Sharif Digital Repository

This paper deals with the dynamic analysis of a delaminated composite beam under the action of moving oscillatory mass. The beam is analyzed as four interconnected sub-beams using the delamination limits as their boundaries. The constrained model is used to model the delamination region. The continuity and equilibrium conditions are satisfied between the adjoining beams. The beam response variation due to the delamination with respect to the intact beam has been investigated. Furthermore, the possible separation of the moving oscillator from the beam during the course of the motion is investigated by monitoring the contact force between the oscillator and the beam. The effect of the... 

In this paper, nonlinear oscillation of a pendulum wrapping and unwrapping around two cylindrical bases is studied and an analytical solution is obtained using multiple scales method. Equations of motion are derived based on energy conservation technique. Applying perturbation method on the equations, nonlinear natural frequency of the system is calculated along with its time response. Analytical results are compared with numerical findings and good agreement is found. Effect of nonlinearity due to large amplitude and radius of cylinders on the system frequency is evaluated. Results indicate that as the radius of cylinder is increased, nonlinear frequency is enhanced. Initial amplitude plays... 

In this paper, nonlinear vibration of a micro cantilever exposed to a constant velocity flow is studied. In order to obtain vibration frequency and time response of the micro beam the variational iteration method is used as a novel tool for solving nonlinear differential equations. Results of the analytical solution are compared with those obtained by Runge-Kutta method which shows very good agreement between them. Results confirm that frequency of vibration depends on the flow velocity. Also, the high sensitivity of the vibration frequency to the flow velocity means that it can be an effective indicator of velocity  

Several lower extremity exoskeletal systems have been developed for augmentation purpose. Common actuators, have important drawbacks such as complexity, and poor torque capacities. The main scope of this research is to propose a series elastic actuator for lower extremity exoskeletal system which was designed based on muscle functional analysis. For this purpose, a biomechanical framework consisting of a musculoskeletal model with ten degrees-of-freedom actuated by eighteen Hill-type musculotendon actuators per leg is utilized to perform the muscle functional analysis for common daily human activities. The simulation study illustrated functional differences between flexor and extensor... 

The vibration suppression of semi-actively controlled jacket-type offshore platforms using Magnetorheological (MR) dampers is studied. The main goal of using MR damper system is to reduce vibration caused by wave hydrodynamic forces. A fixed jacket-type offshore platform affected by wave-induced hydrodynamic forces and controlled by MR dampers is modelled as a semi-active controlled system with 30 DOFs. In comparison with earlier studies, an improvement in problem modelling is made. Based on the wave theory and Morison equation, an exosystem is designed to simulate regular wave forces. The necessary input voltage to MR dampers to generate desired damping force is derived by clipped optimal... 

A novel semi active control system for eleven Degrees of Freedom passenger car's suspension system using Magneto rheological damper is presented. The considered suspension system is modeled using mass spring damper model. The semi active vibration control is designed to reduce the amplitude of vehicle's vibration due to by road profile. The applied control strategies are based on a Linear Quadratic Gaussian optimal control algorithm to obtain desired damping forces of MR dampers. In considered system, the damping coefficient of the shock absorber changes actively through inducing magnetic field. The necessary input voltage to MR dampers to generate desired damping forces are derived using... 

In this paper, a novel microfabrication process of a six DOF thermal compliant nanopositioner is presented. The microfabrication process was based on bulk micromachining process. By using this process some important operational restrictions which are usually created by surface micromachining were removed. Moreover, this novel process does not need SOI wafers and needs only ordinary wafers. Therefore, it makes microfabrication process cheaper than surface micromachining processes where SOI wafer should be used. This method is completely appropriate for microactuators which have 120 degree misalignment. Finally, a primary test by using interferometer method was used to test connection of... 

In this paper, the agent velocity in robotic swarm was determined by using particle swarm optimization (PSO) to maximize the robotic swarm coordination velocity. A swarm as supposed here is homogenous and includes at least two members. Motion and behavior of swarm members are mostly result of two different phenomena: interactive mutual forces and influence of the agent. Interactive mutual forces comprise both attraction and repulsion. To be more realistic the field of the swarm members' view is not infinity. So influence of the coordinator agent on the robotic swarm would be local. The objective here is to guide the robotic swarm with maximum possible velocity. According to equation motion... 

In this research, we have modeled nano-Beams using molecular dynamics. The scope of our study is FCC metals, therefore an appropriate inter-atomic potential for this kind of materials must be chosen. A multi-body long-range potential proposed by Sutton-Chen, which has been used in many physical investigations of FCC metals is applied in our study. Using conducted simulations, the different mechanical properties of material such as elastic modulus, shear modulus and poison's ratio are calculated. The results show that the elastic properties decrease with increase in nano cantilever size. ©2008 IEEE  

This paper focuses on the biomechanical aspects of human load carrying in order to provide a physiological framework for designing the more anthropometric assistive systems. An 8degrees-of-freedom musculoskeletal model with twenty functional muscle groups in the lower extremity was developed to simulate the movement in sagittal plane. Inverse dynamics based optimization approach was employed to estimate the excitation level of the muscles. Activation patterns of the muscles illustrate the importance role of the soleus in supporting of the body during load carrying. Also power distribution analysis of the muscles reveals that the plantar flexors of the ankle, extensors of the knee and hip... 

