@article { author = {Rad, M. and Firoozabadi, B. and Afshin, Hossein}, title = {Hydrodynamics Analysis of Density Currents}, journal = {International Journal of Engineering}, volume = {21}, number = {3}, pages = {211-226}, year = {2008}, publisher = {Materials and Energy Research Center}, issn = {1025-2495}, eissn = {1735-9244}, doi = {}, abstract = {Density Current is formed when a fluid with heavier density than the surrounding fluid flows down an inclined bed. These types of flows are common in nature and can be produced by; salinity, temperature inhomogeneities, or suspended particles of silt and clay. Driven by the density difference between inflow and clear water in reservoirs, density current plunges clear water and moves towards a dam, while density current flows on a sloping bed. The vertical spreading due to water entrainment has an important role in determining the propagation rate in the longitudinal direction. In this work, two-dimensional steady-state salt solutions' density currents were investigated by means of experimental studies and data used in turn to verify the numerical model. In the laboratory experiments, the density current enters the channel via a sluice gate, into a lighter ambient fluid and it moves down-slope. Experiments were performed for different concentrations and discharges. Vertical velocity distributions were measured at various stations by Acoustic Doppler Velocimeter (ADV). Results showed a variety of phenomena depending strongly on the entrance buoyancy flux, and Richardson number. As the discharge increases, maximum velocity and current thickness increase as well, but when concentration decreases, the current thickness increases. In the numerical simulation, the governing equations were solved numerically and k-ω turbulence model was used for closure. The buoyancy term was implemented in the numerical model and its constant was calibrated by experiments. For verification, the height and velocity profiles of the dense layer were compared with the experimental data and a good agreement was found.}, keywords = {Density current,K,ω Turbulence Model,Laboratory Experiments,Numerical modeling}, url = {https://www.ije.ir/article_71716.html}, eprint = {https://www.ije.ir/article_71716_da5af4e5c4c52bad0199386cb84f1440.pdf} } @article { author = {Yahyaeii, M. and Sadrnejad, S. A. and Chaboki Khiabani, A.}, title = {Stress Transfer Modeling in CNT Reinforced Composites using Continuum Mechanics (TECHNICAL NOTE)}, journal = {International Journal of Engineering}, volume = {21}, number = {3}, pages = {227-234}, year = {2008}, publisher = {Materials and Energy Research Center}, issn = {1025-2495}, eissn = {1735-9244}, doi = {}, abstract = {Because of the substantial difference in stiffness between matrix and nanotube in CNT composite, the stress transfer between them controls their mechanical properties. This paper investigates the said issue, analytically and numerically, in axial load using representative volume element (RVE). The analytical model was established based on the modified Cox’s shear lag model with the use of some simplified assumptions. Some, in the developed shear lag model, the CNT assumes hollow fiber. Solving the governing differential equation, led the high shear stress in interface especially in the CNT cap. In addition, some finite element models were performed with different aspect ratios and the shear stress pattern especially in interface was calculated numerically. Despite some simplified assumptions that were performed with these two models such as elastic behavior and full connectivity, and the comparison of their results with other numerical models show adequate agreement.}, keywords = {Nanotube,Continuum,FEM,RVE,Shear,Lag}, url = {https://www.ije.ir/article_71719.html}, eprint = {https://www.ije.ir/article_71719_2964e6abbebce5d8c895e1592714ed2a.pdf} } @article { author = {Shafie Zadeh, Nadia and Gharavi, M.