Showing 657 results for Type of Study: Research
M. M. Saadatpour and N. A. Falah, ,
Volume 14, Issue 2 (1-1996)
Abstract
A solution technique for the dynamic analysis of asymmetric base-isolated buildings, subject to earthquake ground motion, is presented. To develop the formulation, a yield surface as a function of both shear force and torsion moment of the sliding surface with rigid perfectly plastic behavior is constituted. To achieve the objective, the yield stress is defined by the friction coefficient through a simple relation. Having introduced the mathematical model of the yield surface, the simple conditions of being at the onset of sliding and nonsliding phases of motion are given. Based on the elaborated model, the earthquake dynamic analysis of a 3-D structure is performed. The results are in good agreement with those obtained by the finite-element modeling of the surface.
A. Meghdari,
Volume 15, Issue 1 (7-1994)
Abstract
Recent developments in the area of smart structures indicate that variable geometry / stiffness truss network is of fundamental importance in designing smart transformable structures and systems for space applications. This paper presents the conceptual design and dynamic modeling of a cooperative re-configurabel dual-arm robotic structure called Dual-Arm Cam-Lock Manipulator. The Manipulator is designed to be capable of performing a wide variety of tasks by automatically reconfiguring itself to form a variable geometry, stiffness, and workspace robotic structure. Hence, it may also be referred to as a Variable Geometry Robot Manipulator (VGRM).
M. R. Behbahanifard, M.m. Saadatpour,
Volume 15, Issue 1 (7-1994)
Abstract
A frequency domain dynamic analysis is needed to obtain the response of structures constructed on a system of base isolators on flexible soil when subjected to earthquake ground motion. In such systems, the lateral stiffness of the base isolators is so small, compared to the structural stiffness, that in an earthquake attack the fundamental vibration mode dominates the response. With this in mind, a simple equivalent model is introduced for the assembled structure and its flexible isolators. Next, this simple model is modified to include the effect of soil flexibility. This final model is believed to be appropriate for the frequency domain analysis of the whole system. Frequency independent dynamic characteristics of the model are determined and several response spectra pairs are prepared for both the exact and developed models. The results are in good agreement while the computational efforts for the simplified model is less.
N.najaf- Zadeh, M.ghorbani,
Volume 15, Issue 1 (7-1994)
Abstract
The effects of carbon content on the dynamic and static softening mechanisms of Ti microalloy steels were investigated both in ferrite and austenite regions.
The results obtained showed that recrystallization rate decreased as the percentage of carbon content was increased from 0.0035 to 0.110. This is due to the Ti(CN) and TiC precipitates and also the free carbon content. In the ferrite region, the main obstacles for dynamic recrystallization are interstitial elements such as C and N. The interrupted compression tests also showed that increasing temperature leads to the increasing rate of static recovery and recrystallization in both ferrite and austenite regions.
B. Gholizadeh,
Volume 15, Issue 1 (7-1994)
Abstract
This paper proposes a triangulation method for a digitized surface whose points are located on a regular lattice. The method relies on an iterative and adaptive splitting of triangular faces of an initial polyhedral surface. Assuming a bijection between the digitized surface and its approximation, a partition of the data base is performed. The method allows the measurement of the local quality of the approximation and avoids the generation of triangles with sharp corners. Its low computational complexity permits the approximation of very large sets of points.
M. Rezaiee-Pajand and M.r. Salari,
Volume 15, Issue 1 (7-1994)
Abstract
This paper is about discrete sensitivity analysis. A triangular bending element with constant moment and six degrees of freedom is used. The required derivatives for sensitivity analysis are calculated explicitly. These formulations, finite element method and sequential linear programming are utilized to find shape optimization of plate bending structures. The numerical examples, which show the ability of the derivatives, are presented.
Ail A. Rostami, and M. R. Khosravi,
Volume 15, Issue 1 (7-1994)
Abstract
Natural convection between vertical parallel plates occurs frequently in applications such as solar collectors and cooling of electronic instruments. The problem is a two dimensional developing buoyant flow. In this work, the two dimensional conservation equations are solved numerically for constant wall temperature and constant wall heat flux. The results for the local Nusselt number at the duct exit are compared with the experimental data and the agreement is reasonable.
M. Monir-Vaghefi, A Saatchi and J.hejazi,
Volume 15, Issue 1 (7-1994)
Abstract
In this work the effects of various methods of agitation on the properties of electroless Ni-P-MoS2 composite coatings were investigated. Magnetic stirring as well as purging the solution with gas (Air, Oxygen, Nitrogen) were used. Plating rate, chemical composition, MoS2 distribution, and hardness of the deposit were measured. Topography of coating was studied with metallography and scanning electron microscopy. It was concluded that purging the solution with air produced optimum results, i.e. high rate of deposition, uniform distribution of MoS2 particles and appropriate surface morphology.