In this paper, a novel design approach for determination of the optimal Fractional Order PID (FOPID) controllers, using the Particle Swarm Optimization (PSO) method is presented. Fractional calculus can provides good performance and robustness for FOPID controllers in comparison with the conventional PID and even other types of classical controllers, because of the arbitrary order of fractional calculus presented in this scheme. This paper demonstrates in details how to employ the PSO method to search efficiently for the optimal FOPID controller parameters in SISO and MIMO systems. The proposed approach is applied to an electromagnetic suspension system as an example to illustrate the design... 

Tipover issue is an important problem in autonomous mobile manipulators. This issue is becoming more important in new generation of mobile robots where their size and weight are reduced, and they are designed to work on uneven terrains with higher speeds. Estimating the distance from the tipover stability margin would enhance the capability of the mobile manipulators in correcting their motion. For a valid estimation of the tipover margin one must take into account the full dynamic interaction between the vehicle and its manipulator. In mobile manipulators with several degrees of freedom a huge amount of time is needed to solve equations of motion while real-time tipover control needs a fast... 

In this paper, we consider a control strategy of multi-robot systems, or simply, swarms, based on emotional control technique. First, we briefly discuss a "kinematic" swarm model in n-dimensional space introduced in an earlier paper. In that model, motion of every swarm member is governed by predefined inter-individual interactions. Limitations of every member's field of view are also considered in that model. After that, we consider a general model for vehicle dynamics of each swarm member, and use emotional control theory to force their motion to obey the dynamics of the kinematic model. Based on the kinematic model, stability (cohesion) analysis is performed and coordination controller.is... 

System Identification is a key technology for the development and integration of modern engineering systems including gas turbines. These systems are highly parametric with complex dynamics and nonlinearities. Small turbojet engines are special class of gas turbines that are suitable for scientific purposes and researches in the area of stability, performance, simulation and fuel control design. The motivation behind the presented study is to improve the speed, quality and cost of engine testing and to gain insight into alternatives to traditional identification methods for gas turbines. It discusses the identification of small turbojet engine dynamics by validating the thermodynamic model... 

Due to the nonlinear dynamics of hydraulic systems, applying high performance closed-loop controllers is complicated. In this paper, a single-rod hydraulic actuator is considered in which load displacement (for positioning purposes) is controlled via manipulation of the input voltage to the servo-valve. Dynamics of the servo-valve is described by first and second order transfer functions (named as Models 1 and 2). Through linearization of the system around its operating points, dynamics of the hydraulic actuator is represented in the state space. A full-order observer is designed for on-line states estimation. Then, feedback control system is designed for both regulation and tracking... 

The accuracy of multi dimensional simulation of vehicle dynamics has been significantly increased for both passive and active vehicles which are equipped with advanced electronic components. Recently, one of the subjects that has been considered is increasing the car safety in design. Therefore, many efforts have been done to increase vehicle stability especially during the turn. It is also very important in three wheel car. One of the most important efforts is adjusting the camber angle in the car suspension system. Camber angle as well as the vehicle stability has major effects on the wheel slip, reducing rubber abrasion, acceleration and braking. Since the increase or decrease in the... 

Considerable attention has been devoted recently to vibration control using intelligent materials as sensor/actuator. An intelligent control technique using a neural network is proposed for vibration control of micro-cantilever beam with bonded piezoelectric sensor and actuator. Structure modal characteristic analysis is done to determine the optimal configuration of piezoelectric sensor and actuator. With the piezoelectric elements are surface-bonded near the same position to the fixed end of micro-cantilever beam, an optimal controller, linear quadratic Gaussian (LQG), and an intelligent strategy based on neural network are investigated. Finally, the simulation results are given to... 

This paper will first describe the Linear-Quadratic-Gaussian (LQG) and Lead-Compensator when the Proportional-Integral-Derivative (PID) controllers are inactive for procedures that have large delay time (LDT) in transfer stage. Therefore in those states, LQG and Lead Compensator perform better than the PID controllers. The constrained LQG is optimal and stabilizing. The solution algorithm is guaranteed to terminate in finite time with a computational cost that has a reasonable upper bound compared to the minimal cost for computing the optimal solution. In this work all actual working area condition for instance noises and disturbances are considered. Eventually, LQG and Lead Compensator have... 

Buried pipe lines are an efficient way of transporting of water, sewage, oil, and gas resources in all over the world. Since the buried pipe lines are exposed to many unexpected conditions, such as landslides, corrosion, fatigue, earthquakes, material flaws or even intentional damaging, so the inspection requirements lead to adoption of new method of maintenance, protection and conserving. This report aims to improve the trustworthiness, reliability, yet economical technologies for monitoring of behavior and manner of buried pipe lines during operation and assessing the risk of pipe lines failure. Distributed sensors (piezoelectric) are surface designed and embedded to investigate the... 

The dynamics of the flexible robot arm subjected to tip mass during an actual deployment is studied. The Euler-Bernoulli beam theory and the real deployment are considered in the simulation. A new real axial velocity profile is developed. This new suggested profile simulates the actual deployment such that the arm movement starts from immovability and after attaining the final required length comes back again to the static state. Using Lagrange's equation, the equations of motion of the system are derived to study the system dynamics in this suggested deployment profile. A series approximation is used to represent the lateral elastic displacements. Using variables separation and also some...