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Surge is one of the two destructive factors in compressors. surge is the stream instability phenomenon in compressor that imposes severe damages to the compressors. Nowadays, suppressingsurge phenomenon is one of the most important issues in oil and gas industries, especially when flow reduction or gas reflux is considered. According to Moore-Greitzer compressor model, this paper designs an active controller for surge control in constant speed centrifugal compressors. As such, the applied operator considered for surge control is Close Couple Valve (CCV) and it is designed to stabilize a centrifugal compressor system with disturbaces using nonlinear predictive controller. The proposed controller, without any information about the amount of Throttle Valve variations, could control the surge instability and reduce the distance between compressor operation point and the surge line. Finally, the compressor system with controller is simulated and the obtained results will show the efficiency of the designed nonlinear predictive controller

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This paper deals with experimental measurements of the instantaneous ionic wind velocity induced by Dielectric barrier discharge (DBD) plasma actuator in quiescent air at atmospheric pressure. A parametric study has been performed in order to increase the velocity of the ionic wind induced by the DBD actuators. The electrical and mechanical characteristics of the plasma actuator have been studied under different conditions. The main objective of this work was to help to optimize the geometrical and electrical parameters to obtain more effective ionic wind for flow control. The time averaged velocity profiles of the ionic wind show that the position of the maximum velocity come near the surface by increasing the excitation frequency. Our results indicate that the DBD plasma actuators generate vortices at the same frequency of the excitation frequency of the applied high voltage. The power, of the vortices that are shed from the actuators, increases by increasing duty cycle percentage. Unlike other similar works in this field, this study has examined the behavior of unsteady plasma actuator.

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This research discuss about the effect of simultaneous usage of Propellant Utilization (PU) system and Flight Apparent Velocity Regulation (AVR) system. These systems were used for sending OBC commands to engine for adapting the engine working regime with flight conditions and fame to active control systems. Each of PU and AVR systems has an effective roll in access to final parameters such as mass and velocity at the end of active phase and simultaneous usage of these systems lead to increase the range accuracy and payload mass. We study these effects on final parameters in this paper. Therefore, with dynamic simulation of liquid propellant engine in during of active phase in flight simulator, sending commands of these systems to change the engine working regime is provided. For a specific mission results show that with working of the PU, range increased and presence of AVR, is assist to reach this range in front of disturbance during the flight. Another main result of this research is, increasing of payload mass for a specific mission with simultaneous usage of PU and AVR systems.

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Piezo‌electric materials are used as sensor and actuator in order to control the vibrations of structures. Geometry and location of the piezoelectric sensors and actuators have a substantial effect on the consumed electric energy and performance of the control system, therefore, in this study by defining an appropriate cost function, an optimum length and location of the piezoelectric actuator was determined in order to achieve a desirable decrease on vibration amplitude of a cantilever beam by using appropriate control energy. The standard quadratic function of beam displacement and control energy was used as the cost function. Mathematical modeling was based on Euler Bernoulli beam theory and Hamilton's principle was used in order to achieve the equations of motion. In this approach, the control voltage of actuator layer is emerged in the boundary conditions of the problem, which turns it to a time varying boundary condition problem. By defining special displacement functions and homogenizing the boundary conditions, control voltage of the actuator is appeared as external excitement in the equations of motion. In the current study, optimum LQR and LQG controllers were investigated and Kalman filter theory was used in order to estimate the state variables. In numerical simulations, by investigating the performance of optimized limited or unlimited patches in comparison with complete one, the effective role of the objective function and optimization have been shown in decreasing applied control voltage.

