Sharif Digital Repository

This paper presents a mathematical model for Brushless Doubly-Fed Machine (BDFM) based on Stator Flux Orientation (SFO) in positive and negative reference frames under unbalanced grid voltage conditions. A negative controller is designed to eliminate the effects of unbalanced conditions on electrical torque. The model and controller performance during unbalanced conditions is validated by time domain simulation in MATLAB/Simulink  

Effect of different conditions on shear behaviour of rock has been investigated by various researchers. As known, in larger scale the continuity of the rock material is interrupted by separated planes such as bedding planes, faults, shear zones, closure and the behaviour converts to be inelastic and anisotropic. Generally, discontinuities appear repeatedly in more than one preferential direction, creating a three dimensional structure, reducing its stiffness and shear strength as mechanical effects and increasing its transport velocity associated with discontinuity flow as hydraulic effects. They also make rock behavior more complex and different compared to the behavior of soil. According... 

Dynamic properties of soil, such as shear modulus and damping ratio, are necessary for analyzing the dynamic response of the soil in geostructures. This study investigates the effects of partially inherent anisotropy and stress-induced anisotropy on the shear stiffness of unsaturated soil through a series of dynamic hollow cylinder tests at medium strain levels. The different inherent anisotropy in tested sand specimens was introduced through different compaction water contents in the sample preparation stage while keeping the void ratio nearly constant. Moreover, the influences of the angle of maximum principal stress, α, and intermediate principal stress parameter, b = (σ2 − σ3)/(σ1 − σ3),... 

The cosmological constant term can be seen as a constant potential for a (scalar) field. In this viewpoint, at late times, the field is stopped rolling and behaves as a cosmological constant (w=-1). While at the early Universe, its kinetic term can be dominant and behaves as a stiff fluid (w=+1). This new phase lowers the cosmological sound horizon by increasing the Hubble parameter for very high redshifts. Consequently, the lower cosmological sound horizon results in the higher Hubble constant at the present time. This early phase ends before the photon decoupling, so we do not expect any new physics after the last scattering surface. We checked this model in the presence of (reduced) CMB,... 

Free surface vortex and air entrainment are not favorable experiences in hydropower and pumping projects. While complete omission of vortex and air entrainment is not always cost effective, partially weakened free-surface vortex flow is more economical and practical. Hence, in this study, a comprehensive set of experiments were conducted to partially reduce vortex strength and air entrainment at vertical pipe intakes, using rectangular anti-vortex plates. This phenomenon results in increasing water discharge compared with a corresponding free-surface vortex for the same water depth, i.e. in cases of shaft spillway. The plates were used as singles and in pairs and placed symmetrically and... 

The study of air-water, two-phase flows in hydraulic structures such as pressurized flow tunnels, culverts, sewer pipes, junctions, and similar conduits is of great importance for design purposes. Air can be provided by vortices at water intakes, pumping stations, aerators, steep channels, etc. Under certain conditions, air may also be introduced into pressurized intake systems, which may form large bubbles in portions of the pipe. The bubbles may, in turn, cause an unstable slug flow, or other flow patterns, that leads to sever periodic transient pressure. In this paper, an experimental model (a circular and transparent pipeline, 90 mm in ID and 10 m in length) is used to predict pressure... 

One of the sources of disturbance at intakes is the occurrence of free-surface vortices with an air core. The most common solution for avoiding air-entrainment is the use of anti-vortex devices and, especially, plates for large pipe or shaft intakes. If plates are used, then, the geometry and position of them should be studied experimentally. Since only general guidance for use of plates is available, a study for the more precise placement of plates is needed. Hence, a comprehensive set of experiments have been carried out using rectangular plates with different dimensions and at various positions with respect to the vertical outlet pipe intakes and two different pipe diameters (D = 75 and... 

Sigma-Delta modulator ADCs used in signal processing applications are usually implemented by switched-capacitor (SC) circuits and CMOS transmission gates. Clock feed-through effect is one of the main non-ideal parameters existing in SC integrators degrading modulator total SNDR and its linearity. In this paper, a comprehensive analysis of clock feed-through effect on CMOS transmission gates on both rising and falling edges on output node will be presented. The main interferer parameters such as clock signal timing model, input signal level and switch parameters effect on output error will be analyzed. Finally, circuit simulations using 0.18um CMOS technology in ADS environment show the... 

Thee enclosed basin has certain natural frequencies of seiche, depending on the geometry of the water boundaries and the bathymetry of water depths. Therefore, the variation in the water surface at a point becomes irregular, as caused by the combination of several natural frequencies, which may be considered as the superposition of sinusoidal frequency components of different amplitude. This paper is mainly concerned with the motion of an incompressible irrotational fluid in a closed rectangular basin with internal impervious barriers. An analytical solution is presented for predicting the characteristic of generated waves in these types of basin. The equations of free water surface... 

Different factors cause vibration. These vibrations make the voyages difficult and reduce comfort and convenience in passenger ships. In this paper, the creating factors of vibration have discussed first, then with mathematical modelling it will be attempted to minimize the vibration over the crew's seat. The modelling consists of a system with two degrees of freedom and by using vibration visolation with passive method of Tuned Mass Damper (TMD) it will be tried to reduce the vibration over personnel. Moreover using active control systems will be compared with passive systems  

A rectangular labyrinth weir has a very good flood release capacity as well as strong economical and structural advantages. In this study, combined analytical and experimental investigations were undertaken for a rectangular labyrinth weir. The analytical model is based on the synthesis of general weir equations and spatially varied flow dynamic equations. A comprehensive set of experiments led to characterisation of the flow behaviour for low and high heads over the weir and indicated the influences of weir geometry on the release capacity. The results show that this type of weir represents an effective weir alternative and could be five times more efficient than a corresponding traditional... 

In the present study, methods for improving the hydraulic performance of labyrinth side weirs in a rectangular channel are reported based on model experimentation. For this purpose different arrangements and configurations of groups of guide vane plates and piles in the side weir flow field were tested. Experiments were conducted on labyrinth side weirs of different lengths and sill heights fitted in the test section of a rectangular glass-walled channel. Depths of flow were measured in both longitudinal and crosswise directions at regular intervals and their profiles were studied. It was found that the discharge coefficient of the labyrinth side weirs under these conditions gave...