نشریه مهندسی مکانیک مدرس
سال سیزدهم شماره 9 (آذر 1392)

In this paper، interlaminar stresses resulting from static behavior of laminated plates، which were made from composite materials، were evaluated. To this end، out-of-plane stresses and displacements were considered as a primary variable. In addition، for the problem analysis، the boundary value problem method was expanded in order to form a first-order linear differential equations system which depended on the laminate thickness. This method could consider normal and transverse stresses and investigates a three-dimensional stress field near the free edge of the layers. In the proposed model، a laminated plate was placed on a simply supported boundary condition and under transverse loading. It was also assumed that the interlaminar transverse stresses، and displacements were continuous in layers'' interfaces. The governing differential equations system was solved using Navier''s approach and shooting method and، finally، the obtained results were compared with the results of other references. The results indicated good accuracy and high speed of the method used in analyzing stress field.

Chaotic dynamics of spin-orbit motion of a triaxial gyrostat satellite under the gravity gradient perturbations is considered. The Hamiltonian approach is used for modeling of the coupled spin-orbit equations of motion. The complex Hamiltonian of the system is reduced via the extended Deprit canonical transformation. This reduction yields to the derivation of the perturbation form of the Hamiltonian which can be used in the Ricci curvature criterion based on the Riemannian manifold geometry for the analysis of chaos. The results obtained from Ricci method as well as the values from the Lyapunov exponent demonstrate the presence of a strange attractor and chaos phenomenon in the perturbed system. The simulation results based on the numerical methods such as Poincare'' section، trajectories of phase portrait، and time series responses confirm the heteroclinic bifurcation and chaos in the system.

One of the methods of blade production is forging. But according to the complexities of the blades، they cannot be produced in one stage and it''s necessary for them to consider preform. In this research، a basic geometry with elliptical cross section for airfoil of blade، was considered and response surface method was used to optimize this preform. Optimization purposes were considered completely die filling and reduction of flash volume، forging load and strain variance. At the end، optimized preform was compared with the model of mass distribution method. Results show response surface method give better results than mass distribution method. Also physical modeling was used for verification of simulation results. Results show simulation results have a good corresponding with experimental results.

In this research the Magnetic Abrasive Finishing capabilities in AISI 4140 steel polishing was studied. Surface roughness was considered as a function of the tool rotational speed، working gap، abrasive material and abrasives particle mesh size. To conduct the tests، a specific magnetic tool was designed to polish the flat steel surfaces by a milling machine. Experiments were arranged based on Taguchi method and using abrasive material consisting of Aluminum Oxide or Silicon Carbide with paraffin oil and Carbonyl Iron powders with different mesh sizes. After surface roughness measurement of samples، the effect of each parameter on the surface quality was inspected by ANOVA method. Results showed that in Magnetic Abrasive Finishing of mentioned steel، the parameters of working gap، tool rotational speed and the abrasive material type are of the most importance as ordered. Finally، a roughness predictor function was introduced by regression method.

Present study describes the approach of applying Response Surface Methodology (RSM) with a Pareto-based multi-objective genetic algorithm to assist engineers in optimization of sheet metal forming. In many studies، Finite element analysis and optimization technique have been integrated to solve the optimal process parameters of sheet metal forming by transforming multi objective problem into a single-objective problem. This paper aims to minimize the objective functions of fracture and wrinkle simultaneously. Design variables are blank-holding force and draw-bead geometry (length and Diameter). Response surface model has been used for design of experiment and finding relationships between variables and objective functions. Forming Limit Curve (FLC) has been used to define the objective functions. Finite element analysis applied for simulating the forming process. Proposed approach has been investigated on a cross-shaped cup drawing case and it has been observed that it is more effective and accurate than traditional finite element analysis methods and the ‘trial and error’ procedure.

In this paper a two dimensional elasticity for free vibrations and the effect of elastic foundantion on a two-direction functionally graded beams with integrated surface piezoelectric layers with combination of differential quadrature method and space-state method is presented here. Differential quadrature method in axial direction and space-state method in transverse direction is used. It’s considered that two parameters model or winkler-pasternak for elastic foundation which has been considered two kinds of boundary conditions include simply support and clamped-clamped. Also، It is assumed that beam properties in thickness and axial direction varying exponentially and poison factor is constant which has been considered the effects of materials properties gradient index and number waves on free vibrations beams. The obtained results show that this method has good accuracy and high speed of convergence.

In this paper، ratcheting behavior of stainless steel 304L cylindrical shells under cyclic combined and axial loadings are studied، experimentally. Tests were performed by a servo-hydraulic INSTRON 8802 machine and the shells were fixed normal and oblique under 20 degree and subjected to cyclic loads. In this paper، the effect of length of cylindrical shell and the effect of angle of cylindrical shell on ratcheting behavior were investigated. Based on the experimental results، it was found that bending moment plays a crucial role in waste of energy and increase in plastic deformations. Seen that due to the existence of bending moment in different cross section of oblique cylindrical shell، there are more plastic deformation and accumulation in comparison to normal cylindrical shell. Also، analyzing the loading history of cylindrical shell under combined loading، it has been seen that by keeping the mean force at constant value while increasing the force amplitude، the ratcheting displacement became higher and by the prior load with higher force amplitude retards the ratcheting behavior and plastic deformation with samller force amplitude.

