M. Rabbani,
Volume 21, Issue 1 (7-2002)
Abstract
In most stochastic inventory models, such as continuous review models and periodic review models, it has been assumed that the stockout period during a cycle is small enough to be neglected so that the average number of cycles per year can be approximated as D/Q, where D is the average annual demand and Q is the order quantity. This assumption makes the problem more tactable, but it should not be adopted when the beck order and lost sales penalty costs are relatively small. In this paper, considering a continuous review inventory model, we relax the above assumption and we explicitly take into account the stockout period when computing the expected cycle length. Further, we consider the effect of using exact number of cycles rather than using approximate of cycles in a continuous review inventory model.
Keywords: Inventory control, Stochastic demand, Continuous review, Inventory cycle
D. Mostofinejad and M.davoodnabi,
Volume 21, Issue 1 (7-2002)
Abstract
In most cases, structural engineers assume a concrete floor to be a rigid diaphragm. Although this simplification is in most cases acceptable, it should be noted that such an assumption may be distrusted due to certain problems. Concrete structures with staggered shear walls are among those whose analysis should be conducted with special concern for the behavior of their floor diaphragms. However, in the structures with staggered shear walls, the horizontal shear due to lateral loads is transmitted to the lower stories through the floor diaphragm since the walls are not usually located over each other in consecutive stories. Therefore, the rigidity of the floor diaphragm is of great importance. In the present study, a parametric analysis was performed to investigate the effect of the rigidity of the floor diaphragm on the load-carrying procedure of the structures with staggered shear walls. The investigated parameters were the number of stories, the ratio of length to width of the plan, and the thickness of walls and diaphragms. Furthermore, the study was carried out for both rectangular and I-shaped plans. All analyses were dynamically performed by ANSYS 5.4 using acceleration spectrum recommended by Iranian Building Code Standard No. 2800. Finally, the behavior of these structures and comparison of the frequencies, the maximum lateral displacements and the shear in the walls and columns as the responses of rigid and flexible diaphragms were highlighted and outlined.
Keywords: Reinforced concrete, staggered shear wall, load carrying, floor diaphragm, rigidity.
M. Ghafoori- Ashtiani and A. Foyooz,
Volume 21, Issue 1 (7-2002)
Abstract
The importance of the equipment and secondary systems in seismic design and performance evaluation is well recognized and has been the subject of many studies. In all of these studies, earthquake is considered as a single component, and in most of them the primary system is considered as shear building. Most attention has been concentrated on the response of secondary system and its response spectrum. In this paper, the transfer function for absolute acceleration of the secondary system is obtained.
The squared modulus of transfer function relates the power spectral density function of the input (excitation) to the output (response), which is useful in the study of the various dynamic parameters of the system. In addition to transfer function, the autocorrelation and power spectral density function of absolute acceleration of the secondary system are obtained. Earthquake is considered as a multi-component system and the necessary formulation is developed for the calculation of these functions as well as the critical angle with and without interaction between the two systems. The damping of the system is considered as proportional in the decoupled analysis, and nonproportional in the coupled analysis. The formulation developed has been illustrated by considering a ten-story torsional builing. Various parameters such as eccentricity, correlation between components, tuning interaction and nonproportional damping are studied. Results show that eliminating the effect of multicomponentness of earthquake can cause large errors especially at large eccentricities.
Keywords: transfer function, Random vibration, secondary systems, critical angle, interaction, nonproportional damping
M. R. Soltani, H. Fazeli, B. Farahanieh and A. R. Davari,
Volume 21, Issue 1 (7-2002)
Abstract
An extensive experimental investigation to understand the aerodynamic behavior of wrap around fin (WAF) missile configuration has been conducted. Various tests using at first a standard model (TTCP) in the trisonic wind tunnel of Imam Hossein University has been performed. The tunnel has attest section of 60×60 cm2 and can operate at Mach numbers of 0.4≤M∞≤2.2 and at attack angles of -4˚≤α≤10˚. Experimental longitudinal results are compared with those of NASA and an engineering code. The results for TTCP model are in good agreement. After gaining confidence on the TTCP results, a new model of WAF rocket was designed, built and tested. This paper compares the results of two models tested under the same conditions.
Keywords: Wind tunnel, Wrap around fin, Missile, Balance WAF-TTCP
M. H. Rahimian and M. Farshchi,
Volume 21, Issue 1 (7-2002)
Abstract
The internal flow circulation dynamics of a liquid drop moving in a co- or counter-flowing gas stream has been numerically studied. The present work is concerned with the time accurate numerical solution of the two phase flow field at the low Mach number limit with an appropriate volume tracking method to capture motion and deformation of a liquid drop. It is shown that relative velocity between gas and liquid and the parameters controlling the deformation of the drop have the strongest influence on its internal circulation, too. The effects of the liquid Weber number, ranging from 8 to 32, and of gas stream Reynolds number, ranging from 1 to 20 are studied. It was revealed that the largest and the most lasting internal circulation are observed in drops with small deformation in high Reynolds number gas streams. In the case of counter-flowing gas stream, there is a strong internal circulation inside the liquid drop. The locations of the gas separation points on the drop are strongly influenced by the internal circulation of the drop, resulting in a complex wake dynamics.
