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The graphical technique for nonlinear circuits was described that enable us to optimize circuits to obtain maximum output power, maximum efficiency or minimum intermodulation. According to this method a high power amplifier in the Ka band was designed. Using a nonlinear model of the transistor, optimum slope for load-line was determined so that maximum power at the output was obtainable, then the output matching circuit was synthesized. Finally, the nonlinear network of the high power amplifier was analyzed by the harmonic balance method and the output load cycles were optimized by modification of the bias point or output matching network.

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In this paper, a novel design approach for a hydro mechanical actuator of LPE control system is investigated. In point of admissible response rate, actuator mechanism is designed rotational. Pay special attention to the control element profile in the design of the actuator. This profile determines the conversion efficiency of the liquid propellant engine. Fitness of engine+ servomotor+ hydro mechanical actuator model to the open loop reference model is the key idea that considered as optimized design basis. Reference model would be determined based on desired dynamic behavior criteria's. With the availability of LPE mathematical model and after the design of hydro mechanical actuator, its parametric model is developed. When engine+ servomotor modeling development are completed and optimization criteria is assigned, parametric model optimization based on evaluation algorithm would be accomplished. Finally, fitness improvement between integrated and open loop reference models is evaluated. Before starting the optimized design process, the input signal and its corresponding cost function properly defined. Results shown by correction of actuator geometrical parameters and compensator gain, cost function amount – based on tracking error of liquid propellant engine combustion chamber pressure reference signal - 4 times is improved.

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In this paper, the algorithms for low frequency non-linear dynamic modeling and frequency model determining of LPRE is presented. Considerations that facilitate modeling and debugging processes is also investigated. Using of defined algorithms and also presented considerations is considered for a liquid propellant engine with oxidizer and fuel tanks. Describing equations of LPE is classified as many subsystems. Simulation is done in the SIMULINK environment of MATLAB software. Each simulated subsystem show one or more physical subsystem that their interaction is determined in LPE configuration modeling results demonstrate excellent dynamic behavior of LPE. Then SISO engine model in frequency domain is outcome based on resulted non-linear model of LPE using describing function. Frequency response code is developed for derivation of engine frequency model. Adequate frequency interval and input or excited signal amplitude are selected regarding LPE operating modes. In next step, frequency model is derived by stimulation of non-linear dynamic model with sinusoidal inputs includes considered amplitudes and frequencies. This subject is done by integration and engine output obtaining and Furrier integrals calculation at time that output get to steady state. Then system gains and phases calculation is done at the various amplitudes and frequencies for obtaining describing functions models. Frequency model evaluation characterized that can provide more efficient, simple and adequate conditions for analysis of LPE dynamics.

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In this paper, a novel test rig for a quarter car suspension system of Samand with McPherson mechanism is fabricated and its elasto-damping elements are dynamically identified. The inputs of test rig are road roughness and its acceleration and the outputs are sprung mass acceleration, un-sprung mass acceleration, suspension deflection, and tire deflection which are recorded by sensors. The test rig of suspension system includes McPherson mechanism with nonlinear spring and damper. This system is categorized as a multi-input-multi-output (MIMO) identified system. The nonlinear least squares iterative method, as a gray-box identification method, is used for finding the elasto-damping coefficients of tire and suspension elements. In this method, a nonlinear mathematical model is considered for the system and its parameters are calculated using the test rig data. The Levenberg–Marquardt algorithm (LMA) is used to solve the non-linear least squares problem. The outputs of the identified nonlinear model are compared with the measured experimental data. As a result, the test rig outputs are followed by the outputs of the identified model with acceptable errors. The compared results indicate a good performance of the proposed model to estimate the behavior of the nonlinear suspension elements.

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This paper presents a nonlinear predictive approach, for Stewart platform (6 degrees of freedom). The optimal control is computed directly from the minimization of receding horizon cost function with offline optimization. The main purpose of this research is designing the predictive controller for Stewart platform. In this study, the kinematics and dynamics of Stewart robot is introduced, considering the dynamics of actuators. Following the introduction of nonlinear model predictive control will be discussed and according to robot dynamics, controller will be design. In addition, given the various uncertainties, robot dynamic equation could be rewritten. The controller is designed according to these uncertainties and then stability control is confirmed using Lyapunov theory. Due to the limited engine power and the output torque electric drive in practice, the proposed controller manages Stewart platform in such a way that it could track the desired trajectory well. To review the proposed method at the end of the study, Stewart platform is simulated and the control method proposed in this paper was compared with computed torque control (CTC) method, sliding mode control and Proportional-Integrator-Differentiation (PID) controller.