Ttriangulation technique is one of the most commonly techniques used in three dimensional measurements. Hardware and software used in 3D scanning systems are main error sources affected the accuracy of scanners. Depth reconstruction accuracy is a direct impact of the quantization process، and so it is related to the pixel size of the sensor. Dithering technique may be used to reduce the errors during quantization. The current study introduces a technique in which a relative fine movement between object and sensor is generated during picture capture. Although، using this technique will improve the accuracy of scanning but changing the hardware set up during the process is also time consuming. So to deal with this problem the dithering technique is simulated using the linear regression to reduce the scanning time. The paper firstly describes the theory of the noise introduction technique followed by modeling and simulation of the process by regression function. The results obtained from simulation show great improvement in measurement accuracy. To evaluate the result in a real world، a control rig was designed and built following which experiment was performed. The results showed considerable improvement in measurement accuracy. The result of both simulation and experiments are reported.

In the present paper،by performing a two-dimensional simulation،the heat transfer from a hot cylinder to a cold square enclosure has been studied parametrically and the consequent effect of changing in cylinder diameter has been investigated. The 2-D governing equations have been solved using the finite volume method and TDMA in an ADI procedure for different diameters of cylinder inside a square enclosure with a constant characteristic length for two different Rayleigh numbers of 104 and 105. Results showed that the patterns of streamlines، isotherms and the Nusselt number values depend strongly on the Rayleigh number and also ratio of cylinder diameter to characteristic length of enclosure (2R/H). In this case، the centers of vortices created around the cylinder appear in bottom half of enclosure in 2R/H=0. 4 for Ra=104 and in 2R/H= 0. 5 for Ra=105. Moreover، it is observed that increasing the Rayleigh number and 2R/H ratio، the heat transfer rate from the enclosure is also increased. For example،in 2R/H=0. 5، by increasing the Rayleigh number from 104 to 105، the average Nusselt enhances about 30 percent of its initial value and in Ra=105، by changing the 2R/H ratio from 0. 2 to 0. 5، the average Nusselt climbs almost 35 percent of its initial value.

At a Compressed Natural Gas (CNG) filling station، natural gas is stored in the high pressure reservoirs. The pressures within these reservoirs have huge effects on fast filling process of a natural gas vehicle’s (NGV) cylinder and the difficulties associated with the filling process. The accurate modeling of the fast-fill process is a complex procedure which should be thoroughly studied to optimize the filling process. Here، a theoretical analysis has been developed to study the effects of various parameters on the CNG filling process and the conditions. The analysis is based on the first and second laws of thermodynamics، conservation of mass and the AGA8 equation of state. The required properties of natural gas mixtures have been calculated making use of the AGA8 equation of state (EOS) and thermodynamics relationships. It is found that، the composition of natural gas is very effective on the CNG filling process and final in-cylinder values. For various Iranian natural gas compositions، the optimized filling stations'' reservoirs pressure has been found.

In this paper، we propose the design of a novel gait rehabilitation passive orthosis to training the people who lost their walking ability due to neurological injuries، such as spinal cord injury and stroke. As known، the movements of pelvis play an important role in balance and propulsion during a gait cycle. In this research، we present and simulate a passive orthosis to assist the motion of pelvis of gait patients for regaining their initial walking pattern. This optimized pelvic device is un-motorized and contains only passive elements. The accomplished simulation is based on presentation of a proper 3D dynamic model of human body by focusing on motions of lower legs during gait on treadmill. Also، structural parameters of orthosis are derived during solution of optimization problem defined on related dynamic model. The simulation results show optimized time trajectories of pelvic rotations are close to corresponding desired diagrams and optimum passive device can create the desired motion of pelvis without any effort from subject.

Layout design of a complex system such as a satellite or an airplane is a difficult problem to solve. This problem is known as an NP-complete problem in terms of computational complexity. The main difficulties encountered in the layout design problem are formulation of the problem in mathematics and the solution strategy and practical approaches in engineering. This paper reviews the research work of the authors to automatic layout design process in satellite in last 10 years and the methods of layout design of satellite divides to three main categories that consist of practical method، human-computer interaction and three dimensional layout design and then studies methods of the current state of the art of 3D layout design

Metals have a crystalline structure and the plastic flow in these materials occurred in the special crystalline planes and special crystalline directs that occurs in the planes. This mechanism is related to metals plastic deformation in the microscopic level. In this mechanism، non homogenous microstructure and the effect of crystalline direction play a major rule in the material behavior. Crystal plasticity constitutive equations are used for investigation of the crystalline direction effect and material texture. Voronoi method is used for simulating the non homogenous microstructure in plastic deformation. In this study، the elastic modulus parameters obtained by molecular dynamic simulations. Finally، the plastic deformation of Fe metal is simulated with finite element method that good agreement was observed with the experimental data.

An advance cooling method for buildings is use of radiant cooling system، which is not only economically feasible but also enhances thermal comfort for occupants. In this numerical study the flow and temperature fields in a room equipped with radiant cooling panel، either on the ceiling or on the wall، are studied. Outside summer design temperatures of Tehran and Semnan have been considered and to model the presence of an occupant a cube is placed in the center of the room with its external walls having constant heat flux. The results show that the vertical and horizontal temperature distributions become uniform and the maximum absolute air speed is around 0. 2 m/s. The share of radiation heat transfer to the ceiling or the wall cooling panel is at least 58% or 65%، respectively، which increases due to presence of a human model. The net radiation decreases by increasing the panel temperature، but increases by increasing the outside temperature. The wall cooling uses less energy and regarding temperature and velocity distribution provides a better comfort condition