Year:2005 | Volume:39 | Issue:1 (89)|Papers Count:13

In this work an experimental investigation is carried on the injection characteristics of double swirl injectors using PDA method. In double swirl injectors, be caves of effective mixing of the fuel and the oxidizer, the combustion process will be efficient with a minimal instability. More over as compared to ordinary swirl injectors, it is possible to achieve higher mass flow rates with the double swirl injectors as this type in effect plays the role of two separate injectors for fuel and the oxidizer.

In this paper, green function and transfer function are used for analytical solution of mass equation, nonlinear spring and damping with effective wind force. This equation has been used to model space structure, wing and all of the structure used at high altitude. Furthermore this equation is applied frequently in modeling foundation similar to nonlinear spring and damping and the equation is better solved analytically where answer of the analytical solution is similar to the mechanical action.

Mobile robotic systems, in which manipulators are mounted on a moving base, are to be employed in performing different tasks, e. g. astronaut assistance in space, rescuing operations, nursing, book keeping, storing, etc. To manipulate an object with several cooperating manipulators, the Multiple Impedance control (MIC) as a Model-Based algorithm enforces a designated impedance on all cooperating manipulators, the manipulated object, and the moving base if applied on a mobile robotic system. To apply model-based control laws, it is needed to extract explicit system dynamic model. In this paper, using Lagrange coefficients, the non-slipping non-holonomic constraint is applied on the dynamic equations for robotic systems with free moving base. Then, the Lagrange coefficients are omitted from the motion equation by using "Natural Orthogonal Complement" method and the explicit motion equations are obtained for mobile robotic system with constrained base. By designing the appropriate path of motion, the multiple impedance control law is applied on a robotic systems with two manipulators while the moving base is driven with two differentially driver wheels. The simulation results reveal good tracking performance even in the presence of disturbances and impact due to contact with the environment.

This paper introduces a novel method that enhances the heat transfer from a given surface by using an array of porous fins under laminar force convection. It is found that using porous fin increase the fin performance compared to solid fin and more enhancement in the fin performance may be achieved as porosity increases and also an improvement in the heat transfer coefficient cause much increase in the porous fin performance as compared to the improvement in the conventional fin performance until it reaches to a constant value. It is shown that the Nusselt number decreases as the injection velocity increases and then Nusselt number increases as the injection velocity decreases until it reaches a constant value that depend on fin length and thermal conductivity ratio. Also it is found that Nusselt number increases as the fin length increases.

In this paper, the transient response of Plate Heat Exchangers under time dependant temperature of the fluid on hot and cold sides has been studied. The effect of viscosity variations has also been considered. In addition the misdistribution of the fluid (unequal flow in different channels) has also been investigated. The governing equations have been solved using finite difference numerical methods. U flow arrangement has been considered in this simulation. It is shown that the transient response of a system of PHE significantly depends on the viscosity variations, as well as the misdistribution parameters. The effect of these parameters on the thermal efficiency of the PHE is also discussed.

In this paper a new method for linear modeling of nonlinear systems is presented. The method is based on the design of an artificial neural network with two layers. The network is trained only according to the input-output data of the system. The weights of connections in this network, represents the coefficients of the transfer function. For systems with linear behavior the method of least square error (LSE) represents the best linear model of the system. However, for nonlinear systems, such as some subsystems in power plants boilers LSE does not represent the best linear approximation of the system, necessarily. In this paper a new linear modeling method is presented and applied to some subsystems in a power plant boiler. Comparison between the transfer function obtained in this way and by LSE method, shows that the neural network method gives better linear models for these nonlinear systems.

Results for a typical abnormal drill-string failure (DSF) in a specific formation in oil fields located in the Southern part of Iran are presented. In this work efforts were made to define the challenge as precisely as possible as to where, how and why the problem occurred. Possible reasons and practical solutions to this challenge are evaluated. Drill-string vibration in torsion mode (stick-slip vibration phenomenon) is the most probable reason of failure in Iranian oil fields due to two reasons. Firstly, it was observed in practice that abnormal drill-pipe failures occurred only in a specific formation while in other formation it did not, even though the bottom hole assembly (BHA) structures were designed identically. Secondly, the rock characterization of the hazardous formation is sticky and hard compared to the layers above and below the hazardous formation. Stick-slip vibrations are self-excited by the interaction of drill-string, drill bit, and formation. Self-excited stick-slip vibrations may also induce severe axial and lateral vibration excitations in the BHA, causing damage to the equipment. The work is motivated by the need to understand the complex vibration states and concludes that vibrations are the main factor leading to drill-string failures (DSF) for the field under investigation in the southern part of Iran. In order to reduce abnormal DSF, several methods and recommendations are presented and discussed.

Using of TWB (Tailor Welded Blank) parts have been increased in vehicle manufacturing, therefore analysis of deep drawing of TWB is necessary to achieve quality targets. In this paper effects of parameters such as thickness difference and the position of butt-welded joint on strain distribution and the required load for deformation has been investigated. The blank with square shape has been modeled with AUTOFORM software and the effects of draw bead with circular sections, also included in the research, while the analysis will predict the maximum allowable thickness difference between the panels.

Shape memory alloys (SMAs) have the ability to recover a predetermined shape when heated. The property in SMAs is due to a martens tic phase transformation which occurs with a change in their temperatures. SMA composite beams and actuators are a kind of smart structures which are composed of a matrix material with SMA sheets or wires embedded in and/or bonded on the matrix part, and can be activated with heating the SMAs. Shape memory alloys have nonlinearities in their thermo-mechanical behavior, and their material properties change with temperature. Also, due to occurrence of large stress and strains in SMAs, the SMA composite structures have geometrical nonlinearities. The nonlinear behaviors make the modeling of SMA composites complicated. In the present research, a nonlinear finite element model is developed for the transient response of 3D SMA composite beams and actuators. The F.E. model is derived by utilizing the weak forms of the equilibrium and energy balance equations, and a constitutive relation with variable material functions for SMA. The model can simulate active and passive responses of the structures. The developed F.E. model is implemented on an example beam, and the numerical results are presented graphically.

Axisymmetric Buckling of polar orthotropic circular plates of linearly varying thickness with elastically restrained edge is studied. The edge of plate is subjected to uniform pressure. In this paper an approximate solution of the problem is obtained by the Optimized Rayleigh-Ritz method using functions based on static deflection of polar orthotropic circular plates. Various effects such as thickness and material property variation on buckling characteristics of circular plate is verified.

The AZ31 alloys with moderate strength and high formability as one of the wrought magnesium alloys are utilized in various industries. To optimize the manufacturing processes and final mechanical properties of these alloys the precise study of the hot deformation characteristics is necessitated. In this regard, one of the effluent parameter is the strain rate. The hot compression testing was carried out investigating the effect of strain rate on the hot deformation behavior of AZ31 alloy. The true stress-true strain curves and the final microstructures were analyzed and the results were discussed relying on the hot deformation fundamentals of the magnesium alloys.

In the current research, the method for Monte Carlo simulation of heat affected zones microstructure of 5010 and 6063 aluminum alloys has been studied using high-energy electron beams. The welded samples from both alloys, in 5 seconds, 6mA (current beams) and 10Mev (beam energy) with different doses were irradiated by a non-linear induction accelerator (Rudotron) statically. The comparison of the experimental results and Monte Carlo Simulation exhibit that the method of simulation is very well.