}, title = {A Comparison of Underground Opening Support Design Methods in Jointed Rock Mass (TECHNICAL NOTE)}, journal = {International Journal of Engineering}, volume = {21}, number = {3}, pages = {235-248}, year = {2008}, publisher = {Materials and Energy Research Center}, issn = {1025-2495}, eissn = {1735-9244}, doi = {}, abstract = {It is of great importance to consider long-term stability of rock mass around the openings of underground structure, during design, construction and operation of the said structures in rock. In this context, three methods namely, empirical, analytical and numerical have been applied to design and analyze the stability of underground infrastructure at the Siah Bisheh Pumping Storage Hydro-Electric Power Project (HEPP) in Iran. The geological and geotechnical data utilized in this article were selected and based on the preliminary studies of this project. In the initial stages of design, it was recommended that, two methods of rock mass classification Q and RMR should be utilized for the support system of the underground cavern. Next, based on the structural instability, the support system was adjusted by the analytical method. The performance of the recommended support system was reviewed by the comparison of the ground response curve and rock support interactions with surrounding rock mass, using FEST03 software. Moreover, for further assessment of the realistic rock mass behavior and support system, the numerical modeling was performed utilizing FEST03software. Finally both the analytical and numerical methods were compared, to obtain satisfactory results complimenting each other.}, keywords = {Empirical Method,analytical method,Numerical method,Ground Response Curve,Design,Stability Analysis}, url = {https://www.ije.ir/article_71721.html}, eprint = {https://www.ije.ir/article_71721_e154a7ff3bcba88a6e4fe78f59db8e17.pdf} } @article { author = {Goel, A.}, title = {Twin Plate Weir: A Flow Measuring Device (TECHNICAL NOTE)}, journal = {International Journal of Engineering}, volume = {21}, number = {3}, pages = {249-256}, year = {2008}, publisher = {Materials and Energy Research Center}, issn = {1025-2495}, eissn = {1735-9244}, doi = {}, abstract = {For efficient use of water, accurate measurement of flow in (field/laboratory) channels is required for many water resource projects. The present work is aimed to study the flow characteristics of a twin plate weir (two sharp-crested plates are placed one behind the other at some distance) under free and submerged flow conditions. Experiments are performed with four spacing of the twin plate weir ranging from 10 cm to 40 cm under free and submerged flow conditions. It was observed that the coefficient of discharge (Cd) is a function of head over the crest (H1) and height of the plate of the weir (P) in free flow condition. The critical submergence (H2/H1) increases as the discharge increases, for a particular spacing of the twin plate weir (L). The critical submergence also increases with the increase in the spacing of the weir plates for any discharge. When some material fills the space between the two plates, the Cd increases as the percentage of filling increase. The device may prove quite useful when siltation occurs between the twin plate weirs. The device could be utilized in laboratory/industry channels for the discharge measurement.}, keywords = {Channels,Coefficient of Discharge,Weirs,Discharge measurement}, url = {https://www.ije.ir/article_71723.html}, eprint = {https://www.ije.ir/article_71723_9f3c1e5da4b6b3264075c8d8ebcb9eff.pdf} } @article { author = {Pournadaf Haghi, M. and Nateghi, F. and Vasseghi, A.}, title = {Effect of Link Slab on Seismic Response of Two Span Straight and Skew Bridges}, journal = {International Journal of Engineering}, volume = {21}, number = {3}, pages = {257-266}, year = {2008}, publisher = {Materials and Energy Research Center}, issn = {1025-2495}, eissn = {1735-9244}, doi = {}, abstract = {Highway bridges are frequently constructed as simple span structures with steel or concrete girders and a cast-in-place concrete deck, spanning from one pier to another. At each end of the simple span deck, a joint is provided for deck movement due to temperature, shrinkage, and creep. Bridge deck joints are expensive and pose many problems with regard to bridge maintenance. Elimination of deck joints at the support of multi-span bridges has been the subject of recent studies. Recent researches have led to the development of a design concept and approach for jointless bridges where the expansion joints are replaced with continuous link slabs. Further studies have indicated the proper performance of such bridges under service loading conditions. This paper presents analytical study of seismic behavior and response of a two span bridge connected by link slabs. Three dimensional finite element analyses of straight and skew bridges with skew angles varying from 15 to 60 degrees is performed. Both linear time history and response spectrum analyses method are carried out in order to investigate the response of the bridge. The results indicate that the force and displacement demands of the interior bent maybe reduced considerably, if link slab is used in the middle of the bridge instead of an expansion joint.