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In this paper the dynamic behavior of a rotating system which includes rotor (shaft), ball bearing and disk in stationary condition and different speeds is investigated. There are nonlinear characteristics in these systems which cause the linear modeling is not sufficiently accurate. So, in this paper the nonlinear dynamic equations of the system are derived and solved. To derive the equations of the system, Hamiltonian method is used, and complex coordinate transform is used to reduce the number of equations. After solving the equations, to investigate the vibrational properties of the system, time response diagram, dynamic orbit, frequency response, and mode shape of the rotor is plotted. To validate the analytical results, finite element method by ANSYS (workbench) software is used.There is a good conformity betweenthe analytical results and finite element results in resonance frequencies of the system in the first three modes which indicates the sufficient accuracy in nonlinear modeling. It can be concluded from nonlinear modeling that the decay rate is negative for the all modes which is indicates the stability of the all modes. Also, the maximum vibration amplitude in the bearing and rotor occurs in third and second modes respectively. Unbalance phase difference of 90 degrees in two discs causes the excitation of all three frequency modes, whereas by unbalance phase difference of 0 or 180 degrees in two discs,only the odd modes (first and third) and the even modes (second) is excited respectively.

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Recently, H-Infinity adaptive fuzzy controller (HAFC) and its potential application in improving vehicle stability has some attention. This paper studied this application by developing a nonlinear model for the vehicle suspension mounting point displacement (SMD) and the variable geometry suspension system (VGS). The VGS model was developed by deriving the kinematic equations from the vehicle double wishbone suspension system for the vehicle handling model with eight degrees of freedom (8DOF). The limited area of the SMD necessitates the use of a proper controller, so this paper investigated the suitability of a proportional-integral-derivative controller (PID), an adaptive fuzzy controller (AFC), and HAFC for this purpose. The stability status and adaptation laws were assessed by Lyapunov synthesis and the result showed that integral of square error (ISE) achievable by HAFC for two standard maneuvers is lower than PID and AFC. The result also showed that SMD of HAFC is lower than AFC and extremely PID. The use of HAFC also resulted in the best vehicle stability, soft response and robustness.

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A nonlinear model for Autonomous Underwater Vehicles is proposed. In order to describe a more precise dynamic behavior, the nonlinear model for both Lateral and Longitudinal subsystems is derived based on all applied forces and moments. The proposed model can be explained as an extended linear model for AUV in depth and azimuth motions where some nonlinearities are taken into account. Due to some practical issues as well as the form of proposed model, the identification problem based on Least Square method is formulated to achieve the system parameters. By considering unstable dynamic of system, the open loop system cannot be excited. In this case, the PID regulators with simple tuning parameters are proposed in both Lateral and Longitudinal subsystems and the identification problem by utilizing sinusoidal inputs is followed within a feedback loop. Based on measurable variables i.e. linear moments, angular velocities and Euler angles, and utilizing some dynamic filters, the Least Square method is then applied to estimate the model parameters. The effectiveness of proposed nonlinear model as well as the parameter identification approach are finally demonstrated through some numerical simulations.

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In the present study, performance of nonlinear low Reynolds number k-ε model of turbulence has been investigated in order to predict turbulent flow field through three dimensional U bend channel of intercooling passage of gas turbine blade. Finite volume method is used to solve governing equations of mean fluid flow. In this study, linear low Reynold number model of turbulence and Zonal Eddy Viscosity model k-ε/1-eq. and cubic nonlinear low Reynolds number model has been used to model the turbulence field. Results of Computations show that the zonal model predicts the profiles of velocity and turbulent stress as same as linear model and overestimate the turbulent stresses in separated zones but results of nonlinear model shows improvement in prediction of velocity and turbulent stresses in separated zones. Also, linear, nonlinear and zonal models have similar prediction about separation point of flow but nonlinear model has been predicted the level of Reynolds stresses and its changes from inner side toward outer side and maximum level of Reynolds stresses more accurate in comparison with zonal and linear models specially on near-wall plane.

