• Proceedings of the KSR Conference
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• 2008.11b
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• pp.416-421
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• 2008

Recent high-speed trains around the world have achieved remarkable improvement in speed. In Korea, the new high-speed train with maximum speed of 400km/h has been developing through the 'Future High-Speed Rail System Project'. The improvement in train speed brings numerous aerodynamic problems such as strong aerodynamic resistance, noise, drastic pressure variation due to the crosswind or passing by, micro-pressure wave at tunnel exit, and so on. Especially, the nose shape of high-speed train is closely related to the most of the aerodynamic problems. Also the pantograph has to be considered for noise prevention and detachment problems. In this paper, the project, 'Research on the Aerodynamic Technology Advancement of the High-Speed EMU' is introduced briefly, which is one of the efforts for the speed improvement of the 'HEMU400x'. Finally, two main results of train nose and pantograph will be shown. First, the optimization of the cross-sectional area distribution of the high-speed train nose to reduce tunnel micro-pressure wave, and second, robust design optimization of the panhead shape of a pantograph.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.1034-1039
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• 2006

Large-amplitude, combustion-induced oscillations are observed in most systems involving continuous flow, such as aeroengine afterburners, gas boilers and rocket motors. Strong furnace vibration is typically characterized by the presence of well developed standing waves in the furnace, generating high pressure pulsation and causing structural vibration of the furnace walls. 320MW NG boilers have been experienced high vibration frequently since reconstruction works. Excessive furnace vibration was encountered when a burner air rate is suddenly reduced during load zone changed from 270MW to 300MW. An investigation showed that the primary cause of the vibration was induced by combustion low air flow rate. This paper describes phenomenon examination on strong furnace vibration due to the change of boiler operating conditions.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.12 no.3
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• pp.139-148
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• 2000

In this paper, the interaction of oblique incident waves with a bottom-mounted and fluid-filled flexible membrane structure is investigated in the frame of linear hydro-elastic theory. The static shape of a membrane structure containing the fluid of a specific density is initially unknown and must be calculated before the hydrodynamic analysis. To solve hydrodynamic problem, the fluid domain is divided into the inner and outer region. The inner solution based on discrete membrane dynamic model and simple-source distribution over the entire fluid boundaries is matched to the outer solution ba~ed on an eigenfunction expansion method. The numerical results were compared to a series of Ohyama's experimental results. The measured reflection and tran¬smission coefficients reasonably follow the trend of predicted values. Using the computer program developed, the performance of a bottom-mounted and fluid-filled flexible membrane strocture is tested with various system parameters (membrane shape, internal pressure, density ratio) and wave characteristics (wave frequencies, incident wave angle). It is found that a bottom-mounted and fluid-filled flexible membrane structure can be an effel;tive wave barrier if properly designed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.5
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• pp.476-482
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• 2009

The effect of pintle shape on the thrust level of pintle-nozzle Solid Rocket Motor(PNSRM) was studied numerically using the Spalart-Allmaras turbulent model of Fluent. Mass flow rate of PNSRM was always less than theoretical value and the extent of decrease in mass flow rate grew in the large pintle because of increase in the relative boundary layer thickness between pintle body and nozzle wall. The bigger pintle size was, the more thrust of pintle tip pressure was obtained. Meanwhile the more thrust of nozzle and chamber pressure decreased. Hence, total thrust of big pintle was less than a small pintle under same throat area condition. Specific impulse was relatively flat for all pintle shape.

• Nuclear Engineering and Technology
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• v.17 no.4
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• pp.279-289
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• 1985

The purpose of this paper is to investigate the density-wave oscillation type instability in the recirculating loop of U-tube steam generator (UTSG). The perturbed and nodalized conservations equations based on the drift-flux model have been derived to obtain the single-and two-phase pressure drop perturbations, by taking into account the slip between phases, nonuniform heat flux and heated wall dynamics. To assess the stability, the frequency domain technique with the Nyquist criterion has been used under the constant pressure drop boundary condition through the loop. The computer implementation of this model, SASG, was used for the parametric study of the steam generator in Kori-Unit 1. The results of the parametric study revealed important factors influencing UTSG stability margin.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.1
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• pp.24-32
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• 2019

