Sharif Digital Repository

This paper deals with the investigation of the size-dependent nature of nonlinear dynamics, in a doubly clamped shallow nano-arch actuated by spatially distributed electrostatic force. We employ strain gradient theory together with the Euler-Bernoulli and shallow arch assumptions in order to derive the nonlinear partial differential equation governing the transverse motion of the arch with mid-plane stretching effects. Using the Galerkin projection method, we derive the lumped single degree of freedom model which is then used for the study of the size effects on the nonlinear snap-through and pull-in instabilities of the arch nano-electro-mechanicalsystem (NEMS). Moreover, using strain... 

An algorithm, by cooperation of multiple flying vehicles, is developed to localize a moving target in the presence of measurement noise and mis-modeling. It works based on jointly sharing information and data fusion by using a recursive Bayesian estimator and a searching guidance law to direct each flying vehicle to a position where the probability of target detection is maximum. To evaluate this algorithm, a high fidelity simulation program with six degrees of freedom dynamics is also developed  

A method is presented to synthesize 5 degrees of freedom (DoFs) of 3 translational and 2 rotational (3T2R) parallel kinematic structures. This method is based on the theory of linear transformation and geometrical analysis. Central to this method is a set of novel 5 DoFs 3T2R parallel mechanisms (PMs). Based on the legs configuration, the generated mechanisms are classified. Moreover, the promising mechanisms of each class are introduced with respect to some criteria, i.e.: (a) degree of coupling between the actuators and degrees of freedom; (b) easy kinematics and control command; (c) easy construction (or low cost construction); and, (d) manufacturability. With reference to these criteria,... 

In this study, the nonlinear free vibration of conservative two degrees of freedom systems is analyzed using the homotopy analysis method (HAM). The mathematical model of such systems is described by two second-order coupled differential equations with cubic nonlinearities. First, novel approximate analytical solutions for displacements and frequencies are established using HAM. Then, the homotopy Padé technique is applied to accelerate the convergence rate of the solutions. Comparison between the obtained results and those available in the literature shows that the first-order approximation of homotopy Padé technique leads to accurate solutions with a maximum relative error less than 0.068... 

A bilateral nonlinear adaptive impedance controller is proposed for the control of multi-degrees-of-freedom (DOF) teleoperation systems. In this controller, instead of conventional position and/or force tracking, the impedance of the nonlinear teleoperation system is controlled. The controller provides asymptotic tracking of two impedance models in Cartesian coordinates for the master and slave robots. The proposed bilateral controller can be used in different medical applications, such as telesurgery and telerehabilitation, where the impedance of the robot in interaction with human subject is of great importance. The parameters of the two impedance models can be adjusted according to the... 

Tolerance analysis is an analytical tool for the estimation of accumulating effects of the individual part tolerances on the functional requirements of a mechanical assembly. This article presents a comprehensive feature-based method for tolerance analysis of mechanical assemblies with both dimensional and geometric tolerances. In this method, dimensional and geometric tolerance zones are described by the combination of fuzzy modelling and small degrees of freedom (SDOF) concept. In this model, the uncertainty in dimensions and geometric form of features is mathematically described using fuzzy modelling, and the kinematic effects of tolerances in assemblies are expressed by SDOF concept. In... 

Due to the increasing number of people suffering from physical disabilities in the elbow and wrist, developing an assistive wearable robot seems crucial. These disabilities are mostly common in elderly people and people who are suffering from spinal injury or stroke. In this paper, a wearable assistive robot for rehabilitation of the wrist and elbow is developed. The mechanism has 3 Degree of Freedom (DoF); two active DoF for assisting the exion/extension of the elbow and wrist, and a passive one in order to have unconstrained supination/pronation of the forearm. The motors and sensors were chosen based on kinematic constraints governing the motion of arms and wrists. Finally, with the... 

The concept of equivalent linearization is extended for the soil-structure systems, in which the strength ratio (defined as the ratio of the yielding strength to the elastic strength demand) is known rather than the ductility ratio. The nonlinear soil-structure system is replaced by a linear single-degree-of-freedom (SDOF) system, which can capture the response of the actual system with sufficient accuracy. The dynamic characteristics of the equivalent linear SDOF system are determined through a statistical approach. The super-structure is modeled by an inelastic SDOF system with bilinear behavior, and the homogeneous half space beneath the structure by a discrete model, following the Cone... 

We consider a K-user Interference Channel where each transmitter is interested in conveying a message to its corresponding receiver. In addition, we assume a fully connected noiseless backhaul network through which receivers can collaborate and help each other recover their desired messages. In this paper, we fully characterize the trade-off between the rate in wireless link (per user) in terms of degrees of freedom (DoF) versus backhaul load (per user) for large values of K. In particular, we characterize the optimal trade-off for all values of K, where K is an even number. For odd values of K, we characterize the trade-off within a gap of 2(k - 1)/k(k + 1), which goes to zero as K... 

Recently, it has been shown that in a cache-enabled interference channel, the storage at the transmit and receive sides are of equal value in terms of Degrees of Freedom (DoF). This is derived by assuming full Channel State Information at the Transmitter (CSIT). In this paper, we consider a more practical scenario, where a training/feedback phase should exist for obtaining CSIT, during which instantaneous channel state is not known to the transmitters. This results in a combination of delayed and current CSIT availability, called mixed CSIT. In this setup, we derive DoF of a cache-enabled interference channel with mixed CSIT, which depends on the memory available at transmit and receive... 

