مجله فناوری اطلاعات در طراحی مهندسی
سال سوم شماره 1 (زمستان 1388)

Voltage collapse is an event that causes major concern to the power system utility nowadays. The effect can be catastrophic to the power system where it can cause total collapse to the operation of the system. The study of the voltage collapse phenomenon can provide way to prevent this event from happening. Static analysis provides the best way to study this phenomenon and there had been many methods developed to study the criteria of this phenomenon. Conventional Newton Raphson method has the singularity problem on its Jacobian matrix and thus could not give the solution. To overcome this problem، many methods had been proposed that can avoid the problem and one of them is the Continuation Power Flow (CPF) method. CPF method is a very powerful method that can give the solution without having the singularity problem. The CPF method is improved using the new CPF-GMRES method. Also، NRS (Newton – Raphson – Seydel) is old method but is fast and accurate. This paper expands NRS method and had been proven Expanded NRS reliable and faster than CPF-GMRES. The idea is demonstrated on 350 bus network in IRAN (Khorasan region).

Parrondo’s paradox is a paradox in game theory. According to original formulation of Parrondo’s paradox، two separate losing games can be combined to win via a random or periodic strategy. In this paper the role of irrational numbers (e، and Feigenabum constant) as a new switching strategy for combination of two losing games on Parrondo’s paradox was investigated and the effects of this new strategy on the final gain of Parrondo’s paradox was compared to random strategy. Results showed that the highest final gain of Parrondo’s paradox is related to the “e” switching strategy.

Fluid-structure interaction may affect strongly on the seismic response of the arch dams. However، the modeling of the arch dams by including the mentioned effect may considered as more complicated problem، especially in the case that the reservoir extended to the infinity and it should be modeled as the semi-infinite domain. In this article، several methods for dynamic analysis of dam with infinite reservoir in frequency domain are reviewed briefly، without any concerning on the mathematical background. After that، some of them are employed in the practical problem. The numerical results show the dynamic responses of “Karoon II” arch dams، which are obtained by including the compressible fluid-structure interaction effect. Furthermore، these results are compared against the results of another famous arch dam (Morrow Point dam)، and some novel remarks are concluded.

The small deflection equation for isotropic and Functionally Graded thin annular sector subject to transverse loading is derived in polar coordinate. The Poisson''s ratio of the plate is assumed to be constant، but the young''s modulus varies continuously through the radial direction according to the power-law function. A closed-form solution using the extended Kantorovich method and the first order shear deformation theory is presented for the plate analysis. The validity of results are confirmed by resolving the problems by the well-known Levy''s method as well as commercial finite element code ABAQUS. A good agreement between mentioned methods either for deflections or stress resultants is obtained.

Nowadays، huge human needs for energy forced petroleum and drilling companies to drill deeper into the earth which means spending more time on drilling and passing through numerous layers with different layer characteristics to hit the target. Since major part of a well cost depends on the duration of drilling phase، an organized drilling program seems vital to save the time and cost. Occurrence of different drilling problems like lost circulation and pipe sticking may deviate the drilling operation from the schedule. Mechanical pipe sticking is likely to occur after complete loss. Lost circulation is one of the common drilling problems in the industry which expose heavy expenses to the oil companies. This problem commences from beginning if the drilling and continues till putting the casing in place. Mud loss can occur in low fluxes up to complete loss that finally can lead to well blowout or severe pipe stuck. Freeing the pipes may waste a week or even more time from the rig. Thus، having accurate information about returned fluid and recording mud loss rate can be great help to prevent drilling problems from taking place. Drilling fluid loss is affected by different factor that make modeling of mud loss suffered from analytical point of view. Thus، employing artificial neural networks which its capability in simulation of complicated phenomena is proven، looks very effective. In this research، using drilling daily report of some wells in Maroum oilfield (SouthWest of Iran)، attempts are directed to predict lost circulation in different areas of this field. Network results in prediction of drilling fluid loss show good compatibility with real data were recorded in drilling daily reports.

In the present research a building with 45m height and 15m width is exposed to an uniform wind flow with a velocity of 31m/sec. Finite Element Method(FEM) is utilized to simulate the wind flow around the building. A two-dimensional model is presented and is used to calculate the turbulence viscosity. The flow field is solved with two different meshes and independency of results from the meshes has been achieved. The results for dynamic pressure computed by the FEM model are compared with those of ASCE; the results are in good agreement. Limitations of models presented in ASCE are discussed and the reasons of some differences between the FEM results and those of ASCE are presented.

One of the methods in production of composite materials with different chemical composition is the centrifugal casting method. In this research the centrifugal casting method has been used for making the alloy of Al-15%Si. With this method، reduction in volume of silicon particles on the surface zone of the samples is 25%. As a consequence the alloy hardness is increased and this alloy becomes applicable to resistance in suitable wearing. In this direction obtained results in wearing tests characterized that the formation of silicon particles in the distance of 20 mm from the surface causes the increase in the hardness of samples in the rate of 95 HV and consequently the increase to resistance in the wearing in these zones. In addition this microhardness shows one reduction almost linear with respect to the increase of distance from the surface. Also the studies on the wearing surfaces with the use of electronic microscope shows that the wearing surfaces containing of silicon particles separated and also the tribologic layers are attached together. These two cases both indicate the resistance to wearing of the produced samples by this method.

In the multiuser systems، after signal is received in the antenna، users will be detected by complicated processing of signals. Thus، not to waste the processing power we prefer the signal convey information on its whole time. Meanwhile we know the transmitted signals don’t contain information all the time. The Internet traffic is a non-real time traffic and owns a statistical behavior. We have utilized the packet payload information in this paper and tried to enhance the capacity through a new view on the traffic model by a new Traffic Activity Factor (TAF). In line with that in this paper we used two we proved a theorem indicating TAF effect on the capacity and also we used a signal to noise relation with TAF parameter. We used the popular traffic services such as www، ftp، email، telnet in the multiuser systems. Both methods proved our vision.

Electroencephalogram (EEG) is a reliable reflection of many physiological factors modulating the brain. The aim of this study is to evaluate nonlinear dynamics of electroencephalogram signals during meditation. For this purpose، we collected EEG signals of seven female meditators in two states: before meditation and during meditation. Correlation Dimension، Hurst Exponent and the maximum Lyapunov Exponents were calculated. The results of this study show that the Correlation Dimension was significantly lower during meditation، as well as the maximum Lyapunov Exponents. This reduction indicates that the number of parallel functional processes active in the brain is less and the brain goes to a more relaxed state. Besides that، the Hurst Exponent is increased during meditation. The finite values of Correlation Dimension and positive values of Lyapunov Exponents suggest that all of EEG signals have low dimensional chaos، and the complexity of signals are decreased during meditation.

There are high variability in acoustic features of children\''s speech signals compared to adults\'' which is the causes some problems in automatic recognition of children\''s speech. Using children\''s speech as input in acoustic models trained by adults\'' speech reduces performance significantly. Error rate for children speech recognition is about 2 to 4 times more than adults\''. The recognition rate depends on many factors like age، gender، fundamental frequency and height. In this paper some approaches for improving recognition performance including vocal tract length normalization (VTLN)، speaker adaptive training (SAT) and Constrained MLLR based Speaker Normalization (CMLSN) are studied and VTLN is implemented to improve recognition of Persian children\''s speech. Finally an approach based on combining normalization methods and clustering is proposed for recognition of children\''s speech. Using clustering of input speech and assigning to appropriate model، recognition rate will improve about 50%.