Sharif Digital Repository

This paper deals with investigation of fluid flow on static and dynamic behaviors of carbon nanotubes under electrostatic actuation. The effects of various fluid parameters including fluid viscosity, velocity, pressure and mass ratio on the deflection and pull-in behaviors of the cantilever and doubly clamped carbon nanotubes are studied. Furthermore, the effects of temperature variation on the static and dynamic pull-in voltages of the doubly clamped carbon nanotubes are reported. The results reveal that altering the fluid parameters significantly changes the mechanical and pull-in behaviors. Hence, the proposed system can be applied properly as a nano fluidic sensor to sense the various... 

This paper summarizes a research project in the field of design and manufacturing of a water brake dynamometer for power testing facilities. In the current study, the design process of a water brake with drilled rotor disks is presented. This process is examined against the development of a water brake for a 4MW gas turbine power measurement at 15,000 RPM speed. The proposed algorithm is based on vital assumptions such as; applying product designing issues and limited modular analysis that urges the disciplinary attitude and leads to the possibility of rapid development, easy maintenance and ease of access. The final scheme is divided into six disciplines with functional classification.... 

The nonlinear dynamic and static deflection of a micro/nano gyroscope under DC voltages and base rotation are investigated. The gyroscope undertakes two coupled bending motions along the drive and sense directions and subjected to electrostatic actuations and intermolecular forces. The nonlinear governing equations of motion for the system with the effect of electrostatic force, intermolecular tractions and base rotation are derived using extended Hamilton principle. Under constant voltage, the gyroscope finds the preformed shape. First, the deflection of the micro/nano gyroscope under electrostatic forces is obtained by static and dynamic analyses. Furthermore, the static and dynamic... 

In this paper, we present an analytical model to analyze the influence of deep level traps on the static and dynamic responses of transistor laser (TL). Our analyze is based on analytically solving the continuity equation and rate equations including the effect of the deep level trap (DLT), which incorporate the virtual states as a conversion mechanism. The results of simulation show that the main characteristics of laser such as threshold current, quantum efficiency, output power, and modulation bandwidth are affected by total density of traps in the active region  

In this paper we present an analytical model to analyze the influence of deep level traps on the static and dynamic responses of transistor laser (TL). Our analysis is based on analytically solving the continuity equation and rate equations including the effect of the deep level trap (DLT), which incorporates the virtual states as a conversion mechanism. The results of simulation show that the main characteristics of laser such as threshold current, quantum efficiency, output power, and modulation bandwidth are affected by total density of traps in the active region  

A series of experiments were conducted to study the effect of leading-edge roughness on the state of the boundary layer of a wind turbine blade section using multiple hot-film sensors. The experiments involved static and dynamic tests, where airfoil motion was of plunging type oscillation. The application of surface grit roughness simulates surface irregularities that occur on the wind turbine blades. The measurements showed that increasing the angle of attack results in movement of transition locations toward the leading edge. Surface roughness moved the transition point toward the leading edge and caused early trailing edge turbulent separation, which resulted in reducing the effectiveness... 

In this paper, we present an analytical model for the large-signal analysis of the double quantum well (DQW) transistor laser. Our model is based on solving the continuity equation and the rate equations which incorporate the virtual states as a conversion mechanism. By using the presented model, effects of barrier width on DQW transistor laser static and dynamic performances are investigated. Also the static and dynamic responses of DQW transistor lasers are compared with single quantum well ones. Simulation results are in agreement with the numerical and experimental results reported by other researchers  

In this paper size-dependent static and dynamic behavior of nonlinear Euler-Bernoulli beams made of functionally graded materials (FGMs) is investigated on the basis of the strain gradient theory. The volume fraction of the material constituents is assumed to be varying through the thickness of the beam based on a power law. As a consequence, the material properties of the microbeam (including length scales) are varying in the direction of the beam thickness. To develop the model, the usual simplifying assumption which considers the length scale parameter to be constant through the thickness is avoided and equivalent length scale parameters are introduced for functionally graded microbeams... 

In this paper, a size-dependent formulation is developed for Timoshenko beams made of functionally graded materials (FGM). The developed formulation is based on the strain gradient theory;a non-classical continuum theory able to capture the size-effect in micro-scaled structures. Considering the material length scale parameters of the FG beams vary through the thickness, the new equivalent length scale parameters are proposed as functions of the constituents' length scale parameters to describe the size-dependent static and dynamic behavior of FG microbeams. The governing differential equations of equilibrium and both classical and nonclassical sets of boundary conditions are derived for the... 

Accurate prediction of static and dynamic response of nano structures under external excitations has been one of the interests of scientists in the last decade. Several applications of nano machines make it necessary to analyze their components, such as nano bearing, precisely. In this paper, the static and vibrational behavior of a fullerene as a sensitive part of nano bearing under external forces is simulated by a newly designed spherical super element. This super element is designed in such a way that the user can select as many numbers of nodes as desired, so that it can be implemented in different desired precisions. In this study, a 228-node super element, which is similar to a hollow... 

