• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.10a
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• pp.123-126
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• 2003

This paper describes the development procedure for Tail-Fan system which has the role of anti-torque and yaw control in helicopter. A detailed design of Tail-Fan system was done and structural analysis also was done. After finishing detailed design, Detailed drawings were generated for manufacture. Through detailed design and manufacture, required techniques were achieved for helicopter development. After validation through performance and stability test, acquired techniques will be applied to development of Korea Multi-role Helicopter(KMH) which will be launched

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.82-87
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• 2000

During the operation, fatigue failures and cracks of duct plate due to excessive duct vibration occurred in the fan-duct systems of fossil fueled boilers. We measured static pressure variation(pressure pulsation) in the outlet, and also measured vibration at the outlet duct of a centrifugal fan. It was found that strong pressure pulsation caused by the inlet vortex occurred in inlet vane of centrifugal fan in the middle range of vane opening. Thus, excessive duct vibration is caused by strong pressure pulsation. In this paper, it is shown that the frequency and amplitude of pressure pulsation depend mainly on vane opening and are compared with duct vibration. Also, effective solution for reducing pressure pulsation and vibration are presented.

• Proceedings of the KSR Conference
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• 2008.06a
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• pp.1781-1788
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• 2008

This report is the result of a basic experiment done on a mock-up tunnel, of what happens to the ventilated flow and fire driven flow inside a railway tunnel as the current inside the tunnel changes when an anti-smoke or a radio frequency invert control is installed. The duct used in this experiment is 10m in length, 0.5m in height and 0.25m in width and made of acrylic. An anti-smoke system with a motor that can produce current of 10m/sec maximum in order to create ventilated flow, has been installed. A honeycomb has been installed at the entrance of the duct to create a current flow that exists in tunnels. In order to create a ventilated flow, a current of 4m/s, 6m/s and 8m/s were generated using the anti-smoke system, as the study of current developed. A Hot-wire(TSI) and Pressure sensor(ENDEVCO) was installed in the duct, 1m apart, as the measurement of current and pressure went on. The current and pressure were automatically measured through the Lap View program and PC; the current flow in the mock-up tunnel generated by the honeycomb has been analyzed the pressure distribution and pressure drop has been analyzed.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.2
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• pp.319-333
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• 2017

The construction of long sub-sea tunnel does not provide the favorable condition for the installation of ventilation system to be used during construction due to the constrained construction space. For the ventilation system required during construction, the artificial island where ventilation shaft is located is constructed at some location along the sub-sea tunnel route, which requires a high construction cost. Therefore, it is intended, as much as possible technically, to minimize the construction of artificial island. However, this requires a longer distance between ventilation shafts, there-by causing increased air leakage at the ventilation duct connection points due to the higher fan pressure being required to deliver ventilation air. Previously the air leakage was studied as an important issue. In this study experiments were carried out to develop the improved duct connection method considering various conditions such as, tunnel length, etc. Additionally, its performance results with leakage rates are shown and compared to the "S" class leakage rate of SIA. As a result, the new duct coupling type of improved method is analyzed as applicable to such a 30 km long tunnel with the leakage rate of $1.46mm^2/m^2$, which is better performance than SIA leakage rates.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.5
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• pp.107-114
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• 2019

In many military aircraft, s-shaped diffusers are used to prevent the fan blades of the turbofan engine from being exposed to the outside. The inlet configurations of the air intakes for military aircraft vary, such as the rectangular intake of the F-22, the crescent-like intake of the F-16, elliptical intake of the MQ-25. In this study, the aerodynamic performance of s-shaped diffusers with various inlet configurations was evaluated using numerical analysis. In addition, the configuration of the middle section of an s-shape duct was changed to the crescent shape, and the effects on its aerodynamic performance were investigated. As a result, there was a slight difference in total pressure recovery according to various inlet configurations with ellipse-shaped middle sections. Also, the total pressure distortion was the lowest in the rectangular inlet shape. When the configuration of the middle section was changed from an ellipse to a crescent shape, the total pressure recovery remained at a high level, except for the ellipse-shaped inlet configuration. In terms of total pressure distortion, the duct with the crescent-shaped middle section showed a significantly more uniform pressure distribution than that with the ellipse-shaped middle section.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.1
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• pp.145-160
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• 2018

