فهرست مطالب

  • Volume:28 Issue: 3, Mar 2015
  • تاریخ انتشار: 1394/01/15
  • تعداد عناوین: 20
  • H. Sharifi Pajaie, M. Taghizadeh* Pages 330-337
    In order to enhance the catalytic performance of SAPO-34 catalyst for the reaction of methanol to olefins (MTO), ultrasonic and microwave-assisted aging method was employed in static hydrothermal method to synthesize nano-sized SAPO-34. The effects of the application of this method on the chemical composition, morphology, surface area and total acidity of SAPO-34 were investigated by XRD, FE-SEM, nitrogen adsorption–desorption and NH3-TPD techniques. The catalytic performance of synthesized SAPO-34 was investigated for MTO reaction in a fixed-bed reactor under the same operating conditions (T = 450 °C, P = 1 atm, and WHSV = 4 h−1). Comparing with the SAPO-34 synthesized with conventional hydrothermal method, the sample synthesized with simultaneous use of US and MW-assisted aging methods possessed larger surface area and small crystal size and exhibited higher selectivity to light olefins (2 4) C = - C = and longer lifetime.
    Keywords: SAPO, 34, Nanocatalysts, MTO Reaction, Lifetime, Light Olefins
  • M. Saberi, F. Behnamfar *, M. Vafaeian Pages 338-349
    In the current work, the seismic analysis of bent region in buried pipes is performed, and effects of soil properties and modeling methods on pipe’s response are investigated. To do this task, beam, beamshell finite element modeling, and a continuum shell FE model of a 90-degree elbow are employed. In the beam model, the pipe is simulated by beam elements while combined shell-beam elements are used for the continuum shell finite element model. The surrounding soil is simulated by nonlinear springs and solid elements; moreover, soil hardening behavior and soil-pipe slippage are considered in the models. In addition, an equivalent boundary condition has been employed at the end of each elbow leg to simulate far field effects more closely. From these analyses, it can be revealed that axial strain at bends is larger in stiffer soil due to smaller slippage. In addition, a full three dimensional soil-pipe interaction using continuum shell FE model causes a substantial increase of elbow strain.
    Keywords: Buried Pipe Elbow, Finite Element Method, Hybrid Model, Continuum Model
  • A. A. Maghsudi*, Y. Askari D Pages 350-359
    Based on the bending experiment for two-span continuous post-tension beams with unbounded tendons and externally applied CFRP sheets, the analysis of the stress increment of unbonded tendons is monitored in the loading process. Since self-compacting concrete (SCC) is a suitable innovation,, understanding the implementation of this type of concrete on the ultimate unbonded tendon stress is critical. For these aims, results of four continuous un-bonded post-tensioned I-beams in two groups were cast and monitored by electrical strain gauges and are presented here. In the first group, the beams (UPN1-12, SUPN1-12) consisted of high strength normal concrete (HSNC), while in the second group (UPS1-12, SUPS1-12) high strength self-compacting concrete (HSSCC) were tested. The beams are made which are compared with the theory proposed by different codes, and a preliminary modification is given for each code equation. The results of standard error of estimate Sy/x, indicates that for two types of HSCs (strengthened and non-strengthened beams), the ACI 318 2011 provides better estimates than AASHTO-2010 model, whereas this model provides better estimates as compared toBS 8110-97.Comparison of increase in experimental ultimate tendon stress of beams indicates that the increase in tendon stress at ultimate state in strengthened beams is lower than that in nonstrengthened beams cast with HSCs.
    Keywords: Strengthened, CFRP Sheet, Unbonded Tendons, Stress Increases, High Strength Normal, Self, Compacting Concrete, Continuous Beams
  • H. Bonakdari*, M. Tooshmalani, Z. Sheikh Pages 360-367
    This study makes use of the Tsallis entropy to predict the shear stress distribution in rectangular channels. Given a definition of the Tsallis entropy, it is maximized using the probability density function, which then is used to attain a novel shear stress equation. This is then employed for calculating the shear stress distribution in rectangular channels in different aspect ratios and finally, for viability, these calculations are compared with some relevant experimental results. This derived shear stress equation is capable of describing the variation of shear stress in both the wall and the bed of channels. The comparison shows that this equation appears to be efficient for predicting the shear stress distribution in rectangular open channels. The shear force percentage and mean values of the bed and wall shear stress calculated by the proposed equation have good agreement with the experiments.
