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Circularly Polarized Microstrip Ferrite Phase-shifter with Uneven Excitation
Get PDFA low-cost and externally controlled planar microstrip ferrite phase shifter is designed, where the differential phase shift is considerably improved by introducing circularly polarized electromagnetic waves in the structure. Simulated phase response of the designed phase shifter is presented to demonstrate the improvement in the differential phase shift compared to an equivalent traditional microstrip ferrite phase shifter
Evaluation of Silicone Rubber Insulators used in High-Voltage Transmission Lines
Get PDFThree long-rod silicone rubber composite insulators used in 230 kV power transmission lines were evaluated for aging affects. The insulators were obtained from various outdoor desert locations within Saudi Arabia where they had been in service for 6 years. Surface degradation associated with the aging process was analyzed by using Scanning Electron Microscopy (SEM) coupled with Energy Dispersive X-ray Spectroscopy (EDS), Fourier Transform Infra-Red Spectroscopy (FTIR), and Electron Spectroscopy for Chemical Analysis (ESCA). Electrical performance of insulators was evaluated by Rapid Flashover Voltage Tests (RFVT) and Pollution Severity Measurement Tests. Depending on their locations of service, the samples exhibited various types of pollutants at their surfaces. The analysis indicated that the insulator material showed localized surface degradation while there was no evidence of micro-cracking. Furthermore, it was noted that the electrical performance of the insulators was not significantly affected by exposure during the in-service period
Stochastic Finite Element Analysis of the Free Vibration of Functionally Graded Material Plates
Get PDFExperimental and Numerical Investigation of 65-deg Delta and 65/40-deg Double-Delta Wings
Get PDFIn this study, an experimental and numerical investigation was carried out to obtain lift, drag, and pitching moment data on 65-deg delta and 65/40-deg double-delta wings. The experimental tests were conducted at the KFUPM low-speed wind tunnel facility whereas the numerical tests were performed using the commercial CFD software FLUENT. Results from both experiments and numerical predictions were compared to other experimental data found in literature as well as to the theory of Polhamus. The results of comparison of surface pressure coefficient distribution and vortex breakdown location show good agreement with experiments. Overall the comparison of result shows good agreement between different experimental studies as well as good agreement with the CFD predictions and the theoretical calculation
Inverse Airfoil Design Method for Low-Speed Straight-Bladed Darrieus-Type VAWT Applications
Get PDFThe paper demonstrates the application of inverse airfoil design method to improve performance of a low-speed straight-bladed Darrieus-type VAWT. The study shows that an appropriate tailoring of the airfoil surface using the inverse airfoil design technique can help improve performance by eliminating undesirable flow field characteristics at very low Re, such as early transition due to presence of separation bubbles. The increase aerodynamic efficiency then translates into an improved aerodynamic performance of VAWTs specifically at very low chord Reynolds numbers. The study employs an interactive inverse airfoil design method (PROFOIL) that allows specification of velocity and boundary-layer characteristics over different segments of the airfoil subject to constraints on the geometry (closure) and the flow field (far field boundary). Additional constraints to satisfy some desirable features, such as pitching moment coefficient, thickness, camber, etc., along with a merit of performance of the VAWT, such as the required power output for a given tip-speed ratio, are specified as part of the inverse problem. Performance analyses of the airfoil and the VAWT are carried out with the aid of state-of-the-art analyses codes, XFOIL and CARDAAV, respectively. XFOIL is a panel method with a coupled boundarylayer scheme and is used to obtain the aerodynamic characteristics of resulting airfoil shapes. The final airfoil geometry is obtained through a multi-dimensional Newton iteration. A design example is presented to demonstrate the merits of the technique in improving performance of small VAWTs at low speeds. The main findings of the study suggests that the strength of the method lies in the inverse design methodology whereas its weaknesses is in reliably predicting aerodynamic characteristics of airfoils at low Reynolds numbers and high angles of attack. This weakness can, however, be overcome by assessing relative performance of the VAWT with the assumption that the changes in airfoil characteristics be kept small. The results indicate that a 10-15% increase in the relative performance of the VAWT can be achieved with this method
