• Aerospace Engineering and Technology
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• v.6 no.2
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• pp.111-118
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• 2007

KSLV-I which is being developed in KARI is composed with two stages, and adaptor ring is used for coupling stage. Cables for interconnecting between stage is exposed on the outside. Also 8 pyro bolts which are installed in adaptor ring are used for separation of stage. In general, cowl is used for protecting exposed parts or structure which are anxious about damage from outer environment. In KSLV-I, two kind of cowls are designed. The one is umbilical cowl, and the other is pyro bolt cowl. Because cowl is exposed on the outside, heat and pressure load developed from air have effect on cowls. Therefore verification of structural strength through static analysis is required. In this study, static analysis in load condition except heat load is accomplished. In result of analysis, structural strength of pyro bolt cowl is verified. But breakage of umbilical cowl is confirmed in pressure load condition. So design of umbilical cowl is modified for satisfying required structural strength. And structural strength of umbilical cowl through analysis is verified.

• The Journal of the Acoustical Society of Korea
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• v.16 no.2
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• pp.10-15
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• 1997

The hydrophones is mounted in many applications on a vibrating surface and functions as an underwater acoustic signal receiver without sensing the vibrations from the mounting surface. However, their performance is usually degraded by the interference of exterior noises such as acoustic cavitation in water stream, host structural vibration in the hull, and propeller motions. This paper describes the design and evaluation of a self noise suppressing hydrophones which shows very poor sensitivity to the external noises, first, effects of the external noise on the its receiver performance is simulated with finite element method(FEM). Second, the geometrical variations are implemented on the original structure that include additional air pockets and acoustic walls which work as acoustic shied or scatter of the noises. The results show that the effect of the external noise is the most significant when it is applied near to the bottom of the side wall of the hydrophones. The transverse noise induced by the outside water flow is isolated most effectively when a thin compliant (damping) layer combined with two air pockets is inserted to the circumference of the nose. Noise level is reduced about fifty nine percent of that of the original structure.

• Journal of Bio-Environment Control
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• v.29 no.1
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• pp.52-61
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• 2020

The natural change of winter night temperature from 00:00 to 04:30 O'clock with the different height of thermal screen in a venlo type glasshouse (W59×L68×H5.9 m) was studied using computational fluid dynamics (CFD). At the early stage of CFD analysis, the room temperature decrease of glasshouse with the 5.9 m height of thermal screen were faster than it with the 4.1m height of thermal screen, but at 2 hr after analysis it was slower than in it with the 4,1m, the temperature difference was 0.6℃ after 4 hr. If we consider that turn on the heater when the temperature were decrease below 13℃ at 1hr after CFD analysis, it is good for energy saving in the glasshouse with the 4.1 m height of thermal screen rather than in it with the 5.9 m height, because of the temperature decrease were slow during 2 hrs after analysis. The airflow at the height of 2 m which were grown tomato were fast and wide in the glasshouse with the 5.9 m height thermal screen rather than in it with the 4.1 m, the speed difference was 0.034m·s^-1 at 1hr after CFD analysis. The effect of temperature decrease in summer season were compared with the different height of shading screen from 12:00 to 14:30 O'clock. The height of shading screen were 5.7, 3.9 m, the gap of it were 30%. The air-inflow quantity by the fan with duct at lower part of venlo glasshouse was 0.67 ㎥·s^-1 until 1hr and to increase 3 times of it from 1hr after analysis. The roof window were open 100%. Until 1hr of CFD analysis, the temperature in the 30% open of shading screen was 0.9℃ higher than in the none shading screen. From 13:00 O'clock when the air-inlet quantity to increase 3 times, the temperature in case 30% gap of shading screen were decreased compare with the none shading screen, the temperature difference was 0.5℃ at 14:30 O'clock. The temperature on the floor surface in case 30% gap of shading screen were lower with it's height increase, the temperature difference was 8℃ compare with none shading screen. The relative humidity difference were insignificant by the height and gap of shading screen.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.10
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• pp.6641-6646
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• 2015

Heat exchanger tube array in a heat recovery steam generator is exposed to the hot exhaust gas flow and it could cause the flow induced vibration, which could damage the heat exchanger tube array. It is needed to establish the characteristics of flow induced vibration in the tube array for the structural safe operation of the heat exchanger. Several researches for the flow induced vibration of typical heat exchangers had been conducted and the nondimensional PSD(Power Spectral Density) function with the Strouhal number, fD/U, had been derived by experimental method. The present study examined the results of the previous experimental researches for the nondimensional PSD characteristics by CFD analysis and the basis for the application of flow induced vibration to the heat recovery steam generator tube array would be prepared from the present CFD analysis. For the previous mentioned purpose, the present CFD analysis introduced circular cylinder tube array and calculated with the unsteady laminar flow for the tube array. The characteristics of lift fluctuation over the cylinder tube array was investigated. The derived nondimensional PSD was compared with the results of the previous experimental researches and the characteristics of lift PSD for circular cylinder tube array was established from the present CFD study.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.8
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• pp.72-81
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• 2004

