Variable pitch propeller (VPP) is used in advanced helicopters in order to achieve greater efficiency, better stability and attain higher altitudes. This study assesses the behavior of VPP propeller with coupled non-linear displacement in three degrees of freedom. Accordingly, the behavior of this type of propeller with changes of elastic axis distance, length, mass, speed, polar radius of gyration, stiffness in three degrees of freedom, and pitch have been investigated. In this paper, Gallerkin method is used to extract natural frequencies and the results compared with the results reported by other researchers. The results show convergence and accuracy of the used method. In this study, it was found that parameters of mass, length and rotational speed of the propeller have an effect on the natural frequencies, and all modes of vibration. However, other parameters except for the pitch angle effect on the odd or even number of frequency modes. It was also found that the pitch angle in the static mode does not influence on natural frequencies, but in the case of rotation of propeller, affects the natural frequency of vibration modes as sine or cosine form.

Hydro screw is a small micro hydro turbine. Due to increase in demand for clean energy production, a comprehensive project at the Iranian Research Organization for Science and Technology (IROST) for the design and construction of very small turbines (micro turbines), including hydro screw, has been developed. Hydro screw is suitable for a low head and discharge that does not have a guide vane and draft tube; thus, it is simple, small, inexpensive, and portable. This turbine, with a 15 cm blade diameter, can generate power up to 2 kW. Hydro screw blade is inspired by the Archimedes turbine, and difference between them is that the blade pitch of hydro screw is variable and horizontally mounted. In this project, the effect of spiral variable pitch on turbine has been studied numerically. Based on the results, it was found that the turbine had the best efficiency at a spiral pitch of 1. 5. Subsequently, the small model of hydro screw was made and tested in the laboratory. The results of this study have been presented in the form of standard curves of turbine performance and the accuracy of the results has been proved by comparison of numerical and experimental results. The results show the integrity of the numerical calculations and, therefore, they can be used in line with next turbine studies. The results indicate that the maximum turbine output is between 62% and 68%.

The paper discusses the results of investigations performed for the segments of straight-through labyrinth seals of constant length. Increasing the number of teeth of a segment resulted in a reduction of the pitch length to obtain the slot seals. The phenomena occurring during gas flow in labyrinth and slot seals differ significantly. They are described with different calculation models. The analysis presented in this paper is related to the change of the tightness and the nature of the flow from a straight-through labyrinth seal to a slot seal. The paper includes the results of experimental research and CFD calculations. Models applied for the Neumann and Scharer labyrinth seals as well as the model of the Salzman and Fravi slot seals were discussed. For the Neumann and Scharer models, correction coefficients for the tested geometry were proposed. Based on the assumptions for the said models and the obtained results, the phenomena responsible for the minimization of the leakage were discussed. The leakage rate in segments of different gap heights depending on the number of teeth and the pressure ratio upstream and downstream of the segment has been analyzed. Based on the experimental data, an optimum number of teeth in the segment for minimum leakage was determined. CFD calculations allowed determining the minimum leakage geometry. The experimental data contained in this paper confirm that the determined optimum pitch range is independent of the pressure drop.

This paper concerned with the performance improvement of quad rotor using by variable pitch control system. The methodology was laid out based on dynamic modeling of six degree of freedom motion, trim calculations, linearization, and robust control system design for a candidate variable pitch quad-rotor at hover. Therefore, a comprehensive mathematical model of rotors was derived based on the blade element-momentum theory (BEMT) at low Reynolds number, and then, the engine and propulsion models were appended to form the real quad-rotor as a whole. Two control loops including of an inner loop for attitude control system and the outer loop for motion control applied with the robust control system, is the main structure of control system design. Linear controller and feedback linearization controller was also implemented to cover the stability of the quad rotor and compensation of fixed and variable pitch control mechanisms. . Variable pitch quad rotor helped the user to made bigger quad rotor with the less problem in control system which prepared from gyroscopic effect in fixed pitch quad rotor.

In this paper, an optimal adaptive robust pitch controller is proposed for variable speed wind turbines (VSWTs). The proposed pitch controller has stability analysis, while it simultaneously keeps the generated power of the wind turbine at the rated power and mitigates the mechanical loads on the gearbox. The proposed pitch controller in this paper has two terms. The first term is a radial basis function neural network (RBFNN), to approximate unknown nonlinear functions of the wind turbine. Another term is a chattering-free continuous robust structure, which can cope with the approximation error. The weights of RBFNN and the gain of the robust structure are derived via the Lyapunov synthesis approach. It is proved that the closed-loop signals are semi-globally uniformed and ultimately bounded. The optimal parameters of the proposed controller are derived by solving a proposed multi-objective optimization problem using non-dominated sorting genetic algorithm-II (NSGA-II) and multi-objective particle swarm optimization (MOPSO) algorithm. The effectiveness of the proposed controller is compared to the baseline PI controller designed by NREL. First, both the proposed and the baseline PI controllers are applied to the general model (2-mass model) of the wind turbine, and then they are validated via a highly reliable simulator called FAST. The results demonstrate the effectiveness and applicability of the proposed pitch controller.

