فصلنامه مدل سازی در مهندسی
پیاپی 41 (تابستان 1394)

In this research, delamination in an asymmetric double cantilever beam (ADCB) has been studied. The ADCB specimen is one the most proper samples for testing and calculating the mixed mode I/II fracture. First, a semi-empirical relation for calculating the total strain energy release rate (SERR) and the values of mode I and II of this parameter has been extended. Moreover, the total SERR of a laminated composite is determined using the virtual crack closure technique (VCCT). Furthermore, by the use of this method fracture toughness of ADCB specimen and its modes can be calculated by testing of a unidirectional DCB specimen. Therefore, testing of ADCB samples is not required. Also, for verifying results obtained by the semi-empirical relation of the total SERR, experimental, analytical and numerical methods are used. By modeling of the mentioned specimen in ABAQUS/Standard, values of mode I and II SERR are calculated. This method can be used for assessment of the semi-empirical relation. Finally, it was observed that results of the semi-empirical relation are in very good agreements with the experimental, analytical and numerical results. This method reduces the volume of calculations of numerical methods and costs of experimental tests significantly.

Time-of-flight diffraction (ToFD) is an ultrasonic nondestructive testing technique used for detection, sizing and location of defects in industrial parts. This method has better abilities and benefits than other nondestructive testing techniques. The advantages of this method are fast speed, low cost, better evaluation of defects without depending on their orientation and high accuracy in measuring defects. This technique is usually applied for thick sections (>15 mm), the application of the ToFD technique to thin sections like pressure vessels and piping requires simulation of this technique. Also doing practical experiments for specification appropriate parameters is very time consuming and expensive. Using simulation, one can perform the experiments with low cost and fast speed. In this paper, the ultrasonic time-of-flight diffraction (ToFD) technique has been modeled in two different parts by using the finite element method (FEM). The explicit solution method of the finite element package ABAQUS is used for solving the propagation problem of ultrasonic waves. Finite element modeling of ToFD technique and in general simulation of ultrasonic wave propagation, has provided a better understanding of the propagation of ultrasonic waves and their interaction with different discontinuities.

Fuel pipeline systems are one of the most important lifelines in city and have a key role in increase and decrease of damages and vulnerability to earthquake. Kermanshah has three lines for transferring oil products and crude oil into the main refinery of the city from two transfer centers out of the city, Naftshahr and Tange Fanni, from which oil products are transferred to the terminal facilities in Sanandaj. This paper, In order to assess the seismic damage to buried fuel pipelines of Kermanshah with the help of characteristics and information of network components, PGA and PGV values are initially determined for two probable scenario earthquakes in the study area, using the attenuation relations of the same area. Then, using the repair rate relations, damage to pipelines is estimated. The probability distribution function for the area, the population and the number of houses exposed to fire and explosion after the earthquake are calculated using the Monte Carlo simulation method through numerous repetitions All the steps of damage assessment for buried pipelines were written in a GIS environment. In order to give a better description of the output results, the probability distribution functions for each output are provided. In summary, the damage inflicted on the fuel pipelines of Kermanshah is equal to 17 leaks, 4 breaks and 21 ignitions for scenario 1 and 4 leaks, 1 break and 1 ignition for scenario 2. The purpose of this paper, an efficient algorithm present is for seismic damage analyze of buried fuel pipelines and simulating fire ignition and explosion in urban areas. The proposed algorithm for the city of Kermanshah has been used as a case study.

In this paper the results of numerical simulations for heat transfer of a nanofluid flow inside a counter flow heat exchanger is presented. Effects of addition oftheAl2O3 nanoparticles on the entropy generation ofthesystem are investigated. Single fluid model is used for simulation of the nanofluid flow. Analytical and experimental formulations are used for density, specific heat, viscosity and conductivity of nanofluid. Finite volume method (FVM) has been used for numrerical simulation and SIMPLE algorithm is applied for pressure velocity coupling. It is found that adding nano particles in annulus, causes a little incerement in entropy generation which can be overlooked. On the other hand, the increasing of volume fraction of nanoparticles leads to ascend heat transfer coefficient (U) and total heat transfer (Q) significantly, and it results in decreased entropy number (Ns).

