• Proceedings of the Korean Society of Marine Engineers Conference
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• 2001.05a
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• pp.58-62
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• 2001

A numerical investigation was performed to determine the effect of airfoil on the optimum flap. height using NACA 0006, 0009, 0012, 0015, 0018, 0021 and 0024 airfoils. The six flaps which have 0.5% chord height difference were used. A Navier-Stokes code, FLUENT, was used to calculate the flow field of the airfoil. The code was first tested as a benchmark by modelling flow around a NACA 4412 airfoil. Predictions of local pressure coefficients are found to be in good agreement with the result of the experimental result. For every NACA 00XX airfoil, flap heights ranging from 0.0% to 2.5% chord were changed by 0.5% chord interval and their effects were also studied. Representative results from each case are presented graphically and discussed. It is concluded that this initial approach gives a promise for the future development of wind turbine optimum design.

• Journal of the Korean Society of Industry Convergence
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• v.25 no.3
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• pp.433-441
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• 2022

In general, in an emergency generator system for an electric facility including an induction motor load, an emergency power generation facility larger than the facility load capacity is built due to the initial starting current of the induction motor. In order to reduce this economic burden, various methods to reduce the inrush current of induction motors are applied to suppress the additional expansion of generators due to the reduction of power generation facilities and the increase in electrical facilities. Among these methods, when a system with a built-in soft start function of an induction motor using an inverter is built, it is the best way to reduce the inrush current of the induction motor to less than the rated current. However, in this case, the installation cost of the inverter to drive the induction motor increases. This paper proposes a soft start method of an induction motor by expanding the frequency and voltage control operation area of an emergency generator. In addition, proposed a speed calculation method based on power factor information, which is essential information for stable soft start of an induction motor, and a method for generating a speed command value of the governor for starting with maximum torque.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.35 no.6
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• pp.527-534
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• 2017

The purpose of this study is to develop unmanned equipment that can automatically move to the desired point and measure water quality at the correct depth. For this purpose, we constructed a water sampling lift and water sampling container, an unmanned vessel equipped with a VRS-GPS, an acoustic echo sounder, and a water quality sensor. Also, we developed an automatic navigation algorithm and program, an automatic water sampling program, and a water quality map generation program. As a result of the experiment in the detention pond, the unmanned vessel sailed along the planned route with an accuracy of about 93% within the error range of 3m. In addition, the water quality sensor installed in the lift was able to acquire the water quality of the target area in real time and transmit it to the server via wireless Internet, and it was possible to monitor the water quality of each site in real time. Through field experiments, the water sampling lift was able to control the desired length with an accuracy of about 94%. The stretch length accuracy experiment of the water sampling lift was impossible to measure directly in the water, so it was replaced land-based experiment. We also found some unstable problems due to the weight of the water sampling lift and the weight of the air compressor to operate the water container. Except these two problems, we accomplished purpose of this study. An automated water quality measurement method using an unmanned vessel can be used to measure the quality of water in a difficult to access area and to secure the safety of the worker.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.11
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• pp.18-25
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• 2006

Unsteady aerodynamic force measurements were carried out in order to investigate the effects of phase difference of a dragonfly-type model with two pairs of wing. A load-cell was employed to measure the aerodynamic force generated by a plunging motion of the dragonfly-type model. The dragonfly-type model has a dynamic similarity with real one, and incidence angles of fore- and hind-wing are 0° and 10°, respectively. Other experimental conditions are as follows: The freestream velocity was 1.6 m/sec and corresponding chord Reynolds number was 2.88×103, and phase differences of fore- and hind-wing were 0°, 90°, 180° and 270°. The variation of aerodynamic coefficients during one cycle of the wing motion is presented. Results show that the lift is generated during the downstroke motion and the drag generated during the hind-wing‘s downstroke motion with the lift generation.

• Journal of the Korean Data and Information Science Society
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• v.23 no.6
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• pp.1127-1135
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• 2012

Association rule mining is the method to quantify the relationship between each set of items in a large database. One of the well-studied problems in data mining is exploration for association rules. There are three primary quality measures for association rule, support and confidence and lift. We generate some association rules using confidence. Confidence is the most important measure of these measures, but it is an asymmetric measure and has only positive value. Thus we can face with difficult problems in generation of association rules. In this paper we apply the similarity measures by probabilistic interestingness measure to find a solution to this problem. The comparative studies with support, two confidences, lift, and some similarity measures by probabilistic interestingness measure are shown by numerical example. As the result, we knew that the similarity measures by probabilistic interestingness measure could be seen the degree of association same as confidence. And we could confirm the direction of association because they had the sign of their values.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.489.2-489.2
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• 2014