    Keywords: Tsallis Entropy, Open Channel, Shear Force, Channel Wall, Channel Bed
  • M. J. Emamgholizadeh*, A. R. Mostafa Gharabaghi, K. Abedi, M. H. Sedaaghi Pages 368-377
    Submarine pipelines are appropriate method for transferring oil, gas and other liquids from the seabed.Free spans may occur due to the natural uneven seabed or by under-scouring. Vortex Induced Vibration (VIV) can happen in such free spans at high Reynolds number. Resonance will occur if the frequency of vortex shedding is close to the pipeline’s natural frequencyleading to its fatigue that can break the pipeline causing economical and environmental losses. In literature, there are different methods for suppressing the vortex shedding and pipeline vibration and consequent scouring under the pipe such as the usage of splitter plates. In this paper, the effect of splitter plate’s angle on the scouring beneath the pipeline is studied experimentally. For this purpose, a new experimentalsetup is designed and constructed in order to allow for the cylinder to vibrate in both in-line and cross flow directions over an erodible bed. The reduced velocity for the experiments is in the range of 2.45 5.06 with different gap ratios. Experimental results indicate that the relative scour depth is reduced with increasing the ratio of gap to pipe diameter. The relative vibration frequency approaches to a constant value for large gap ratio (1 < e < 2) and the pipe does not have more effect on the bed. Therefore, the usage of splitter plate with the angle of 0-30 degrees with the horizon reduces the scouring depth below the mean location of the pipe compared with a pipe without splitter plate. Vice versa, the results were reversed for the pipes which used splitter plates with the angle of 60-90 degrees.
    Keywords: Pipeline, Vortex Induced Vibration, Splitter Plate, Two Degree of Freedom, Free Span
  • D. Nezamolmolki*, A. Aftabi Sani Pages 378-386
    This article deals with the free vibration analysis and determination of dynamic characteristics of a sloping-frame. First of all, a closed-form solution is proposed and then, a numerical analysis is performed for some verification purposes. The closed-form solution is developed by solving the frame equations of motion, directly. For this reason, some mathematical techniques are utilized, such as Fourier transform and the well-known complementary solutions. In this way, some differential equations must be solved, and several boundary conditions should be satisfied. Herein, the more accurate derivation of one of twelve boundary conditions is the most important challenge of this paper. This boundary condition is expressed as three distinctive versions, and the free vibration parameters of the frame for the three versions are obtained. Moreover, these results are obtained by the use of the finite element method. In this comparison process, some differences are observed between the closedform and the numerical results. This fact motivated us to propose some modifications in the characteristic matrices of the finite element model of the frame. This modification makes the results of the finite element method similar to the results of the first version of the closed-form solution. Finally, the natural frequencies and mode shapes are presented for a wide range of angles of the sloping member.
    Keywords: Free Vibration Analysism, Sloping, Frame, Boundary Condition, Euler, Bernoulli Beam, Boundary Value Problem
  • E. Mirzaei, Y. Minatour, H. Bonakdari*, A. A. Javadi Pages 387-395
    Cargo terminals are the gateways for entrance of commodities into the transportation network. Therefore, locating them in optimal locations could have a major impact on the cost effectiveness and efficiency of transport, traffic safety and reduction in environmental pollutions. Due to the presence of a large number of parameters involved and the existing uncertainties, decision making in this field is a complex task. If the decision makers cannot reach an agreement on the method of defining linguistic variables based on the fuzzy sets, favorable results and more accurate modeling can be achieved by using the interval-valued fuzzy sets (IVFSs) which provide an additional degree of freedom to represent the uncertainty and fuzziness in the real world. This study presents a group fuzzy analytic hierarchy process (AHP) based on IVFSs (IVF-AHP), and its application to find the optimal location for the Ghaen (Qayenat) cargo terminal in Ghaen City, Iran. The results show that the proposed method is a reliable method in selecting the optimal location for cargo terminals.
