ESTEGHLAL
Year:2006 | Volume:25 | Issue:2|Papers Count:16

The theory of distributed detection is receiving a lot of attention. A common assumption used in previous studies the conditional independence of the observation. In this paper, the optimization of local distributed detection network with fixed fusion rules to develop a numeric algorithm based on neyman-pearson criterion. Simulation results are presented to demonstrate the efficiency and convergence properties of the algorithm.

Department of industrial engineering and systems, isfahan university of technology this paper deals with resource unconstrained project scheduling problems with the objective of maximizing the net present value (NPV) of project cash flows. Here we present a heuristic algorithm named as differential procedure (Dif_AoA).In order to evaluate the efficiency of this algorithm, networks with node numbers between 10-1000 and network complexity coefficients between 1.3-6.6 have been generated. We have compared both the total time for solving the problem and NPV of the Dif_AoA with those of the recursive search procedure. Computational results show that the Dif_AoA performs very effectively. Extensive analysis has been performed to evaluate the node number, complexity network coefficients (CNC), and deadline.

it is well know that the characteristics of concrete components greatly affect the durability of high strength/high performance (HS/HP) concrete against frost action. Undoubtedly, précis recognition of this relationship leads to appropriate selection of the type and proportions of concrete components in any particular project. In the current study, the aim is to investigate the possibility of developing some mathematical-experimental models to explain the frost of high-performance concrete, regarding the role of some of its main components. To do so, the effects of four key elements, i.e. water, silica fume, coarse aggregate, and number of freeze-thawing cycles, were studied on the frost resistance of HS/HP concrete were studied. 24 concrete mix designs including 3 ratios water to cementations materials, i,e.0.4,0.3, and 0.025; 4 ratios of silica fume to cementations materials i.e. 0, 5, 10 and 15 percent; and 2 types of coarse aggregates, i.e. limestone and quartzite were utilize for HS/HP concrete. Overall about a bout 432 concrete cubes were cast, cured and tested under freeze-thaw cycles. Finally, some models were proposed for describing the frost resistance of high strength concrete.

In recent years, destructive earthquakes have shown the deficiencies of the existing building. One of the most effective mechanisms for dissipating the steel components. The objective of this research is to study the application of metallic dampers for dissipation of the earthquake energy and to investigate the behavior of concrete structures. Finally, the building are subjected to various earthquakes to generalize the results. The results show that the incorporation of the metallic dampers significantly decreases the relative and absolute drift, the structure and the stories damage indices and, finally, the number of plastic hinges. Furthermore, the hysteretic energy dissipation demand also decreases in structural components. Despite the reduction in the inner forces of structural, story shear forces slightly increase due ARE to increase of lateral stiffness, but much of these of these forces will concentrate in dampers. Moreover, the combination of moment resisting frame, shear wall, and metallic dampers are studied. The results show a similar trend in the stated parameters-especially the drift and hysteresis energy dissipation dissipation demand.

Jaketing of reinforced concrete column is a common and useful strengthening method. This method substantially improves mechanical properties of the column, such as flexural strength as well as shear and ductility. In this paper, the behavior of confined reinforced concrete columns is investigated. The results indicate that the method is more effective for slender columns in the region of their failure zone.

The assessment of seismic performance of existing structures is becoming an important problem in earthquake engineering. Some important ructures are considerably old and, therefore, their strengths and ductility's are less than strength and ductility demands because of changes in codes and design in code and methodologies. Such structures structures must be strengthened to resist future earthquakes. First, a structural model must be developed and then, based on seismic hazard and seismic risk analysis or code quantities, the design (or control) parameters can be determined. The next step is defining the damage indices in order to quantify te structural damage. Then the nonlinear dynamic analysis is carried out and damage indices are calculated. In the present paper, a power plant stack (located in mashhad) is investigated for some levels of peak ground acceleration (PGA) considering return periods of 75, 500, 1000, and 2500 year. The height of stack is 100 m and the external diameter of the structure is 10 m. several records are used for nonlinear dynamic analysis. It has been used from park-ang damage index that is a suitable model for concert structures structures and has been considered in IDARC. It is clear that nonlinear dynamic analysis is necessary for the seismic vulnerability of existing structures. Special structures such stacks can be modeled with some 2-D or 3-D elements. However, the beam-column element is a proper model for special structures such as chimneys, considering calculation cast.

