• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.10 no.2
• /
• pp.93-99
• /
• 1998

Parabolic approximation and sponge layer are applied as open boundary condition for elliptic finite difference wave model. Generalized conjugate gradient method is used as a solution procedure. Using parabolic approximation a large part of spurious reflection is removed at the spherical shoal experiment and sponge layer boundary condition needs more than 2 wave lengths of sponge layer to give similar results. Simulating the propagation of waves on a rectangular harbor, it is identified that iterative scheme can be applied easily for the non-rectangular computational region.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.34 no.1
• /
• pp.1-7
• /
• 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 Society of Naval Architects of Korea
• /
• v.34 no.1
• /
• pp.41-49
• /
• 1997

Computational results from Navier-Stokes equations are presented for the Stokes-wave/flat-plate boundary-layer and wake for small wave steepness(Ak=0.01), including exact and approximate treatments of the viscous free-surface boundary conditions. The macro-scale flow indicate that the variations of the external-flow pressure gradients cause acceleration or deceleration of the streamwise velocity component and alternating direction of the cross flow. Remarkably, the wake displays a greater response, i.e., a bias with regard to favorable as compared to adverse pressure gradients. The micro-scale flow indicates that the free-surface boundary conditions have a profound influence over the boundary layer and near/intermediate wake. Order-of-magnitude estimates are conformed to the computational results. And appreciable errors are introduced through approximations to the free-surface boundary conditions.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.12 no.2
• /
• pp.349-358
• /
• 1988

Natural convection velocity and temperature profiles are obtained approximately in the core at boundary layer flow regime for varying Prandtl number in a low aspect ratio rectangular Enclosure. Analysis is based on the formally obtained core flow equations using the multiple scales method. Results show good agreement with the existing works for $P_{r}$ ~ 1. No comparison, however, is possible yet for $P_{r}$ >> 1 and $P_{r}$ < 1 due to the lack of available date. It is shown here that boundary layer flow regimes are governed by two parameters, A $R_{a}$$^{1}$4/ and A( $P_{r}$ $R_{a}$)$^{1}$4 for $P_{R}$.geq. 1 and $P_{r}$ < 1 respectively.ely.ively.ely.y.

• Journal of the Korean GEO-environmental Society
• /
• v.8 no.6
• /
• pp.37-43
• /
• 2007

The interface layer having different consolidation properties and nonlinear material function with permeability needs to be considered to predict consolidation behavior. In this study, interface equation between different layers has been derived and then applied to existing finite difference scheme for conducting consolidation analysis. These results have been compared with those by conventional method in which different layers are converted to single layer having conversion value of properties. Also, although the conventional consoilidation analysis is used to consider non-linearity of the permeability with effective stress, an approximated nonlinear method as a function of consoilidation coefficient with effective stress have been developed and applied to the consoilidation analysis for various cases.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2011.04a
• /
• pp.406-413
• /
• 2011

This paper presents the shape optimization of a nonaxisymmetric endwall and endwall boundary layer fence which improve the aerothermal environment of a gas turbine passage. The endwall and fence methods were used simultaneously. The turbine passage was simulated by a $90^{\circ}$ turning duct ($Re_D$=360,000). The main purpose of the present investigation was to focus on finding a nonaxisymmetric endwall and boundary layer fence with minimum total pressure loss in the passage and heat transfer coefficient on the endwall of the duct. An approximate optimization method was used for the investigation to secure the computational efficiency. Results indicated that a significant improvement in aerothermal environment can be achieved through the application of a nonaxisymmetric endwall and boundary layer fence.

• The Journal of Engineering Geology
• /
• v.13 no.1
• /
• pp.17-27
• /
• 2003

In this study, a phenomenon of saltwater intrusion was monitored under various conditions regarding recharge and pumping rate using time domain reflectometry for a laboratory scale unconfined aquifer to verify the basic theory behind seawater intrusion and to investigate movement of salt-freshwater interface in accordance with the ratio of pumping and recharge rate. Results showed that a thick mixing zone was formed at the boundary instead of a sharp salt-freshwater interface that was assumed by Ghyben and Herzberg who derived an equation relating the water table depth $(H_f)$ to the depth to the interface $(H_s)$. Therefore our experimental results did not agree with the calculated values obtained from the Ghyben and Herzberg equation. Position of interface which was adopted as 0.5 g/L isochlor moved rapidly as the Pumping rate $(Q_p)$ increased for a given recharge rate $(Q_r)$. In addition, interface movement was found to be about 7 times the ratio of $Q_p/Q_r$ in our experimental condition. This indicates that Pumping rate becomes an important factor controlling the seawater intrusion in coastal aquifer.

• Proceedings of the Korean Society of Computer Information Conference
• /
• 2012.01a
• /
• pp.73-75
• /
• 2012

본 논문에서는 복부 초음파 영상에서 근육 영역의 명암 대비를 강조하기 위해서 Multiple 연산을 적용한 후, 명암 대비가 강조된 영상에서 수직 방향의 명암도가 200 이상인 픽셀들에 대해 퍼지 기법에 적용하여 이진화한다. 이진화된 영상에서 피부층과 외복사근 사이에 존재하는 피하지방을 추출하기 위해 Thick-Search 방법을 적용하여 피부층과 외복사근을 추출한 후, 피부층과 외복사근의 사이에 Up-Down Search 방법을 적용하여 피하지방층을 추출한다. 피하지방층이 추출된 영상에서 근막의 형태학적 정보를 이용하여 근막을 추출한다. 추출된 근막 사이에 대해 Up-Down Search 방법을 적용하여 근육의 후보 영역을 추출한 후, 근육의 형태학적 정보를 이용하여 최종적인 근육 층을 추출한다. 추출된 근육의 경계선을 Monotone Cubic Hermite 보간법을 이용하여 근육의 경계선을 보정한 후, 최소자승법을 이용하여 근육의 두께를 측정한다. 제안된 방법을 복부 초음파 영상에 적용하여 근막 및 근육 영역을 추출한 결과, 기존의 근육 추출 방법보다 정확하게 추출되었고, 근육의 두께 측정 결과도 전문의가 육안으로 측정한 결과와 근사한 것을 확인할 수 있었다.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.16 no.1
• /
• pp.25-35
• /
• 2012

An endwall boundary layer fence technique was adapted to improve the aerothermal environment of a gas turbine passage. The shape optimization of the fence was performed to maximize the improvement. The turbine passage was simulated by a $90^{\circ}$ turning duct (ReD=360,000). The main purpose of the present investigation was to focus on finding a endwall boundary layer fence with minimum total pressure loss in the passage and heat transfer coefficient on the endwall of the duct. Anothor objective function was to minimize the area on the endwall of the duct. An approximate optimization method was used for the investigation to secure the computational efficiency. Results indicated that a significant improvement in aerodynamic environment can be achieved through the application of the fence. Improvement of the thermal environment was smaller than that of the aerodynamic enviroment.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.13 no.1
• /
• pp.97-103
• /
• 1993

This paper presents a quasi-analytical method using integral equations to obtain head distributions in unsaturated porous media with different hydrogeologic properties. One-dimensional soultion algorithms were developed for two cases of boundary conditions at the top: 1) constant head and 2) constant flux. Water table elevation at the bottom was assumed known for both cases. The methodology was applied to a fly ash disposal facility in an alluvium area. The results showed that the pressure head distributions had high nonlinearity with large gradients slightly above the interface of two media which made preliminary numerical solutions implausible. The developed method helped to structure finite element grids for improving convergence and accuracy.