    Keywords: Cargo Terminal, Fuzzy AHP, Ghaen (Qayenat) City, Interval, valued Fuzzy Sets, Group Decision Making
  • H. Moghadam*, Fard, F. Samadi Pages 396-401
    The purpose of designing the active suspension systems is providing comfort riding and good handling in different road disturbances. In this paper, a novel control method based on adaptive neuro fuzzy system in active suspension system is proposed. Choosing the proper database to train the ANFIS has an important role in increasing the suspension system’s performance. The database used to train the proposed ANFIS system is extracted from the outputs of fuzzy, LQR and sliding mode controllers. A quarter-car model is considered to study the performance of the proposed controller. Performance of this controller is compared with the passive system, and active suspension systems with fuzzy and LQR controllers. The results demonstrate that proposed ANFIS controller is better than passive suspension system and active fuzzy and LQR based suspension systems in suspension deflection, body acceleration, settling time and also control force.
    Keywords: Active Suspension System, Fuzzy Logic Controller, ANFIS, Quarter Car Model
  • A. Golzarfar, A. R. Sedighi *, A. Asadi Pages 402-409
    In this paper, the effect of number and fault current limiter (FCL) location has been investigated in order to have maximum reduction of short circuit current level in all buses in a real network. To do so, the faulty buses were identified in terms of short circuit current level by computing short circuits on the desired network. Then, while the fault current limit was modeled, its optimal location and amount for the greatest reduction in the fault current level of the whole critical buses was determined. Optimization computations have been done using the genetic algorithm and method of reducing the search space and all implementation stages of the proposed algorithm and reduction of search space has been conducted in DIgSILENT software using programming language DPL. The results indicate the high efficiency of the proposed method in reducing the short circuit current level of faulty buses and simultaneous improving the power quality.
    Keywords: Fault current limiter, Short circuit capacity, Genetic algorithms, DIgSILENT
  • H. Akbarpour, G. Karimi *, A. Sadeghzadeh Pages 410-418
    Placement process is one of the vital stages in physical design. In this stage, modules and elements of the circuit are placed in distinct locations based on optimization processes. Hence, each placement process influences one or more optimization factor. On the other hand, it can be stated unequivocally that FPGA is one of the most important and applicable devices in our electronic world. So, it is vital to spend time for better learning of its structure. VLSI science looks for new techniques for minimizing the expense of FPGA in order to gain better performance. Diverse algorithms are used for running FPGA placement procedures. It is known that particle swarm optimization (PSO) is one of the practical evolutionary algorithms for this kind of applications. So, this algorithm is used for solving placement problems. In this work, a novel method for optimized FPGA placement has been used. According to this process, the goal is to optimize two objectives defined as wire length and overlap removal functions. Consequently, we are forced to use multi-objective particle swarm optimization (MOPSO) in the algorithm. Structure of MOPSO is such that it introduces set of answers among which we have tried to find a unique answer with minimum overlap. It is worth noting that discrete nature of FPGA blocks forced us to use a discrete version of PSO. In fact, we need a combination of multi-objective PSO and discrete PSO for achieving our goals in optimization process. Tested results on some of FPGA benchmark (MCNC benchmark) are shown in “experimental results” section, compared with popular method “VPR”. These results show that proper selection of FPGA’s size and reasonable number of blocks can give us good response.
    Keywords: Discrete MOPSO, Optimization Algorithm, FPGA Placement, VLSI Design, Wire Length Cost Function, Overlap Removal
  • H. Rahimpour, M. Gholami *, G. Ardeshir, H. Miarnaimi Pages 419-425
    Delay Locked Loops (DLLs) and Phase Locked Loops (PLLs) are commonly used as a synthesizer or clock and data recovery circuit in most of the communication systems. In this paper, a new DLL is designed based on PRP conjugate gradient algorithm. The proposed DLL do not need any phase frequency detector, charge pump and loop filters, hence it can contribute better jitter performance and higher speed in comparison with conventional DLLs. In this design, PRP conjugate gradient algorithm is used to optimize the delay amount of each delay cells therefore helps the DLL to lock more accurately and quickly compared with gradient algorithm. In addition, for applying the PRP conjugate gradient algorithm a digital signal processor is used in the proposed architecture. To show the accuracy of the proposed structure’s operation, simulation has been done for 15 delay cells and fREF is chosen 14MHz to have output frequency 14×15=210MHz. fOUT=210 MHz is one of the channels in Iran VHF frequency band. As shown with simulation, the proposed architecture has a locking time of approximately 286nsec which is equal to 4 clock cycles of the reference clock.