This paper introduces an accurate, fast, and applicable method for slip surfaces in slopes. Using genetic algorithm (GA) which is one of the modern and non-classic optimization methods, in conjunction with the well-known bishop applied method, the optimum slip surface in an slop is investigated and its corresponding lowest safety factor is determined. Investigation have shown that selection of variables to define and to solve the problem and determination of a good rang for these variables have a profound effect an the speed of convergence. In the present study, appropriate variables have been defined for solving the problem n a the number of repetitions required to reach convergence are considerably considerably reduced by up to 50% compared with other approaches. This has led to a drastic reduction in time and the memory required. The accuracy of the method is shown first by solving examples related to search for optimum failure surfaces of some homogenous and earth dam slopes and then by comparison of the present method in modern geotechnical engineering, a reinforced earth slope is studied and its failure surface is finally optimized.

The cross-stream migration of a deformable drop in two-dimensional poiseuille flow at finite Reynolds numbers is studied numerically. In the limit of a small Reynolds (<1), the motion of the drop depends strongly on the ratio of the viscosity of the drop fluid to the viscosity of the suspending fluid. For a viscosity ratio 0.125, the drop moves towared the centre of the channe while for the ratio 1.0, it moves a way from the center until halted by wall repulsion. The rate of migration increases with the deformability of the drop. At higher Reynolds numbers (5-50), the drop either moves to an equilibrium lateral position about halfway between the centerline and the wall according to the so-called segre-sillberberg effect or undergoes oscillatory motions. The steady-state position depends only weakly on the various physical parameters of the flow but the length of the transient oscillations increases as Reynolds number is raised, the density of the drop is increased, or the viscosity of the drop is decreased. Once the Reynolds umber is high enough, the oscillations appear to persist forever and no steady state is observed. The numerical results are in good agreement with experimental observations, especially for drop that reach steady-state lateral position.

In this study, turbulent flow around a tube bundle in non-orthogonal grid is simulation (LES) technique and parallelization of fully coupled navier-stokes (NS) equation. To model the small eddies, the smagorinsky and a mixed model was used. This model represents the effect of dissipation and the grid-scale and subgrid-scale interactions. The fully coupled NS equations with the multiblock method were parallelize. Parallelization of the computer code was accomplished by splitting the calculation domain into several subdomains and using different processors in such a way that the computational work was equally distributed among processors.  The discretized governing equation are second order in time and in space and the pressure is calculated by momentum interpolation method (MIM) to prevent the checerbord problem the results are obtained for the turbulent flow over five parallel tube rows. The computational efficiency, flow patterns, and flow properties are also determined. The results showed high parallelization efficiency and high speed up for the computer code. The flow characteristics were determined and compared with experimental results which showed good agreement. Also, the results showed that the mixed model is better than the smagorinsky model for evolution of flow characteristics and lift and drag forces on tubes.

The continuum mechanic simulation of micro-structural damage process is important in the study of ductile fracture mechanics. In this paper, the continuum damage mechanics model formulation proposed by lematire has been validated against ductile damage evolution experimentally measured in A533B-CI steel under stress triaxiality conditions. First, a procedure to identify the model parameters from test was defined. Then, the finite element model was used simulate the experiment carried out on a notched flat rectangular bar. Good agreement was observed between the experimental results and finite element predictions. Next, the identified parameters on A533B-CI steel were used to simulate the results at necking stage and ultimate lode calculated by the damage based method were compared with those obtained from the test. The comparisons indicate a good agreement between the simulated and the experimental results.

