• International Journal of Aeronautical and Space Sciences
• /
• 제18권1호
• /
• pp.91-98
• /
• 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%.

• 터널과지하공간
• /
• 제5권1호
• /
• pp.1-10
• /
• 1995

The behavior of a jointed rock mass depends mainly on the geometrical and mechanical properties of joints. The failure mode of a rock mass and kinematics of rock blocks are governed by the orientation, spacing, and persistence of joints. The mechanical properties such as dilation angle, shear strength, maximum closure, strength of asperities and friction coeffiient play important roles on the stability and deformation of the rock mass. The normal and shear behaviour of a joint are coupled due to dilation, and the joint deformation depends also on the boundary conditions such as stiffness conditons. In this paper, the joint constitutive law including the dilatant behaviour of a joint is numerically modelled using the edge-to-edge contact logic in distinct element method. Also, presented is the method to quantify the input parameters used in the joint law. The results from uniaxial compression and direct shear tests using the numeical model of the single joint were compared to the analytic results from them. The boundary effect on the behaviour of a joint is verified by comparing the results of direct shear test under constant stress boundary condition with those under constant stiffness boundary condition. The numerical model developed is applied to a complex jointed rock mass to examine its performance and to evaluate the effect of joint dilation on tunnel stability.

• Current Research on Agriculture and Life Sciences
• /
• 제27권
• /
• pp.69-75
• /
• 2009

This research regard it as most meaningful to realize the importance of the hedgerow in cultivated areas functioning as a residual landscape element in rural landscape and set improvement guidelines through landscape character and value analysis to cope with landscape malfunction. The results of summary are as follows. 1) First of all, as a result of landscape character analysis of edge stripe in cultivated land in total of 7 case areas, for example, the edge stripe in cultivated land in case area 4 and 8 maintain the width of 10m and are assessed satisfactory in terms of vegetation development condition, appearance of living species, connectivity, buffer capacity and so on. Also, as a result of structural character of correlation analysis among items, the correlation coefficient between width and appearance of living species showed 0.941, the highest. Following are connectivity and appearance of living species and width and buffer capacity respectively: 0.841 and 0.740. 2) As a result of landscape character analysis of uncultivated stripe in total of 6 case areas, it is analyzed that case area 4 maintains the widest width as almost 4.5m average width and considered valuable as I degree in vegetation development condition, filtering, and connectivity. 3) As a result of problem analysis of uncultivated stripe, for example, case 3, 9, and 10 was analyzed that the width was below 1.25m which is too small to carry out the function of buffer and habitat for living creature, so minimum standard width was set between 4~5m through comprehensive analysis of character of each case area. Based on the result above landscape character, value and problem analysis, main improvement guidelines are set in terms of width, connectivity, filtering, and vegetation development, restrictive practices and so on.

• Korean Chemical Engineering Research
• /
• 제48권4호
• /
• pp.490-498
• /
• 2010

K사의 방진고무 사출성형에 있어서 애로사항인 토크로드부시(torque rod bush)의 캐비티 가장자리(edge) 구간에서의 에어트랩(air-trap) 발생 및 다이내믹 댐퍼(dynamic damper)에 있어서 사출시 미성형(short shot) 발생 등의 문제점을 해결하기 위하여, 상용 CAE 프로그램인 MOLDFLOW(Ver. 5.2)를 이용한 전산모사를 수행하여 적정금형설계를 도출하고 적정작업조건을 구축하였다. 그 결과 방진고무 중에서 토크로드부시의 사출성형에서의 에어트랩 발생 등의 공정문제를 최적 캐비티 가장자리 경사각 및 게이트 수를 조절함으로써 캐비티 가장자리에서의 유동선단(flow-front)의 유동정체를 방지하고 유동을 원활하게 하여 해결하였다. 한편 다이내믹 댐퍼의 사출시 충전(filling) 단계에서의 캐비티 비충전으로 인한 미성형 불량은 에어벤트(air-vent) 구를 에어트랩 발생 빈도가 매우 높은 유동선단 상향류와 하향류의 두 흐름이 만나는 지점에 설치함으로써 미성형 불량을 해결하였다. 또한 게이트 위치를 댐퍼 상단에서 중단으로 변경하거나 게이트 수를 증가시킨 경우에 미성형 불량이 K사의 경우보다 개선되었다.