    Keywords: DLL, Delay Locked Loop PRP, Conjugate Gradient, Algorithm, Synthesizer
  • M. Zolfaghari *, S. A. Taher Pages 426-432
    This paper presents a new controller for speed control problem of the BLDC motors. The nonlinear model of the motor is approximated by implementation of fuzzy rules. The uncertainties are considered in the fuzzy system. Using this model and linear matrix inequality (LMI) optimization, a robust controller for purpose of speed control of the motor has been designed and applied to it. The effectiveness of the designed controls demonstrated through simulation results.
    Keywords: BLDC Motor, Fuzzy Approximation, Robust Controller
  • H. Moshrefzadeh, Sani*, B. Saboori, M. Alizadeh Pages 433-439
    In this paper, a continuum model is proposed so that a Stone-Wales (SW) defected carbon nanotube (CNT) is replaced by an initial circumferential crack in a continuum cylindrical shell. For this purpose, the critical energy release rate and then the fracture toughness of a defected CNT are calculated using the results of an existing atomistic-based continuum finite element simulation. Finally, the equivalent crack length is obtained from the fracture toughness. The proposed model can be applicable tovarious kinds of continuum-based simulations of nano-structures like nano-composites and nano probes where the fracture resistance studies become important. It is concluded for a case study that the armchair (12, 12) CNT containing a SW defect could be replaced with a continuum cylindrical shell with a circumferential crack length of 0.83 nm. Furthermore, the damage variable is discussed to achieve a method for estimating the effective Young's modulus of defected nanotubes with numerous defects subjected to the progressive damage. This estimation method is evaluated by the atomistic based FE simulation of a double defected CNT.
    Keywords: Nanotube, Continuum Model, Racture Toughness, Energy Release Rate, Damage
  • A. Bhatnagar *, R. K. Shrivastav, A. K. Singh Pages 440-446
    The aim of this paper is to study the effect of slip velocity and shape of stenosis on non Newtonian flow of blood through a stenosed arterial segment. Blood is modeled as Bingham-Plastic fluid in a uniform circular tube with a radially non-symmetric stenosis. The problem is investigated by a joint effort of analytical and numerical techniques. The influence of stenosis shape parameter, slip velocity, stenosis height and yield stress on blood flow through a stenosed artery has been examined. The variations of wall shear stress, resistance to flow, volumetric flow rate and axial velocity with stenosis shape parameter, yield stress and slip velocity have been shown graphically. It is noticed that axial velocity and volumetric flow rate was increased with slip but was decreased with yield stress. This information of blood could be useful in the development of new diagnosis tools for many diseases.
    Keywords: Stenosis, Bingham, plastic Fluid Model, Stenosis Shape Parameter, Slip Velocity, Resistance to Flow, Wall Shear Stress
  • R. Nikoi, M. M. Sheikhi, N. Bani Mostafa Arab* Pages 447-453
    In the present study, the ultrasonic welding process of plastics is used for overlap joining of polypropylene composites reinforced with glass fiber. The effect of three process parameters such as welding time, air pressure, vibration amplitude and the amount of glass fiber in the composite on tensile- shear strength of weld joints is investigated. To reduce the number of tests and cost, the response surface methodology of design of experiments is employed by considering the above four parameters at three levels. These parameters are also optimized to obtain maximum weld tensile-shear strength. The results showed that a maximum failure force of about 2.30 KN is obtained when air pressure, vibration amplitude, welding time and amount of glass fiber are 1.5bar, 32 microns, 0.4 seconds and 10 percent, respectively.
    Keywords: Ultrasonic Welding, Polypropylene Composite, Response Surface Methodology, Weld Failure Force
  • M. Bidabadi, M. J. Noroozi* Pages 454-459
    Flame stability inside a cylindrical micro-combustor was studied. Considering the occurrence of heat recirculation, the respective relations were written; with parameters such as motion speed of reactants, flame propagation speed and thermal conductivity of the combustor wall. The flame stability as well as its location inside the micro-combustor were also studied. It was found that for each thermal conductivity of the combustor wall, there was only one point inside the micro-combustor. If the flame was formed in that point, it would remain stable inside the micro-combustor. It was also found that for each thermal conductivity of the combustor wall, the flame inside the combustor remained stable, only in one specified range of motion speed of the reactants. In addition, blow-off limits were obtained for high and low speeds of reactants inside the combustor for different values of thermal conductivity of the combustor wall.