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In this paper, new approach is presented for controlling the structural vibrations. In spite of previous methods, which are used mathematical concepts, the proposed active control technique is based on structural dynamics theories in which multi actuators and sensors are utilized. Each actuator force is modeled as an equivalent viscous damper so that several lower vibration modes are damped critically. This subject is achieved by simple mathematical formulation. First, the proposed multi actuators control method is formulated based on structural dynamics theories. Then the sensors and actuators' locations are determined by simple algorithm. For numerical verification of the proposed technique, the displacement's variations of a five-story shear building, excited by seismic load (Elcentro Earthquake), are evaluated. This study shows that the proposed method has suitable efficiency for reducing structural vibrations. According to the results, the maximum shift in the structure of the upper floors 5 degrees of freedom are reduced by 70%.Smart structures are systems that can teach and protect themselves against the external excitation such as wind and earthquake. Analyzing and designing of smart structures is based on set of sciences including materials science, applied mechanics, electronics, bio-mechanics and structural dynamics. In this procedure, maintaining the structural performance against the external hazards is very important issue called control system. Many studies have been performed in the field of structural control. These methods can be categorized into three groups i.e. passive, semi-active and active procedures (Akutagawa et al. 2004). Due to the simplicity, low cost of assembly and no need to the external power, the passive control systems are numerous. However, the constant control feature makes these systems fail during the earthquakes. In other words, these systems are designed to work only for a certain excitation and limited frequency bound. The passive control system tries to remove the kinetic energy from the structure. Because of the mentioned constraints in passive algorithms, active control is highly regarded systems to cope with the earthquake. These techniques have suitable efficiency in different excitation so that they could exactly sense and adopt the structural vibrations. To achieve this goal, each active control method is constructed based on algorithm, which verifying its efficiency and accuracy. The application of such systems began in 1989.In these systems an external power source is required so that this applied force is affected the structural equilibrium equation. This applied force may lead to instable vibrations if the active control algorithm is not suitable. Hence, the complexity, the calculations volume, the instability risk and the uncertainty factor are some difficulties arise from active control systems. It should be noted that, good performance of active methods depends on some parameters such as the reliable algorithm and the suitable positions for both sensors and actuators (Guclu et al. 2008; Chen et al. 2001;Rudinger et al.2007; Hoang et al.2008). The common active control algorithms have been listed in Table 1, followd by the main idea used in each method (Datta et al.2003).

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One of the most important goals of optimal control of structures is the achieving the desired reduction in responses using minimal control forces. In many research efforts that have been studied over the past few decades in the field of active control, several control algorithms have been proposed that most of them calculates the required control forces by optimizing a second-order performance index. There are simplifying assumptions in formulation of these classic algorithms and constraints in mathematical optimization techniques that have been used in optimizing the performance index, for example, because of unknown nature of earthquakes, the LQR classic controller don’t consider the external forces such as earthquake excitation in calculation of control signal. This may make difficult to finding the optimal solution in optimization process and obtained relatively optimal solutions for optimization problem. Metaheuristic optimization methods, such as differential evolution are modern algorithms and because of their special capabilities in finding global optima are powerful tools that can be used in solving of complex problems. But despite the many advantages, these methods has not been used extensively for solving civil engineering problems especially in field of active control of structures. In this paper we considered the active control of structures as an optimization problem and proposed a controller that used the differential evolution metaheuristic algorithm for finding gain matrix elements of active control problem. The gain matrix elements were globally searched by differential evolution algorithm to minimizing the LQR performance index. Because of the proposed method is repetitive and does not need to solve the Ricatti differential equation; it is possible to consider the effect of external excitation in finding the gain matrix and calculation of control signal. The controller was applied on sample 2DOF and 10DOF structures and responses of these structures under the excitation of several historical earthquake records were obtained by MATLAB programming. In addition to the performance index, the maximum control force and maximum control displacement, 9 benchmark indexes that measured in controlled structures are calculated in this study. These indexes represented the reduction of controlled maximum and average responses of structure in comparison with uncontrolled responses. In order to evaluate the effectiveness of the proposed controller, these 9 performance index for 2DOF and 10DOF examples against 7 historical earthquakes for proposed and LQR controller was calculated and compared. The simulation results indicate that the proposed method is effective in keeping the controlled responses of structures in desired range and reducing the vibrations of structures with lower need to control energy in comparison with LQR algorithm. Because of great capabilities of DE algorithm in searching large spaces and the iterative nature of controller unlike the LQR method, this controller consider the effects of external forces in control process. Numerical simulation showed that the performance of the presented control algorithm is better than the LQR controller approach in finding of optimal displacements and control forces. Therefore, metaheuristic algorithms such as differential evolution can be used in active control of structures to achieving more efficient results in comparison with classic controllers.

