Sharif Digital Repository

In this paper, the whirling frequencies of simply supported and clamped rotating cylindrical shells surrounded by an elastic foundation are investigated. The Love's shell theory is used along with the Winkler foundation to obtain the governing equations of motion. An exact power series solution is obtained for arbitrary boundary conditions and the results are verified with the literature. Several case studies are performed, and the effect of spinning speed, foundation stiffness, and geometrical dimensions of the cylinder on the whirling frequencies are investigated  

Variable reluctance (VR) resolvers have some distinguish features over wounded rotor resolvers that make them suitable for industrial applications. Among different types of VR resolvers, sinusoidal-rotor resolvers are preferred due to simple structure and high performance under eccentricities. However, their accuracy is affected by inevitable run-out error. As they work based on sinusoidal variation of coupling area between stator and rotor and under run-out error the coupling area is impaired. Hence, in this study, a new disk shape configuration is proposed for sinusoidal-rotor resolver that is robust against run-out error. Geometrical dimensions are calculated based on optimisations to... 

The main purpose of the present work is multi-objective shape optimization of a projectile tip for impacting and normal penetrating. Velocity drop, weight and inner volume of projectile have been considered as three conflicting objective functions. For this purpose, at the first step, finite element modeling was done using ABAQUS/Explicit and projectile penetration was examined in different geometric dimensions. Hammersley sequence sampling was employed for designing computer experiments. In the next step, results of the FEM were employed as raw data for MLF-type neural network training to achieve a mathematical model which is able to describe velocity drop behavior. Projectile weight and... 

Nano-micro grippers are able to pick-transport-place the micro or nanometer -sized materials, such as manipulation of biological cells or DNA molecules in a liquid medium. This paper proposes a novel monolithic nano-micro gripper structure with two axis piezoresistive force sensor which its resolution is under nanoNewton. The results of the study have been obtained by the simulation of the proposed gripper structure in Matlab software. Motion of the gripper arm is produced by a voice coil actuator. The behavior of the cell has been derived using the assumptions in the literatures. Moreover, two simple PID controllers, one for control of the gripper motion and another for control of the force... 

In the present work, effects of height, length, and width of a single-slope basin-type solar still on its distillate production was investigated. For this purpose, a radiation model was developed which accounts for the influences of all walls on quantities of received solar radiation by the base and saline water of the still. Moreover, in this radiation model, the side walls of the still were considered as the trapezoid and the diffuse as well as beam components of solar irradiance were separately taken into account for the first time. Abilities of the present model were compared with earlier ones. Furthermore, the predictions of the current model were compared with the present experimental... 

The wide utilization of nanomanipulation as a promising approach in microorganisms, nanoelectromechanical systems, and assembly of nanostructures remarks the importance of nanostructures' motion in electric fields. Here, we study the rotational dynamics of metallic and non-metallic nanowires (NWs) in a static uniform electric field in viscous dielectric liquids. For metallic NWs, it has been theoretically shown that the electric field-induced rotation is practically independent of the geometrical dimensions and the electrical properties of NWs. Our experimental results for suspended silver (Ag) NWs in microscope oil are perfectly in agreement with this model. However, in the case of TiO2... 

Plasma actuator is a flow control device to improve the aerodynamic performance of wind turbine blades at low airspeeds. One of the most robust numerical models for simulation of plasma actuator interaction with the fluid flow is the electrostatic model. This model is improved recently and is extensively verified by the authors. Due to the high cost of performing experimental optimizations, the optimized geometrical dimensions and materials of a plasma actuator may be sought by this numerical model. The aim of the present study is the aerodynamic enhancement of a DU21 wind turbine blade airfoil in which the effect of geometric parameters and the dielectric material is examined separately.... 

Josephson junction in superconductor circuits and metamaterials is modeled as a tunable inductance. The Josephson inductance is tunable by the bias current passing through it and can be tuned from an initial value to a very large value as much as one can push bias current near the critical current but not exceeding it. Tunability by bias current allows design of programmable metamaterials with flexible functions in microwave regime. In High-Temperature Superconductivity (HTS) tunable metamaterials, Josephson junctions should be used in series configuration to give usable tunable inductance. Each Step-Edge Josephson junction (SEJs) in HTS has a critical current that is dependent on its... 

Josephson junction in superconductor circuits and metamaterials is modeled as a tunable inductance. The Josephson inductance is tunable by the bias current passing through it and can be tuned from an initial value to a very large value as much as one can push bias current near the critical current but not exceeding it. Tunability by bias current allows design of programmable metamaterials with flexible functions in microwave regime. In High-Temperature Superconductivity (HTS) tunable metamaterials, Josephson junctions should be used in series configuration to give usable tunable inductance. Each Step-Edge Josephson junction (SEJs) in HTS has a critical current that is dependent on its... 

-In this paper, a new optimized structure for two-speed, capacitor-run, single-phase axial flux induction motor (AFIM) for direct-drive operation is presented. Although, there are many advantages for direct-drive systems, their axial forces between the stator and rotor increases with reduction in air-gap length and is of serious concern. An increase in the air-gap length will result in the deterioration of performance characteristics of the motor. In this paper, a new construction technique is proposed to fabricate an AFIM with adjustable air-gap length. After presenting a comprehensive design algorithm, all geometrical dimensions and electrical equivalent circuit parameters are analytically... 

Dynamic modeling of piezo-driven compliant mechanisms is necessary to predict dynamic behavior of nanopositioning systems, and also to optimize their controlling methods. Dynamic tests on a real system or dynamic analyses on a FEM model is very time consuming when they must be carried out iteratively. According to previous works, obtaining static specifications of model is possible within a reasonable error margin. But all geometric dimensions and mass distribution details of the whole moving parts should be considered to calculate dynamic specifications of the model. In this paper, a functional method is described to obtain dynamic specifications of an planar compliant mechanism, by means... 

In the present paper, conceptual duct shape design for kinetic energy extraction with hydrokinetic turbines is discussed. The goal is to find a single-passage axisymmetric geometry that holds stable flow with maximum kinetic energy flux at duct throat. For finding the optimum duct shape, the fluid flow was numerically simulated in a wedge shaped space with Flow-Simulation Software. In a multi-stage conceptual design, tabulated configurations were employed to study each geometrical characteristic separately. These include curvature of profile camber, trailing edge shape, profile tip shape, and duct exit cross sectional area. The revolved profile of each duct consists of a well constrained... 

By considering the Bauschinger effect and the yield criterion of Tresca, an exact elasto-plastic analytical solution for a thick-walled cylindrical vessel made of elastic linear-hardening material is derived. Having the working pressure and geometric dimensions of the vessel, the distribution of the hoop and equivalent stresses are optimized in the way that the distribution of stresses becomes smooth in the vessel wall. Based on two optimizing methods of the hoop and equivalent stresses, the best autofrettage pressure is determined. It is shown that this pressure is more than the working pressure and depends on the three following variables: Bauschinger effect, working pressure and geometric... 

Josephson junction in superconductor circuits and metamaterials is modeled as a tunable inductance. The Josephson inductance is tunable by the bias current passing through it and can be tuned from an initial value to a very large value as much as one can push bias current near the critical current but not exceeding it. Tunability by bias current allows design of programmable metamaterials with flexible functions in microwave regime. In High-Temperature Superconductivity (HTS) tunable metamaterials, Josephson junctions should be used in series configuration to give usable tunable inductance. Each Step-Edge Josephson junction (SEJs) in HTS has a critical current that is dependent on its...