فصلنامه مدل سازی در مهندسی
پیاپی 23 (زمستان 1389)

This paper deals with the analysis of plate bending by the finite element method. Since vast findings have been achieved so far, advancing research in this area is very difficult. Nevertheless, three triangular elements for analyzing plate bending will be formulated. The patch test for one and some elements for the suggested elements will be preformed. Moreover, a variety of problems will be solved by the author's program. In addition to these, the responses of the suggested three elements with the other investigator's results, and also accurate answers will be compared. The findings of this article reveal that the new elements have the ability to reach the precise solution. It should be added that one of three proposed elements has the best convergence rate.

In this paper, a new silicon-on-insulator (SOI) device structure is proposed to reduce self-heating effects. Using Si3N4 material is main idea in the structure that has high thermal conductivity respect to silicon dioxide. The device has been verified in two-dimensional device simulation. The results show that the structure provides a new path to reduce the temperature of the channel of SOI Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) and decreases the temperature in the channel.

This paper proposes a hybrid approach based on the Artificial Neural network and Genetic algorithm to optimize surface roughness at the abrasive water jet (AWJ) cutting of glass material. At first, Artificial Neural Network (ANN) was developed in order to model and predict surface roughness by considering the controllable cutting parameters such as water pressure, abrasive flow rate, jet traverse rate and stand of distance. Then the results of the neural network were compared with corresponding experimental tests. According to the obtained results, it was shown that the ANN model is able to present a predictive model of the process in order to estimate the surface roughness successfully. After that, ANN model was combined by genetic algorithm to obtain suitable machining parameters yield to minimal surface roughness. Finally, obtained results showed that, utilized hybrid technique in this paper was employed properly for optimizing AWJ cutting process.

Post-tensoned concrete flat slabs recently are widely used for multi-story structures of commercial, administrative,residential buildings of all types, offices, hospitals and parkings, specific in places that need to large spans. The major benefits of these slabs are the flush soffit, which provides the minimum story height, the maximum flexibility for horizontal service distribution, large spans,reduce cracks, more strength against water influence and lightweight slabs. Special construction technology lift-slabs method, which utilizes prefabricated post-tensioned slabs, makes the construction period significantly shorter, thus, making prestressed lift slabs a very cost effective solution. Most defect of this system is that increase shear force due to increase of span and post-tensioned slab is against punching shear failure due to transfer of shear and unbalanced moment. In most of cases,when slabs were post-tensioned, Some of the problems that our infrastructures with un-bonded post-tensioning facing today are: excess loading, inadequate maintenance, and need for periodic repair and strengthening. Some form of external reinforcement is needed to repair and strengthen these deficient structures. Fiber Reinforced Polymer (especially CFRP) system can be a possible strengthening system for the un-bonded post-tensioned concrete structures.In this thesis, strengthening post-tensioned slab-column connections with Fiber Reinforced Polymer studied with ANSYS, finite element softeware. First,it modeled an actual experimental post-tensioned slab for assurance of accuracy of numeral solution results and compare numeral model with experimental results. Then, three deferent models studied for concrete material. After calibere, widely studies is done about punching failure mechanism, main operative that create failure,cracking patterns and stress-strain states in ultimate state. Then, importance and influence of deferent parameters was studied about post-tensiond slab behavior, for example influence of post-tensioning value on slab behavior that experiment on them need much time and cost.

Due to the some uncertainties during manufacture and assembly of double layer grids with ball joint system, the behavior of this jointing system in the structure is different from the behavior of individual and discrete joints. In the present work, the behavior of a ball joint system has been determined in true conditions of its operation in a double layer grid by the general framework of inverse problem. A full scale double layer grid was constructed using ball joint system. A series of modal testing were performed on the double layer grid in free-free support conditions and its FRFs (Frequency Response Functions) were measured in appropriate degrees of freedom. Using the measured FRFs, natural frequencies of the eight vibration modes of the grid were extracted. A beam element was used at each end of members in the finite element model of the grid in order to simulate the ball joint behavior. Through modal analysis of the finite element model, natural frequencies of the eight vibration modes of the grid were calculated for different section properties of the joint beam element. With the finite element model updating of the grid through reduction of difference between its experimental and analytical natural frequencies, section properties of the beam element representing behavior of the ball joint system in the model were obtained. Whilst the updated model resulted in a very good approximation of the natural frequencies of the double layer grid, a flexible behavior in different degrees of freedom was obtained for the ball joint system. Also, the analytical frequency response functions that were calculated using the obtained section properties for the joint beam element, had a good correlation with the experimental ones.

In this paper a rectangular dielectric resonator antenna (DRA) fed by a microstrip line is studied. Therefore, at first radiation performance of DRA is studied, and the improvement techniques are reviewed. Then propose a novel configuration for broadening of the impedance bandwidth. In the proposed arrangement, by using multi-segment structure with different dimensions, increase the antenna impedance bandwidth. However for decreasing the design parameters, variations limited to the segments width. So, with the non-uniform configuration by variable width, it is possible to create remarkable increase in frequency bandwidth. Utilizing the symmetrical seven-segment DRA and skillfully varying its aspect ratio, an appropriate structure is obtained that illustrates more than 52% impedance bandwidth for S11>10.

Determining structural maximum deformation under earthquake excitation is an important problem in seismic design of structures. There are several approaches in order to estimate an acceptable accurate response for maximum drift of the structure in nonlinear region. Both ATC and FEMA approaches are good ideas to evaluate maximum drift but more simplified approaches should be applied in seismic design codes. Most of seismic design codes suggest a very simple relation for estimating maximum drift in design base earthquake. Iranian seismic code of practice (Standard No. 2800) proposes such a relation. In this paper a comparison between nonlinear dynamic results and code suggested relation is carried out. 3 scaled records have been used for analysis. Based on reduction factor calculated for the structure, a comparison has been carried out with the suggested factor in Iranian Code of Practice (Standard No. 2800).