• 한국추진공학회지
• /
• 제22권2호
• /
• pp.96-107
• /
• 2018

고체추진기관 내에 점화기와 추진제 그레인 간격에 따라 화염에 의해 발현되는 내부 유동 형태에 대해 전산유체해석(CFD)를 이용하여 살펴보았다. 실린더형과 슬롯형 추진제 그레인에 대해 실린더형은 간격 1 mm, 3 mm, 5 mm, 슬롯형은 점화기의 화염 분출구가 넓은 간격에 위치한 경우와 좁은 간격에 위치한 경우에 대해 수치 해석을 수행하였다. 실린더형은 간격이 좁을수록 점화기와 추진제 사이에 고압력이 형성되며, 점화기 말단 부근에서 압력 강하 또한 상대적으로 크게 나타났다. 실린더형은 간격에 영향을 받았으나, 슬롯형은 화염 분출구 위치에 관계없이 압력 형태가 유사하게 나타났으며, 실린더형 간격 5 mm와 유사한 결과를 보였다.

• 한국전자파학회논문지
• /
• 제11권4호
• /
• pp.514-522
• /
• 2000

본 논문에서는 위상천이기 없이 전 방향으로 빔의 주사를 가능하도록 하기 위해 기존의 능동 위상배열 안테 나의 슬롯라인 결합구조를 이용하여 패치 안테나와 능동 소자를 Via-hole을 이용하여 접합함으로써 $4\times4$ 능동 위상배열 안테나를 설계하고 제작하여 그 특성을 고찰하였다. 제안된 이차원 능동 위상배열 안테나는 슬롯라인 결합구조를 이용하여 기생방사 결합에 의한 방사패턴의 왜곡울 방지하고, 전체 안테나의 크기도 최소화하며 F FET의 바이어스 전압 조정으로 발진 주파수를 조정할 수 있도록 하였다 .. $4\times4$ 소자를 이용하여 주파수 12.5 GHz에서 발진 주파수가 locking하는 배열된 능동 위상배열 안테나의 일차원 빔 주사 범위는 브로드사이드로부터 $-17^{\circ}~18^{\circ}$로 나타났고, 시율레이션 결과와 대체로 일치했으나 사이드 로브 레벨이 약간 높게 나타났 다. 이차원 빔 주사를 이용하여 $\phi_0=45^{\circ}$일 때의 빔 주사 범위는 $-5^{\circ}~10^{\circ}$로 나타났다. 이를 이용하여 2차원 빔 주사에 응용할 수 있음을 확인하였고, 이것은 위성을 이용한 방송 및 통신 시스탬이나 radar 시스댐에 응용될 수 있을 것이다.

• 한국구조물진단유지관리공학회 논문집
• /
• 제16권1호
• /
• pp.9-17
• /
• 2012

본 연구는 소규모 지하통로, 저류시설 및 지중구조물에 많이 적용되고 있는 파형강판구조의 이음부강도를 실험적으로 평가하고자 하였다. 대골형파형강판을 사용하는 지중 강구조물은 압축력에 대하여 충분한 안정성을 확보하여야 한다. 그러나 현장에서 볼트 연결되는 이음부가 강판의 두께, 캐스킷, 와셔, 슬롯홀과 같은 연결상세에 따라 강도가 변화함에도 불구하고 이음부강도에 대한 실험적 이론적 결과가 설계에 반영할 수 있을만큼 충분히 축적되지 않은 상태이다. 본 연구에서는 다양한 연결상세를 적용한 경우의 이음부 압축거동을 실험적으로 분석하였다. 연구결과 강판의 두께가 증가함에 따라 강판지압파괴에서 볼트전단의 형태로 파괴 형태가 변화하는 것으로 나타났으며, 6.omm 이상의 플레이트에서는 개스킷과 슬롯홀을 적용한 이음부가 와셔를 적용한 경우보다 효과적인 거동을 보이는 것으로 관찰되었다.

• Steel and Composite Structures
• /
• 제20권4호
• /
• pp.731-748
• /
• 2016

Pile-to-pilecap connection performance is important as Integral abutment bridges (IABs) have no expansion joints and their flexible weak-axis oriented supporting piles take the role of the expansion joint. This connection may govern the bridge strength and the performance against various lateral loads. The intention of this study is to identify crack propagation patterns when the pile-to-pilecap connection is subjected to lateral loadings and to propose novel connections for improved performance under lateral loadings. In this study, eight different types of connections were developed and modeled, using Abaqus 6.12 to evaluate performances. Three types were developed by strengthening the connections using rebar or steel tube: (i) PennDOT specification; (ii) Spiral rebar; and (iii) HSS tube. Other types were developed by softening the connections using shape modifications: (i) cylindrical hole; (ii) reduced flange; (iii) removed flange; (iv) extended hole; and (v) slot hole connection types. The connections using the PennDOT specification, HSS tube, and cylindrical hole were shown to be ineffective in the prevention of cracks, resulting in lower structural capacities under the lateral load compared to other types. The other developed connections successfully delayed or arrested the concrete crack initiations and propagations. Among the successful connection types, the spiral rebar connection allowed a relatively larger reaction force, which can damage the superstructure of the IABs. Other softened connections performed better in terms of minimized reaction forces and crack prevention.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2007년도 춘계학술대회B
• /
• pp.3529-3533
• /
• 2007

