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Showing 12 results for Fakhari


Volume 2, Issue 2 (Issue 2 (Tome 3)- 2012)
Abstract

The growth of energy consumption in modern societies has confronted world with threatening changes along with the peril of depletion of fossil resources. Therefore, exploiting the methods of sustainable design has found a high status in international planning and policy making.The most energy consumptions are happening in the building industry, about 40%, and the major part of which is spent for cooling, heating and ventilation. Therefore, using suitable measures to reduce energy consumption has a great influence on energy balance of building. Solar energy for natural ventilation has been used for centuries. Air ventilation is necessary for removing or depleting pollution that can be supplied through solar chimney. Solar chimney is a simple idea to increase natural ventilation in surrounding spaces by using solar energy and chimney effect in an air gap. The driving force in solar chimney is buoyancy force. The solar energy absorbed by chimney causes heat up the air in the chimney so that the air flows upward because of the stack effect. That can be a driving force to enhance natural ventilation. Therefore, the breeze inside the space lets the fresh air enter the space through window. There are a lot of cases which show the use of solar energy for ventilation by some absorption effect in building. The commonest design of solar chimney for ventilation is in vertical form. In the present study, the effect of solar chimney on ventilation rate has been examined in four cities of Iran with different climates. The cities were Rasht (moderate and humid climate), Tabriz (cold climate), Isfahan (hot and dry climate), Bandar Abas (hot and humid climate). Due to the lack of access to the implemented samples, the computerized simulation was used as an alternative method for field studies, the results of which by Energy Plus software in four cities of different climates show that the most suitable city is Isfahan (hot and dry climate) and the maximum ventilation is obtained there. There are also other factors that impacts solar chimney efficiency. Three cities (Isfahan, Yazd, Shiraz) of hot and dry climate were investigated to define their impact of latitude on ventilation rate.

Volume 6, Issue 11 (Spring & Summer 2019)
Abstract

GhairMonsaref nouns in Arabic include some numbers which, due to being descriptions and non-repetitive, are called Ma’dule numbers. The concept of Mosana and Solas and Roba’ in Quran consists of a series of such numbers that are grouped under Maf’al and Fo’al and can be found in verse 3 of Nisa and verse 1 of Fatir in Quran. Although some translators of Quran have stick to the idea of repetition while translating these numbers, many of them have offered translations that do not match this target meaning. This has created different and sometimes contradictory understandings in the minds of readers and has problematized the process of reading each verse. The present study adopts a descriptive-analytic approach in order to closely examine the meaning of Ma’dule numbers in Farsi translations of Quran. The semantic analysis of Ma’dule numbers highlights the idea of “repetition and variety” for Mosana and Solas and Roba’ at the same time as bringing forth the meaning of numbers and counting in the words. This sense is more in line with “binary, tertiary and fourfold” that can be used as translations for the above words.


 

Volume 12, Issue 3 (12-2012)
Abstract

This paper presents a parameterization method to optimal trajectory planning and dynamic obstacle avoidance for Omni-directional robots. The aim of trajectory planning is minimizing a quadratic cost function while a maximum limitation on velocity and acceleration of robot is considered. First, we parameterize the trajectory using polynomial functions with unknown coefficients which transforms trajectory planning to an optimization problem. Then we use a novel method to solving the optimization problem and obtaining the unknown parameters. Finally, the efficiency of proposed approach is confirmed by simulation.  

Volume 12, Issue 4 (3-2013)
Abstract

Microgrids are small-scale, low voltage (LV) power networks which employ renewable distribution energy resources (DERs) with power electronic interfaces (PEIs). Microgrids as single controlled units and active distribution networks require flexible control systems to ensure reliable and secure operation in different modes. These various operations of microgrid cause variations in voltage and frequency especially in island mode. In this paper, a new control method with two optimization algorithms (genetic algorithm (GA) & imperialist competitive algorithm (ICA)) are proposed to eliminate both voltage and frequency disturbances. Also, a new concept of conventional droop control in format of fast droop controller (FDC) is designed to guaranty the microgrid system reliability with cooperation of a modern frequency controller. Simulation results show the truth behavior of proposed approach in comparison with previous methods

