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ÖgeAerodynamic performance evaluation of a coaxial octocopter based on taguchi method(ASME, 2024)The design and optimization of propellers for unmanned aerial vehicles (UAVs) are essential for optimal performance and high efficiency. This study presents a numerical investigation of the aerodynamic performance of coaxial octocopters using openfoam as flow solver. While the aerodynamic performance is affected by many parameters, the current study focuses on four main parameters: the propeller type, the horizontal and vertical separation distances between the propellers, and the ratio between the rotational speeds of the upper propeller and the lower one. To find the minimum number of simulations to be performed within defined limits, and reduce the number of computational fluid dynamics (CFD) simulations that cause high computational cost, Taguchi method was employed. In this study, average thrusts were calculated for the preliminary design of the octocopter by examining an isolated single propeller and dual- and quad propellers taking their rotation directions into account. The Taguchi design matrix revealed that for all cases investigated, the propeller type is the most dominant design parameter followed by the velocity ratio of the upper propeller to the lower one ( ) and vertical (z/D) and horizontal ( ) orientation of coaxial propellers. However, it was shown that and z/D may play a significant role in vortex formation and pressure fluctuations which should be considered as design criteria for coaxial octocopters associated with flow attributes. The results showed that the aerodynamic performance parameters are not dependent on all the selected parameters, and demonstrated that the selected propeller designs improved aerodynamic performance.
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ÖgeExperimental test of fault tolerant real time operational modal analysis method by voting algorithm for aircrafts(ACM, 2024)Operational modal analysis (OMA) is a key technique to obtain real-time modal parameters (natural frequency, damping ratio, mode shapes) for aircraft. Due to the nature of an aircraft, an extended flight envelope leads to the flexible structures being highly nonlinear and time-variant. For structural health monitoring and real-time flutter test purposes, automated and robust operational modal analysis methods are required. However, each automated OMA method has its own advantages and disadvantages in specific conditions. In this paper, stochastic subspace identification (SSI), autoregressive poly reference (AR PR), Ibrahim time domain (ITD), eigensystem realization algorithm (ERA) and frequency-spatial domain decomposition method (FSDD) operational modal analysis algorithms were investigated on real-time aircraft flight data. Automated versions of these algorithms are used to obtain real-time modal parameters (natural frequency, damping ratio, and mode shapes). Furthermore, the present work focuses on the development of an enhanced method by utilizing each algorithm simultaneously. The enhanced method aims to calculate the real-time modal parameters without the requirement of users to pick physical modes by voting algorithm between the calculated parameters from each method. Each method and enhanced method were tested for flight data and results were verified by ground vibration test (GVT). It is observed that the voting algorithm improves the robustness of the real-time results in different flight conditions when disadvantageous methods in that specific condition are influenced, by compensating with advantageous methods.
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ÖgeThe investigation of the effect of operating conditions in gearboxes on efficiency(Sage Publications, 2024)Efficiency is a concept that evaluates the optimal utilization of resources, including time, energy, finances, or materials, in order to accomplish a particular goal or objective. As widely acknowledged, energy losses occur in systems involving relative motion between interacting machine elements due to friction. In the case of a gearbox, these losses can arise from tooth friction in the gear mechanism, friction in sealing elements, friction in roller bearings, and the influence of the lubricant used in the system, all of which are subject to environmental conditions. This study aims to experimentally determine the efficiency of the gearbox under various operating conditions by considering the gearbox as a comprehensive system encompassing all its components. A measurement system was designed in order to obtain the efficiency of a gearbox. Experiments and measurements were carried out via software support. The measurement system contains two torque transducers, electrical resistive load device, an electrical motor with temperature measurement thermocouple, and two stage helical gearbox. In experiments conducted through computer commands, input revolutions were incrementally increased with 400 rpm intervals within the range of 700–2700 rpm. Moreover, experiments were carried out at different lubricant levels in the gearbox. At the same time lubricant temperature was measured and effects to the gearbox efficiency were investigated. Subsequently, different lubricant with distinct viscosity indices were employed. As a result of this experimental design, regime efficiency values were obtained for each case. Thus, power loss of the gearbox system has been determined. These results were examined using a general full factorial design. Analysis of variance (ANOVA) tables were created and the effects of the parameters on the system and the efficiency results were determined by checking whether the parameters were interacting or not. Finally, regression analysis was performed and the regression function was obtained in order to develop a predictive model to estimate the efficiency of a gearbox.
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ÖgeOptimization of laser direct structuring process parameters for material extrusion of polycarbonate(Wiley, 2023)Laser direct structuring (LDS) is critical in the integration of circuits onto 3D-shaped plastic parts, such as antennas and radio frequency components. The LDS process encompasses three stages: deposition of 3D parts, laser structuring, and metallization. While laser-direct structurable parts have been manufactured through plastic injection molding, material extrusion (MEX) is a favored additive manufacturing process for economic low-volume production and fast prototyping advantages. Although injection-molded LDS literature is available, 3D-printed laser-direct structured components merit further investigation. This study focuses on the MEX of catalyst-loaded polycarbonate (PC) parts and its LDS process. The parameters from the nanosecond fiber laser, including scan speed, power, and frequency, are thoroughly analyzed to understand the surface property changes and metallization performance of the printed PC parts. The single scan track width, which corresponds to the accuracy of conductive path width and metallization thickness, is employed to elucidate the findings. A process map is built to keep the track width constant aimed at enhancing the uniform metallization of intricate components. Thresholds are established, identifying a minimum track width of 22.1 μm and metallization thickness of 2.5 μm. These delineate clusters of process parameters that yield conductivity levels suitable for various applications.
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ÖgePrecise orientation control of gimbals with parametric variations using model reference adaptive controller(Wiley, 2024)This study focuses on a model reference adaptive control method that ensures identical orientation outputs for different prototypes of a two-axis gimbal produced in mass production. In this method, unlike traditional MRAC structures, an MRAC structure is used in conjunction with state feedback control. First, the reasons for the need for an adaptation mechanism in gimbals and why Model Reference Adaptive Control (MRAC) alone won't be sufficient have been discussed. In the first section, various applications of MRAC have also been mentioned. Then, the mathematical foundation of the model reference adaptive controller used in this study is elaborately explained, followed by stability analyses. In the next step, an ideal reference model exhibiting desired behavior and a real system model with different dynamics are created in a simulation environment. This allows a comparison of the adaptation capabilities of only MRAC and MRAC+State Feedback controllers. Based on the information gathered in this section, the recommended approach in the article is tested on a real gimbal system, and the results are shared. The obtained results demonstrate that the MRAC+State Feedback control structure significantly reduces the error in the gimbal's orientation response compared to the reference model.