Sharif Digital Repository

In this article, we design a compatible waveform for the purpose of high-quality synthetic aperture radar (SAR) imaging in conjunction with sparse recovery methods for image formation. Namely, we consider minimizing the mutual interference between our radar and coexisting licensed emitters and also minimizing the jamming signal power while enforcing some constraints over the waveform features, such as peak-to-average-power ratio. We introduce a new constraint to our proposed optimization problem and show its effectiveness. By nulling some frequency bands in the optimized waveform due to the interference sources (licensed or unlicensed), our sampled data in the frequency domain, which makes... 

The dependence of undrained behavior of silty sand on initial state of stress and direction of principal stresses with respect to vertical (ff) is assessed under generalized loading paths using hollow cylinder apparatus. During applying shear load, value of intermediate principal stress parameter (b) is held constant and ff value is increased from zero to the aimed value and held constant. Specimens are consolidated, both, isotropically and anisotropically to evaluate the effect anisotropic consolidation on the behavior of these soils. The wet tamping method was selected to prepare specimen. Shear loading was carried out under strain-controlled condition to capture post-peak strain-softening... 

The notable effeets of time delay aid time discretization on the torque and current ripple amplitude of the direct torque controlled induction motor scheme are investigated. A simply modified torque hysteresis comparator structure is proposed. It minimizes the undesirable effects of the time delay and time discretization on the torque ripple and allows a sensible reduction of torque and current ripple amplitudes and switching frequency in the whole rotor speed range. Numerical simulations and experimental tests have been carried out to validate the proposed torque comparator effect. © 2004 IEEE  

In the classical DTC scheme, due to the limited number of the VSI voltage vectors, large and small errors can not be distinguished. In fact, the switching vectors chosen for large errors are the same as those chosen for small errors. In this paper, in order to overcome this problem, after considering the primary ideas of the DSVM-DTC technique, a new approach for the realization of the DSVM-DTC methodology of the induction machine is proposed. The proposed method, along with its simplicity, has an improved performance in terms of the torque and the current ripple and can be easily extended. In addition, it minimizes the steady state torque error. By using the proposed DSVM-DTC methodology,... 

The blade element momentum (BEM) theory is based on the actuator disc (AD) model, which is probably the oldest analytical tool for analysing rotor performance. The BEM codes have very short processing times and high reliability. The problems of the analytical codes are well known to the researchers: the impossibility of describing inside the one-dimensional code the three-dimensional (3D) radial flows along the span-wise direction. In this work, the authors show how the 3D centrifugal pumping affects the BEM calculations of a wind turbine rotor. Actually to ascertain the accuracy of the analytical codes, the results are compared with rotor performance, blade loads and particle image...