Sharif Digital Repository

Optical fiber torsion sensors have significant importance for structural health monitoring. In this paper, an optical fiber torsion sensor based on computer-generated-hologram (CGH) is proposed and investigated theoretically. In the proposed structure a dual mode fiber (DMF) is used as a sensing element. An acoustic source can be employed to induce a fiber grating. The acoustic induced fiber grating (AIFG) causes the fundamental LP01 mode of DMF couples to LP11 o and LP11 e fiber modes. In the presence of torsion in DMF, the profiles of LP01, LP11 o and LP11 e modes rotate relative to the absence of fiber torsion. At the end of DMF a suitable CGH can be employed to resolve spatially the... 

Distributed optical fiber sensors (DOFS) based on stimulated Brillouin scattering (SBS) are increasingly gaining popularity due to their vast practical applications. There have been a lot of Brillouin-based distributed fiber sensing methods proposed so far but they suffer from a trade-off between spatial resolution, dynamic range and measurement time. In this paper, we propose a scanning-free Brillouin optical time domain analyzer (BOTDA) based on multiple short pulse stimulated Brillouin scattering. The accumulation of acoustic phonons which are stimulated due to the passage of successive pico-second pulses along the sensing fiber causes the sub-centimeter spatial resolution and kilometer... 

A comprehensive dynamic model of a catenary anchor leg mooring system has been developed and the governing equations of notion were derived. The equations of motion are found to be nonlinear parametric ordinary differential ones of the order two. The necessary and sufficient conditions, for the existence of a stable periodic response of this system, were found using the Green's function and Schauder's fixed-point theorem. The validity of the assumptions has been fully demonstrated with a few case studies. Results obtained from the dynamic modeling reiterate the presence of inherently nonlinear and time-varying characteristics of the system and hence a stability condition in terms of the... 

A comprehensive dynamic model of a catenary anchor leg mooring system has been developed and the governing equations of notion were derived. The equations of motion are found to be nonlinear parametric ordinary differential ones of the order two. The necessary and sufficient conditions, for the existence of a stable periodic response of this system, were found using the Green's function and Schauder's fixed-point theorem. The validity of the assumptions has been fully demonstrated with a few case studies. Results obtained from the dynamic modeling reiterate the presence of inherently nonlinear and time-varying characteristics of the system and hence a stability condition in terms of the... 

It has been shown that there exists the necessary and sufficient condition for the existence of stable periodic response for a type of catenary anchor leg mooring system, (CALM). The mathematical model shows that the governing equation of motion for the system is a non-linear parametric second-order ordinary differential equation. The above-mentioned conditions have been obtained using the Schauder's fixed-point theorem. The validity of the assumptions has been fully demonstrated by analyzing a few examples. © 2001 Elsevier Science Ltd  

An investigation into the dynamics of vehicle-occupant-structure-induced vibration of bridges traversed by moving vehicles is presented. The vehicle including the driver and passengers is modelled as a half-car planar model with six degrees-of-freedom, and the bridge is assumed to obey the Euler-Bernoulli beam theory with arbitrary conventional boundary conditions. Due to the continuously moving location of the variable loads on the bridge, the governing differential equations become rather complicated. The numerical simulations presented here are for the case of vehicle travelling at a constant speed on a uniform bridge with simply supported end conditions. The relationship between the... 

We prepared porous silicon samples coated by continuous palladium layer in electroless process. Scanning electron microscopy (SEM) showed cauliflower-shape Pd clusters on the surface. I–V curves of Schottky like Pd/porous Si samples were measured in air and in hydrogen. These measurements showed a metal–interface–semiconductor configuration rather than an ideal Schottky diode. Variations of the electrical current in the presence of diluted hydrogen at room temperature revealed that the samples can sense hydrogen in a wide range of concentration (100–40,000 ppm) without any saturation behavior. Hydrogen sensing properties of these samples were investigated at room temperature for a duration... 

The use of adaptive feed-forward controllers has proven to be a very successful strategy for controlling noise and vibration in a variety of applications. One reason is that the feed-forward controller is an open loop controller, which can be designed to cancel the undesired noise in a position with any accuracy. However, the feed-forward controller requires an input signal, called a reference signal, correlated to the noise source. Consequently, a single reference controller can only reduce noise radiated from a single noise source. In many applications, there is a need to attenuate noise produced by several noise sources. In this paper, three different structures, single, modulating and... 