Competition between the managers of industrial and service organizations to provide their financial needs and credit facilities via the bank's loan is growing daily. Other hand, financial resources and credit of banks and financial institutions to provide accommodations to applicants is limit. Accordingly the optimal allocation of limit financial resources with the aim of making the maximum value for their investment is a necessity. In this study, the validation criteria to identify applicants receive legal facilities; using improved techniques of data envelopment analysis (DEA), an efficient method for legal clients of categories is presented. Improved techniques of DEA by defining a perfect organization in each time of runs that cause to reduce of computing and operation speed of decision-making and improved available DEA method. The improved DEA model also offers a short, direct and dynamic route to achieve more efficiency in each of efficient and inefficient the companies. Prioritizations provided by the improved DEA method in all case studies, were equal with priorities of the available DEA approach.

In this paper, c. For this purpose, stress distribution and deformation of the major parts of the valve; and also, the hydrodynamic torque, which is applied to the valve-disk, have been calculated at different opening angles of the disk. To carry out the numerical analysis, coupled Computational Fluid Dynamics (CFD) and Finite Element based solid mechanics solution methods have been used. To validate the numerical results, the displacements of some critical points on the valve-disk have been measured and the results are compared with those obtained using numerical solution. Also, the hydrodynamic torque of a model valve has been measured using an experimental rig and the data are compared with the numerical results. Both comparisons show good agreement and approve the accuracy of the numerical solution method. The results show that maximum stress occurs at the valve shaft when it is fully closed; and, hydrodynamic torque exerted on the disk becomes maximum when the valve is at almost fully open angle. The effect of different parameters such as disk-off set, flow direction and shape of the valve-disk on the hydrodynamic torque of the valve has been investigated. In this process, a modeling method to study the hydro dynamic behaviour of large size butterfly valves has been developed which can be implemented in other case studies by the manufacturers.

The application of Viscoelastic (VE) supports in order to dampening dynamic forces and energy dissipation has been investigated herein. Properties of viscoelastic substances are important in the quality and quantity of the dissipation. The viscoelastic materials were described using the generalized Kelvin-Voigt mechanical model and the resulting governing equations were solved using the finite element method in time domain. To investigate the effects of the viscoelastic characteristics of supprots on axial vibration, dynamic and quasi-steady analysis of a rod subject to axial step excitations was carried out. Finally, some important criteria were presented to improve the performance of these substances in energy dissipation. In addition, axial vibration of an elastic and a viscoelastic rod with end and middle VE supports subject to harmonic excitations were investigated. It reveals that the use of VE supports considerably damps out structural vibrations, especially at low frequencies. Whereas in high frequencies, the amount of the energy dissipation depends on the retardation times of the Kelvin-Voigt elements.

This paper uses an analytical formulas to estimate frequency response for the Square metal patch and strip periodic cells. Analytical expressions for frequency response are verified by fullwave simulations. The analytical formulas used in design of one-order, bandpass FSS based on circuit model. This bandpass FSS is made up of periodic array of metallic patches separated by thin air-gaps backed by a wire mesh having the same periodicity. The frequency responses are obtained for different thickness and dielectric constants substrate. The simulations are carried out using ful-wave and analytical methode, and results are compared to understand limitations of proposed designing method. Principles of operation, detailed synthesis procedure, and designing guideline for this type of FSS are presented and discussed in this paper.

the purpose of this paper is to compare two artificial intelligence algorithms for forecasting supply chain demand. In first step data are prepared for entering into forecasting models. In next step, the modeling step, an artificial neural network and support vector machine is presented. The structure of artificial neural network is selected based on previous researcher's results. For measuring errors we use Mean squared error and we use another index for time which is used running the algorithms. The results show that artificial neural network can forecast more accurate meanwhile support vector machine is faster.

