• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.6_spc
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• pp.705-713
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• 2016

Underwater noise produced by ships has been becoming an increasing issue. A dominantly contributing noise source is a ship propeller. Therefore, it is important to predict the propeller noise at the propeller design stages. This study applied the acoustic analogy based on Ffowcs Williams equation for the prediction of the marine propeller BPF noise. A marine propeller BPF noise is investigated experimentally as well as numerically. Propeller BPF noise measurement and propeller cavitation observation tests are performed in the KRISO medium size cavitation tunnel. Numerical prediction schemes of marine propeller BPF noise are presented together with the noise measurement method. Propeller BPF noise predictions and experiments are performed under the various propeller operating conditions including non-cavitating and caveating conditions. Numerical and experimental results are compared and analyzed. It is shown that numerical prediction results are generally in good agreement with the measured data.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.5
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• pp.357-362
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• 2016

Various species of insects display vivid colors, widely known as 'structural color' due to their optical interference. Morpho butterflies are famous for their brilliant iridescent colors, which arise from the photonic-nanostructures of optical interference on their wings. In this paper, we outline the results of a comparative study of the optical properties of bio-inspired Morpho butterfly structures with the widely known Distributed Bragg Reflector (DBR), conducted using a rigorous coupled-wave analysis (RCWA) method for the two structures. Almost analogous tendencies were observed for both Morpho and DBR structures. With variation in the surrounding media, however, Morpho structures showed an obvious peak shift while no significant changes were observed in DBR, which can be applicable.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.3
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• pp.215-222
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• 2010

Long and slender body, like a fuel rod, oscillating in axial flow can be unstabilized even by the small cross flow which can be activated by the flow mixer or turbulent generator. It is important to include these effects of flow disturbance in dynamic stability analysis of nuclear fuel rod. This work shows how eigen frequency of a multi-span fuel rod can be changed by the swirl flow, which is discretely generated by a flow mixer. By solving a state-space form of the eigenvalue equation for a multi-span fuel rod system, the critical velocity at which a fuel rod becomes unstable was calculated. Based on the simulation results, we evaluated how stability of a multi-spanned nuclear fuel rod with mixing vanes can be affected by the coolant flow in an operating reactor core.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.4
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• pp.49-55
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• 2013

This paper deals with the flight test of propulsion system of middle size electrically powered UAV (EAV2, Electric Aerial Vehicle 2) which is under development in KARI. EAV2 is low speed endurance type UAV whose wing span is 6.9 m, and weight is 18 kg. The UAV has flown for 22 hours in June of 2012. The flight test result showed that the propulsion system worked well suppling power for any circumstances during the test flight. Each power source worked according to the design purpose.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.1
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• pp.93-100
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• 2019

The cavitation of a turbopump inducer develops from the inception to a critical point, and encounters breakdown finally. In this study, we evaluated the characteristics and predictions of cavitation inception for the turbopump inducer using empirical equations. The empirical equation for the elliptical plate predicted the generation of cavitation inception of the turbopump inducer relatively well. However, in case of the marine propeller, it showed a considerable difference owing to the Reynolds number of the operating point. The cavitation inception occurred earlier as the number of blades increased. However, the solidity had no major impact on the cavitation inception because the cavitation occurred locally at the tip of the leading edge.

• Journal of the Korean Society of Propulsion Engineers
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• v.25 no.1
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• pp.29-41
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• 2021

The PID controller with fin angle and thrust as control input was designed based on the aerodynamic data of scramjet system. Flight simulation following a given trajectory which strike the target point after climb and cruise with constant dynamic pressure was conducted. After that, the required thrust for the climb and cruise was calculated and the required fuel flow rate for the hydrogen fuel dual mode scramjet combustor was analyzed. The combustor analysis of this study which conducted on integrated model of independently developed inlet, combustor, nozzles and external aerodynamic models, laying the foundation for the integrated design of the air breathing hypersonic system.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.60 no.1
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• pp.80-86
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• 2024