Volume 15, Issue 3 (10-2012)
Abstract

Objective: Environmental pollution is of major concern today and lead is considered to be one of the most important environmental pollutants. Long-term contact with lead causes harmful effects to humans. This study seeks to determine the effects of Curcuma longa (turmeric extract) consumption and exercise training on glutathione peroxidase and protein carbonyl in kidney and spleen tissues from rats exposed to lead. Methods: We randomly classified 60 male rats into the following six groups of 10 rats per group: 1) control; 2) sham (turmeric extract solvent); 3) lead; 4) training + lead; 5) turmeric extract + lead; and 6) training + lead + turmeric extract. The training program for groups 3 and 6 consisted of running on a level treadmill for 40 sessions (eight weeks at five sessions per week) at a speed of 22 to 15 m/min for 26 to 64 minutes. Turmeric extract (30 mg/kg) was injected three times per week for eight weeks. Amounts of glutathione peroxidase and protein carbonyl were measured by ELISA. Results: The amount of protein carbonyl in the kidney and spleen tissues of the lead group increased compared to the sham, training, combined and extract groups. Rats in the combined, extract and practice groups (F=4.787; P=0.002) had lower levels of protein carbonyl in their kidney and spleen tissues compared to the sham group (F=6.970, P=0.000). Glutathione peroxidase levels in the kidney and spleen tissues were less in the lead group compared to the sham group. However these levels in the training, extract, and combined groups increased compared with the sham group (respectively, in kidney and spleen P=0.051, F=2.466 and P=0/086, F=2.11). Conclusion: Intake of turmeric extract and exercise alone did not cause complete inhibition of the oxidative effects in kidney and spleen tissues. However, exercise and consumption of turmeric extract can be effective in reducing the harmful effects of lead.
Amin Fakhari, Mehdi Keshmiri,
Volume 15, Issue 8 (10-2015)
Abstract

Using the soft fingers increases stability and dexterity in object grasping and manipulation. This is because of the enlarged contact interface between soft fingers and object. Although slippage phenomenon has a crucial role in robust grasping and stable manipulation, in the most of previous researches in the field of finger manipulation, it is assumed that the slippage between finger and object does not occur. In this paper, slippage dynamic modeling in object grasping and manipulation using soft fingers is studied. Because of the enlarged contact interface between soft fingers and object, a frictional moment along with tangential frictional force and normal force is applied on the contact interface. Therefore, a novel method for dynamic modeling of planar slippage using the concept of Friction Limit Surface is presented. In this method, equality and inequality relations of different states of planar contact is rewritten in the form of a single second-order differential equation with variable coefficients. These coefficients are determined based on the slippage conditions. This kind of dynamic modeling of contact forces can be used for designing the controllers to cancel the undesired slippage. The method is used in study of slippage analysis of a three-link soft finger manipulating a rigid object on a horizontal surface. In order to increase the accuracy of dynamic modeling of soft finger, dynamics of soft tip is integrated with the dynamic of finger linkage. Dynamic behavior of this system is shown in the numerical simulations.

Volume 16, Issue 63 (6-2019)
Abstract

“Dash Akol” is one of the most important fictions in Persian literature. This short story is different from other fictions of Sadegh Hedayat. Sacrifice and “gheyrat” are important concepts in this fiction and this is questionable. The hypothesis of this article was that, unlike popular belief, “Dash Akol” is not entirely realistic but it`s a semi-Modernist short story because of central subjectivity of Akol. In other words, characterization in the second part of this story is Modernist. A Modern subject has three features and all of them are observable in the main character of “Dash Akol”: 1) Consciousness 2) Agency 3) Personhood. Akol have some secondary features too: 1) Overthinking 2) Attention to the unconsciousness 3) Solitude 4) Thinking about death. This short story is written in a period of contemporary Persian fiction that Modernist literature arose and this story has shown the evolution of contemporary Persian fiction.

Volume 18, Issue 4 (11-2018)
Abstract

In this paper, for the first time using of Bayesian regularized artificial neural network (BRANN) model, which is a novel method of among soft computing (SC) methods (such as fuzzy logic, genetic programming, neural network) to predict the rotational capacity of wide-flange steel beams. Steel is one of the most commonly used materials in construction industries, mainly in steel structures. There are many researches and studies on the behavior of a structural member of steel structure such as beams under different types of loading. The accurate estimation of rotation capacity (plastic rotation capacity) is of significant importance issue for plastic and seismic analysis and design of steel structures especially for high rise building (nonlinear behavior). Similarly, the moment redistribution in a steel structure also depends on the rotation capacity of the section. So the determination and accurate prediction of rotation capacity of steel structures members such as wide flange beams become an important task. Using different methods such as finite element, regression and statistical methods in previous studies has been used in recent years. Therefore, in order to estimate the more accurate value of the rotational capacity of wide flange beams, Artificial neural networks are used with the Bayesian learning process. The Bayesian regularized network assigns a probabilistic nature to the network weights, allowing the network to automatically and optimally penalize excessively complex models. The proposed technique (BRANN) reduces the potential for overfitting and overtraining, improving the prediction quality and generalization of the network. The proposed model (BRANN) is based on experimental data that collected from previous studies. After a comprehensive review of existing literature, 77 data of wide flange beam were selected which had experienced to determined rotation capacity. For this purpose, Half-length of flange, height of web, thickness of flange, thickness of web, length of beam, yield strength of flange and yield strength of web were consider as input parameters (six inputs) while rotation capacity is treated as target of the Bayesian regularized artificial neural network model. The Bayesian regularized artificial neural network is modeled in MATLAB software and applied to predict the rotation capacity. The results of this model were compared with experimental results and other models and equations that presented in the past (including Genetic programming (GP), Li equation and Kemp Equation. An analysis is carried out to check the performance of the proposed BRANN model based on the common criteria such as Mean Absolute Percentage Error (MAPE). The optimal and best model should have the lowest values of MAPE, this parameter is 20.32% for BRANN, 23.49% for a Genetic Programming model that proposed by Cevik, 47/20% for Li’s Equation and 56.98% for Kemp’s equations. The results of Bayesian regularized artificial neural network approach indicate a good agreement between the predicted and measured data. Furthermore, the Bayesian regularized artificial neural network model shows the most optimized results compared to all the previous model and equations. The result indicated that the Bayesian regularized artificial neural network could be used as a powerful tool for engineers and researcher to solve this kind of problems.
Meysam Elyasi, Vahid Fakhari, Pedram Safarpour,
Volume 18, Issue 6 (10-2018)
Abstract