}, keywords = {bridge,structure,Concrete,Earthquake,Link Slab}, url = {https://www.ije.ir/article_71725.html}, eprint = {https://www.ije.ir/article_71725_63ec503213d4afad297b0b74a36542d6.pdf} } @article { author = {Razavi, A.R. and Poursaeidi, Esmaeil}, title = {The Causes of Local Hardness Increasing in Powerplant Rotors and its Modification by Tempering (TECHNICAL NOTE)}, journal = {International Journal of Engineering}, volume = {21}, number = {3}, pages = {267-274}, year = {2008}, publisher = {Materials and Energy Research Center}, issn = {1025-2495}, eissn = {1735-9244}, doi = {}, abstract = {Local hardness increasing on the surface of the power plant rotor may result in severe damages. One major solution for rapid repairing of the rotors is the adaptive tempering heat treatment. For this purpose, after identification of the damaged rotor, initial investigations and tests (such as visual inspection, chemical analysis, nondestructive hardness measurements and replica or on-site metallographic tests) were performed on the rotor journal. The results showed that, the occurrence of local phase transformation (i.e. tempered bainite to austenite and finally martensite) is the main factor. Finally, based on the aforementioned results, tempering heat treatment method was selected as a modifying solution for the following purposes: 1. Decreasing hardness in embrittled places (i.e. 400-690 HV) and, 2. invariable or admissible decrease of hardness in undamaged areas (250-300 HV). Experiments showed that by choosing the 680˚C/4hr as an optimum condition for tempering heat treatment, the two mentioned objectives can be met.}, keywords = {Hardness,Power Plant Rotors,Tempering Heat Treatment}, url = {https://www.ije.ir/article_71726.html}, eprint = {https://www.ije.ir/article_71726_1507d46be2ca0458694c85395ee67976.pdf} } @article { author = {Yaghmaee, Maziar and Razavi, Mansour and Rahimipour, M. R.}, title = {Synthesis of TiC-Al2O3 Nanocomposite from Impure TiO2 by Mechanical Activated Sintering}, journal = {International Journal of Engineering}, volume = {21}, number = {3}, pages = {275-280}, year = {2008}, publisher = {Materials and Energy Research Center}, issn = {1025-2495}, eissn = {1735-9244}, doi = {}, abstract = {In this research, the production possibility of TiC-Al2O3 nanocomposite, as a useful ceramic from commercially pure TiO2, aluminum powder and carbon black has been investigated. Routile (TiO2) with carbon black and aluminum were placed in a high energy ball mill and sampled during different milling times. Then, the activated powders were synthesized at different temperatures in an atmosphere control tube furnace. Our results show that using this method has decreased the synthesizing temperature to 1000-1250˚C by increasing the milling time. Also the width of X-ray patterns peaks, had made it apparent that, the size of produced TiC crystals was in order of nanometer. Furthermore it was detected that the lattice parameter deviated slightly from the standard size.}, keywords = {nanocrystal,Mechanical Activated,Titanium Carbide,Routile}, url = {https://www.ije.ir/article_71728.html}, eprint = {https://www.ije.ir/article_71728_f1594abbec16bf3a003a369e2b93bd71.pdf} } @article { author = {Razavi, A.R. and Poursaeidi, Esmaeil}, title = {An Investigation on the Causes of a Rotor Bending and its Thermal Straightening (TECHNICAL NOTE)}, journal = {International Journal of Engineering}, volume = {21}, number = {3}, pages = {281-290}, year = {2008}, publisher = {Materials and Energy Research Center}, issn = {1025-2495}, eissn = {1735-9244}, doi = {}, abstract = {Distortion or bend in a turbine rotor (especially HIP rotors) may be caused by a number of factors, either singularly or in combination. In general, the causes of rotor bend can be classified invariably in two categories: Rapidly forming permanent rotor bends and/or Slower forming rotor bends, which could trip the turbines’ emergency stop. One of the major modifying solutions for rapid repairing of bent rotors is hot spotting. For this purpose, after the initial tests (visual inspection, chemical analysis, nondestructive hardness), the hot spotting was performed seven consecutive times. The results of experimental investigations and experiences with different temperatures and times showed that, the 690 ± 20˚C and 210 S. are as an optimum temperature and time respectively, for hot spotting which can provide a noticeable straightening in bent areas, in addition to having no affects on mechanical properties. Also, this results were simulated by F.E.M in view of heat distribution in different temperatures in three states (without insulation, with moisture and dry insulation), in order to find out the optimum restraint effects around hot spot area.