Keywords: Numerical solution, Two phase flow, Moving droplet, Droplet internal circulation
B. Ghasemi,
Volume 21, Issue 1 (7-2002)
Abstract
In this paper, mixed forced and natural convection heat transfer in a rectangular cavity has been numerically studied. the cavity receives a uniform heat flux from one side and is ventilated with a uniform external flow. The external flow enters the cavity from the heated side and leaves the cavity from the opposite side. The velocity and temperature fields and heat transfer rate are determined by solving the two-dimensional continuity, momentum and energy equations. In this research, steady-state flow with constant Reynolds number, Re=100, is considered. Rayleigh number is in the range of 0≤Ra≤107. First, the results are presented for a cavity with constant aspect ratio, AR=2, and four different inlet and exit opening positions. Then cases with a fixed opening position and different aspect ratios including 0.1, 0.25, 1, 4 and 10 are modeled. In the cavities with opening in the bottom or cavities with aspect ratios less than one, the results show weak effects of natural convection on heat transfer. This research has been done for air as a working fluid (Pr=0.71). In some cases, the results are compared with those from previous studies.
Keywords: Convection, Natural, Forced, Cavity, Rayleigh, Ventilate
S. Aminorroaya and H. Edris,
Volume 21, Issue 1 (7-2002)
Abstract
In electric arc furnace steelmaking units, the essential parameters are reducing price, increasing production and decreasing environmental pollution. Electric arc furnaces are the largest users of electric energy in industry. The most important techniques that can be used to reduce the electric energy consumption in electric arc furnaces are scrap preheating, stirring, use of burners and hot charge and foamy slag. Between these methods, the use of foamy slag is the most useful and economical factor. Foamy slag can reduce the amount of energy, electrodes, refractory consumption, and tap to tap time while it also increases productivity.
In this study, method of production and optimum conditions for foamy slag in a 200-ton electric arc furnace were investigated. The use of foamy slag in this research can reduce the electric energy consumption from 670 to 580 kwh/t and the melting time from 130 to 115 min. and that the electric power input can be increased. It also shows that with foamy slag, the optimum amount of FeO in slag is 20-24 percent and the optimum basicity is 2-2.2.
Keywords: electric arc furnace, energy, DRI, foamy slag
M.r. Bannazadeh, A. A. Bidokhti, M. Kherandish and H. F. Hosseini,
Volume 21, Issue 1 (7-2002)
Abstract
Observations of the Caspian Sea during August-September 1995 are used to develop a three-dimensional numerical model to be used in calculating temperature and current. The model has variable grid resolution and horizontal smoothing that filters out small scale vertical motion. Data from the meteorological buoy network on the Caspian Sea are combined with routine observations at first-order synoptic station around the lake to obtain hourly values of wind stress and pressure fields. The hydrodynamic model of the Caspian Sea has 6 vertical levels and a uniform horizontal grid size of 50 km. The model is driven with surface fluxes of heat and momentum derived from observed meteorological data. The model was able to reproduce all the basic features of the thermal structure in the Caspian Sea and larger-scale circulation patterns tended to be anticyclone, with anticyclone circulation within each sub-basin. The results matched observation data.
Keywords: Circulation, Temperature, Numerical model, Vorticity, wind stress
J.bazargan and H. Bayat,
Volume 21, Issue 1 (7-2002)
Abstract
As a result of the limitations in the application of Darcy Law (V=ki) to linear-laminar flow regimes through porous media and due to the fact that in coarse alluviums, the Reynolds number may exceed its critical value, the so-called Laplas equation cannot be used for precise analyses of coarse granular foundations. A more general relationship is, therefore, required for such cases. However, a common relationship between piezometric gradient "i" and the approach velocity "v" within porous media shown as i=mVn leads to major difficulties in undertaking complicated tests to determine the values of m and n. It is shown that by combining the above-mentioned relationship with the continuity equation, a differential equation may be obtained to give piezometric head and a potential function Φ, which in turn, leads to the uplift force distributions and the seepage quantities through porous media. To overcome difficulties associated with m and n estimations in the model and as a result of fulfilling an extensive research programme, a fresh and reliable procedure has been developed and explained to assess m and n by means of a simple stepped pump-out test. The practical applicability of the method for a given confined aquifer is also examined. Findings indicates that the proposed procedure a) makes the use of the differential equation for turbulent flow in porous media possible, and b) provides means to determine the nonlinear equation parameters (m&n) at an acceptable precision. The computed values of the parameters are also submitted.
