Sharif Digital Repository

Self-excited and forced vibrations are important topics in machining processes because their occurrence results in poor surface finish, increase in tool wear and hampers productivity. In this paper, turning process is modeled as a SDOF dynamic system including quadratic and cubic structural nonlinearities. The effect of tool flank wear, as a contact force between the work-piece and tool, is addressed vigorously. Multiple scale method is used to find the solution of the nonlinear dynamic equation including regenerative chatter, forced excitation and tool wear. It is shown that, width of cut can be considered as the bifurcation parameter of the system. Primary, super-harmonic and sub-harmonic... 

The aim of this paper is to use higher-order energy balance method as a novel solution procedure for investigation the nonlinear oscillation of various systems. The method is associated with collocation method and employed for a group of nonlinear problems including pure cubic nonlinearity, fractional elastic force and duffing harmonic terms. Obtained results are evaluated by comparing with the classical balance method and also the exact solutions computed numerically. It is shown our solution procedure achieves more accurate results versus the classical solution and higher agreement are observed between the newer solutions and the exact ones for the systems. Effect of initial conditions in... 

This paper deals with the existence and the characteristics of the limit cycles in the fractional-order Arneodo system. The analysis is done using the describing function method. Our focus is on a special case where two limit cycles exist. The parametric range for the case of interest is derived, and the frequency and the amplitude of the oscillation are predicted. Numerical simulation results are presented to further demonstrate the reliability of the analysis  

We study stationary entanglement properties of an optomechanical system containing an atomic ensemble. We focus onto the case of the movable mirror strongly coupled to the cavity field through both radiation pressure and photothermal force. Exploiting a quantum Langevin equation approach we investigate the bipartite entanglement properties of various bipartite subsystems as well as stationary tripartite entanglement of the system. We particularly study robustness of the atom-mirror entanglement against temperature. We show that, even though the photothermal force is a dissipative force, it can significantly improve the cavity mediated atom-mirror entanglement  

When an integer order linear time invariant system possesses unrepeated pure imaginary poles it can generate oscillatory response which is represented by invariant closed contours in the phase plane. In linear time invariant fractional order systems with the same property, due to their special characteristics, this behavior will be more complicated and the contours would not be invariant. In this paper we will investigate the behavior of fractional order systems under such conditions  

This paper investigates the secondary Bjerknes force for two oscillating bubbles in various pressure amplitudes in a concentration of 95% sulfuric acid. The equilibrium radii of the bubbles are assumed to be smaller than 10 μm at a frequency of 37 kHz in various strong driving acoustical fields around 2.0 bars (1 bar=10 5 Pa). The secondary Bjerknes force is investigated in uncoupled and coupled states between the bubbles, with regard to the quasi-adiabatic model for the bubble interior. It finds that the value of the secondary Bjerknes force depends on the driven pressure of sulfuric acid and its amount would be increased by liquid pressure amplitude enhancement. The results show that the... 

A Green's function to describe the time behavior of the locking phases in a circular planar array of mutually coupled microwave oscillators is proposed. Using this Green's function the dynamic behavior of the array can be described for any arbitrary free running frequency of elements of the oscillator array. Beam steering is realized via detuning the edge oscillators of the array from a reference frequency and the beam direction is controlled by the amount of detuning for each oscillator at the edge. Some detuning functions such as sinusoidal, triangular and rectangular ones have been applied and, the resulting array patterns are compared with one another  

Although many complex real-world networks are weighted, unweighted networks are used in many applications such as sensor networks. In this Letter it is shown using properly weighted networks the performance can be greatly enhanced by reducing the time necessary for the average consensus. Random geographical models are adapted as network models and a method based on mutually coupled phase oscillators is used for providing average consensus over the network. The consensus time is calculated by numerically solving the network's differential equations and monitoring the average error. The simulation results on some sample networks show that the consensus time is dramatically reduced when the... 

In this paper we introduce a new low phase noise cascode Cross-coupled oscillator by use of the general topology of Cross-coupled oscillator and cascode amplifier. By simulation a comparison between the conventional Cross-coupled oscillator and the new cascode Cross-coupled oscillator is also presented, which shows that the latter improves the phase noise by 2dB under the same conditions. The figure of merit (FOM) of -186.4 dBc/Hz is achieved for the new oscillator by simulation  

The effects of resonator topology on the phase noise of LC oscillators are studied in this paper. It is shown that there is a neglected factor that can considerably influence the phase noise behavior of the oscillator. We designate this factor as the Inductance Energy Factor (IEF), which directly depends on the topology of the resonator. It is shown that through proper design of the resonator for a better IEF, the oscillator phase noise can be improved. It is also shown that by modifying the resonator structure to improve IEF, the phase noise does not have to be constrained by the minimum realizable inductance and its maximum quality factor. Therefore, the power-phase noise trade-off remains... 