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In the present study numerical simulation of synthetic jet is performed to optimize geometric parameters and excitation frequency to maximize mass flow rate and velocity of the jet and to avoid separation on the airfoil. Geometric parameters include: diameter and height of the cavity and orifice and excitation frequency of diaphragm which are selected as variable parameters for optimization. Using Response Surface Method (RSM) in this research, the simulations for optimization of the momentum of jet flow are designed. After studies and initial simulations, the range of variations in the effective variable parameters for the maximization of the target function (jet velocity and mass flow rate) are determined. Then, using the RSM, 32 separate tests are defined based on geometric and frequency parameters to find a second-order relationship, which relates the target functions to their variable parameters and their interactions. In this case the RSM prediction for the maximum velocity and mass flow rate of the jet are 22.16 m/s 0.0006 kg/s, respectively. Using RSM to optimize the geometric parameters and excitation frequency, jet momentum increases considerably in comparison with the first simulation. The velocity, mass flow rate, and momentum of the jet are increased by 31%, 36% and 78%, respectively.

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One of the challenges in the field of civil engineering is to mitigate the seismic vibration of structures induced by dynamic loads, such as earthquake and strong wind in order to prevent undesirable damages causing human discomfort and economic consequence. The vibration control systems can be categorized as passive, active and semi-active. In recent years, semi-active control systems demonstrate better control effects than both passive and active systems. Semi-active control devices can behave as passive devices in the event of a power loss, and are therefore more reliable and consume less power than the active systems. In this study, to evaluate the effectiveness of the semi-active tuned mass damper using MR damper and a fuzzy logic controller, the nonlinear model of the nine-story benchmark structure is subjected to earthquake excitation. The semi-active tuned mass damper consists of a 1000 kN magnetorheological damper and the damping force of the MR damper is controlled by the fuzzy logic controller.The Bouc–Wen model is utilized to model the dynamic behavior of the MR damper. For this purpose, the increment dynamic analysis (IDA) is conducted to consider the effectiveness of the maximum acceleration of two near- and far-field acceleration records on the performance of the control systems. Two near-field earthquake acceleration records including Kobe (1995) and Northridge (1994) and two far-field earthquake acceleration records including El Centro (1940) and Hachinohe (1968) are used in this study. To achieve the optimum parameters of tuned mass damper, a numerical search method is used to reduce the displacement of the last floor of the structure. The optimal mass ratio, damping and the frequency of the tuned mass damper of these analysis for this structure are 3.5 %, 10 % and 2 rad/s. Also, this benchmark structure is modeled in OpenSees and the fuzzy inference system was implemented in MATLAB. In order to implement the semi-active control system, it’s necessary to communicate between OpenSees and MATLAB. For this purpose TCP-IP method is used. The displacement and velocity response of the ninth floor of structure equipped with tunned mass damper are considered as the input values for the fuzzy inference system. Furthermore, the required voltage of MR damper in this floor is defined as the output parameter of the fuzzy system. Moreover, the membership functions of fuzzy control are triangle and trapezoidal functions. The obtained results of the FLC are compared with the those of passive controlled structure. Therefore, absolute displacement and acceleration values of the last floor of the structure, the maximum relative displacement and the base shear values are investigate. The results showed that the FLC reduces the maximum last floor displacement, the maximum relative displacement and the maximum base shear by 17.75 %, 15.88 % and 16.85 % as compared to the uncontrolled structure, respectively and also, it reduces those responses by 3.62 %, 1.17 % and 15.76 % as compared to the passive response, respectively. Furtheremore, the fuzzy control system has effective performance than the passive system to decrease the maximum and residual displacement of the stories. On the other hand, the fuzzy control system has a low performance in reducing the maximum last floor acceleration.