Today, with increasing consumption of non-renewable energy sources, scientists are looking for an alternative for these resources. The Stirling engine is one of the ideas that have recently attracted engineers' attention. The purpose of this study is to optimize the output power and stability of a beta type free-piston Stirling engine. In this regard, at first by deriving the thermodynamic and dynamic equations of the system and combining them, the governing equations are obtained including the nonlinear function of the pressure loss in heat exchangers. The governing nonlinear equations are solved and for the purpose of validation, simulation results obtained in this study are compared with experimental and simulation results presented in the literature. In free-piston Stirling engines, increasing the output power by keeping their stability is very important. Therefore, by performing parametric study, the parameters with more effects on the output power and stability are determined and considered as optimization variables. In order to perform multi-objective optimization of output power and stability of the free-piston Stirling engine, a proper objective function is selected and one of the methods in genetic algorithm is employed using optimization software Modefrontier. Finally, values of variables, before and after optimization and also, percentage of improvements in output power and stability of the free-piston Stirling engine are presented.
Vahideh Vahidifar, Mostafa Taghizadeh, Vahid Fakhari, Pedram Safarpour,
Volume 18, Issue 9 (12-2018)
Abstract

In this paper, control position of a pneumatic actuator with the PWM solenoid on/off valves using two different pneumatic circuits performed. After deriving the governing dynamic equations, to investigate the circuit effect on system performance, mentioned two pneumatic circuits are introduced. Then in order to control the position of the pneumatic actuator, for both circuits, sliding mode and proportional-integral-derivative controllers are designed. In proceeding, optimum controller parameters are determined by genetic algorithm to achieve minimum control energy and position error. Finally, by performing simulations in Matlab Simulink, performance of designed controllers with optimal parameters is evaluated and compared in the presence of disturbance. According to the obtained results, by comparing the performance of two circuits, it is observed that the first pneumatic circuit with two solenoid valves can track the high-frequency sine reference input better and more precisely in the presence of a nonlinear sliding mode controller. The position tracking error in low-frequency sine reference input using a classic proportional-integral-derivative controller, for a single-valve pneumatic circuit is considerably less than that of a pneumatic circuit of two valves. This indicates the input-output quasi linear behavior of the pneumatic actuator in a single-valve circuit.
M.m. Fakhari, H.r. Bokaei, B. Shahriari,
Volume 20, Issue 2 (February 2020)
Abstract

In this paper, the effect of nozzle divergent section geometry on fluid flow and heat transfer within the convergent-divergent nozzle numerically and experimentally is investigated. Axisymmetric supersonic flow simulation for the converging-diverging nozzle is conducted. The flow field is a steady turbulent two-dimensional flow. The working fluid is a combustion product and is considered as a compressible ideal gas. The flow field is simulated using the commercial code FLUENT. The equations are discretized implicitly with the second order of accuracy. In this study, two convergent-divergent nozzles have been analyzed that the divergent part of one is a cone-shaped and the other is bell-shaped. The calculated parameters in the simulation have been compared with the experimental results. Based on the simulation results and the values obtained in the experimental test, the error is less than 4% that is acceptable and appropriate. According to the results, flow simulation accuracy is appropriate.
 


Siavash Gitifar, Amir Saman Mirjalili, Ali Jamali, Saeed Pirvalizadeh, Vahid Fakhari,
Volume 23, Issue 2 (February 2023)
Abstract

These days, societies' need for energy increased due to the expansion of societies, industries, and technology. The production of electricity from renewable energy sources such as solar energy, which does not harm the environment and has little pollution, has attracted the attention of many researchers and engineers. This article will present a new plan for the dual polar axis solar tracker, its design and construction in laboratory dimensions, and the experimental evaluation of its performance using the open-loop control method. For this purpose, after examining the advantages and disadvantages of the previous designs, a new and different conceptual design for the tracker is proposed. Among the features of the proposed tracker, we can point out the ability to combine, install and operate quickly and easily, the self-locking feature, and the ability to rotate 360 ​​degrees around both axes. This tracker has no restrictions for use in different geographical areas, including areas near the North or South Pole and in the early and late hours of the day when the direction of the sun's radiation is strongly inclined. In the following, the detailed design of the proposed detector and the presentation of the open-loop control method will be discussed. Finally, by conducting experimental tests, the production power of the proposed detector is evaluated in comparison with a fixed solar panel. Based on the results, the electricity energy produced from the proposed solar tracker is 49% more than the fixed solar panel.
 

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