• Journal of Biosystems Engineering
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• v.33 no.4
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• pp.253-259
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• 2008

In this paper an optimum design of a lab-scale biofilter for absorbing ammonia has been proposed and analyzed. This biofilter is using pine chaff and wood shaving as filter materials. It is assumed that the biofilter can be used as a storage tank of swine manure slurry or swine stall. To evaluate the biofilter performance, the ammonia, mainly offensive odor ingredient, was measured. Swine compost was mixed with filter materials in ratio of 1:1 on weight base. Each test continued for 20 days. The ammonia emissions were reduced by 97.9% and 98.3% in case of using biofilter filled with pine chaff and compost, and wood shaving and compost, respectively. The system was tested with and without adding compost. It was found that the biofilter with wood shaving and compost has an ammonia removal efficiency of 94.1%, while biofilter with wood shaving only has 85.3%. The biofilter with wood shaving and compost showed 8.8% higher removal efficiency than that of wood shaving only. By mixing the compost, the number of microorganism was found to be about 2.3 times more than that of wood shaving only. Therefore it can be concluded that adding compost has a positive effect on the formation of microorganism.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.27 no.10
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• pp.21-29
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• 2013

The short circuit and overload is presented by main cause of electrical fire. However, 85% of the fan directly connected the outlet box without switch in total 110 fans as a research in manufacturing industries. In installation direction of vertical type fans which was placed on the horizontal surface, only 39 vertical type fans were placed on vertical surface and 71 fans were placed on the horizontal type. The installation direction of the fans warns of the risk of the fire hazard due to the motor stall to the user manual of the maker. However, it is the representative nonconformity example of construction which the people or builder disregards. In addition, the condition of ground connection with the earth leakage prevention was investigated in grounding of 5 fans, non-grounding of 105 fans. The double insulation structure is generally used for small fan and it can't connect ground wire as electric plug of non-grounding type. However, industrial iron fan needs ground wire for electric leakage and to protect against electric shock.

• International Journal of Aeronautical and Space Sciences
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• v.10 no.2
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• pp.23-33
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• 2009

The inherent aeromechanical complexity of a rotor system necessitated the comprehensive analysis code for helicopter rotor system. In the present study, an aerodynamic analysis module has been developed as a part of rotorcraft comprehensive program. Aerodynamic analysis module is largely classified into airload calculation routine and inflow analysis routine. For airload calculation, quasi-steady analysis model is employed based on the blade element method with the correction of unsteady aerodynamic effects. In order to take unsteady effects - body motion effects and dynamic stall - into account, aerodynamic coefficients are corrected by considering Leishman-Beddoes's unsteady model. Various inflow models and vortex wake models are implemented in the aerodynamic module to consider wake induced inflow. Specifically, linear inflow, dynamic inflow, prescribed wake and free wake model are integrated into the present module. The aerodynamic characteristics of each method are compared and validated against available experimental data such as Elliot's induced inflow distribution and sectional normal force coefficients of AH-1G. In order to validate unsteady aerodynamic model, 2-D unsteady model for NACA0012 airfoil is validated against aerodynamic coefficients of McAlister's experimental data.

• Aerospace Engineering and Technology
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• v.8 no.1
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• pp.197-206
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• 2009

To improve the aerodynamic efficiency of Smart Unmanned Aerial Vehicle (SUAV), vortex generators and flow fence are applied on the surface and the tip of wing. The initially applied vortex generator increased maximum lift coefficient and delayed the stall angle while it produced excessive increase in drag coefficient. It turns out reduction of the airplane's the lift/drag ratio. The new vortex generators with L-shape and two different height, 3mm and 5mm, were used to TR-S4 configuration to maintain the desired level of maximum lift coefficient and drag coefficient. Flow fence was also applied at the end of both wing tip to reduce the interaction between nacelle and wing when nacelle tilting angles are large enough and produce flow separation. To examine the effect of flow fence, flow visualization and force and moment measurements were done. The variation of the aerodynamic characteristics of SUAV after applying flow control devices are summarized.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.04a
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• pp.63-67
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• 2009

The previous work (Cheong et al., 2006) where the characteristics of acoustic emissions of wind turbines has been investigated according to the methods of power regulation, has showed that the acoustic power of wind turbine using the stall control for power regulation is more correlated with the wind speed than that using the pitch control. In this paper, basically extending this work, the noise generation characteristics of large modern upwind wind turbines are experimentally indentified according to the power regulation methods. To investigate the noise generation mechanisms, the distribution of noise sources in the rotor plane is measured by using the Beam-forming measurement system (B&K 7768, 7752, WA0890) consisting of 48 microphones. The array results for the 660 kW wind turbine show that all noise is produced during the downward movement of the blades. This result show good agreement with the theoretical result using the empirical formula with the parameters: the convective amplification; trailing edge noise directivity; flow-speed dependence. This agreement implies that the trailing edge noise is dominant over the whole frequency range of the noise from the 660 kW wind turbine using the pitch control for power regulation.