Nowadays, increasing use of electronic instruments and nonlinear loads in Power systems, make the power quality problem as one of the most important issues. In this article, the produced data from mathematical equations and PSCAD software simultaneously have been used to simulate power quality disturbances. Because of super performance of neural networks in pattern recognition and classification, the MLP neural network for classification of power quality disturbances is used in this paper. The neural networks have been developed by simulation of nonlinear terms, and they indicated their priority for pattern recognition and classification. STFT and DWT transform to extract signal's features have been used. After classification of disturbances using MLP, the neural network robustness has been examined in different levels in presence of the noise. With presence of noise, neural network classifies all the events with 98.22 percent of accuracy. Finally, results of this article are compared with other researcher's works.

Structural damage detection technique helps to locate and detect damage that occurred in a structure by using the observed changes of its dynamic and static characteristics. The existing approaches proposed in this area can be divided into two main groups: the dynamic damage detection methods using dynamic data and the static damage detection methods using static data (static displacement, static strain etc.). As the static equilibrium equation is only related to the structural stiffness, accurate static displacement and strain data, it can be obtained rapidly and cheaply. For the reasons stated, the static damage detection methods have attracted more attention in recent years This paper presents a non-destructive global structural damage detection and assessment algorithm using static data. A set of static forces is applied to a set of degrees of freedom and the static responses (displacements) are measured at another set of DOFs. Some simultaneous equations characterized from Changes in the static response which structural damage caused. The method is determined damage as a change in the structural stiffness parameter. Genetic Algorithms are powerful tools for solving large optimization problems. Optimization is considered to minimize objective function involve difference between the load vector of damaged and healthy structure. As mentioned above the static damage identification methods have many advantages, but some difficulties still exist. The main problems the first of all is, the information used in the static damage identification methods is less than in the dynamic identification, which makes it more difficult to get the ideal identification result. For example, the angular displacement or rotational freedom is difficult to determine. Second, the effects of the damage may be concealed due to the limited load paths. Lastly, the static data provide only the local structural damage information, and the measured static data are very limited. So it is important to achieve the best damage identification and if the best result is obtained it means that the method is Reliable. Damage defined by several scenarios included single scenario and multiple scenarios. For example in plane truss scenario two means: 40% damage in element No. 2 and 60% damage in element No. 10. Numerical results in this paper for a plane arch bridge and a plane truss show the ability of this method in detecting damage in given structures. Also Figures show damage detections in multiple damage scenarios have really nice answer. Even existence of noise in the measurements doesn’t reduce the accuracy of damage detections method in these structures.

A system of Polymer gel is widely used in oil production wells in order to reduce unwanted water production. The efficiency of these systems in porous media depended on various parameters such as the composition concentration and the media condition of the polymer gels performance. So it is necessary to study the effective parameters and their interactions in order to increase the efficiency of systems of polymer gels. Therefore، in this research، two-level factorial design as a statistical method was used to study the effective parameters on the gelation time of polymer gel containing sulfonated polyacrylamide copolymer and chromium triacetate as crosslinker to not only reduce the number of experiments in the lowest time and cost، but also present the most effective parameters among the eight studied parameters (pH، CaCl2 concentration، crosslinker/co-polymer ratio، NaCl concentration، co-polymer concentration، sodium lactate، nanoclay and thiouria) on gelation time of polymer gels using 32 bottle testing experiment and finally by modeling the process، the optimum condition is presented. The presented model in 99% significant to predict the gelation time of the polymer gel based on the effective parameters. The results showed that sodium lactate، co-polymer concentration، nanoclay، thiouria and crosslinker/co-polymer ratio are the main effects respectively. Also، among the interactions between parameters، the interaction of sodium lactate and crosslinker/co-polymer ratio has the most effect on the gelation time of the hydrogel.