The planar type flexible piezoelectric energy harvesters (PEH) based on PbZr0.52Ti0.48O3 (PZT) thin films on the flexible substrates are demonstrated to convert mechanical energy to electrical energy. The planar type energy harvesters have been realized, which have an electrode pair on the PZT thin films. The PZT thin films were deposited on double side polished sapphire substrates using conventional RF-magnetron sputtering. The PZT thin films on the sapphire substrates were transferred by PDMS stamp with laser lift-off (LLO) process. KrF excimer laser (wavelength: 248nm) were used for the LLO process. The PDMS stamp was attached to the top of the PZT thin films and the excimer laser induced onto back side of the sapphire substrate to detach the thin films. The detached thin films on the PDMS stamp transferred to adhesive layer coated on the flexible polyimide substrate. Structural properties of the PZT thin films were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). To measure piezoelectric power generation characteristics, Au/Cr inter digital electrode (IDE) was formed on the PZT thin films using the e-beam evaporation. The ferroelectric and piezoelectric properties were measured by a ferroelectric test system (Precision Premier-II) and piezoelectric force microscopy (PFM), respectively. The output signals of the flexible PEHs were evaluated by electrometer (6517A, Keithley). In the result, the transferred PZT thin films showed the ferroelectric and piezoelectric characteristics without electrical degradation and the fabricated flexible PEHs generated an AC-type output power electrical energy during periodically bending and releasing motion. We expect that the flexible PEHs based on laser transferred PZT thin film is able to be applied on self-powered electronic devices in wireless sensor networks technologies. Also, it has a lot of potential for high performance flexible piezoelectric energy harvester.

• Journal of Advanced Navigation Technology
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• v.25 no.3
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• pp.203-210
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• 2021

In many metropolitan cities around the world, ground and underground transportation networks are saturated due to urbanization. In addition, regulations on carbon emissions to prevent global warming are becoming stricter, and eVTOL, which will be operating in complex cities, is gaining popularity as the next generation of eco-friendly transportation. In this study, the hover lift efficiency and disc loading of eVTOLs for each type were calculated by classifying eVTOLs into following types: multicopter, lift+cruise, and vectored thrust. In addition, using the aerodynamic analysis programs OpenVSP, Fluent and Javaprop, the specific battery energy required for the smooth operation of eVTOL, which will be realized in the near future, was calculated and analyzed base on reports published by Uber and airworthiness authorities of each country.

• Journal of KSNVE
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• v.6 no.5
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• pp.661-669
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• 1996

Proposed is an aero-acoustic performance prediction method of axial fan. The fan aerodynamic performance is predicted by combining pitch-averaged quasi 3-D flow analysis with pressure loss models for blade boundary layer and wake, secondary flow, endwall boundary layer and tip leakage flows. Fan noise is assumed to be radiated as dipole distribution type, and its generation is assumed to be mainly due to the vortex street shed from blade trailing edge. The fluctuating pressure and lift on the blade surface are analyzed by incorporating the wake vortex stree shed from blade trailing edge. The fluctuating pressure and lift on the blade surface are analyzed by incorporating the wake vortex street model with thin airfoil theory. The aero-acoustic performance prediction results by the present method are in good agreement with the measured results of several axial fans. With the present prediction method, parametric studies are carried out to investigate the effects of blade chord length and spacing on the efficiency and the noise level of fan. In the case of lightly loaded fan, both efficiency improvement and noise reduction can be achieved by decreasing chord length or by increasing blade specing. However, when fan is designed at highly loaded condition, the noise reduction by increasing blade spacing penalizes the attaninable efficiency of fan.

• 한국전산유체공학회:학술대회논문집
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• 1998.11a
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• pp.90-95
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• 1998

The two-dimensional incompressible and compressible Navier-Stokes codes are developed for the computation of the viscous turbulent flow over high-lift airfoils. Incompressible code using pseudo-compressibility and dual-time stepping method involves a conventional upwind differencing scheme for the convective terms and LU-SGS scheme for time integration. Compressible code also adopts an FDS scheme and LU-SGS scheme. Several two-equation turbulence models (the standard $k-{\varepsilon}$ model, the $k-{\omega}$ model. and $k-{\omega}$ SST model) are evaluated by computing the flow over single and multi-element airfoils. The compressible and incompressible codes are validated by computing the flow around the transonic RAE2822 airfoil and the NACA4412 airfoil, respectively. Both the results show a good agreement with experimental surface pressure coefficients and velocity profiles in the boundary layers. Also, the GA(W)-1 single airfoil and the NLR7301 airfoil with a flap are computed using the two-equation turbulence models. The grid systems around two- and three-element airfoil are efficiently generated using Chimera grid scheme, one of the overlapping grid generation methods.

• Journal of computational fluids engineering
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• v.18 no.1
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• pp.1-6
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• 2013

Missile and fighter aircraft have been challenged by low restoring nose-down pitching moment at high angle of attach. The consequence of weak nose-down pitching moment can be resulting in a deep stall condition. Especially, the pressure oscillation has a huge effect on noise generation, structure damage, aerodynamic performance and safety, because the flow has strong unsteadiness at high angle of attack. In this paper, the unsteady aerodynamics coefficients were analyzed at high angle of attack up to 50 degrees around two dimensional NACA0012 airfoil. The two dimensional unsteady compressible Navier-Stokes equation with a LES turbulent model was calculated by OHOC (Optimized High-Order Compact) scheme. The flow conditions are Mach number of 0.3 and Reynolds number of $10^5$. The lift, drag, pressure, entropy distribution, etc. are analyzed according to the angle of attack. The results of average lift coefficients are compared with other results according to the angle of attack. From a certain high angle of attack, the strong vortex formed by the leading edge are flowing downstream as like Karman vortex around a circular cylinder. The primary and secondary oscillating frequencies are analyzed by the effects of these unsteady aerodynamic characteristics.