فصلنامه مدل سازی در مهندسی
پیاپی 45 (تابستان 1395)

In the Current seismic codes, the earthquake load on the buildings depends to period of structure. More of these codes use the empirical relations to estimate the period of structures. These relations are suggested for the rigid floor structures. Then use of these relations for semi-rigid and flexible diaphragms is not accurate and cause error in determination of seismic load of structures. This topic is more important for the stiffened structures such as: structures with shear wall or bracing together joist-floors with lower rigidity in one direction and semi-rigid behavior. In this paper, the period of the braced steel building with block-joist floors for two different cases of real modeling without rigid diaphragm assumption and ideal modeling with rigid diaphragm assumption are compared and effect of flexibility of diaphragms on the period of structure is investigated. Also, for fast estimation of period of structures with flexible diaphragms, the simple equations are proposed.

The consolidation phenomenon occurs in the construction of structures on saturated clay soils which in effect this phenomenon the soil particles is compressed. In sometimes an irreparable damage occurs in the development projects affected of the soil settlement. Hence the prediction of soil settlement is necessary. The compression index (Cc) is one of the coefficients which apply to calculations of soil settlements. This coefficient is determined by odoemeter test which is test is very expensive and much time is wasted. So that in past years an extensive function for prediction of Cc with physical properties of soil have been developed by various researchers. In this study, the important and valuable results of consolidation test were gathered at different locations in khuzestan province of Iran. Using the gathered data the compression index was determined. Then the results were evaluated using the simultaneous implementation technique of artificial neural network and fuzzy logic (ANFIS). In this research, also, the results of ANFIS system were compared to the results of empirical formula. The error of empirical functions to measured data in the best cases was predicted about 20 percent. However, the most of empirical relationships in the study area have not acceptable accuracy. Findings show that ANFIS adaptive system predicates compression index which it is a fundamental parameter for determining of clay soil settlement. The results of this system were satisfactory with void ratio and wet content variable in situ clay soils. In addition, this system with 15 percent RMSE and 12 percent error has a better result than past empirical function and artificial neural network.

In this paper, the effect of tubes distance on the mechanical behavior and energy absorption characteristics of nested thin-walled tubes is investigated using LS-DYNA. Thin-walled cylindrical tubes made of aluminum and steel. Axial impact load is carried out and by increasing the distance between the tubes the absorbed energy is calculated. Finally, the optimum distance to maximize this parameter is determined. Results showed that aluminum tubes in both material models used in the analysis, in an almost identical and the same distance (about 4 to 5 mm) from each other had the highest amount of absorbed energy. Steel pipes in both material models, at different distances showed the highest amount of energy absorption, although the number of folds in different distances was the same. Furthermore, the overall crushing and behavior of the steel tubes were different than those of aluminum tubes.

In this paper, a cable actuated mechanism is introduced as a new rehabilitation method. Having the need for a rehabilitation system consistent with the physical characteristics has led to certain new projects. Considering joint compliance during the motion can make the patient feel better and thus, bring success for the rehabilitation program. The advantages of the proposed low-cost and light weight mechanism are having a smooth joint motion with a stiffness which is adjustable, compensate gravity effects, remote actuation for delivering torque to a joint, motor size reduction and in the developed versions, ability to control multiple joints movements and deliver force to links with one source of power. In this paper, the joints torque and stiffness is investigated in the performance of the elbow rehabilitation device. This is effectively compatible with the elbow joint stiffness. Being similar to the behavior of human arm, the mechanism can be used more widely in the field of medical robotics.

An ejector is a pumping device that uses a high-speed primary fluid jet to entrain a secondary stream. In this work, using CFD we simulate subsonic air – air ejector numerically. Governing equations including continuity, momentum and energy equations are solved numerically based on finite volume method. Numerical simulation is carried out in 3 dimensions and flow is assumed to be conservative, viscous and turbulent. To simulate turbulences, Reynolds averaged Navier–Stokes, K-ε Standard, K-ε RNG, K-ε Realizable, K-ω Standard and K-ω SST are applied. Ejecting coefficient for various pressure ratios was an effective parameter which was used to validate numerical results. Error was at its minimum for K-ε RNG turbulence model. Therefore, it was used to simulate turbulences. After validating results, we analyzed the effect of geometrical parameter of diffuser outlet diameter and divergence angle on performance of subsonic air – air ejector. Results demonstrate that in addition to divergence angle, diffuser outlet diameter has a significant influence on performance and efficiency of such devices.