Nowadays, with the advancement of technology, humans are looking for ways to cure various diseases. Meanwhile, musculoskeletal injuries usually have a long treatment period. Therefore, in recent years, Researchers working one exoskeleton with rehabilitation application which conduct physiotherapy tasks. In current study, a portable two degree of freedom hand exoskeleton is designed which its mechanism is a combination of cable and link mechanism, MCP1 1Metacarpophalangeal joint between metacarpal and proximal phalanges joints move by link mechanism, DIP2 2Distal interphalangeal joint between proximal phalanges and middle phalanges and PIP3 3Proximal interphalangeal joint between middle... 

This study addresses the robust stability analysis for an islanded microgrid with droop-controlled inverter-based distributed generators (DGs). Owing to large load changes, microgrid structure reconfiguration, and higher-power demands, the low-frequency (LF) dominant modes of a microgrid stir toward unstable zone and make the system more oscillatory or even unstable. In this study, a robust two-degree-of-freedom (2DOF) decentralised droop controller, which is the combination of the conventional droop with a robust transient droop function, is utilised for each inverter-based DG unit. Unlike conventional tuning of 2DOF droop controllers, a new design procedure is proposed to robustly... 

In this paper, we consider $K$ -user interference channels with $M$ antennas per node and with backhaul collaboration in one side (among the transmitters or among the receivers), for $M,Kin mathbb {N}$ , and investigate the tradeoff between the rate in the channel versus the communication load in the backhaul. In this investigation, each node is equipped with $M$ antennas and we focus on a first order approximation result, where the rate of the wireless channel is measured by the degrees of freedom (DoF) per user, and the load of the backhaul is measured by the entropy of backhaul messages per user normalized by $log $ of transmit power, at high power regimes. This tradeoff is fully... 

An approach based on unitary transformation for the problem of estimating the number of signals is proposed in this study. Among the information theoretic criteria, the authors focus on the conventional Bayesian information criterion (BIC) in the presence of a uniform linear array. The sample covariance matrix of this array is transformed into the real symmetric one by using a unitary transformation. This real symmetric matrix has real eigenvalues and eigenvectors. Therefore its eigenvalue decomposition needs only real computations. Since the eigenvalues of this real symmetric matrix are equal to the eigenvalues of the sample covariance matrix, by replacing them in BIC formula, the term... 

Tapered piezoelectric beams, because of their more efficiency to generate power, are required to be analyzed by simple models. In this paper, single degree of freedom (SDOF) relations are used to model transvers vibration of an exponentially tapered piezoelectric beam. For this purpose, first, response of the damped cantilevered Euler–Bernoulli beam with base excitation is obtained. Then, lumped parameters of the beam are extracted in order to calculate the SDOF model response. Comparing the Euler-Bernoulli beam model with the SDOF model shows that the lumped parameter model is not accurate enough to predict the beam’s response. Therefore, a tapering parameter dependent correction factor is... 

In this paper, a mobile manipulator is developed and studied in order to manipulate the complicated objects and navigate in an indoor environment. The arm consists of an actuator that makes the first linkage to move in two degrees of freedom in the first step of the task. In the next mode of the task, another actuator causes the second linkage to move in the third degree of freedom. In addition, the arm contains a gripper that grabs a variety of objects such as a screw. Therefore, the robotic arm can manipulate objects, and the mobile robot connected to the arm can detect, classify and track targets in its surrounding. Results carried out that the manufactured robot is able to manipulate and... 

Trolling mode atomic force microscopy (TR-AFM) can considerably reduce the liquid-resonator interaction forces, and hence, has overcome many imaging problems in liquid environments. This mode increases the quality factor (QF) significantly compared with the conventional AFM operation in liquid; therefore, the duration to reach the steady-state periodic motion of the oscillating probe is relatively high. As a result, utilizing conventional imaging techniques, which are based on measuring the amplitude and phase, are significantly slower when compared to our proposed method. This research presents a high-speed scanning technique based on an estimation law to obtain the topography of various... 

Effective prevention and treatment management of spinal disorders can only be based on accurate estimation of muscle forces and spinal loads during various activities such as lifting. The infeasibility of experimental methods to measure muscle and spinal loads has prompted the use of biomechanical modeling techniques. A major shortcoming in many previous and current models is the consideration of equilibrium conditions only at a single cross section, rather than along the entire length of the spine, when attempting to compute muscle forces and spinal loads. The assumption of extensor global muscles with straight rather than curved paths and of the spinal segments as joints with no... 

Chatter suppression is an important topic in any type of machining process. In this paper, orthogonal cutting process is modeled as a single degree of freedom dynamic system. A nonlinear delay differential equation is presented that models flank wear of the tool. Uncertainties in cutting velocity, tool wear size and parameters of the dynamic model are included in the model of cutting process. The force provided by a piezo-actuator is taken as the control input of the system. A sliding mode control scheme is used and an effective control law is derived which suppresses the chatter vibration. Results for two distinct cases of a sharp tool and a worn tool are presented and compared which shows... 

Roll control of the Autonomous Underwater Vehicles (AUVs) is a significant issue in the current field of research for many researchers in the subject of AUV control system designation. Especially at higher speeds, the roll angle generated by a single rotating propeller or other external disturbances can considerably influence the whole dynamics and therefore the operation of the vehicle. In this paper, the utilisation of a system of contra-rotating-propellers (CRP) to enhance the roll dynamics of an AUV is evaluated by developing a six-degrees-of-freedom (6DOF) dynamics and control systems’ simulator. The results show that: 1. The single propeller system can cause roll angle deflections...