• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1996년도 춘계 학술대회논문집
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• pp.99-104
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• 1996

The jet pump is being used in many fields for several purposes because of its simple construction and easy operation. The characteristics of the geometrical variables, pressure gradient and velocity distribution of the jet pump are studied using the CFD technique. The flow calculations through a bended nozzle. a mixing chamber and a venturi are presented and phenomenological aspects are discussed. This study solve 3-D steady incompressible Navier-Stokes equations using the Iterative time marching scheme. The governing equations are differenced with 1st-order accurate backward difference scheme for the time derivatives and 3rd-order accurate QUICK scheme for the convective terms. The Mark-and-cell concept was applied efficiently to solve continuity equation, which is differenced 2nd-order accurate central differenced scheme. The 4th-order artificial damping is added to the continuity equation for numerical stability. A O-type of grid system is generated inside a nozzle and venturi of the jet pump. It has concluded that the results of present study properly agree with physical flow phenomena.

• 한국전산유체공학회지
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• 제21권3호
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• pp.55-63
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• 2016

Nowadays, large container ships are continually developed and that's why the bow and stern structural stability problems by slamming become a significant more and more. However, due to the complexity of slamming, it is difficult to consider those problems at the design stage. For this reason, we attempt numerical analysis through SNUFOAM by generating the bow and stern two-dimensional cross-sectional grid in WILS JIP experiment at KRISO. Unlike the conventional method for the computation time saving, by setting the inlet flow conditions referred to the model test, we analyzed the slamming without applying the grid deformation method. As a result, when the stern model, as in the previous studies, it was possible to obtain quantitatively the fluid impulse is close to the experimental results. When the bow model, we can found the change by the position of force sensors which are derived for the bulbous bow and obtained fluid impulse and flow shape at slamming similar to the model test.

• Nuclear Engineering and Technology
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• 제43권3호
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• pp.243-256
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• 2011

This paper considers the concept of analog computing based on a cellular neural network (CNN) paradigm to simulate nuclear reactor dynamics using a time-dependent second order form of the neutron transport equation. Instead of solving nuclear reactor dynamic equations numerically, which is time-consuming and suffers from such weaknesses as vulnerability to transient phenomena, accumulation of round-off errors and floating-point overflows, use is made of a new method based on a cellular neural network. The state-of-the-art shows the CNN as being an alternative solution to the conventional numerical computation method. Indeed CNN is an analog computing paradigm that performs ultra-fast calculations and provides accurate results. In this study use is made of the CNN model to simulate the space-time response of scalar flux distribution in steady state and transient conditions. The CNN model also is used to simulate step perturbation in the core. The accuracy and capability of the CNN model are examined in 2D Cartesian geometry for two fixed source problems, a mini-BWR assembly, and a TWIGL Seed/Blanket problem. We also use the CNN model concurrently for a typical small PWR assembly to simulate the effect of temperature feedback, poisons, and control rods on the scalar flux distribution.

• 한국음향학회지
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• 제38권2호
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• pp.184-192
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• 2019

33-모드 링은 31-모드 링에 비하여 결합상수와 압전상수 d가 높기 때문에 광대역 수중 음향 트랜스듀서로 활용성이 높다. 반면 31-모드 링은 축대칭 구조이므로 수치해석 수행시 2차원 축대칭 모델로 간략히 해석이 가능하지만, 33-모드 링은 3차원 수치해석을 수행해야 한다. 즉, 특성 예측을 위해 많은 전산자원과 계산시간이 소요된다. 따라서 33-모드 링의 전기-기계-음향 응답을 모사할 수 있는 등가의 31-모드 링의 유효 물성을 도출할 수 있다면 소나 트랜스듀서 설계 등에 실용적일 것이다. 본 연구에서는 응답 특성을 모사하기 위해 각 링의 전기, 기계 임피던스 및 변환계수(${\phi}$)가 동일하다고 가정하여 등가 31-모드 링의 유효 밀도(${\rho}_{31_{-}eff}$), 컴플라이언스($s^E_{11_{-}eff}$), 압전 상수($d_{31_{-}eff}$), 유전 상수(${\varepsilon}^T_{33_{-}eff}$)를 유도했다. 도출한 유효 물성을 이용하여 진공상태의 링, 수중에서 공기 배킹의 링, 그리고 수중에서 링 내부에 자유롭게 유체가 드나드는 링에 대하여 수치해석을 하였고 이를 33-모드 링의 응답특성과 비교하였다.