The main objective of the present study is to utilize novel linearization strategy to linearize the convection terms of the quasi-dimensional euler governing equations on collocated grids and to examine its shock-capturing capabilities. To avoid a pressure checkerboard problem on the collocated grids, it is necessary to utilize two velocity definitions at each cell face. Similarly, we define two velocity expressions at cell faces know as convicting and convected velocities. We derive them from the proper combinations of continuity and momentum equations which, in turn, provide a strong coupling among the euler discretized equations. To achieve this, we utilize an advanced linearization strategy known as Newton-raphson to linearize the nonlinear convection terms. The key point in this linearization is to preserve the original physics behind the two velocities in the linearization procedure. The performance of the new formulation is then investigated in a converging-diverging nozzle flow. The results show great improvement in both the performance of the original formulation and in capturing shocks. The results also indicate that the new extended formulation is robust enough to be used as an all-speed flow solver.

Fabrication and characterization of aluminum matrix composites different volume fractions of Ni3Al powder (50-4 vol%) were investigated. Ni3Al powder was produced by mechanical alloying of elemental nickel and aluminum power mixture. Al-Ni3Al composite parts were prepared using a powder metallurgy route involving two stages; Al and Ni3Al powder mixture were first compacted under 500Mpa and then hot-pressed under 250MPa at 420°C for 10min. The microstructure and hardness of consolidated parts were investigated by x-ray diffractomerery, optical and scanning electron microscopy and hardness measurement. Results showed that consolidated Al-Ni3Al Al samples included significant porosity with a nearly uniform distribution of Ni3Al particles. Additionally, structural examinations showed that no significant reaction between Ni3Al and aluminum matrix occurred during sintering process. Al- Ni3Al Al composites exhibited a higher hardness value compared with pure aluminum sample prepared under identical conditions. The hardness value of Al- Ni3Al Al composites increased linearly as Ni3Al content increased.

Using electrostatic spray coating technique, polypropylene (EPD 60r) was applied an carbon steel substrates at room temperature. In order to obtain a uniform coating, steel substrates with powder coating were heated in a vacuum oven at various temperatures up to 250°C for various periods of time up to 45 min and a pressure of 200mb. The coating produced had thickness of around 470 microns. In order to modify the chemical structure of this polymer, the powder coatings containing various weight percentages of maleic (anhydride (MA) and a peroxide (TBHP or DCP) were also applied on to the steel substrates under the above conditions. Adhesion strength, were resistance, and ductility of polymer coatings produced were assessed using ASTM standard methods. Results obtained revealed that the polymer coating containing 5 wt%. MA and 0.1 wt%. TBHP had the best mechanical properties. Adhesive strength and were resistance of this coating were 14.3kgf and 250.3 cm, at 6 kgf, respectively, under the applied load of 6kg. Results obtained from DSC thermographs IR spectroscopy also proved the chemical bond formation (grafting) between the polymer and M.A. the mechanical properties of coating an steel substrate stem from such grafting.

An important consideration in control issues is control of nonlinear system. Sliding control that can control the system desirably in the presence of unstructured uncertainties of carelessness in specifying parameters of the system. In sliding control, also called variable structure control, the main objective of the controller is achieved by introducing a sliding surface. One of the fundamental problems which may occur in sliding control is the chattering phenomenon on unwanted oscillation around the sliding surface. Different solutions are introduced to eliminate chattering. One of the commonest solutions is using a constant boundary layer round the sliding surface. In this paper, efforts are made to reduce chattering and to increase stability of the system by varying the sliding controller with a constant boundary layer. Finally, the mathematical model of a pendulum/cart in the presence of uncertainty is developed and the results of the simulation of the introduced controllers are compare.

An effective approach for strengthening masonry building is to apply shotcrete  reinforced with mesh on the surface of the wall. It is not possible to assess behaviour of coated walls solely using analytical approaches based on simple equations of theory of elasticity without the use of numerical methods. Unreinforcced masonry wall is modeled in this study using the finite element software "ANSYS" to assess the behavior of walls strengthened with reinforced jacket. The accuracy of the models is ensured by calibrating the model against results from laboratory tests. Then the calibrated model is generalized to model the strengthen wall and finally, the analytical results obtained from masonry walls and strengthen walls and strengthed walls are compared and evaluated.