• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.673-679
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• 2000

LNG Carriers are currently known as sole commercial means of shipping natural gas on the sea. They are designed to proven dangerous explosion for shipping a lot of gas over long distance. In this study. In this study, a scaled model chamber was made to investigate ventilation characteristics of the hood room in LNG carrier. Experimental study was performed in model using visualization equipments with laser apparatus and image intensifier CCD camera gated by an AOM controller Twelve different kinds of measuring area were selected as experimental condition. Instant simultaneous velocity vectors at whole field were measured by using 2-D PIV system which software adopts two-frame grey-level cross correlation algorithm. To look into stagnation area of hood room for LNG carrier, a three-dimensional numerical simulation with standard ${\kappa}-{\varepsilon}$ model was carried out by using PHOENICS for three kinds of Reynolds number, $6.5{\times}10^3$, $9.7{\times}10^3\;and\;1.29{\times}10^4$, based on the cavity inlet velocity and cavity height. The flow pattern showed the large scale counter-clockwise forced-vortex rotated at center area, small eddies at each corner and stagnation area located at left-back upper side of model.

• 한국전자파학회논문지
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• 제12권3호
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• pp.425-431
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• 2001

비유전율 ${\epsilon}_{r}$=36인 유전체를 이용한 무선 LAN용 개구 결합 마이크로스트립 원통형 유전체 공진 안테나(DRA)를 설계하고 제작하였다. 우선 급전 소자는 마이크로스트립 전송선로 이론을 이용하여 급전 선로 길이, 선로 폭, 슬롯 길이, 슬롯 폿과 스터브 길이을 계산하였다. 방사 소자는 원통형 유전체 cavity 이론을 이용하여 설계하였다. 제작된 원통형 DRA의 공진주파수는 2.449 GHz이고 VSWR, 반사 손실과 대역폭은 각각 1.009, -47dB 와 70MHz이다. 방사 패턴의 전후방비는 13dB이고 E면과 H 면의 3dB 빔폭은 각각 1$10^{\circ}$과 90$^{\circ}$이다.

• 대한조선학회논문집
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• 제44권5호
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• pp.467-473
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• 2007

Cavitation phenomena appearing on ship propellers have long been interested and recent theoretical analysises give good results comparing with model tests. In accordance with a continuous rise in heavy powered and high speed ships, hull forms have been changed and loads acting on the propeller surface have also been increased, and they result in various and particular cavitations. In some cases, cavitation appears not only on the back but also on the face of the propeller and it causes additive pressure fluctuations and erosion of the propeller and reduces propulsion efficiency of the ship. In this study, we predict the face cavity inception using unsteady propeller analysis based on the panel method and compare the results with experimental observations.

• 한국전자파학회논문지
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• 제29권4호
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• pp.266-269
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• 2018

본 논문에서는 Q 대역에서 사용가능한 무인항공기 라디오미터 응용 소형 도파관-마이크로스트립 전이구조를 제안하였다. 제안된 전이구조는 간단하면서도 소형이며, 쉽게 정합이 되고, 크기와 제작 오차에 덜 민감한 특징을 가진다. E 평면 패치형태를 가지는 제안된 전이구조는 캐비티 장착뿐 아니라, 도파관-마이크로스트립 기판의 정렬오차에도 덜 민감한 것이 특징이다. 주요파라미터의 최적화에는 3차원 시뮬레이터인 ANSYS사의 HFSS를 사용하였다. Back-to-back 구조에 대하여 중심 주파수에서 20 dB 이상의 반사손실과 1 dB 이하의 삽입손실을 가졌으며, 36 GHz에서 42 GHz까지 반사손실 15 dB 이상의 우수한 성능을 가졌다.