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In this paper, the performance of three turbulence models, zonal k-ε, linear low-Reynolds k-ε and nonlinear low-Reynolds k-ε in the prediction of flow and heat transfer through a dimpled channel is investigated. Furthermore, the effect of YAP term replacement with NYP length scale correction term is studied. Dimples are heat transfer devices which are employed in gas turbine blades to increase the heat transfer levels. These devices do not act as an obstacle for flow, and thus they produce low pressure losses. In this study, the governing equations on flow and energy are solved using the finite volume method together with the SIMPLE algorithm. The results obtained with YAP term indicate that the nonlinear model predicts larger recirculation flow inside the dimple than zonal and linear models. Also, the intensity of impingement and upwash flow in this model is greater than other models. Heat transfer results show that the zonal model predicts the heat transfer levels lower than experimental measurement. Using the linear model leads to a better prediction of heat transfer inside the dimples and their back rim. Compared to these models, the nonlinear model yields a better prediction not only for the smooth area between the dimples, but in the back rim of the dimple. The replacement of the YAP term with the NYP term in linear and nonlinear models leads to more accurate results for heat transfer in dimple span-wise direction and back rim.

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The change in the price of real and financial assets is one of the factors that cause business cycle through different channels such as consumption, investment, firm’s balance sheet, and net export. With attention to aware of factor causing on business cycle in Adopting Economic policies, in this paper, we investigated the effect of stock market, house price, exchange rate, and liquidity on business cycle using linear and nonlinear LSTR models and season’s data in the period of 1991-2018. In nonlinear model, which is more suitable for explaining the relationship between variables in comparison with linear model, the cyclical component of the exchange rate selected as the transition variable and the value of the transition parameter was estimated to be 83.89 rials. Considering the estimated value of the transmission parameter, in the period, there were two regimes in the Iranian economy, low-exchange rate regime and a high-exchange rate regime. The results indicate that in both regimes, an increase in stock prices and liquidity cause economic expansion. Also, an increase in house prices and a decline in the exchange rate in the first regime put the economy at an expansion phase and put the economy at a recession phase in the second regime. Therefore, in order to expanding the economy, it is suggested that, on the one hand, the exchange rate be kept low and, on the other hand, increase housing price, stock price and liquidity.
 
 

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The purpose of this paper is to estimate the direct effect of foreign investment on economic growth in agriculture, industry and services sectors in the provinces of Iran during the period 2001-2017. For this purpose, the Panel Smooth Transition Regression (PSTR) model used. It was found that there is a nonlinear relationship between foreign direct investment and the growth of various economic sectors. The results of this study indicate that foreign direct investment affects differently the growth of various economic sectors due to fluctuations in inflation rates. The estimated coefficients for the inflation rate threshold in three-menthioned sectors were 2.55, 1.78 and 1.94, respectively. In addition, one-percent increase in foreign direct investment would increase the growth rates of agriculture, industry, and service sectors by 0.50%, 0.69% and 0.88%, respectively.

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Once a composite laminate is subjected to quasi-static tensile or fatigue loading, some damage modes initiate and propagate in the laminate. The first damage mode is the matrix crack that forms in the layers with an angle to the loading direction. Although not leading to breakage, these cracks reduce the equivalent mechanical properties of the composite laminate. In this paper, a new nonlinear analytical model is presented and used to predict the stiffness degradation of the cross-ply composite laminates. For this purpose, a new third-order polynomial function is proposed as the Helmholtz free energy of the composite, and the appropriate equations are derived. A microscopic experimental test is designed and accompanied by the analytical model to investigate the damage progression in a glass/epoxy cross-ply laminate. Also, finite-element micromechanical models with periodic boundary conditions (PBC) are proposed and used to determine the damage constants. The model is validated against the 3D micromechanical models and the quasi-static uniaxial loading-unloading experimental tests. The validation shows a very good agreement between the model and the experiments.
 

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This experiment was conducted to determine whether 6-phytase has a positive effect on zinc requirements, production performance, and zinc content of tissues in broiler breeders at the end of their production cycle. One hundred and twenty-eight obese Cobb-500 broiler breeder hens (>v4.9 kg) were weighed at 58 weeks of age and assigned to various treatment groups. To deplete the zinc reserves in hens, they were given a zinc-deficient diet (9.5 mg kg^-1 of zinc) and drank water with 35 μg L^-1 zinc for two weeks. Then, hens were randomly allocated to 8 dietary treatments in a factorial arrangement of two levels of phytase (0, 300 FTU kg^-1) and four levels of dietary zinc (30, 60, 90, 120 mg kg^-1) with four replicates of 4 hens in each. Bodyweight, egg production, egg weight, and egg quality were measured during the five-week experimental period. Added zinc significantly increased yolk weight and zinc content of yolk (P< 0.05) and plasma (P< 0.0001). Egg weight was significantly increased by adding phytase (P< 0.05). As the results of this experiment show, adding exogenous phytase can decrease the zinc requirement of broiler breeder hens by releasing 16.9% of the zinc bound to phytate.