• 한국지능시스템학회논문지
• /
• 제14권7호
• /
• pp.821-829
• /
• 2004

얼굴인식기술이 인증 및 보안을 위한 도구로 활용되고 있지만 입력영상의 상태, 즉 조명환경에 따라 적용할 수 있는 범위가 제약적일 수밖에 없다. 본 논문에서는 이러한 제약을 최소화하기 위해 측면과 후면조명 등의 불규칙한 조명환경에서 획득한 입력영상에서 얼굴의 특징을 구분하여 얼굴영상임을 확인하는 방법을 제안한다. 제안된 방법은 에지차영상을 얼굴특징이 두드러지도록 전처리한 후, X와 Y축의 프로파일을 이용하여 얼굴영역을 예측하고 영역 내의 밝기분포를 이용하여 눈, 코, 입 등의 얼굴특징이 놓일 수 있는 수평영역을 분리한다. 수평영역들은 눈, 코, 입을 포함할 수 있는 영역의 그룹으로 나누어지고 각 그룹에서 코와 입, 그리고 눈의 순서로 특징들을 검출한다. 얼굴여부는 검출된 특징들의 구조적인 관계를 검증하여 확인한다. 제안된 알고리즘은 배경색상이나 조명의 방향과 색상 등으로 인해 얼굴의 형태와 특징이 결여된 입력영상에서도 매우 안정적으로 적용됨을 실험을 통해 확인하였다.

• 대한조선학회논문집
• /
• 제29권3호
• /
• pp.21-32
• /
• 1992

자유 수면하를 영각을 가지고 일정 속도로 전진하는 3차원 물체가 만드는 자유 표면 흐름에 대한 수치해를 보인다. 해를 구하기 위해 물체 표면에 Havelock 쏘오스와 법선 다이폴을, Wake 면에는 Havelock 법선 다이폴을 분포시키는 교란 속도 포텐시얼을 기저로 한 패널법을 이용하였다. Trailing Edge의 윗면과 아랫면의 압력 등가 조건을 정확히 만족시키기 위해 반복 기법을 이용한 압력 Kutta 조건을 사용하였다. 무한 유체 영역에 놓인 Ellipsoid와 사각 Wing에 대해 계산 프로그램을 검증한 후 자유 수면하에 잠수하여 전진하는 Spheroid와 스트럿에 대한 문제를 다루었다. 본 연구에서 채택한 Panel Method는 자유 표면 효과, 3차원 물체의 형상을 고려하여 물체에 작용하는 동유체력을 비교적 정확하게 예측하였으며 특히 Wake 형상은 동유체력 계산에 큰 영향을 미치지 않는 것으로 확인하였다.

• Journal of Welding and Joining
• /
• 제27권6호
• /
• pp.74-79
• /
• 2009

Titanium and titanium alloy can be reproduced immediately even if oxide films($TiO_2$) break apart in sea water. Therefore, since titanium demonstrates large specific strength and outstanding resistance to stress corrosion cracking, crevice corrosion, pitting and microbiologically influenced corrosion in sea water environment, it has been widely applied to heat exchanger for ships. In particular, with excellent elongation, pure titanium may be deemed as optimal material for production of heat exchanger plate which is used with wrinkles formed for efficient heat exchange. Conventional plate type heat exchanger prevented leakage of liquid through insertion of gasket between plates and mechanical tightening by bolts and nuts, but in high temperature and high pressure environment, gasket deterioration and leakage occur, so heat exchanger for LPG re-liquefaction device etc do not use gasket but weld heat exchanger plate for use. On the other hand, since welded plate cannot be separated, it is important to obtain high quality reliable welds. In addition, for better workability and production performance, lasers that can obtain weldment with large aspect ratio and demonstrate fast welding speed even in atmospheric condition not in vacuum condition are used in producing products. So far, 1st report and 2nd report compared and analyzed embrittlement degrees by bead colors of weldment through quantitative analysis of oxygen and nitrogen and measurement of hardness as fundamental experiment for the evaluation of titanium laser welding, and evaluated the welding performance and mechanical properties of butt welding. This study welded specimens in various conditions by using laser and GTA welding machine to apply edge welding to heat exchanger, and evaluated the mechanical strength through tensile stress test. As a result of tensile test, laser weldment demonstrated tensile strength 4 times higher than GTA welds, and porosity could be controlled by increasing and decreasing slope of laser power at overlap area.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2006년도 제26회 춘계학술대회논문집
• /
• pp.275-278
• /
• 2006

