• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.167-174
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• 2008

In this study, flutter analyses for supercritical airfoil have been conducted in transonic region. Advanced computational analysis system based on computational fluid dynamics (CFD) and computational structural dynamics (CSD) has been developed in order to investigate detailed static and dynamic responses of supercritical airfoil. Reynolds-averaged Navier-Stokes equations with Spalart-Allmaras (S-A) and SST ${\kappa}-{\omega}$ turbulence models are solved for unsteady flow problems. A fully implicit time marching scheme based on the Newmark direct integration method is used for computing the coupled aeroelastic governing equations of cascades for fluid-structure interaction (FSI) problems. Also, flow-induced vibration (FIV) analyses for various supercritical airfoil models have been conducted. Detailed flutter responses for supercritical are presented to show the physical performance and vibration characteristics in various angle of attack.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.1
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• pp.91-98
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• 2017

Performance of a low speed axial compressor is enhanced through a proper configuration of blade row tip injection and casing treatment of groove type. Air injectors were mounted evenly spaced upstream of the blade row within the casing groove and were all aligned parallel to the compressor axis. The groove, which covers all the blade tip chord length, extends all-round the casing circumference. Method of investigation is based on solution of the unsteady form of the Navier-Stokes equations utilizing $k-{\omega}$ SST turbulence model. Extensive parametric studies have been carried out to explore effects of injectors' flow momentums and yaw angles on compressor performance, while being run at different throttle valve setting. Emphasis has been focused on situations near to stall condition. Unsteady numerical analyses for untreated casing and no-injection case for near stall condition provided to discover two well-known criteria for spike stall inception, i.e., blade leading edge spillage and trailing edge back-flow. Final results showed that with only 6 injectors mounted axially in the casing groove and at yaw angle of 15 degrees opposite the direction of the blade row rotation, with a total mass flow rate of only 0.5% of the compressor main flow, surprisingly, the stall margin improves by 15.5%.

• Smart Structures and Systems
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• v.7 no.2
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• pp.133-152
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• 2011

System identification is a fundamental step towards the application of structural health monitoring and damage detection techniques. On this respect, the development of evolved identification strategies is a priority for obtaining reliable and repeatable baseline modal parameters of an undamaged structure to be adopted as references for future structural health assessments. The paper presents the identification of the modal parameters of the Guangzhou New Television Tower, China, using a data-driven stochastic subspace identification (SSI-data) approach complemented with an appropriate automatic mode selection strategy which proved to be successful in previous literature studies. This well-known approach is based on a clustering technique which is adopted to discriminate structural modes from spurious noise ones. The method is applied to the acceleration measurements made available within the task I of the ANCRiSST benchmark problem, which cover 24 hours of continuous monitoring of the structural response under ambient excitation. These records are then subdivided into a convenient number of data sets and the variability of modal parameter estimates with ambient temperature and mean wind velocity are pointed out. Both 10 minutes and 1 hour long records are considered for this purpose. A comparison with finite element model predictions is finally carried out, using the structural matrices provided within the benchmark, in order to check that all the structural modes contained in the considered frequency interval are effectively identified via SSI-data.

• The KSFM Journal of Fluid Machinery
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• v.17 no.3
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• pp.59-64
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• 2014

The kidney vortex is the important factor adversely influencing film cooling effectiveness. In general, double jet film-cooling hole is designed to overcome the kidney vortex by generating anti-kidney vortices. In this study, the film cooling characteristics and the effectiveness of the double jet film cooling hole were numerically investigated with various area ratios of the first($A_1$) and second($A_2$) cooling hole($A_1/A_2$=0.8, 1.0, 1.25) and lateral ejection angle(${\alpha}$ = $30^{\circ}$, $45^{\circ}$, $60^{\circ}$) as the design parameters. The effects of lateral distance between the first and second row holes are investigated. Numerical study was performed by using ANSYS CFX with the shear stress transport(SST) turbulence model. The film cooling effectiveness and temperature distribution were graphically depicted with various flow and geometrical conditions.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.195-200
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• 2010

Numerical investigation was conducted to study the effects of after-body configurations and nozzle lip on the PIFS(Plume Induced Flow Separation) and eat flux to the base face. Two dimensional and axi-symmetric non-equilibrium Navier-Stoke's solver with $k-{\omega}$ SST turbulence model was used to solve the launching vehicle type configuration with propulsive jet. The experimental result of Robert J. McGhee was compared with our computational results for code validation. Three types of the after-body configurations (Straight, Boat-tail, Flare type) were simulated for this study. And the nozzle lip effect was studies using the three types of base configurations same simulation conditions. As a result of numerical investigations, higher pressure ratio condition and boat-tail after-body configuration caused severe PIFS phenomenon but the flare type after-body configuration and low pressure ratio suppressed PIFS. Flare type after-body configuration and low pressure ratio case reduced heat flux to base face. The nozzle lip dispersed the heat flux widely along the base face and the nozzle lip.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2006.06a
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• pp.271-272
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• 2006

