Year:2002 | Volume:35 | Issue:4 (74)|Papers Count:16

The possibility of shock hardening of the weld heat affected zones of 5010 and 6063 aluminum alloys has been studied using a high energy electron beam. The welded samples from both alloys, statically in 5. seconds, 6mA (current beam) and 10MeV(beam energy) in different dose are irradiated by a non-linear induction accelerator (Rudotron). The results of the hardness measurements exhibit that the maximum hardness in the heat affected zone of 6063 aluminum. alloy induced by irradiation of a beam with the dose of 69.99 KGY. Metallographic studies using, SEM, TEM and Image Analyzer showed that shock hardening in samples don't induce hardness??? and the increased hardness values were due to electron beam material interactions.

Three stiffness reduction functions are used, The formation of plastic hinge is considered in limit load. These functions cause the yielded cross section to be subtracted from the member stiffness. In the limit load, in which plastic hinges may form at both ends of a beam-column element, the entries of stiffness matrix reduce to zero. To consider the secondary effects, like P-δ and P-Δ, exact stability functions are used. A computer program is prepared for structure analysis. An automatic incremental-iterative procedure and Newton-Raphson iterations are used for nonlinear analysis. Also, redistribution of the forces in structure is predicted by computer program. The numerical results are compared with plastic-zone methods and actual structural loading tests. This comparison proved that proposed functions are better than similar methods.

A nonlinear modeling of a two-tooth per stator pole switched reluctance motor (SRM) is carried out using Pspice. Static test data of flux-linkage and torque for different rotor positions from the aligned to the unaligned position for various stator winding excitation currents of the SRM were available. The flux-linkage versus rotor angular position and stator current are fitted with an analytical equation and its coefficients are determined. The electrical part of the motor is modeled by the induced back-electromotive-force (emf) and mechanical part by torque versus rotor position and stator winding current. Performance of the model is studied using a conventional inverter and the simulation results are compared with test and other simulation results. It is shown that Pspice modeling based on the static test data is more accurate than those obtained numerically by the same data and Pspice modeling with the flux-linkage curves.

Navigation of an autonomous vehicle in an uncertain environment requires accurate positioning of obstacles, using several sensors such as radar, laser range finder, Forward Looking Infra Red (FUR), day light camera and sonar sensors. The proposed navigation system considers the data about obstacles as its input and is able to - navigate toward the target in a safe distance from obstacles with acceptable velocity. Our case study is the navigation of a military boat in the sea. The design is based on a new controller structure, which is defined for each new detected obstacle. The outputs of these controllers are fused together by a weighted-combination of outputs of existing units. Introduction of these weights and their implementations and learning processes are major characteristics of this research. Other characteristics are its simplicity, fast and robust features with respect to disturbances and noises. Such sensors have been involved during recent years, but the navigation system for vessels and ships (our case study) is still manual for supervising data acquisition and processing. Manual methods always confront some mistakes and in some cases it is needed to guide the vehicle without human aid. In such conditions an autonomous navigator should be installed on the vessel. Such navigator utilizes the data obtained from different sensors in a Data Fusion System (DFS) to estimate the location of obstacles, while dynamic or static and also submarine of floating. Since these information are instantly variable the vessel should also be guided toward the target instantly. Defining a potential function has been the major method used for autonomous guidance and collision avoidance.

Stator fault detection may be done with different methods. However, If the stator current sensor is to be installed for protection and controlling of an induction motor, signature and FFT analyses are the mostly used for on-line stator fault detection. Also, winding function method is an effective procedure for modeling motors in unbalance conditions. Simulation results with this method are used in this paper for detection of the turn-to-turn, coil-to-coil and phase-to-phase faults. The FFT analysis of line current, interrupting motor power supply; negative sequence currents and R.M.S value of speed are all important criteria for fault diagnosis. Simulation and Experimental results confirm that the FFT analyses and interruption of motor from supply and R.M.S value of the speed are the effective methods for the fault detection. Experimental results are presented to verify the accuracy of the simulation results

The paper discusses a nonlinear analysis of 2-D reinforced concrete frames using the Macroscopic Finite Element Model (Mac.FEM). In the elastic analysis, the reference axis for calculation of the flexural rigidity (EI) is the centroid of the cross section. This axis cannot be used for the nonlinear analysis because of variation of the modulus of elasticity over the depth of the cross section. The paper proposes a rational reference axis for the flexural rigidity (i.e., rigidity center) using the equilibrium equation and finite element theories. The proposed reference axis is used in the nonlinear analysis to predict the structural behavior of reinforced concrete frames. In the analysis, a nonlinear stress versus strain relationship for the confined concrete in compression is used to account for the effect of transverse reinforcement on the strength and ductility of structural frames. Comparison of the test results with the proposed analysis shows that the Mac. FEM can accurately predict the strength and behavior of reinforced concrete frames if the confining effect of transverse reinforcement and the rigidity center are taken into account.  