• 한국전자파학회논문지
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• 제16권1호
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• pp.9-18
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• 2005

본 논문은 격리도가 향상된 US-PCS 대역 댁내용 중계기 안테나를 제안하였다. 일반적으로 중계기는 송신신호와 수신 신호 사이의 간섭을 줄이기 위해 격리도 확보가 필요하다. 그러므로 선형 편파 특성이 우수한 IBD(Integrated Balun Dipole) 안테나에 편파 다이버시티 기법과 캐버티, 멀티 캐버티, 개구정합 방법을 사용하여 안테나의 전후방비 개선을 위한 연구를 하였다. 시뮬레이션과 측정을 통해 개구 정합 방법과 편파 다이버시티 기법을 동시에 사용한 안테나는 US-PCS 대역에서 VSWR < 1.5의 대역폭, 8 dBi 이상의 이득, 그리고 약 15$\~$24dB의 격리도 개선효과가 있음을 확인하였다.

• 대한기계학회논문집B
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• 제31권7호
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• pp.620-627
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• 2007

In this paper, we adapt a modified internal energy non-equilibrium first-order extrapolation thermal boundary condition to the thermal lattice Boltzmann model (TLBM). This model is the double populations approach to simulate hydrodynamic and thermal fields. The bounce-back boundary condition which is a traditional boundary condition of lattice Boltzmann method has only a first order in numerical accuracy at the boundary and numerical instability. A non-equilibrium first-order extrapolation boundary condition has been verified to be of better numerical stability than the bounce-back boundary condition and this boundary condition is proved to be of second-order accuracy for the flat boundaries. The two-dimensional natural convection flow in a square cavity with Pr=0.71 and various Rayleigh numbers are simulated. The results are found to be in good agreement with those of previous studies.

• 한국군사과학기술학회지
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• 제11권6호
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• pp.135-141
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• 2008

본 논문에서는 다중 편파 및 3:1 이하의 대역폭을 갖는 광대역 혼 안테나 설계 기법을 제시하였다. 급전단은 다중 편파 및 광대역 구현을 위하여 4중 릿지(Quadruple Ridge) 형태의 도파관을 적용하였으며, 반구(Semi­sphere) 형태의 백 쇼(Back Short)를 갖는 캐비티 구조내에 쇼팅 바(Shorting Bar)를 삽입함으로써 반사손실을 최소화하였다. 안테나 개구면에서의 위상보정을 통해 안테나 범 패턴을 개선시키기 위하여 주름진 형태의 유전체 렌즈를 설계하였다. 설계 기법을 기반으로 제작된 얀테나의 측정결과를 제시함으로써 설계 방법의 타당성을 겸증하였다.

• 소성∙가공
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• 제9권3호
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• pp.249-256
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• 2000

Tube hydroforming is recently drawing attention of automotive industries due to its seberal advantages over conventional methods. It can produce wide range of products such as subframes, engine cradles, and exhaust manifolds with cheaper production cost by reducing overall number of processes. Tube hydroforming process is divided into prebending process and hydroforming process. Tube bending ins an important factor of the hydroforming process to enable the tube to be placed in the die cavity. This paper presents the theoretical analysis and the simulation results of the tube bending process. With some assumptions, approximate equations are derived to predict the thickness distribution on the cross section and the spring back of the bent tube. Bending simulations are carried out and compared to the analytical and experimental results.

• Archives of Plastic Surgery
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• 제42권3호
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• pp.373-375
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• 2015

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 춘계학술대회 논문집
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• pp.198-203
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• 1995

In the paper, we have proposed a new technique to detemine the initial billet for the forged products using a function approximation in neural network. A three-layer neural network is used and a back propagation algorithm is employed totrain the network. An optimal billet which satisfied the forming limitation, minimum of incomplete filling in the die cavity, load and energyas well as more uniform distribution of effective strain, is determined by applying the ability of function approximation of te neural network. The amount of incomplete filling in the die, load and forming energyas well as effective strain are measured by the rigid-plastic finite element method. The new technique is applied tofind the optimal billet size for the axisymmetric rib-web product in hot forging. This would reduce the number of finite element simulation for determing the optimal billet of forging products, further it is usefully adapted to physical modeling for the forging design.