• 한국습지학회지
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• 제16권3호
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• pp.327-336
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• 2014

물에 잠긴 얇은 벽은 잠제 사각형 블록의 극단적인 경우라고 할 수 있으며, 하천이나 해안지역에서 다양한 목적으로 사용될 수 있다. 잠제구조물의 얇은 벽 주위 흐름과 압력을 계산하기 위하여 동수압이 포함된 ${\sigma}$-격자체계의 3차원 수치모델을 수행하였고, 그 주변의 유속 흐름을 파악하였다. ${\sigma}$-격자체계는 완경사 하상에 유동 시뮬레이션을 적용할 수 있는 강력한 장점을 가지고 있다. 반면에 ${\sigma}$-격자체계는 하상에 날카로운 구조물등에 대한 해석에는 한계를 갖고 있다. 동압력 계산은 직교격자 시스템에서만 유효하다. CST3D시스템 내에 SOLA 기법을 ${\sigma}$-격자체계에 맞게 수정하여 채택하였다. 모델은 2차원 수조에서의 1차원 전자자기식유속계를 통한 관측자료를 통하여 검증하였고, 정수압 가정의 ${\sigma}$-격자체계 수치모형과의 비교를 통하여 정량적인 비교 검토를 수행하였다. 전체적으로 계산된 수평유속과 측정된 수평유속이 유사한 것으로 나타났다. 수리모형실험을 통한 관측자료의 결과를 수치모형이 10% 이내로 정확하게 모의하였고, 관측자료와 대조하였을시 와도의 분포를 유사하게 재현하였다. 수정 SOLA 방식을 채택하여 동수압이 고려되었고, ${\sigma}$-격자체계에 적용한 본 연구는 실제 관측자료를 잘 재현하였으며, 하구, 하천등의 구조물 주변에서의 유속분포를 검증할 시 매우 유용한 것으로 판단된다.

• 대한기계학회논문집B
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• 제27권6호
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• pp.714-725
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• 2003

The theory of the current-type electromagnetic flowmeter for a high temporal resolution was developed for two-phase flow measurements. To predict the output of the current-type flowmeter, the three-dimensional virtual potential distribution C and the newly introduced flow pattern coefficient f were derived and computed. The output of flowmeter depends on the liquid conductivity (sensitive to temperature) and flow configurations of the two-phase flow with the sinusoidal excitation over 100 Hz. The flow pattern coefficient was specially devised to separate the dependency on the flow configuration of the two-phase flow from that on the liquid conductivity which can be expressed with the calibration of single-phase flow. Using the finite difference method, the three-dimensional virtual potential distributions were computed for the electrode of finite size. By taking derivative of the virtual potential, the weight functions were evaluated and compared with existing analytic series solution for the point-electrode. There was a reasonable correspondence between the present and existing results. In addition, the flow pattern coefficients were evaluated for annular flows with various film thicknesses, and compared with the experimental results by the impedance spectroscopy. The numerical results agreed well with the experimental data.