Zinc confers high corrosion resistance by acting as a sacrificial anode, and a zinc coating improves the appearance of steel. Chromate conversion coating (CCC) films are still one of the most efficient surface treatments for steel. Although such films can self-repair via the dissolution of Cr(VI), dissolved Cr(VI) have adverse effects on humans, and the environment. Therefore, we examined the corrosion protection property and morphology of colloidal silica conversion films as an alternative to CCC films. The corrosion behavior was investigated in 3% NaCl solution using electrochemical techniques, including electrochemical impedance spectroscopy, open circuit potential, and the salt spray test(SST). Corrosion was implied by the appearance of red rust on the specimen surface. In corrosion resistance at 3% NaCl solution, red rust appeared at 15-20, 55-70, and 83-98 days on Zn-electroplated steel, colloidal silica conversion-coated specimens, and CCC-coated specimens, respectively. In the salt spray test, the colloidal silica film provided better corrosion protection than CCC films, i.e., red rust appeared at 96 hours on the Zn-electroplated steel sheet, at 432 hours with the CCC films, and at 888 hours with silica conversion coating.

• International Journal of Naval Architecture and Ocean Engineering
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• v.8 no.3
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• pp.219-227
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• 2016

Numerical simulation based on the Reynolds Averaged Naviere-Stokes (RANS) Computational Fluid Dynamics (CFD) method had been carried out with the commercial code ANSYS CFX. The structured grid and SST $k-{\omega}$ turbulence model had been adopted. The impact of non-condensable gas (NCG) on cavitation performance had been introduced into the Schnerr and Sauer cavitation model. The numerical investigation of cavitating flow of marine propeller E779A was carried out with different advance ratios and cavitation numbers to verify the numerical simulation method. Tip clearance effects on the performance of pumpjet propulsor had been investigated. Results showed that the structure and characteristics of the tip leakage vortex and the efficiency of the propulsor dropped more sharply with the increase of the tip clearance size. Furthermore, the numerical simulation of tip clearance cavitation of pumpjet propulsor had been presented with different rotational speed and tip clearance size. The mechanism of tip clearance cavitation causing a further loss of the efficiency had been studied. The influence of rotational speed and tip clearance size on tip clearance cavitation had been investigated.

• Toxicological Research
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• v.18 no.4
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• pp.341-347
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• 2002

Hypertension is a multifactorial disorder in which the genetic and environmental factors are involved. In a view of the effects for hypertension as a risk factor for hypertension, we investigated the genotype and allele frequencies in the four RFLPs of the apo AI-CIII-AIV gene cluster (G to A mutation at position -75 in the apo AI promoter SstI RFLP in the ape CIII gene and HincII and HinfI RFLPs in the apo AIV gene) in the Korean patients with hypertension and normal controls. The AA genotype frequency of the G to A promoter polymorphism in hypertensives was significantly higher than that of normotensives (P < 0.05). None of the other polymorphisms showed a difference in genotype frequency between two groups. Therefore, our result suggest that the G to A promoter polymorphism of the ape AI gene may be useful as genetic marker in the ethiology of hypertension.

• Journal of Distribution Science
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• v.17 no.5
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• pp.29-37
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• 2019

Purpose - This paper analyzes the effects of the SST characteristics at airports on behavioral intention through technology acceptance and customer satisfaction, and presents a strategic plan for introducing SSTs to airports providing differentiated services. Research design, data, and methodology - We examine the role of airport self-service characteristics and access the influence of the Technology Acceptance Model (TAM) on both customer satisfaction and behavioral intentions towards SSTs. To do this, a survey is conducted with passengers having used self-service technologies(SSTs) at Incheon International Airport. A total of 400 questionnaires are then analyzed using structural equation modeling. Results - According to the results, of the self-service characteristics, customer satisfaction and behavioral intention were affected by optimism through perceived ease of use, perceived usefulness, and perceived enjoyment and by innovativeness and insecurity through perceived ease of use. Conclusions - According to the results of the study, the purpose of using TBSS in the airport is to save time and convenience. Therefore, it is necessary to closely analyze the differences in technology acceptance by age and generation, increase user self-efficacy, increasing satisfaction through effective management of cognitive and emotional waiting time will have a positive impact on behavioral intentions.

• Ocean and Polar Research
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• v.37 no.2
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• pp.149-159
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• 2015

The Southern Ocean (SO) plays a primary role in global climate by storing and transporting anthropogenic carbon dioxide through the meridional overturning circulation and the biological pumping process. In this study, we aim to investigate interannual variability of summer chlorophyll concentration in the SO and its relation with the El $Ni{\tilde{n}}o$ Southern Oscillation (ENSO), using satellite ocean color data covering 16 years from 1997 to 2012. During El $Ni{\tilde{n}}o$ periods, chlorophyll concentration tends to increase in the subtropics (north of the subantarctic front). This chlorophyll increase is likely linked to El $Ni{\tilde{n}}o$-induced surface cooling that increases nutrient supply through enhanced vertical mixing in the subtropics. On the other hand, the subpolar gyres show localized chlorophyll changes in response to the ENSO. The localized response seems to be primarily attributed to changes in sea-ice concentrations. Our findings suggest that ENSO contributes interannual variability of chlorophyll in the SO through different mechanisms depending on regions.