AMIRKABIR
Year:2005 | Volume:16 | Issue:61-A|Papers Count:7

The rapid increasing cost of electricity in recent years brought about awareness to the, importance of pricing policies in maximizing the social welfare. In this paper a new method is developed to determine the price of electricity at different nodes in distribution systems. Although location based pricing is complicated but it is an accurate method. The cost function in the developed method consists of all cost components. These components are losses, investment for development and reinforcement of network, operation and maintenance costs. The proposed method has been applied on a real distribution network in both low and medium voltage level. To implement the proposed algorithm various software such as load forecasting, expansion and reinforcement planning are developed.

Microturbine-Generators are one of the important aspects of disperse generations. This equipment will capture cover a noticeable percentage of generation capacity till end of the current decade, therefore obtaining the manufacturing and design knowledge is very important. Thus, considering the importance of field values determination for design procedure extraction, in this paper after a short comparison between disk and round rotors, a new method is presented to specify the field values based on Maxwell equations. Finally the results are compared to the ones obtained by finite element method.

This paper presents delay-dependent stability analysis for some types of nonlinear time-delay systems. Motivated by Lyapunov-Krasovskii functionals and the related theorems on stability of time-delay systems, we introduce a new procedure for generating such functionals. The main reason for considering Lyapunov-Krasovskii functionals is the less conservatism of this method. The obtained conditions are sufficient and local. Applying the introduced procedure on a typical system with time-invariant parameters derives more results and a numerical example presents the capability of the method.

Microcracks development in cortical bone occurs when the tissue is subjected to cyclic and fatigue loading. This phenomenon reduces the fracturer resistance of bone. The underlying mechanisms governing bone fracture, however, require a more thorough study. To this effect a two-dimensional micromechanical fiber - ceramic matrix composite material model for the tissue is presented in this paper. Here, the interstitial tissue was modeled as a matrix and the osteon was modeled as a fiber, followed by the implementation of the linear elastic fracture mechanics theory. The solution for the edge dislocations, as a Green's functions, was adopted to formulate a system of singular integral equations for the radial microcracks in the matrix in vicinity of the osteon. The effects of microstructural morphology and heterogeneity of haversian cortical bone upon the fracture behavior was investigated by computing the stress intensity factor near the microcracks tips. The results indicated that interaction between osteon and microcracks was limited to the vicinity of the osteon. Furthermore, analysis of the microcrack interactions was an indication of the effects of microcrack configuration upon Stress Intensity Factor in shape of either stress amplification or stress shielding.

In this paper, a new approach is presented to model a lightning return-stroke channel and to calculate induced over-voltages on adjacent overhead power transmission lines. In this model, the lightning channel is approximated by a lossy monopole antenna above a perfectly conducting ground. A new electric field integral equation (EFlE) is presented for inductively loaded elements of the channel and its nearby power lines. Solving the new EFIE by the method of moment in time domain, the temporal-spatial current distribution along the lightning chaimel and coupled over voltages on the adjacent metal structures is obtained. An important feature of the proposed model, as opposed to the conventional models, is the fact that the relative permittivity of the surrounding medium equals to unit. In addition, the channel speed can be adjusted using the distributed inductive loads along the channel. The latter enables one to allocate a desired propagation speed to the channel current and the propagated electromagnetic waves. To demonstrate the validity of the model, the current distribution along the channel and the radiated electromagnetic field are computed and compared with the measured data and those obtained using the conventional model. For several power lines, the induced over-voltages are computed and compared with those obtained using the conventional model. It is shown that both the peak value and time duration of the over voltage pulses can remarkably vary. This is sought to be due the effect of propagation speed of the channel current, which can be readily included in the proposed model.