Keywords: Turbulent flow, Rock fill, Alluvium foundation, Reynolds number, Aquifer
M.farzin, M. Salmani-Tehrani and S.h. Hashemolhoseini,
Volume 21, Issue 1 (7-2002)
Abstract
In this study, "Buckling Limit of Strain" (B.L.S.) is introduced as one of the most important limiting factors in cold roll forming process. B.L.S. is calculated by the finite element procedure. Then for two particular processes with existing analysis and experimental results, B.L.S. has been determined and evaluated. LUSAS 12.3 is used for finite element analysis. The results show that when buckling of the sheet metal is the limiting factor, B.L.S. is in good agreement with practical limits. It has also been shown that flower pattern can be well predicted when B.L.S. is obtained and this idea is another new outcome from this study. Using this criterion to define and determine B.L.S. and to design the flower pattern is a new concept accomplished for the first time.
Keywords: Cold Roll-Forming, Nonlinear Finite Element Analysis, Local Buckling
S. Yaghmaei, A. A. Seifkordi and H. Shirzadi,
Volume 21, Issue 1 (7-2002)
Abstract
A mathematical model has been analyzed for in-situ bioremediation with the purpose of remediating organic contaminated soil. Oxygen rich water when passed through the porous media of soil activates the aerobic microorganisms, leading to the biodegradation of the organic content. The model equations comprise three convection-dispersion partial differential solution of these equations has been conducted using the finite difference method. The effects of insufficient oxygen supply, growth of biomass and resistance to contaminant migration on the rate of biodegradation have been analyzed by numerically solving the equations.
The results from the numerical simulation indicate that the rate of biodegradation of contaminants in soil may be constrained not only by insufficient oxygen supply, but also by resistance to contaminant migration within the pore network.
Keywords: Bioremediation, Soil, Porous media, modeling
Gh. Yousefi, H.seifi and M. S. Ghazi-Zadeh,
Volume 21, Issue 1 (7-2002)
Abstract
In a de-regulated open access environment, reactive power is one of the ancillary services which must be provided by an Independent System Operator (ISO). In this paper, a new algorithm is proposed in which reactive power resources are initially so tuned that optimum security in terms of voltage profile and voltage stability are achieved while at the same time, the system losses are minimized. The resulting optimization case is solved as an Extended Multi-objective Optimal Power Flow (EMOPF) problem using Lexico Graphic Method (LGM). Thereafter, using the concept of Fair Resource Allocation (FRA), the reactive powers generated are distributed among existing transactions so that the costs incurred are properly and fairly recovered. The algorithm is successfully tested on a typical power system.
Keywords: Reactive Power, Reactive Power Management, Reactive Power Pricing, Voltage Profile, Voltage Stability, Deregulated Environment, Open Access
M. Jafarboland, H. R. Momeni and N. Sadati,
Volume 21, Issue 2 (1-2003)
Abstract
Various methods are presented to control the attitude of satellite due to lack of information of yaw axis attitude so far.
In this paper, a new method is used which is more general and is applicable to all types of satellites, with at least one controller.
This method is not limited to YAW axis and can control the two other axes as well. One feature of this approach is the ability to be modified for large angle maneuvers for special applications.
A new observer is also proposed for the controller, which causes the angles attitude to be kept in desirable values, with minimum control effort and more accuracy. Simulation results show that compare with methods using the complete all axis information, this approach is satisfactory.
Keywords: Attitude control, PID controlley, BIBO stability, pseudo observer
S. Samavi, A. Torkian and P. Khadivi,
Volume 21, Issue 2 (1-2003)
Abstract
Fabrication of an integrated circuit with smaller area, besides reducing the cost of manufacturing, usually causes a reduction in the power dissipation and propagation delay. Using the static CMOS technology to fabricate a circuit that realizes a specific logic function and occupies a minimum space, it must be implemented with continuous diffusion runs. Therefore, at the design stage, an Eulerian path should be found for the logic function. Every discontinuity causes an increase in the area as well as a reduction in the clock rate and performance.
The realization of a logic function using the static CMOS technology is done through different methods, most of which are based on the Uehara's method. In this paper, an algorithm is suggested that finds the Eulerian path and allows the implementation of the circuit with continuity in the diffusion region that results in minimum area. In a case where there is no Eulerian path, the possible sub-paths are found. In addition, the algorithm gives information that helps the layout generation.
Keywords: VLSI, Uehara's method, Static CMOS, Continous diffusion, Standard cell.