The advantages of the SITVC(secondary injection thrust vector control) technique over mechanical thrust vector systems include a reduction in both the nozzle weight and complexity due to the elimination of the mechanical actuators that are used in conventional vectoring. Computational study is performed to understand the fluidic thrust vectoring control of an axisymmetric nozzle, in which secondary gas injection is made in the divergent section of the nozzle. The nozzle has a design mach number 3. The effect of injection hole number and shape of secondary jet on the mach number distribution of SITVC were investigated. The standard ${\kappa}$ - ${\epsilon}$ turbulence model solved the complex three-dimensional nozzle flows perturbed by the secondary gas jet. The numerical code was validated by experiment. The results showed that the mach number distribution of circular and square nozzle are similar each other. As number of second injection hole increasing, a effect of deflection was decreased.

• 대한기계학회논문집
• /
• 제6권4호
• /
• pp.367-376
• /
• 1982

Stress concentration mainly occurs near holes and notches. Then local stress is larger than nominal stress. It is necessary that stress concentration phenomena are studied because it can act as a cause of fracture of material. In order to analyze fracture of material including holes, stress concentration factor and stress distribution must be studied more carefully. In this paper the stress concentration and distribution of a slotted plate is examined. Hardened 7:3 brass plate with 4 different slots including a circular hole is used. And ratios of slot length to its root radius are 1, 2, 3, 24, 4. The stress distribution is measured by using strain gages attached to the plate with variable width. And obtained experimental data are adjusted by using calibrated gage factor.

• 한국경영과학회:학술대회논문집
• /
• 한국경영과학회 1997년도 추계학술대회발표논문집; 홍익대학교, 서울; 1 Nov. 1997
• /
• pp.41-44
• /
• 1997

This paper is to provide an integration approach between design and process planning for mechanical parts, using feature recognition. We develop a method to extract each individual feature of an object from 3D modeling data using face-edge graph based algorithm and then propose an approach to recognize the volumic form features using heuristic rules. we demonstrate the proposed approaches are effective for such basic shapes as pocket, slot, through hole, etc.

• 한국정밀공학회지
• /
• 제17권6호
• /
• pp.176-184
• /
• 2000

Reverse engineering (RE) is a process to create computer aided design (CAD) models from the scanned data of an existing part acquired using 3D position scanners. This paper proposes a novel methodology of extracting geometric features directly from a set of 3D scanned points, which utilizes the concepts of feature-based technology and artificial neural networks (ANNs). The use of ANN has enabled the development of a flexible feature-based RE application that can be trained to deal with various features. The following four main tasks were mainly investigated and implemented: (1) Data reduction; (2) edge detection; (3) ANN-based feature recognition; (4) feature extraction. This approach was validated with a variety of real industrial components. The test results show that the developed feature-based RE application proved to be suitable for reconstructing prismatic features such as block, pocket, step, slot, hole, and boss, which are very common and crucial in mechanical engineering products.

• 한국정밀공학회지
• /
• 제21권4호
• /
• pp.32-38
• /
• 2004

Laser-induced thermochemical wet etching of titanium in phosphoric acid has been investigated to examine the feasibility of this method fur fabrication of microstructures. Cutting, drilling, and milling of titanium foil were carried out while examining the influence of process parameters on etch width, etch depth, and edge straightness. Laser power, scanning speed of workpiece, and etchant concentration were chosen as major process parameters influencing on temperature distribution and reaction rate. Etch width increased almost linearly with laser power showing little dependence on scanning speed while etch depth showed wide variation with both laser power and scanning speed. A well-defined etch profile with good surface quality was obtained at high concentration condition. Fabrication of a hole, micro cantilever beam, and rectangular slot with dimension of tess than 100${\mu}{\textrm}{m}$ has been demonstrated.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 1994년도 추계학술대회 논문집
• /
• pp.25-32
• /
• 1994

In order to analyse stretching of perforated sheets for shadow masks by the finite element method for use with the associated flow rule, yield functions which can explain the yield stresses and the apparent plastic contraction ratios of the sheets have been obtained. Coefficients in the yield functions could be determined from the measured apparent plastic contraction ratios under uniaxial tension. Using this yield function and estimated coefficients, the stretching of hole-type and slot-type sheets has been analysed and compared with the experimental results. The calculated results were in good agreement with the experimental results.