• International Journal of Fluid Machinery and Systems
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• v.4 no.2
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• pp.217-222
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• 2011

The rotordynamic fluid forces acting on a closed type impeller in whirling motion were measured and the influence of the clearance geometry on the stability of the impeller was examined. At small positive whirling speed, the rotordynamic forces acted as destabilizing forces for all casings. A small clearance between the shroud of the impeller and the casing caused large fluid force, but did not change the destabilizing region. Radial grooves in the clearance were effective for reducing the fluid forces and destabilizing region due to the reduction of the circumferential velocity without the deterioration of the pump performance. A rotating phenomenon like a rotating stall of the impeller occurred at low flow rate and the resonance between it and the whirling motion led to a sudden increase in force at the whirling speed ratio of 0.7.

• Proceedings of the KIEE Conference
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• 2004.07d
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• pp.2307-2309
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• 2004

This paper presents a modeling and simulation of a fuzzy controller for maximum power extraction of a grid-connected wind energy conversion system with a link of a rectifier and an inverter. It discusses the maximum power control algorithm for a wind turbine and proposes, in a graphical form, the relationships of wind turbine output, rotor speed, power coefficient, tip-speed ratio with wind speed when the wind turbine is operated under the maximum power control. The control objective is to always extract maximum power from wind and transfer the power to the utility by controlling both the pitch angle of the wind turbine blades and the inverter firing angle. Pitch control method is mechanically complicated, but the control performance is better than that of the stall regulation method. The simulation results performed on MATLAB will show the variation of generator's rotor angle and rotor speed, pitch angle, and generator output.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.187-188
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• 2008

An ultrasonic motor of high torque with a new configuration for application in automobiles is proposed. The newly designed stator is a two sided vibrator consisting of a toothed metal disk with a piezoelectric ceramic ring bonded on both faces of the disk which generates a flexural traveling wave along the circumference of disk. In this configuration, the displacement on the surface of stator may not be confined. It also produces a large vibrating force and amplitude because the vibrator is sandwiched by two piezoelectric plates. It is possible to increase the torque by improving the vibration characteristics. To compute the vibration mode of the motor of diameter 48 mm, the finite element method was used. A 6th mode was chosen as the operation mode with a resonance frequency of about 64.4 kHz. According to this design and measured its performance, a prototype was fabricated. The performance measurement of the prototype motor showed that its stall torque was about 1.8 Nm and efficiency was 37% at 60% of the maximum torque.

• 유체기계공업학회:학술대회논문집
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• 2000.12a
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• pp.163-168
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• 2000

A method to search the design parameters for optimum stage matching has been used based on a 1-D mathematical model of a compressor, which uses the data obtained from the preliminary test to identify the design parameters. This methodology was applied with a two-stage axial compressor, which was originally designed for a helicopter gas turbine engine. After Identifying design parameters using preliminary test data, an optimization process has been employed to achieve the best matching between the stages (i.e., maximum efficiency of the compressor at its operation modes within a given range of the rotor speed under given restrictions for required stall margins and mass flow). 3-D flow calculations have been performed to confirm the usefulness of the corrections based on 1-D mathematical model. Calculational results agree well with the experimental data in view of the performance characteristics. Some promising results were produced through the methodology proposed in this paper in conjunction with flow calculations.

• 한국전산유체공학회:학술대회논문집
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• 2007.10a
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• pp.60-66
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• 2007

Separation control has been performed using synthetic jets on airfoil at high angle of attack. Computed results demonstrated that stall characteristics and control surface performance could be substantially improved by resizing separation vortices. It was observed that the actual flow control mechanism and flow structure is fundamentally different depending on the range of synthetic jet frequency. For low frequency range, small vortices due to synthetic jet penetrated to the large leading edge separation vortex, and as a result, the size of the leading edge vortex was remarkably reduced. For high frequency range, however, small vortex did not grow up enough to penetrate into the leading edge separation vortex. Instead, synthetic jet firmly attached the local flow and influenced the circulation of the virtual airfoil shape which is the combined shape of the main airfoil with the separation vortex. Theses results show the characteristic of unsteady flow of single synthetic jet. Beside, we researched on multi-array synthetic jet to obtain applicable synthetic jet velocity. Multi-location synthetic jet is proposed to eliminate small vortex on suction surface of airfoil. With the results, we concluded that the flow around airfoil is stable by high frequency synthetic jet with elimination of small vortex and confirmation of stable flow. Moreover, performance of multi-array/multi-location synthetic jet can be improved by changing phase angle of multi-location synthetic jet.