    Keywords: Analytical Model, Heat Recirculation, Wood Particles, Burning Velocity, Blow, Off Limits
  • M. A. Ardekani*, F. Farhani, M. Mazidi, M. A. Ranjbar Pages 460-466
    Wind can adversely affect the thermal performance of a dry cooling tower. In this field study, performance of Heller cooling tower and the use of guide vanes cascade at the intakes of the periphery cooling sectors, which are parallel to the wind direction and have inadequate thermal performance, for enhancement of the cooling tower performance under wind conditions were investigated. Wind velocity around the cooling tower and water flow rates and temperatures at the cooling tower inlet and outlet were measured. It was observed that the air suction through the tower prevented the flow separation at the radiators locations on the tower periphery. Moreover, with increase in wind velocity, the performance of sectors parallel to the wind direction on the tower periphery and those at the back of the tower deteriorated. However, the better airflow distribution over the wind facing cooling sectors resulted in about 20% increase in the thermal efficiency of these sectors with increased wind velocity. Results further showed that the installation of guide vanes cascade caused more uniform temperatures on the surface of the tower radiators and reduced their temperature by 2 ºC, which was translated into 7% enhancement in the thermal performance of the cooling tower.
    Keywords: Wind Velocity, Dry Cooling Tower, Field Measurements, Thermal Performance, Guide Vanes Cascade
  • A. Torkavannejad*, M. Pesteei, M. Khalilian, F. Ramin, I. Mirzaee Pages 467-475
    This article presents the results of a numerical study, using computational fluid dynamics (CFD) analysis to investigate the species distribution of proton exchange membrane fuel cells (PEMFCs) with deflected membrane electrode assembly (MEA). These new geometry were examined while employing three-dimensional, single phase, non-isothermal and parallel flow for model of a PEM fuel cell. This numerical research has concentrated on the effect of new kind of deflected MEA while maintaining the same inlet and boundary condition. Initially, the CFD result of polarization curve has been validated with the available experimental data and shown good concord; then, studied deflected and flatted MEA at cathode and anode side. Investigation showed better results for the PEMFC with having both flatted and deflected MEA at cathode side than base model because of having more reacting area, uniform distribution of reactants, better oxygen transportation to the GDL at shoulder region and having less Cathode Overpotential (COP) which is the main causes of losses.
    Keywords: Deflection, Fuel Cell Performance, PEM Fuel Cells, Single, Phase
  • Y. Vazifeshenas*, M. A. Delavar Pages 476-482
    The article presents a practical technique for enhancing thermo-hydraulic performance of a circular tube. In this way, numerical method focusing on laminar tubular flow is used to compare the effectiveness of utilizing center-cleared twisted tapes instead of typical shape of short width tapes. Numerical analysis represented that using both center-cleared and typical shape oftwisted tapes, Re enhancement reduces the flow resistance. Studying short width twisted tapes showed that decreasing the width of twisted tape, reduces the heat transfer and hydraulic performance. Contrarily, using sufficient clearance for center-cleared twisted tapes can increase the heat transfer. Hence, applying center-cleared twisted tape as a tool of enhancing heat transfer can be a promising and practical idea.
    Keywords: Twisted Tape, Heat Transfer, Friction Factor, Laminar Tubular Flow
  • Y. Bu, Y. Liu*, C. Wan, H. Yuan Pages 483-489
    With the development of highly-deviated well cementing techniques, rotating casing cementing technology has got more and more attention. The rotating casing technique can improve the displacement efficiency of cement paste, and then enhance the quality of well cementation. In the stuck section, the rotating casing can redress the well to make the casing run sequentially. The casing endures shear stress in rotating, besides axial stress, bending stress, circumferential stress and radial stress which are produced by inside and outside casing pressure stress. These forces make it more complicated when calculate the maximum curvature in rotating condition than that without rotation. The paper, by analyzing the casing stresses in rotating condition, assumes a stress model of the casing infinitesimal for rotating casing. It puts forward the calculation method for the maximum allowable borehole curvature in casing bucking deformation, or when casing couplings and thread seal fail under rotating condition. It also determines the biggest borehole curvature that allowed though, laying a base for the design and construction of the highly-deviated well casing.
    Keywords: Rotating Casing, Maximum Allowable Borehole Curvature, Plastic Deformation, Casing Yield Limit, Tensile Strength, Tap Sealed