Dispersive soils are clayey soils, which erode easily under concentrated seepage. Specific characteristic of these soils is existence of high an10untsof sodium ions in their pore water. Identification of dispersive soils is impossible through ordinary soil mechanics tests and for this purpose, conducting four specific tests namely Crumb, Double hydrometer, Pinl10le and Chemical tests is suggested by most of researchers and test codes. Sherard's chemical criterion is one of the commonly used criteria for identifying dispersive soils. For using this criterion, it is suggested by Sherard to extract pore water from the soil close to its liquid limit. However, through former studies on dispersive soils encountered in different regions if Iran, we found that in most cases, pore water extraction around liquid limit is not possible using ordinary S.M. laboratory equipment and requires special extraction device. In this study, a specific device was designed for pore water extraction in low moistures around liquid limit. Then, to determine. the effect of extraction moisture content on the evaluation of dispersive according to Sherard's chemical criteria, necessary identifying tests were conducted on eight soil samples, which were collected from different parts of Iran. The results of these tests showed that by variation of extraction water content, the amount of Sodium, Potassium, Calcium and Magnesium ions and also the ratio of sodium to the total dissolved salts may change notably. In other words, using Sherard's criterion disregard to his suggestion on extraction water content can lead to inaccurate or even incorrect results.

An analytical solution for the upset forging of parts that have some axis of symmetry, using an upper bound approach have been represented in this paper. The method presented in here is general and could be applied to different shapes and sizes. The upsetting pressure and the deformation patterns could be obtained using this analysis. Two and three dimensional deformations during the upset forging of non-circular billets could be . obtained using the present method from which the three dimensional forging of elliptical billets are presented here as an example. The bulging effect has also been taken into account and is predicted very well by the theory. The effect of work hardening has also been taken into account in the present formulations. The theoretical results obtained by the present theory have been compared with the experimental and theoretical results of other workers and good agreement was observed. The main advantage of the present analysis was the computational time taken by this method, which was estimated to be at least 75% less than that of the other workers.

Augmentation of heat transfer and pressure drop during laminar flow of oil inside one smooth tube and seven wire-coil inserted tubes of varying wire diameter and pitch have been investigated experimentally. The experimental set-up which was used in this investigation was an oil system equipped with all necessary instruments. The heater of this system was a double pipe counter flow heat exchanger in which oil is heated inside inner tube by the steam flowing in the annulus. All together 120test runs with various flow rates were performed for plain and roughed tubes (tubes with coiled wire inserts). Results show that increase in the friction factor is comparatively low at lower Reynolds number and at higher values it is very large due to some induced turbulence. Also heat transfer coefficients of tubes with coiled wire insert are significantly higher than plain tube and it is a function of Reynolds number, helix angle and Prandt1 number. The maximum obtained enhancement in heat transfer coefficient was as high as 230 percent.On the basis of the experimental data of this investigation, a correlation was developed for predicting of heat transfer coefficient during heating of oil flowing inside tubes with coiled wire inserts. The heat transfer coefficients calculated by this correlation were within ±20% of the experimental values for most of the data. So there is a good compliance between this correlation and experimental values.

Lift and drag coefficients are predicted for a symmetrical hydrofoil, NACA 66-012, at non-zero angles of attack under supercavitating flow conditions. The hydrofoil is modeled using surface singularities and both the pressure distribution (obtained from potential flow solution) and the wall shear stress distribution (obtained from boundary layer solutions) are used to determine the hydrodynamic forces applied on the hydrofoil. To get the potential flow solution, the Panel method was used. For laminar boundary layer solution, Thwaite's method was used combined with Mitchel criterion to decide on the transition point. Head's method was then used to solve the turbulent boundary layer in combination with Ludwig's formula for the skin friction coefficient. The system of ODE equations were then solved numerically and the hydrodynamic forces (lift and drag) were calculated at two different angles of attack in a range of cavitations numbers. Agreement between predicted values and experimental data appears to be qualitatively good. The work shows that using classic ideas of aeronautics, i.e., dividing the flow about a blunt body to a boundary layer with dominant viscous effects and an in viscid region outside the boundary layer may be used efficiently in order to check the suitability of a given airfoil (or to compare their performance) for use in hydrofoil ships.