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The science of seismic control of the structures always seeks to reduce and control the destructive effects of the forces which are produced during an earthquake event. However, the yield of the soil under intensified seismic loads can cause some irreversible effects on the structural elements and the structure may withstand the increased moments and the forces for which it is not formerly designed. This unfavorable phenomenon significantly affect the seismic response and performance of the structures, and will ultimately leads to disappearance of all functional goals that are sought to create in the structural design stage by the designer of the structure. In this research, by a relatively accurate three dimensional finite element modeling, from a high-rise concrete structure equipped with the active mass damper, and by examining the lesser-known aspects of the problem such as uplift of the foundation and the effects of nonlinear interaction of soil and structure, an attempt has been made to conduct a relatively comprehensive study on the questions of seismic control of structures equipped with active mass dampers due to the nonlinear effects of the underneath soil behavior. For this purpose, time history dynamic analysis was performed on the structural model under the effect of 22 horizontal records of distant basin earthquakes in x and y directions followed by the Appendix A of FEMA P695. The Ibarra model (a reviewed and modified model based on the Clough model) is used for modeling of the hysteresis behavior of concrete materials. The underneath soil is modelled by three springs approach presented in ATC 40 and FEMA 440 with equivalent stiffness based on soil modulus of elasticity and Poisson’s ratio of three categories (the main C category and upper and lower C and E categories ). To achieve the goal of optimization and evaluation of the active mass damper parameters (consist of tuning ratio, mass ratio and damping ratio), the mass damper spectra method with investigation of changes in structural responses has been used. The Fuzzy theory has been used to calculate the control force of an active mass damper. The results indicate that with respect to entrance of the structure to non-linear zone and its interaction with non-linear behavior of the soil, the efficiency of the active mass damper in uplift control of the foundation decreases, but a good efficiency is observed in the lateral displacement and inter story drift control. By evaluation of the three dimensional analysis results of a nonlinear soil structure system equipped with the active mass damper, the researchers observed that for the set of the recorded earthquake and based on the specifications considered for fuzzy algorithm, the active mass damper has a satisfactory effect in the control of displacements and drifts of the structure, in the amount of almost 15 percent. It was also identified that the active mass damper has a negligible effect on the foundation uplift in the structures which constructed on the hard soil. But when the soil becomes softer, a 3 percent mean decrease is observed in the uplift displacements in foundation.

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Damages caused by the impact of adjacent structures in past major earthquakes have shown the importance of structural control systems to reduce the seismic risk of the impact of structures. Connecting energy dissipation devices to adjacent buildings is a practical and effective approach to prevent collisions as well as reduce the seismic responses of structures, and this issue has been an active research field in recent years. One of the semi-active control methods is the use of MR dampers. These dampers use a magnetic fluid that produces large damping forces in a piston-cylinder system that can be controlled instantly by changing the applied voltage to the damper. The Bouc-wen model has been used to take advantage of the unique properties of MR damper as well as to consider its inherent nonlinear behavior. In this study, to evaluate the performance of MR dampers using a fuzzy control system, three- and nine-story standard structures under seismic excitation of two near-field earthquakes including Kobe (1995) and Northridge (1994) and two far-field earthquakes including El centro (1940) and Kern county (1952) with maximum accelerations of 0.1g to 1g are investigated.
The MR damper is connected to the third floor level of the two structures and can produce a controlled force equivalent to 1000 kN. The fuzzy system is designed based on the displacement of the third floor of two structures to reduce the risk of collision of structures as well as reduce seismic responses. the benchmark buildings have been modeled in OpenSees and the fuzzy control system was implemented in MATLAB software. The displacement responses of the third floor of structures are considered as the input value of the fuzzy system and the required voltage of MR damper is considered as the output value of the fuzzy system. In addition, triangular membership functions have been used to determine the degree of membership of input values.
 In general, the control system designed under far-field earthquakes has shown better performance in reducing the responses of two structures compared to near-field earthquakes. According to the results obtained from the dynamical analysis, the fuzzy system used under far-field earthquakes compared to near-field earthquakes and based on evaluation criteria of J1 (maximum roof displacement), J2 (maximum roof acceleration), J3 (maximum Base shear) and J4 (maximum relative displacement of floors) in three-story building 17.35, 4.94, 3.58, 12.17% and in nine-story building 7.93, 7.05, 0.67, 9.13%  showed better performance, respectively. Also, according to the evaluation criterion of J5, which is related to the minimum required gap between two buildings, the fuzzy system used under far-field earthquakes has shown 9.71% better performance than near-field earthquakes.