Current Issue : July - September Volume : 2018 Issue Number : 3 Articles : 5 Articles
This paper proposes an adaptive gain second-order sliding mode control strategy to track optimal electromagnetic torque and\nregulate reactive power of doubly fed wind turbine system. Firstly, wind turbine aerodynamic characteristics and doubly fed\ninduction generator (DFIG) modeling are presented. Then, electromagnetic torque error and reactive power error are chosen\nas sliding variables, and fixed gain super-twisting sliding mode control scheme is designed. Considering that uncertainty upper\nbound is unknown and is hard to be estimated in actual doubly fed wind turbine system, a gain scheduled law is proposed to\ncompel control parameters variation according to uncertainty upper bound real-time. Adaptive gain second-order sliding mode\nrotor voltage controlmethod is constructed in detail and finite time stability of doubly fed wind turbine control system is strictly\nproved.The superiority and robustness of the proposed control scheme are finally evaluated on a 1.5MWDFIGwind turbine system....
A dynamic behaviour of a cylindirical wind tower with variable cross section is investigated under environmental and earthquake\nforces. The ground acceleration term is represented by a simple cosine function to investigate both normal and parallel\ncomponents of the earthquake motions located near ground surface. The function of earthquake force is simplified to apply\nRayleighââ?¬â?¢s energy method. Wind forces acting on above the water level and wave forces acting on below this level are utilized in\ncomputations considering earthquake effect for entire structure. The wind force is divided into two groups: the force acting on the\ntower and the forces acting on the rotor nacelle assembly (RNA). The drag and the inertial wave forces are calculated with water\nparticle velocities and accelerations due to linear wave theory. The resulting hydrodynamic wave force on the tower in an unsteady\nviscous flow is determined using the Morison equation. The displacement function of the physical system in which dynamic analysis\nis performed by Rayleighââ?¬â?¢s energy method is obtained by the single degree of freedom (SDOF) model. The equation of motion is\nsolved by the fourth-order Rungeââ?¬â??Kutta method. The two-way FSI (fluid-structure interaction) technique was used to determine the\naccuracy of the numerical analysis. The results of computational fluid dynamics and structural mechanics are coupled in FSI analysis\nby using ANSYS software. Time-varying lateral displacements and the first natural frequency values which are obtained from\nRayleighââ?¬â?¢s energy method and FSI technique are compared. The results are presented by graphs. It is observed from these graphs that\nthe Rayleigh model can be an alternative way at the prelimanary stage of the structural analysis with acceptable accuracy....
In this paper, a 2D numerical model for wave-girder interaction was proposed to estimate\nthe maximum wave forces on the box girder of a coastal bridge under extreme wave conditions.\nThe Reynolds Averaged Navier-Stokes (RANS) equations were applied to simulate water wave\nmotion and the Volume of Fluid (VOF) method was used to track the free surface. In this study, the\ndeveloped 2D numerical model was validated by first comparing with experimental data. Then, a\nset of parametric studies was conducted to examine the effects of the wave heights, wave periods,\nwater depths and submerged coefficients on the wave force on the box girder under extreme wave\nconditions. Finally, a function to predict the extreme wave-induced forces on the box girder under\nvarious wave conditions was proposed for engineering practice...
In this study, a counter-rotating-type pump-turbine unit was optimized to improve the pump and turbine mode efficiencies\nsimultaneously.Numerical analysis was carried out by solving three-dimensionalReynolds-averagedNavierââ?¬â??Stokes equations using\nthe shear stress turbulence model. The hub and tip blade angles of the rear impeller (in the pumpmode) were selected as the design\nvariables by conducting a sensitivity test. An optimization process based on steady flow analysis was conducted using a radial basis\nneural network surrogate model with Latin hypercube sampling. The pump and turbine mode efficiencies of the unit were selected\nas the objective functions and they combined into a single specific objective function with the weighting factors. Consequently, the\npump and turbine mode efficiencies of the optimum design increased simultaneously at overall range of flow rate, except for low\nflow rate of turbine mode, compared to the reference design....
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