M.h. Fathi, V. Mortazavi, M.a. Golozar and K. Khosravi,
Volume 15, Issue 1 (7-1994)
Abstract
Tarnish and Corrosion behavior of three Commercial dental amalgams namely Am.1, Am.2, Am.3, have been investigated by utilizing in vitro tests. The corrosion and/or dissolution rate of the three dental amalgams were studied in 0.9 wt% NaCl Solution, artificial saliva and Ringers solution. Potentiodynamic polarization technique was employed to study cathodic and anodic polarization behavior, from which the corrosion potentials and corrosion current densities were calculated. The corrosion potential and the corrosion current density of each amalgam was found to be affected by the nature of electrolyte used, as well as the Pre-immersion time. However, the order of corrosion potentials and corrosion current densities of the three dental amalgams examined, was found to be independent of the electrolyte used.
A. R. Azimian,
Volume 15, Issue 1 (7-1994)
Abstract
In this paper it is attempted to investigate the behavior of an inviscid flow in the meridional plane of an axial flow compressor. For this purpose the 3-D unsteady Euler equations in cylindrical coordinate are averaged in tangential direction. Therefore, the equations are reduced to a 2-D system. By averaging the tangential component of momentum equation, a blade force will result. Axial and radial components of the calculated blade force are added to the right hand side of the axial and radial momentum equation. By application of a 4th order Runge-Kutta time marching technique to the resulting 2-D Euler equations, the flow field is solved. Some interesting results are obtained which show the program capability in solving flow in the meridional plane of a compressor at the shortest possible time.
M. Rezaiee-Pajand and H. Asghari,
Volume 15, Issue 2 (1-1997)
Abstract
This paper is on the elasto-plastic analysis of plane stress problems. A five-parameter yield surface is presented. This yield criterion uses associate flow along with mixed hardening rule. The analytical formulations are written and related computer program for non-linear analysis is prepared. Finally, based on the formulations, numerical examples are solved.
R. Hooshmand, H. Seifi, and V. Tahani,
Volume 15, Issue 2 (1-1997)
Abstract
In this article, an effective method to control a power system during emergency conditions is presented. Based on Fuzzy Linear Programming (FLP), a new technique is developed to solve the Load Shedding and Generation Reallocation (LSGR) optimization Problem. The objective function consists of terms of load curtailments and deviations in generation schedules. The constraints are power system variables limitations. The objective function and constraints coefficients are uncertain, thus it is more appropriate to use fuzzy linear programming. Considering the network frequency as an essential variable, and using the electrical load model, a fuzzy environment is prepared to solve more realistically and successfully the LSGR optimization problem. The results of various cases of fuzzy and crisp modes of the problem are demonstrated. It will be observed that the application of the FLP on one hand, will provide a more realistic model of power systems, and on the other hand, will cause a reduction in the values of the objective function.
J. Soltani and Ak. Gozine,
Volume 15, Issue 2 (1-1997)
Abstract
This paper is concerned with development of a technique for performance prediction of current transformers (CT), accurately. In this technique, a new optimized model from view-point of both computation time and memory is introduced in order to simulate the current transformers on digital computers. The introduced software in this paper in combination with relay tester equipments can be used instead of the actual CT to test different types of protection relays.
M. Salehi and A.s. Ayatollahi,
Volume 15, Issue 2 (1-1997)
Abstract
In this research the effect of volume and morphology of eutectic carbides on tribological behaviour of Ni-Hard 4 cast irons have been investigated. Therefore, as a result of the fact that the carbon content effects the carbides morphology of Ni-hard cast irons, the chemical compositions of five different specimens were kept constant with the exception of the carbon content, which was varied from 2.3 to 3.2%. The general composition of these alloys was selected according to Group D Class I of ASTM A532 standard. The microstructure and carbides morphology of homogenized specimens were examined by microhardness testings and metallographic examinations. Metallographic techniques include optical and scanning electron microscopy have been also used to characterize the predominant wear mechanism. The Ni-hard 4 cast iron surfaces worn by a process of plastic deformation and fracture to produce wear debris. SEM examination of worn surface topography and wear debris shows the tendency to plastic deformation and wear decreased as the carbon content of the specimen increased.
