Sharif Digital Repository

Micro grippers are essential tools for manipulation of objects in micron size. An electrostatic micro stepper-motor is used for actuating a proposed gripper mechanism and performance of this gripper is compared with the previous ones. The characteristic of the proposed mechanism is analyzed by simulation and it is shown that the designed gripper has the capability of doing manipulation in micron dimension with an acceptable performance  

Ultra-high precision machining is proposed by externally actuating the work piece in linear motions in the X-Y plane and linear motion in the Z-axis. To solve the problems in the machining process such as nonlinearity and low repeatability positioning accuracy of machining tools in a larger scale, a novel platform for cutting tools in micro machining based on electrostatic linear micromotors and piezoelectric stack actuator system is presented. © 2017 IEEE  

A novel intelligent semi-active control system for an eleven degrees of freedom passenger car's suspension system using magnetorheological (MR) damper with neuro-fuzzy (NF) control strategy to enhance desired suspension performance is proposed. In comparison with earlier studies, an improvement in problem modeling is made. The proposed method consists of two parts: a fuzzy control strategy to establish an efficient controller to improve ride comfort and road handling (RCH) and an inverse mapping model to estimate the force needed for a semi-active damper. The fuzzy logic rules are extracted based on Sugeno inference engine. The inverse mapping model is based on an artificial neural network... 

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... 

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... 

Magnetorheological (MR) damper is a prominent semi-active control device to vibrate mitigation of structures. Due to the inherent non-linear nature of MR damper, an intelligent non-linear neuro-fuzzy control strategy is designed to control wave-induced vibration of an offshore steel jacket platform equipped with MR dampers. In the proposed control system, a dynamic-feedback neural network is adapted to model non-linear dynamic system, and the fuzzy logic controller is used to determine the control forces of MR dampers. By use of two feedforward neural networks required voltages and actual MR damper forces are obtained, in which the first neural network and the second one acts as the inverse... 

Laminated composite structures are vulnerable to failure when subjected to impact and vibration. The present work investigates the impact response of laminated composite structures filled with MR-fluid segments. The mathematical modelling of a composite plate is presented using finite element method with MATLAB® software to study the vibration response due to impact loads. A proof-of-the-concept experimental work has been set up in order to illustrate the performance and functionality of the MR-fluid on damping vibration for MR-laminated composite structures. © 2017 Author(s)  

Regarding the structural health monitoring of pipelines, early detection of cracks may be one of the possible ways to prevent future failures. Among the detection methods which have been known, one is to measure the vibration signals generated due to the hydraulics of pipe. This article discusses application of thin film piezo sensors mounted directly on the pipe. The vibration induced strain is transuded into electric voltage by the piezoelectric sensor. The recorded signals are used for PSD analysis which indicates that this method can be used as an accurate and cost effective detection. Moreover the promising results from the respective experiments on pipes indicated that second natural... 

Application of robotic instruments in minimally invasive surgery (MIS) has been developing in recent years. The urge to implement biocompatible and less invasive devices found way in use of materials like shape memory alloys. However such designs presented the idea of using heat control actuation in the MIS surgery and some have found noticeable position in robotic surgery. Yet the problems relating to insufficient stroke, slow motion and unfavorable generated heat have to be defeated. In this work it is focused to overcome these problems by a new design. Modern SMA grippers take advantage of two techniques: Net SMA and Spiral SMA. Both of these actuators demand application of high electric... 

The dynamic behavior of nonuniform-thickness laminated composite beams, such as helicopter blades, wind turbine blades, and robot arms, is of high importance in the design and fabrication of such elements. Changing the thickness of laminated structures is a significant challenge during fabrication because different tapering configurations may significantly alter the stiffness of the structures and thus the dynamic response of the structures. In this study, the effect of adding nanoparticles to resin on the stiffness and dynamic behavior of nonuniform-thickness laminated composite beam elements was investigated. A set of experiments were conducted to examine the natural frequencies and... 

The influence of structural configuration on vibration responses of smart laminated beams under random loading is studied. The effect of laminate configurations and locations of sensors/actuators in the smart system is also investigated. The layer-wise approximation for displacement and electric potential is utilized to construct the finite element model. The closed-loop control response is determined through an optimal control algorithm based on the Linear Quadratic Regulator (LQR). The correlation coefficient between the input random force and the applied actuating voltage for various configurations is also computed. It is revealed that for softer configurations, the correlation... 