Two sets of governing equations for transverse vibration of non-uniform Timoshenko beam subjected to both axial and tangential loads have been presented. In the first set, the axial and tangential loads were taken perpendicular to the shearing force, i.e., normal to the cross-section inclined at an angle ψ, while in the second set, the axial force is assumed to be tangential to the axis of the beam-column. For each case, there exist a pair of differential equations coupled in terms of the flexural displacement and the angle of rotation due to bending. The two coupled second order governing differential equations were combined into one fourth order ordinary differential equation with variable... 

Direct yaw moment control (DYMC) is one of the most effective method that improves not only the directional stability of the vehicles but also their road handling and controllability to a great extent. In this method by developing a difference in the longitudinal force (often the braking force) on two sides of the vehicle, an external stabilizing yaw moment is applied to the vehicle. In this study, an optimal control law for DYMC is proposed. The control law is based on the yaw rate, the lateral velocity feedback, and the steering angle feedforward. Simulation results obtained indicate that considerable improvement in the vehicle dynamic behavior can be achieved when the optimal yaw moment... 

In this paper, a distributed relative humidity (RH) or moisture sensor is proposed. The proposed structure is a single mode telecommunication optical fiber coated by humidity sensitive and insensitive polymers periodically. The polymer coated fiber is surrounded by a high Young's modulus material such as stainless steel mesh. The swelling of the coated Humidity Sensitive Polymers (HSPs) as a result of moisture absorption induces fiber gratings in the single mode fiber. Depending on the coating period relative to the light wavelength, the induced fiber grating can be Fiber Bragg Grating (FBG) or Long Period Fiber Grating (LPFG). The light reflected by the induced FBG or losses due to the... 

A complete nonlinear finite element model for coupled-domain microelectromechanical system devices with electrostatic actuation and squeeze film effect was developed. for this purpose, a corotational finite element formulation for the dynamic analysis of planer Euler-Bernoulli microbeams considering geometrical nonlinearities due to both large structural deformation and electrostatic actuation is developed. In this method, the internal forces due to deformation and residual stresses, the elemental inertias, and the damping effect of the squeeze-film are systematically derived by consistent linearization of the fully geometrically nonlinear beam theory using d'Alembert and the virtual work... 

Passive control of vibration of beams subjected to moving loads is studied in which, an optimal tuned mass damper (TMD) system is utilized to suppress the undesirable beam vibration. Timoshenko beam theory is applied to the beam model having three types of boundary conditions, namely, hinged-hinged, hinged-clamped, and the clamped-clamped ends, and the governing equations of motion are solved using the Galerkin method. For every set of boundary conditions, a minimax problem is solved using the sequential quadratic programming method and the optimum values of the frequency and damping ratios for the TMD system are obtained. To show the effectiveness of the designed TMD system, simulations of... 

The innovative powertrain configuration of modern electric vehicles with four-wheel independent drive (4WID) provides the possibility of simple and exact yaw moment control by controlling the electric motor of every wheel independently. In this study, a genuine control strategy for optimum direct yaw moment control is proposed. Although this can be considered as a global control system for traction control of 4WID electric vehicles, the analysis is quite general and can be applied to other types of vehicle. The directional vehicle model is derived and, in accordance with the optimal control theory, an optimum yaw moment controller is designed. Two versions of the control law are developed... 

Based on the closed-form solution of a one-dimensional wave equation, the primary, secondary and acoustic feedback paths for the active control of sound in an acoustic duct have been investigated. Accurate models for the condenser microphone and loudspeaker, which include both the electro-mechanical and mechano-acoustical couplings as well as acoustical damping, have been considered. A generalized form of the filtered-x least mean square (FXLMS) algorithm that uses a more general recursive adaptive weight update equation to improve the performance of the FXLMS algorithm has been developed. Computer simulations were carried out to investigate the performance of acoustical feedback and... 

A comprehensive new dynamic model of a four-wheel independent drive electric vehicle has been developed and different types of the motor control laws were addressed. The first part of this study deals with the full description of the model scope in which the structure of the model including the sub-models has been fully developed. Subsequently, the sub-models including the tire sub-model, the body motion, and the motor dynamics were investigated, and the computer model of the vehicle has been simulated. Finally, the proposed motor control laws and the vehicle dynamic behavior of the vehicle were presented. Detailed analyses of the vehicle performance and comparison of the simulation results...