• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.575-576
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• 2014

The Hull Mounted Sonar Dome housing the sonar sensor array is a ship's structure protruded from ship bottom, which is under turbulent flow. The flow of sonar surface is highly disturbed and turbulent. In this case the wall pressure fluctuations within the turbulent boundary layer are one of the most important flow induced self noise sources of the SONAR system. We investigate the characteristics of the wall pressure fluctuations of the hull mounted sonar dome through the model test in the cavitation tunnel. This paper contains the wall pressure fluctuation spectra at various free stream velocities.

• Journal of the Korean Society of Visualization
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• v.8 no.1
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• pp.13-18
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• 2010

An experimental investigation of the flow around a vertical fence was carried out using a PIV velocity field measurement technique. The vertical fence was embedded in a turbulent boundary layer. The instantaneous velocity fields measured at cross-sectional planes reveal complex longitudinal vortices that vary in size and strength, developing from the upstream location. In the instantaneous vorticity and velocity field data, the shear flow separated from the fence top is highly turbulent and shows unsteady flow characteristics. The topography of the ensemble averaged velocity fields, especially the separation bubble formed behind the fence, shows that the spatial distributions of streamwise velocity (U) and vertical (V) are symmetric, the spanwise velocity (W) is skew-symmetric with respect to the central xy-plane(z=0).

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.1
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• pp.1-7
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• 2006

Linear stability analysis of 2-dimensional wall jet is conducted by using parabolized stability equation (PSE). Wall jet is found to be modelled well by boundary layer approximation except for the neighborhood of the nozzle exit, and the introduction of local similarity variable makes the streamwise basic flow Reynolds number independent. Stability characteristics of the wall jet obtained

• Journal of the Korean Society for Heat Treatment
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• v.10 no.4
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• pp.219-231
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• 1997

Inconel alloys used as nuclear power plant components have experienced intergranular stress corrosion cracking problems inspite of their good corrosion characteristics. In order to investigate the effects of heat treatments on carbide precipitation and intergranular stress corrosion cracking(IGSCC) in Inconel alloys, DSC(Differential Scanning Calorimeter), TEM, EDXS and static potential corrosion tests were carried out. Thermal treatment at $750^{\circ}C$ for 15hours in Inconel alloys increased the density of intergranular carbide. The carbides are mainly $Cr_7C_3$ in Inconel 600, and $Cr_{23}C_6$ in Inconel 690. The Cr depletion around grain boundary is not crucial factor on IGSCC. The carbides in grain boundary play an important role as acting dislocation source, and as decreasing stress around growing crack.

• Journal of the Korean Ceramic Society
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• v.40 no.10
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• pp.921-924
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• 2003

A current-voltage relation for Positive Temperature Coefficient of Resistance (PTCR) ceramic was derived and compared with the experimental data. The new current-voltage relation was developed based on Heywangs double Schottky barrier model and a bias distribution across the grain boundary. The voltage limitation V < 4${\Phi}$$\sub$b/ suggested by Heywang is no longer necessary in the new expression for the voltage dependence of the resistance. The pulsed voltages were applied to the PTCR ceramic specimen in order to avoid possible temperature variation during the measurement.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1996.11a
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• pp.265-269
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• 1996

In this paper, electric field interference was analyzed in the Printed Circuit Board to restrain the elcctromagnetic wave using Boundary Element Method and Finite Element Method. First, charge density distribution was simulated using Boundary Element Method and the characteristic impedance was caculated to restrain the reflex wave, and mutual capacitance was caculated in the multi-strip line PCB. Finally, electric field was simulated in the variable patterns using Finite Element Method. As a result, the optimal structure and characteristics of strip line was obtained and the imformations about the optimal design pattern could be obtained with the analysing the feild distribution.

• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.567-571
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• 2004

The 2-dimensional unsteady flows on and around the cambered airfoils were computed by applying LES with the deductive dynamic SGS model. The unsteady flow field were used as inputs to compute the far-field sounds and directivity patterns from rotating blades by a hybrid approach that exploits Farassat's formula. The BEM (Boundary Element Method) was applied to predict the frequency characteristics from the rotating blades for the cases of even- and uneven-pitched fans. The BEM results suggested that the unevenly pitched fan have less pronounced discrete peaks at BEF frequencies, which was confirmed by the experiment.

• Journal of Ship and Ocean Technology
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• v.8 no.4
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• pp.10-16
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• 2004

A response of a swept wing boundary layer to a single free-stream stationary axial vortex of a limited spanwise extent is considered as an example of typical problems that one can find in laminar-turbulent transition research and control. The response is dominated by streamwise velocity perturbations that grow quasi-exponentially downstream. It is shown that the formation of the boundary layer disturbance occurs for the most part close to the leading edge. The disturbance represents itself a wave packet consisted of the waves with characteristics specific for cross-flow instability. However, an admixture of growing disturbances whose origin can be attributed to transient effects and to a distributed receptivity mechanism is also identified.

• Korean Journal of Crystallography
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• v.10 no.2
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• pp.136-144
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• 1999

고주파 마그네트론 스퍼터법을 이용한 Al:ZnO(AZO) 박막 증착시, 증착 조건에 따른 미세구조 변화를 조사하였으며, 이를 전기적 광학적 성질과 상관하여 고찰하였다. 박막은 기판 온도가 증가함에 따라 c축이 기판표면에 수직으로 놓이는 주상구조로 성장하였으며, 스퍼터 파워가 증가함에 따라 증착 속도와 입자의 크기가 증가한 반면 결정성은 저하되었다. 증착된 박막은 가시광선영역에서 85% 이상의 광 투과도를 나타내었으며 Al 첨가에 의해 광학적 밴드갭이 약 0.15 eV 증가하였다. 주상구조로 성장한 입자들은 저각 입계(low angle grain boundary)와 특수 입계(special grain boundary)를 형성하였으며, 특히 Σ=7 [001] (210)A/(110)B 입계의 규칙적인 원자배열 및 원자이완을 HRTEM을 이용하여 고찰하였다.

• Journal of Korea Foundry Society
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• v.12 no.1
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• pp.32-39
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• 1992

In this study, electron microscopy, Fractography and $J_{IC}$ test have been used to investigate the fracture behaviour in the scope of aging temperature which 7075 Al-alloy can have high strength. Conclusions obtained on this study are as followed. 1) When the 7075 Al-alloy was aged for 24hrs at $120^{\circ}C$, it's mechanical properties was excellent but fracture toughness decrement resulted from intergranular fracture was emerged. 2) The state of aged for 24hrs at $100^{\circ}C$, had the highest fracture toughess. 3) We could infer that intergranular fracture occurred because preferrential precpitated precipitates in the grain boundary growed in the form of colinear along the grain boundary.