فصلنامه مدل سازی در مهندسی
پیاپی 30 (پاییز 1391)

Modal testing is a developing expertise in the field of structural dynamics. However، in practice the models that are produced by modal testing procedure face different errors. One of the sources of error is mass-loading effects of accelerometers. This article targets the elimination of mass-loading effects of accelerometers from measured frequency response functions. A strategy based on sensitivity analysis is introduced for this purpose. In this approach the amount of added masses and the locations of structural responses are selected based on the minimum error in correction method. A mass-spring-damper system is used to validate the method numerical. Also، a steel beam is examined to demonstrate the applicability of method in practical cases. The numerical and experimental case studies show the effectiveness of the proposed method.

Ever-increasing need of our country in studying rehabilitation of existing buildings and necessity of using applied analysis in these structures persuade us into searching in the area of effects which exist in analytical procedures. Recently، researchers have developed structures rehabilitation effectively. Their view in providing safe design of strength supply is considered to the structure`s performance. Nonlinear static procedure analysis or push over is one of the new procedures، which in spite of its high speed and simplicity of its calculation، is considered because of using FEMA356 and seismic rehabilitation code. The result of this analysis is targeted displacement which is considered as the basis for determining the structures performance and rehabilitation. If we can recognize this result exactly، it will increase the exactness of pushover analysis efficiency. Nonlinear Dynamic Analysis is the only procedures that study the effects of seismic motive on structures with the highest exactness، but it isn’t as applied as pushover procedure because of wasting a lot of time، high cost and difficulty. One of the coefficients applied to determining target displacement in this procedure is C2 which is used in order to reform the effects of reducing stiffness and strength of hysteresis loops that aren’t considered. In this research، It is tried to influence some reinforced concrete structures with shear walls، with different accelerations which are scaled according to FEMA356 and FEMA273 codes. These structures are designed according to the third edition of Standard 2800. At the end، the amount of C2 which is found is compared with the suggestive amount of rehabilitation code by analyzing push over and comparing its result with the result of Dynamic analysis.

This article reports a numerical study of fluid flow and heat transfer of mixed convection in a shallow cavity with different aspect ratios subjected to a nanofluid with Temperature-dependent dynamic viscosity and thermal conductivity. The side walls of shallow cavity are assumed adiabatic whereas top and bottom walls are kept at low (Tc) and high (Th) temperatures، respectively. Using a developed FORTRAN code، equations of continuity، momentum and energy are solved with associated with boundary condition by a finite volume method (FVM)، numerically. The new models proposed by Xue and Jang are used to calculate the thermal conductivity and dynamic viscosity of nanofluid، respectively. The influence of changes in lids velocity ratios; aspect ratio، Richardson number and existence of nanoparticles on hydrodynamic and thermal characteristics have been investigated. Water and water/Al2O3 nanofluid with particle diameter of 80 nanometers، diameter ratio of 0. 006 and T=298 (K) have been used as working fluids. Results show that in a constant parametric range، heat transfer in a shallow cavity with Length twice the height (A. R=2) is more than compared to other cases. Also the existence of nanoparticles increases the heat transfer inside the cavity.

Available transfer capability (ATC) is a key index to manage future transactions between areas in the open access environment. ATC is a probability index because of the uncertainties related to power system operation. On the other hand، the utilization of wind farm with the stochastic nature as an alternative for electric power generation adds a new probabilistic component to the system and emphasizes employing probabilistic methods to calculate transfer capability. Besides the fluctuating nature of wind farms، other factors such as connection bus of wind farm، its capacity، and wind speed regime can create a considerable impact on transfer capability. This paper uses the Monte Carlo simulation to produce system states and optimal power flow to calculate transfer capability considering operating limits of generating units، voltage and thermal limits. Case studies with the IEEE reliability test system (RTS) discuss about the impact of the mentioned factors on transfer capability.

Contact problems are one of widely used and important branches in solid mechanics. This paper aims at extending the bi-directional evolutionary structural optimization (BESO) algorithm for optimal contact shape design in structures under the multiple load cases. In this study، the gap elements between the corresponding nodes on both surfaces are used not only to model contact states but also to modify the contact profile by changing the spacing to lengthen or shorten the gap between the corresponding nodes. Using gap elements، the analysis of contact problems by finite element method is simplified and the Enormous volume of non-linear calculations is reduced. Evolutionary structural optimization (ESO) method for obtaining the optimal shape of the contact surface، through a simple process with a gradual increase over the length of inefficient gap elements، the shape of the structure will converge to an optimal design. But in this paper by using the bi-directional evolutionary optimization method، there is the Possibility of increasing and decreasing of length gap elements simultaneously and so the speed of convergence has increased. In this paper، weighted average method and stress criterion are used for evaluation of the performance of gap element in optimization algorithm and finally a uniform distribution of stress along the contact surface is obtained.

Fluid catalytic cracking (FCC) is an important petroleum process to convert heavy petroleum cuts into light cuts such as gasoline and LPG. In this work، a steady state one dimensional model of FCC riser using a 4-lump kinetic model was presented. Equations for mass، momentum and energy balance were written and coded by MATLAB. The model was written based on the upward movement of catalyst particles in the riser in a cluster formation. The modeling was based on the assumption that the clusters diameters were not constant، but varies all along the riser. Using the model، product yields، temperature profile in the riser، gas and solid velocity، catalyst decay rate and change in cluster diameter along the riser were investigated. The accuracy of the model was validated by 4 industrial cases that reported in the literature. The obtained results at the end of riser showed to be in good agreement with industrial data by average percentage error of 3. 12% for gasoline yield، 5. 35% for coke yield and 1. 81% for riser temperature. The results showed a decrease in percentage error when they were compared with the assumption of the constant cluster diameter along the riser.