Shape Memory Alloys (SMAs) are a new generation of smart materials with the capability of recovering their predefined shape after experiencing a large strain. This is mainly due to the shape memory effects and the superelasticity of SMA. These properties make SMA an excellent alternative to be used in passive, semi-active, and active control systems in civil engineering applications. This paper presents a comprehensive review of the recent developments in the applications of SMA in civil infrastructures, including, steel, concrete, and timber structures. This review reveals the significance of SMA in civil infrastructures particularly, the enhancement of structural behavior and energy... 

Laminated composite beams with non-uniform thickness are being used as primary structural elements in a wide range of advanced engineering applications. Tapered composite structures, formed by terminating some of the plies, create geometry and material discontinuities that act as sources for delamination initiation and propagation. Any small damage or delamination in these structures can progress rapidly without any visible external signs. Due to this reason early detection of damage in these systems during their service life is receiving increasing attention. The presence of a crack in a component or structure leads to changes in its global dynamic characteristics results in decreases in... 

This paper deals with the problem of vibration based health monitoring (VHM) in multi-stable asymmetrical laminated composite structures. Multi-stable asymmetrical laminates can be snapped between two or more geometries. The ability of snapping between two or more geometries in multistable composite structures makes them vulnerable to delaminate. Because of these reason early detection of damage in these systems during their service life is receiving increasing attention. In the present work, an efficient and accurate finite element model (FEM) based on layer-wise theory by considering the electro-mechanical coupling effect has been developed to investigate the actuation and /or sensing... 

Marine structures, as key elements in the global energy network, constantly are subjected to harsh environmental loading conditions. Therefore, reliable yet efficient structural control mechanisms are required to ensure their safe functionality and structural stability. In the present work, a novel hybrid structural control element for marine structures has been designed in which the superelasticity effect of shape memory alloy (SMA) and damping controllability of magnetorheological fluid (MRF), as smart materials, have been combined. The novel system does not require huge external energy for activation and in addition, the system has the ability to be tuned for variable loading conditions.... 

Structural integrity and ensuring the stability of steel frame structures, including marine and coastal structures, are the main challenges for designers in civil infrastructures, particularly in oil platforms, subjected to tough periodic and non-periodic environmental loading conditions. Variable loadings with different amplitudes and frequencies may lead to the stability of steel structures loss. In order to keep the stability of the steel structures and prevent possible damages, reliable yet efficient structural control systems are in demand. Conventional structural control systems need significant activation energy and/or in-depth users knowledge to be effective. Most recently, smart... 

Wind and ocean waves highly influence the performance and functionality of structures, requiring an efficient control element. The structural behavior of one of the most recent structural control elements, namely shape memory alloys (SMA)-based control element, under cyclic loadings of oceans waves, has been investigated. Shape memory alloys are one of the attractive smart materials with the ability to return to the initial shape after experiencing large deformation. Experimental tests have been conducted to study the effects of cyclic loads on several specimens of the SMA wires. The SMA wires are being used in the SMA-based structural control system to dissipate the energy of external... 

First, an efficient and accurate finite element model for smart composite beams is presented. The developed model is based on layerwise theory and includes the electromechanical coupling effects. Then, an efficient design optimization algorithm is developed which combines the layerwise finite element analysis model for the smart laminated beam, sensitivity analysis based on analytical gradients and sequential quadratic programming (SQP). Optimal size/location of sensors/actuators is determined for dynamic displacement measurement purposes and for vibration control applications. For static and eigenvalue problems, the objective is to minimize the mass of the beam under various constraints... 

Tapered composite beams are increasingly being used in various engineering applications such as helicopter yoke, robot arms, and turbine blades. In the present work, the buckling analysis of laminated tapered composite beams is conducted using a higher order finite element formulation. In tapered laminates, the material and geometric discontinuities at ply drop-off locations lead to significant discontinuities in stress distributions. Higher order formulation ensures the continuity of the stress distribution through the thickness of a laminate as well as across the element interfaces, which is very important for the analysis of tapered laminates. In addition, higher order finite element... 

Civil infrastructures are vulnerable to catastrophic failures when exceeding the limit loading, requiring a reliable structural control mechanism, such as bracing systems, to enhance the integrity and stability of the structure. Bracing systems improve the performance of the structures by increasing the stiffness/strength of structures, the damping coefficient, and/or the energy absorption capacity. However, the functionality of these bracing systems is not controllable and may be altered after strong seismic events. Recently, the smart bracing systems based on multifunctional materials, particularly the shape memory alloy (SMA) and the magnetorheological fluid (MRF) have been developed. The...