This is an experimental study on the boundary layer over an airfoil under steady and unsteady conditions. It specifically deals with the effect of plunging oscillation on the laminar/turbulent characteristics of the boundary layer. The wind tunnel measurements involved surface-mounted hot-film sensors and boundary-layer rake. The experiments were conducted at Reynolds numbers of 0.42×10 6 to 0.84 × 10 6 and the reduced frequency was varied from 0.01 to 0.11. The results of the quasi-wall-shear stress as well as the boundary layer velocity profiles provided important information about the state of the boundary layer over the suction surface of the airfoil in both static and dynamic cases. For... 

We present an analytical model to analyze the influence of carrier dynamics on the static and dynamic responses of transistor laser (TL). Our analysis is based on solving the continuity equation and the rate equations which incorporate the virtual states as a conversion mechanism. We show that the details of the dc and small signal behavior of transistor lasers are strongly affected by the escape and capture times of carriers in quantum well (QW). Also, the effects of carrier recombination lifetime in the quantum well and base regions on the TL static and dynamic performances are investigated  

Accurate prediction of static and dynamic response of nano structures is one of the important interests of scientists in the last decade. Nano bearing as an important part of nano machines has been extensively implemented in recognizing and disassembling cancerous cells and building molecular support structures for strengthening bones. For this reason, Molecular Dynamic Method and some experimental methods are implemented in this area. As nano ball bearing is one of the most important components of nano machines, a large number of studies are concentrated to analyze it statically and dynamically. In this paper, a Fullerene is simulated by a spherical super element whose stress, deformation... 

Electrostatically actuated beams are fundamental blocks of many different nano and micro electromechanical devices. Accurate design of these devices strongly relies on recognition of static and dynamic behavior and response of mechanical components. Taking into account the effect of internal forces between material particles nonlocal theories become highly important. In this paper nonlinear vibration of a microano doubly clamped and cantilever beam under electric force is investigated using nonlocal continuum mechanics theory. Implementing differential form of nonlocal constitutive equation the nonlinear partial differential equation of motion is reformulated. The equation of motion is... 

Accurate prediction of static and dynamic response of nano structures is one of the important interests of scientists in the last decade. Nano bearing as an important part of nano machines has been extensively implemented in recognizing and disassembling cancerous cells and building molecular support structures for strengthening bones. For this reason, Molecular Dynamic Method and some experimental methods are implemented in this area. As nano ball bearing is one of the most important components of nano machines, a large number of studies are concentrated to analyze it statically and dynamically. In this paper, a Fullerene is simulated by a spherical super element whose stress, deformation... 

With respect to the influence of nanoparticles on mass transfer characteristics, limited number of studies available in the literature, deal primarily with gas-liquid systems. In this work, mass transfer performance and hydrodynamic characteristics including static and dynamic dispersed phase hold-ups of nanofluids have been investigated for pulsed liquid-liquid extraction column (PLLEC). The nanofluids used were prepared by dispersing SiO2 nanoparticles of 0.01, 0.05 and 0.1 volume percent with two different hydrophobicities in kerosene as base fluid using ultrasonication. UV-vis spectrophotometer was also used for evaluation of the nanofluids stability. The results were compared with... 

Structures of tapered geometry are customarily used in a variety of applications. The analysis of such structures is usually made through finite element method using traditional beam, shell or brick elements. In this paper, a new tapered superelement is presented that lends itself to modeling revolving geometries under lateral, axial and torsional loads. The presented tapered superelement has 16 nodes. The performance of this element under static and dynamic loading and in rotating condition is examined. It is shown that this element yields accurate results with higher computational efficiency compared to conventional elements. Furthermore, it is verified that a single tapered superelement... 

In this paper, a relatively novel approach is established to estimate different limit states and accurate behavior of jacket platforms against environmental wave loading. This novel approach which is called Incremental Wave Analysis (IWA) can be an appropriate substitute to current pushover practice. The IWA can take into account the effects of variation in wave height and wave-in-deck loading in the estimating of platforms' behavior. This paper aims to introduce the applications of this approach in deterministic assessment of offshore platforms, comprehensively. The IWA can estimate the collapse-prevention limit state of jacket platforms properly. In addition, an appropriate parameter for... 

A new method, based on the concepts of matrix analysis as well as the learning capabilities of neural networks, for the analysis of nonlinear trusses under dynamic loading is presented. The method can be applied to static trusses too. While there have been attempts in the past to use neural networks to identify and model different structures based on data measured on structural response directly, the main feature and advantage of this new method is in its capability to model a nonlinear truss by assembling the data collected on the response of its members. The basics of the method are: (1) for each truss member, a neural network is trained to learn and simulate its loadresponse behavior, (2)... 

Prior to the design and fabrication of MEMS/NEMS devices, analysis of static and dynamic behaviors of these systems is necessary. In the present study, the nonlinear dynamic behavior of micro- and nano-mechanical resonators is investigated and classified based on the resonator’s physical parameters for first time. The Galerkin method is used to convert the distributed-parameter model to a nonlinear ordinary differential equation where mid-plane stretching, axial stress, DC electrostatic and AC harmonic voltages are taken into account. To obtain the analytical frequency response of the micro resonator near its primary resonance, the second order multiple scales method is applied to the...