We analyzed the performance of hubless rim propellers based on the number of blades, maintaining a fixed pitch ratio and expanded area ratio, using computational fluid dynamics (CFD). Thrust coefficient, torque coefficient and efficiency according to the number of blades were analyzed. In addition, the pressure distribution on the discharge and suction sides of the blade was analyzed. As the advance ratio increases, the thrust coefficient decreases. The highest thrust was shown when the advance ratio was lowest. For the three, four, five and six-blades, the torque coefficient tended to decrease as the advance ratio increased. In the case of seven and eight-blades, the torque coefficient tended to increase as the advance ratio increased. The maximum efficiency was found when the advance ratio was 0.8. When the three-blade, it showed high efficiency at all advance ratios. A high pressure distribution was observed at the leading edge of the discharge blade, and a low pressure distribution was observed at the trailing edge. Applying a hubless rim-driven thruster with the three-blade can generate higher thrust and increase work efficiency.

• Journal of Aerospace System Engineering
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• v.14 no.1
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• pp.28-35
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• 2020

This paper presents the design improvements made for the crack which is in the mounting structure of the mechanical structure of rotary wing aircraft. The doubler added to the mounting structure of rotary wing aircraft was designed and manufactured based on the load at the development stage, and a crack was found in the surface of doubler at a certain point during the operation of the aircraft. To identify the cause of the crack, the initial deformation of the structure, which may occur as a result of fastening condition, was considered and the dynamic analysis of the natural frequency of the structure comparing to the blade passing frequency of the aircraft were additionally reviewed. As a result of this study, a shim was added to remove the physical gap of the fastening area, and a doubler with thickened reinforcement was installed. The increase of structural strength is shown by reviewing the results of dynamic analysis for the structural verification of the improved design, and the fatigue evaluation complied to the requirement of the aircraft lifetime.

• Korean Chemical Engineering Research
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• v.59 no.1
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• pp.94-99
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• 2021

It was found that mixing patterns suddenly changed at an impeller rotation speed in a dished bottom vessel with dual Rushton turbines. Two isolated mixing regions like doughnuts rings generated at a low rotational speed and three isolated mixing regions generated at a higher speed. This phenomenon was observed at the mixing condition in transition area, where the power number with baffle was the same as that without baffle. We found a phenomenon in which the flow state in a dish-bottom agitation tank equipped with a two-stage Rushton turbine blade changes at a certain rotational speed. In the laminar flow region, the isolated stable donut rings were formed even when the rotational speed was changed, and no specific variation in the mixing pattern was observed. In the transition region, the two isolated thick unmixed donut rings do not change even if the rotation speed is changed in the flat bottom vessel, whereas in the dished bottom vessel, when the rotation speed is 450 rpm, the two isolated thick unmixed donut rings are changed to three isolated thin donut rings and then improved mixing. In the dished bottom vessel, in the range of Re=138~178, the isolated ring-shaped unmixed region appeared in three places and the size was also large. But in the flat bottom vessel, the isolated thick ring-shaped unmixed region appeared in two places in Re=116~176 and the size was also small. It appeared in two places, and the size was also small. The condition in which this phenomenon is observed is a transition region, and it was found that when the baffle plate is attached, the power number starts to increase compared to when the baffle plate is not present. In addition, when the mixing Reynolds number exceeded 300 and a slight turbulence was mixed in the flow state, the disconnection of these flow pattern was resolved and the mixture was completely mixed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.1
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• pp.1-12
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• 2022

Wind tunnel test for a small scale electric ducted fan with a 104mm diameter was conducted to analyze the aerodynamic characteristics when it was used as a propulsion system of tilt-propeller UAV. Experimental conditions were derived from flight conditions of a sub-scaled OPPAV. Forces and moments of the ducted fan model were measured by a 6-axis balance and 3-dimensional wake vectors which could induce an aerodynamic influence in the vehicle were measured by 5-hole probes. Thrust and torque on hover and cruise conditions were measured and analyzed to drive out the operating conditions when it was applied in the sub-scaled OPPAV. On transition conditions, thrust keep its value with tilt angle variation below 40° and increase after that. But, sideforce increase constantly until 75°. The maximum axial velocity in the wake on hover and cruise conditions was around 60m/s and tangential velocity was around 12m/s. The position of the maximum axial velocity and vortex center move off the fan rotation center line as the tilt angle increases.