Numerical simulations were carried out in a supersonic nozzle to investigate the possibility of using dual-throat nozzle concept in fluidic thrust vector control. Validation of the methodology showed an excellent agreement between the computational fluid dynamics results and the experimental data available, which were based on the well-assessed SST $k-{\omega}$ turbulence mode. The deflection angle, system resultant thrust ratio, and thrust efficiency were investigated in a wide range of nozzle pressure ratios and injection pressure ratios. The performance variations of the dual-throat nozzle thrust vector control system were clearly illustrated with this two-dimensional computational domain. Some constructive conclusions were obtained that may be used as a reference for further studies in the fluidic thrust vector control field.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.6
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• pp.53-60
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• 2020

In liquid-fuel spray combustion, an experimental study was conducted to observe the effect of ultrasonic excitation on the ultrasonically-atomized liquid fuel flame by controlling pressure field through an ultrasonic standing wave. Flame of the ultrasonically-atomized kerosene aerosol was visualized by using a high speed camera, DSLR, and Schlieren photography. The amount of fuel consumed was obtained by a precise flow-rate measurement technique during combustion, through which the ratio of carrier gas (air) to fuel mass was able to be obtained, too. As a result, it could be found that the combustion reaction-rate of the liquid-fuel aerosol was increased by applying an ultrasonic standing wave to the secondary flame zone of the flame.

• Journal of the Korean Society for Marine Environment & Energy
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• v.19 no.1
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• pp.62-73
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• 2016

The variation of groundwater by wave, tide and precipitation conditions is closely related to the vegetation environment at the natural vegetation and sandy based beach, and it has a significant impact on the vegetation development and ground stabilization. In this study, the water temperature, electrical conductivity, and pressure were monitored at five observational stations normal to the Jinu-do(Island) shoreline of Nakdong river estuary from March 2012 to September 2014 (approximately 799 days) with the aim of measuring the variation in groundwater-table characteristics. The purpose of the study was to identify factors (tide, wave etc.) affecting groundwater-table variation using time series and correlation analysis, and to record spatial variations in the groundwater level and electrical conductivity as a result of storm events. The observational station in the intertidal zone was strongly affected by wave period and tide level. During the storm period, the groundwater-table and electrical conductivity were stabilized at the edge of sand dunes, vegetation, and areas of transition between freshwater and seawater.

• Journal of Biomedical Engineering Research
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• v.21 no.3 s.61
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• pp.261-271
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• 2000

The present study investigated flow dynamics of a two-dimensional abdominal aortic bifurcation model under sinusoidal flow conditions considering wall motion. impedance phase angle(time delay between pressure and flow waveforms), and non-Newtonian fluid using computational fluid dynamics. The wall shear stress showed large variations in the bifurcated region and the wall motion reduced amplitude of wall shear stress significantly. As the impedance phase angle was changed to more negative values, the mean wall shear stress (time-averaged) decreased while the amplitude (oscillatory) of wall shear stress increased. At the curvature site on the outer wall where the mean wall shear stress approached zero. influence of the phase angle was relatively large. The mean wall shear stress decreased by $50\%$ in the $-90^{\circ}$ phase angle (flow wave advanced pressure wave by a quarter period) compared to the $0^{\circ}$ phase angle while the amplitude of wall shear stress increased by $15\%$. Therefore, hypertensive patients who tend to have large negative phase angles become more vulnerable to atherosclerosis according to the low and oscillatory shear stress theory because of the reduced mean and the increased oscillatory wall shear stresses. Non-Newtonian characteristics of fluid substantially increased the mean wall shear stress resulting in a less vulnerable state to atherosclerosis.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.5
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• pp.466-472
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• 2009

An acoustic leak monitoring system(ALMS) using acoustic emission(AE) technique was applied for leakage detection of nuclear power plant's pipeline which is operated in high temperature and pressure condition. Since this system only monitors the existence of leak using the root mean square(RMS) value of raw signal from AE sensor, the difficulty occurs when the characteristics of leak size and shape need to be evaluated. In this study, dual monitoring system using AE sensor and accelerometer was introduced in order to solve this problem. In addition, artificial neural network(ANN) with Levenberg.Marquardt(LM) training algorithm was also applied due to rapid training rate and gave the reliable classification performance. The input parameters of this ANN were extracted from varying signal received from experimental conditions such as the fluid pressure inside pipe, the shape and size of the leak area. Additional experiments were also carried out and with different objective which is to study the generation and characteristic of lamb and surface wave according to the pipe thickness.