S.m. Saghaian and F.farahmand,
Volume 15, Issue 2 (1-1997)
Abstract
In this article our objective is to obtain steady state characteristics of shunt, series, and separately excited DC motors coupled with a centrifugal water pump supplied through a step-up, step-down, and cuk converter from photovoltaic generator. We assume that there are no storage batteries and, of course, the system must operate on maximum utilization i.e. maximum water must be pumped. It is proven that if maximum utilization is obtained by duty ratio tuning, system utilization maximization and generator peak power tracking will be equal. Thus, a DC/DC converter is used as a peak power tracker. However, a single exception exists in the case of separately excited motors operated in constant converter duty ratio and tuned excitation for maximum utilization. In this case, system utilization maximization and generator peak power tracking will be different. In addition, with the assumption of generator peak power tracking, as in the case of shunt and series motors, system efficiency relative to generator terminals will also be maximized.
A. Kianvash,
Volume 15, Issue 2 (1-1997)
Abstract
The effects of high temperature homogenization and low temperature annealing treatments on the microstructure and magnetic properties of sintered magnets of an Nd17Fe76.5B5Cu1.5 type alloy have been investigated. The microstructure of the as-cast alloy, consisted of three phases including a Nd2Fe14B1 (2:14:1- type) matrix phase Cu-containing Nd-rich Phase and Free α-iron. The as-sintered magnet showed a eutectic and and Nd6Fe13Cu1 (6:13:1- type) phase distributed between the 2:14:1 -type grains. In the homogenized magnet at 1100˚C, a substantial reduction in the amount of the 6:13:1 -type intergranular phase was observed. The homogenized (1100˚C) and annealed (600˚C) magnet exhibited a microstructure similar to that of the as-sintered magnet, but with a more amount and uniform distribution of the 6:13:1 -type phase furthermore, some additional grain boundaries were present in this magnet with an appearance of a substructure which had the effect of reducing the effective grain size. The remarkable improvements in the magnetic properties of the homogenized + annealed magnets have been attributed to these microstructural changes during the heat treatment sequences.
M. Salimi and H. R. Malek,
Volume 15, Issue 2 (1-1997)
Abstract
This paper is concerned with investigations into the effect of tension between the stands of the finishing mill on width control in a hot rolling process. An analysis is given to predict satisfactorily the variation in width due to spreading and also due to strip tension between the stands. Wusatowskis model which is developed to give an account of spreading is specified and a similar model to give an account of width reduction due to strip tension between the stands is developed. It is shown that the theoretical values of the model are in good agreement with the experimental results obtained from a hot rolling line of steel strip.
Seyed H. Iran-Manesh and Seyed T. A. Niaki,
Volume 16, Issue 1 (7-1997)
Abstract
In this paper an application of the cluster analysis technique in educational planning is demonstrated by means of a developed computer software with some characteristics of an expert system. The main idea is based on the knowledge-based systems which have been applied in group technology. The software is applied to weekly schedules of the courses and professors of the Industrial Engineering Department of Sharif University of Technology. The results show that the technique can be applied to reduce the number of variables and constraints of a zero-one programming model of an educational planning (a typical example of an assignment problem).
S. H. Mansouri, S. M. Hosseini Sarvari, A. Keshavarz and M. Rahnama,
Volume 16, Issue 1 (7-1997)
Abstract
In this paper, a Schwarz-Christoffel method for generating two-dimensional grids for a variety of complex internal and external flow configurations based on the numerical integration procedure of the Schwarz-Christoffel transformation has been developed by using Mathematica, which is a general purpose symbolic-numerical-graphical mathematics software. This method is highly accurate (fifth order) with mesh size, and is highly flexible for treatment of complex internal flow geometries, for a high degree of control of mesh spacing, and for generation of either orthogonal or non-orthogonal grids. In addition, this method directly generates two-dimensional incompressible potential flow solutions for internal flow, and simply or symmetrical multiply connected external flows: it generates a C type grid for a general multiply connected two-dimensional external flow. The capabilities of this method has been shown by sample cases including external flow over symmetric and antisymmetric airfoils, a car profile, and internal flows with arbitrary shapes. To facilitate further applications, a computer program using Mathematica software has been developed.
M. Fahimi and M. Yarandi,
Volume 16, Issue 1 (7-1997)
Abstract
DEXSY2 is a dental expert system, which diagnoses oral diseases and offers a treatment course. The system which is designed and implemented from scratch is capable of diagnosing among thirty five oral diseases and offering a course of treatment for each. It uses a decision tree for its representation of knowledge, and each of its nodes contains a frame. The knowledge base of the system contains a tree for diagnosing the diseases, a tree for its drug treatment, and a set of signs used in the diagnosis and treatment. Reasoning in the system is based on a forward chaining and depth-first search of the tree. It takes into consideration the uncertainties involved and avoids asking repetitive questions. DEXSY2 also diagnoses a combination of diseases. It also provides various explanations for its decisions.
