dam break and oblique hydraulic jump. A comparison of numerical and analytical results represents reasonable degree of similarity.

Divergence is one of the most important problems in nonlinear analysis. In this paper, the reason why this problem may exist is explained, then the proposed method of analysis to prevent this problem is introduced. Finally with the help of some practiced examples, capability of the especial introduced mutuation functions is represented.

Natural draft concrete cooling towers arc special structures in most of the power plants. For design of these structures, there are varieties of loadings that each one can be determinant. Among these loads, earthquake can cause instability in such structures. Previous research has shown that the columns supporting a cooling tower are sensitive to earthquake forces, so in this study the columns of these towers were regarded. As a case, Shazand cooling towers were chosen in which the columns length are very high. Finite element model of them were provided and nonlinear dynamic behavior of them were studied under the effect of real vertical and horizontal components of Tabas, Naghan and Barn earthquakes. The results show columns damage and instability of the towers.

Stress and strain around underground spaces in reality are three dimension. Therefore, in order to analyze the stress and displacement around underground spaces, 3D methods should be applied. In this investigation, stability analyzing of Shibli tunnel is used to comparing between 2D and 3D analyze. Shibli tunnel is a double track railway tunnel, will excavate in the Shibli region. The rock type of tunnel consists of an alternation of shaley limestone and Cretaceous conglomerate. Flac, and Flac3D codes are applied for stability analysis of the tunnel. Further, a hazard warning level was defined using Sakuraii's critical strain and for estimating stability of the tunnel, displacements around tunnel are compared with that of the hazard warning level. According to the results of 2D and 3D analysis, in weak rocks, if the effect of advancing face is considered in numerical modeling and the tunnel is open-ended, displacements in 3D model will be more than displacements in 2D model.

The comparative advantage of mining ores from production and exports point of view is an important factor in economic planning. This issue is central in developing countries. In Iran, promoting the non-petroleum exports and hence departing from the single-product economy to a wider range of exports is a major issue. Also, This is one of the main objectives of the Forth Economic and Social Plan of Iran. Mining reserves play an important role in providing the raw materials used in related industries. Spread due to the geographical and geological situation of Iran, there are significant and valuable ore reserved situated in different parts of the country. This is an excellent potential for the mining investment. In this paper the comparative advantage of operating copper mines in Iran, from production to exports stage, is evaluated by applying the Domestic Resources Cost (DRC) method. Finally, this study recommends a regime for promotion of production and export of the ore. Accuracy of the results obtained in the paper is tasted by comparing these with the real standard ratios being used in other countries.

According to the mineral compositions, paragenesis, relationships and the fluid inclusion microthermometry two stages of skarn alteration within the Rize pluton area have been identified. The first stage (stage I) was characterized by the Spurrite, vesuviavite, wollastonite, magnetite, pyroxene, gelignite and garnet assemblages at high temperatures (~750° GC).The second stage (II) occurred at lower temperature (~500° DC) when the system collapsed, and is characterised by tremolite, low temperature vesuvianite, rustumite, epidote, calcite, apatite, titanite and hematite. The vesuvianite displays complex zoning due to fluctuations in the Al +3/Fe+3 The oscillation zones are interpreted to reflect fluid and rock-dominated control of Fe+3 and Al+3 activities, respectively, and batch-rise or episodic influx of fluid. It is also concluded that the original magma was so poor in metal complexes (CuCl2, MgCl2, AuCl2, ...) to form any economic deposit. The vesuvianite also acts as an index mineral to follow up the geochemical changes within the skarn.

Sediment transport as a complicated and important phenomenon has attracted a lot of researchers during the last century; however there are some formulae to evaluate sediment loads in aquatic systems. Most of them still face two major problems: firstly, lack of accuracy and secondly, involvement of many parameters which makes them more challenging.Artificial Neural Networks are known as model-free universal function approximators well suited to deal with real life engineering problems including time series predictions and parameter estimation. In this paper, sediment loads are predicted using two different types of multilayer feedforward neural networks, namely Multi-Layer perception (MLP) and Radial Basis Function (RBF). The input variables for both structures are considered to be flow discharge, mean flow depth and width, mean bed material's diameter and water surface slope and the output is sediment discharge. Some different cases have been studied. The results are promising. It has been also observed that mean square prediction errors for the developed MLP is equal to 0.0063 while the devised RBF networks produces much larger mean square errors, namely 0.01260. This indicates that the MLP-load-predictor outperforms the RBF-predictor.