This study aims to improve operational efficiency and enhance the flight performance of variable pitch Quadrotors in hover with the scope of achieving sustainable inverted flight, or fulfilling a special mission in automated mass flights. The objectives of this study, a robust control system design for a candidate variable pitch quad rotors is paced classically. The methodology is based on mathematical modeling developments extracted specifically for a candidate variable pitch Quadrotors. Trim calculation and linearization of equations along with \ design, implementation and integration of a robust controller \ for the quad \ rotor are therefore \ following \ steps in this study. The challenges associated with the dynamic modeling of rotors, aerodynamic modeling in small \ Reynolds numbers \ and \ modeling of the \ electric \ propulsion system are removed \ using \ the Blade \ Element-Momentum Theory (BEMT). To improve the performance, two control loops including an attitude control system and a control motion were implemented using H\infty optimization and \mu synthesis. Results showed that H\infty optimization is a suitable approach to reducing the unstructured uncertainties, and thus it can be used for control system design with 30 percent of uncertainty relevant to the aerodynamic coefficients. Results also revealed that the stabilized inverted flight as a novel ability of operation in variable pitch Quadrotors could be obtained. In both approaches Bilin transformation is aimed to pole shifting and avoidance of singularity in H\infty optimization and \mu synthesis. By using the Bilin transform, design of weight functions is avoidable, thus controller design would be easier. On the other hand, robust controllers frequently have the high order transfer functions which make the implementation of it difficult, thus the model reduction approach was applied to reduce the order of controller designed with \mu synthesis method. Overall, without problem caused from gyroscopic effect in fixed pitch Quadrotor, a variable pitch mechanism to develop the bigger Quadrotor, with the less problems in control system.

This paper has proposed a gain-scheduled controller with stability proof and guaranteed cost for a turboshaft driving a variable pitch propeller. In order to overcome the complexity of the nonlinear model, a linear parameter varying (LPV) model is proposed for the first time which is in affine form. Proposed model is established based on a family of local linear models and is suitable for LPV gain scheduling methods. Thus a gain scheduled design procedure is proposed which considers parameter dependent Lyapunov matrices to ensure stability and a quadratic cost function for guaranteed performance of the closed loop system. Proposed procedure also has the advantage of considering an upper bound for change rate of the scheduling signal which decreases conservativeness. Controller design problem and calculating its gain matrices is formulated in a set of Linear Matrix Inequalities which easily can be solved using LMILAB toolbox. Simulation results showed the effectiveness and practicality of the proposed procedure.

Conspicuously, pitch angle control strategy has been applied to mitigate the influence of mechanical load and also output power control at above-rated wind speeds. In this paper, a wind turbine is modeled based on simplified two-mass model and an adaptive sliding mode controller (ASMC) is designed based on individual pitch control (IPC) strategy. To do this, the single-blade approach is used and the wind turbine was divided into aerodynamics and mechanical subsystems and governing equations of each subsystem were derived. By designing and applying the ASMC to two-mass model, system behavior is observed and simulated in terms of step and turbulent wind speed inputs. In addition, to verify the validity of the ASMC, the proposed controller is implemented in the FAST environment and the wind speed profiles are generated using TurbSim. In order to analyze the environmental effects on the dynamic behavior of the system, the controller performance is explored in presence of parametric uncertainties. It should be noted that rotor speed tracking error is evaluated and demonstrated through different criteria.

In recent years, because of need to energy production at low cost, using micro hydro turbines has been very attractive. The low construction costs, easy installation and maintenance, low head and flow requirements, small size, no need for the extensive power network and decentralization of hydro power are some of the unique characteristics of Micro hydro turbines. Hydrocoil turbine as a new, efficient and affordable axial flow turbine is one of the best options for distributed generation of electricity. Although Hydrocoil’ s design is mainly inspired by Archimedes screw turbine, there are differences in their blade’ s pitch and installing angle. In this work, two different samples of hydrocoil turbine with constant and variable pitches have been studied numerically under identical conditions to study the effect of pitch changes on operating point at constant head and five different rotational speeds. The results indicate that efficiency and power of variable pitch turbine are 30 to 40 percent more than constant pitch turbine. These results provide necessary background to build optimized variable pitch hydrocoil for the first time in Iran.

This research studies the model reference adaptive control strategy based on the fuzzy theory to control a wind turbine with a doubly-fed induction generator (DFIG). The model reference adaptive control method, incorporating Takagi-Sugeno (T-S) fuzzy logic, is proposed to control the turbine rotor speed using a pitch angle control. The aim of the proposed control system is to address the shortcomings of the traditional wind turbine controllers, such as unknown dynamics and system nonlinearities. The proposed hybrid adaptive-fuzzy structure provides an effective tool for controlling the wind turbine system, which exhibits complex nonlinear dynamics. The superiority of the proposed method over the traditional model reference adaptive control lies in modeling the nonlinear system with multiple fuzzy linear models instead of a single linear model. Additionally, the use of the fuzzy method enhances the adaptability of this control method, resulting in more accurate outcomes. Stability analysis of the closed-loop system with the proposed fuzzy model reference adaptive control (FMRAC) is conducted using the Lyapunov method. The proposed FMRAC method is simulated for a 0.2 Mw variable speed wind Turbine and compared with the traditional model reference adaptive control. The simulation results of the proposed method demonstrate higher performance and an accurate response despite the unknown dynamics and nonlinearities of the model.