The flow-induced oscillation (FIO) of bluff bodies is commonly encountered in the fluid structure interaction (FSI) problems. In this study, we use an unstructured moving grid strategy and simulate the FIO of two rigid plates, which are elastically hinged at the two ends of a fixed flat plate in a cross-flow. We use a hybrid finite-element-volume (FEV) method in an arbitrary Lagrangian–Eulerian (ALE) framework to study FIO of the two hinged plates. The current simulations are carried out for wide ranges of flow Reynolds number (50–175), spring stiffness coefficient, and the two hinged plates’ moment of inertia magnitudes. The influences of these parameters are investigated on the magnitudes... 

In this study a synchronization method is developed to prevent the blocking arrhythmias which are caused by lack of synchronization between the two major heart pacemakers called the Sino-Atrial (SA) node and Atrio-Ventricullar (AV) node. Such pacemakers can be modeled by the Van der Pol oscillators. Feedback linearization method is used in synchronization. Since all states are not always available, they are estimated by a new observer in this research. To design the observer, first we introduce a robust observer for a unique Van der Pol oscillator. The robustness of proposed observer is obtained using gain and phase margins test. The observer variables are such that the error dynamical... 

This chapter describes performance of the power system stabilizer (PSS) of a large thermal power plant as tuned by the manufacturer. The stabilizer was redesigned based on extended phase compensation of the exciter input-the electrical torque transfer function and root locus analysis; and its effect on local, interplant, and interarea electromechanical oscillations was thoroughly analyzed. Participation factors and mode shapes were effectively employed to identify local, interplant, and interarea modes, as well as their characteristics. The PSS designed with extended phase compensation improves the damping of local and interplant oscillation modes considerably, and has some positive damping... 

In the last decade, many potent analytical methods have been utilized to find the approximate solution of nonlinear differential equations. Some of these methods are energy balance method (EBM), homotopy perturbation method (HPM), variational iteration method (VIM), amplitude frequency formulation (AFF), and max-min approach (MMA). Besides the methods mentioned above, the Akbari-Ganji method (AGM) is a highly efficient analytical method to solve a wide range of nonlinear equations, including heat transfer, mass transfer, and vibration problems. In this study, it was constructed the approximate analytic solution for movement of two mechanical oscillators by employing the AGM. In the derived... 

An analytic method for prediction of oscillation amplitude and supply current of differential CMOS oscillators is presented. The validity of this method has been verified by designing an LC CMOS oscillator in a 0.24 μm CMOS technology. The predictions are in good agreement with simulation results over a wide range of supply voltage  

The interinjection locking of microwave oscillators is investigated using differential equations governing the locking behaviour of two mutually coupled oscillators. The behaviour of the oscillators before and after locking is described, and the common oscillation frequencies, locking range and transient time constant are calculated. The spectra of the oscillators in the unlocked condition are also investigated, with particular attention to the spacing and amplitude variation of the spectral lines. Experimental results in connection with the theoretical investigations are also presented  

Dynamic behavior of a laminated composite beam (LCB) supported by a generalized Pasternak-type viscoelastic foundation, subjected to a moving two-degree-of-freedom (DOFs) oscillator with a constant axial velocity is studied. Analytical solution using the Galerkin method is sought and the couplings of the bending-tension, shear-tension, and bending-twist with the Poisson effect are considered. The possible separation of the moving oscillator from LCB during the course of motion is investigated by monitoring the contact force between the oscillator and LCB. The effects of the non-rigid foundation, oscillator parameters, and the load speed on the separation are also studied. It is found that... 

Arrays of N weakly coupled oscillators are considered in different configurations. The locking bandwidth for these arrays is defined statistically. Various factors affecting the locking bandwidth and the effect of the coupling network topology on locking bandwidth are studied by solving the dynamic equations of the array numerically. The analytical locking bandwidth for two configurations of arrays is computed and the results are compared with the numerical solution of dynamic equations. © The Institution of Engineering and Technology 2008  

In this paper an array of N weakly coupled oscillators Is considered. The stability of the main mode (In phase mode) In linear arrangement of oscillators has been proven and the Instability of other modes In this configuration Is demonstrated. For circular arrangement It Is shown that other stable modes may exist If N Is greater than 5