Long subsea tunnel is subject to many restrictions in terms of spatial limitation when vertical or inclined shafts are built for tunnel ventilation. So, the construction of some artificial island is required to provide ventilation. But, because of construction difficulty and cost increase, it is necessary to minimize the artificial island construction. As a result, ventilation distance become longer and supply airflow becomes excessive due to air leakage, So, duct mounting for temporary ventilation is impossible or fan pressure and power increase exponentially. Therefore, in order to build a long subsea tunnel, it is necessary to overcome these practical problems and to develop technical solution that can keep the comfortable condition of tunnel environment during construction. In previous study, we have found that air leakage is the key factor in solving these problems and experimental results show that the new connection method has a leakage rate of about $1.46mm^2/m^2$ (Jo et al., 2017). In this study, we present the experimental results of the measurement of the leakage rate of the prototype with the new connection method, and analyze experimentally the improvement of the leakage rate when applying the flexible cover inside the duct to improve the leakage performance of the existing connection method.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.433-438
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• 1999

This paper describes Active Noise Cancellation/Control(ANC) method that removes the information of the unnecessary noise and doesn't remove the informations of the necessary noise(warning sound, operating sound etc.) for the induced noise of the mechanical system. In this paper, the noise source Is axial fan, and the Feedback Active Noise control method that can effectively control BPF generated from the axial fan is used, and the Filtered-X LMS algorithm for adaptive algorithms is used. The experiments are executed for two case(propagating noise in the duct, emission noise for exterior free field). The part to be removed is BPF noise, and the band-pass filter not to effect to the other frequencies is used. Also, to investigate the effect of the noise reduction for human, we are compared with the results that are controlled for using Loudness before and after. As a results, we are certified that the BPF is decreased only and frequencies outside of BPF are not affected, and we acquire the reduction effects of 6.7 dB Loudness Level, then the frequency to be removed is controlled. Therefore, we can be certified that sound pressure as well as loudness can be effectively decreased for human sound quality

• Journal of the Korean Society of Propulsion Engineers
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• v.14 no.6
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• pp.53-59
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• 2010

This research aims in finding a more optimal ejector size for evacuating engine exhaust gasses and 20% of the cell cooling air. The remaining 80% of cell cooling air pumped into the test chamber is separately exhausted from the test chamber via a discharge port fitted with flow control valves and vacuum pump. Unlike its predecessor this configuration utilizes a smaller capture area to improve pressure recovery. The modified ejector size has a diameter of 1100mm enough to evacuate 66kg/s jet engine exhaust in addition to about 20%, 24kg/s of the cell cooling air tapped from the sterling chamber. This configurations has an area ratio of the engine exit and ejector inlet of about 1.2. Simulation results of the proposed ejector configuration, indicates improved pressure recovery.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.5
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• pp.1-9
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• 2019

Infrared signal and exhaust gas temperature distribution with bypass ratio were measured using a micro turbojet engine. Micro turbojet engine was modified to simulate the turbofan engine behaviour. Core flow was simulated using the jet flow of the micro turbojet engine, and high-pressure air was supplied to its external duct to simulate bypass flow. The effects of bypass ratios (0.5, 1.0, and 1.4) were examined. The experimental results indicate that the infrared signal decreases as the bypass ratio increases. And also gas temperature decreases with bypass ratios. Additionally, Schlieren visualization of the exhaust gas plume was conducted. From the exhaust gas temperature distribution and Schlieren images, the structure of jet plume with various bypass ratios was understood.

• Clean Technology
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• v.20 no.2
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• pp.171-178
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• 2014

In this study we have examined the health risk factors and analyzing data of laborers working at the welding operation at large-sized casting process. In order to improve the working environment of workplace, an effective ventilation method was proposed after performing CFD (computational fluid dynamics) modeling and measurement of pollutants. As a result of examining the health risk factors of workers, oxidized steel dust is the main pollution source in the company A, welding fume in the companies B and C, and welding fume and oxidized steel dust in the company D. The fume concentration in the workers' breathing zone was $0.05{\sim}4.37mg/m^3$, and the fume concentration in the indoor air at the welding process was $0.13{\sim}7.54mg/m^3$. From a result of CFD, a local exhaust with an exhaust duct adjacent to welding point was found to be most effective in case of the exhaust process. In case of air supply, we found that a desired location of air supply fan would be at the end of the opening. If a standardizing the ventilation system for tunnel-type semi-enclosed space at a large-sized casting process is introduced in welding work places in the future, it would be more effective to protect the health of welding workers working at the casting industry and shipbuilding industry and improve the work environment.