}, keywords = {Thermal Straightening,Rotor Bending,Hot Spotting}, url = {https://www.ije.ir/article_71730.html}, eprint = {https://www.ije.ir/article_71730_6283c6d3cb549557fc57ae5df8eb2e0c.pdf} } @article { author = {Ali, I. and Abu Bakar, Rosli and Ismail, A. R. and Semin, Semin}, title = {Effect of Direct Injection Diesel Engine Convert to Sequential Injection CNG Engine in Intake Port Gas Flow Pressure Profile}, journal = {International Journal of Engineering}, volume = {21}, number = {3}, pages = {291-302}, year = {2008}, publisher = {Materials and Energy Research Center}, issn = {1025-2495}, eissn = {1735-9244}, doi = {}, abstract = {The one dimension computational model of a sequential injection engine, which runs on compressed natural gas (CNG) with spark ignition, is developed for this study, to simulate the performance of gas flow pressure profile, under various speed conditions. The computational model is used to simulate and study of the steady state and transient processes of the intake manifold. The sequential injection CNG engine model is developed using GT-Power software. The size of this model engine is developed from the real diesel engine data and was input into the software's' library. The simulation model engine runs with various speeds from 1000 up to 4000 rpm. The simulation results of the performance with gas flow pressure, in the intake manifold are collected from two data sets; the GT-Post post processing plots for pressure performance versus crank angle, and post processing cases RLT for pressure performance versus engine speed. The simulation results of the intake manifold and the performance of the gas flow pressure profile, with various engine speed, for the CNG sequential injection engine are shown by characters. The Pressure profile of the engine and the numerical accuracy of the model is verified and validated by comparing the average total of the intake manifold pressure, with the measured intake manifold pressure, of a CNG sequential injection engine. The simulation results show that, the conversion of diesel engine to a CNG sequential injection engine with spark ignition will increase the pressure performance in the intake manifold of the engine.}, keywords = {Diesel engine,Intake Manifold,pressure,Sequential Injection CNG Engine}, url = {https://www.ije.ir/article_71731.html}, eprint = {https://www.ije.ir/article_71731_ad67f3f43b2b0528761faf4f4d6168e5.pdf} } @article { author = {Gharehaghaji, A. A. and Moghassem, Abdolrasool}, title = {Evaluating Pile Yarn Characteristics in Hand Woven Carpet using Stress-Strain Behavior in Compression}, journal = {International Journal of Engineering}, volume = {21}, number = {3}, pages = {303-312}, year = {2008}, publisher = {Materials and Energy Research Center}, issn = {1025-2495}, eissn = {1735-9244}, doi = {}, abstract = {Many factors such as production methods and structural parameters have distinctive influence on the quality and performance of a hand woven carpet. To investigate the effects of some variables, eighteen samples of carpet vary, in knot density, pile height and percentage of slipe wool, were manufactured. Pile yarn performance was assessed by using load-displacement compression curve, obtained from Zwick tensile tester under cyclic loading, up to 30 kPa. Based on the results, compression and matting of the pile yarn decreased and its elastic recovery increased with the increase in knot density. Increase in pile height caused an increase in the degree of variation for carpet samples. Matting of samples decreased with increase in pile height to certain level, but further increase caused increased reduction in matting. Elastic recovery of pile yarn had a reverse trend as the pile height changed. Consequently, increase in percentage of slipe wool caused an increase in compression and matting, and also reduction in elastic recovery of pile yarn.}, keywords = {Slipe Wool,Virgin Wool,compression,Elastic Recovery,Matting,Stress,Strain Compression Curves}, url = {https://www.ije.ir/article_71733.html}, eprint = {https://www.ije.ir/article_71733_4bc6af32dbcdad1f6f016681abcb4fe4.pdf} }