• 한국지반공학회논문집
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• 제32권1호
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• pp.55-62
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• 2016

본 연구에서는 공극 네트워크 모델을 이용하여 사질토의 함수특성곡선을 수치해석적으로 획득하였다. 주문진표준사의 시편을 고해상도 3차원 X-ray CT 촬영하여 공극 영상을 획득하였고, 이를 공극방과 공극목으로 이루어진 관망으로 재구성하였으며 이 때 관의 반경은 공극목의 최소반경으로 정의하였다. 모세관압에 영향을 미치는 공극목의 반경은 세선화알고리즘과 유클리디언 거리변환을 통해 계산하였다. 수치해석적으로 얻은 함수특성곡선을 실험결과와 비교하였으며, 수치해석 결과는 실험결과에 비해 공기함입치가 과대평가 되었으나 전체 모세관압은 유사한 분포를 나타냈다. 또한 실험결과로부터 도출된 상대투수율은 높은 포화도에서 수치해석 결과에 비해 큰 값을 보였다.

• 한국통신학회논문지
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• 제21권12호
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• pp.3205-3214
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• 1996

In this paper, the microstrip phased array antennas with coupling-slots for the base station of mobile communication is proposed and anlyzed with accurate analysis method which is based on both reciprocity principle and full-wave analysis. The basis functions used for the numerical analysis are determined depending upon the accuracy, convergence properties of the solution, and the computation time. The patch uses 3 EB mode and the slot uses IPWS mode. The designed phased array antenna has 8 slot-coupled microstrip patch array elements and the beam scanning capability is obtained by using the 4-bit PIN-diode phase shifters as switching devices which are consisted of the loaded line phase shifters for 30.deg. and 60.deg. and the reflection type phase shifters for 90.deg. and 180.deg. repectively. The 4-bits phase shifters which aremade by connecting each phase shifter have about 2.deg.-3.deg. phase errors and their insertion loss are about 3dB for each phase state. The fabricated 8-element phased array antenna with 4-bits phase shifters provides 12.deg.-14.deg. beamwidths depending on the scanning angle and is capable of scanning its beam to .+-.45.deg. with 9.deg. intervals, and the gain 12dBi. The overall results show that the slot-coupled phased array antenna has great advantages of wideband, high gain and reduced spurious radiation. Also, the antenna can be made small and thin. Furthermore, the scanning property of this antenna allows for its application in several areas, such as mobile communication system and PCS.

• ETRI Journal
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• 제22권2호
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• pp.11-19
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• 2000

If the right and left signals of a binaural sound recording are reproduced through loudspeakers instead of a headphone, they are inevitably mixed during their transmission to the ears of the listener. This degrades the desired realism in the sound reproduction system, which is commonly called 'cross-talk.' A 'cross-talk canceler' that filters binaural signals before they are sent to the sound sources is needed to prevent cross-talk. A cross-talk canceler equalizes the resulting sound around the listener's ears as if the original binaural signal sound is reproduced next to the ears of listener. A cross-talk canceler is also a solution to the problem-how binaural sound is distributed to more than 2 channels that drive sound sources. This paper presents an effective way of building a cross-talk canceler in which geometric information, including locations of the listener and multiple loudspeakers, is divided into angular information and distance information. The presented method makes a database in an off-line way using an adaptive filtering technique and Head Related Transfer Functions. Though the database is mainly concerned about the situation where loudspeakers are located on a standard radius from the listener, it can be used for general radius cases after a distance compensation process, which requires a small amount of computation. Issues related to inverting a system to build a cross-talk canceler are discussed and numerical results explaining the preferred configuration of a sound reproduction system for stereo loudspeakers are presented.

• Journal of Advanced Marine Engineering and Technology
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• 제32권4호
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• pp.498-505
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• 2008

Many researches have been studied on in-cylinder flow as one of dominant effects for an engine combustion. The combustion phenomena of reciprocating engine is one of the most important processes affecting performance and emissions. One effective way to improve the engine combustion is to control the motion of the charge inside a cylinder by means of optimum induction system design. It is believed that the tumble and swirl motion generated during intake breaks down into small-scale turbulence in the compression stroke of the cycle. However, the exact nature of their relationship is not well known. To know this relationship definitely, this paper describes analytical results of the tumble motion, swirl motion, turbulence intensity, turbulence inside the cylinder of marine engine. 3-D computation has been performed by using STAR-CD solver and es-ice.