As the need for seismic designing of the earthquake resistant structures increases, numerous laboratory and numerical studies are being done to estimate the nonlinear response of these structures. With respect to the height to width ratio, the concrete shear walls are divided into two categories of cantilever and short shear walls. Cantilever shear walls with the aspect ratio greater than 2 demonstrate flexural behavior while short shear walls with the aspect ratio smaller than to 2 exhibit shear behavior. In this study the behavior of short reinforced concrete shear walls are investigated using the nonlinear finite element software ATENA 3D. The failure mode and the ultimate and residual shear resistance of the short shear walls, as well as the affecting parameters such as concentration of longitudinal and transverse bars at the edges of the wall, change of the horizontal and vertical bars spacing and the use of diagonal bars are studied. It is revealed that unlike the cantilever walls, the concentration of the bars at the edges have no influence on the increasing of ductility.

Many industries including power-plants, refineries and so on are using high pressure control valves. Many of these valves have traditional geometries like butterfly valves. Unfortunately, because of the special design of these valves, cavitation causes very rapid corrosion. In the last decade, a next generation of control valves have been introduced which are designed to prevent cavitation. Because of the special fluid paths in the Labyrinth valves, the pressure drop is very graduated which prevents cavitation. In this article, the geometry of fluid path is optimized using Taguchi method. To this end, four parameters are considered including path's height, number of corners, corner radii and input area. For each parameter three levels are assumed and using a standard Taguchi array the optimum geometry is predicted. Then the pressure drop in optimum geometry is simulated using finite element method and the results validated the optimized geometry.

Product development process has its specific complexity. This complexity can also be due to overlapping and dependent relationships (coupling) amongst activities in a product development process. On one hand overlapping may reduce duration of a project on the other, it engenders rework risk. In addition, coupled activities are another reason for rework risk too. This iteration and rework caused by overlapping and coupling of activities results in increasing time and cost of the project. In this article, a mathematical model is presented to study the characteristics of the product development process and also to balance the duration and cost of it. According to the overlapping and the amount of dependent relationships among activities, four types of time models have been formulated. Furthermore to verify the process, the model has been implemented in MATLAB and an example has been solved. It is observed that the proposed model is easily able to calculate the time and cost of the process in all four types.

In this paper a new voltage amplifier is investigated which is employed in the time and voltage domain converters such as analog to digital converters (ADCs) and time to digital converters (TDCs). The time and voltage amplifiers are used in the time and voltage domain converters for increasing the time resolution and accuracy. The voltage and time amplifiers are basically utilized in the ADCs and TDCs which employ the pipeline or interpolation techniques for digitizing the time interval between two input signals. In these converters, the main time or voltage residue is amplified by a time or voltage amplifier and fed to the next stage. The proposed voltage amplifier uses a charge pump technique for voltage amplification. The proposed circuit does not use delay lines in its structure and features low circuit complexity, low sensitivity to temperature, power supply and process (PVT) variation and high accuracy compared with the time or voltage amplifiers which previously proposed. The amplifier improves dynamic range of the converters. Therefore, the amplifier produces a exact voltage gain. Also, the linear range of the proposed voltage amplifier is appropriate.

In recent years, the electrical industrial convert to a competitive market in some of the countries which is named a deregulated systems. To maintain the stability of power grids and reliable power transmission, in addition to providing active power, reactive power supply is also needed to improve the safety system should be optimized by the operation of the power system. In this paper, we proposed a new solution to management the reactive power which is presented as a long term and non-linear optimization problem. Hence, the planning and improving the power market based on optimal distribution of reactive power has been presented as an optimization problem. The mentioned problem is solved by a new meta-heuristic algorithm which is based on shark smell abilities named Shark Smell Optimization (SSO). This algorithm improved with Pareto criterion to increase the abilities of proposed strategy in nonlinear problem with different constrains. The effectiveness of the proposed method has been applied over tow power system case studies through the comparison with other techniques.