H. Farzanehfard, G. Askari and S. Gazor,
Volume 21, Issue 2 (1-2003)
Abstract
In recent years, active filters have been considered and developed for elimation of harmonics in power networks. Comparing with passive, they are smaller and have better compensating characteristics and resistance to line distortions. In this paper, a novel idea based on adaptive filter theory in presented to develop an active filter to eliminate the distortions of an arbitrary signal. Using this idea, new methods of active power filters, are introduced to remove harmonic distortions in single phase power networks. Stability of these methods are analyzed and the simulation results are shown. Design and implementation of this adaptive active filter are done and the performance and advantages of this technique are affirmed by the practical results. Exact estimation of amplitude, frequency and phase of input signal first harmonic is the most important advantage of this adaptive technique. Furthermore, this method is for canceling the harmonic of any arbitrary signal and can easily be modified for other systems, and three phase networks.
Due to its adaptive nature, this technique can adopt itself with variation in environment and system parameters and be adjusted for optimal behaviour.
Keywords: Adaptive active filter, ac network, amplitude, Phase and frequency Estimation, Floque theorem, Averaging theorem.
A. N. Mashayekhi and B. Arbabshiriani,
Volume 21, Issue 2 (1-2003)
Abstract
Knowledge is one of the most important organizations' assets. To manage knowledge effectively, it is necessary to be able to measure knowledge. There are few methods for knowledge measurement with certain limitations. One important weakness of current methods is their insufficient attention to definition, dimensions and attributes of knowledge.
In this paper, we propose a new method for measuring the level of an engineering organization's knowledge. According to our proposed method, the level of an organization's knowledge is a function of both "knowledge hierarchy" and "knowledge dimensions". The method is applied to an engineering organization to measure the level of knowledge at two different times and the results are presented.
Keywords: Knowledge, Knowledge management, Knowledge measurement, Knowledge hierarchy, Knowledge dimensions
A. Hagilouy, M. Ghelich Khani and S. Ghasemi,
Volume 21, Issue 2 (1-2003)
Abstract
In order to carry out experimental investigations on radial inflow gas turbine, a special test laboratory was designed and constructed at Sharif University of Technology. This laboratory is introduced in the present paper and experimental procedures are elaborated on. Then, some test results are presented and discussed. The trends of performance characterisitics match our expectation and show good agreement with the published research results in this field.
Keywords: Radial inflow gas turbine, Experimental, Laboratory, Performance characteristics
K. Mazaheri and H. Assadollahi,
Volume 21, Issue 2 (1-2003)
Abstract
One of the basic equations to analyze the detonation of high explosives is the equation of state of the detonation products. Due to the very high pressure of the product, the direct measurement of the thermodynamic variables such as pressure or temperature is not possible. In this research, the parameters of BKW and HOM equations of state of detonation products are determined via experimental measurement of the detonation velocity. Comparing the calculated parameters show good agreement with the published results for a vast range of explosives.
It is also shown that the curve fitting of the enthalpy of the products in standard states to a forth degree polynomial of temperature improves the results with respect to entropy fitting used by Mader.
Keywords: BKW, HOM, Equation of state, Detonation product, Explosion simulation
M. R. Forouzan, M. Salimi and M. S. Gadala,
Volume 21, Issue 2 (1-2003)
Abstract
A new method (thermal spokes) is proposed to simulate the guide rolls in FE analysis of the ring rolling process. So far this method is the only one, capable of calculating guide rolls reaction contact forces related to the stiffness of their adjustment mechanism. The method is simple to use, does not introduce further nonlinearities and could be used in any kind of FE formulations. The method is successfully employed in FE analysis of rectangular and T-section rings. The results of the thermal spokes method, a new analytical method based on lever arm principle with experimental results are in good agreements. This analysis shows that the guide rolls greatly affect the process.
Keywords: ring rolling, finite element method, guide rolls, thermal spokes
S. M. R. Khalili, M. Zohouri and A. Khorrami,
Volume 21, Issue 2 (1-2003)
Abstract
Due to the widespread applications of fiber reinforced polymer composites in various industries, the machining of these materials to reach the desired shapes, close tolerances and surface finish quality is of great importance. But the composite materials are anisotropic and are mostly prepared in laminated form and, therefore, they have special chip formation behaviour. Among the effective parameters in machining of these materials, the angle between the fiber orientation and machining direction and also the properties of fiber and matrix are of great significance. In the present paper, using the latest theories in the field of machining of FRP materials, a mathematical model to improve the feed rate as well as the cutting speed with respect to the fiber orientation has been introduced and, a computer package was developed for the 3-dimensional CNC machining of fiber composite materials. A number of composite pieces were fabricated and machined to check the output of the programme and the work pieces. Besides the reduction in the machining time, the machined work pieces had desired surface quality, while the common defects like matrix burning, delamination and fiber pullout were completely absent.
Keywords: Fiber composite Materials, Machining, Software, Cutting force, fiber orientation