[ $CH_4-He/Air$ ] 대향류 확산화염의 저 화염 신장율에서 진동 불안정성에 관하여 실험적으로 연구하였다. 저 화염 신장율에서 진동 불안정은 Le가 1보다 클 때 소화한계 부근에서 발행하고 측면방향 열손실이 중요한 역할을 한다. 화염이 진동할 때 화염의 형태는 전진하거나 후퇴하는 edge flame이고 진동의 동적거동은 성장, 조화 그리고 감쇠 진동 모드 세 가지로 나타났다. 전체 화염 신장율이 감소하면 진동의 진폭은 커지게 되는데 이는 화염의 크기가 감소하게 되어 측면 열손실이 증가하였기 때문이다. 저 화염 신장율에서 edge flame의 진동 불안정성은 Le 뿐만 아니라 복사와 측면 열손실도 밀접한 관계가 있다.

• 한국정밀공학회지
• /
• 제15권10호
• /
• pp.65-72
• /
• 1998

The BTA drilling chip is better for deep hole drilling than other self-piloting with pad drilling chips because the large length to diameter ratio allows a unique cutting force dispersion and better supplies the high pressure fluid. Therefore the BTA is useful for many tasks, such as coolant hole drilling of large scale dies, as well as tube seat drilling, which is essential for the heat exchanger, and variable component drilling for automobiles. Deep hole drilling has several significant problems, such as hole deviation, hole over-size, circularity, straightness, and surface roughness. The reasons for these problems, which often result in quality short comings, are an alignment of the BTA drilling system and the unbalance of cutting force by work piece and tool shape. This paper analyzes the properties through an experiment which com¬pared single-edge BTA drills with multiple-edge BTA drills, as well as the shapes of the tools to cause an unbalance of cutting force, and its effect on the precision of the worked hole. Conclusions are as follows. 1) In SMSSC drilling, 60m/min of BTA with single and multi-edged tools proved the best cutting condition and the lowest wear character. 2) The roundness got a little worse as cutting speed was increased, but surface roughness was hot affected. 3) It was proved that the burnishing torque of both drills approached 26%. which is almost the same as the 24% insisted on by Griffiths, and the dispersion characteristic of the multi-edged BTA drill proved better than the single-edge BTA drill.

• 한국환경복원기술학회지
• /
• 제8권5호
• /
• pp.56-67
• /
• 2005

Rapid and reckless economical development is causing nationwide deforestation; more and more forest is being developed to be used as a base for economic advancement. While benefiting the national economy, this destruction of forest is creating a serious problem in the National Land Plan. To solve this problem, it is imperative to understand the current condition of damaged forest and make an environment-friendly plan. This paper explains the principles of spatial plan and sets the criteria for the plan, such as patch size, connectivity, and edge of the Landscape Ecology. The paper assesses the conservational value of area that are currently being developed or planned to be developed to figure out the current environmental situation. This conservational value was verified by the field survey. The result of assessment appears that the patch size of the major mountains in site is over 1,000ha and edge is located widely beside roads. The area of the high connectivity is located agriculture area in valley or narrow roads. The research shows that the patch size is related to biodiversity the larger the patch size, the more populated the species are. The research also reveals the conservational value indicated by degree of connection to forest, difference in the structure of vegetation between core area and edge area, and effects of surrounding environment. In further study, we will assess other criteria of conservation value, such as patch shape and fragmentation to the Landscape Ecology, and apply those criteria in biological aspects of the spatial plan.