• Proceeding of EDISON Challenge
• /
• 2016.03a
• /
• pp.604-609
• /
• 2016

슬롯판을 이용한 경사충격파와 경계층 간섭유동 제어에서, 슬롯판 아래에 있는 공동부의 형상을 바꾸어 가며 제어 성능을 비교하는 수치적 연구가 수행되었다. 공동형상 직사각형 5개, 사다리꼴 3개를 선정하여 shock 뒤에서 경계층 안정성, 전압손실을 기준으로 제어 성능을 평가하였다. 수치해석 결과 모든 형상에 대해 제어하지 않은 상태보다 좋은 성능을 얻었다. 그 중 경계층 안정성 측면에서는 형상 L과 R, 전압손실 감소 측면에서는 형상 M과 A가 효과적임을 확인하였고, 종합적으로 슬롯의 끝 면과 공동의 길이방향 끝 면이 일치하는 형상에서 상대적으로 좋은 결과를 얻음을 확인했다. 또한 슬롯과 공동 내부유동을 분석하면서 경계층 안정성과 전압손실 감소에 영향을 미치는 것은 separation 영역을 얼마 원활히 흡입하는지의 여부임을 알 수 있었고, 상류 슬롯에서 발생하는 shock에 대한 추후 해결 연구도 필요함을 알 수 있었다.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.10 no.2
• /
• pp.193-205
• /
• 2008

The construction of underground structures such as oil and food storage caverns are recently increasing in our country. The stability of those underground caverns are greatly influenced by their shape and size. In this study therefore, the effect that the shape of an underground cavern have on its stability were analyzed in terms of safety factor. To this end, caverns with 5 different shapes were investigated and sensitivity analyses were performed based on rock class, overburden, and lateral earth pressure coefficient. The proper amount of shotcrete and rockbolt as supports of a cavern was also assumed based on the shape and site of the cavern and rock conditions. This study is expected to be helpful in designing and evaluating the stability of caverns in future.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.26 no.4A
• /
• pp.809-816
• /
• 2006

More than effectively judging the existence of reinforcing bars under multi boundary layers and void shapes in concrete, this study aims to develop the analysis algorithm of radar response on multi boundary layers in reinforced concrete and radar capable of estimation of the shape of specific voids in plain concrete. To detect or estimate reinforcing bars and void shapes in these conditions, the simulation analysis model of transmission and reflection wave of electromagnetic radar is used. This radar simulation model is carried out with reinforced or non reinforced concrete of various boundary conditions and void shapes. And, the output signals (images) of radar simulation results are calculated and represented by convolution method. As the results, it is clarified that this simulation analysis technique can be used to analyze radar response on multi boundary layers in reinforced concrete and void shapes in concrete.

• Geotechnical Engineering
• /
• v.14 no.1
• /
• pp.93-108
• /
• 1998

In this study, the analytic solutions and numerical methods were used to estimate the shape and size effects on the stability of underground openings. The stability of underground openings was evaluated by scrutinizing the effects of the rock mass quality, the state of in-situ stresses and the lateral earth pressure coefficient on the displacement, the stress concentration and the plastic region developed in the vicinity of the openings. The analytic solutions have shown that the stress concentration factor is inversely proportional to the radius of curvature of openings. Through parametric study on the various shapes and sizes of underground openings the characteristics of the controlling factors concerned with the stability were analyzed. Then, the study was extended to the horseshoe-shaped openings commonly used for under ground storage. Through the extended study the effects of the stress ratio and the height-towidth ratio of openings on the maximum displacement and plastic region developed around the openings were estimated. The results have shorn that the height-to-width ratio of domestic storage caverns can be increased economically without stability problem, as far as the lateral earth pressure coefficient is appropriate.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.39 no.1
• /
• pp.79-88
• /
• 2015

This study numerically examined the mixing characteristics of rectangular cavity flows by using the hybrid lattice Boltzmann method (HLBM) applied to the finite difference method (FDM). Multi-relaxation time was used along with a passive scalar method which assumes that two substances have the same mass and that there is no interaction. First, we studied numerical results such as the stream function, position of vortices, and velocity profile for a square cavity and rectangular cavity with an aspect ratio of 2. The data were compared with previous numerical results that have been proven to be reliable. We also studied the mixing characteristics of a rectangular cavity flow such as the concentration profile and average Sherwood number at various Pe numbers and aspect ratios.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.11a
• /
• pp.165-168
• /
• 2008