There has been many methods for calculation and analysis of chemical engineering problems. Number of phases in equilibrium and mole content of each component in existing phases has been one of the most important subjects of research in recent years. Among all conventional methods in phase stability analysis the Michelsen (1982) Stability Analysis Method" is of much interest. Regardless of what Method(s) is (are) being used for calculation of engineering problems, the key operation is solving the set of generated Equations. Presence of complicated empirical and theoretical equations, which are usually non-linear, mostly leads the solution to multiple roots for dominating set of equations. The conventional mathematical algorithms are not of enough robustness to yield all co-existing roots for these sets of equations. Number of coexisting roots is not predictable. Uncertainty about number of phases in equilibrium is a further problem. Therefore the importance of a robust method to yield all co-existing phases in equilibrium together with the mole contents of each phase is obvious. The idea of this paper is to describe Homotopy continuation method, as a solution and extend the capability of this method to complex domain.

Cattle manure is the most susceptible feed for anaerobic digestion anl0ng organic waste materials. Cyclic batch reactors with periodical feeds and discharges are often used in anaerobic digestion of cattle manure. On the other hand, mixing is an important factor for optimal performance of cyclic batch reactors and its modeling is essential for performance prediction of real reactors. In this study a mathematical model for anaerobic digestion of cattle manure was developed. to describe the dynamic behavior of non-ideally mixed cyclic batch reactors. The microbial kinetic model includes an enzymatic hydrolysis step and four bacterial steps, together with the effects of substrate inhibition, pH and thermodynamic considerations. The biokinetic expressions were linked to a simple two-region liquid mixing model, which considered the reactor volume split into two sections, the flow-through and the retention regions. Changing the relative volume of the flow-through region and the flow rate of the internal exchange to the feed flow rate ratio represented deviations from an ideal completely mixed regime. The dynamic model described the effects of retention time and reactant's distribution, resulting from the mixing conditions, on the process performance. The evaluation of the impact of the characteristic mixing parameters on anaerobic digestion showed that the relative volume of the flow-through region has a more significant effect than the turnover time. However, retention time and reactant's distribution and consequently, the methane yield were complex functions of both mixing parameters. In addition, the simulation results showed that the feeding interval is efficient on reactants' distribution of both regions. So that the methane yield is improved when the cyclic batch reactor is approached to a continuously reactor.

It dynamically models a traffic assignment problem. This model is a nonlinear goal programming mixed with integer variables. It belongs to a class of dynamic system optimal traffic assignment problems. Taking into consideration that these problems are known as NP-Hard problem, most of them don't have polynomial behavior from the time complexity viewpoint. Regarding this fact, this study was carried out to find heuristic algorithms for solving such problems in order to improve the efficiency of solving this kind of models. A special genetic algorithm (GA) was designed in this study, which in addition to constraints handling in decision-making space and improving the generation members, will improve the evolution process and concludes the problem solving with an acceptable speed. Therefore an efficient heuristic algorithm has been proposed to solve such problems. At this point, the results of the solution is compared and analyzed with the results of solving the exact algorithm based on the generalized reduced gradient (GRG). These results demonstrate that solving the suggested model with the GRG and GA doesn't have considerable differences in the amount of a goal objective function. Meanwhile, solving a suggested model with genetic algorithm with population size ([m]<=30) and generation cardinality ([gen]<=300) on numerous samples indicates that the time taken for solving a model is lower, compared to the GRG. If population size and generation cardinality increased from the above values, using the parallel genetic algorithm would be more efficient.

In this paper we address the railway crew-scheduling problem, for which we have solved it for head of crew (train master) in passenger trains with real data of Iranian I.R. Railways. All possible activities of crew during a period of time are classified into two groups of activities, tasks and transfers. First, these activities and the precedence relationships among them are shown graphically by a multi depot network containing tasks and transfers arcs. According to the designed network, a new mathematical model, is, then, presented which is able to optimally solve small and medium size problems. In order to solve large size or real world problems, a heuristic algorithm which is called constraints logic pattern is developed. Based on real data taken from passenger train scheduling of Iranian Railways, using branch and bound method, several problems in different sizes are solved. These problems are, also, solved and compared by a simplified method and the constraints logic pattern method. By comparing these two latter heuristic solution approaches with the present approach at Iranian Railways, it is concluded that constraints logic pattern, while improving quality of solutions, can solve real world problems and provide noticeable savings.