Sharif Digital Repository

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... 

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... 

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... 

A new optimal control law for direct yaw moment control, to improve the vehicle handling, is developed. Although, this can be considered as part of a multi-layer system, for the traction control of a motorized wheels electric vehicle, but the results of this study are quite general and can be applied to other types of vehicles. The dynamic model of the vehicle system is initially developed and, using the well-known optimal control theory, an optimal controller is designed. Two different versions of control laws are considered here and the performance of each version of the control law is compared with the other one. The numerical simulation of the vehicle handling with and without the use of... 

The use of adaptive feedforward controllers has proven to be a very successful strategy for controlling noise and vibration in a variety of applications. One reason is that the feedforward controller is an open loop controller, which can be designed to cancel the undesired noise in one position with any accuracy. However, the feedforward controller requires an input signal, called a reference signal, correlated to the noise source. As a consequence, 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... 

Dynamic and stability analysis of non-uniform Timoshenko beam under axial loads is carried out. In the first case of study, the axial force is assumed to be perpendicular to the shear force, while for the second case the axial force is tangent to the axis of the beam column. For each case, a pair of differential equations coupled in terms of the flexural displacement and the angle of rotation due to bending was obtained. The parameters of the frequency equation were determined for various boundary conditions. Several illustrative examples of uniform and non-uniform beams with different boundary conditions such as clamped supported, elastically supported, and free end mass have been... 

An investigation into the dynamics of vehicle-passenger-structure-induced vibration of suspension bridges traversed by accelerating vehicles is carried out. The vehicle including the driver and passengers is modeled as a half-car planer model with six degrees-of-freedom. In addition, the stiffness of compliant bushings at the connecting points of the shock absorbers to the body is considered. The bridge is assumed to obey the Timoshenko beam theory with axial load and arbitrary conventional boundary conditions. The roughness of the bridge is assumed as a differentiable function of location. Due to continuously moving the location of the variable loads on the bridge, and in the presence of...