A Wind tunnel test for a high speed ground vehicle was conducted to investigate the aerodynamic interactions between the vehicle and a solid channel. The free stream velocity was 30m/see and Reynolds number per unit length was $3.1{\times}10^5/m$. Experimental devices such as a variable channel ground and guide way were used for the test. As the vehicle was close to the channel ground and guide way, lift was significantly increased, drag was slightly decreased and pitching moments were restricted to augment static stability. Using smoke-wire, flow visualization was made to confirm these results by comparing the channel and non-channel flow characteristics of the vehicle. Under the influence of the channel ground and guide way, the flow beneath the vehicle was not discharged outside wing end plates, which was the major reason of the increase in lift of the vehicle.

• Journal of the Korean Institute of Gas
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• v.4 no.2 s.10
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• pp.7-14
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• 2000

LNG (Liquified Natural Gas) carried by LNG ship is unloaded into the LNG storage tanks at the very low temperature (a little lower than the boiling point of LNG). Because LNG is unloaded through the pipeline, two phase flow appears in the pipeline. In this study, we have studied the pressure-drop mechanisms of the two-phase flow in the pipeline, and the calculation method of BOG (Boil-off Gas) amount based on the heat transfer mechanism through the insulation and the surface of the pipeline. We have developed a computer program for thermal-hydraulic analysis on the LNG pipeline system. We have also developed the optimal design program to find the optimal thickness of insulation and the pipeline size. The program searches the optimal design with the minimum capital cost of pipelines and insulation on the operating conditions of maximum allowance pressure-drop and BOG amount, etc.

• Journal of the Korean Society for Marine Environment & Energy
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• v.3 no.2
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• pp.18-24
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• 2000

A two-dimensional numerical method for inviscid two-fluid flows with a significant entrainment into both directions is established, and the oil leakage from a non-pressurized underwater pipe is studied. The interface between two fluids is modeled at a vortex sheet. The flow field and the subsequent interface evolution are solved by using the vortex-in-cell method. For longer flow simulation with a realistic two fluids interaction, an efficient merging scheme is introduced. In the Boussinesq limit, the speed of the external fluid intrusion into the pipe is very close to the existing mathematical models, and the lock exchange is observed in spite of a significant roll-up of the interface and entrainments. It is believed that the developed method can be utilized effectively for further detailed studies on various two-fluid flows which are encountered in many different marine oil spill problems.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.590-593
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• 2009

To identify the detailed 3D flow characteristics of a model scramjet engine, a unified 3D numerical analysis was performed. The numerical domain of concern includes the entire flow path of the model scramjet engine extending from the intake to the nozzle exhaust. Turbulent models($k-{\omega}$ SST and low Reynolds number k-e with Sarkar model) were applied with comparison of experiment result. Intake side wall's effect on flow characteristics was analyzed in view points of flow quality at inlet duct and near the flame holder as well. The code is paralleled with multi-block feature using MPI(Massage Passing Interface) library to speed up the 3D calculation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.7
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• pp.671-677
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• 2010

In the present study, we designed a microfluidic platform for generating monodisperse droplets with diameters ranging from hundreds of nanometers to several micrometers. To generate fine droplets, T-junction and flow-focusing geometry are integrated into the microfluidic channel. Relatively large aqueous droplets are generated at the upstream T-junction and transported to the flow-focusing geometry, where each droplet is broken into smaller droplets of the desired size by the action of pressure and viscous stress. In this configuration, the flow rate of the inner fluid can be made very low, and the ratio of the inner- and outer-fluid flow rates in the flow-focusing region can be made very high. It has been shown that the present microfluidic device can generate droplets with diameters of approximately $1\;{\mu}m$ (standard deviation: <3%).

• Journal of the Korean Magnetics Society
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• v.23 no.1
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• pp.26-30
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• 2013

This article is experimentally to investigate thermal-flow characteristics of the magnetic fluid for concentric annuli under externally fixed magnetic fields using visualization technique. Temperatures of the inner tube and outer tube in the tested concentric annuli were constantly maintained at both $30^{\circ}C$ and $25^{\circ}C$ and the middle tube was filled with the magnetic fluid. Magnetic field was uniformly applied using 4 permanent magnets at 4 directions of the concentric annuli. As a result, the thermal-flow characteristics of the magnetic fluid for concentric annuli could be controlled by directions of the external magnetic fields.