This study performed the 3-dimensional inspection analysis for cavitation by using the ultrasonic pulse velocity method to detect detailed various cavitations in a concrete test material. The internal-void are made of non-void test material and two types of which a regular square type and a rectangle type that produced through the 3-dimensional cavitation to put into a $500{\ast}500{\ast}500mm$ sized non-reinforced concrete test material. The tomography method for the ultrasonic pulse velocity method was used for the non-destructive test. As a result, this study has found that it is possible to visualize the cavitation as an image, and to analyze the internal-void in detail by the non-destructive method.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2008.05a
• /
• pp.82-85
• /
• 2008

When a projectile travels at high speed underwater, supercavitating flowarises, in which a huge cavity is generated behind the projectile so that only the nose, i.e., the cavitator, of the projectile is wetted, while the rest of it should be surrounded by the cavity. In that case, the projectile can achieve very high speed due to the reduced drag. Furthermore if the nose of the body is shaped properly, the attendant pressure drag can be maintained at a very low value, so that the overall drag is also reduced dramatically. In this study, shape optimization technique is employed to determine the optimum cavitator shape for minimum drag, given certain operating conditions. Simultaneous optimization technique is proposed for efficient cavitator shape optimization, in which the cavity and cavitator shape are determined in a single optimization routine.

• Proceeding of EDISON Challenge
• /
• 2014.03a
• /
• pp.603-609
• /
• 2014

차세대 제트 추진기관으로 주목받고 있는 스크램제트 엔진의 핵심은 연소기 내부에서의 성공적인 초음속 연소를 필요로 한다. 초음속 연소는 공기-연료 혼합(fuel-air mixing)의 정도에 따라 연소효율이 영향을 받게 된다. 공동형 화염 보염기(cavity flameholder)는 재순환 영역(recirculation zone)을 생성하여 연료 혼합의 효율을 높여 지속적인 초음속 연소가 진행될 수 있는 시간을 제공한다. 본 연구에서는 EDISON 전산유체역학 소프트웨어를 이용하여 공동형 화염 보염기를 지나는 초음속 유동의 재순환 영역과 전압력 변화에 대한 전산 해석을 수행하였다. 초기 형상을 생성하여 유동 해석을 수행한 후, 3개의 형상 변수에 대한 매개 변수 연구를 통하여 공동의 형상과 위치에 따른 재순환영역의 제어가 가능함을 확인하였다.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.11 no.2
• /
• pp.189-198
• /
• 2009

Recently the concern about the construction of underground structures such as oil and food storage caverns is increasing in Korea and abroad. The stability of those underground caverns is greatly influenced by shape factor and the size of excavation area as well as the joint conditions. In this study, therefore, the effect of the shape factor of an underground cavern on its stability was analyzed in terms of safety factor. To this end, four different shape factors of a cavern excavated in good rock conditions were investigated and sensitivity analyses were performed based on overburden, lateral earth pressure coefficient, joint spacing, properties, and orientation. The stability of a cavern is evaluated in terms of safety factor estimated numerically based on the shear strength reduction technique. In future, this study is expected to be helpful in designing and evaluating the stability of caverns excavated in discontinuous rock masses.

• Journal of the Korea Concrete Institute
• /
• v.17 no.2 s.86
• /
• pp.221-227
• /
• 2005

The presence of voids behind tunnel linings is very likely to result in settlement or structural collapse. One proposed method of detecting such voids by non-destructive method is radar. More than effectively judging the existence of voids behind tunnel linings, this study aims to develop the analysis algorithm of radar capable of estimation of the shape of specific voids. To acquire directional information and estimate the shape of three-dimensional voids, the radar of three-dipole antenna type is used. As a foundation to this ongoing research, an investigation of microwave polarization methods using three-dipole antenna carried out with various void orientations and void geometries. As a result, it is clarified that the response of four microwave polarization modes depends on void geometry and thus there is a possibility of identifying the geometry and orientation (the shape) of specific voids using radar of three-dipole antenna type.